Atlas of Pediatric EEG
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Atlas of Pediatric EEG Pramote Laoprasert, MD Assistant Professor University of Colorado School of Medicine Director of Surgical Epilepsy Program and Epilepsy Monitoring Unit Department of Pediatric Neurology The Children’s Hospital of Denver Aurora, Colorado
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Dedicated to my wife Nan, my children Maddy and Rick, and my parents Saman and Vilai For their unconditional love, enthusiastic support, encouragement, and long-suffering tolerance during preparation of this book. And to my patients and their families. Without them, this book would be impossible.
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CONTENTS Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
3 Newborn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201
8 Generalized Epilepsy . . . . . . . . . . . . . . . . . . . . . . . . 613
Preface
xi
4 Focal Nonepileptoform Activity . . . . . . . . . . . . . . 275
9 Focal Epilepsy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xii
1 Normal and Benign Variants . . . . . . . . . . . . . . . . . . . 1
5 Generalized Nonepileptiform Activity . . . . . . . . 389 6 ICU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 471
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 861
2 Artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
7 Epileptic Encephalopathy . . . . . . . . . . . . . . . . . . . 529
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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FOREWORD Epilepsy is a common and frequently disabling disorder in children. Linking its clinical manifestations to electrographic and imaging changes is essential to correct diagnosis and management. This multimedia work provides an accessible, comprehensive, and timely tool for the child neurologist or epileptologist in training or in practice to become familiar with the extraordinary richness of the clinical and electrographic manifestations of childhood epilepsy. The text represents the distillation of an extraordinary body of clinical experience and painstaking attention to detail, which is characteristic of Dr. Laoprasert. I first had the privilege of making his acquaintance two decades ago, when he began his child neurology training at Mayo Clinic. Since that time, he has established himself as a first-class pediatric epileptologist and scholar. This
fine work is an appropriate testament to his diligence and skill. The text is laid out in a systematic and thoughtful fashion, beginning with common and not-so-common patterns and variants in the electroencephalogram, which can be a source of confusion and diagnostic error to the novice. Subsequently, pathological conditions are explored in a similarly logical and comprehensive fashion. Since most of us learn from our patients, I predict that this case-based approach will be extremely effective. I commend this work to anyone who wishes to improve his or her grasp of epilepsy in childhood. It will be essential reading for pediatric epilepsy trainees but will also be a frequently consulted resource for residents in training. By the same token, the child neurologist who is not an expert in epilepsy, and even
experienced pediatric epileptologists, will find a great deal of valuable material to enhance the care of their patients. Whether read cover-to-cover, used to review specific problems, or dipped into at random, this text makes learning about epilepsy in children a pleasure and will ultimately enhance the quality of their lives and those of their families. Marc C. Patterson, MD, FRACP, FAAN Professor of Neurology, Pediatrics and Medical Genetics Chair, Division of Child and Adolescent Neurology Mayo Clinic Rochester, Minnesota
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PREFACE EEG presents a tremendous challenge to the neurologist. Although EEG has been used for almost a century, it is still and will continue to be one of the most important diagnostic tools in neurology, especially in pediatric neurology and epilepsy. The rapid advances in digital and prolonged video-EEG as well as in epilepsy surgery enhance the usage of the EEG to the higher level. Atlas of Pediatric EEG presents both common and uncommon EEG diagnoses in a case-study-oriented
manner. Unlike other EEG atlases that catalog only the EEG patterns, this book stresses the viewpoint of the practicing neurologists and neurophysiologists. Integration of the EEG, clinical information, and neuroimaging is the heart of this book and is consistently presented throughout. Cited references for further study are extensive and up to date. This will help the readers to have a better understanding of the EEG and its applications.
Atlas of Pediatric EEG is designed for the electroencephalographer, child neurologist, EEG/ epilepsy fellow, neurology resident, pediatrician, and EEG technologist with an interest in pediatric EEG. Other healthcare providers, such as nurse practitioners and physician assistants who care for children with neurologic conditions, as well as medical students during the pediatric neurology clerkship who want to learn about the EEG in children, will also find this atlas valuable.
xi
ACKNOWLEDGMENTS I would like to acknowledge Dr. Marc Patterson for his extraordinary mentoring and for a very kind and thoughtful foreword. I thank Dr. Paul Moe and Dr. Andy White for their critical review and proofreading. I also thank my colleagues, epilepsy fellows, and neurology residents at the Denver Children’s Hospital in the preparation of this book.
xii
I am also deeply grateful to the editorial staff at McGraw-Hill, especially to Anne Sydor, Christine Diedrich, Sherri Souffrance and Priscilla Beer, as well as Sandeep Pannu and Aakriti Kathuria of Thomson Digital, for their generous support and competent assistance.
1
1
Alpha rhythm or posterior dominant rhythm (Figures 1-1 to 1-5, 1-11, and 1-16)
䡲
Normal and Benign Variants
Monomorphic either sinusoidal or having sharp points at the top or bottom, 8–13 Hz in older children and adults during relaxed wakefulness with eyes closed.
䡲
Eye opening attenuates alpha rhythm (AR) and eye closure accentuates AR.
䡲
AR also attenuates with:
䡲
䊳
Drowsiness
䊳
Concentration
䊳
Stimulation
䊳
Visual fixation
䊳
Anxiety
䊳
Eye closure with mental calculation
AR responsive to eye opening occurs in 75% of infants between 3rd and 4th months.
Frequency 䡲
䡲
Mean AR frequency: 䊳
4 months – 4 Hz
䊳
12 months – 6 Hz
䊳
36 months – 8 Hz
䊳
9 years – 9 Hz
䊳
10 years – 10 Hz
䊳
Elderly – above 9 Hz
Abnormal AR: 䊳
1 year: <5 Hz
䊳
4 year: <6 Hz
䊳
5 year: <7 Hz
䊳
≥ 8 year: < 8 Hz (8.5 Hz by some authors)
䊳
Incidence of AR as slow as 8 Hz in adult is <1%; therefore, consistent 8 Hz of AR is considered mild abnormality by some authors.
䊳
Frequency of AR is constant throughout adult life, a decline of ≥1 Hz is abnormal even if their absolute frequency remains in the range ≥8 Hz.
䊳
䡲
Difference of AR frequency >1 Hz in the two hemispheres.
Good AR is seen during crying and passive eye closure.
䡲
Drowsiness must be considered if muscle artifact is seen less than usual. 䡲 Fever and hypermetabolic states, including hyperthyroidism and amphetamine intoxication, may increase the AR’s frequency. High fever in children can either increase or decrease the AR’s frequency. 䡲 Extreme upward gaze or lateral eye deviations may facilitate AR frequency.
Voltage 䡲
Most adults have AR voltages of 15–45 μV; Children (3–15 years) 50–60 μV; Children (6–9 years) 100 μV or more.
䡲
6–7% of adults have voltage less than 15 μV.
䡲
Only 1.3% of children >12 years have AR voltage less than 30 μV. Low voltage (< 20 μV) EEG (electroencephalography) is abnormal in children. Low voltage (< 10 μV) EEG is more likely to be abnormal in adult. Very low voltage ≤ 2 μV EEG is seen in electrocerebral inactivity and marked subdural fluid collection. High-voltage AR alone should never be considered abnormal.
䡲 䡲 䡲 䡲 䡲
Reduced voltage AR with advancing age is more likely due to increased bone density and electrical impedance of the intervening tissue rather than decreased electrical brain activity.
Regulation 䡲
Sustained rhythm, in which the mean frequency does not vary more than ± 0.5 Hz, and the smoothness of the envelope of the waxing and waning of voltage. 䡲 Best regulation between 6 months and 3 years. 䡲 Poor regulation between 3 and 4 years (low voltage). 䡲 Affected by mental activity and anxiety.
2
Distribution
Beating or waxing and waning of the AR
䡲
䡲
AR is in occipital region in 65% of adults and 95% of children. 䡲 Variant: central and temporal regions and widely distributed AR. 䡲 Although slight AR in the frontal regions is occasionally seen, prominent anterior alpha frequency rhythm is considered abnormal. Alpha frequency activity restricted to the frontopolar electrodes is eyelid flutter until proven otherwise. 䡲 AR may be prominent in frontocentral region during drowsiness.
Asymmetry
䡲 䡲 䡲 䡲
60% of adults and 95% of children, AR is higher voltage in the right side with asymmetry less than 20%, regardless of handedness. Most likely due to difference in skull thickness. Asymmetry >20% is seen in 17% and >50% is seen in 1.5% in all ages. Voltage asymmetry >20% is seen in 5% of normal children. Persistent asymmetry of 50% or more is considered abnormal. Persistent asymmetry of 35–50% is considered suspect if the lower voltage AR is on the right side. Symmetry is best measured in referential montage to avoid phase cancellation.
Effect of two separate alpha frequencies.
Bancaud phenomenon 䡲
䡲
䡲
When unilateral cerebral lesions or transient cerebral dysfunction (such as migraine or TIA) are present in the occipital or, less commonly, parietal or temporal lobes, the side of defective reactivity (eye opening and alerting) occurs ipsilateral to the side of the lesion. When both phenomena exist, the same side of the brain is affected.
䡲
≥ 13 Hz; most common 18–25 Hz; less common 14–16 Hz; rare 35–40 Hz. 䡲 First develops between 6 months and 2 years 䡲 䡲 䡲
Distribution: frontocentral >widespread>posterior. Voltage <20 μV in 98% and <10 in 70% Voltage of >30 μV is rare but should generally not be considered abnormal, although generalized but anterior-predominant fast activity called “extreme spindles” can be seen in mental retardation or cerebral palsy as well as lissencephaly. Drugs including barbiturates, benzodiazepine, and chloral hydrate increase amplitude and amount of beta activity.
䡲
Increase in amount and amplitude during drowsiness, stage 2 sleep and rapid eye movement (REM); decrease during deeper stages of sleep.
䡲
Squeak effect
Consistently low voltage on one side >35% is indicative of: 䊳 Cortical injury
䡲
䊳
䡲 䡲
The same rule is applied to mu and temporal theta activity.
Immediately after eye closure, alpha frequency may be accelerated for 0.5–1 sec. Therefore, alpha frequency assessment should not be done during this period.
Paradoxical AR 䡲
AR presents with eye opening if the environment is devoid of light as the result of partial alerting. Paradoxical AR is seen in drowsiness and sedation.
䊳
䊳
Transient conditions such as postictal state Subdural or epidural fluid collection
More sensitive than focal polymorphic delta activity (PDA) 䡲 Amplitude asymmetry of >35% is considered abnormal. 䡲 Focal increased amplitude is seen in: 䊳
Skull defect (breach rhythm)
Focal structural abnormality, especially focal cortical dysplasia 䡲 Presence of beta activity is almost always a good prognostic sign. 䊳
Slow alpha variant (Figures 1-6 to 1-7) 䡲
Beta activity
䡲
䡲
1
Normal and Benign Variants
䡲 䡲
䡲
䡲
䡲
A rare physiologic variant of AR (less than 1% of normal adults), seen during relaxed wakefulness, has a harmonic relationship and interspersed with the normal AR, and shows similar distribution and reactivity as a normal AR. Usually alternates with AR. Rhythmic sinusoidal, notched theta, or delta activities that have a harmonic relationship with the AR (one-third or, more commonly, one-half the frequency). Should not be misinterpreted as occipital intermittent rhythmic delta (OIRDA) or theta activity activities, and pathologic findings seen in children and adults. Slow alpha variant may be differentiated from pathologic slow waves by: 䊳 Morphology (notched appearance) 䊳 Frequency (subharmonic of normal AR) 䊳 Reactivity to eye opening 䊳 Disappearance with sleep Sometimes mimics rhythmic temporal theta bursts of drowsiness (RTTD), except that it occurs only over the posterior head regions.
Fast alpha variant pattern (Figures 1-8 to 1-10) 䡲
Harmonic of the AR that has a frequency approximately twice that of AR, usually within the range of 16–20 Hz, with a voltage of 20–40 μV. 䡲 Usually intermingled with AR and shows reactivity and a distribution similar to AR.
1 Posterior slow waves of youth (youth waves or polyphasic waves) (Figures 1-12 to 1-15)
Normal and Benign Variants
䡲
Amplitude varies, but is generally below 50 μV. Duration is 100–250 msec except in 1–3 years that can be up to 400 msec.
䡲
Most commonly seen in children aged 8–14 years and are uncommon in children under 2 years. 䡲 A 15% incidence in healthy individuals aged 16–20 years but rare in adults above 21 years of age.
Resemble positive occipital sharp transients of sleep (POSTS) and visual evoked potential. Subjects with prominent lambda waves also have prominent POSTS. 䡲 In children, highest amplitude and sharpest component is surface negative in the occipital region. 䡲 Random and isolated waveforms but may be recur at intervals of 200–500 msec.
䡲
䡲
Visual evoked potentials occur in association with saccadic eye movement.
䡲
Do not occur before 1 year of age. Most common during the middle years of childhood. The prevalence of lambda waves between 3 and 12 years of age is about 80%.
䡲
Physiologically high-voltage theta or delta waves accompanied by the AR and creating spike wave-like phenomenon
䡲
䡲
Typically seen both unilaterally and bilaterally in a single recording. They are always accompanied by the AR, attenuated with eye opening, disappear with the AR during drowsiness and light sleep, and may be accentuated by hyperventilation and stress. Characteristic findings: 䊳 Monorhythmic occipital rhythm attenuates with eye opening 䊳
Normal slower waveforms rarely >1.5 times the amplitude of AR.
䊳
Normal slower waveforms attenuate with AR during alerting. Slower waveforms has the same asymmetry in the ongoing AR
䊳
䡲
Index of abnormality of theta/delta slowing. 䊳 Complexity and variability of waveforms 䊳 Incidence (how often slow waves occur) 䊳
䊳 䊳
䡲
Lambda waves have been described as biphasic or triphasic; their predominant positive component is preceded and followed by a negative component.
䡲
Strictly bilateral synchronous although may be asymmetrical on the two sides. Rarely present only on one side.
䡲
Marked asymmetry indicates an abnormality on the side of lower amplitude. 䡲 The most important precipitating factor is voluntary scanning eye movements. 䡲 Lambda wave is attenuated by:
Voltage ratio (normal slow waves rarely >1.5 times the amplitude of AR) Persistence with eye opening Symmetry (consistently predominant on one side).
Lambda waves (Figures 1-17 to 1-19) 䡲
䡲
Sharp transients of sawtooth shape (biphasic or triphasic) occurring over the occipital region of waking subjects during visual exploration (scanning complex picture), mainly positive relative to other areas and time locked to saccadic eye movements.
䊳 䊳
Darkening room Staring at a blank card
Eye closure Lambda waves usually occur as random and isolated waveforms but may recur at intervals of 200–500 msec. 䡲 Accompanied by eye movement and eyeblink artifacts. 䡲 Sometimes, especially when present unilaterally, they may be mistaken for focal abnormalities, but the distinction can be made by replacing the geometric image with a blank surface. 䊳
3
䡲
Marked and persistent asymmetry indicates an abnormality on the side of lower amplitude.
Positive occipital sharp transients of Sleep (Figures 1-20 to 1-24) 䡲
Best seen at the age of 15–35 years and rarely <3 years. 䡲 Seen in 50–80% of healthy adults. 䡲
Amplitude 20–75 μV; duration 80–200 msec. Absent in individuals with poor central vision. 䡲 Sharply-contoured, surface positivity, occurring in trains with a repetitive rate of 4–5 Hz, and monophasic checkmark-like waveform seen singularly or in clusters over the occipital regions. 䡲
䡲
Always bilaterally synchronous but are commonly asymmetric on the two sides. Asymmetry of 50% is normal.
䡲
POSTS occur during deep drowsiness and stage 2 sleep. Rare in REM sleep.
Posterior slow-wave transients associated with eye movements (Figures 1-25 to 1-28) 䡲
Seen in children age 6 months to 10 years, but most commonly in children aged 2–3 years. 䡲 Consisting of a monophasic or biphasic slow transient with a duration of 200–400 msec and a voltage of up to 200 μV in the occipital regions. 䡲
A latency of 100–500 msec is noted after the eyeblinks or eye movements.
䡲
The initial component of the transient is surface positive. The ascending phase is steeper than the descending phase.
䡲
Occipital slow transients (Figures 1-29 to 1-31) 䡲
Physiologic waves presenting during non-REM sleep, especially a transition from light to deep sleep in infancy until 5 years of age
4
䡲
Bilateral, isolated, medium- to high-amplitude, monomorphic, triangular-shaped, delta waves with a typical duration greater than 250 msec in the occipital regions. 䡲 These waves vary from a cone-shaped configuration (cone waves or “O” waves) to a biphasic slow transient. These transients occur every 3–6sec during light sleep and more frequently during deeper stages of sleep.
H-Response (Figures 1-32 to 1-34) 䡲
Prominent photic driving response at flash rates beyond 20 Hz.
䡲
Sensitivity varied from 25% to 100%, and specificity from 80% to 91%. 䡲 Although there are relatively high sensitivities and specificities of the H-response in distinguishing migraine patients from controls and tension headache, H-response is not more effective than the history and examination in diagnosing headaches and not recommended for use in clinical practice. 䡲
May be useful for clinical diagnosis in complicated headache and help to monitor therapeutic response.
Needle-like spikes of the blind (occipital spikes of blindness) (Figures 1-35 to 1-37) 䡲
Occipital or parietal regions in most patients with congenital blindness and retinopathy during early infancy.
䡲
Prevalence of 75% in retrolental fibroplasia age 3–14 years and 35% in all causes of blindness. 䡲 Amplitude 50–250 μV. 䡲
Isolation or burst. 䡲 Activated by sleep. 䡲
1
Normal and Benign Variants
Low amplitude at 10 months; typical features at 2.5 years; after-going slow waves in mid-childhood; disappear by the end of adolescence. 䡲 Functional deafferentation of the visual cortex gives rise to an increase in its irritability (denervation hypersensitivity).
䡲
Not an epileptiform activity.
䡲
Arousal at this stage can be correlated with sleep disorders (somnambulism, nocturnal terror, or enuresis), and can cause confusion.
䡲
Occasionally, spikes in temporal lobe epilepsy will only appear in stage 3 and 4 sleep.
䡲
Seen more commonly in patients with mental retardation and epilepsy. 䡲 Disappear during childhood or adolescence.
Sleep stages Drowsiness (Figures 1-38 to 1-39) 䡲
Alpha dropout (earliest sign)
䡲
Increased beta activity over the frontocentral regions Diffuse rhythmic theta activity with anterior predominance 䡲 Slow eye movement 䡲 Mu rhythm, wicket wave, and 14 and 6 Hz positive spikes can be seen. 䡲 Deep drowsiness is marked by the vertex waves and POSTS that persist during light sleep and deep sleep 䡲
䡲
Hypnagogic hypersynchrony in 3 months to 8 years.
Stage 2 sleep (Figures 1-40 to 1-41) 䡲
Symmetric, synchronous theta rhythms with posterior predominance, 12–15/sec spindles, vertex sharp waves, K-complexes, and POSTS.
䡲
Sleep spindles in the 12–15/sec range are hallmark of sleep onset.
Stage 3 sleep (Figure 1-42) 䡲
Delta frequencies in the 0.75–3/sec range are prominent over the anterior regions. 䡲 Sleep spindle in the 10–12/sec and even in the 12– 14/sec ranges are still present but gradually become less prominent. 䡲
Rhythmic activity of 5–9/sec is common.
䡲
Rhythmic and symmetrical delta activity is noted between 20% and 50% of the recording
Stage 4 sleep (Figure 1-43) 䡲
Over 50% of the recording is delta rhythm.
䡲
Spindles are rare.
REM sleep (Figure 1-44 and 2-1) 䡲
Low-voltage activity, polyrhythmic waves, and slower alpha waves. 䡲 Short bursts of “saw-tooth waves” over the frontal or vertex leads and quick lateral eye movements. 䡲
Appearance of REM sleep in routine EEG is seen in narcolepsy and in patients who are withdrawn from CNS depressants such as alcohol or phenobarbital.
K-Complex (Figures 1-45 to 1-48) 䡲
Contain 3 components including sharp, slow, and fast. Seen in stage 2 sleep and arousal. 䡲 Largest in older children and adolescence. With advanced age, the K-complexes show the decline in voltage with tiny superimposed spindle-like waves. 䡲 First appears at 4 months of age. They have high amplitude but their rise is not as abrupt and the configuration is not as sharp as seen in older children. 䡲
Sleep spindles (Figures 1-49 to 1-58) 䡲
Arise from synchronized activity in neuronal networks linking the thalamus and the cortex. Spindles result from rhythmic spike bursts in inhibitory (GABAergic) thalamic reticular neurons that induce rhythmic rebound bursting in cortical neurons resulting in effective deafferentiation of the cerebral cortex. Cortical neurons show enhanced synaptic plasticity that might have a role in memory and learning processes. 䡲 First seen at 1.5–2 months with a frequency of 14/sec. 䡲 Throughout infancy, they are maximal over the central and parietal areas with shifting asymmetry. They usually are electronegative with rounded positive component that is a typical hallmark of sleep spindles in infancy. These surface-negative spindles with
1 wicket or comb-like shape can be erroneously interpreted as 14/sec positive spikes 䡲
䡲
䡲
䡲
Between the ages of 3 and 6 months, sleep spindles appear to be biphasic and as prolonged runs, up to 10– 15 sec. The prolonged run of spindles is a very useful developmental marker and is rarely seen beyond this age range. Subharmonic or harmonic of sleep spindles with a frequency approximately half or double that of sleep spindles and notched appearance can be seen. In the second half of the first year of life, the spindles appear to be monophasic and are often asynchronous between the two sides. The frequency of spindles also changes, with 12/sec components becoming more prominent. Asynchronous spindles may occasionally continue from 1 to 2 year of age but rarely are seen after the age of 2 years when interhemispheric synchrony of the spindles appears.
Mitten patterns (Figures 1-59 to 1-62) 䡲
Normal and Benign Variants
䡲
䡲
Asymmetric hypnagogic hypersynchrony with shifting predominance can be seen and is not considered abnormal.
䡲
At 2–3 months, first appears. At 9 months, more prominent and continuous.
䡲 䡲
Between 4 months and 2 years, seen in almost all infants.
䡲
Few infants do not show this pattern but show occipital or widespread rhythmical and synchronous 4–5 Hz waves of low to medium amplitude. At 4 years, shorter in duration and more paroxysmal. At 9–11 years, it becomes rare (10%). Although the presence of hypnagogic hypersynchrony at age 12 years is considered abnormal by some authors, it may be seen in normal children up to the age of 12–13 years. Occasionally, small sharp or spiky discharges may be interspersed between the theta waves. These discharges should not be interpreted as epileptiform activity unless they are definitely distinct from background activity and not only occur during drowsiness or at the onset of sleep but persist into deeper stages of sleep.
䡲 䡲 䡲
䡲
Consist of a sharp-contoured waveform on the slope of a slow wave of the same polarity that resembles a mitten, with a thumb of mitten formed by the last wave of a spindle and the hand portion by the slower wave component.
䡲
Maximal at the frontocentral vertex with spread into parasagittal regions. The location is different from K-complexes in that it is centered anterior to the central vertex where K-complexes are maximal. 䡲 Variant of a vertex wave or K-complex and should not be mistaken for a spike-and-wave discharge. 䡲 It is best seen in referential montage in stage 3 sleep.
Hypnagogic hypersynchrony (Figures 1-63 to 1-70) 䡲
Seen in early drowsiness and arousal from deeper sleep. 䡲 Characterized by bilateral synchronous, high voltage, rhythmic 3–5 Hz activity.
The frequency of hypnagogic hypersynchrony is 3–4 Hz at the age of 2–3 months and increases to 4–5 Hz in older children.
5
Midline theta rhythm (Figure 1-71) 䡲 䡲
Rhythmic train of 5–7 Hz theta activity occurring in the central vertex but may also be seen in the frontal vertex. 䡲 Morphology includes sinusoidal, aciform, spiky, or mu-like appearance. 䡲 Seen during wakefulness and drowsiness. 䡲 Variable reactivity to eye opening, alerting, and limb movement. The rhythm usually lasts from 3 to 20 sec and does not evolve.
Frontal arousal rhythm (FAR) (Figures 1-72 to 1-76) 䡲 䡲
䡲
䡲
Hypnic myoclonia (hypnagogic jerks) (Figures 1-67 and 1-70)
䡲
䡲
This wake-to-sleep transition event is characterized by a sudden, single, brief muscular contraction of the legs and occasionally the arms, head, and postural muscles. 䡲 Sensory hallucinations (hypnagogic hallucinations) often occur before the hypnic myoclonia. 䡲 Hypnic myoclonia occurs in 60–79% of normal population. Although it may occur at any age, 90% of patients stop these movements by age of 4 years. 䡲 They are more common in boys than girls by 4:1.
Rare nonspecific finding of no clinical significance.
Rare nonspecific EEG pattern of no clinical significance. Frontal regions (F3 and F4 electrodes with minimal spread to nearby scalp areas) during arousal from sleep in children. Characterized by 30–150 μV, predominantly monophasic negative waves, occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec) with a characteristic notching of the ascending or descending phase of each wave that may represent harmonics of the waveforms. The waxing and waning of the amplitude often leads to a spindle-like morphology. 70% of patients having epileptic seizures; a reported case in which FAR representing ictal electrographic seizure activity.
Rhythmic temporal theta bursts of drowsiness, rhythmic midtemporal discharges (RMTD), psychomotor variant (Figures 1-77 to 1-82) 䡲 䡲
Benign variant of no clinical significance. Seen in 0.5–2.0% of normal adult population and less common in adolescence. No prevalence in childhood.
6
䡲
Bursts or runs of rhythmic, 5–7 Hz or 4–7 Hz (typically 5–5.5 Hz), theta activity with flat-topped, sharply contoured, often notched appearance in the temporal regions. 䡲 Maximally expressed in the mid- or anterior temporal electrodes. 䡲 Monomorphic pattern with amplitude of 50–200 μV. 䊳 Duration: commonly 5–10 sec; vary from 1 to >60 sec with gradual onset and offset. 䊳 The sharper component of the wave usually has a negative polarity in the anterior temporal region. 䊳 Unilaterally with shifting from side to side greater than bisynchronous. 䊳 Differentiated from ictal epileptiform activity by 앫 Monomorphic and monorhythmic (no evolution
into other frequencies although amplitude can vary) 앫 No alteration of background activity 앫 Occurrence in relaxed wakefulness and
drowsiness (most common) and disappearance in deeper levels of sleep. 䡲
Although it has no clinical significance, it was considered by some authors to be a pathologic finding in selected cases.
䡲
Electropositive of sharp component and electronegative of smooth component. 䡲 Widespread field lasting for 0.5–1 sec.
䡲
䡲
䡲
Occurs in children after age 3 to young adult but more common between 12 and 20 years with a peak at age 13–14 years. 䡲 Best seen in contralateral ear reference montage. 䡲 Appearance in diffuse encephalopathy EEG pattern in a wide variety of encephalopathies of childhood suggesting that they are epiphenomena or a resilient normal. Frequency is more variable and can be elicited by alerting stimuli.
Small sharp spike (SSS) or benign epileptiform transients of sleep (BETS) (Figures 1-93 to 1-96) 䡲 䡲
Benign variant of no clinical significance. 20–25% of a normal adult population.
䡲
Appearance in deep drowsiness and very light sleep and disappearance in deeper stages of sleep. 䡲 Usually low voltage, short duration, single monophasic, or biphasic spike with an abrupt ascending limb and a steep descending limb. 䡲
Fourteen and six per second positive spike discharge (Figures 1-83 to 1-92, 5-44 to 5-48, 6-44) 䡲 䡲
Benign variant of no clinical significance. Bursts of arch-shaped waves at 13–17 Hz and/or 5–7 Hz, most commonly at 14 and/or 6 Hz. The 14 Hz component is more commonly seen than 6 Hz.
䡲
Maximal over the posterior temporal and adjacent areas of one or both sides of the head.
䡲
Amplitude <75 μV. Appearance in deep drowsiness and very light sleep and disappearance in deeper levels of sleep.
䡲
1
Normal and Benign Variants
± After coming slow wave. 䡲 Either unilaterally or bilaterally.
Six-hertz spike-wave bursts (phantom spike-wave) (Figures 1-97 to 1-98) 䡲 䡲
25% of phantom spike and wave have repetitive rate of 4 Hz. 䡲 At times, spikes are difficult to see. Six-hertz spikes with minimal or no associated waves may represent a transitional pattern between 6-Hz spike-wave bursts and 14 and 6-Hz positive bursts. 䡲 Waking, high-amplitude, anterior, male (WHAM) vs female, occipital, low-amplitude, drowsy (FOLD). 䡲 WHAM is more likely to be associated with seizures if the repetitive rate is <5 Hz or amplitude of spike greater than slow wave.
Wicket waves (Figures 1-99, 1-101, 1-102) 䡲
䡲
Benign variant pattern and is not associated with epilepsy. 䡲 Rare waveform (0.9%). 䡲
It occurs in clusters or trains, but also as single sharp transients, of 6- to 11-Hz negative sharp aciform waves with amplitude of 60–200 μV.
䡲
Anterior or midtemporal regions. Seen during relaxed wakefulness but facilitated by drowsiness and may occur in light sleep. Recently wicket waves have also been reported to occur during REM sleep. Unilaterally with a shifting asymmetry between the two hemispheres. During the wakefulness, wicket waves are often masked by background EEG activity. Cardinal feature is a changing mode of occurrence through any single recording, from intermittent trains of more or less sustained, aciform, discharges resembling mu rhythm, to sporadic single spikes. Amplitude may be high, but the transient arises out of an ongoing rhythm and does not stand out.
䡲
䡲
Benign variant of no clinical significance.
2.5% of both adolescents and young adults; 0.5–1% overall. 䡲 Appearance in relaxed wakefulness, drowsiness, and light sleep and disappearance in deeper levels of sleep. 䡲 Bursts of 1–2 sec duration diffuse, low voltage (<40 μV), short duration (<30 msec), 5–7 Hz, spike-andwave discharges, commonly bifrontal or occipital.
One of the most common over-read EEG patterns seen almost exclusively in adults, most commonly >30 years of age and, usually, older than 50 years.
䡲 䡲
䡲
1 䡲
When occurring singly, wicket waves can be mistaken for anterior or middle temporal spikes. Isolated wicket wave can be differentiated from epileptiform discharge by the following criteria: 䊳 No slow wave component following the wicket wave 䊳 Occurring in trains or in isolation and do not disrupt the background 䊳 Similar morphology to the waveforms in the train when occurring as a single spike 䡲 More commonly seen in patients with cerebrovascular disease. 䡲 The age (younger than 30 years) and abnormal background activity are strongly against the diagnosis of wicket waves and supportive of epileptiform activities.
Third rhythm (independent temporal alphoid rhythm) (Figure 1-100) 䡲
Rhythmical activity in the alpha and upper theta range over the midtemporal region. 䡲 Not seen in scalp EEG except the presence of skull defect. 䡲 Physiologic rhythm that is clearly independent from mu or AR.
Normal and Benign Variants
䡲
It needs to be differentiated form the rhythmical activity seen in anterior- and midtemporal regions seen in patients with stroke.
7
䡲
Occurs in less than 5% of children younger than 4 years of age and in 18–20% between the age of 8 and 16 years.
䡲
Not blocked with eye opening, but blocked by touch, movement of limbs (especially contralateral limbs) or thought of movement.
Photomyogenic response (Figures 1-103 to 1-106) 䡲
Occurs in 0.1% of the normal population and 1% of patients with epilepsy. 䡲 Most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching during eye closure and stops with flash.
䡲
䡲
䡲
Immediate cessation of the response at the end of stimulation and prominent electromyographic activity help to distinguish this photomyogenic response from photoparoxysmal response. 䡲 Normal variant although it can coexist with photoparoxysmal response or rarely progress to generalized tonic-clonic seizures (GTCS).
Mu rhythm (Figures 1-107 to 1-115) 䡲
Physiologic EEG finding of no clinical significance. 䡲 Central rhythm of an alpha frequency band (8–10 Hz) with an arciform configuration, intermix or alternate with beta activity.
Usually asymmetric, asynchronous and independent in the two hemispheres. 䡲 Consistent asymmetry of amplitude or frequency of mu suggests an abnormality on the side of lower amplitude or frequency. Believed to be the rhythm of the sensorimotor cortex at rest. 䡲 Prominent in the patients with underneath skull defect (breach rhythm). 䡲
Paradoxical mu rhythm – induced by contralateral movement or touch after the mu rhythm has dropped out in drowsiness. Paradoxical AR may be induced at the same time.
8
Normal and Benign Variants
1
FIGURE 11. Normal Alpha Rhythm and Squeak Effect. An alpha rhythm appears immediately after eye closure and disappears with eye opening. Immediately after eye closure, alpha frequency may be accelerated for 0.5–1 sec. Therefore, alpha frequency assessment should not be done during this period. This is called the “squeak effect.”1
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Normal and Benign Variants
9
FIGURE 12. Alpha Rhythm in Subdural EEG. Subdural recording shows the alpha rhythm in the right occipital lobe with reaction to eye opening and eye closure. Harmonic of the alpha rhythm is frequently seen in an intracranial EEG. In addition, alpha rhythms usually are sharper in morphology because the scalp and skull act as a high-frequency filter and pass lower frequencies more efficiently than higher frequencies.2 All the normal EEG rhythms seen in the scalp EEG can be seen in the intracranial EEG.3
10
Normal and Benign Variants
1
FIGURE 13. Beating (Waxing and Waning of Amplitude). The beating or waxing and waning of the alpha rhythm is the effect of two separate alpha frequencies.
1
Normal and Benign Variants
11
FIGURE 14. Alpha and Mu Rhythm. Eye opening (open arrow) attenuates the alpha rhythm but reveals a prominent mu rhythm (C3 and C4) at the same frequency (11 Hz). Note lateral eye movement (X) after the eye opening. Mu is an arc-like central rhythm with negative sharp component and positive slow component. The frequency is similar to alpha rhythm and it is intermixed with 20-Hz beta activity. It is located at the C3, C4, and Cz electrodes. It is not blocked by eye opening but is attenuated by movement of extremities or thinking about moving with greater effect on opposite hand. The apiculate phase may resemble spikes.
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Normal and Benign Variants
1
FIGURE 15. Alpha and Mu Rhythm. Eye opening attenuates the alpha rhythm (open arrow), and eye closure accentuates the alpha rhythm. Eye opening or closure does not affect the mu rhythm (C3 and C4). Mu is an arc-like central rhythm with negative sharp component and positive slow component. The frequency is similar to alpha rhythm and it is intermixed with 20-Hz beta activity. It is located at C3, C4, and Cz electrodes and is not blocked by eye opening but attenuated by movement of extremities or thinking about moving with greater effect on opposite hand. The apiculate phase may resemble spikes.
1
Normal and Benign Variants
13
FIGURE 16. Slow Alpha Variant. Slow alpha variant (open arrow) is described as rhythmic sinusoidal, notched theta or delta activities, which have a harmonic relationship with the alpha rhythm (one-third or, more commonly, one-half the frequency). Slow alpha variant is a rare physiologic variant of alpha rhythm (less than 1% of normal adults) seen during relaxed wakefulness, has a harmonic relationship and is interspersed with the normal alpha rhythm, and shows similar distribution and reactivity as a normal alpha rhythm.4, 5 It should not be misinterpreted as occipital intermittent rhythmic delta (OIRDA) or theta activity activities, pathologic findings seen in children and adults. Slow alpha variant may be differentiated from pathologic slow waves by morphology (notched appearance), frequency (subharmonic of normal alpha rhythm), reactivity to eye opening, and disappearance with sleep. It sometimes mimics RTTD, except that it occurs only over the posterior head regions.
14
Normal and Benign Variants
1
FIGURE 17. Slow Alpha Variant. EEG of a 7-year-old boy with recurrent syncope showing semi-rhythmic notched theta activity, a subharmonic of the baseline alpha rhythm at channels 4, 8, 14, and 18, which appears immediately following the eye blink. Slow alpha variant is a rare, benign EEG variant (less than 1% of normal adults), has a harmonic relationship with the alpha rhythm, and shows similar distribution and reactivity as a normal alpha rhythm, reactivity to eye opening and eye closure (arrow), and disappearance with sleep.4 It should not be misinterpreted as occipital intermittent rhythmic delta activity (OIRDA) or theta activity, pathologic findings seen in children and adults.
1
Normal and Benign Variants
FIGURE 18. Fast Alpha Variant. The fast alpha variant pattern (arrow) is a harmonic of the alpha rhythm that has a frequency approximately twice that of alpha rhythm, usually within the range of 16 to 20 Hz, with a voltage of 20-40 μV. It is usually intermingled with alpha rhythm and shows reactivity and a distribution similar to that of alpha rhythm.
15
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Normal and Benign Variants
1
FIGURE 19. Fast Alpha Variant. The fast alpha variant pattern (within the rectangle) is a harmonic of the alpha rhythm that has a frequency approximately twice that of alpha rhythm, usually in the range of 16 to 20 Hz, with a voltage of 20-40 μV. It is usually intermingled with alpha rhythm and shows reactivity and distribution similar to that of alpha rhythm.
1
Normal and Benign Variants
FIGURE 110. Fast Alpha Variant. The fast alpha variant pattern (box) is a harmonic of the alpha rhythm that has a frequency approximately twice that of alpha rhythm, usually in the range of 16 to 20 Hz, with a voltage of 20-40 μV. It shows reactivity and a distribution similar to that of alpha rhythm.
17
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Normal and Benign Variants
1
FIGURE 111. Low-Voltage Background Activity. EEG of a 16-year-old-boy with recurrent syncope. Low-voltage EEG during wakefulness characterized by activity of voltage ≤ 20 μV over all head regions. With higher gain, a wide variety of different frequency waveforms are noted including beta, theta, and, to a lesser degree, delta waves with or without a posterior alpha rhythm, over the posterior areas.6 Waves of higher amplitude can sometimes be activated by hyperventilation, photic stimulation, and sleep. Low voltage EEG is a normal EEG variant and does not represent an abnormality unless the frequency band shows abnormal local or diffuse slowing, asymmetries, or paroxysmal events. The prevalence of low-voltage EEG was 1% between ages 1 and 20 years, 7% between 20 and 39 years, and 11% between 40 and 69 years.7 The prevalence increases sharply after the age 13.8 Low-voltage EEG in children below age 10 years is considered abnormal if neither hyperventilation nor non-REM sleep changes the low voltage character. Low voltage EEG can be seen in adults with chronic vertebrobasilar artery insufficiency and chronic alcoholism.9
1
Normal and Benign Variants
19
FIGURE 112. Posterior Slow Waves of Youth. EEG of a 9-year old boy with recurrent headaches and numbness shows bilateral occipital slow waves (Box) intermixed with and briefly interrupting the alpha rhythm. “Posterior slow waves of youth” (youth waves or polyphasic waves) are physiologically high-voltage theta or delta waves accompanied by the alpha rhythm and creating spike wave-like phenomenon. They are most commonly seen in children aged 8 to 14 years but are uncommon in children under 2 years. They have a 15% incidence in healthy individuals aged 16 to 20 years but are rare in adults after age 21 years. They are typically seen both unilaterally and bilaterally in a single recording. They are always accompanied by the alpha rhythm, attenuated with eye opening, disappear with the alpha rhythm during drowsiness and light sleep, and may be accentuated by hyperventilation.10–12
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Normal and Benign Variants
1
FIGURE 113. Posterior Slow Waves of Youth; Attenuated with Eye Opening. EEG of a 10-year-old boy with syncope showing occipital slow theta and delta waves (arrows) mixed with and briefly interrupting the alpha rhythm in both occipital regions but maximally expressed in the left hemisphere. These are so-called “posterior slow waves of youth,” which are physiologic findings seen commonly in children aged 8 to 14 years. They are always accompanied by the alpha rhythm, are attenuated with eye opening (open arrow). and disappear with the alpha rhythm during drowsiness and light sleep.10–12
1
Normal and Benign Variants
21
FIGURE 114. Intermittent Right Occipital Delta Slowing; Simulating Posterior Slow Wave of Youth. An 8-year-old boy with autism and few generalized tonic-clonic seizures. The 24-hour ambulatory EEG performed to rule out ESES persistently shows decreased alpha reactivity to eye closure (open arrow) and intermittent polymorphic delta slowing (arrow head) in the right occipital region without shifting lateralization. This EEG can simulate “posterior slow waves of youth,” which is a physiologic finding. However, persistent lateralization raises a concern of abnormality in the right posterior quadrant.
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Normal and Benign Variants
1
FIGURE 115. Asymmetric Alpha Rhythm. (same EEG recording as in Fig. 1-14) EEG shows a train of spikes in the right parietal region (open arrow) as well as theta and polymorphic delta slowing in the right occipital region. Persistent lateralization of theta and delta slowing is a red flag for posterior slow wave of youth and should raise the concern of focal abnormality in that area.
1
Normal and Benign Variants
23
FIGURE 116. Squeak Effect. EEG of a healthy 10-year-old boy with migraine. Immediately after eye closure, the alpha frequency may be accelerated for 0.5–1 sec; therefore, alpha frequency assessment should not be done during this period. This is called the “squeak effect.”1
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Normal and Benign Variants
1
FIGURE 117. Lambda Waves. Lambda waves are “sharp transients occurring over the occipital region of the head of waking subjects during visual exploration, mainly positive relative to other areas and time locked to saccadic eye movement. Amplitude varies, but is generally below 50 μV.”6 Lambda waves do not occur before 1 year of age and are most common during the middle years of childhood. The prevalence of lambda waves between 3 and 12 years is about 80%. Lambda waves have been described as biphasic or triphasic; their predominant positive component is preceded and followed by a negative component. They may be asymmetrical on the two sides or may be present only on one side. Strictly speaking, they are bilaterally synchronous. The most important precipitating factor of lambda waves is voluntary scanning eye movements. Lambda waves usually occur as random and isolated waveforms but may recur at intervals of 200–500 msec as in this EEG page.9 Sometimes, especially when present unilaterally, they may be mistaken for focal abnormalities, but the distinction can be made by replacing the geometric image with a blank surface.13
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Normal and Benign Variants
25
FIGURE 118. Lambda Waves and Alpha Rhythm. Lambda waves (open arrow) are “sharp transients occurring over the occipital region of the head of waking subjects during visual exploration,” mainly positive relative to other areas and time locked to saccadic eye movement. Amplitude varies, but is generally below 50 μV.6 Lambda waves have been described as biphasic or triphasic; their predominant positive component is preceded and followed by a negative component. They are most commonly seen in children aged 2–15 years. They may be asymmetrical, appearing bilaterally, or may be present only on one side. Strictly speaking, they are bilaterally synchronous. The most important precipitating factor of lambda waves is voluntary scanning eye movements.9 Note alpha rhythm with eye closure (double arrows).
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Normal and Benign Variants
1
FIGURE 119. Lambda Waves. Lambda waves (A) are “sharp transients occurring over the occipital region of the head of waking subjects during visual exploration,” mainly positive relative to other areas and time locked to saccadic eye movement. Amplitude varies, but is generally below 50 μV.6 Lambda waves have been described as biphasic or triphasic; their predominant positive component is preceded and followed by a negative component. They are most commonly seen in children aged 2–15 years. They may be asymmetrical on the two sides or may be present only on one side although are strictly bilateral synchronous. The most important precipitating factor of lambda waves is voluntary scanning eye movements.9 POSTS (B, sample from the other EEG), also known as “lambdoid waves” are usually monophasic, sharply contoured electropositive waves seen mainly during light to moderate levels of sleep.
1
Normal and Benign Variants
27
FIGURE 120. Positive Occipital Sharp Transients of Sleep (POSTs). EEG of a 4-year-old asymptomatic male during drowsiness. Characteristics of POSTS include sharply-contoured, surface positive, occurring in trains with a repetitive rate of 4–5 Hz, and monophasic checkmark-like waveform seen singularly or in clusters over the occipital regions. POSTS are always bilaterally synchronous but are commonly asymmetric on the two sides and should not be misinterpreted as epileptiform activity or focal nonepileptiform activity.10,14 POSTS occur during drowsiness and stage 2 sleep.
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Normal and Benign Variants
1
FIGURE 121. Positive Occipital Sharp Transients of Sleep (POSTs). EEG of a 3-year-old asymptomatic male during stage 2 sleep. Characteristics of POSTS are sharp-contoured, surface positivity, occurring in trains with a repetitive rate of 4–5 Hz, and monophasic checkmark-like waveform seen in singly or in clusters over the occipital regions. POSTS are always bilaterally synchronous but are commonly asymmetric on the two sides and should not be misinterpreted as epileptiform activity or focal nonepileptiform activity.10,14 POSTS occur during, drowsiness and stage 2 sleep.
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Normal and Benign Variants
FIGURE 122. Posterior Occipital Sharp Transients of Sleep (POSTS). POSTS (Box) can simulate epileptiform activity. Their triangular morphology, persistent lack of slow wave following sharp transients, positive polarity, constant symmetry, and occurrence during sleep differentiate them from epileptiform activity.
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Normal and Benign Variants
1
FIGURE 123. Aymmetric Posterior Occipital Sharp Transient of Sleep (POSTS). A 7-year-old boy with recurring staring episodes and behavioral issues. The routine EEG during sleep shows bilaterally synchronous but asymmetric POSTS. Characteristics of POSTS are surface positivity, occurring in trains with a repetitive rate of 4–5 Hz, and monophasic checkmark-like waveforms. POSTS are always bilaterally synchronous but are commonly asymmetrical on the two sides and should not be misinterpreted as epileptiform activity or focal nonepileptiform activity.10
1
Normal and Benign Variants
31
FIGURE 124. Pathologically Asymmetry of Positive Occipital Sharp Transients of Sleep (POSTS). A 7-year-old girl born 24 weeks gestational age with grade 4 intraventricular hemorrhage (IVH). Subsequently, she developed spastic quadriparesis and global developmental delay. Cranial MRI showed periventricular leukomalacia with bilateral white matter involvement, greater on the left. Prolonged 72-h-video-EEG demonstrates persistent suppression of POSTS and anterior beta activity in the left hemisphere throughout the drowsy and sleep EEG recording. Although persistent asymmetric POSTS in this case are pathologic, physiologic POSTS can be quite asymmetric and may be present on only one side in the routine EEG. Therefore, asymmetric POSTS without other associated abnormalities should not be misinterpreted as abnormal.
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Normal and Benign Variants
1
FIGURE 125. Posterior Slow-Wave Transients (Occipital Sharp Transients); Associated with Eye Movements. Posterior slow-wave transients associated with eye movements is an EEG pattern consisting of a monophasic or biphasic slow transient with a duration of 200–400 msec and a voltage of up to 200 μV in the occipital regions (*). The latency of 100–500 msec is noted after the eyeblinks or eye movements. The initial component of the transient is surface positive. The ascending phase is steeper than the descending phase. This EEG pattern is seen in children age 6 months to 10 years, but seen most commonly in children aged 2–3 years. This EEG pattern is a normal phenomenon but may be misinterpreted as epileptiform activity.9,10
1
Normal and Benign Variants
FIGURE 126. Posterior Slow-Wave Transients (Occipital Sharp Transients); Associated with Eye Movements. Posterior slow-wave transients associated with eye movements is an EEG pattern consisting of a monophasic or biphasic slow transient with a duration of 200–400 msec and a voltage of up to 200 μV in the occipital regions (open arrow). The latency of 100–500 msec is noted after the eyeblinks or eye movements. The initial component of the transient is surface positive. The ascending phase is steeper than the descending phase. This EEG pattern is seen in children age 6 months to 10 years, but seen most commonly in children aged 2–3 years. This EEG pattern is a normal phenomenon but may be misinterpreted as epileptiform activity.9,10
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Normal and Benign Variants
1
FIGURE 127. Posterior Slow-Wave Transients (Occipital Sharp Transients); Associated with Eye Movements. Posterior slow-wave transients associated with eye movements is an EEG pattern consisting of a monophasic or biphasic slow transient with a duration of 200–400 msec and a voltage of up to 200 μV in the occipital regions (*). The latency of 100–500 msec is noted after the eyeblinks or eye movements. The initial component of the transient is surface positive. The ascending phase is steeper than the descending phase. This EEG pattern is seen in children age 6 months to 10 years, but seen most commonly in children aged 2–3 years. This EEG pattern is a normal phenomenon but may be misinterpreted as epileptiform activity.9,10
1
Normal and Benign Variants
35
FIGURE 128. Posterior Slow-Wave Transients (Occipital Sharp Transients); Associated with Eye Movements. Posterior slow-wave transients associated with eye movements is an EEG pattern consisting of a monophasic or biphasic slow transient with a duration of 200–400 msec and a voltage of up to 200 μV in the occipital regions (*). The latency of 100–500 msec is noted after the eyeblinks or eye movements. The initial component of the transient is surface positive. The ascending phase is steeper than the descending phase. This EEG pattern is seen in children aged 6 months to 10 years, but seen most commonly in children aged 2–3 years. This EEG pattern is a normal phenomenon but may be misinterpreted as epileptiform activity.9,10
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Normal and Benign Variants
1
FIGURE 129. Occipital Slow Transients; Cone Wave and Diphasic Slow Transient. In children, the transition from light to deep sleep may be associated with bilateral high-voltage slow transients in the occipital regions. These waves vary from a cone-shaped configuration (double arrows) to a biphasic slow transient (open arrow). These transients occur every 3–6 sec during light sleep and more frequently during deeper stage of sleep.10
1
Normal and Benign Variants
37
FIGURE 130. Occipital Slow Transients; Cone Waves. In children, the transition from light to deep sleep may be associated with bilateral high-voltage slow transients in the occipital regions. These waves vary from a cone-shaped configuration to a biphasic slow transient. These transients occur every 3–6 sec during light sleep and more frequently during deeper stages of sleep.10 Cone waves or “O” waves (arrow) are physiologic waves presenting during non-REM sleep from infancy until 5 years of age. They are isolated, medium- to high-amplitude, monomorphic, triangular shaped, delta waves with a typical duration greater than 250 msec that occur over the occipital region.15
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Normal and Benign Variants
1
FIGURE 131. Occipital Slow Transients; Cone Wave. In children, the transition from light to deep sleep may be associated with bilateral high-voltage slow transients in the occipital regions. These waves vary from a cone-shaped configuration to a biphasic slow transient. These transients occur every 3–6 sec during light sleep and more frequently during deeper stage of sleep.10 Cone waves or “O” waves (arrow) are physiologic waves presenting during non-REM sleep from infancy until 5 years of age. They are isolated, medium- to high-amplitude, monomorphic, triangular shaped, delta waves with a typical duration greater than 250 msec that occur over the occipital region.15
1
Normal and Benign Variants
39
FIGURE 132. Excessive Photic Response at High Frequency Stimulation (H Response); Migraine. A 17-year-old with recurrent headaches after the epilepsy surgery (resection of epileptogenic zone in the right frontal region). The patient had headache characteristics compatible with the common migraine, normal neurologic examination, and a strong family history of migraines. His headaches resolved with amitryptylline. The neuroimaging was not performed. This EEG was performed as a routine postoperative follow-up. The “H-response” is a prominent photic driving response at flash rates beyond 20 Hz. The sensitivity of the H-response varied from 25% to 100%, and the specificity from 80% to 91%. Although the relatively high sensitivities and specificities of the H-response in distinguishing migraine patients from controls and tension headache patients, the American Academy of Neurology concluded that the H-response was not more effective than history and examination in diagnosing headaches. They, therefore, did not recommend its use in clinical practice. However, in the presence of complex or prolonged aura, visual hallucinations, disorders of consciousness, history of recent trauma, and in infants with vomiting and ocular and head deviation, the EEG may be useful for clinical diagnosis and help to monitor therapeutic response.16,17
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Normal and Benign Variants
1
FIGURE 133. Excessive Photic Response at High Frequency Stimulation (H Response) Migraine. The “H-response” is a prominent photic driving response at flash rates beyond 20 Hz. In a critical review of the literature, the reported sensitivity of the H-response varied from 25% to 100%, and the specificity from 80% to 91%. Although the relatively high sensitivities and specificities reported suggest that the H-response may be effective in distinguishing migraine patients from controls, and possibly migraineurs from tension headache sufferers, the Quality Standards Subcommittee (QSS) of the American Academy of Neurology concluded that the H-response was not more effective than the neurological history and examination in diagnosing headaches and not recommended in clinical practice. However, in the presence of complex or prolonged aura, visual hallucinations, disorders of consciousness, history of recent trauma, and in infants with vomiting and ocular and head deviation, the EEG may be useful for clinical diagnosis and help to monitor therapeutic response.16,17
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Normal and Benign Variants
41
FIGURE 134. Cyclic Vomiting; Migraine; Excessive Photic Response. A 2-year-old boy with cyclic vomiting who had normal extensive GI work-up. Cranial MRI was normal. EEG shows excessive photic response intermixed with sharply-contoured waves. Very strong family history of migraines was noted. The patient was diagnosed with “cyclic vomiting” caused by migraine. He showed dramatic improvement in vomiting after the treatment with cyproheptadine. Photic driving responses in children <6 years are relatively small.18 Stimulus frequencies <3 Hz rarely produce a response. The maximal responses are obtained with stimulus frequencies near the frequency of individual’s posterior dominant rhythm.15 Although excessive photic response can be seen in normal individuals, it is more commonly seen in migraine patients. However, AAN concluded that the photic response was not more effective than history and examination in diagnosing headaches and did not recommend its use in clinical practice.16 In 2–4% of normal children, posteriorly predominant paroxysmal slow activity is sometimes associated with sharp components.11
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Normal and Benign Variants
1
FIGURE 135. Needle-Like Occipital Spikes of the Blind. A 4-year-old girl with congenital blindness due to congenital CMV infection who developed acute encephalopathy due to enteroviral infection (hand-foot-mouth syndrome). This EEG was requested for altered mental status. EEG demonstrates diffuse delta slowing with occipital predominance and frequent needle-like spikes in the occipital region. The patient regained her mental status completely 4 days later without treatment with anticonvulsant. Needle-like spikes (*) develop in the occipital region in most patients with congenital blindness. Functional deafferentation of the visual cortex gives rise to an increase in its irritability and this makes it fire off in this special manner. These spikes are not correlated with epileptic seizures. These discharges disappear during childhood or adolescence.19
1
Normal and Benign Variants
FIGURE 136. Needle-Like Occipital Spikes of the Blind. A 7-month-old girl with congenital blindness due to septo-optic dysplasia and with pendular nystagmus. This EEG was requested to evaluate for possible seizure as a cause of nystagmus. EEG demonstrates frequent low-amplitude and short-duration spikes in the occipital regions (open arrows). Needle-like spikes develop in the occipital region in most patients with congenital blindness. Functional deafferentations of the visual cortex give rise to an increase in its irritability that make it fire off in this special manner. These spikes are not correlated with epileptic seizures. These discharges disappear during childhood or adolescence.19
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Normal and Benign Variants
1
FIGURE 137. Needle-Like Spikes of the Blind. A 25-month-old girl with congenital blindness and epilepsy due to congenital toxoplasmosis who has pendular nystagmus. This EEG was requested to evaluate for epileptiform activity as a cause of her nystagmus. EEG demonstrates frequent low-amplitude and short-duration spikes in the occipital regions (*). Needle-like spikes develop in the occipital region in most patients with congenital blindness. Functional deafferentation of the visual cortex gives rise to an increase in its irritability, which makes it fire off in this special manner. These spikes are not correlated with epileptic seizures. These discharges disappear during childhood or adolescence.19
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Normal and Benign Variants
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FIGURE 138. Drowsiness; Older Children and Adults. In older children and adults, early drowsiness is associated with (1) alpha dropout (earliest sign); (2) increased beta activity over the fronto-central regions; (3) diffuse rhythmic theta activity with anterior predominance; and (4) slow eye movement. Mu rhythm, wicket wave and 14- and 6 Hz positive spikes can be seen during drowsiness. Drowsiness must be differentiated from increased alertness after eye opening or caused by emotional stress that can cause alpha blocking. In such cases the slow frequency component is absent and beta frequency predominates. Deep drowsiness is marked by the appearance of vertex waves and POSTS that persist during light sleep and deep sleep.20
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FIGURE 139. Drowsiness; 14-and-6 Hertz Positive Bursts. In older children and adults, early drowsiness is associated with (1) alpha dropout (earliest sign); (2) increased beta activity over the fronto-central regions (double arrows); (3) diffuse rhythmic theta activity with anterior predominance (open arrow); and (4) slow eye movement (doublehead arrow). Mu rhythm, wicket wave and 14- and 6 Hz positive spikes (*) can be seen during drowsiness. Drowsiness must be differentiated from increased alertness after eye opening or caused by emotional stress that can cause alpha blocking. In such case slow frequency component is absent and beta frequency predominates. Deep drowsiness is marked by the appearance of vertex waves and POSTS that persist during light sleep and deep sleep.20
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FIGURE 140. Stage 2 (Light Sleep). Stage 2 sleep shows symmetric, synchronous theta rhythms with posterior predominance, 12–15/sec spindles, vertex sharp waves, K-complex and POSTS. The appearance of sleep spindles in the 12–15/sec range is a hallmark of sleep onset.20
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FIGURE 141. Sleep Spindles During Subdural EEG Recording. Subdural recording showing the sleep spindles in the parietal lobe during sleep. A harmonic of the sleep spindles is more frequently seen in intracranial EEG. In addition, the sleep spindles usually appear sharper in morphology as the scalp and skull act as a high-frequency filter and pass lower frequencies more efficiently than higher frequencies.2 Disappearance during wakefulness helps to differentiate the sleep spindles from low-voltage fast activity. All normal EEG rhythms seen in the scalp EEG can be seen in the intracranial EEG.3
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FIGURE 142. Stage 3 (Moderate Deep Sleep). Delta frequencies in the 0.75–3/sec range are prominent over the anterior regions. Sleep spindles in the 10–12/sec and even in the 12–14/sec ranges are still present but gradually become less prominent. Rhythmic activity of 5–9/sec is common. Rhythmic and symmetrical delta activity occurs during 20% to 50% of the recording.20
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FIGURE 143. Stage 4 (Very Deep Sleep). Over 50% of the recording is delta rhythm. Spindles are rare. Arousal at this stage can be correlated with sleep disorders (somnambulism, nocturnal terror, or enuresis), and can cause confusion. Occasionally, spikes in temporal lobe epilepsy will only appear in stage 3 and 4 sleep.20
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FIGURE 144. REM Sleep. EEG reveals low-voltage activity, polyrhythmic waves, slower alpha waves, and short bursts of “saw-tooth waves” over the frontal or vertex leads (Box B), and quick lateral eye movement (Box A). Appearance of REM sleep in routine EEG is seen in narcolepsy and in patients who are withdrawn from CNS depressants such as alcohol or phenobarbital.20,21
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FIGURE 145. K Complexes. K complexes contain 3 components including sharp, slow, and fast. They are seen in stage 2 sleep and arousal. The K complexes are largest in older children and adolescence. With increasing age, the K complexes show the decreasing voltage with tiny superimposed spindle-like waves.
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FIGURE 146. Subdural EEG Monitoring; K-Complex During Arousal. Subdural recording showing a run of vertex waves and widely distributed K-complexes, maximally expressed in the parietal lobe during arousal. Harmonic of the sleep spindles is frequently seen in intracranial EEGs. In addition, the sleep spindles usually are sharper in morphology as the scalp and skull act as a high-frequency filter and pass lower frequencies more efficiently than higher frequencies.2 Disappearance during wakefulness helps to differentiate the K-complexes from low-voltage fast activity. All normal EEG rhythms in the scalp EEG can be seen in the intracranial EEG.3
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FIGURE 147. Pathologic vs Physiologic Wave Forms in Intracranial EEG. The differentiation of physiologic waveforms and pathologic waveforms is extremely important in intracranial EEG recording (open arrow-epileptiform in depth electrode; arrow-sleep spindles; double arrows-vertex waves). Harmonic and sharp morphology of the physiologic waveforms in an intracranial EEG make distinguishing between nonepileptiform and epileptiform activities more difficult. Disappearance of spindles and vertex waves during wakefulness, distribution, and morphology help to differentiate them from epileptiform activity, especially between sleep spindles and low-voltage fast epileptiform activity.
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FIGURE 148. Early K-Complex (16 Week CA). K-complex first appears at 4 months of age. They have high amplitude but their rise is not as abrupt and the configuration is not as sharp as one seen in older children.20
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FIGURE 149. Normal Sleep Spindles (2 Months); Definite 14/sec Spindles. Sleep spindles arise from synchronized activity in functionally important neuronal networks linking the thalamus and the cortex. Spindles result from rhythmic spike bursts in inhibitory (GABAergic) thalamic reticular neurons that induce rhythmic rebound bursting in cortical neurons. This process has been shown to result in effective deafferentiation of the cerebral cortex. Cortical neurons show enhanced responsiveness and properties of synaptic plasticity that may have a role in memory and learning processes.22 At 1.5 to 2 months, 14/sec spindles are first seen.23
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FIGURE 150. Normal Sleep Spindles (8 Weeks CA); Harmonic of Sleep Spindles. EEG of an 8-week-old full-term boy shows low-voltage 22–24 Hz biphasic beta activity diffusely in the central vertex and bilateral central-parietal areas. This exceptional waveform most likely represents a harmonic of sleep spindles. More commonly spindles occur independently from faster 18–25 Hz activity and both patterns may be seen at the same time.24
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FIGURE 151. Normal Sleep Spindles (10 Weeks CA). Trace alternant disappears in the first month of life. Sleep spindles usually appear in the second months of life with frequency between 12 and 15/sec. Throughout infancy, they are maximal over the central and parietal areas with shifting asymmetry. They usually are electronegative with a rounded positive component.20 A complete absence of spindles at age 3–8 months indicates a severe abnormality.25
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FIGURE 152. Normal Sleep Spindles (3-6 Months CA); Prolonged Runs of Spindles. Between the ages of 3–6 months, sleep spindles appear to be biphasic and occur as prolonged runs, up to 10–15 sec.22,23,26 The prolonged run of spindles is a very useful developmental marker and is rarely seen beyond this age range.
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FIGURE 153. Prolonged Sleep Spindles (3-6 Months CA). Between the ages of 3–6 months, sleep spindles appear to be biphasic and occur as prolonged runs, up to 10–15 sec.22,23,26 The prolonged run of spindles is a very useful developmental marker and is rarely seen beyond this age range.
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FIGURE 154. Prolonged Sleep Spindles (3-6 Months CA). Between the ages of 3–6 months, sleep spindles appear to be biphasic and occur as prolonged runs, up to 10–15 sec.22,23,26 The prolonged run of spindles is a very useful developmental marker and rarely seen beyond this age range.
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FIGURE 155. Normal Sleep Spindles (16 Weeks CA). Between the ages of 3–6 months, sleep spindles appear to be biphasic and as prolonged runs, up to 10–15 sec.22,23,26 The prolonged run of spindles is a very useful developmental marker and rarely seen beyond this age range. Throughout infancy, sleep spindles are maximal over the central and parietal areas with shifting asymmetry. They usually shows electronegative with rounded positive component that is a typical hallmark of sleep spindles in infancy.20,27 These surface-negative spindles with wicket or comb-like shape can be erroneously interpreted as 14/sec positive spikes (below).
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FIGURE 156. Sleep Spindles with Subharmonic. Subharmonic of sleep spindles with a frequency approximately half that of sleep spindles with a notched appearance can be seen. The subharmonic has the same reaction and distribution as sleep spindles.
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FIGURE 157. Normal Sleep Spindles (9 Months); Asynchronous Spindles. In the second half of the first year of life, the spindles appear to be monophasic and are often asynchronous between the two sides. Asynchronous spindles may occasionally continue from 1 to 2 years of age but rarely are seen after the age of 2 years when interhemispheric synchrony of the spindles are.22,23
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FIGURE 158. Normal Sleep Spindles (14 Months); Synchronous Spindles. After 1 year, interhemispheric synchrony of the spindles is seen although not constant until the infant is nearly 2 years old. The frequency of spindles also changes, with 12/sec components becoming more prominent.22
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FIGURE 159. Mitten Pattern. Mitten patterns are seen during sleep and consist of a sharply-contoured waveform on the slope of a slow wave of the same polarity that resemble a mitten, with the thumb of the mitten formed by the last wave of a spindle and the hand portion by the slower wave component. Mittens are a variant of a vertex wave or K-complex and should not be mistaken for a spike-and-wave discharge.14 It is best seen in the referential montage and in stage 3 sleep.20
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FIGURE 160. Mitten Pattern. Mitten patterns are seen during sleep and consist of a sharply-contoured waveform on the slope of a slow wave of the same polarity that resemble a mitten, with the thumb of the mitten formed by the last wave of a spindle and the hand portion by the slower wave component. Mittens are a variant of a vertex wave or K-complex and should not be mistaken for a spike-and-wave discharge.14 It is best seen in the referential montage and in stage 3 sleep.20
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FIGURE 161. Mittens. Mitten patterns are seen during sleep and consist of a sharp-contoured waveform on the slope of a slow wave of the same polarity that resemble a mitten, with a thumb of mitten formed by the last wave of a spindle and the hand portion by the slower wave component. Mittens are a variant of a vertex wave or K-complex and should not be mistaken for a spike-and-wave discharge.14 It is best seen in referential montage and stage 3 sleep.20
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FIGURE 162. Mittens. Mitten patterns are seen during sleep and consist of a sharply-contoured waveform on the slope of a slow wave of the same polarity that resemble a mitten, with the thumb of the mitten formed by the last wave of a spindle and the hand portion by the slower wave component. Mittens are a variant of a vertex wave or K-complex and should not be mistaken for a spike-and-wave discharge.14 It is best seen in the referential montage and in stage 3 sleep.20
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FIGURE 163. Hypnagogic Hypersynchrony. Hypnagogic hypersynchrony is an activity seen in early drowsiness and in arousal from deeper sleep. It is characterized by bilateral synchronous, high voltage, rhythmic 3-5 Hz activity. This activity first appears at the age of 2 to 3 months and becomes prominent and continuous at 9 months. At age 4 years, it becomes shorter in duration and more paroxysmal in appearance. By age 9 to 11 years, it becomes rare. Although the presence of hypnagogic hypersynchrony at age 12 years is considered abnormal by some authors,21 it may be seen in normal children up to the age of 12-13 years.10 The frequency of hypnagogic hypersynchrony is 3-4 Hz at the age of 2-3 months and increases to 4-5 Hz in older children. This EEG also shows slow eye movement (SEM), maximally seen at F7 and F8, which is also one of the signs of drowsiness.
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FIGURE 164. Hypnagogic Hypersynchrony. Nearly continuous hypnagogic hypersynchrony in a 22-month-old infant. Hypnagogic hypersynchrony appears at approximately 3 months of age and is characterized by monorhythmic, slow generalized activity with the frequency of 3-4 Hz during drowsiness. It may be seen in older children up to 12-13 years but is rare after 11 years (incidence of only 10%). The frequency increases to 4-5 Hz in older children.10
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FIGURE 165. Asymmetric Hypnagogic Hypersynchrony. EEG of a 25-month-old boy with asymmetric hypnagogic hypersynchrony with shifting predominance. The paroxysmal bursts of generalized high-voltage, rhythmically monotonous theta activity superimposed on low-voltage background activity, so-called “hypnagogic hypersynchrony,” is the hallmark of drowsiness in early childhood. Occasionally, small sharp or spiky discharges may be interspersed between the theta waves. These discharges should not be interpreted as epileptiform activity unless they are definitely distinct from background activity and not only occur during drowsiness or at the onset of sleep but also persist into deeper stages of sleep. Asymmetric hypnagogic hypersynchrony with shifting predominance can be seen and is not considered abnormal.10,11,28,29
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FIGURE 166. Hypnagogic Hypersynchrony. EEG of a 4-year-old boy with hypnagogic hypersynchrony. The paroxysmal bursts of generalized high-voltage, rhythmically monotonous theta activity superimposed on low-voltage background activity, so-called “hypnagogic hypersynchrony” is the hallmark of drowsiness in early childhood. Occasionally, small sharp or spiky discharges may be interspersed between the theta waves. These discharges should not be interpreted as epileptiform activity unless they are definitely distinct from background activity and not only occur during drowsiness or at the onset of sleep but also persist into deeper stages of sleep.
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FIGURE 167. Hypnic Myoclonia (HM) (Sleep Starts or Hypnogogic Jerks). Video-EEG of a 5-year-old boy with well-controlled focal epilepsy shows a burst of high-voltage 3–4 Hz delta activity intermixed with low-amplitude spikes during chin quivering (*). This EEG pattern is compatible with hypnagogic hypersynchrony associated with HM. This wake-to-sleep transition event is characterized by a sudden, single, brief muscular contraction of the legs and occasionally the arms, head, and postural muscles.30 Hypnagogic hallucinations often occur before the sleep starts, and the perception of falling may occur, ending with the myoclonic jerk. HM is a physiologic finding unless it is frequent and results in sleep-onset insomnia. It also must be differentiated from seizure, especially if it occurs in patients with known epilepsy.31,32 HM occurs in 60–79% of normal individuals. Ninety percent of patients stop these movements by age 4 years. It is more common in boys than in girls by 4:1.33 It may be frightening when observed by a parent, especially if associated with a vocalization or cry. Injury from the massive movement is rare, but foot injuries secondary to kicking a bedpost or crib rail may occur.34
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FIGURE 168. 14-and-6-Hertz Positive Spikes; Hypnagogic Hypersynchrony. EEG of a 5-year-old asymptomatic boy shows 14- and 6 Hz positive spikes (arrow head) immediately after hypnagogic hypersynchrony (open arrow). Fourteen and six hertz positive spikes (arrow head) are commonly seen during drowsiness.35
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FIGURE 169. Asymptomatic Centro-Temporal Spikes; Hypnagogic Hypersynchrony. An 8-year-old boy with recurrent syncope without other associated symptoms suspicious of seizures or other neurologic conditions except borderline ADHD. There was a history of GTCS in his 4-year-old brother. EEG during drowsiness shows hypnagogic hypersynchrony and bilateral-independent centro-temporal spikes. Characteristic spikes over the rolandic area are regarded as neurobiological markers of BECTS. However, rolandic (centro-temporal) spikes have been reported in normal children without clinical seizures or neurologic manifestations. They are seen in 1.2–3.5% of normal healthy children in the community36,37 and 6–34% of siblings of patients affected by BECTS.38,39 The risk of epilepsy is higher if rolandic spikes remain unilateral during sleep, rolandic spikes continue during REM sleep, and if they occur in the presence of generalized spike-wave discharges.40 The frequency of rolandic spikes in children with ADHD (3–5.6%) is significantly higher than expected from epidemiologic studies although how ADHD symptoms are related to rolandic spikes is still unclear.41–44
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FIGURE 170. Hypnic Myoclonia; Hypnagogic Hypersynchrony. Video-EEG of a 5-year-old boy with well-controlled focal epilepsy shows a burst of high-voltage 4 Hz delta activity intermixed with low-amplitude spike-like during right arm jerks (arrow). This EEG pattern is compatible with hypnagogic hypersynchrony and the right arm jerking is most likely to be hypnic myoclonia. Sleep starts (hypnic myoclonia) also have been termed “hypnagogic jerks”. This wake-to-sleep transition event is characterized by a sudden, single, brief muscular contraction of the legs and occasionally the arms, head, and postural muscles.30 Sensory hallucinations (hypnagogic hallucinations) often occur before the sleep start, and the subjective perception of falling may occur, ending with the myoclonic jerk. Sleep starts are common, occur in most individuals, and are not pathologic unless they are frequent and result in sleep-onset insomnia. They also must be differentiated from seizure, especially if they occur in patients with known epilepsy.31 Hypnic myoclonia occurs in 60–79% of normal individuals. Although it may occur at any age, 90% of patients stop these movements by age 4 years. They are more common in boys than girls by 4:1.33 It may be frightening when observed by a parent, especially if associated with a vocalization or cry. Injury from the massive movement is rare, but foot injuries secondary to kicking a bedpost or crib rail may occur.34
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FIGURE 171. Midline Theta Rhythm (Ciganek Rhythm). The midline theta rhythm is a rhythmic train of 5–7 Hz theta activity occurring in the central vertex but may also be seen in the frontal vertex. The morphology includes sinusoidal, aciform, spiky, or mu-like appearance. The midline theta rhythm is seen during wakefulness and drowsiness and shows variable reactivity to eye opening, alerting, and limb movement. The rhythm usually lasts from 3 to 20 sec and does not evolve. It is a nonspecific finding of no clinical significance.35,45
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FIGURE 172. Frontal Arousal Rhythm (FAR). Frontal arousal rhythm (FAR) is a rare EEG rhythm, seen in the frontal regions during arousal from sleep in children. The FAR is characterized by 30–150 μV, predominantly monophasic negative waves, occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec) with a characteristic notching of the ascending or descending phase of each wave. The notched appearance may represent harmonics of the waveforms. The waxing and waning of the amplitude often leads to a spindle-like morphology. The FAR appears at the F3 and F4 electrodes with minimal spread to nearby scalp areas.46 The incidence of the FAR in a normal population is unknown. Although it was first reported in children with minimal cerebral dysfunction or a seizure disorder, it is later considered to be a nonspecific EEG pattern of no clinical significance.35
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FIGURE 173. Frontal Arousal Rhythm (FAR). EEG of an 8-year-old girl with idiopathic generalized epilepsy. Frontal arousal rhythm (FAR) is a rare EEG rhythm, seen in the frontal regions during arousal from sleep in children between ages 2 and 12 years, mainly 2 and 4 years. The FAR is characterized by 30–150 μV predominantly monophasic negative waves, occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec), maximally over the frontal midline, with a characteristic notching of the ascending or descending phase of each wave. The notched appearance may represent harmonics of the waveforms. Waxing and waning of the amplitude often leads to a spindle-like morphology. The FAR appears at the F3 and F4 electrodes with minimal spread to nearby scalp areas.46 The incidence of the FAR in the normal population is unknown. Although it was first reported in children with minimal cerebral dysfunction or a seizure disorder, it is now considered to be a nonspecific EEG pattern of no clinical significance.35
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FIGURE 174. Frontal Arousal Rhythm (FAR). An 8-year-old girl with a history of GTCS. EEG demonstrates trains of rhythmic 6-Hz sharp waves in bifrontal regions during arousal state. Frontal arousal rhythm (FAR) is a rare EEG rhythm, seen in the frontal regions during arousal from sleep in children. The FAR is characterized by 30–150 μV, predominantly monophasic negative waves, occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec) with a characteristic notching of the ascending or descending phase of each wave. The notched appearance may represent harmonics of the waveforms. The waxing and waning of the amplitude often leads to a spindle-like morphology. The FAR appears at the F 3 and F 4 electrodes with minimal spread to nearby scalp areas.46 The incidence of the FAR in a normal population is unknown. Although it was first reported in children with minimal cerebral dysfunction or a seizure disorder, it is now considered to be a nonspecific EEG pattern of no clinical significance.35
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FIGURE 175. Frontal Arousal Rhythm (FAR). EEG of a 10-year-old boy with idiopathic generalized epilepsy. Frontal arousal rhythm (FAR) is a rare EEG rhythm, seen in the frontal regions during arousal from sleep in children between ages 2 and 12 years, mainly 2 and 4 years. The FAR is characterized by 30–150 μV predominantly monophasic negative waves, occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec), maximally over the frontal midline, with a characteristic notching of the ascending or descending phase of each wave. The notched appearance may represent harmonics of the waveforms. Waxing and waning of the amplitude often leads to a spindle-like morphology. The FAR appears at the F3 and F4 electrodes with minimal spread to nearby scalp areas.46 The incidence of the FAR in a normal population is unknown. Although it was first reported in children with minimal cerebral dysfunction or a seizure disorder, it is now considered to be a nonspecific EEG pattern of no clinical significance.35
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FIGURE 176. Frontal Arousal Rhythm (FAR). EEG of a 6-year-old boy with frontal lobe epilepsy during arousal from sleep. Frontal arousal rhythm (FAR) is a rare EEG rhythm, seen in the frontal regions during arousal from sleep in children between ages 2 and 12 years, mainly 2 and 4 years. The FAR is characterized by 30–150 μV predominantly monophasic negative waves, occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec), maximally over the frontal midline, with a characteristic notching of the ascending or descending phase of each wave. The notched appearance may represent harmonics of the waveforms. Waxing and waning of the amplitude often leads to a spindle-like morphology. The FAR appears at the F3 and F4 electrodes with minimal spread to nearby scalp areas.46 The incidence of the FAR in a normal population is unknown. Although it was first reported in children with minimal cerebral dysfunction or a seizure disorder, it is now considered to be a nonspecific EEG pattern of no clinical significance.35 Its mildly abnormal character is likely, but its clinical significance was thought to be debatable.47 Hughes found 70% of patients having epileptic seizures and demonstrated a case in which FAR representing ictal electrographic seizure activity.48
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FIGURE 177. Rhythmic Temporal Theta Bursts of Drowsiness (RTTD); Rhythmic Midtemporal Discharges (RMTD); (Psychomotor Variant). RTTD is seen in 0.5–2.0% of normal adult population and less common in adolescence. It is described as bursts or runs of rhythmic, 5–7 Hz (typically 5–5.5 Hz), theta activity with flat-topped, sharply contoured, often notched appearance in the temporal regions, maximally expressed in the midanterior temporal electrode. The sharper component of the wave usually has a negative polarity in the anterior temporal region. It can occur unilaterally, bilaterally, or shifting from side to side with gradual onset and offset. The pattern is distinguished from ictal epileptiform activity because it is monomorphic and monorhythmic (no evolution into other frequencies), does not alter background activity, occurs in relaxed wakefulness and drowsiness (most common), and disappears in deeper levels of sleep. This pattern has no clinical significance35. However, it was considered by some authors to be a pathologic finding in selected cases.49 This pattern was previously called “psychomotor variant.”50,51 They are also now called “rhythmic midtemporal discharges (RMTDs).”52,53
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FIGURE 178. Rhythmic Temporal Theta Bursts of Drowsiness (RTTD). A 15-year-old girl with recurrent passing out episodes. EEG during drowsiness shows rhythmic 5-6 Hz, theta activity with flat-topped, sharply contoured over the temporal regions with a phase reversal in the posterior temporal electrodes. Rhythmic temporal theta waves of drowsiness (RTTD) is also called rhythmic midtemporal discharges (RMTDs) or psychomotor variant. RTTD is seen in adult and, less commonly, in adolescent. This EEG pattern is distinguished from ictal epileptiform activity in that it is monomorphic and monorhythmic (no evolution), does not affect background activity, and occurs in only in relaxed wakefulness and drowsiness. This EEG pattern is of uncertain significant 35.
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FIGURE 179. Rhythmic Temporal Theta Bursts of Drowsiness (RTTD). A 16-year-old girl with recurrent vertigo who had been diagnosed with simple partial seizures and was treated with carbamazepine. The treatment failed to stop the symptoms and caused side effects. Brain MRI was unremarkable. EEGs were performed four times in the past and were interpreted as epileptiform activity in the temporal regions. This EEG during drowsiness shows a burst of rhythmical 5.5 Hz theta activity in the left temporal region (open arrow) with negative polarity of the sharper component of the burst in the midtemporal region. Note no disruption of alpha rhythm in the left occipital region (arrow heads). The patient was completely normal throughout the discharge. This EEG pattern is compatible with RTTD and is considered a normal variant and has no clinical significance. The patient has done well since stopping carbamazepine.
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FIGURE 180. Rhythmic Temporal Theta Bursts of Drowsiness (RTTD). A 17-year-old boy with recurrent headache and numbness of his right arm. EEG during resting wakefulness shows bilateral-independent 5.5 Hz theta activity in the temporal regions in the 2 hemispheres. As the discharge proceeds, the morphology does not change (monomorphic and monorhythmic). The discharge continues during drowsiness but disappears in stage 2 sleep. These differentiate the RTTD from focal ictal activity.
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FIGURE 181. Rhythmic Temporal Theta Bursts of Drowsiness (RTTD). A 17-year-old boy with a new-onset GTCS. EEG during drowsiness shows runs of bilateral-independent 5.5 Hz sharply-contoured theta activity in the midtemporal regions in the two hemispheres. As the discharge proceeds, the morphology does not change (monomorphic and monorhythmic). The discharge continues during drowsiness but disappears in stage 2 sleep. These findings differentiate the RTTD from focal ictal activity.
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FIGURE 182. Rhythmic Temporal Theta Bursts of Drowsiness (RTTD). EEG during drowsiness shows long runs of monomorphic and monorhythmic notched theta activity that does not evolve into other frequencies or waveforms (same EEG tracing as in Figure 1-81). The patient was completely normal throughout the run of discharge. The discharge disappears during deeper states of sleep. These findings differentiate RTTD from an electrographic seizure. Note an unusual morphology of the discharge that shows positive polarity in the posterior temporal areas.
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FIGURE 183. 14 and 6/sec Positive Spike Discharge. This EEG pattern is defined as bursts of arch shaped waves at 13–17 Hz and/or 5–7 Hz, most commonly at 14 and/or 6 Hz, seen generally over the posterior temporal and adjacent areas of one or both sides of the head during deep drowsiness and very light sleep. The sharp peaks of its components are electropositive compared to other regions. The bursts have a widespread field and last for 0.5–1 sec. This EEG pattern occurs in children from the age of 3 up to young adulthood but more commonly occur between 12 and 20 years with a peak at age 13–14 years. It is best displayed in the contralateral ear reference montage. 14 and 6/sec positive spike discharge is a benign variant of no clinical significance.6,54
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FIGURE 184. 14 and 6/sec Positive Spike Discharge. Fourteen and six per second positive spike discharge shows mainly 13 Hz positive spikes (same EEG recording as in Figure 1-83).
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FIGURE 185. 14 and 6/sec Positive Spike Discharges; (Anterior-Posterior Bipolar). This EEG pattern is defined as bursts of arch shaped waves at 13–17 Hz and/or 5–7 Hz, most commonly at 14 and/or 6 Hz, seen generally over the posterior temporal and adjacent areas of one or both sides of the head during deep drowsiness and very light sleep (arrow). The sharp peaks of its components are positive with respect to other regions. This pattern occurs in the children after age 3 to young adult with a peak at age 13–14 years. This pattern is a benign variant of no clinical significance.6,54
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FIGURE 186. 14 and 6/sec Positive Spike Discharges; (Contralateral Ear Reference). The 14 and 6/sec positive spike discharges are best seen during a contralateral ear reference run (same EEG page as in Figure 1-85).
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FIGURE 187. 14-and-6-Hertz Positive Spikes; Diffuse Encephalopathy. A 12-year-old boy with symptomatic Lennox-Gastaut syndrome after the treatment of status epilepticus with intravenous midazolam. EEG showed continuously diffuse polymorphic delta activity with superimposed “14-and-6-Hertz positive spikes.” Although 14- and 6 Hz positive spikes in diffuse encephalopathy EEG pattern was once thought to be seen exclusively in coma due to Reye’s syndrome,55,56 it was later reported in other encephalopathies of childhood as well57 suggesting that they are epiphenomena or a resilient normal. The 14- and 6 Hz positive spikes are best seen in contralateral ear reference montage.
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FIGURE 188. 14-and 6-Hz Positive Spikes. With contralateral ear reference, 14- and 6 Hz positive spikes (arrow head) are diffusely seen over both hemispheres but maximal in the right posterior temporal region. The opposite polarity in the EEG electrodes over the left hemisphere may be suggestive of the dipole character of this waveform.
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FIGURE 189. 14 and 6/sec Positive Spike Discharge; Referential Montage. Diffuse 14 and 6/sec positive spike discharges with right hemispheric predominance during referential run in a 12-year-old adolescent girl with nonepileptic events.
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FIGURE 190. 14 and 6/sec Positive Spike Discharge; Polyspike-Wave-Like Discharge. When a 14 and 6/sec positive spike discharge is intermixed with diffuse delta or theta slowing, it can simulate spike-wave or polyspike-wave activity (same EEG recording as in Figure 1-89). Note the similarity of the configuration, distribution, and polarity of the waveforms in this EEG page with the Figure 1-89.
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FIGURE 191. 14-and-6-Hertz Positive Spikes. Fourteen and six hertz positive spikes (**) can be mixed with sleep spindles (*). These 2 waveforms can be differentiated from each other by configuration and distribution. Fourteen and six hertz positive spikes occur predominantly during drowsiness and light sleep and consist of short trains of arch-shaped waveforms with alternating positive spiky components and a negative, smooth, rounded waveform. a 14 and 6/sec positive spike maximal amplitude over the posterior temporal region. Sleep spindles occur predominantly during stage 2 sleep and consist of trains of sinusoidal waveforms. It usually has maximal amplitude over the fronto-central region.
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FIGURE 192. 14-and 6-Hertz Positive Spikes (Subdural EEG Monitoring). During a subdural EEG recording in the patient with right neocortical temporal lobe epilepsy, 14 and 6/sec positive spikes are noted in the right anterior temporal region (open arrow) outside of the epileptogenic zone (blue). This is an uncommon location of this EEG pattern that is usually seen in the posterior temporal region. This may be due to brain plasticity. The patient has been seizure free since the epileptogenic zone, excluding the area containing 14 and 6/sec positive spike discharge, was resected. This strongly supports the benign nature of this EEG pattern. The 14 and 6/sec positive spikes EEG pattern has never been reported in the literature.
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FIGURE 193. Small Sharp Spikes (SSS); Benign Epileptiform Transients of Sleep (BETS). Small sharp spike (SSS) is a benign EEG pattern that is seen in 20–25% of a normal adult population. SSS are seen in adults during drowsiness or light sleep. They are usually low voltage, short duration, single monophasic or biphasic spike with an abrupt ascending limb and a steep descending limb. The prominent after coming slow wave may not occur. SSS occur unilaterally or bilaterally.35
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FIGURE 194. Small Sharp Spikes (SSS); Benign Epileptiform Transients of Sleep (BETS). A 16-year-old girl with a history of migraine who presented with recurrent passing out episodes. EEG obtained during light non-REM sleep shows low voltage, short duration, biphasic spikes with an abrupt ascending limb and a steep descending limb. The negative and positive components are of approximately equally spiky character. The spikes are widely distributed in both hemispheres (*). Small sharp spikes (SSS) or BETS occur almost exclusively during drowsiness or light non-REM sleep. A prevalence of 1.36% was found in adult with a peak between ages 30 and 40. It is uncommonly seen in adolescents. There is a debate whether this is a normal or an epileptogenic pattern. In nonepileptics, these discharges may be seen in stroke, syncopal attacks, and psychiatric patients.35,58,59
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FIGURE 195. Small Sharp Spikes (SSS); Benign Epileptiform Transients of Sleep (BETS); Benign Sporadic Sleep Spikes (BSSS). A 17-year-old-right-handed girl with recurrent episodes of déjà vu. The presurgical work-up was consistent with right mesio-temporal epilepsy. EEG shows frequent small sharp spikes (SSS) during drowsiness and light sleep (arrow head). The patient has been seizure free since the right anterior temporal lobectomy. “Small sharp spikes (SSS)” is a benign EEG pattern that is seen in 20–25% of a normal adult population. SSS are seen in adults during drowsiness or light sleep, usually low voltage (less than 50 μV), short duration, single monophasic or biphasic spikes with an abrupt ascending limb and a steep descending limb. The prominent after coming slow wave may not occur. SSS are almost always bilaterally represented, either occurring independently or having reflection to the opposite hemisphere. The bilateral occurrence of the SSS should not be misinterpreted as bilateral epileptogenic foci.35,60
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FIGURE 196. Small Sharp Spikes (SSS). A 9-year-old girl with right mesio-temporal epilepsy caused by mild MCD. She has been seizure free since the left temporal lobectomy. EEG during drowsiness shows diffuse SSS, predominantly in the left hemisphere. “Small sharp spikes (SSS)” is a benign EEG pattern that is seen in 20–25% of a normal adult population. SSS are seen in adults during drowsiness or light sleep, usually low voltage, short duration, single monophasic or biphasic spikes with an abrupt ascending limb and a steep descending limb. The prominent after coming slow wave may not occur. SSS occur unilaterally or bilaterally.35 Some authors believed this pattern indicates a “moderate degree of epileptogenicity.”59
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FIGURE 197. Six-Hertz Spike-and-Wave Bursts; (Phantom Spike-and-Wave Discharge). This EEG pattern can be seen in 2.5% of both adolescents and young adults. It occurs during relaxed wakefulness, drowsiness, and light sleep and disappears during deeper stages of sleep. It is described as bursts of 1–2 sec duration, diffuse, low voltage, 5–7 Hz, spike-and-wave discharges, commonly bifrontally or occipitally. At times, spikes are difficult to see. This EEG pattern is regarded as a benign variant of uncertain significance.35 Six-hertz spikes with minimal or no associated waves may represent a transitional pattern between 6-Hz spike-wave bursts and 14 and 6 Hz positive bursts.61
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FIGURE 198. Six-Hertz Spike-and-Wave Bursts. Six-hertz spike and wave bursts in an 11-year-old girl with recurrent syncopal attacks associated with migraine. Six-hertz spike and wave bursts (arrow) can be very difficult to distinguish from atypical spike-wave activity. The clue to make a distinction is that benign 6-Hz spike and wave bursts occur during relaxed wakefulness and drowsiness and disappear during deeper stages of sleep.62 Two types of 6-Hz-spike-and-wave discharges have been described, FOLD (Female, Occipital, Low amplitude, Drowsiness) and WHAM (Wake, High-amplitude, Anterior, Male). FOLD is more benign, and WHAM is more likely to be associated with seizures.63
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FIGURE 199. Wicket Wave. Wicket waves are one of the most common over-read EEG patterns64 seen almost exclusively in adults, most commonly >30 years of age and, usually older than 50 years.65 Wicket waves are relatively rare with an incidence of 0.9%. It occurs in clusters or trains, but also as single sharp transients, of 6- to 11-Hz negative sharp aciform waves with amplitude of 60–200 μV. They are seen over the anterior or midtemporal regions during relaxed wakefulness but facilitated by drowsiness and may occur in light sleep. Wicket waves occur unilaterally with a shifting asymmetry between the two hemispheres. During the waking portion of the record, wicket waves are often masked by background EEG activity. Recently, wicket waves have also been reported to occur during REM sleep.66 Their cardinal feature is a changing mode of occurrence through any single recording, from intermittent trains of more or less sustained, aciform, discharges resembling mu rhythm, to sporadic single spikes. Amplitude may be high, but the transient arises out of an ongoing rhythm and does not stand out. When occurring singly, wicket waves can be mistaken for anterior or mid-temporal spikes. Isolated wicket wave(s) can be differentiated from epileptiform discharge (s) by the following criteria: (1) no slow wave component following the wicket wave; (2) occurring in trains or in isolation and do not disrupt the background; (3) having a similar morphology to the waveforms in the train when they occur as a single spike. Wicket wave is considered a benign variant pattern and is not associated with epilepsy.54,67–75
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FIGURE 1100. Rhythmic Temporal Rhythm (Psysiologic). Subdural recording showing the “Third Rhythm” (Independent Temporal Alphoid Rhythm) that is described as rhythmical activity in the alpha and upper theta range over the midtemporal region. This rhythm is not seen in scalp EEG except if there is a skull defect. The “Third Rhythm” is a physiologic rhythm that is clearly independent from mu or alpha rhythm.76 It needs to be differentiated form the rhythmical activity seen in anterior- and midtemporal regions seen in patients with stroke.65
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FIGURE 1101. Wicket-Wave Like Waveform; Nonaccidental Trauma. A 12-year-old-right-handed boy with medically intractable epilepsy caused by nonaccidental trauma in infancy. Interictal EEG shows trains of negative sharp arciform waves in the right anterior temporal region (box), continuously low-amplitude polymorphic delta activity (PDA), and suppression of background activity over the right hemisphere, maximal in the temporal region. The trains of sharp waves are similar to “wicket waves.” MRI demonstrates multifocal encephalomalacia but maximal over the right anterior temporal region (open arrow). Wicket waves are most commonly seen in individuals older than 30 years of age. Wicket waves are relatively rare with a prevalence of 0.9% in adults but unknown in children. They occur in clusters or trains, but also as single sharp transients, of mid- or anterior temporal 6–11 Hz negative sharp arciform waves with amplitude of up to 200 μV. Wicket waves can be differentiated from temporal lobe epileptiform discharges based on the following criteria: (1) no slow wave component following wicket spikes; (2)occurring in trains or in isolation and do not disrupt the background; (3) having a similar morphology to the waveforms in the train when they occur as a single spike. Wicket waves are more commonly seen in patients with cerebrovascular disease.65 In this EEG, the age and abnormal background activity are strongly against the diagnosis of wicket waves and supportive of epileptiform activities.
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FIGURE 1102. Wicket-Wave Like Waveform; Left Frontal-Temporal Infarction. A 4-month-old boy who developed a right-sided focal motor seizure after cardiac surgery for complex congenital heart defects. MRI with DWI shows cerebral infarction in the left fronto-temporal region. Interictal EEG shows trains of negative sharp arciform waves in the left posterior temporal region (box) and suppression of background activity over the left hemisphere. The trains of sharp wave configuration are similar to “wicket waves.” Wicket waves are most commonly seen in individuals older than 30 years of age. Wicket waves are relatively rare with a prevalence of 0.9% in adult but unknown in children. They occur in clusters or trains, but also as single sharp transients, of mid- or anterior temporal 6–11 Hz negative sharp arciform waves with amplitude of up to 200 μV. Wicket waves can be differentiated from temporal lobe epileptiform discharges based on the following criteria: (1) no slow wave component following wicket spikes; (2) occurring in trains or in isolation and do not disrupt the background; (3) having a similar morphology to the waveforms in the train when occurs as a single spike. In this EEG, the age and abnormal background activity are strongly against the diagnosis of wicket waves but supportive of epileptiform activities. In adult, wicket waves are more common seen in patients with cerebrovascular disease.65
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FIGURE 1103. Photomyognic (Photomyoclonic) Response. A 14-year-old girl with well-controlled idiopathic generalized epilepsy. EEG performed due to frequent eye fluttering shows spikes of muscle origin time locked to the flash stimuli. This so-called “photomyogenic response” occurs in 0.1% of the normal population and 1% of patients with epilepsy. The response is most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching during eye closure and stops with flash. Immediate cessation of the response at the end of stimulation and prominent electromyographic activity help to distinguish this photomyogenic response from photoparoxysmal response. Photomyogenic response is considered a normal variant, although it can coexist with photoparoxysmal response or rarely progress to GTCS.
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FIGURE 1104. Photomyognic Response. Another example of photomyoclonic response with widespread involvement of orbicularis oculi, frontalis, and temporalis muscles.
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FIGURE 1105. Photomyognic Response. EEG of a 9-year-old girl with childhood absence epilepsy showing spikes of muscle origin time locked with the flash stimuli. They are most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching. Photomyogenic response is considered a normal variant, although seen slightly more commonly in patients with idiopathic generalized epilepsy.
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FIGURE 1106. Photomyognic Response; Eyelid Artifacts Intermixed With Electromyographic Potentials. A 13-year-old girl with well-controlled idiopathic generalized epilepsy. EEG shows eyeblinking artifact intermixed with spikes of muscle origin time locked to the flash stimuli that is confined exclusively to the prefrontal electrodes (Fp1, Fp2). This is the so-called “photomyogenic response” that occurs in 0.1% of the normal population and 1% of patients with epilepsy. The response is are most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching during eye closure and stops with flash. Immediate cessation of the response at the end of stimulation and prominent electromyographic activity help to distinguish this photomyogenic response from photoparoxysmal response. Photomyogenic response considered a normal variant, although it can coexist with photoparoxysmal response or rarely progress to GTCS. There is mild involvement of temporalis muscles noted.
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FIGURE 1107. Mu Rhythm. Mu is a central rhythm of an alpha frequency band (8–10 Hz) with an arciform configuration. Mu rhythm occurs in less than 5% of children younger than 4 years and has the adult incidence of 18–20% between the age of 8 and 16 years. It is not blocked with eye opening, but blocked by touch, movement of limbs (especially contralateral limbs), or thought of movement. Mu rhythm is usually asymmetric, asynchronous, and seen independently in the two hemispheres. It may present on only one side. Mu rhythm is believed to be the rhythm of the sensorimotor cortex at rest. Mu rhythm is prominent in the patients with underneath skull defect (breach rhythm). Mu is a physiologic EEG finding of no clinical significance.
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FIGURE 1108. Breach Rhythm; Prominent Mu Rhythm During Photic Stimulation. EEG of a 12-year-old boy with recurrent syncope shows prominent mu during photic stimulation. Mu rhythm is enhanced during photic stimulation and pattern vision.77,78
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FIGURE 1109. Breach Rhythm; Prominent Mu Rhythm. A 9-year-old boy with a history of right occipital ganglioglioma resection. T1-weighted coronal and sagittal MRIs with GAD reveal skull defects and an area of previous surgical resection (arrow head). EEG during wakefulness with eye opening shows frequent runs of asymmetrical rhythmic 9 Hz arc-like activity in the central regions which is higher in amplitude on the right side.
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FIGURE 1110. Breach Rhythm; Prominent Mu Rhythm. (next EEG page of the same patient as in Fig. 1-109) The arc-like activity in the central regions is attenuated by left hand movement. This is consistent with mu rhythm which can become very prominent beneath a skull defect. Sometimes, mu rhythm can simulate ictal EEG activity especially in patients with skull defects; therefore, activation procedures such as limb movement are very important in their differentiation.
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FIGURE 1111. Mu Rhythm activated by Intermittent Photic Stmulation. Mu rhythm is enhanced during intermittent photic stimulation77 and pattern vision78. It is maximally expressed at C3 and C4 electrodes, and occasionally at Cz. Some spread to the parietal region is not uncommon. In older children and adults, the most common frequency is 10 Hz, slightly higher than alpha frequencies.9
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FIGURE 1112. Mu Rhythm in Young Child. A 3-year-old girl who underwent epilepsy surgery in the right frontal-temporal region. EEG shows breach rhythm with higher amplitude of mu rhythm at the C4 electrode. In infants and young children whose alpha rhythm is still less than 6 Hz, mu rhythm can lack its characteristic waveform.10
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FIGURE 1113. Mu Rhythm in Subdural EEG Monitoring. Subdural recording during wakefulness showing a run of mu rhythm. Harmonic of the mu rhythm is more frequently seen in intracranial EEG. In addition, the mu rhythm usually shows sharper morphology, as the scalp and skull act as a high-frequency filter passing lower frequencies more than higher frequencies.2 Disappearance during limb movement helps to differentiate the mu rhythm from a spike run. All normal EEG rhythms seen in the scalp EEG can be seen in the intracranial EEG.3
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FIGURE 1114. Mu Rhythm in Depth EEG (Bipolar). Mu rhythm during bipolar run of the combined depth electrode-subdural EEG recording during wakefulness. The wave disappeared during sleep and was attenuated by limb movement (not shown).
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FIGURE 1115. Mu Rhythm in Depth EEG Implantation During Seizure. (continued from the Fig. 114) Intracranial EEG shows mu rhythm (in the box) during the seizure with the epileptogenic focus at DC3 (depth electrode contact #3) (arrow). Mu rhythm disappears during the burst of ictal EEG activity. Recognition of mu rhythm prevents misinterpretation of mu as an ictal EEG activity in the DD3 electrode which can cause false localization of epileptogenic onset.
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1 66. Gélisse P, Kuate C, Coubes P, Baldy-Moulinier M, Crespel A. Wicket spikes during rapid eye movement sleep. J Clin Neurophysiol. 2003;20(5):345. 67. Krauss GL, Abdallah A, Lesser R, et al. Clinical and EEG features of patients with EEG wicket rhythms misdiagnosed with epilepsy. Neurology. 2005; 64: 1879–1883. 68. Drury I, Beydoun A. Interictal epileptiform activity in elderly patients with epilepsy. Electroencephalogr Clin Neurophysiol. 1998;106(4):369–373. 69. Westmoreland BF. Epileptiform electroencephalographic patterns. Mayo Clin Proc. 1996;71(5):501–511. 70. Reiher J, Klass DW. Two common EEG patterns of doubtful clinical significance. Med Clin North Am. 1968;52(4):933. 71. Reiher J, Lebel M. Wicket spikes: clinical correlates of a previously undescribed EEG pattern. Can J Neurol Sci. 1977;4(1):39–47. 72. White JC, Langston JW, Pedley TA. Benign epileptiform transients of sleep: clarification of the small sharp spike controversy. Neurology. 1977;27(11):1061. 73. Tatum WO, Husain A, Benbadis SR, Kaplan P. Normal adult EEG and patterns of uncertain significance. J Clin Neurophysiol. 2006;23:194–207. 74. Mushtaq R, Van Cott AC. Benign EEG variants. Am J Electroneurodiagnostic Technol. 2005;45(2):88–101. 75. MacDonald D. Normal electroencephalogram and benign variants. Neurosciences. 2003;8(2):110–118. 76. Niedermeyer E. The Normal EEG of the waking adult. In: Niedermeyer E, Da Silva F, eds. Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. Philadelphia: Lippincott Williams & Wilkins. 2005. 77. Brechet R, Lecasble R. Reactivity of mu-rhythm to flicker. Electroenceph Clin Neurophysiol. 1965;18:721–722. 78. Koshino Y, Niedermeyer E. Enhancement of Rolandic mu-rhythm by pattern vision. Electroencephalogr Clin Neurophysiol. 1975;38(5):535.
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Characteristics of artifact
䡲
䡲
If the activity is limited to a single channel or electrode, it should be assumed to be an artifact until proven otherwise.
Slow or Roving Eye Movement (SEM) (Figure 2-2) 䡲
SEM is a sign of drowsiness in older children and adults.
䡲
Opposite polarity of slowing (<1 Hz) in the left and right fronto-temporal regions (F7 and F8) associated with other signs of drowsiness including:
Repetitive, irregular, or rhythmic waves that occur simultaneously in unrelated head regions.
䊳
Physiological artifacts
䊳
Eye movements
䊳
䡲
Eyeball acts as a dipole with positive polarity of 100 mV at the cornea with respect to the retina. 䡲 Bell’s phenomenon (upward eye deviation during eye closure) causes positive electrical activity at Fp1 and Fp2. 䡲
Artifacts
Lateral eye movement causes positivity to the side of which gaze is directed to (either F7 or F8). 䡲 Oblique eye movement is more difficult and can be misinterpreted as a focal abnormality. 䡲
Courses of asymmetric eye movements include: 䊳 Decreased movement of one eye or eyelid 䊳 䊳 䊳
Absence of an eye or retina Asymmetric electrode placement Frontal skull defect
Rapid Eye Movement (REM) (Figure 2-1) 䡲
With lateral eye movements, the eyes are moving to the side where positivity is noted. This is caused by the positivity of the cornea (100 mV positive compared to retina) coming closer to the F7 or F8 electrodes making positive the one toward which the eyes are moving. 䡲 Asymmetric waves with steeper rise than fall. 䡲 REM stage in healthy children does not occur within the first cycle but after one complete cycle (stage 1 to 4 and then back from 4 to 1), usually 90 minutes after sleep onset. If REM sleep appears near the onset of sleep (early REM), narcolepsy must be considered. However, early REM can be seen in individuals withdrawing from CNS depressants such as barbiturates or alcohol.
Alpha dropout (earliest sign) Increased beta activity over the fronto-central regions Diffuse rhythmic theta activity with anterior predominance
Horizontal Nystagmus (Figures 2-3 to 2-6) 䡲 Horizontal nystagmus normally occurs bilaterally, but it is often only recorded unilaterally at either F7 or F8 on the side of the direction of the fast nystagmus due to larger positive voltage generated by the proximity of the cornea to that electrode. 䡲 Vertical and rotatory nystagmus are rarely detected at the Fp1 and Fp2 due to the low voltage. Electroretinogram (ERG) (Figure 2-7) 䡲
Low-voltage (<50 mV) response to light stimulus of the retina. 䡲 Synchrony with the flashes of light. 䡲
Most commonly seen in, but does not invalidate, the diagnosis of brain death. 䡲 The artifact disappears over the blocked eye with an opaque card. 䡲 Consists of two peaks. 䡲
Amplitude of ERG is usually low and obscured by normal EEG activity in Fp1 and Fp2 䡲 ERG can be confused with an electrode artifact generated by the exposed silver metal of chipped EEG electrode during photic stimulation (photocell artifact). 䡲 These physiological and artifactual potentials can be differentiated by using high photic stimulus frequencies. With 30-Hz photic stimulus frequency, amplitude of ERG diminishes while amplitude of electrode artifact is constant.
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Eye Blink (Figures 2-8 to 2-10) 䡲 EEG shows biphasic sharp theta activity in bilateral prefrontal regions that simulate frontal sharp transients. 䡲 Eye lead channels can differentiate between cerebral activity and eye movement artifact. When activity points to the different directions (out-of-phase), it indicates that it is eye movement artifact rather than cerebral activity.
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Electrocardiographic artifacts
When the dipole axis of the EEG generator is oriented perpendicular to the skull defect, the defect usually increases the EEG voltage as seen in the breach rhythm. On the other hand, when the dipole axis of the EEG generator is parallel to the skull defect, as seen in the eye movement, the skull defect decreases the EEG voltage.
Photomyoclonic Response (Figures 2-11 and 2-14) 䡲
Occurs in 0.1% of normal population and 1% of patients with epilepsy. 䡲 Most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching during eye closure. Stops with flash. 䡲
Immediate cessation of the response at the end of stimulation and prominent electromyographic activity help to distinguish this photomyoclonic response from photoparoxysmal response. 䡲 Photomyoclonic response is considered a normal variant, although it can coexist with photoparoxysmal response or rarely progress to GTCS. Eyelid Flutter (Figure 2-11 to 2-14) 䡲 Associated with a rhythmic 5- to 8-Hz activity at Fp1 and Fp2 with or without falloff of the voltage detected at F3, F4, or Fz because of the low voltage of the flutter. 䡲 Alpha frequency activity restricted to the frontopolar electrodes is eye movement (flutter) artifact until proven otherwise. 䡲 Eye lead electrodes help to distinguish this artifact from intermittent rhythmic slow activity by showing out-of-phase potentials.
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Artifacts
More rapid, more rhythmic, and lower amplitude appearance than eye blink. 䡲 When periocular muscle contractions accompany the eye movements, bifrontal liked may be noted. 䡲 May be falsely diagnosed as focal frontal delta activity in prosthetic eye, 3rd nerve palsy, or unilateral eye movement artifact.
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Identified by touching the electrode generating it. If the patient is lying on the involved electrode, the artifact sometimes may be eliminated by moving the head slightly. 䡲 Relocation of electrode may eliminate the artifact.
EKG Artifact (Figures 2-17 and 2-18) 䡲 Most prominent when the neck is short and wide. 䡲 Diphasic is the most common wave form.
Ballistocardiographic Artifact (Figure 2-21) 䡲 Caused by movement of electrodes, electrode wires, or head. 䡲 Rocking movement of the patient’s entire body and head each time the heart beats. 䡲 This is in part due to the pulsatile force on the aortic arch from the abrupt redirection of blood flow.
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Maximal in the temporal region, greater on the left side.
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Similar in morphology to pulse artifact but is more widespread.
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Most obvious in referential montage. Dipole with A1 positive and A2 negative in referential montage run.
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EKG demonstrates the relationship to the pulsations, although is not necessarily time-locked to the signal.
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Regularity and bilateral synchronous nature distinguish EKG artifact from PLEDs.
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Location distinguishes EKG artifact (temporal) from GPEDs (bifrontal). 䡲 Irregular heartbeats can be mistaken for cerebral activity.
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Mimic diffuse delta slowing indicating the presence of brain activity. 䡲 Seen more frequently during the electrocerebral inactivity recording. 䡲
Pulse Artifact (Figures 2-19 and 2-20) 䡲
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Mechanical movement caused by pulsation artifact that occurs when an EEG electrode is placed over the pulsating blood vessel.
The mechanical movement caused by pulsation of an artery can cause a rhythmic smooth or sharply contoured slow wave (sawtooth) that sometimes simulates EEG activity. 䡲 Time-locked with the EKG but is delayed by approximately 200 msec after the R wave, because the pulse requires time to travel from the heart to the blood vessel. 䡲 Occurs in any lead but most commonly at frontal and temporal regions, and less commonly over the occipital region.
Very difficult to correct and it frequently obscures the entire recording. This artifact may be removed by moving the patient’s head or by putting a pillow under the patient’s neck to minimize electrode movement against the bed.
Electromyographic artifacts Lateral Rectus Spike (Figures 2-15 and 2-16) 䡲
Single motor unit potential, best seen in F7 and F8 electrodes during a lateral eye movement. 䡲 Characterized by short-duration spike superimposed on slow wave activity caused by rapid lateral eye movement. Hemifacial Spasms (Figure 2-22) 䡲 Burst of diffuse muscle and movement artifacts in ipsilateral electrodes. 䡲 Other similar artifacts: focal motor seizures, facial myokymia, facial synkinesias.
2 Chewing Artifact (Figure 2-59) 䡲 Muscle artifact from scalp and facial muscle occur mainly in the frontal or temporal regions. 䡲 Bursts of muscle activity followed by slow waves. It usually occurs bilaterally but sometimes unilaterally. 䡲 To reduce, get the patient more relaxed. 䡲 May persist in sleep.
Glossokinetic artifact (Figures 2-23 and 2-24) 䡲
Movement of tongue, which produces DC potential. Tip of the tongue is surface negative with respect to the base. 䡲 Either unilateral or bilateral depending on the direction of tongue movement. 䡲 Electrical field can be widely distributed, although it is most often noted in the anterior head region, especially temporal electrodes. 䡲
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Bursts of diffuse delta activity, often accompanied by superimposed muscle artifact. 䡲 Simulates cerebral slow wave activity, especially when the mouth remains closed during tongue movements. 䡲 This artifact can be reproduced by asking the patients to say “lilt la” and “tom thumb” or by asking them to move the tongue in vertical and lateral directions. 䡲
Extra-electrodes above and below the mouth, and slightly off center in opposite directions on either side, may help to enhance this artifact.
Galvanic skin response Sweat (Perspiration) Artifact 䡲 Long-duration artifact >2 sec involving more than one channel. 䡲 Slow shifts of the electrical baseline. 䡲
Simultaneous occurrence of slow background activity raises the diagnosis of hypoglycemia. 䡲 Can be avoided by cooling the patient, drying the scalp with a fan, alcohol, or an antiperspirant, and having adequate air conditioning.
Artifacts
Salt Bridge Artifact (Figure 2-25) 䡲 Excessive application of electrode paste smeared on the scalp can act as a “salt bridge.” The salt bridge results in the same potential at both electrodes. Using bipolar montage , this can result in extremely low voltage due to "phase cancellation" effect.
Physiological movements Patting Artifact (Figures 2-26 to 2-34) 䡲 Sometimes simulate an electrographic seizure. 䡲
Differentiate from electrographic seizure by: 䊳 Invariable rhythmic activity
Absence of frequency evolution Abrupt start-and-stop of activity associated with patting activity 䡲 Annotation of patting activity by an EEG technologist and viewing the video recording are extremely helpful in identifying this artifact. 䊳
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Head Movement (Figures 2-48 and 2-49) 䡲 Causes semi-rhythmic activity simulating spike-wave discharges or rhythmical wave forms. 䡲 Artifacts can be diminished by asking the patient to stop moving. 䡲 Movement artifacts are usually easily recognized except when the technologist fails to document the occurrence of movements. 䡲
Can be avoided by raising the patient’s head from the bed.
Respiratory Artifact (Figures 2-53, 2-54, 2-56, 2-57 and 2-58) 䡲 Periodic positive sharp transients time-locked with body movement related to artificial respirator.
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Hiccup Artifact (Figures 2-35 to 2-42) 䡲 Repetitive or quasiperiodic pattern associated with head movement from hiccup or sobbing. 䡲 Hiccup or sobbing can also cause “glossokinetic artifact.” Sucking Artifact (Figures 2-43 to 2-45) 䡲
Spike-like activity, mainly in bi-temporal regions.
Tremor and Limb Movement and Shivering Artifact (Figures 2-46, 2-47, 2-50 to 2-52, and 2-55) 䡲
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Vibratory movement of multiple electrodes, especially occipital electrodes which can mimic an electrographic seizure.
Monorhythmic theta activity occurring abruptly and isolated from the ongoing background activity is most likely due to tremor artifact. 䡲 Additional electrodes to monitor tremor may be needed.
Nonphysiological artifacts Telephone ring artifact (Figure 2-60) 䡲
Low-amplitude, high-frequency artifact. 䡲 Other interference: signals from nearby television stations, radio paging, cardiac pacemakers, or movement of a charged body near the recording electrodes.
Sixty-cycle artifact (Figure 2-61) 䡲 䡲
Most common external source of artifacts.
Arises from the 60-cycle power lines and equipment. Occurs in the electrodes that have a high resistance from grease, dirt, and dead skin. 䡲 Reducing impedance to less than 5 kΩ and having stable ground electrode on the patient will eliminate this artifact. 䡲 The 60-Hz filter helps to eliminate this electrical artifact but should not be used on a routine basis, as the 60-cycle artifact is a useful warning sign of poor electrode contact or an improper input selection. 䡲 Sixty-cycle artifact in all channels of the EEG recording raises the concern about electrical safety and should be further investigated. It is important to rule out ground loops or double grounding.
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The patient’s head and the connection to an EEG instrument should be kept as far as possible from the power cables. If possible, the other equipment should be unplugged.
High-frequency ventilator artifact (Figures 2-62 and 2-63) 䡲
Diffuse, invariant, rhythmic, sinusoidal activity in all EEG electrodes caused by vibratory effect on the entire body.
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Seen in high-impedance and poor-contact electrode.
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Characteristic morphology of very steep rise and a shallower fall that “squares off ” at the top.
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Occurring intermittently or regularly.
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Superimposed on normal background activity.
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Additional electrode placed close to the one in question may help if simple methods such as filling or replacing the electrode do not eliminate it.
Electrode pop (Figures 2-64, 2-69 and 2-70) 䡲
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Most common electrode artifact described as a single or multiple spike-like, either negative or most commonly positive discharges. Caused by abrupt increase in electrode impedance, which may be related to impurity in the metal portion of the electrode.
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Artifacts
Photocell artifact (Figure 2-65) 䡲
During flash photic stimulation, high impedance in electrodes may cause a “photocell artifact.”
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Each flash causes a minute photochemical reaction that, in the presence of high impedance, causes the electrode to act as a photocell, producing
a corresponding spike-like transient that appears simultaneously with the flash. 䡲 Distinguish from photomyoclonic responses that have small but measurable latencies. Detectable by increasing paper speed to 60 mm/sec.
Ground lead artifact (Figures 2-66 to 2-68) 䡲
A ground electrode on the patient eliminates a 60-Hz AC artifact from power lines. 䡲 A problem occurs when the impedance of one of the active electrodes connected to G1 or G2 of the amplifier becomes large relative to the other active electrode and the ground of the amplifier. In this case, the ground electrode becomes an active electrode. Depending on its site, it may introduce false cerebral activity.
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FIGURE 21. Early Rapid Eye Movement (REM); Narcolepsy. A 15-year-old girl with recurrent episodes of daytime drowsiness and brief paralysis precipitated by laughing. Routine EEG shows frequent REM occurring around 15 minutes into the recording. Subsequent sleep study (MSLT) confirmed the diagnosis of narcolepsy. With lateral eye movements, the eyes are moving to the side where positivity is noted caused by the positivity of the cornea coming closer to the F7 or F8 electrode, making one of them positive, the one toward which the eyes are moving. If the eyes are moving to the left, then the positivity on the cornea is directed to the left side (F7), making F7 a positive polarity (double-head arrows) and F8 a negative polarity. If the eyes are moving to the right, the opposite effect is noted at F7 and F8 (asterisk). REM stage in healthy children does not occur within the first cycle but after one complete cycle (stage 1 to 4 and then back from 4 to 1), usually 90 minutes after sleep onset. If REM sleep appears near the onset of sleep (early REM), narcolepsy or withdrawing from CNS depressants such as barbiturates or alcohol must be considered.1
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FIGURE 22. Slow Eye Movement (SEM); Drowsiness. EEG of a 10-year-old girl during drowsiness shows slow (roving) eye movement. With lateral eye movements, the positively charged cornea comes closer to either the F7 or F8 electrode, making the one toward which the eyes are moving more positive. If the eyes are moving to the left, then the positivity on the cornea is directed to the left side (F7 electrode), making F7 a positive polarity (pen separation) (double-head arrows) and F8 a negative polarity (pen coming together). If the eyes are moving to the right, the opposite effect is noted at F7 and F8 (asterisk). SEM is a sign of drowsiness in older children.
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FIGURE 23. Eye Movement Artifact (Nystagmus); Holoprosencephaly. An 8-year-old boy, who developed constant horizontal nystagmus, with congenital hydranencephaly and microcephaly with severe global developmental delay. EEG shows flattening of the background activity with rapid lateral eye movements characterized by “out-of-phase” potentials between F7 and F8. The cornea produces a potential of approximately 50–100 mV. When the eye moves to the left, the cornea comes closer to the F7 electrode, causing a positive phase reversal with maximal positive potential at the F7 electrode, and a negative phase reversal with maximal negative potential recorded at the F8 electrode (open arrow).2 This EEG supported that the nystagmus in this patient was nonepileptic. Ophthalmic findings in hydranencephaly include pupillary abnormalities, strabismus, nystagmus, ptosis, optic nerve hypoplasia, chorioretinitis, retinal vessel attenuation, and incomplete anterior chamber cleavage.3
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FIGURE 24. Eye Movement Artifact (Horizontal Nystagmus and Eye Closure). Another example of horizontal nystagmus. Cornea produces a potential of approximately 50–100 mV. When the eye moves to the left, the cornea comes closer to the F7 electrode, causing a positive phase reversal with maximal positive potential at the F7 electrode, and a negative phase reversal with maximal negative potential recorded at the F8 electrode (double-head arrow). When the eyes are closed (open arrow), the eyeballs are in a neutral position (Bell’s phenomenon), and this upward eye movement is detected by a maximal positive potential recorded at the Fp1 and Fp2 electrodes with a falloff potential recorded at the next electrodes (F3 and F4). These cause downward deflections of EEG at Fp1-F3 and Fp2-F4 channels. When the eyeball moves in a downward direction, the inverse occurs.
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FIGURE 25. Eye Movement Artifact (Nystagmus). Constant horizontal nystagmus. EEG shows flattening of the background activity with rapid lateral eye movements characterized by “out-of-phase” potentials between F7 and F8. The cornea produces a potential of approximately 50–100 mV. When the eye moves to the left, the cornea comes closer to the F7 electrode, causing a positive phase reversal with maximal positive potential at the F7 electrode, and a negative phase reversal with maximal negative potential recorded at the F8 electrode.2
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FIGURE 26. Eye Movement Artifact (Nystagmus). Horizontal nystagmus with fast component to the left side. Horizontal nystagmus normally occurs bilaterally, but it is often only recorded unilaterally at either F7 or F8 on the side of the direction of the fast nystagmus due to a larger positive voltage generated by the proximity of the cornea to that electrode.2
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FIGURE 27. Electroretinogram (ERG). Amplitude of ERG is usually low and obscured by normal EEG activity in Fp1 and Fp2. ERG can be confused with an electrode artifact generated by an exposed silver metal of chipped EEG electrode during photic stimulation. These physiological and artifactual potentials can be differentiated by using high photic stimulus frequency. With 30-Hz photic stimulus frequency, the amplitude of ERG diminishes while the amplitude of electrode artifact is constant.
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FIGURE 28. Eye Movement Artifact. A 38-week CA infant with apnea. EEG shows biphasic sharp theta activity in bilateral prefrontal regions, which simulate frontal sharp transients. Eye lead channels can differentiate between these two conditions. When activity points to different directions as in this EEG, it indicates that this is eye movement artifact rather than brain waves.
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FIGURE 29. Skull Defect; Effect on Eye Blinking Artifact. A 17-year-old boy with a skull defect in the right frontal region. EEG shows asymmetric eye blinking artifact (asterisk) with lower voltage in the right prefrontal region and breach rhythm over the right hemisphere, especially parasagittal region. When the dipole axis of the EEG generator is oriented perpendicular to the skull defect, the defect usually increases the EEG voltage as seen in the breach rhythm. On the other hand, when the dipole axis of the EEG generator is parallel to the skull defect, as seen in the eye movement, the skull defect decreases the EEG voltage.4
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FIGURE 210. 3-Hertz Spike-and Wave Discharges in Absence Epilepsy. EEG shows rhythmic 3- to 4-Hz spike-and-wave discharges in the anterior head region simulating eye blink artifact. Widely distributed activity, not limited to only F3 or F4, helps to distinguish these two wave forms. Eye lead recording showing in-phase activity supports 3-Hz spike-and-wave discharges.
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Artifacts
FIGURE 211. Eye Fluttering During Photic Stimulation. A 9-year-old girl with well-controlled idiopathic generalized epilepsy. EEG shows spikes of muscle origin timelocked to the flash stimuli, which is confined exclusively to the prefrontal electrodes (Fp1, Fp2). This so-called “photomyoclonic response” occurs in 0.1% of normal population and 1% of patients with epilepsy. It is most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching during eye closure and stops with flash. Immediate cessation of the response at the end of stimulation and prominent electromyographic activity help to distinguish this photomyoclonic response from photoparoxysmal response. Photomyoclonic response is considered a normal variant, although it can coexist with photoparoxysmal response or rarely progress to GTCS. In this case, the involvement was limited to only frontalis and orbicularis oculi and did not involve temporalis muscles.
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FIGURE 212. Eye Flutter. Eyelid flutter is usually associated with a rhythmic 5–8 Hz activity at Fp1 and Fp2 with or without falloff of the voltage detected at F3, F4, or Fz because of the low voltage of the flutter. Eye lead electrodes help to distinguish this artifact from intermittent rhythmic slow activity by showing out-of-phase potentials.
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FIGURE 213. Eye Flutter During Photic Stimulation. Eye flutter in the alpha frequency range without falloff of the voltage detected at F3, F4, or Fz due to low voltage of the flutter can be seen during photic stimulation. Alpha frequency activity restricted to the frontopolar electrodes is eye movement (flutter) artifact until proven otherwise.
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FIGURE 214. Eye Fluttering During Photic Stimulation. An 8-year-old girl with recurrent headaches and numbness of arms. EEG shows spikes of muscle origin timelocked to the flash stimuli, which is confined exclusively to the prefrontal electrodes (Fp1, Fp2). This so-called “photomyoclonic response” occurs in 0.1% of normal population and 1% of patients with epilepsy. They are most prominent in the frontal regions as a result of orbicularis oculi and frontalis muscle twitching during eye closure and stops with flash. Immediate cessation of the response at the end of stimulation and prominent electromyographic activity help to distinguish this photomyoclonic response from photoparoxysmal response. Photomyoclonic response is considered a normal variant, although it can coexist with photoparoxysmal response or rarely progress to GTCS. In this case, the involvement was limited to only frontalis and orbicularis oculi and did not involve temporalis muscles.
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Artifacts
FIGURE 215. Lateral Rectus Spikes. A lateral rectus spike (open arrows) is a single motor unit potential, best seen in frontal electrodes during lateral eye movement. It is characterized by a short-duration spike overriding a slow wave resulting from rapid lateral eye movement. Immediately after the lateral rectus spike (open arrows), a leftward lateral eye movement is noted. As the cornea has a positive electrical potential, it causes F7 to be positive with opposite polarity at F8.
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FIGURE 216. Lateral Rectus Spikes. A lateral rectus spike is a single motor unit potential, best seen in frontal electrodes during lateral eye movement. It is characterized by a short-duration spike overriding a slow wave resulting from rapid lateral eye movement. Eye lead channels (not shown) demonstrate eye movement time-locked with lateral rectus spikes.
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FIGURE 217. Electrocerebral Inactivity (ECI); Severe Hypoxic Ischemic Encephalopathy (HIE) with Central Herniation Synodrome. A 4-day-old girl who was born full term with Apgar scores of 0, 3, 3, and 5. Cord arterial gas was 6.91/66/-20. Initial venous blood gas 7.15/13/123/9/-22. She had a seizure described as tonic posturing. She was placed in a head-cooling device. She developed another clinical seizure with rhythmic head twitching and tongue thrusting lasting 10 minutes. She received treatment with phenobarbital and levetriacetam. No EEG was performed until the fourth day of life. MRI performed at the fourth day of life shows severe global abnormality involving cerebellum, brainstem, thalamus, basal ganglia, deep white matter, and cortical gray matter. DWI MRI shows markedly increased signal intensity that suggests severe injury with liquefaction. Cardiorespiratory support was withdrawn 1 day after the EEG. EEG shows no cerebral activity (potentials > 2 μV when reviewed at a sensitivity of 2 μV/mm) consistent with electrocerebral inactivity (ECI). EKG artifact was noted with a dipole between A1 and A2. Although A1 is usually positive and A2 is usually negative, the opposite is noted in this EEG.5 ECI is indicative of death only of the cortex, not the brainstem; therefore, a newborn can have prolonged survival despite having an EEG of ECI.6
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FIGURE 218. EKG Artifacts Intermingled with Electrical Status Epilepticus During Slow Sleep (ESES); Left Cerebral Hemiatrophy. EKG artifact intermixed with bilateral synchronous spike-wave activity seen in ESES (asterisk).
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FIGURE 219. Pulse Artifact; Electrocerebral Inactivity (ECI). Pulse artifact (open arrow) is caused by mechanical movement resulting from pulsation artifact that occurs when an EEG electrode is placed over the pulsating blood vessel. The mechanical movement caused by pulsation of an artery can cause a rhythmic smooth or sharply contoured slow wave (sawtooth) that sometimes simulates EEG activity. Pulse artifact is time-locked with the EKG but is slightly delayed by approximately 200 msec, since the pulse requires time to travel from the heart to the blood vessel. Pulse artifact can occur in any lead but most commonly in frontal and temporal regions, and less commonly over the occipital region. Pulse artifact can be identified by touching the electrode generating it. If the patient is lying on the involved electrode, the artifact sometimes may be eliminated by moving the head slightly. Relocation of electrode may eliminate the artifact.5,7,8
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FIGURE 220. Pulse Artifact. Pulse artifact can simulate polymorphic delta activity. It can be confirmed by examining the EKG lead, which shows the signal time-locked to the slow wave. It is seen only in one electrode (T3 in this patient) and caused by a loosely applied EEG electrode placing on the artery.
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FIGURE 221. Ballistocardiographic Artifact. EEG in a 6-year-old boy with severe anoxic encephalopathy shows diffuse, low-voltage 2- to 2.5-Hz delta activity, maximally expressed in Fp1, time-locked to the EKG. Ballistocardiographic artifact is the result of rocking movement of the patient’s entire body and head each time the heart beats. This may be due partly to the pulsatile force on the aortic arch from the abrupt redirection of blood flow. Ballistocardiographic artifact is similar in morphology to pulse artifact but is more widespread. EKG demonstrates the relationship to the pulsations, although it is not necessarily time-locked with the signal. The ballistocardiographic artifact can mimic diffuse delta slowing indicating the presence of brain activity. This artifact is seen more frequently during the electrocerebral inactivity recording. The artifact can be removed by moving the patient’s head or putting a pillow under the patient’s neck so that electrode movement is against the bed.2,8
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FIGURE 222. Artifactual Spikes Caused by Hemifacial Spasms. EEG of a 16-year-old boy with left hemifacial spasms. EEG shows a burst of muscle and movement artifacts (arrow) during episodes of hemifacial spasms.
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FIGURE 223. Glossokinetic Artifact. Glossokinetic artifact is caused by movement of tongue, which produces a DC potential. The tip of the tongue has a negative electrical charge with respect to the root. The activity can be either unilateral or bilateral depending on the direction of tongue movement. The electrical field can be widely distributed, although it is most often noted in the temporal electrodes. Sometimes it can simulate cerebral slow wave activity, especially when the mouth remains closed during tongue movements.
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FIGURE 224. Glossokinetic Artifact; Polymorphic Delta Activity (PDA) Caused by Complicated Migraine. EEG in a patient with hemiplegic migraine shows polymorphic delta activity in the left temporal region. Also note glossokinetic artifact (arrow). Glossokinetic artifact is caused by movement of tongue, which produces a DC potential. The tip of the tongue has a negative electrical charge with respect to the root. The activity can be either unilateral or bilateral depending on the direction of tongue movement. The electrical field can be widely distributed, although it is most often noted in the temporal electrodes. Sometimes it can simulate cerebral slow wave activity, especially when the mouth remains closed during tongue movements.
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Artifacts
FIGURE 225. Excessively Low Impedance Due to Salt Bridge. Excessive application of electrode paste smeared on the scalp can act as a “salt bridge” between two electrodes ( Fp1 and F3) and causes falsely low voltage activity.9
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FIGURE 226. Patting Artifact. A 10-month-old girl being burped after feeding. She was patted on her back by her mother. EEG during referential montage run showed continuously diffuse rhythmic sharp-contoured wave form, which stopped immediately after burping was discontinued. This EEG can easily mimic a generalized electrographic seizure.
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FIGURE 227. Patting Artifact. Patting artifact can sometimes simulate an electrographic seizure. It is differentiated from an electrographic seizure by its invariable rhythmic activity and absence of frequency evolution.
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FIGURE 228. Unilateral Patting Artifact. This patient was patted by his mother on the left side of his body while he was lying on his right side. The intensity of the patting increased over time. Patting artifact can simulate an electrographic seizure, although invariable rhythmic activity and absence of frequency evolution help to differentiate between these two EEG findings. Annotation by EEG technologists and video-EEG recordings are extremely helpful.
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Artifacts
FIGURE 229. Patting Artifact. Another example of patting artifact. Patting artifact can sometimes simulate an electrographic seizure. It is differentiated from an electrographic seizure by its invariable rhythmic activity and absence of frequency evolution.
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FIGURE 230. Patting Artifact. Another example of patting artifact in an 11-month-old girl with congenital CMV infection with severe global developmental delay, blindness, and recurrent cyanotic spells. Her mother was patting her on the back at the same rate as the rhythmic sharp-contoured theta activity.
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FIGURE 231. Patting Artifact. EEG shows a run of monomorphic and monophasic spike-like activity at the Cz (asterisk), which is time-locked with patting on the back by her grandmother.
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FIGURE 232. Patting Artifact. (Same patient as in Figure 2-31) The next page of EEG shows electrode artifact in the Cz, which is caused by loosening of the electrode. This gives a good explanation why patting artifact in the previous page occurred only in the Cz electrode.
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FIGURE 233. Patting Artifact (Focal); Left Hemispheric Stroke. Patting artifact can sometimes simulate an electrographic seizure. It is different from electrographic seizure because of its invariable rhythmic activity, absence of frequency evolution, and abrupt start-and-stop of activity associated with patting activity. Annotation of patting activity by an EEG technologist and viewing the video recording are extremely helpful to confirm this artifact.
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FIGURE 234. Patting Artifact. Patting artifact can sometimes simulate an electrographic seizure. It is differentiated from electrographic seizure by its invariable rhythmic activity, absence of frequency evolution, and abrupt start-and-stop (arrow head—patting started; open arrow head—patting stopped) of electrical activity associated with patting activity. Annotation of patting activity by an EEG technologist and viewing the video recording are extremely helpful to confirmation of this artifact.
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FIGURE 235. Hiccup Artifact; Associated with Epidural Bupivacaine. A 1-day-old full-term infant with trachea-esophageal fistula and esophageal atresia, who received epidural bupivacaine for acute pain after the surgical repair at 2 days of age. Immediately after the treatment, the patient developed nearly continuous hiccups. Bedside EEG was performed to rule out seizures as a cause of hiccup. The background EEG activity showed mildly diffuse delta slowing due to the effect of general anesthesia. During the hiccups (three very brief hiccups with shivering), EEG showed bilateral synchronous high-voltage 5- to 6-Hz theta activity with occipital predominance, followed by diffuse background attenuation. Hiccups stopped within 1 hour after bupivacaine was discontinued. Hiccup artifact can mimic a diffuse electrodecremental event seen in infantile spasms. Video-EEG recording or annotation by an EEG technologist is invaluable for the diagnosis. There was a single case report of persistent hiccups after epidural administration of bupivacaine in an adult.10 The exact mechanism of hiccup is not completely understood, although it is likely caused by a stimulation of the central or peripheral components of hiccup reflex arc.11
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FIGURE 236. Hiccup Artifact. (Same patient as in Figure 2-35) Movement artifact from hiccup can sometimes simulate diffuse electrodecremental pattern seen in epileptic spasm.
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FIGURE 237. Movement Artifact. A 2-year-old boy with recurrent staring episodes. EEG during photic stimulation shows wave forms simulating spike-wave discharges at O1 electrode. They are associated with head movements that are time-locked with photic stimuli. These mimicks are caused by head movement. The patient has done well without any treatment for seizures.
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FIGURE 238. Hiccup Artifact. Hiccup artifact in an 8-week-old infant with recurrent cyanotic episodes. EEG shows quasi-periodic sharply-contoured waves in the O1 electrode with diffuse blunt theta activity, mimicking spike-wave discharges (asterisk). These artifacts are caused by movement of EEG electrodes during the hiccups.
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Artifacts
FIGURE 239. Hiccup Artifact. Movement artifact from hiccups can sometimes simulate epileptiform discharge (asterisk). The presence of repetitive pattern associated with movements, annotation of the clinical symptoms by an EEG technologist, and simultaneous video recording are extremely helpful in recognition of this artifact.
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FIGURE 240. Hiccup Artifact. EEG and respiratory monitoring (Abd: abdominal lead) shows hiccup artifacts (asterisk) with variable degree of effect on the EEG electrodes.
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FIGURE 241. Sobbing Artifact. Sobbing artifact in a 9-month-old boy. EEG shows bilateral synchronous high-voltage biphasic delta waves in the posterior head regions time-locked with head movement during sobbing.
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FIGURE 242. Sobbing Artifact. EEG in a neonate with apnea. Sobbing causes artifactual sharp-like wave form due to rapid movement of electrodes.
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FIGURE 243. Sucking Artifact. Sucking artifact in a 3-month-old boy with recurrent staring episodes. Note spike-like activity (arrow) in bi-temporal regions.
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FIGURE 244. Sucking Artifact. Sucking artifact in a 5-day-old neonate with HIE. Note spike-like activity in bi-temporal regions (X).
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FIGURE 245. Sucking Artifact. Sucking artifact in a 5-day-old neonate with HIE. Note (poly)spike-like activity in bi-temporal regions.
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FIGURE 246. Tremor Artifact. EEG of a 9-year-old boy with tremors. His entire body, especially both hands, was shaking, which caused vibratory movement of multiple electrodes, especially occipital electrodes; rhythmic 11 Hz accompanied by muscle potential at the occipital electrodes.
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FIGURE 247. Movement Artifact (Tremor). A 10-year-old boy with essential tremor. EEG showing movement artifact during tremor can mimic electrodecrement as seen in an epileptic spasm.
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FIGURE 248. Movement Artifact. Head movement caused semi-rhythmic activity simulating spike-wave discharges.
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FIGURE 249. Head Movement Artifact. Head movement artifact simulating diffuse delta slowing.
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FIGURE 250. Clonic Limb Movement Artifact. EEG of an infant 41 weeks of conceptional age who had recently been diagnosed with early epileptic encephalopathy. EEG shows diffuse high-voltage sinusoidal 6- to 7-Hz activity time-locked with bilateral clonic limb movement. Clonic limb movement artifact can mimic an electrographic seizure.
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FIGURE 251. Movement Artifact; Erratic Myoclonus in Early Myoclonic Encephalopathy (EME). EEG of a 1-week-old boy with early myoclonic encephalopathy (EME). The patient developed frequent body, limb, or facial twitching, mostly with no EEG correlation. During one of his repetitive body jerking episodes, the EEG shows rhythmic sinusoidal theta activity time-locked with the body movement (open arrow).
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FIGURE 252. Muscle and Movement Artifact; Nonepileptic Event (Shivering). A 5-year-old girl with recurrent shivering episodes accompanied by loss of consciousness. Background EEG was within normal limits. During the typical spells, the EEG shows bursts of bilateral synchronous high-frequency muscle artifact, maximal in the posterior head regions (arrow head). Preservation of alpha rhythm is noted during the spells. Also note EKG artifact at T3. Movement during the EEG recording can produce artifact through both the electrical fields generated by muscle and the effect of movement on the EEG electrodes. Muscle artifact has a more disorganized appearance and occurs most commonly in regions with underlying muscle, especially the frontalis and masseters (frontal and temporal regions).
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FIGURE 253. Respiration Artifact. Periodic positive sharp transients time-locked with body movement related to artificial respirator indicate respiratory artifact. Movement causes mechanically induced impedance changes in electrodes. Respiratory artifact may also appear as a slow or sharp wave.7
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FIGURE 254. Ventilator Artifact. Another example of respiratory artifact associated with body movement due to an artificial respirator.
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FIGURE 255. Movement Artifact (Shivering). EEG of a 4-year-old boy during shivering episodes shows movement artifact that can mimic abnormal fast activity such as seizure.
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FIGURE 256. Movement Artifact & Respiration Artifact. Two types of artifact are noted: spike-like activity due to rapid body movement (open arrow) and slow activity caused by respiration and head movement (double arrows).
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FIGURE 257. Respiratory Artifact. Periodic bursts of unusual activity time-locked with body movement related to artificial respirator indicate respiratory artifact. Movement causes mechanically induced impedance changes in electrodes. Respiratory artifact may also appear as a slow or sharp wave. The artifact can simulate burst-suppression pattern.
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FIGURE 258. Breath Holding Artifact. A 9-year-old girl with recurrent apnea and cyanosis. During the breath-holding episodes, EEG shows diffuse muscle artifact alternating with normal background activity, which indicates the spells are nonepileptic in nature.
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FIGURE 259. Chewing Artifact (Unilateral). Chewing artifact is described as bursts of muscle activity followed by slow waves. It usually occurs bilaterally but sometimes unilaterally.
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FIGURE 260. Telephone Ring Artifact. Telephone ring can cause low-amplitude high-frequency artifact as seen in the right occipital region in this patient.
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FIGURE 261. Sixty-Cycle Artifact. Sixty-cycle artifact arises from the 60-cycle power source, especially in the electrodes that have a high resistance from grease, dirt, and dead skin. Reducing impedance to less than 5-kΩ and having a stable ground electrode on the patient will eliminate this artifact. The 60-Hz filter (arrow head) helps to eliminate this electrical artifact but should not be used on a routine basis, as the 60-cycle artifact is a useful warning sign of poor electrode contact or an improper input selection. Sixtycycle artifact in all channels of the EEG recording raises the concern about electrical safety and should be further investigated, specifically looking for ground loops or double grounding.2,7,1,12
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FIGURE 262. Electrocerebral Inactivity (ECI); High-Frequency Ventilator Artifact. An infant 40 weeks of conceptional age with severe hypoxic ischemic encephalopathy (Apgar scores of 0, 0, and 3 at 1, 5, and 10 minutes, respectively) who developed multiorgan failure and subsequently brain herniation syndrome. EEG shows no cerebral activity. High-frequency ventilator artifact described as diffuse, invariant, rhythmic, sinusoidal activity in all EEG electrodes caused by vibratory effect on the entire body is noted. Also note EKG artifact.
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FIGURE 263. Low Voltage EKG Activity Due to Scalp Edema; High Frequency Jet Respirator Artifact. An 18-day-old boy with diaphragmatic hernia, pulmonary hypoplasia, and severe scalp edema due to hypoalbuminemia who had been on ECMO since birth. Head CT showed significant extra-axial CSF space. His level of consciousness had been improving. EEG demonstrates very low-voltage background activity mainly caused by scalp edema. Note artifactual, low-voltage, rhythmic, 7-Hz theta activity in the right occipital electrode caused by the effect of high-frequency jet ventilator, which can vibrate a patient’s entire body and the recording EEG electrodes (arrow). This artifact can mimic a focal electrographic seizure.
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FIGURE 264. Electrode Pop. An electrode pop is the most common electrode artifact described as a single or multiple spike-like, negative or positive discharge. It is more commonly positive. The popping is caused by an abrupt increase in electrode impedance, which may be related to impurity in the metal portion of the electrode.
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FIGURE 265. Photocell Artifact. During flash photic stimulation, high impedance in electrodes may cause a “photocell artifact.” Each flash causes a minute photochemical reaction that, in the presence of high impedance, causes the electrode to act as a photocell, a brief spike-like transient appearing simultaneously with the flash. One can distinguish this photoelectric response from photomyoclonic responses because the latter have small but measurable latencies, detectable by increasing paper speed to 60 mm/sec.13
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FIGURE 266. Ground Lead Recording. A ground electrode on the patient eliminates the 60-Hz AC artifact from power lines. A problem occurs when the impedance of one of the active electrodes connected to grid 1 (G1) or G2 of the amplifier becomes large relative to the other active electrode and the ground of the amplifier. In this case, the ground electrode becomes an active electrode. Depending on its site, it may introduce false cerebral activity (Ford, 1981): Ford, R.G. (1981): A practical guide to EEG recording technique. Am. J. EEG Technol. 21: 79-101 In this patient, the ground electrode was placed on the forehead and the low-impedance active electrode occurred in the occipital region. Therefore, the eye movement artifacts were noted in the occipital region (asterisk) when the patient blinked his eyes. Due to the open circuit in channel 4 (O1-A1), O1 was not punched on G1 selection on the selector board. Blink artifacts appear in channel 4 because ground electrode was on forehead. Artifacts appear in phase because Fp1, Fp2, and “active ” ground are on G1.13
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FIGURE 267. Ground Lead Recording. A ground electrode on the patient eliminates the 60-Hz AC artifact from power lines. A problem occurs when the impedance of one of the active electrodes connected to grid 1 (G1) or G2 of the amplifier becomes large relative to the other active electrode and the ground of the amplifier. In this case the ground electrode becomes an active electrode. Depending on its site, it may introduce false cerebral activity (Ford, 1981). In this patient, the ground electrode was placed on the forehead and the low-impedance active electrode occurred in the occipital region. Therefore, the eye movement artifacts were noted in the occipital region (asterisk) when the patient blinked his eyes. Due to the open circuit in channel 4 (T5-O1), O1 was not punched on G2 selection on the selector board. Blink artifacts appear in channel 4 because ground electrode was on forehead. Artifacts appear out of phase because Fp1 and Fp2 are on G1 while “active ” ground is on G2.13
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FIGURE 268. Misplacement of Ground Electrode. Erroneous placement of ground electrodes at Fp2 causes upward reflection of the wave at channels 12 (Fp2-F4) and 16 (Fp2-F8) during an eye blinking.13
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FIGURE 269. Electrode Artifact. EEG in a 4-year-old boy with severe encephalomalacia in the right hemisphere. Electrode noise at T4 (arrow) can simulate an electrographic seizure. The electrode test reveals impedance in excess of 60 kΩ. It is caused by an electrically unstable electrode. Replacement of the electrode, reapplication of electrode, or application of a different electrode can correct the problem.7
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FIGURE 270. Positive Sharp Waves. Positive sharp waves in older children and adults, especially if they are very focal as if from only one electrode, almost always represent electrode artifacts caused by defective electrodes (“electrode pop”). However, positive sharp waves confined to only one electrode (open arrow) are not uncommon in neonates and are usually associated with deep white matter abnormalities such as intraventricular hemorrhage, periventricular leukomalacia, or infarction. They are also associated with seizures in 29%,14 although they are not epileptiform activity.15
2 References 1. Hughes JR. EEG in Clinical Practice. Boston: Butterworth-Heinemann. 1994. 2. Klem G. Artifacts. In: Ebersole JS, Pedley TA, eds. Current Practice of Clinical Electroencephalography. Philadelphia: Lippincott Williams & Wilkins: 2003:271–287. 3. Herman D, Bartley G, Bullock J. Ophthalmic findings of hydranencephaly. J Pediatr Ophthalmol Strabismus. 1988;25(3):106-11. 4. Sharbrough F. Nonspecific abnormal EEG patterns. In: Niedermeyer E, Lopes du Silva F, eds. Electroencephalography. 4th ed. Baltimore: Lippincott Williams & Wilkins. 2005:235–254. 5. Blume W, Kaibara M. Atlas of Adult Electroencephalography. Baltimore: Lippincott Williams & Wilkins. 2002.
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6. Mizrahi E, Pollack M, Kellaway P. Neocortical death in infants: behavioral, neurologic, and electroencephalographic characteristics. Pediatr Neurol. 1985;1(5):302-305. 7. Tyner F, Knott J, Mayer W. Fundamentals of EEG Technology: Clinical Correlates. Lippincott Williams & Wilkins. 1989. 8. Stern J, Engel J. Atlas of EEG Patterns. Baltimore: Lippincott Williams & Wilkins. 2004. 9. American Electroencephalographic Society Guidelines in EEG, 1-7 (revised 1985). J Clin Neurophysiol. 1986;3(2):131–168. 10. R.K. McAllister, A.J. McDavid, T.A. Meyer and T.M. Bittenbinder, Recurrent persistent hiccup after epidural steroid injection and analgesia with bupivacaine, Anesth Analg 2005;100;1834–1836. 11. Bilotta F, Pietropaoli P, Rosa G. Nefopam for refractory postoperative hiccups. Anesth Analg. 2001;93(5):1358.
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12. Fisch BJ. Fisch and Spehlmann’s EEG Primer: Basic Principles of Digital and Analog EEG. Amsterdam: Elsevier Science Health Science Division. 1999. 13. Brittenham D. Artifacts. In: Daly D, Pedley T, eds. Current Practice of Clinical Electroencephalography. New York: Lippincott Williams & Wilkins; 1990. 14. Hughes J, Kuhlman D, Hughes C. Electro-clinical correlations of positive and negative sharp waves on the temporal and central areas in premature infants. Clin Electroencephalogr. 1991;22(1):30. 15. Clancy R, Bergqvist, Dlugos J. In: Ebersole JS, Pedley TA, eds. Current Practice of Clinical Electroencephalography. 3rd ed. Philadelphia: Lippincott Williams & Wilkins; 2003.
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Tracé discontinu (Figures 3-1 to 3-3 and 3-7)
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Earliest electroencephalography (EEG) activity that appears in viable neonate at 22–23 weeks of gestational age (GA).
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Short bursts, consisting of slow and fast rhythm, interspersed against a flat or quiescent background of less than 25 μV.
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Appear at a very early age of 22–24 weeks GA; may vary from 5 sec to 8 min. 䡲 As age increases, the periods of inactivity shorten. The longest acceptable single interburst interval (IBI) duration has been reported to be 26 weeks conceptional age (CA), 46 sec; 27 weeks CA, 36 sec; 28 weeks, 27 sec; less than 30 weeks CA, 35 sec; 31–33 weeks CA, 20 sec; 34–36 weeks CA, 10 sec; and 37–40 weeks CA, 6 sec.
Newborn
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In infants less than 30 weeks CA, the average IBI or “quesence” is about 6–12 sec. The longest acceptable IBI is 30–35 sec. 䡲 This is the first EEG pattern occurring during quiet sleep that differentiates wakefulness from sleep in the premature infant at around 30–32 weeks CA. 䡲 Infants at less than 30 weeks CA have “paradoxical hypersynchrony” whereby bursts of cerebral electrical activities are well synchronized between the two hemispheres. 䡲 After 30 weeks CA, bursts of cerebral activities appear to be more asynchronous. The bursts of cerebral activities during quiet sleep are synchronized in approximately 70% at 31–32 weeks CA, 80% at 33–34 weeks CA, and 100% after 37 weeks CA.
Delta brushes (DBs) (“brushes,” “spindles-delta bursts,” “ripples of prematurity,” “spindles-like fast waves,” and “beta-delta complexes”) (Figures 3-4 to 3-7, 3-12, 3-13) 䡲
First appear at 24–26 weeks CA.
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Consist of a combination of a specific delta frequency transient (0.3–1.5 Hz, 50–250 mV) waves with a superimposed “buzz” of 8- to 22-Hz activity.
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DBs are symmetrical but asynchronous, except when they are associated with monorhythmic occipital delta activity, between the two hemispheres. 䡲 Before 33 weeks CA, they occur more frequently during active than quiet sleep. After that, they are more numerous in quiet sleep. 䡲
In the youngest premature infants DBs are most commonly seen in the central and midline areas.
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At the peak of 32–34 weeks CA, they are seen in occipital and temporal regions. 䡲 By term, DBs are only seen in the bursts of trace alternant. DBs disappear completely at 44 weeks CA. 䡲 If DBs are found more than 2 every 10 sec at term, they should be considered abnormal. DBs are prominent during rapid eye movement (REM) and nonrapid eye movement (NREM) sleep between 26 and 33 weeks CA and 33 to 37 weeks CA, respectively.
Monorhythmic occipital delta activity (Figures 3-5 to 3-7 and 3-12 to 3-13) 䡲
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䡲 䡲 䡲 䡲
Run of monomorphic, high amplitude (50–250 μV), surface-positive polarity, 0.3- to 1.5-Hz delta waves, occurring symmetrically and synchronously in the bi-occipital regions. The run can last from 2 to 60 sec, rarely longer than 5–6 sec in duration in an infant less than28 weeks CA and commonly greater than 30 sec at 28–31 weeks CA. Appears at 23–24 weeks CA, peaks between 31 and 33 weeks, and then significantly fades by 35 weeks. Intermixed with occipital delta brushes (DBs). Principal landmark regional electrographic feature of the preterm infant. Strong rhythm and may persist in the presence of severe acute encephalopathy.
Sharp theta on the occipitals of prematures (STOP) (Figures 3-8 to 3-11) 䡲
Five- to 6-Hz sharply-contoured theta activity, either unilateral or bilateral and maximal in the occipital regions.
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Similar to temporal theta bursts in configuration, but faster in frequency and lower in amplitude. 䡲 The incidence was highest at the youngest age, 22– 25 weeks CA, decreasing to zero near term. 䡲 In the youngest age these rhythms are mainly bilateral; in the older neonates, they are unilateral. 䡲 Seen more often in active sleep, but reduced in incidence in patients with abnormal slow waves, ictal, or immature patterns. 䡲
Right-sided sharp theta on the occipitals of prematures (STOP) was more frequently associated with abnormal EEGs, especially in males with rightsided sharp waves, often noted in the patients with seizures and intraventricular hemorrhages (IVHs).
amplitude (resembles the EEG during wakefulness and active sleep and consists of mixed frequencies with 25–50 μV). 䡲 Begins to wane by 38–40 weeks CA and disappears by 44–46 weeks CA when it is replaced by continuous slow-wave activity. After that, sleep spindles present at around 46 weeks CA. 䡲 The distinction between trace alternant and trace discontinu (TD) is the amplitude of IBI. In TD, it is less than 25 μV, whereas in trace alternant, it is more than 25 μV.
Frontal sharp transients (encoches frontales) (Figures 3-22 to 3-26) 䡲
Temporal theta bursts (Figures 3-11 and 3-14 to 3-18) 䡲
Rhythmic 4- to 6-Hz sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV.
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Arising independently in the left and right midtemporal regions. 䡲 Appears at the age of 26 weeks CA, is expressed maximally around 29–32 weeks CA, then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.
Physiologic findings. 䡲 Isolated high amplitude (50 to >150 μV), broad, biphasic transients (either negative–positive or positive–negative) with blunt configuration, seen maximally in frontal–prefrontal regions (Fp3–Fp4). 䡲 They usually are isolated or occur in brief runs, alone or in combination with anterior slow dysrhythmia, symmetrically, bilaterally, and synchronously. 䡲 䡲
Temporal alpha bursts (Figure 3-19) 䡲
Similar character of amplitude, burst duration, and spatial distribution as temporal theta bursts. 䡲 Very specific developmental marker for 33 weeks CA because they appear at the 33 weeks CA and disappear by 34 weeks CA.
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Trace alternant (Figures 3-20 and 3-21) 䡲
Between 36 and 38 weeks CA, two NREM EEG patterns present: (1) continuously diffuse high-voltage, slowwave activity and (2) trace alternant. 䡲 Bursts of activity (delta activity admixed with faster frequencies) with amplitude of 50–300 μV, interspersed between periods of decreased
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Newborn
They occur in transition from active to early quiet sleep. Although the premature form with polyphasic potentials and very high amplitude may appear very early at 26–31 weeks CA, the typical biphasic frontal sharp transients (FST) are maximally expressed at 35–36 weeks, are diminished in number and voltage after 44 weeks CA, are rarely seen during sleep after 46 weeks CA, and are absent at 48 weeks CA. Minor pathologic FST include (1) excessive amount, (2) long duration, (3) high amplitude, (4) occurrence in active sleep/wakefulness, (5) atypical morphology, (6) marked asymmetry, and (7) appearance beyond 48 weeks.
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Usually admixed with frontal sharp transients.
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Occurs most prominently during transitional sleep. It is a normal developmental EEG pattern. However, when it is abundant, persistently asymmetric, and high in amplitude or dysmorphic, it may be considered abnormal
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Rhythmic midline central theta bursts (Figure 3-30) 䡲
Bursts of rhythmic 50- to 200-μV, 5- to 9-Hz activity occurring in the midline central region. 䡲 Either a normal variant or in association with other abnormalities, especially central sharp waves in patients with various central nervous system (CNS) insults.
Transient unilateral attenuation of background activity (Figures 3-31 and 3-32) 䡲
Occurs during the beginning of quiet sleep.
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Seen in 3–4% of newborns. Consists of a sudden flattening of the EEG activity occurring in one hemisphere. Asymmetry is transient, lasting from 1 to 5 min (less than 1.5 min in 75% of cases). EEG activity before and after the asymmetry is almost always normal. May reflect the unusual functioning of mechanisms underlying the normal process of change from the low-voltage continuous EEG in REM sleep to the higher-voltage discontinuous pattern of quiet sleep. Uncertain significance and must be differentiated from asymmetric background activity associated with structural abnormalities. The latter is usually shorter in duration, occurs in all states, and is associated with other EEG abnormalities such as sharp waves or delta slowing.
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Anterior slow dysrhythmia (Figures 3-27 to 3-29) 䡲
Intermittent semirhythmic 1.5–2-Hz high-voltage delta activity (50–100 μV) in the frontal regions bilaterally.
Burst suppression (Figures 3-33 to 3-35) 䡲
Most extreme degree of discontinuity.
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Represents an intermediate degree between depressed and undifferentiated EEG and electrocerebral inactivity (ECI).
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During the burst, activity is comprised of an intermixed of poorly organized delta and theta frequencies, at times, with spikes or sharp waves. 䡲 The IBI contains very low voltage (<5 μV) activity that can last more than 20 sec. 䡲 Burst suppression is different from TD: 䊳
Excessively discontinuous
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Invariant Completely unreactive to noxious stimulation
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Newborn
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PRSs have low sensitivity but high specificity for IVH and are seen in 69.2% of grade III and IV IVH and in 31.8% of lower grades IVH.
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PRSs may represent “white matter necrosis” with and without IVH and infarction. They are associated with seizures in 29%.
Focal negative sharp waves (Figures 3-44 to 3-46) 䡲
No spontaneous cycling of state Some patients may have myoclonic jerks during the bursts.
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Poor outcome is noted in 85–100% The rhythmic alpha activity within the burst suppression activity indicates encephalopathy rather than epileptiform activity (alpha seizure).
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Positive sharp waves (Figures 3-36 to 3-43) 䡲
Neither epileptiform activity nor directly associated with neonatal seizures. 䡲 Associated with underlying structural abnormalities, especially in the deep cerebral white matter.
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Positive rolandic sharp waves (PRSs) and positive temporal sharp waves (PTSs) are often associated with, but are not pathognomonic of, IVH. The earlier descriptions of the neonatal positive sharp wave (PSW) placed them on the central regions, but later discharges of the same kind have been described on the temporal regions.
Complex morphology, especially polyphasic, followed by extremely high-voltage slow wave Spikes rather than sharp waves Positive polarity Repetitive runs, especially burnt-out sharp waves
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Persistent localization or lateralization (even as early as 30 weeks CA)
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Occurrence during wakefulness, especially in term infants Moderately or severely abnormal background activity Frequency more than 1 per 1 min Any sharp waves or spikes after 2 months CA
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Seen in a variety of conditions including periventricular leukomalacia. 䡲 Hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or hypoxic ischemic encephalopathy (HIE).4
Although there are no rigid criteria to distinguish abnormal from normal focal sharp waves in neonates, some findings, especially in combination, may be helpful to identify abnormal sharp waves:
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High-amplitude (>150 μV) and long-duration (>150 msec), 10) multifocal sharp waves.
Zip-like electrical discharges (zips) (Figures 3-47 to 3-49) 䡲
Common ictal EEG pattern in neonates, which consists of focal episodic rapid spikes of accelerating and decelerating speed that look like zips. 䡲 Zips may be associated with subclinical, subtle, focal clonic, and tonic seizures. Zips of subtle seizures are often multifocal and of shifting localization.
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Seizures of the depressed brain (Figures 3-47 to 3-51) 䡲
Seen in neonates whose background EEG activity is depressed and undifferentiated. 䡲 The discharges are typically low in voltage, long in duration, highly localized, may be unifocal or multifocal, and show little tendency to spread. 䡲
This pattern is typically not accompanied by a clinical seizure and suggests a poor prognosis.
Focal clonic seizure (Figure 3-52) 䡲
Stroke or hemorrhage is the most common structural abnormality that causes focal clonic or tonic seizures. 䡲 In addition, focal tonic or clonic seizures are also associated with some metabolic conditions such as hypocalcemia, hypoglycemia, and hypomagnesemia.
Alpha seizure discharge (Figures 3-53 to 3-56) 䡲
Typically occurs in unilateral temporal or central region or can evolve from activity that is more clearly epileptic. It can also occur simultaneously, but asynchronously with other electrographic seizures. 䡲 The alpha seizure discharge is associated with severe encephalopathy and poor prognosis. It may occur without clinical accompaniment.
Théta pointu alternant (Figures 3-57 to 3-58) 䡲
Interictal EEG in benign familial and idiopathic neonatal convulsions was normal, discontinuous, and showed focal or multifocal sharp waves or “théta pointu alternant” pattern. 䡲 Seen during waking and sleep and up to 12 days after the seizures are stopped. 䡲 Bursts of unreactive dominant 4–7 Hz theta activity intermixed with sharp waves with frequent interhemispheric asynchrony and shifting predominance between the two hemispheres.
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Nonspecific EEG pattern seen in status epilepticus caused by a variety of conditions such as HIE, hypocalcemia, meningitis, subarrachnoid hemorrhage, and benign idiopathic/familial neonatal convulsions.
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The patterns suggesting poor prognosis such as a paroxysmal, inactive, or burst suppression have never been reported in benign idiopathic/familial neonatal convulsions. 䡲 Théta pointu alternant pattern is associated with good prognosis.
Early myoclonic encephalopathy (Figure 3-59)
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Etiologies are heterogeneous but prenatal brain pathology such as malformation of cortical development is suspected in most cases and metabolic disorders are rare. 䡲 Evolution into West syndrome is often observed in surviving cases.
Depression and lack of differentiation EEG (Figure 3-61) 䡲
Malformation of cortical development is an uncommon etiology. 䡲 Pyridoxine dependency was reported in one patient with EME who had complete recovery after the treatment with pyridoxine. 䡲
Almost all patients with EME have very poor prognosis.
Ohtahara syndrome (Figure 3-60) 䡲
Very rare and devastating form of epileptic encephalopathy of very early infancy. 䡲 Onset of seizure is mainly within 1 month and often within the first 10 days of life, sometimes prenatally or the first 2–3 months after birth. 䡲
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Metabolic diseases, especially nonketotic hyperglycinemia, are usually the causes of early myoclonic encephalopathy (EME).
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Tonic spasms and, less commonly, erratic focal motor seizures and hemiconvulsions.
EEG shows burst-suppression pattern occurring in both sleep and waking states.
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Very rare epileptic syndrome characterized by myoclonus with onset of seizures in the neonatal period. 䡲 EEG shows burst-suppression pattern.
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Newborn
Indicative of severe brain insult but is nonspecific in etiology and can be due to a wide variety of conditions including severe HIE, severe metabolic disorders, meningitis or encephalitis, cerebral hemorrhage, and IVH. Depressed and undifferentiated EEG within the first 24 h after birth that persists indicates a poor prognosis.
Electrocerebral inactivity (Figures 3-62 to 3-64) 䡲
EEG shows no cerebral activity with the EEG sensitivity of 2 μV/mm. 䡲 Represents the ultimate degree of depression and lack of differentiation. 䡲 Serial EEGs are required to demonstrate a persistent degree of cortical inactivity. 䡲
Isoelectric EEG is indicative of death of the cortex but not of brainstem. Therefore, patients may continue to survive with cardiorespiratory support despite the presence of this EEG pattern. 䡲 ECI can be interpreted as a sign of brain death if there is absence of cortical and brainstem functions, and no evidence of intoxication, or hypothermia.
Minimal technical standards for the EEG recording in brain death by The American Encephalographic Society are required.
Symptomatic focal epilepsy caused by focal cortical dysplasia (Figures 3-65 to 3-67) 䡲
Intrinsic epileptogenicity in focal cortical dysplasia (FCD) is caused by abnormal synaptic interconnectivity and neurotransmitter changes within the lesion.
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FCD has intrinsic epileptogenicity with unique EEG patterns including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.
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The incidence of intrinsic epileptogencity in FCD was 11–20%. Polymorphic delta activity indicative of white matter involvement is commonly seen in FCD. 䡲 Trains of continuous or very frequent rhythmic spikes or sharp waves and recurrent electrographic seizures on the scalp EEG were seen in up to 44% of FCD in one series. 䡲 Similar discharges (low-voltage fast activity), also called “regional polyspike,” especially in extratemporal location, is highly associated with FCD (80%). 䡲 In all patients with FCD, the seizure onset zone (SOZ) was located within the lesion. Lesional non-SOZ areas might not be directly involved in the seizure origin but might turn into a seizure focus after the removal of primary epileptogenic tissue; therefore, removal of the entire lesion and surrounding interictally active tissue is necessary. Removal of the FCD alone does not lead to a good outcome, suggesting a more widespread epileptogenic network in these patients.
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FIGURE 31. Tracé Discontinu. EEG of a 27-week CA infant with severe HIE. Tracé discontinu (TD) is the earliest EEG activity that appears in viable neonate at 22–23 weeks of gestational age (GA). The waves are described as short bursts, consisting of slow and fast rhythm, interspersed against a flat or quiescent background of less than 25 μV.1 At a very early age of 22–24 weeks GA may vary from 5 sec to 8 min.2 As age increases, the periods of inactivity shorten. The longest acceptable single interburst interval (IBI) duration has been reported to be 26 weeks CA, 46 sec; 27 weeks CA, 36 sec; 28 weeks CA, 27 sec3; less than 30 weeks CA, 35 sec; 31–33 weeks CA, 20 sec; 34–36 weeks CA, 10 sec; and 37–40 weeks CA, 6 sec.4–6 The TD is also the first EEG pattern occurring during quiet sleep that differentiates wakefulness from sleep in the premature infant at around 30–32 weeks CA. Infants less than 30 weeks CA show interhemispheric hypersynchrony whereby the majority of bursts arising within the two hemispheres appear at the same time.5
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FIGURE 32. Interhemispheric Hypersynchrony. EEG of an infant 28 weeks CA with apnea. The tracing is discontinuous. Infants at less than 30 weeks CA have “paradoxical hypersynchrony” whereby bursts of cerebral electrical activities are well synchronized and appear simultaneously between the two hemispheres. The pathophysiology of this phenomenon is unknown. After 30 weeks CA, bursts of cerebral activities appear to be more asynchronous. The bursts of cerebral activities during quiet sleep are synchronized in approximately 70% at 31–32 weeks CA, 80% at 33–34 weeks CA, and 100% after 37 weeks CA. In infants less than 30 weeks CA, the average interburst interval (IBI) or quiescence is about 6–12 sec. The longest acceptable IBI is 30–35 sec.
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FIGURE 33. Tracé Discontinu. EEG of a 28-week CA infant with severe HIE. Tracé discontinu (TD) is the earliest EEG activity that appears in the viable neaonate at 22–23 weeks of gestational age (GA). It is described as short bursts, consisting of slow and fast rhythm, interspersed against a flat or quiescent background of less than 25 μV.1 At a very early age of 22–24 weeks GA, it may vary from 5 sec to 8 min.2 As age increases, the periods of inactivity shorten. The longest acceptable single interburst interval (IBI) duration has been reported to be 26 weeks CA, 46 sec; 27 weeks CA, 36 sec; 28 weeks, 27 sec3; less than 30 weeks CA, 35 sec; 31–33 weeks CA, 20 sec; 34–36 weeks CA, 10 sec; and 37–40 weeks CA, 6 sec.4–6 The TD is also the first EEG pattern occurring during quiet sleep that differentiates wakefulness from sleep in the premature infant at around 30–32 weeks CA. Infants less than 30 weeks CA show interhemispheric hypersynchrony in which the majority of bursts arising within the two hemispheres appear at the same time.5 Note frequent low-voltage sharp waves at Cz.
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FIGURE 34. Delta Brushes (Central Predominance). EEG of a 28-week CA infant with apnea. Delta brushes (DBs) (“brushes,” “spindles-delta bursts,” “ripples of prematurity,” spindles-like fast waves,” and “beta-delta complexes”) first appear at 24–26 weeks CA and consist of a combination of a specific delta frequency transient (0.3–1.5 Hz, 50–250 mV) waves with a superimposed “buzz” of 8- to 22-Hz activity. DBs are symmetrical but asynchronous, except when they are associated with monorhythmic occipital delta activity. Before 33 weeks CA, they occur more frequently during active than quiet sleep. After that, they are more numerous in quiet sleep. In the youngest prematures, DBs are most commonly seen in the central and midline areas. At the peak of 32–34 weeks CA, they are seen in occipital and temporal regions. By term, DBs are only seen in the bursts of trace alternant. DBs disappear completely at 44 weeks CA.4,5 If DBs are found at a frequency of greater than 2 every 10 sec at term, they should be considered abnormal.12 DBs are prominent during REM and NREM sleep between 26–33 weeks CA and 33–37 weeks CA.5
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FIGURE 35. Monorhythmic Occipital Delta Activity and Delta Brushes; Extremely Low-Voltage Background Activity. Monorhythmic occipital delta activity in an infant 31 weeks of conceptional age (CA) with severe hypoxic ischemic encephalopathy. This activity is described as a run of monomorphic, high amplitude (50–250 μV), surface-positive polarity, 0.3- to 1.5-Hz delta waves, occurring symmetrically and synchronously in the bi-occipital regions. The run can last from 2 to 60 sec, rarely longer than 5–6 sec in duration in an infant less than 28 weeks CA and commonly greater than 30 sec at 28–31 weeks CA. It is present at 23–24 weeks CA, peaks between 31 and 33 weeks, and then significantly fades by 35 weeks. It serves as the constituent of, and can intermix with, occipital delta brushes (arrow). Monorhythmic occipital delta activity is a principal landmark regional electrographic feature of the preterm infant. It is a strong rhythm and may persist in the presence of severe acute encephalopathy.4,8 Also note EEG signs, bitemporal attenuation, and interhemispheric hypersynchrony in an infant less than 28 weeks CA. Bitemporal attenuation probably reflects interhemispheric asynchrony and underdevelopment of the inferior frontal and superior temporal gyri.9 The physiology of interhemispheric hypersynchrony is unknown.4
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FIGURE 36. Delta Brushes (Occipital Predominance); Monorhythmic Occipital Delta Activity. EEG of a 31-week CA infant with HIE showed bilateral synchronous monorhythmic occipital delta activity intermixed with delta brushes (DBs) in the occipital regions (arrow). DBs (“brushes,” “spindles-delta bursts,” “ripples of prematurity,” “spindles-like fast waves,” and “beta-delta complexes”) first appear at 24–26 weeks CA and consist of a combination of a specific delta frequency transient (0.3–1.5 Hz, 50–250 mV) waves with a superimposed “buzz” of 8- to 22-Hz activity. DBs are symmetric but asynchronous, except when they are associated with monorhythmic occipital delta activity. Before 33 weeks CA, they occur more frequently during active than quiet sleep. After that, they are more numerous in quiet sleep. In the youngest prematures, DBs are most commonly seen in the central and midline areas. At the peak of 32–34 weeks CA, they are seen in occipital and temporal regions. By term, DBs are only seen in the bursts of trace alternant. DBs disappear completely at 44 weeks CA.4,5 If DBs are found more than 2 every 10 sec at term, they should be considered abnormal.12 DBs are prominent during REM and NREM sleep between 26–33 weeks CA and 33–37 weeks CA.5
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FIGURE 37. Markedly Excessive Discontinuity; Gross Interhemispheric Asynchrony; Extremely Low Voltage. (Same EEG recording as in Figure 3-5) A 31-week CA with severe HIE. EEG during comatose state shows extremely low-voltage background activity, excessive interburst interval of more than 2 min (not shown), and marked interhemispheric asynchrony. Also note monorhythmic occipital delta activity (open arrow), delta brushes in the occipital, temporal, and central regions (arrow), and STOP (double arrows). The patient died 1 day after this EEG. Extremely low-voltage (<5 μV) background, markedly excessive discontinuity for age, burst suppression pattern, gross hemispheric asynchrony, depressed and undifferentiated, and isoelectric background activity are indicative of death or poor outcome.4,8,10–13
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FIGURE 38. Sharp Theta on the Occipitals of Prematures (STOP). STOP (open arrow) refers to 5–6 Hz sharp-contoured theta activity, either unilateral or bilateral and maximal in the occipital regions. The STOP pattern is similar to temporal theta bursts in configuration, but is faster in frequency and lower in amplitude. The incidence was highest at the youngest age, 22–25 weeks CA, decreasing to zero near term. In the youngest age these rhythms are mainly bilateral; in the older neonates they are unilateral. STOP is seen more often in active sleep, but is reduced in incidence in patients with abnormal slow waves, ictal or immature patterns. Right-sided STOP was more frequently associated with abnormal EEGs, especially in males with right-sided sharp waves, often noted in the patients with seizures and intraventricular hemorrhages.2,14 Note excessive delta brushes, maximally expressed in central and temporal regions.
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FIGURE 39. Sharp Theta Rhythm on the Occipital Areas of Prematures (STOP). STOP refers to 5–6 Hz sharp-contoured theta activity, either unilateral or bilateral and maximal in the occipital regions. The STOP pattern is similar to temporal theta bursts in configuration, but is faster in frequency and lower in amplitude. The incidence was highest at the youngest age, 22–25 weeks CA, decreasing to zero near term. In the youngest age these rhythms are mainly bilateral; in the older neonates they are unilateral. STOP is seen more often in active sleep, but is reduced in incidence in patients with abnormal slow waves, ictal or immature patterns. Right-sided STOP was more frequently associated with abnormal EEGs, especially in males with right-sided sharp waves, often noted in the patients with seizures and intraventricular hemorrhages.2,14
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FIGURE 310. Sharp Theta on the Occipitals of Prematures (STOP). A 39 weeks CA boy with severe hypoxic ischemic encephalopathy with shock, DIC, cardiorespiratory failure, and seizures. He recovered after the treatment. EEG shows frequent bursts of unilateral or bilateral dependent 5–6 Hz sharp-contoured theta activity in the occipital regions (arrow) superimposed on very low-voltage background activity. STOP refers to 5–6 Hz sharp-contoured theta activity, either unilateral or bilateral and maximal in the occipital regions. The STOP pattern is similar to temporal theta bursts in configuration, but is faster in frequency and lower in amplitude. The incidence was highest at the youngest age, 22–25 weeks CA, decreasing to zero near term. In the youngest age these rhythms are mainly bilateral; in the older neonates they are unilateral. STOP is seen more often in active sleep, but is reduced in incidence in patients with abnormal slow waves, ictal or immature patterns. Right-sided STOP was more frequently associated with abnormal EEGs, especially in males with right-sided sharp waves, often noted in patients with seizures and intraventricular hemorrhages.2,14
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FIGURE 311. STOP and Temporal Theta Bursts Patterns. (Same recording as in Figure 3-10) The EEG shows both temporal theta bursts (double arrows) and sharp theta on the occipitals of prematures (STOP) patterns (open arrow). Temporal theta bursts are rhythmic 4- to 6-Hz, sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV, arising independently in the left and right midtemporal regions. This activity appears at the age of 26 weeks CA, is expressed maximally around 29 weeks,15 29–31 weeks,2 or between 30 and 32 weeks CA,5 then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.5,16 STOP refers to 5 to 6 Hertz sharp-contoured theta activity, either unilateral or bilateral and maximal in the occipital regions. The STOP pattern is similar to temporal theta bursts in configuration, but is faster in frequency and lower in amplitude. The incidence was highest at the youngest age, 22–25 weeks CA, decreasing to zero near term.2,14
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FIGURE 312. Extremely Low Voltage Background; Monorhythmic Occipital Delta Activity and Delta Brushes. EEG of a 31-week CA newborn with severe HIE. DWI MI shows bilateral basal ganglia hyperintensity (open arrow). EEG shows monorhythmic occipital delta activity and delta brushes superimposed on extremely low-voltage background activity with amplitude less than 5 μV. The patient died 1 day after this EEG. Monorhythmic occipital delta activity is a principal landmark regional electrographic feature of the preterm infant. It is a strong rhythm and may persist in the presence of severely acute encephalopathy. Extremely low-voltage (<5 μV) background, in the absence of drug intoxication, acute hypoxemia, hypothermia, severe metabolic disturbances, and postictal state, along with markedly excessive discontinuity for age, burst suppression pattern, gross hemispheric asynchrony, depressed and undifferentiated, and isoelectric background activity are indicative of death or poor outcome.4,8,10–13
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FIGURE 313. Monorhythmic Occipital Delta Activity and Delta Brushes. Monorhythmic occipital delta activity in an infant 31 weeks of conceptional age (CA) with moderate hypoxic ischemic encephalopathy. This activity is described as a run of monomorphic, high-amplitude (50–250 μV), surface-positive polarity, 0.3- to 1.5-Hz delta waves, occurring symmetrically and synchronously in the bi-occipital regions. The run can last from 2 to 60 sec, rarely longer than 5 or 6 sec in an infant less than 28 weeks CA and commonly greater than 30 sec at 28–31 weeks CA. It is present at 23–24 weeks CA, peaks between 31 and 33 weeks, and then significantly fades by 35 weeks. It serves as the constituent of, and can intermix with, occipital delta brushes (arrow). Monorhythmic occipital delta activity is a principal landmark regional electrographic feature of the preterm infant. It is a strong rhythm and may persist in the presence of severely acute encephalopathy.4,8 Also note EEG signs, bitemporal attenuation, and interhemispheric hypersynchrony in infants less than 28 weeks CA. Bitemporal attenuation probably reflects interhemispheric asynchrony and underdevelopment of the inferior frontal and superior temporal gyri.9 The physiology of interhemispheric hypersynchrony is unknown.4
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FIGURE 314. Temporal Theta Bursts (Temporal Sawtooth Waves, Temporal Sharp Transients). Temporal theta bursts are rhythmic, 4- to 6-Hz, sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV, arising independently in the left and right midtemporal regions. This activity appears at the age of 26 weeks CA, is expressed maximally around 29 weeks,15 29–31 weeks2 or between 30 and 32 weeks CA,5 then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.5,16
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FIGURE 315. Temporal Theta Bursts. Temporal theta bursts are rhythmic 4- to 6-Hz, sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV, arising independently in the left and right midtemporal regions. This activity appears at the age of 26 weeks CA, is expressed maximally around 29 weeks,15 29–31 weeks,2 or between 30 and 32 weeks CA,5 then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.5,16
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FIGURE 316. Temporal Theta Burst. Temporal theta bursts (arrow) are rhythmic 4- to 6-Hz, sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV, arising independently in the left and right midtemporal regions. This activity appears at the age of 26 weeks CA, is expressed maximally around 29 weeks,15 29–31 weeks,2 or between 30 and 32 weeks CA,5 then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.5,16 Also note delta brushes (arrow head) in the left frontal and temporal regions.
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FIGURE 317. Temporal Theta Bursts (Temporal Sawtooth Waves). Temporal theta bursts are rhythmic 4- to 6-Hz, sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV, arising independently in the left and right midtemporal regions. This activity appears at the age of 26 weeks CA, is expressed maximally around 29 weeks,15 29–31 weeks,2 or between 30 and 32 weeks CA,5 then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.5,16
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FIGURE 318. Temporal Theta Bursts. Temporal theta bursts are rhythmic 4- to 6-Hz, sharply contoured theta waves in short bursts of 1–2 sec with voltage varying from 20 to 200 μV, arising independently in the left and right midtemporal regions. This activity appears at the age of 26 weeks CA, is expressed maximally around 29 weeks,15 29–31 weeks,2 or between 30 and 32 weeks CA,5 then rapidly disappears, and is replaced by temporal alpha bursts at 33 weeks CA.5,16
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FIGURE 319. Temporal Alpha Bursts; Normal Newborn: 33 Weeks Conceptional Age (CA). Temporal alpha bursts have similar character of amplitude, burst duration, and spatial distribution as temporal theta bursts (as described in Fig. 3-14 to 3-18). The presence of temporal alpha bursts is a very specific developmental marker for 33 weeks CA, because they appear at 33 weeks CA and disappear by 34 weeks CA.5
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FIGURE 320. Trace Alternant. Background activity in NREM sleep is discontinuous before 36 weeks CA. Between 36 and 38 weeks CA, two NREM EEG patterns present (1) continuously diffuse high-voltage, slow-wave activity and (2) trace alternant—this consists of bursts of activity (delta activity admixed with faster frequencies) with an amplitude of 50–300 μV, interspersed between periods of decreased amplitude (resembles the EEG during wakefulness and active sleep and consists of mixed frequencies with amplitudes of 25–50- μV). Trace alternant begins to wane by 38–40 weeks CA and disappears by 44–46 weeks CA when it is replaced by continuous slow-wave activity. After that, sleep spindles present at around 46 weeks CA. The distinction between trace alternant and tracé discontinu is the amplitude of IBI (interburst interval). In tracé discontinu, it is less than 25 μV, whereas in trace alternant, it is more than 25 μV.2,4,5
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FIGURE 321. Trace Alternant. Background activity in NREM sleep is discontinuous before 36 weeks CA. Between 36 and 38 weeks CA, two NREM EEG patterns present (1) continuously diffuse high-voltage, slow-wave activity and (2) trace alternant—this consists of bursts of activity (delta activity admixed with faster frequencies) with an amplitude of 50–300 μV, interspersed between periods of decreased amplitude (resembles the EEG during wakefulness and active sleep and consists of mixed frequencies with amplitudes of 25–50- μV). Trace alternant begins to wane by 38–40 weeks CA and disappears by 44–46 weeks CA when it is replaced by continuous slow-wave activity. After that, sleep spindles present at around 46 weeks CA. The distinction between trace alternant and tracé discontinu is the amplitude of IBI (interburst interval). In tracé discontinu, it is less than 25 μV, whereas in trace alternant, it is more than 25 μV.2,4,5
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FIGURE 322. Frontal Sharp Transients (encouche frontales) (FSTs); Temporal Sharp Waves. A 39-week CA infant with apnea. EEG shows frontal sharp transients (open arrow) and left anterior temporal sharp waves. The rest of EEG recording is within normal limits. FSTs are physiological findings described as isolated high-amplitude, broad, biphasic transients with blunt configuration, seen maximally in frontal–prefrontal regions. They usually either are isolated or occur in brief runs, alone or in combination with anterior slow dysrhythmia, symmetrically, bilaterally, and synchronously. They occur in transition from active to early quiet sleep. Although the premature form, which is polyphasic and of very high amplitude, may appear very early at 26–31 wks CA, the typical biphasic FSTs are maximally expressed at 35–36 wks, are diminished in number and voltage after 44 wks CA, are rarely seen during sleep after 46 wks CA, and are absent at 48 wks CA.17 Minor criteria for pathologic FSTs include (1) excessive amount, (2) excessive duration duration, (3) high amplitude, (4) occurrence in active sleep/wakefulness, (5) atypical morphology, (6) marked asymmetry, and (7) FSTs beyond 48 weeks.4,5,7,8,16,18 Although there are no rigid criteria to distinguish abnormal from normal focal sharp waves in neonates, some findings, especially in combination, may be helpful to identify abnormal sharp waves: (1) complex morphology, especially polyphasic, followed by extremely high-voltage slow wave, (2) spikes rather than sharp waves, (3) positive polarity, (4) repetitive runs especially burnt-out sharp waves, (5) persistent localization or lateralization (even as early as 30 weeks CA), (6) occurrence during wakefulness (especially in term infants) term infants, (7) moderately or severely abnormal background activity, (8) frequency of more than 1 per 1 min, (8) any sharp waves or spikes after 2 months CA, (9) high amplitude (>150 μV) and long duration (>150 msec), and (10) multifocal sharp waves.2,4,5,19
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FIGURE 323. Frontal Sharp Transients (encouche frontales). Frontal sharp transients (encoches frontales) are physiologic findings described as isolated high amplitude (50 to >150 μV), broad, biphasic transients (either negative–positive or positive–negative) with blunt configuration, seen maximally in frontal–prefrontal regions (Fp3–Fp4). They usually are isolated or occur in brief runs, alone or in combination with anterior slow dysrhythmia, symmetrically, bilaterally, and synchronously. They occur in transition from active to early quiet sleep. Although the premature form, which are polyphasic and very high amplitude may appear very early at 26–31 weeks CA, the typical biphasic FST are maximally expressed at 35–36 weeks, are diminished in number and voltage after 44 weeks CA, are rarely seen during sleep after 46 weeks CA, and are absent at 48 weeks CA.17 Minor criteria for pathologic FSTs include (1) excessive amount, (2) excessive duration, (3) high amplitude, (4) occurrence in active sleep/wakefulness, (5) atypical morphology, (6) marked asymmetry, and (7) FSTs beyond 48 weeks.4,5,7,8,16,18
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FIGURE 324. Frontal Sharp Transients (encouche frontales); Anterior Slow Dysrhythmia. Frontal sharp transients (FST) or encoche frontales (arrow) are physiologic sharp waves occurring between 34 and 44 weeks CA. They are high-voltage, broad-based, biphasic, or, less commonly, triphasic sharp waves maximally seen in the prefrontal regions. FST occur symmetrically and synchronously on both sides during sleep, particularly during transition from active to quiet sleep. An immature form of FST described as very highvoltage polymorphic sharp waves can be seen at earlier ages between 27 and 31 weeks CA. The frequency of FST sharply declines between 43 and 45 weeks CA and disappears at 48 weeks CA. They may occur alone or in combination with “anterior slow dysrhythmia” (arrow head).
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FIGURE 325. Premature Frontal Sharp Transients (FST) in 31 weeks CA Infant. Frontal sharp transients (encoches frontales) are physiologic findings described as isolated high amplitude (50 to >150 μV), broad, biphasic transients (either negative–positive or positive–negative) with blunt configuration, seen maximally in frontal–prefrontal regions (Fp3–Fp4). They usually are isolated or occur in brief runs, alone or in combination with anterior slow dysrhythmia, symmetrically, bilaterally, and synchronously. They occur in transition from active to early quiet sleep. Although the premature form which is polyphasic and very high amplitude may appear very early at 26–31 weeks CA, the typical biphasic FST are maximally expressed at 35–36 weeks, are diminished in number and voltage after 44 weeks CA, are rarely seen during sleep after 46 weeks CA, and are absent at 48 weeks CA.17
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FIGURE 326. Eye Movement Artifact. A 38-week CA infant with apnea. EEG shows biphasic sharp theta activity in bilateral prefrontal regions that simulate frontal sharp transients. Eye lead channel can differentiate between these two conditions. When activity points in the different directions as in this EEG, it indicates that this is eye movement artifact rather than brain wave.
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FIGURE 327. Anterior Slow Dysrhythmia; (Anterior Dysrhythmia, Bifrontal Delta Activity). A 40 weeks CA infant with apnea and cyanosis. EEG shows “anterior slow dysrhythmia,” which is described as intermittent semirhythmic 1.5- to 2-Hz high-voltage delta activity (50- to 100 μV) in the frontal regions bilaterally. Anterior slow dysrhythmia is usually admixed with frontal sharp transients. It occurs most prominently during transitional sleep. It is a normal developmental EEG pattern. However, when it is abundant, persistently asymmetric, and high in amplitude or dysmorphic, it may be considered abnormal.2,4,5,10
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FIGURE 328. Anterior Slow Dysrhythmia & Frontal Sharp Transients. A 38-week CA baby girl with mild hypoxic ischemic encephalopathy and clinically suspected seizures. EEG shows bilateral synchronous, rhythmic 1.5-Hz sharp-contoured delta activity in bilateral frontal regions, intermixed with frontal sharp transients. Repetitive frontal sharp transients and anterior slow dysrhythmia is considered a normal, developmental EEG pattern.
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FIGURE 329. Frontal Sharp Waves; Intraventricular/Periventricular Hemorrhage. A 2-day-old full-term infant with intraventricular hemorrhage associated with congenital CMV infection and cardiomyopathy. EEG shows marked and persistent spike/sharp-wave activity in the right frontal region intermixed with focal theta and delta slowing in the same region. This spike/sharp wave activity is more likely to be epileptiform activity rather than anterior slow dysrhythmia. In the same recording (not shown), the patient also has focal electrographic seizures in the right frontal region.
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FIGURE 330. Rhythmic Midline Central Theta Bursts. A 39-week CA infant with jitteriness. EEG shows bursts of rhythmic 4–5 Hz sharply-contoured theta activity in Cz and C4. The rest of the EEG recording was unremarkable. Note an electrode artifact at F7. Rhythmic midline central theta bursts are bursts of rhythmic 50- to 200 -μV, 5- to 9-Hz activity occurring in the midline central region. It can be either a normal variant or can occur in association with other abnormalities, especially central sharp waves, in patients with various CNS insults.5,20
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FIGURE 331. Transient Unilateral Attenuation of Background Activity During Sleep. A 41-week CA newborn with recurrent apneic episodes associated with cyanosis. The neurologic examination was normal. Head CT was unremarkable. A routine EEG during slow sleep shows intermittent attenuation of background activity over the left hemisphere lasting for 1–2 min. Transient unilateral attenuation of background activity during quiet sleep is seen in 3–4% of newborns and consists of a sudden flattening of the EEG activity occurring in one hemisphere. The asymmetry is transient, lasting from 1 to 5 min (less than 1.5 min in 75% of cases). It occurs at the beginning of quiet sleep. The EEG activity before and after the asymmetry is almost always normal. This EEG pattern may reflect the unusual functioning of mechanisms underlying the normal process of change from the low-voltage continuous EEG in REM sleep to the higher voltage discontinuous pattern of quiet sleep. This EEG phenomenon is of uncertain significance and must be differentiated from asymmetric background activity associated with structural abnormalities. The latter is usually shorter in duration, occurs in all states, and is associated with other EEG abnormalities such as sharp waves or delta slowing.5,20–22
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FIGURE 332. Transient Unilateral Attenuation of Background Activity During Sleep. A 41-week CA newborn with recurrent apneic episodes associated with cyanosis. The neurologic examination was normal. Head CT was unremarkable. A routine EEG during slow sleep shows intermittent attenuation of background activity over the left hemisphere lasting for 1–2 minutes. Faster paper speed enhances the “transient unilateral attenuation of background activity during sleep”. Transient unilateral attenuation of background activity during quiet sleep is seen in 3–4% of newborn and consists of a sudden flattening of the EEG activity occurring in one hemisphere. The asymmetry is transient, lasting from 1 to 5 min (less than 1.5 min in 75% of cases). It occurs at the beginning of quiet sleep. The EEG activity before and after the asymmetry is almost always normal. This EEG pattern may reflect the unusual functioning of mechanisms underlying the normal process of change from the low-voltage continuous EEG in REM sleep to the higher voltage discontinuous pattern of quiet sleep. This EEG phenomenon is of uncertain significance and must be differentiated from asymmetric background activity associated with structural abnormalities. The latter is usually shorter in duration, occurs in all states, and is associated with other EEG abnormalities such as sharp waves or delta slowing.5,20–22
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FIGURE 333. Burst-Suppression Pattern; Severe Hypoxic-Ischemic Encephalopathy. (Same patient as in Figure 3-5 and 3-7) A 31-week CA infant with severe HIE. EEG shows a nonreactive burst suppression pattern. The burst of activity contains sharp waves and spikes intermixed with delta and faster frequencies. The interburst interval (IBI) is of very low amplitude. The patient died 1 day after this EEG. Burst suppression is the most extreme degree of discontinuity and represents an intermediate degree between depressed and undifferentiated EEG and electrocerebral inactivity. During the burst, activity contains intermixed components of poorly organized delta and theta frequencies, at times, with spikes or sharp waves. The IBI contains very low-voltage (<5 μV) activity that can last more than 20 sec. Burst suppression is different from tracé discontinu in that it is excessively discontinuous and invariant and completely unreactive to noxious stimulation. Also, there is no spontaneous cycling of state. Some patients may have myoclonic jerks during the bursts. Poor outcome is noted in 85–100%.4,5,8
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FIGURE 334. Burst-Suppression Activity with Diffuse Rhythmic Alpha Activity. A 35-week CA infant with moderate hypoxic ischemic encephalopathy who developed hypotonia and focal clonic seizures. EEG shows diffuse moderate-voltage rhythmic alpha activity (open arrow) during the burst suppression EEG pattern. Note asymmetric monorhythmic occipital delta activity at O1 and O2 (double arrows) and delta brushes in multifocal regions (arrow head). The rhythmic alpha activity within the burst suppression activity indicates encephalopathy rather than epileptiform activity (alpha seizure).5
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FIGURE 335. Burst-Suppression Activity With Diffuse Rhythmic Alpha Activity. (Selected portion of the EEG in Figure 3-34) A 35-week CA infant with hypotonia and focal clonic seizures caused by moderate hypoxic ischemic encephalopathy. EEG shows diffuse moderate-voltage rhythmic alpha activity (open arrow) during the burst suppression EEG pattern.5 (Note asymmetric monorhythmic occipital delta activity at O1 and O2 (double arrows) and delta brushes in multifocal regions (arrow head).
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FIGURE 336. Positive Rolandic Sharp Waves (PRSs); Intracerebral Hemorrhage due to Venous Sinus Thombrosis. A 40-week CA infant born with Apgar scores of 1, 5, and 7 at 1, 5, and 10 min, respectively. The patient developed right focal clonic seizures. He was subsequently found to have a left frontal-parietal hemorrhage caused by venous sinus thrombosis (arrow). EEG shows trains of left positive rolandic sharp waves (PRSs) (open arrow). Positive sharp waves (PSWs) are not epileptiform activity and not directly associated with neonatal seizures but rather with underlying structural abnormalities, especially in the deep cerebral white matter, and can be seen in a variety of conditions, including periventricular leukomalacia, hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or HIE.4 PRSs and positive temporal sharp waves (PTSs) are often associated with, but are not pathognomonic of, intraventricular hemorrhage (IVH). The earlier descriptions of the neonatal PSW placed them on the central regions, but later the same kind of discharges have been described on the temporal regions.2,23,24 PRSs have low sensitivity but high specificity for IVH and are seen in 69.2% of grade III and IV IVH and in 31.8% of lower grades IVH. PRSs may represent “white matter necrosis” with and without IVH and infarction.11,25 They are associated with seizures in 29%.23
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FIGURE 337. Positive Temporal Sharp Waves (PTSs); Periventricular-Intraventricular Hemorrhage (PVH-IVH). A 7-day-old boy born at 27 weeks gestational age with grade 4 intraventricular hemorrhage (IVH). MRI shows PVH-IVH, maximally expressed in the right hemisphere. EEG shows a train of positive sharp waves (PSW) (asterisk) in the right temporal area with some spreading to the right rolandic area. PSWs are not epileptiform activity and not directly associated with neonatal seizures but rather with underlying structural abnormalities, especially in the deep cerebral white matter, and can be seen in a variety of conditions, including periventricular leukomalacia, hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or HIE. Positive temporal sharp waves (PTSs) in full-term infants are seen in structural cerebral lesions, including periventricular leukomalacia, intracerebral hemorrhages, HIE, and infarctions.4,23,24,26 PTSs present within 2–3 days of the acute illness and disappear within 4–5 weeks. The significance of PTSs in premature infants is uncertain. PTSs in normal neonates are seen in 15% at 33–34 weeks CA and 0.75% by 39–40 weeks CA.27 Positive rolandic sharp waves (PRSs) and PTSs are often associated with intraventricular hemorrhage (IVH) but they are not pathognomonic of such a condition. The earlier descriptions of the neonatal PSW placed them on the central regions, but later the same kind of discharges have been described on the temporal regions.7,23,24 PRSs have low sensitivity but high specificity for IVH. PRSs were seen in 69.2% of grade III and IV IVH and in 31.8% of lower grades IVH.11 PRSs may represent “white matter necrosis” with and without IVH.25
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FIGURE 338. Positive Temporal and Rolandic Sharp Waves in Intraventricular Hemorrhage (IVH); Tracé Discontinu. An infant 30 weeks of conceptional age (CA) with grade IV intraventricular hemorrhage (IVH). MRIs show bilateral IVHs (arrow). EEG shows excessive trace discontinu. During the bursts of trace discontinu, there are repetitive positive temporal sharp waves (PTSs) and, to a lesser degree, positive rolandic sharp waves (PRSs) occurring independently in the two hemispheres at T3, T4 (open arrow) and C3, C4 (double arrows), respectively.
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FIGURE 339. Positive Temporal and Rolandic Sharp Waves in Intraventricular Hemorrhage (IVH). (Same recording as in Figure 3-38) Positive temporal sharp waves (PTSs) and, to a lesser degree, positive rolandic sharp waves (PRSs) occurring independently in the two hemispheres at T3, T4 (open arrow) and C3 (double arrows), respectively. Background activity is very low in amplitude.
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FIGURE 340. Positive Temporal Sharp Waves (PTSs); Congenital Toxoplasmosis. A 9-day-old boy born full term with congenital toxoplasmosis. Axial T2-weighted image and DWI show hyperintense signal abnormality in the right temporal region (double arrows and open arrow). EEG shows a train of positive sharp waves (PSWs) in the right temporal region lasting for 2 sec. PSWs are not epileptiform activity and not directly associated with neonatal seizures but rather with underlying structural abnormalities, especially in the deep cerebral white matter, and can be seen in a variety of conditions, including periventricular leukomalacia, hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or HIE. Positive temporal sharp waves (PTSs) in full-term infants are seen in structural cerebral lesions, including periventricular leukomalacia, intracerebral hemorrhages, HIE, and infarctions.4,23,24,26 PTSs present within 2–3 days of the acute illness and disappear within 4–5 weeks. The significance of PTSs in premature infants is uncertain. PTSs in normal neonates are seen in 15% at 33–34 weeks CA and 0.75% by 39–40 weeks CA.27
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FIGURE 341. Positive Sharp Waves. Positive sharp waves (PSWs) in older children and adults, especially if they are very focal as if from only one electrode, almost always represent electrode artifacts caused by defective electrodes (”electrode pop”). However, PSWs confined to only one electrode (open arrow) are not uncommon in neonates and are usually associated with deep white matter abnormalities such as intraventricular hemorrhage, periventricular leukomalacia, or infarction. They are also associated with seizures in 29%,23 although they are not epileptiform activity.4
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FIGURE 342. Positive Temporal Sharp Waves. (Same recording as in Figure 3-41) The burst of positive sharp waves (PSWs) leads the ictal EEG activity at T4. Therefore, they confirm that the PSWs shown in Figure 3-41 represent EEG activity and not “electrode pop” caused by a defective electrode.
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FIGURE 343. Electrographic Seizure (Continued from the previous EEG page) The ictal EEG activity from the Figure 3-42 evolves into (poly)spike-wave discharges at T4 (open arrow) and then rhythmic delta activity at O2 (arrow) with some spread to O1 (double arrows).
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FIGURE 344. Neonatal Seizure (Focal Clonic Seizure); Venous Sinus Thrombosis. A 3-day-old girl (40 weeks CA) with clonic seizures caused by venous sinus thrombosis of uncertain etiology. The patient had some fetal heart rate acceleration and trace meconium. At 4 h of age, she developed clonic seizures of her left arm. MRI with DWI was consistent with cytotoxic edema related to ischemia in multiple areas including bilateral posterior temporal and parietal-occipital lobes, bilateral posterior thalami, and corpus callosum (arrow), maximally expressed in the right temporal region (open arrow). Routine EEG shows multifocal epileptiform activity, maximal in the T4, right temporal region (*). Focal clonic seizures were probably caused by a lesion in the right rolandic region (large arrow) as seen in the DWI. Neuropsychological testing at 4 years of age was within normal limits. Focal clonic seizures are most commonly associated with structural abnormalities, especially focal infarction or hemorrhage. They are also associated with focal cortical dysplasia or metabolic derangements such as hypocalcemia, and hypomagnesemia.28
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FIGURE 345. Right Middle Cerebral Artery Infarction; Left-sided Focal Clonic Seizures. A 5-day-old full-term newborn with Left-sided focal clonic seizures caused by a right middle cerebral artery infarction (arrow). EEG shows very active epileptiform activity and, at times, periodic lateralized epileptiform discharges (PLEDs) in the central vertex and right central regions. The significance of negative sharp waves is controversial. Criteria for abnormality (not absolute) of temporal sharp waves are (1) complex morphology, (2) spikes rather than sharp waves, (3) positive polarity, (4) repetitive runs (especially burnt-out sharp waves), (5) persistent localization or hemisphere (even as early as 30 weeks CA), (6) occurrence during wakefulness, (7) moderately or severely abnormal background activity, (8) frequency more than 1 per min, and (9) any sharp waves or spikes after 2 months CA.2,4,5,19 Focal clonic or tonic seizures are most often associated with infarction and hemorrhage, and also with metabolic disorders such as hypocalcemia, hypoglycemia, and hypomagnesemia.28
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FIGURE 346. Focal Clonic Seizure; Schizencephaly with Polymicrogyria Associated with Herpes Simplex Encephalitis. A 40-week CA infant with HSV encephalitis who developed clonic jerking of left arm. T2WI MR shows right frontal-temporal polymicrogyria. EEG consistently shows short runs of sharp waves in the right central region (double arrows). The significance of negative sharp waves is controversial. Criteria for abnormality (not absolute) of negative sharp waves are (1) complex morphology, (2) spikes rather than sharp waves, (3) positive polarity, (4) repetitive runs (especially burnt-out sharp waves), (5) persistent localization or hemisphere (even as early as 30 weeks CA), (6) occurrence during wakefulness, (7) moderately or severely abnormal background activity, (8) frequency more than 1 per min, and (9) any sharp waves or spikes after 2 months CA.2,4,5,19
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FIGURE 347. Zip-Like Electrical Discharges (Zips). A 30-day-old full-term newborn with pulmonary hypoplasia associated with diaphragmatic hernia and severe hypoxic ischemic encephalopathy, who developed frequent clonic jerking of the left arm. Ictal EEG shows low-voltage rhythmic, arc-like spikes in the right central region (open arrow) superimposed on very low-voltage background activity. “Zip-like electrical discharges (Zips)” is a common ictal EEG pattern in neonates, which consists of focal episodic rapid spikes of accelerating and decelerating speed that look like zippers. Zips may be associated with subclinical, subtle, focal clonic, and tonic seizures. Zips of subtle seizures are often multifocal and of shifting localization.29
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FIGURE 348. Electrographic Seizure (Same recording as in Figure 3-47) The ictal EEG activity evolves from zip-like electrical discharges in the right central region to a train of sharp waves in the right central-temporal region.
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FIGURE 349. Focal Clonic Seizure. (same recording as in Figure 3-47 and 3-48) The EEG demonstrates evolving of the “zips” to rhythmic sharply-contoured delta waves with phase reversal at T4. Note continuation of trace discontinued pattern during the seizure. “Seizures of the depressed brain” are seen in neonates whose background EEG activity is depressed and undifferentiated. The discharges are typically low in voltage, long in duration, highly localized, may be unifocal or multifocal, and show little tendency to spread. This pattern is typically not accompanied by clinical seizure and suggests a poor prognosis.5
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FIGURE 350. Seizures of the Depressed Brain; Severe Hypoxic Ischemic Encephalopathy (HIE) with Herniation Syndrome. A 4-day-old full-term infant with severe hypoxic ischemic encephalopathy (HIE) who developed central herniation syndrome. Cranial CT and MRI show bilateral posterior cerebral artery infarction. The patient was intubated and lacked brainstem reflexes. EEG shows nonreactive, very low-voltage EEG activity with status epilepticus with the total seizure duration greater than 50% of the recording. The subclinical electrographic seizures are multifocal but maximally expressed in the left centro-temporal regions. The patient was withdrawn from cardiorespiratory support and died 1 day after this EEG recording. The effect of electrographic neonatal seizures on subsequent neurological outcomes is associated with the underlying cause of the seizures, the degree of background abnormality, and the seizure frequency.4 Neonates with seizures superimposed on a normal background have good outcomes, whereas those with electrographic neonatal seizures and a moderately or severely abnormal background have worse outcomes. Only 8% of patients with multifocal abnormalities, low amplitude, or periodic background activities had normal outcomes.30
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FIGURE 351. Ictal EEG Activity; Periventricular-Intraventricular Hemorrhage (PVH-IVH). (Same recording as in Figure 3-37) EEG shows electrographic seizure in the right centro-temporal region associated with left arm clonic jerking, most likely caused by deep white matter hemorrhage indicated by positive sharp waves in the right temporal region as noted in Figure 3-37.
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FIGURE 352. Focal Clonic Seizure; Neonatal Stroke Due to Systemic Infection. A 7-day-old female with low-grade fever and frequent right arm clonic jerking. CSF findings were unremarkable. Her mother had a history of fever and URI symptoms. Hypercoagulation studies were negative. The presumptive diagnosis was neonatal stroke caused by systemic viral infection. T2-weighted and DWI MRI support the diagnosis of stroke in the left parietal region (arrow). Ictal EEG demonstrates rhythmic spike-wave activity in the left central region time-locked with right arm clonic jerking. Seizures were stopped after topiramate was added to phenobarbital. Stroke or hemorrhage is the most common structural abnormality that causes focal clonic or tonic seizures. In addition, focal tonic or clonic seizures are also associated with some metabolic conditions such as hypocalcemia, hypoglycemia, and hypomagnesemia.28 MRI, especially with diffusion-weighted imaging (DWI), is the investigation of choice for arterial stroke in the newborn. DWI can reliably detect ischemic injury within 24 h of its onset. However, DWI may become falsely negative 1 week after stroke (pseudonormalization), by which time established changes should be evident on conventional T1- and T2-weighted imaging.31,32
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FIGURE 353. Pyruvate Dehydrogenase Deficiency. A 4-week-old girl with hypotonia, poor feeding, apnea, and seizures. Her seizures are described as tonic posturing and multifocal myoclonic jerks. Interictal EEG activity shows diffuse background slowing with very frequent multifocal spikes and sharp waves. Pyruvate dehydrogenase deficiency (PDH), a deficiency in the E1 (pyruvate dehydrogenase) component of the pyruvate dehydrogenase complex, is one of the most common genetic defects of mitochondrial energy metabolism. PDH deficiency is an extremely heterogeneous condition, both in clinical presentation and in the severity of the biochemical abnormality, with a clinical spectrum ranging from fatal lactic acidosis in the newborn period to a chronic neurodegenerative condition with gross structural abnormalities in the central nervous system.
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FIGURE 354. Alpha Seizure Discharge; Pyruvate Dehydrogenase Deficiency. (Same patient as in Figure 3-53) A sudden appearance of rhythmic sinusoidal 9–12 Hz, 30–60 μV alpha activity in the left occipital region. No definite clinical seizure noted during this rhythmic run of alpha activity. The sudden but transient rhythmic alpha activity is referred to as alpha seizure activity. It typically occurs unilateral to the temporal or central region or it can evolve from activity that is more clearly epileptic. It can also occur simultaneously, but asynchronously with other electrographic seizures. The alpha seizure discharge is associated with severe encephalopathy and poor prognosis. It may occur without clinical accompaniment.5
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FIGURE 355. Alpha Seizure Discharge; Pyruvate Dehydrogenase Deficiency. (Continued) An alpha seizure discharge spreads to the temporal and less so the parasagittal regions in the same hemisphere with subsequent buildup of periodic sharp waves in the left midtemporal region (asterisk). Patients with PDH deficiency typically develop symptoms soon after birth. There are two forms of presentation, metabolic and neurologically , occurring with equal frequencies. The metabolic form presents as refractory lactic acidosis. Many of these patients die in the newborn period. Patients with neurological presentation are hypotonic, feed poorly, are lethargic, and develop seizures, either tonic/clonic convulsions or epileptic spasms. They usually progress to profound mental retardation, microcephaly, blindness, and spasticity. Seizure types in PDH include asymmetric posturing, generalized tonic, complex partial, absence, focal motor, versive and myoclonic seizures.
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FIGURE 356. Alpha Seizure Discharge; Pyruvate Dehydrogenase Deficiency. (Continued) Ten seconds later in the same recording the ictal EEG activity evolves into continuous sharp-and slow-wave discharges, mainly in the left temporal region. The patient moves her arms slightly during this ictal EEG activity.
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FIGURE 357. Théta Pointu Alternant Pattern; Benign Familial Neonatal Convulsion (BFNC). An EEG of a younger twin who developed similar types of seizures on the same day as his older twin. EEG showed bursts of théta pointu alternant pattern. An interictal EEG in BFNC was normal, discontinuous, and showed focal or multifocal sharp waves or “théta pointu alternant” pattern. The théta pointu alternant pattern may be seen during waking and sleep and up to 12 days after the seizures have stopped. The théta pointu alternant pattern is a nonspecific EEG pattern seen in status epilepticus caused by a variety of conditions such as HIE, hypocalcemia, meningitis, SAH, and benign idiopathic neonatal seizure. It is described as bursts of an unreactive dominant theta activity intermixed with sharp waves with frequent interhemispheric asynchrony. The patterns suggesting poor prognosis such as a paroxysmal, inactive, or burst suppression have never been reported in BNFC. The théta pointu alternant pattern is associated with good prognosis.36
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FIGURE 358. Theta Pointu Alternant Pattern; Benign Neonatal Convulsion (Non-Familial) or “Fifth Day Fits”. A 6-day-old full-term boy. He developed seizures on the 6th day described as either unilateral or bilateral clonic jerking and apnea. He was otherwise normal. Work-up was negative. The seizures lasted for approximately 36 h. There was no family history of seizures. Interictal EEG shows bursts of unreactive theta activity mixed with sharp waves alternating with relative background suppression. Interictal EEG was normal, discontinuous, and showed focal or multifocal sharp waves or “theta pointu alternant” pattern. The theta pointu alternant pattern is described as bursts of an unreactive dominant 4–7 Hz theta activity intermixed with sharp waves with frequent interhemispheric asynchrony and shifting predominance between the two hemispheres. It may be seen during waking and sleep and up to 12 days after the seizures have stopped. It is a nonspecific EEG pattern seen in status epilepticus caused by a variety of conditions such as HIE, hypocalcemia, meningitis, SAH, and BFNC. The patterns suggesting poor prognosis such as a paroxysmal, inactive, or burst suppression have never been reported in benign non-familial neonatal convulsions. The theta pointu alternant pattern is associated with good prognosis.36
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FIGURE 359. Early Myoclonic Encephalopathy (EME); Pyridoxine Dependency. A 7-day-old girl with intermittent irritability, jitteriness, lethargy, and myoclonic jerks. A subsequent gene tests confirmed the diagnosis of pyridoxine dependency. Her MRI was unremarkable. Her initial EEG (as shown) demonstrates diffuse suppression burst pattern. After an administration of intravenous pyridoxine, the patient showed dramatic improvement in her clinical symptoms and EEG. During her subsequent neurology visits, she continued to have no seizures and had normal developmental milestones. Her EEGs performed at 1 and 3 months of age were appropriate for age. EME is a very rare epileptic syndrome characterized by myoclonus with onset of seizures in the neonatal period. The EEG shows suppression burst pattern. Metabolic diseases, especially nonketotic hyperglycinemia, are usually the causes of EME. Malformation of cortical development is an uncommon etiology. Pyridoxine dependency was reported in one patient with EME who had complete recovery after the treatment with pyridoxine. Almost all patients with EME have a very poor prognosis.37
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FIGURE 360. Severe Neonatal Epilepsy With Suppression-Burst Pattern; Ohtahara Syndrome. A 1-week-old boy with a history of frequent tonic spasms starting on the first DOL with subsequent developmental regression, spastic quadriparesis, and intractable infantile spasms. Serial neuroimaging studies showed progressive cerebral atrophy. (A) CT performed at 10 months of age. (B) Axial T1-weighted image performed at 2½ years of age. The patient died at 2.5 years of age. After intensive investigation including autopsy, no specific metabolic or degenerative disease was found. EEG performed at 1 week of age shows suppression burst (SB) pattern (Courtesy of Dr. B. Miller, Department of Neurology, The Children’s Hospital, Denver, CO). Ohtahara syndrome is a very rare and devastating form of epileptic encephalopathy of very early infancy. Onset of seizures is typically within 1 month of birth and often within the first 10 days of life. It can range from prenatally to the first 2–3 months after birth. Characteristic clinico-EEG features are tonic spasms and, less commonly, erratic focal motor seizures and hemiconvulsions with SB pattern in the EEG occurring in both sleep and waking states. Although the etiologies of Ohtahara syndrome are heterogeneous, prenatal brain pathology such as malformation of cortical development is suspected in most cases and metabolic disorders are rare. Evolution into West syndrome is often observed in surviving cases.37,38
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FIGURE 361. Very Low-Voltage Background Activity; Hypoxic-Ischemic Encephalopathy (HIE). A 6-day-old infant who was born at term with Apgar scores of 0, 0, 0, 3, 4, 6, and 7 at 1, 5, 10, 15, 20, 25, and 30 min of life. The infant was cyanotic, depressed, and floppy at delivery and received intubation, chest compressions, and epinephrine. He underwent head cooling. MRI performed at DOL 5 shows restricted diffusion in the basal ganglia (arrow) and medial temporal lobes bilaterally (double arrows). EEG performed on DOL 6 shows low-voltage background activity and lack of differentiation. Note frequent positive sharp waves (PSWs) in multifocal areas (open arrows). All patients with HIE and bilateral basal ganglia involvement have developmental delay. “Depression and lack of differentiation” EEG is indicative of severe brain insult but is nonspecific as to etiology and can be due to a wide variety of conditions including severe HIE, severe metabolic disorders, meningitis or encephalitis, cerebral hemorrhage, and IVH. A depressed and undifferentiated EEG within the first 24 h after birth that persists indicates a poor prognosis.5 PSWs in full-term infants are seen in structural cerebral lesions, including periventricular leukomalacia, intracerebral hemorrhages, HIE, and infarctions.4,23,24,26
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FIGURE 362. Electrocerebral Inactivity (ECI); High-Frequency Ventilator Artifact. An infant 40 weeks of conceptional age with severe hypoxic ischemic encephalopathy (Apgar scores of 0, 0, and 3 at 1, 5, and 10 min, respectively) who developed multiorgan failure and subsequently brain herniation syndrome. EEG shows no cerebral activity. High-frequency ventilator artifact described as diffuse, invariant, rhythmic, sinusoidal activity in all EEG electrodes, caused by vibratory effect on the entire body is noted. Also note ECG artifact.
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FIGURE 363. Severe Hypoxic Ischemic Encephalopathy (HIE); Electrocerebral Inactivity (ECI). A 2-day-old full-term newborn with severe hypoxic ischemic encephalopathy. Axial T1WI MR shows loss of signal in the posterior limb of internal capsule (open arrow) and increased signal in posterior putamen, GP, lateral thalamus (arrow), and cortex and subcortical white matter. Sagittal T1WI MR shows increased signal in basal ganglion (double arrows). EEG shows no cerebral activity with the EEG sensitivity of 2 μV/mm. ECI can be interpreted as a sign of brain death if there is absence of cortical and brainstem functions, no evidence of intoxication, and no hypothermia. Minimal technical standards for the EEG recording in brain death by the American Encephalographic Society39 are required.
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FIGURE 364. Electrocerebral Inactivity (ECI); Severe Hypoxic Ischemic Encephalopathy. A 3-day-old full-term newborn with severe hypoxic ischemic encephalopathy. Axial T1W1 MR shows loss of signal in the posterior limb of internal capsule (open arrow) and increased signal in posterior putamen, GP, lateral thalamus (arrow), and cortex and subcortical white matter. Axial DWI MR shows increased signal in basal ganglion (double arrows). EEG shows no cerebral activity with the EEG sensitivity of 2 μV/mm. ECI represents the ultimate degree of depression and lack of differentiation. Serial EEGs are required to demonstrate a persistent degree of cortical inactivity. An isoelectric EEG is indicative of death of the cortex but not of brainstem. Therefore, patients may continue to survive with cardiorespiratory support despite the presence of this EEG pattern. ECI can be interpreted as a sign of brain death if there is absence of cortical and brainstem functions, no evidence of intoxication, and no hypothermia. Minimal technical standards for the EEG recording in brain death by the American Electroencephalographic Society39 are required. Note continuous ECG artifact due to the very high sensitivity setting.
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FIGURE 365. Focal Low Voltage Fast Activity (Intrinsic Epileptogenicity); Focal Cortical Dysplasia. A 2-month-old boy with symptomatic infantile spasms caused by focal cortical dysplasia (FCD) in the right parietal-occipital region (small arrows). The interictal EEG shows focal low-voltage fast activity in the right occipital region (asterisk). Note the similarity of these interictal discharges with the ictal discharges seen in FIGURE 3-66. This low-voltage fast activity most likely represents high-frequency oscillations (HFOs) that indicate intrinsic epileptogenicity. Intrinsic epileptogenicity in FCD is caused by abnormal synaptic interconnectivity and neurotransmitter changes within the lesion.40–42 FCD has intrinsic epileptogenicity with unique EEG patterns including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.43 The incidence of intrinsic epileptogencity in FCD was 11–20% in different series. Polymorphic delta activity indicative of white matter involvement is commonly seen in FCD.44–46 Trains of continuous or very frequent rhythmic spikes or sharp waves and recurrent electrographic seizures on the scalp EEG were seen in up to 44% of FCD in one series.44 A similar discharge (low-voltage fast activity) is also called “regional polyspike” by Noachtar et al.,47 who concluded that regional polyspikes, especially in an extratemporal location, are highly associated with FCD (80%). In all patients with FCD the seizure onset zone (SOZ) was located within the lesion. Lesional non-SOZ areas might not be directly involved in the seizure origin but might turn into a seizure focus after the removal of primary epileptogenic tissue; therefore, removal of the entire lesion and surrounding interictal active tissue is necessary.48 Removal of the FCD alone does not necessarily lead to a good outcome, suggesting a more widespread epileptogenic network in these patients.49,50
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FIGURE 366. Infantile Spasms; Akinetic and Extensor Types of Epileptic Spasms. (Same EEG recording as in Figure 3-65) EEG during a cluster of epileptic spasms. EEG during the first 1–3 sec shows the “akinetic type” of epileptic spasm. The patient stopped moving for 1–2 sec and then resumed his activity without confusion (arrow head), consistent with “akinetic type” of infantile spasm. A few seconds later, the patient developed a typical asymmetric epileptic spasm with left arm extension, mild movement of left arm, and eye jerking to the left side (open arrow), consistent with asymmetric infantile spasm. EEG shows some similarity in that there are bursts of low-voltage fast activities in the left occipital region during both akinetic and asymmetric epileptic spasms. The difference is the pattern of spreading, with mild spreading of ictal activity to the parietal area during the akinetic spasm and more prominent anterior spreading to the motor area (Cz and C4) during the asymmetric epileptic spasms (double arrows). These EEG finding may explain the difference in seizures and confirm that the origin of epileptic focus is in the right occipital region. original epileptic focus in the right occipital region. The epileptic spasms are probably subcortically mediated, but are modified by input from the cortex, which is believed to be abnormally excitable and disorganized in infantile spasms. The bursts during flexor spasms are too long for epileptic myoclonus. Therefore, the nature of epileptic spasms is tonic rather than myoclonic. However, the infrequent spontaneous myoclonic jerks, which can occur without spasms, and the head nodding could represent positive and negative myoclonus, respectively.51 Atonia is probably an expression of transient disruption of cortical function in the sensorimotor cortex. The focal epileptic event that operates through an inhibitory interference on the areas preparing the movements, or that directly involves a negative motor area provokes this disruption.52 Focal spike-induced cerebral transitory impairment can be related to the slow component of the spike-wave discharge.53 Epileptic negative myoclonus has been described in different heterogeneous epileptic syndromes in children and even in the newborn.54
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FIGURE 367. Ictal FDG PET Scan. (Same patient as in Figure 3-63) An FDG-PET was performed during very active epileptiform activity. One of his clinical seizures (epileptic spasms) occurred approximately 5 min prior to the PET scan. The area of hypermetabolism in PET (large arrow) overlaps with the area of focal cortical dysplasia in MRI scan (small arrow). The patient has been seizure free after the right functional hemispherectomy. The extent of the PET hypometabolism may be substantially larger than the electrical focus.55 The relationship between the area of hypometabolism and the extent of surgical resection needed for seizure control—particularly in extratemporal foci—has not been clearly defined.56 Planned ictal FDG-PET imaging of patients with frequent or continuous partial seizures may offer a unique opportunity to study the metabolic pattern of the brain during ictal events. This may be especially important in patients with extensive underlying structural brain abnormalities in whom both routine morphologic and interictal functional imaging may not sufficiently localize the epileptogenic tissue for surgical planning. Planned ictal PET imaging may be a useful and potentially superior approach to ictal SPECT for identifying the epileptic focus in a selected group of patients with continuous or frequent simple partial seizures.57 Ictal FDG-PET showing intense hypermetabolism in a hypothalamic hamartoma in a patient with gelastic seizures has been reported.58
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3 30. Rose A, Lombroso C. Neonatal seizure states: A study of clinical, pathological, and electroencephalographic features in 137 full-term babies with a long-term followup. Pediatrics. 1970;45(3):404. 31. Hunt R, Inder T. Perinatal and neonatal ischaemic stroke: a review. Thromb Res. 2006;118(1):39–48. 32. Mader I, Schoning M, Klose U, Kuker W. Neonatal cerebral infarction diagnosed by diffusion-weighted MRI: pseudonormalization occurs early. Stroke. 2002;33:1142–1145. 33. Brown GK, Otero LJ, LeGris M, Brown RM. Pyruvate dehydrogenase deficiency. J Med Genet.1994;31:875–879. 34. Canafoglia L, Franceschetti S, Antozzi C, Carrara F, Farina L, Granata T, et al. Epileptic phenotypes associated with mitochondrial disorders. Neurology. 2001;56:1340–1346. 35. Nordli D, Leary L, De Vivo L. Progressive pediatric neurological syndromes. In: Ebersole J, Pedley T, eds. Current Practice of Clinical Electroencephalography. Philadelphia: Lippincott Williams & Wilkins; 2003:483. 36. Plouin P, Anderson V. Epileptic syndromes in infancy. In: Dravet C, et al., eds. Childhood and Adolescence. London: John Libbey; 2005:3–17. 37. Aicardi J, Othahara S. Severe neonatal epilepsies with suppression–burst pattern. In: Roger J, Bureau M, Dravet C, Genton P, Tassinari CA, Wolf P, eds. Epileptic syndromes in infancy, childhood and adolescence. 3rd ed. Eastleigh, UK: Libbey; 2002:33–44 38. Aicardi J, Ohtahara S. Severe neonatal epilepsies with suppression-burst pattern. In: Dravet C, et al., eds. Epileptic Syndromes in Infancy, Childhood and Adolescence. London: John Libbey; 2005:39–52. 39. American EEG Society. Guideline three: minimum technical standards for EEG recording in suspected cerebral death. J Clin Neurophysiol. 1994;11:10–13 40. Ferrer I, Pineda M, Tallda M, et al. Abnormal local circuit neurons in epilepsia partialis continua associated with focal cortical dysplasia. Acta Neuropathol. 1992;83:647–652. 41. Mattia D, Olivier A, Avoli M. Seizure-like discharges recorded in human dysplastic neocortex maintained in vitro. Neurology. 1995;45(7):1391. 42. Chassoux F, Devaux B, Landré E, et al. Stereoelectroencephalography in focal cortical dysplasia: a 3D approach to delineating the dysplastic cortex. Brain Dev. 2000;123:1733–1755.
3 43. Sullivan LR, Kull LL, Sweeney DB, Davis CP. Cortical dysplasia: zones of epileptogenesis. Am J Electroneurodiagnostic Technol. 2005;45:49–60. 44. Palmini A, Gambardella A, Andermann F, Dubeau F, da Costa JC, Olivier A, et al. Intrinsic epileptogenicity of human dysplastic cortex as suggested by corticography and surgical results. Ann Neurol. 1995;37:476–487. 45. Ambrosetto G. Treatable partial epilepsy and unilateral opercular neuronal migration disorder. Epilepsia. 1993;34(4):604–608. 46. Raymond AA, Fish DR, Boyd SG, Smith SJ, Pitt MC, Kendall B. Cortical dysgenesis: serial EEG findings in children and adults. Electroencephalogr Clin Neurophysiol. 1995b;94:389–397. 47. Noachtar S, Bilgin O, Remi J, Chang N, Midi I, Vollmar C, Feddersen B. Interictal regional polyspikes in noninvasive EEG suggest cortical dysplasia as etiology of focal epilepsies. Epilepsia. 2008;49:1011–1017.
Newborn
48. Jacobs J, Zelmann R, Jirsch J, Chander R, Dubeau CE, Gotman J. High frequency oscillations (80–500 Hz) in the preictal period in patients with focal seizures. Epilepsia. 2009;50(7):1780–1792. 49. Tassi L, Colombo N, Garbelli R, et al. Focal cortical dysplasia: neuropathological subtypes, EEG, neuroimaging and surgical outcome. Brain. 2002;125:1719–1732. 50. Li LM, Cendes F, Watson C, Andermann F, Fish DR, Dubeau F, et al. Surgical treatment of patients with single and dual pathology: relevance of lesion and of hippocampal atrophy to seizure outcome. Neurology. 1997a;48:437–444. 51. Pranzatelli M. Infantile spasms versus myoclonus: is there a connection? Int Rev Neurobiol. 2002;49:285. 52. Guerrini R, Dravet C, Genton P, et al. Epileptic negative myoclonus. Neurology. 1993;43:1078–1083. 53. Shewmon D, Erwin R. Focal spike-induced cerebral dysfunction is related to the after-coming slow wave. Ann Neurol. 1988;23(2):131–137.
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54. Griffiths PD, Welch RJ, Garnder-Medwin D. The radiological features of hemimegalencephaly including three cases associated with Proteus syndrome. Neuropediatrics. 1994;25:140–144. 55. Swartz BE, Tomiyasu U, Delgado-Escueta AV, et al. Neuroimaging in temporal lobe epilepsy: test sensitivity and relationships to pathology and postoperative outcome. Epilepsia. 1992;33:624–634. 56. Henry, TR. Functional neuroimaging with positron emission tomography. Epilepsia. 1996;37:1141–1154. 57. Meltzer C, Adelson P, Brenner R, Crumrine P, Van CA, Schiff D, Townsend D, Scheuer M. Planned ictal FDG PET imaging for localization of extratemporal epileptic foci. Epilepsia. 2000;41:193–200. 58. Palmini A, Van Paesschen W, Dupont P, et al. Status gelasticus after temporal lobectomy: ictal FDG-PET findings and the question of dual pathology involving hypothalamic hamartomas. Epilepsia. 2005;46: 1313–1316.
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Abnormalities of alpha rhythm, photic response, and mu rhythm (Figure 4-1 to 4-25 and 4-28) Normal variations must be identified 䡲
Posterior slow wave of youth.
䡲
Slow alpha variant.
Voltage attenuation of alpha rhythm 䡲
Higher in voltage over the right hemisphere, independent of handedness. 䡲 Abnormal voltage attenuation of alpha rhythm: 䊳 Voltage of the alpha rhythm on the right side more than 1½ times that on the left side. 䊳 Voltage of the alpha rhythm on the left side approximately 30% more than that on the right side. 䊳 Voltage asymmetry alone, unless extreme, constant, or in combination with other abnormalities (slowing of frequency, decreased reactivity, or modulation of alpha rhythm as well as focal polymorphic delta activity (PDA), is the least reliable finding and of little clinical significance. 䊳 Rarely, increased voltage of alpha rhythm may be observed on the side of abnormality. 䡲 Location of the lesions causing voltage attenuation of alpha rhythm: 䊳 Underlying cortex, especially occipital lobe 䊳 Thalamus and midbrain or its connections to the underlying cortex (thalamo-cortical circuit) 䊳 Frontal or central areas (unknown mechanism)
Slowing of alpha frequency 䡲
Consistent focal slowing of alpha rhythm by 1 Hz or more on one side reliably identifies the side of focal abnormality whether the voltage of the rhythm is increased or decreased. 䡲 Asymmetrical slowing of mu has the same rule as alpha rhythm. 䡲 Enhancement of amplitude of background activity is rarely seen over the side of focal cerebral lesion. The clue to determine lateralization of the lesion is
to identify slowing of alpha frequency and loss of reactivity and modulation, which are more important than voltage attenuation of alpha rhythm. In addition, other associated findings, especially focal PDA, are usually noted. 䡲 Loss of reactivity and modulation (eye opening/ mental alerting) 䡲 Loss of reactivity of the alpha rhythm to eye opening (Bancaud’s phenomenon) or to mental alerting.
Voltage accentuation of alpha rhythm 䡲
Rarely, voltage accentuation of alpha rhythm can be seen on the side of focal abnormality. 䡲 Enhancement of alpha rhythm can rarely be seen contralateral to the side of a focal PDA and is due to compression or interference with the blood supply of that hemisphere.
Photic response 䡲
Attenuation of either ipsilateral (more common) or contralateral (rare) to the epileptic focus.
Mu 䡲
Asymmetrical slowing of mu has the same rule as alpha rhythm (usually associated with an increase in amplitude, often of a chronic nature).
Focal attenuation of beta activity and voltage attenuation (Figures 4-29 to 4-31, 4-64, 4-66 to 4-81, 4-83 to 4-85) 䡲
Reduction in voltage of beta activity is the earliest and most sensitive electroencephalography (EEG) finding of focal cortical dysfunction. 䡲 Barbiturate-induced beta activity can help to enhance the beta asymmetry. Focal reduction of beta activity is considered abnormal. 䡲
Consistent depression of beta activity of more than 35% is considered abnormal.
Involvement of cortical EEG generator 䡲
Structural damage or functional abnormality of the cortical EEG generator, especially large pyramidal neurons.
276
䡲
Most often occurs with PDA (“smooth PDA”).
䡲
Etiology: 䊳 Developmental, degenerative, and demyelinating conditions 앫 Porencephaly, holoprocencephaly, focal brain atrophy, and unilateral hydrocephalus 앫 Sturge-Weber syndrome 앫 Multiple sclerosis 䊳
䊳
䊳 䊳 䊳 䊳 䊳
Toxic and metabolic encephalopathy 앫 Complications of toxic and metabolic encephalopathy such as infarction, posterior reversible leukoencephalopathy, hypoxia, hypoglycemia, hypertension, SDH in hepatic and Wernicke’s encephalopathy Cerebrovascular accident 앫 Stroke, transient ischemic attack (TIA), subdural hemorrhage (SDH), subarrachnoid hemorrhage (SAH), or migraine Traumatic brain injury Post-brain surgery Brain tumor Seizure Infectious diseases 앫 Encephalitis, abscess, venous sinus thrombosis, or progressive multifocal leukoencephalitis
Increased products of low impedance
䊳
Paget’s disease (thickening of bone)
Focal enhancement of background activity Breach rhythm (Figures 4-95 to 4-98) 䡲
Focally enhanced physiological activities including beta, mu, alpha, sleep architectures (vertex waves, spindles, hypnagogic hypersynchrony, and K-complex) as well as the presence of sharp transients caused by craniotomy, burr hole or, less commonly, skull fractures. Breach rhythm is usually associated with focal PDA. 䡲 Beta activity 䊳 Enhanced beta activity is maximal nearest a burr hole or craniotomy margin and typically a broad voltage distribution. 䊳 Enhance the voltage of frontal beta activity as much as threefold. Mu 䊳 Breach rhythm is most evident at C3/C4 or T3/ T4 because of their proximity to underlying mu rhythms or temporal rhythmic activity in the alpha frequency range. 䡲 Sleep architectures: 䊳 Enhancement of spindles, hypnagogic hypersynchrony, vertex waves, and K-complex 䡲 Alpha rhythm in either temporal or occipital regions. 䡲
In an acute postoperative period, lower amplitude background activity on the side of craniotomy caused by brain edema can be seen. A follow-up EEG performed months or years later usually shows higher amplitude of the background activity on the side of craniotomy. Persistent lower amplitude of the background activity on the side of craniotomy suggests significant underlying cortical injury.
Higher amplitude of the background activity (Figures 4-99 to 4-106) 䡲
Especially beta activity on the side of a focal cerebral lesion is rarely seen in the following conditions:
䊳
Tumor
䊳
Focal cortical dysplasia Abscess Stroke and arteriovenous malformation
䊳 䊳
Increased products of low impedance (such as blood or cerebrospinal fluid) 䡲
Act as conductors within the volume underneath the EEG electrodes and shunt the potential differences before they reach the EEG electrodes.
䡲
Act as a high-frequency filter.
䡲
Background activity is usually associated with focal low-voltage PDA. 䡲 Etiology:
䡲
䡲
Increased products of low impedance, such as blood or cerebrospinal fluid, act as conductors within the volume underneath the EEG electrodes and shunt the potential differences before they reach the EEG electrodes. These act as a high frequency filter, and background activity is usually associated with focal low-voltage PDA. 䡲 Etiology: 䊳 Epidural, subdural, or subgaleal fluid or blood collection 䊳 Scalp edema
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Focal Nonepileptoform Activity
䊳
Epidural, subdural or subgaleal fluid or blood collection
䊳
Scalp edema Paget’s disease (thickening of bone)
䊳
Unilateral attenuation of Sleep Architectures (Figures 4-26, 4-31 to 4-42, 4-73) 䡲
Consistent attenuation of hypnagogic hypersynchrony, vertex waves, spindles, or K-complex. 䡲 Involvement of thalamocortical circuit (especially parietal lobe and thalamus).
Focal polymorphic delta activity (Figures 4-27, 4-43 to 4-63, 4-65, 4-75, 4-77 to 4-86) 䡲
Definition: Arrhythmic delta wave activity (<4 Hz) with constantly changing of morphology, frequency, and voltage. 䡲 May be due to either permanent structural damage or a transient disturbance in the area of subcortical white matter or thalamic nuclei. 䡲 PDA is one of the most reliable findings of a focal cerebral disturbance, although focal depression of beta activity is an earlier and more sensitive sign.
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Focal Nonepileptoform Activity
䡲
more hyperpolarized leading to intrinsic thalamic delta oscillation. The delta oscillating thalamic cells then passively transfer the rhythm to the cortex by thalamocortical pathways. This suggests that thalamic deafferentation from the cortex rather that cortical deafferentation from below may be the slow wave mechanism.
Involvement of superficial cortex does not generally produce significant PDA. 䡲 Brain edema alone, even when extensive, does not generate PDA unless it causes a significant compression of midline structures. 䡲
PDA can occur without demonstration of lesion in the MRI. 䡲 Location of lesions causing PDA and their distributions. 䊳 Cortical lesions. 앫 Lesions in the superficial cortex without white
matter involvement do not generally produce significant PDA. 䊳
Subcortical white matter lesions 앫 Cause PDA in the overlying cortex
䊳
Thalamic lesions 앫 Cause variable degree and extent of PDA but tend to involve the entire hemisphere ipsilateral to the lesion
䊳
䊳
䡲
䡲
The more persistent, the less reactive, and the more nonrhythmic or polymorphic of the PDA, the more reliable as indicator it becomes for the presence of a focal cerebral disturbance. 䡲 The acute process will disrupt background rhythms to a greater extent in young children than in adolescents or adults. 䡲
277
䡲
Persists during changes in physiologic states and may not be facilitated by HPV.
䡲
PDA is often surrounded by theta waves.
䡲
Maximally expressed over the lesions.
䡲
Superficial lesions cause more restricted field and deeper lesions cause hemispheric or even bilateral distribution.
䡲
Lower voltage of PDA is seen over the area of maximal cerebral involvement, but higher voltage PDA is noted in the border of lesions.
䡲
More severe PDA (closer to the lesion, more acute, higher association with underlying structural abnormality) consists of the following:
Reactivity and the persistence of focal abnormalities (continuous versus intermittent) were considerably the best indicators of degree of damage. Continuous slow wave activity suggests severe brain damage (likelihood of increased mass effect, large lesion, or deep hemispheric involvement), whereas intermittent slow activity usually indicates a small lesion and the absence of mass effect on midline structures.
䊳
Greater variability (most irregularity or least rhythmic)
䊳
Slower frequency
䊳
Greater persistence
䊳
Less reactive
䊳
No superimposed beta activity
䊳
Less intermixed activity above 4 Hz
Hypothalamic or mesencephalic reticular formation lesions 앫 Unilateral lesions may or may not produce PDA.
Intermittent PDA
“Smooth PDA,” “flat polymorphism,” or “flat PDA” (concomitant loss of faster frequencies):
앫 Bilateral lesions produce generalized delta
䡲
䊳
Very significant PDA and usually affects both gray and white matter
䊳
No intermixed activity of over 4 Hz or superimposed beta activity
䊳
Often seen over the lesion
䡲
activity. Posterior fossa
Attenuated with eye opening and other alerting procedures 䡲 Fails to persist into sleep
앫 Rarely produces PDA
䡲
Occurs only during drowsiness, light sleep, or HPV
䡲
Clinical correlation is less well defined and is usually caused by reversible causes when mixed with substantial amount of theta activity such as TIA, lacuna infarction, migraine, hypertension, metabolic processes, partial seizure, postictal state, mild encephalitis, or mild traumatic brain injury.
Possible Mechanisms (Debatable): 1. Interruption of the afferent input to the cortex either in the white matter, thalamus, hypothalamus, or mesencephalon produced delta activity suggests that deafferentation of overlying cortical neurons may be responsible for PDA. 2. Dorsal thalamus produces intrinsic 1–2 cycles/ sec rhythm. Depolarizing corticothalamic inputs prevent the manifestation of the thalamic delta rhythm. When the cortex is ablated and the corticothalamic encroachment on thalamic neurons is diminished, the thalamic cells become
Continuous PDA (persistent nonrhythmic delta activity; PNDA) 䡲
Highly correlated with a focal structural lesion, more prominent in acute than chronic processes.
䡲
Characteristics of chronic lesions: 䊳
Marked attenuation and often total absence of rhythmic activities
䊳
Very little, if any, slow activity over the involved hemisphere
䡲
Posterior fossa lesion rarely causes PDA, although, occasionally, it can produce PDA in the bilateral occipital regions that may be due to either pressure or ischemic effects or both.
䡲
Focality of the PDA depends on the lesion locations:
278
Anterior- and midfrontal lesions often spread to homologous contralateral frontal region 䊳 Occipital lesions often spread to homologous contralateral occipital region 䊳 Posterior frontal and parietal lesions can be falsely localized to the temporal area. 䊳 Posterior PDA 앫 More attenuated with eye opening 앫 More disruption of alpha rhythm 䊳 Spreading of PDA, usually of lower amplitude, to the homologous contralateral hemisphere, especially in anterior- and midfrontal and occipital regions, due to: 앫 Effects of compression, edema, ischemia in neighboring parts of opposite hemisphere 앫 Traveling via commissural fibers 앫 Volume conduction Other EEG abnormalities associated with PDA: Widespread asynchronous slow waves 䊳 Either unilateral or bilateral PDA 䊳 Acute > chronic 䊳 Deeply located lesions Bilateral synchronous slow waves 䊳 May be larger or more persistent on the side of PDA 䊳 Frontal predominance 䊳 Deep midline structure lesions Combination of frontal intermittent rhythmic delta activity (FIRDA) or occipital intermittent rhythmic delta activity (OIRDA) and continuous focal PDA is the classic EEG sign of impending cerebral herniation from a focal structural lesion if clinical features indicated. Focal spike or sharp waves do not arise within a structural lesion but at the periphery where cortical structures are affected but not destroyed. Holoprosencephaly may cause focal PDA and spikes, emanating from islands of preserved brain tissue. 䊳
䡲 䡲
䡲
䡲
䡲
䡲
4
Focal Nonepileptoform Activity
䊳
Focal or lateralized intermittent rhythmic delta activity (IRDA) (Figures 4-87 to 4-94) 䡲
Definition:
Bursts/runs of high voltage, bisynchronous (sinusoidal or saw-toothed wave), and rhythmic delta activity of fixed frequency (close to 2.5 Hz) with more rapid ascending than descending phase. 䡲 Localizing value is limited when compared to PDA. 䡲 Age-dependent (maximal frontal in adult and maximal posterior in children less than 10–15 years of age). 䊳
䡲
Independence of the lesion locations, which may be at some distance, either in the supratentorial or infratentorial space.
䡲
Nonlocalizing rhythm, even when associated with an intracranial lesion leading to its earlier misled designation as a “projected” or “distant rhythm.”
Frontal intermittent rhythmic delta activity (FIRDA) 䡲
FIRDA is usually seen in adult or children older than 10–15 years of age. The difference in location between FIRDA and OIRDA is most likely due to maturation-related spatial EEG features. 䡲 Indicative of widespread brain dysfunction and mild-to-moderate degree of encephalopathy. 䡲 Earliest clinical feature of FIRDA is fluctuation level of alertness or attention. 䡲
Indicative of active fluctuating, progressing, or resolving widespread brain dysfunction and is less likely to be associated with chronic, stable brain dysfunction. As the condition progresses, often leading to more persistent, bilateral abnormalities, frank alteration in consciousness appropriates to the degree of persistent bilateral abnormalities.
䡲
When presents in association with focal cerebral lesion, it usually implies that the pathological process is beginning to produce an active widespread brain disturbance likely to be associated with clinical signs of encephalopathy.
䡲
Although frequently bilateral, IRDA may occur predominantly unilaterally. Even when it occurs unilaterally in association with lateralized supratentorial lesion, the lateralization of the IRDA, although usually ipsilateral, may even be contralateral to the focal lesion. Therefore, when IRDA is present, determining whether it is due to a focal lesion, is based on persistent localizing signs, and not on the morphology or even the laterality of IRDA. This misled designation as a “projected” or “distant rhythm.” in the earlier reports. 䡲 Reactivity: 䊳 IRDA is activated by eye closure, hyperventilation and drowsiness and disappeared in stage 2 and deeper sleep stages, and reappears again in REM IRDA is attenuated with eye opening/alerting Pathophysiology: 䊳 Only partially understood 䊳
䡲
Generally related to diseases states effecting neurons at both cortical and subcortical levels and not specific to deep midline pathology or intracranial pressure
䊳
Partial dysfunction and overreactivity of thalamocortical circuit (especially dorsal thalamus)
䡲
Shifting predominance is seen in diffuse encephalopathy. 䡲 Persistent ipsilateral FIRDA is commonly seen in ipsilateral deep lesion, although lateralizing value is not as good as PDA. 䡲
Nonspecific in etiology and caused by a wide variety of pathologic processes. 䡲 Seen in normal individuals during HPV. 䡲
Seen in diverse systemic and intracranial processes or a wide variety of pathologic processes varying from systemic, toxic or metabolic disturbances to focal intracranial lesions.
4 䡲
FIRDA is rarely reported to be associated with generalized epilepsy.
Occipital intermittent rhythmic delta activity (OIRDA) 䡲 䡲
Seen in children younger than 10–15 years of age.
“Maturation-related spatial EEG features.” 䡲 Clinical significance is similar to FIRDA in the mean of encphalopathy.
Focal Nonepileptoform Activity
䡲
The major difference between OIRDA and FIRDA is that OIRDA is highly associated with generalized epilepsy especially absence epilepsy.
Temporal intermittent rhythmic delta activity (TIRDA) 䡲
Monomorphic burst of delta activity in the temporal region.
279
䡲
TIRDA is an important epileptogenic abnormality, highly pathognomonic for temporal lobe epilepsy, especially caused by mesial temporal sclerosis. 䡲 Often associated with interictal epileptiform activity and PDA 䡲 Seen in drowsiness and light sleep.
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FIGURE 41. Posterior Slow Wave of Youth. EEG of an 11-year old girl with a new onset of insomnia, weight loss, and depression shows occipital slow theta and delta slow waves (arrows) mixed with and briefly interrupting the alpha rhythm on both sides. Posterior slow waves of youth (youth waves or polyphasic waves) are physiologic theta or delta waves accompanied by the alpha rhythm and creating spike-wave-like phenomenon. They are most commonly seen in children aged 8–14 years but are uncommon in children under 2 years. They have a 15% incidence in persons aged 16–20 years but are rare in adults after age 21 years. They are typically seen both unilaterally and bilaterally in a single recording. They are always accompanied by the alpha rhythm, and are attenuated with eye opening, disappear with the alpha rhythm during drowsiness and light sleep, and may be accentuated by hyperventilation.1–3
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FIGURE 42. Posterior Slow Wave of Youth. EEG of a 10-year old boy with recurrent syncope shows occipital slow waves (arrows) mixed with and briefly interrupting the alpha rhythm on the right side. Posterior slow waves of youth (youth waves or polyphasic waves) are physiologic theta or delta waves accompanied by the alpha rhythm and creating spike-wave-like phenomenon. They are most commonly seen in children aged 8–14 years but are uncommon in children under 2 years. They have a 15% incidence in persons aged 16–20 years but are rare in adults after age 21 years. They are typically seen both unilaterally and bilaterally in a single recording. They are always accompanied by the alpha rhythm, and are attenuated with eye opening, disappear with the alpha rhythm during drowsiness and light sleep, and may be accentuated by hyperventilation.1–3
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FIGURE 43. Posterior Slow Wave of Youth; Attenuated with Eye Opening. EEG of a 10-year-old boy with syncope showing occipital slow theta and delta waves (arrows) mixed with and briefly interrupting the alpha rhythm in both occipital regions but maximally expressed in the left hemisphere. This is so-called “posterior slow waves of youth” that are physiologic findings seen commonly in children aged 8–14 years. They are always accompanied by the alpha rhythm, and are attenuated with eye opening (open arrow), and disappear with the alpha rhythm during drowsiness and light sleep.1–3
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FIGURE 44. Posterior Slow Wave of Youth; Activated with Eye Closure. (Same EEG as in Figure 4-3) Alpha rhythm and posterior slow waves of youth are activated by eye closure.
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FIGURE 45. Slow Alpha Variant. EEG of a 9-year-old boy with recurrent vertigo showing rhythmic notched theta or delta activities that have a harmonic relationship with the alpha rhythm (one-third or half the frequency). Slow alpha variants are rare benign EEG variants (less than 1% of normal adult), have a harmonic relationship with the alpha rhythm, and show similar distribution and reactivity as a normal alpha rhythm.4 It should not be misinterpreted as occipital intermittent rhythmic delta or theta activity activities, pathologic findings seen in children and adults.
4
Focal Nonepileptoform Activity
FIGURE 46. Slow Alpha Variant. EEG of an 11-year-old girl with recurrent staring episodes showing slow alpha variants that are activated by eye closure.
285
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4
FIGURE 47. Slow Alpha Variants. EEG of a 10-year-old boy with behavioral disturbance and headache showing slow alpha variants (subharmonic of the alpha rhythm) with notched appearance. They are intermingled with normal alpha rhythms and activated by eye closure.
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FIGURE 48. Asymmetric Alpha Rhythm; Dyke-Davidoff-Mason Syndrome Due to Intrauterine Stroke. A 9-year-old-left-handed girl with right hemiparesis and hemiatrophy due to intrauterine stroke of who developed a new-onset right-sided focal motor seizure with secondarily generalized tonic-clonic seizure. Cranial MRI shows encephalomalacia in the left frontal-temporal region, left cerebral hemiatrophy, and thickening of the clavarium. These findings are compatible with Dyke-Davidoff-Mason syndrome. EEG shows consistent suppression of alpha rhythm and intermixture of theta and delta activities in the left occipital region. Focal lesions in the thalamocortical circuit including occipital cortex and anteroventral thalamus can cause changes in alpha rhythm including (1) slowing of frequency (1 Hz or more differences between both sides), (2) loss of reactivity and modulation, (3) voltage attenuation, (4) Bancuad’s phenomenon (failure of reactivity of alpha rhythm to eye opening), (5) intermixed theta or delta activity (must be differentiated from posterior slow waves of youth), and (6) epileptiform activity.5 Dyke-Davidoff-Mason syndrome is first reported in 1934 by Dyke.6 The syndrome includes contralateral hemiatrophy and hemiparesis and seizure accompanied by cerebral hemiatrophy and compensatory bone alterations in the clavarium, such as thickening, hyperpneumatization of the paranasal sinuses and mastoid cells, and elevation of the petrous pyramid and the upper edge of the orbita.6–9
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FIGURE 49. Alpha Rhythm Changes Affected by Right Occipital Tumor. A 20-year-old boy with intractable epilepsy caused by low-grade tumor in the right occipital region. His seizures are described as simple visual hallucination (colors and shapes) with or without versive seizure (head and eyes deviating to the left) and GTCS. MRIs show a well-defined tumor in subcortical area of the right occipital region without mass effect. EEG shows asymmetry of alpha rhythm, which is normal on the left but significantly attenuated (>30%), poorly regulated on the right, and failure of the alpha rhythm to attenuate with eye opening (*). There is focal theta and polymorphic delta activity intermingled with the alpha rhythm. Focal lesions in the occipital cortex and anteroventral thalamus can cause changes in alpha rhythm including (1) slowing of frequency (1 Hz or more differences between both sides), (2) loss of reactivity and modulation, (3) voltage attenuation, (4) Bancuad’s phenomenon (failure of reactivity of alpha rhythm to eye opening), (5) intermixed theta or delta activity (must be differentiated from posterior slow waves of youth), and (6) epileptiform activity.5
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FIGURE 410. Bancaud's Phenomenon; Dyke-Davidoff-Mason Syndrome. (Same patient as in Figure 4-8) EEG demonstrates failure of alpha rhythm to attenuate with bilateral eye opening in the left occipital region (open arrow). This is so-called “Bancaud’s phenomenon.” In 1995, Bancaud described unilateral failure of alpha blocking with eye opening.7,8 The patients had focal structural lesions in the temporal, parietal, and occipital regions. The side on which alpha activity failed to attenuate with eye opening was ipsilateral to the side of the lesion. In the study of 120 patients with defective alpha activity by mental arithmetic at Mayo Clinic, 32 patients had Bancaud phenomenon. Associated focal slowing and/or epileptiform abnormalities were present over the temporal region in 60 patients, the parietal region in 33, posterior head regions in 14, and the frontal region in 6.9
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FIGURE 411. Symptomatic Focal Epilepsy; Congenital Hydrocephalus with Ventriculoperitoneal Shunt. An 11-year-old boy with congenital hydrocephalus and ventriculoperitoneal shunt insertion who developed recurrent staring spells accompanied by “gulping sound.” CT shows dilatation of temporal horn of the right lateral ventricle, multiple hypodensity areas of the right occipital lobe, and VP shunt catheters. EEG demonstrates marked attenuation of alpha rhythm in the right occipital region and polymorphic delta activity and spikes in the right temporal region. VP shunt insertion can cause injury to the cortex or interfere with postnatal neuronal migration or in combination. These can lead to focal seizures. Epilepsy is an important predictor of poor intellectual outcome in the children with hydrocephalus with shunts. Epilepsy was significantly affected by the causes of hydrocephalus, shunt complications, increased ICP caused by hydrocephalus or shunt malfunction, and the presence of a shunt by itself.10
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FIGURE 412. Ipsilateral Attenuation of Alpha Rhythm & Polymorphic Delta Activity (PDA); Focal Cortical Dysplasia, Left Occipital Lobe. EEG of a 6-year-old girl with intractable occipital lobe epilepsy due to focal cortical dysplasia in the left occipital region. There is consistent slowing and decreased voltage (less than 50% of the right side) of physiologic alpha rhythm and intermingled theta and polymorphic delta activity (PDA) in the left occipital region. Consistent focal slowing of physiological rhythms by 1 Hz or more on one side is a reliable sign of focal abnormality of the side of slower frequency whether the amplitude of the rhythm is increased or decreased.11 In this patient, the EEG also shows focal PDA and alpha asymmetric (decreased voltage by more than 50%, compared to the right side).
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FIGURE 413. Intermittent Polymorphic Delta Activity & Attenuation of Alpha Rhythm; Systemic Lupus Erythrematosus (SLE). A 17-year-old boy with a history of SLE and epilepsy. EEG shows asymmetric alpha rhythm with suppression in the left occipital region, intermittent polymorphic delta activity in the left temporal region, and left temporal sharp transients. EEG was abnormal in 87.1% of the patient with SLE who had a history of seizures. Left hemisphere abnormalities were identified in 79.6% and right hemisphere abnormalities in 7.4%. Abnormalities included theta, delta slowing, and sharp wave. In 74.4% of the patients with left hemisphere abnormalities, the abnormalities were localized to the left temporal leads. These findings suggest selective damage to the left temporal limbic region in patients with SLE.12
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FIGURE 414. Asymmetric Reactivity of Alpha Rhythm; Hemorrhagic Stroke Caused by Streptococcal Infection. A 6-year-old girl with a new-onset seizure described as fall followed by generalized tonic-clonic seizure associated with streptococcal infection. Her MRI/MRA is compatible with the diagnosis of hemorrhagic infarction in the left temporal-occipital region. CT angiogram was normal. EEG shows depression of reactivity to eye closure (open arrow), decreased amplitude, and frequency of alpha rhythm in the left occipital region. Simultaneous EEG and fMRI study revealed the correlation between increased alpha power and decreased MRI signal in multiple regions of occipital, superior temporal, inferior frontal, and cingulate cortex, and with increased signal in the thalamus and insula.13 Using simultaneous EEG and PET scan, a correlation between alpha power and metabolism of the bilateral thalamus and the occipital and adjacent parietal cortex was found.14 These results support the role of thalamus as, in part, a generator of alpha rhythm. Therefore, involvement of thalamocortical circuit can cause suppression of alpha rhythm.
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FIGURE 415. Unilateral Attenuation of Alpha Rhythm; Right Thalamic Heterotopia. A 6-year-old boy with intractable symptomatic absence epilepsy caused by right thalamic heterotopia (arrow). EEG showed secondary bilateral synchrony with lateralized epileptic focus in the right hemisphere. In addition, background activity shows attenuation of alpha rhythm in the right hemisphere. Not only the lesions in the occipital lobes but also the lesions in the anteroventral thalamus or thalamocortical circuit can cause unilateral attenuation of alpha rhythm.15 The studies using combined EEG/fMRI indicated the alpha rhythm may be generated, in part, by the thalamus.13,16 The studies using combined EEG/PET showed a correlation of alpha rhythm in the pons, anterior midbrain, hypothalamus, medial thalamus, amygdala, the basal prefrontal cortex, insula, and the right dorsal premotor.14,17,18 It is therefore possible that the mesencephalic-medial thalamic network is correlated with occipital EEG alpha rhythm.
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FIGURE 416. Attenuation of Alpha Rhythm & Focal Polymorphic Delta Activity; Acute Focal Axonal Injury. A 5 1/2-year-old boy with a new-onset generalized tonicclonic seizure followed by right-sided Todd paralysis caused by traumatic brain injury. Axial T2-weighted image shows small hemorrhage in the left mesial temporal area (open arrow). EEG performed 2 hours after the seizure shows polymorphic delta activity (PDA) in the left temporal region and slowing of frequency of alpha rhythm in the left occipital region. Focal PDA and slowing of alpha frequency are supportive of focal structural abnormality in the left temporal-occipital region consistent with the MRI finding. PDA mixed with substantial amount of theta or alpha activity usually indicates reversible cause such as mild TBI, migraine, postictal, or mild viral encephalitis.
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FIGURE 417. Ipsilateral Attenuation of Alpha Rhythm; Focal Cortical Dysplasia, Left SSMA. (Same EEG recording as in Figure 4-31 to 4-36) A 7-year-old-left-handed girl with multiple types of seizures including focal myoclonic seizure, drop attack, and secondarily generalized tonic-clonic seizure. (A) MRI with FLAIR sequence shows focal cortical dysplasia (FCD) in the left SSMA (arrow). (B) Interictal PET demonstrates diffuse hypometabolism in the left hemisphere but maximal in the left lateral frontal (open arrow) and SSMA (double arrows) regions, corresponding to the lesion seen in the MRI in A. EEG shows suppression of amplitude and reactivity of the alpha rhythm as well as diffuse theta activity in the left hemisphere. These findings are consistent with involvement of the thalamocortical circuit in the left hemisphere.
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FIGURE 418. Ipsilateral Attenuation of Photic Response; Hemispheric Malformation of Cortical Development (MCD). (Same patient as in Figure 6-16 to 6-18) EEG during photic stimulation with different stimulus frequencies constantly shows asymmetric photic response with lower amplitude and less reactivity in the left compared to the right hemispheres. Although mild and inconsistent asymmetry of photic response is frequently seen in normal individuals, consistently lateralized voltage and reactivity on one side with all photic stimulus frequencies raises the possibility of structural abnormality in the hemisphere of lower voltage.19
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FIGURE 419. Ipsilateral Attenuation of Photic Response; Focal Cortical Dysplasia, Left Temporo-Occipital. EEG of a 12-year-old girl with intractable occipital lobe epilepsy due to focal cortical dysplasia. There is depression of photic response in the left occipital region caused by focal cortical dysplasia. Axial FLAIR sequence and coronal T2-weighted MRIs show thickened cortex, decreased gyral pattern, increased signal intensity, and blurring of gray-white matter junction in the left temporal-occipital region.
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FIGURE 420. Asymmetric Photic Response (Ipsilateral Suppression); Left Temporo-Occipital Tumor. A 4-year-old girl with medically intractable epilepsy caused by tumor. Her seizures were described as pupillary dilatation, right facial distortion, and eyes deviating to the left side, followed by left arm stiffening and shaking. (A) Axial FLAIR shows high signal abnormality over the right temporo-occipital region. (B) Sagittal view demonstrates hypointense lesion in the left temporo-occipital region. EEG shows consistent asymmetry of photic driving response during all flash frequencies over the left occipital region that is concordant with the location of the tumor in the left temporo-occipital region. A mild and inconsistent asymmetry of photic driving response is frequently seen in normal individuals. An asymmetry in photic driving response may result from a lesion on the side of lower voltage, but an asymmetry in voltage only, although consistently lateralized, in the absence of other EEG changes can be seen in some normal individuals and should not be viewed as abnormal.19
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FIGURE 421. Asymmetric Photic Response; Left Thalamic Atrophy and Calcification. (Same patient as in Figure 4-26 and 4-27) EEG shows attenuation of photic response in the left hemisphere. MRI and CT show bilateral thalamic calcification, greater expressed on the left with left thalamic atrophy (arrows). Lesions in thalamocortical circuit can cause ipsilateral attenuation of alpha rhythm and photic response.
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FIGURE 422. Alpha Asymmetry with Decreased Photic Response; Hemorrhagic Infarction. A 6-year-old girl with a new-onset seizure described as fall followed by generalized tonic-clonic seizure associated with streptococcal infection. Her MRI/MRA is compatible with the diagnosis of hemorrhagic infarction in the left temporal-occipital region. EEG shows consistent slower frequency and less reactivity of alpha rhythm (open arrow) and attenuation of photic response in the left occipital at all stimulus frequencies (double arrows). Also note left posterior temporal sharp waves (*). Focal lesions in the occipital cortex and anteroventral thalamus can cause changes in alpha rhythm including (1) slowing of frequency (1 Hz or more differences between both sides), (2) loss of reactivity and modulation, (3) voltage attenuation, (4) Bancuad’s phenomenon (failure of reactivity of alpha rhythm to eye opening), (5) intermixed theta or delta activity (must be differentiated from posterior slow waves of youth), and (6) epileptiform activity. Although mild and inconsistent asymmetry of photic driving response (amplitude and reactivity) is frequently seen in normal individuals, constant asymmetry of photic driving response may result from a lesion on the side of lower voltage or less reactivity. Asymmetry in voltage only, although consistently lateralized, in the absence of other EEG changes can be seen in some normal individuals and should not be viewed as abnormal. Consistent focal slowing of alpha rhythm by 1 Hz or more on one side reliably identifies the side of focal abnormality whether the voltage of the rhythm is increased or decreased.5,19
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FIGURE 423. Enhancement of Ipsilateral Alpha Rhythm; Unilateral Polymicrogyria (PMG). EEG of a 4-year-old boy with developmental delay and well-controlled focal epilepsy shows alpha asymmetry with voltage higher in the right occipital region. MRIs demonstrate polymicrogyria in the right perisylvian and occipital regions. Voltage asymmetry alone, unless extreme, constant, or in combination with other abnormalities (slowing of frequency, decreased reactivity or modulation of alpha rhythm and focal PDA) is the least reliable finding and of little clinical significance. Although increased voltage of alpha rhythm may rarely be observed on the side of abnormality, it is usually less reactive and poorly modulated.5
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FIGURE 424. Enhancement of Ipsilateral Photic Response; Unilateral Polymicrogyria (PMG). (Same patient as in Figure 4-23) Excessive photic response is noted in the ipsilateral cerebral hemisphere (open arrows).
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FIGURE 425. Alpha Asymmetry; Focal Cortical Dysplasia. A 7-year-old boy with recurrent seizures described as loss of the right visual field followed shortly by eyes rolling and tongue biting. He was confused and disoriented for 45–90 sec. MRI shows a focal cortical dysplasia in the left occipital region (open arrow). EEG demonstrates consistent asymmetry of alpha rhythm with higher amplitude, slowing of alpha frequency and intermixed theta activity in the left occipital region (arrows). Consistent focal slowing of alpha rhythm by 1 Hz or more on one side reliably identifies the side of focal abnormality whether the voltage of the rhythm is increased or decreased .5,20
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FIGURE 426. Suppression of Vertex Sharp Waves and Spindles; Congenital Infection; Remote Stroke, Multiple Calcifications and Schizencephaly. A 7-year-oldleft-handed girl with microcephaly, spastic right hemiparesis, and mental retardation due to unknown congenital infection and new-onset right focal clonic seizures. MRI and CT show encephalomalacia and open-lip schizencephaly in the left frontal-parietal region (open arrows) and multiple parenchymal calcifications (arrows). EEG during stage 2 sleep demonstrates persistent asymmetry of vertex waves (asterisk) and sleep spindles with voltage lower in the left hemisphere. Vertex waves and sleep spindles can be affected by cerebral structural abnormalities with abnormality on the side of lower voltage. Lesions in parietal lobe or thalamus can attenuate sleep spindles.5,21,22
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FIGURE 427. Lateralized Polymorphic Delta Activity in the Left Hemisphere; During Arousal. (Same patient as in Figure 4-26) EEG shows attenuation of photic response in the left hemisphere. MRI and CT show bilateral thalamic calcification, greater expressed on the left with left thalamic atrophy (arrows). Lesions in thalamocortical circuit can cause ipsilateral attenuation of alpha rhythm and photic response.
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FIGURE 428. Asymmetric Lambda Waves; Status Post Resection of Epileptogenic Zone, Left Parietal. Twenty-four-hour video-EEG of a 5-year-old boy with a history of two-step epilepsy surgery for intractable epilepsy caused by a focal cortical dysplasia in the left frontal-parietal region. There are constant depression of lambda waves (*), alpha rhythm, and photic response (not shown) in the left occipital region associated with polymorphic delta activity in the left parietal-occipital region throughout the waking record. These findings are compatible with breach rhythm occurring at the posterior margin of the previous craniectomy. Asymmetry of lambda waves is common and should not be interpreted as being abnormal unless there are associated abnormalities such as polymorphic delta activity and persistence of lambda asymmetry.
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FIGURE 429. Anterior Beta Asymmetry; Remote Left Middle Cerebral Artery Stroke. (Same patient as in Figure 4-8 and 4-10) EEG shows attenuation of beta activity (arrows) in the left frontal-temporal region without definite polymorphic delta slowing. Persistent voltage difference of beta activity of 35% or more between homologous areas of both hemispheres is considered a reliable sign of focal cerebral abnormality or extra-axial blood or cerebrospinal fluid.5 Suppression of anterior beta activity is usually more sensitive than focal polymorphic delta activity in determining structural abnormality.
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FIGURE 430. Background Asymmetry and Polymorphic Delta Activity (PDA); Embolic Stroke Secondary to Pneumococcal Septicemia. A 15-year-old boy with metastatic medulloblastoma who developed a sudden-onset high fever, mental status change, right hemiparesis, and focal seizures described as head and eyes deviating to the right side followed by GTCS. Blood culture was positive for streptococcal pneumoniae. Cranial MRI reveals multiple infarctions caused by septic emboli, maximal in the right parietal region. EEG during sleep demonstrates continuously diffuse polymorphic delta activity (PDA), maximally expressed in the left hemisphere with suppression of beta activity, spindles, and vertex waves in the left hemisphere. Sleep spindles are generated in the reticular nucleus of the thalamus, and through thalamocortical neurons the cortex is triggered to generate spindle bursts.21 Extended cortical areas in the centroparietal regions (pyramidal neurons), most likely the whole parietal cortex and the posterior part of the frontal cortex, are involved in the generation of sleep spindles as recorded using the MEG.22 Lesions in the thalamocortical circuit, especially thalamus and parietal lobe, can attenuate the sleep spindles.5,23,24
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FIGURE 431. Asymmetric Beta, Sleep Spindles and Vertex Waves; Encephalomalacia Caused by Acute Viral Meningoencephalitis in Newborn. A 12-year-old with mild cognitive impairment, left hemiparesis, and intractable epilepsy due to extensive involvement of the right frontal-parietal-temporal, insula, and thalamic regions caused by acute viral encephalitis at the age of 2 weeks. EEG during sleep shows marked suppression of spindles over the right hemisphere. Sleep spindles are generated in the reticular nucleus of the thalamus, and through thalamocortical neurons the cortex is triggered to generate spindle bursts.21 Extended cortical areas in the centroparietal regions (pyramidal neurons), most likely the whole parietal cortex and the posterior part of the frontal cortex, are involved in the generation of sleep spindles as recorded using the MEG.22 Lesions in the thalamocortical circuit, especially thalamus and parietal lobe, can attenuate the sleep spindles.5,23,24
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FIGURE 432. Focal Cortical Dysplasia; Attenuation of Background Activity During Drowsiness. (Same patient as in Figures 4-104 and 9-106) A 4-week-old boy with very frequent seizures described as epileptic nystagmus and versive seizures. MRI demonstrates extensive focal cortical dysplasia over the left parieto-temporo-occipital regions (arrow). Suppression of premature hypnagogic hypersynchrony over the left hemisphere during drowsiness.
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FIGURE 433. Suppression of Hypnagogic Hypersynchrony; Focal Cortical Dysplasia (FCD). A 2-year-old girl with a history of frequent seizures due to FCD. Her seizures were stereotypic and described as asymmetric tonic seizure with head and eyes deviating to the right side. (A) CT shows mixed hyperdense and hypodense areas in the left mesial frontal region (arrow). (B, C, D) Axial, coronal, and sagittal MR images demonstrate mixed density lesion in the mesial frontal region without enhancement (arrows). These findings are consistent with balloon cell-type focal cortical dysplasia. EEG during drowsiness shows persistently asymmetric hypnagogic hypersynchrony with lower amplitude on the left side. Although asymmetric hypnagogic hypersynchrony with shifting predominance is common, persistent asymmetric hypnagogic hypersynchrony is indicative of structural abnormality in the side of lower amplitude.
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FIGURE 434. Suppression of Hypnagogic Hypersynchrony; Focal Cortical Dysplasia. (Same patient as in Figure 9-41 ) A 13-month-old-right-handed boy with medically intractable epilepsy due to focal cortical dysplasia (FCD) in the right parietal region. His typical seizure was described as a sudden onset of irritability, left facial twitching, left arm stiffening, and eyes deviating to the left side. EEG shows persistent suppression of hypnagogic hypersynchrony on the right side throughout the recording during drowsiness. The lesion in the parietal lobe can suppress sleep architectures such as hypnagogic hypersynchrony, vertex waves, and sleep spindles.
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FIGURE 435. Unilateral Attenuation of Hypnagogic Hypersynchrony; Subcortical Focal Cortical Dysplasia (FCD). (Same patient as in Figures 4-87 and 4-88 ) A 4-year-old girl with medically intractable epilepsy due to focal cortical dysplasia. Her seizure was described as stiffening and clonic jerking of her left arm and leg. Cranial MRI reveals a large focal cortical dysplasia in the right temporal region causing dilatation of a temporal horn of left lateral ventricle. EEG during drowsiness shows attenuation of hypnagogic hypersynchrony (arrow) in the right hemisphere corresponding to the focal cortical dysplasia. Hypnagogic hypersynchrony is seen in drowsiness in children aged 3 months to 13 years but is rarely seen after age 9 years. This is described as paroxysmal bursts of highvoltage, rhythmic 3–5 Hz activity, maximally expressed in the frontocentral regions. Normal sleep patterns can be affected by cerebral lesions. Lesions of the parietal lobe or thalamus can attenuate sleep spindles.21,22
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FIGURE 436. Insular Epilepsy with Nocturnal Hypermotor Seizures; Focal Cortical Dysplasia. A 7-year-old-left-handed girl with nocturnal hypermotor seizures and mild mental retardation. She also had frequent episodes of simple partial seizures described as “buzzing in her right ear.” Axial T2-weighted and sagittal T1-weighted MRIs show thickened cortex intermixed with a small abnormal signal intensity (increased in T1 and decreased in T2) in the left insula area (arrow). Interictal EEG shows a run of spikes in the left centrotemporal region (dot) with suppression of physiologic vertex sharp waves (X) in the left hemisphere. The patient underwent resection of epileptogenic zone after extraoperative subdural/depth electrode EEG-video monitoring without any complication. Pathology showed focal cortical dysplasia without balloon cell and microcalcifications (FCD type 2A). The patient has been free of seizures for over 2 years since the surgery. The anterosuperior portion of the insula and temporal lobe plays a major role in generating nocturnal hypermotor seizures.25,26 Although it is well known that auditory cortex is located in the superior temporal gyrus, there were case studies supporting for a major role of human insula cortex in auditory processing.25
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FIGURE 437. Late Post-Traumatic Epilepsy; Encephalomalacia Due to Cerebral Contusion (Contrecoup). A 7-year-old girl with a history of head trauma at 13 months of age. She fell down and hit the left side of her forehead on the concrete floor. She was lethargic and vomited without seizures. (A) CT performed immediately after the injury shows multiple small intraparenchymal hemorrhages in the right parietal region. This finding is compatible with countercoup injury. She had had recurrent episodes of very brief imbalance, left leg tingling, “left ear popping,” dizziness and unable to focus without loss of consciousness for over 3 years prior to this EEG recording. (B and C) MRI performed 1 day prior to this recording shows linear area of gliosis with decreased volume of the gray matter and increased T2 signal intensity in the area of calcification seen in the CT. EEG during sleep demonstrates spike in the right centroparietal region corresponding to the lesion seen in both MRI and CT. The seizures disappeared completely after the treatment with carbamazepine. Late posttraumatic epilepsy usually occurs within the first 2 years after the injury. Seizures are believed to originate from a cerebromeningeal scar.26 The 5-year and 30-year cumulative incidence after severe head injury was 10% and 16.7%, respectively.27 The likelihood of late posttraumatic epilepsy is increased by the presence of any of 3 factors: an acute hemorrhage, a depressed skull fracture, and early epilepsy.28–31 Annegers and colleagues found that the presence of early posttraumatic epilepsy did not predict late posttraumatic epilepsy.32
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FIGURE 438. Sturge-Weber Syndrome; Suppression of Sleep Spindles, Vertex Waves, and Beta Activity. A 5-year-old right-handed girl with right-sided facial hemangioma presenting with a new-onset seizure described as eye fluttering and clonic jerking of the left upper and lower extremities lasting for approximately 45 minutes. (A) CT shows calcification in the right parietal region. (B) MRI with FLAIR sequence shows right cerebral atrophy with decreased signal intensity in the white matter. (C) Axial T1-weighted image with GAD shows contrast enhancement over the right hemisphere. EEG demonstrates persistent depression of sleep spindles, vertex waves, and beta activity over the right hemisphere throughout the sleep recording. These findings support the diagnosis of Sturge-Weber syndrome (SWS). EEG in vertex waves and spindles can be affected by cerebral structural abnormalities with abnormality on the side of lower voltage. Lesion in parietal lobe or thalamus can attenuate sleep spindles.5,23,24 The typical EEG in SWS is asymmetric, with local voltage depression and background slowing ipsilateral to the affected hemisphere. This asymmetry may be seen from the first months of life, but becomes more evident as atrophy of the hemisphere progresses. Decreased diazepam-enhanced β activity in the EEG is a sensitive criterion of functional abnormality. In patients with subtle structural abnormalities diazepam-enhanced EEG may have added value in diagnosing functional involvement and in monitoring disease progression in patients.33,34
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FIGURE 439. Ipsilateral Attenuation of Vertex Waves and Spindles; Open-Lip Schizencephaly. A 3-year-old boy with global developmental delay, mild left hemiparesis, and intermittent simple partial seizures described as funny sensation in her left arm with or without left arm stiffening. (A) Axial FLAIR image shows the right narrow open-lip schizencephaly with surrounding irregular gray matter (double arrows). A dimple in the ventricular wall shows the opening of the cleft into the ventricle (open arrow). (B and C) Coronal and sagittal images showed polymicrogyria lining around the cleft (arrows). EEG reveals depression of vertex and sleep spindles in the right frontal-central region (F4-C4). EEG also shows (not shown) sharp waves in the right frontal-temporal region. Suppression of sleep architecture indicates that there is a functional involvement of the thalamocortical circuit over the right hemisphere. The abnormal cortex lining of the schizencephalic cleft, not the cleft itself, which is epileptogenic. Background activity is more altered in the unilateral than in the bilateral form. The background EEG activity can be normal in some patients. In addition to slow waves over the cleft location, contralateral spikes were sporadically seen. There is a causal relation between schizencephaly and epilepsy; the seizure symptoms and EEG interictal and ictal abnormalities were consistent with the cleft location. Epileptiform abnormalities are seen in all patients with seizures and EEG focal abnormalities were on the same side as the cleft location in 60% of cases. EEGs in some patients show focal or bilateral synchronous ESES.37–39
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FIGURE 440. Suppression of Sleep Architecture; Intrauterine Stroke. A 6-month-old boy with intrauterine stroke. Cranial CT shows encephalomalacia in the right parietal region. EEG demonstrates consistent suppression of sleep spindles and vertex waves in the right hemisphere throughout the recording. Note prolonged sleep spindles in the Cz and C3 that is a physiological finding at 3–6 months of age. Lesion in the parietal lobe or thalamus can attenuate sleep spindles.5,23,24 A more recent study demonstrates that sleep spindles are generated in the reticular nucleus of the thalamus, and through thalamocortical neurons the cortex is triggered to generate spindle bursts.21 A study using magnetoencephalogram (MEG) suggests involvement of the pre- and post-central areas in the generation of MEG sleep spindles.22
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FIGURE 441. Suppression of Sleep Spindles and Focal Polymorphic Delta Activity (PDA); Left Middle Cerebral Artery Stroke. A 2 1/2-month-old girl who developed left MCA stroke after cardiac catheteralization. T2-weighted axial MRI (A) and DWI (B) show infarction in the left parietal region. EEG demonstrates depression of spindles as well as diffuse polymorphic delta activity in the left hemisphere. Sleep spindles are generated in the reticular nucleus of the thalamus, and through thalamocortical neurons the cortex is triggered to generate spindle bursts.21 Equivalent dipoles of MEG spindles were distributed over the centroparietal region that suggests involvement of the pre- and post-central areas in the generation of MEG sleep spindles.22
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FIGURE 442. Unilateral Slowing of Spindle Frequency. A 7-month-old right-handed boy born at 28 weeks GA due to abruptio placenta and PROM. He had a normal development until 5 months of age when he started having seizures described as head and eyes deviating to the left and clonic jerking of the left arm and left side of the face. He had developmental regression and preferred to use his right hand more after the onset of his very first seizures. A: Axial T2-weighted image shows heterogeneous signal abnormality (double arrows) extending inward from the abnormal gyri to the surface of the frontal horn of the right lateral ventricle (arrow). B: Sagittal T1-weighted image shows heterogeneous signal abnormality (black arrow) over the surface of the right lateral ventricle. Interictal EEG demonstrates suppression of sleep spindles over the right central region and PLEDs (open arrow) in the right fronto-parietal region. Focal transmantle dysplasia is a malformation of cortical development that extends through the entire cerebral mantle, from the ventricular surface to the cerebral cortex. The presence of balloon cells suggests that these malformations are associated with maldifferentiation of the stem cells generated in the germinal zone. A focal cerebral lesion is often associated with voltage asymmetry of sleep spindles, usually with depressed voltage on the side of the lesion, and was reported to cause frequency asymmetry in addition to a voltage asymmetry of sleep spindles with the slower frequency spindles occurring on the side of the lesion.
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FIGURE 443. Subtle Delta and Theta Slowing; Focal Cortical Dysplasia, Right Mesial Temporal. EEG of a 14-year-old boy with well-controlled focal epilepsy caused by focal cortical dysplasia in the right mesial temporal region. There is subtle low-voltage smooth polymorphic delta activity (open arrow) and theta activity (double arrows) noted at the F8 and T6 electrodes, respectively. Chronic lesions can cause very little, if any, slow activity over the involved hemisphere, especially deep-seated lesions such as in the mesial temporal region.
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FIGURE 444. Posterior Reversible Leukoencephalopathy; Right Posterior Temporal Theta Slowing. A 7-year-old boy with severe asthma who was admitted to the PICU for status asthmaticus. He received a treatment with high-dose corticosteroid and developed. He became lethargic and developed a new-onset seizure described as headache, vomiting, blindness followed by head and eyes deviating to the left side, left arm clonic jerking and then GTCS after a shooting of blood pressure to 170/110 mmHg. Axial FLAIR-sequence MRI shows multiple hyperintensity lesions in the white matter of the right occipital region (open arrow), the gray matter of the left occipital (double arrows) and periventricular white matter in the left occipital region (arrow). These are consistent with posterior reversible encephalopathy syndrome (PRES) caused by hypertension due to steroid treatment. The patient recovered within 1 week after hypertension was controlled. EEG after the seizure shows rhythmic theta activity intermixed with small spikes in the right parietal-posterior temporal region. Hypertensive encephalopathy is the cause of this syndrome caused by suddenly increased systemic blood pressure exceeding the autoregulatory capability of the brain vasculature. Regions of vasodilatation and vasoconstriction develop, especially in arterial boundary zones, and there is breakdown of the blood–brain barrier with focal transudation of fluid and petechial hemorrhages. Functional vascular changes and edema, rather than infarction, play a major role. The patients usually have a rapid resolution of clinical and imaging abnormalities when blood pressure is lowered. The hyperintense signal seen mainly in the hemisphere where the seizures predominated. FLAIR is the sensitive sequence to the characteristic cortical and subcortical edema of PRES. The FLAIR sequence shows involvement of gray matter to be a much greater part of this syndrome than previously thought; the vasogenic edema may even originate in the cortex.35,36
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FIGURE 445. Ipsilateral Beta Attenuation & Monorhythmic Theta Activity; Focal Cortical Dysplasia, Right Parietal. EEG of a 13-year-old girl with intractable epilepsy and mental retardation. Her seizures include a negative myoclonus of her left arm, drop attack, and secondarily GTCS. Axial FLAIR image shows a focal cortical dysplasia in the right parietal (open arrow). Interictal PET scan is concordant and demonstrates hypometabolism in the same area (open arrow). EEG shows depression of anterior beta and persistent monorhythmic theta activity in the right hemisphere, maximal in the parasagittal region throughout the entire recording. Frontocentral region has fastest-frequency of beta activity and highest level of cerebral blood flow.37 Depression of beta activity is the most sensitive and earliest finding in focal cortical dysfunction. Constant reduction in voltage more than 50% (normal voltage < 20 μV) is strongly suggestive of gray matter abnormality in the hemisphere with lower voltage. Persistent rhythmic theta is also indicative of severe focal cerebral dysfunction.
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FIGURE 446. Pulse Artifact. Pulse artifact can simulate polymorphic delta activity. It can be confirmed by EKG lead that shows the signal time-locked to the slow wave. It is seen only in one electrode (T3 in this patient) and caused by a loosely-applied EEG electrode placing on the artery.
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FIGURE 447. Polymorphic Delta Activity and Sharp Wave; Left Temporal-Occipital Tumor. (Same patient as in Figure 4-20) A 4-year-old girl with medically intractable epilepsy caused by a low-grade tumor. Her seizures were described as pupillary dilatation, right facial distortion, and eyes deviating to the left side, followed by left arm stiffening and shaking. A: Axial FLAIR image shows high signal abnormality over the left temporo-occipital region. B: Sagittal T1-weighted image demonstrates hypointense lesion in the left temporo-occipital region. EEG during a Laplacian montage shows a sharp wave and polymorphic delta activity in the left temporal-occipital with some spreading to the homologous area in the right hemisphere. Asymmetric photic driving response (previous page), in combination with lateralized polymorphic delta activity and sharp wave, supports the diagnosis of focal epilepsy caused by structural abnormality in left temporal-occipital area. The homologous area in the contralateral hemisphere, especially in the frontal and occipital regions, may be associated with similar slow waves and sharp waves, usually of lower amplitude. These findings may be caused by compression, edema, ischemia in the opposite hemisphere, transmission through commissural fibers, or volume conduction.
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FIGURE 448. Polymorphic Delta Activity (PDA) and Right Temporal Sharp Waves; Focal Cortical Dysplasia (FCD). A 17-year-old boy with intractable epilepsy and mild mental retardation. He developed his first seizure at 2 years of age after severe head trauma. His typical seizure types are generalized tonic-clonic seizure and complex partial seizure described as shouting and crying, taking off his clothes, running away, and confusion. This EEG was performed 1 hour after his last GTCS that was followed by Todd paralysis. MRI was unremarkable except diffuse cerebral atrophy, greater on the right side, especially in the sylvian area (open arrow). Ictal SPECT shows hyyperperfusion in the right lateral temporal area. EEG shows continuously diffuse polymorphic delta activity (PDA) over the right hemisphere, maximally expressed in the midtemporal region (T4). Note sharp waves at the T4 electrode. He has been seizure free after the two-step epilepsy surgery of the right temporal lobe. Pathology revealed focal cortical dysplasia (FCD 2A) with mesial temporal sclerosis. EEG performed within 24 hours after the seizure has a high yield. The presence of continuously focal PDA and sharp waves are indicative of epileptic focus caused by structural abnormality. Seizures caused by FCD can be precipitated by head trauma. The closer of the epileptic focus to the hippocampus, the higher the risk of secondary hippocampal sclerosis.
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FIGURE 449. Prolonged Complex Febrile Convulsion; Large Hippocampal Volume and Hyperintensity. A 2-year-old girl with mildly global developmental delay and complex febrile seizures described as prolonged right hemiconvulsion. (A and B) Axial T2-weighted image and DWI shows left amygdala hyperintensity. (C) Coronal T2-weighted image shows mild enlargement and hyperintensity of the left hippocampus. EEG demonstrates constant polymorphic delta activity (PDA) with intermixed spikes in the left anterior temporal region. There was a positive correlation between hippocampal volume and seizure duration. DWI showed hyperintensity in unilateral hippocampus in 3/12 patients with intractable seizures, ipsilateral thalamus in 2/12, and cingulate in 1/12. EEG showed abnormalities in temporal areas ipsilateral to the DWI abnormalities in these patients. Large hippocampal volume and hyperintensity on DWI were seen in patients with prolonged febrile convulsion. Prolonged febrile convulsion lasting for 60 minutes or longer may cause permanent structural changes in limbic structures that could promote later epileptogenesis.38
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FIGURE 450. Prolonged Febrile Convulsion (PFC); Mesial Temporal Sclerosis (MTS). A 4-year-old left-handed boy with a history of first prolonged generalized tonicclonic seizure associated with high fever at the age of 13 months. (A) Coronal T2-weighted MRI at that time shows increased signal abnormality in the left hippocampus (open arrow). He subsequently developed spastic right hemiparesis, global developmental delay and intractable epilepsy. At 4 years of age, he underwent another MRI (B) that shows definite left hippocampal atrophy (arrow). EEG shows polymorphic delta activity and spikes in the left temporal region. In acute febrile convulsion, MRI shows acute edema with increased hippocampal T2-weighted signal intensity and increased volume predominantly in the hippocampus in the hemisphere of seizure origin.39 Patients with a history of PFC had a higher proportion of more severe mesial sclerosis (MTS) compared with those with no PFC. These findings confirm a correlation between early childhood prolonged febrile convulsion, the severity of atrophy of mesial structures, and MTS.40 During prolonged febrile convulsion, additional acute hippocampal injury may be superimposed on the original problem such as mild MCD, and this may evolve into MTS.41
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FIGURE 451. Focal Polymorphic Delta Activity (PDA), Right Temporal; Focal Cortical Dysplasia, Right Posterior Frontal. An 8-month-old girl presenting with prolonged left arm clonic and versive seizures during a febrile episode. Sagittal and axial MRIs with FLAIR sequence performed 36 hours after the seizure show transmantle cortical dysplasia in the right posterior frontal region (arrow). EEG reveals nearly continuous polymorphic delta activity (PDA) in the right midtemporal region (T4-T6). PDA results from lesions affecting white matter tracts. The lesions differentiate the overlying cortex from its underlying white matter input.47,48 Lesions involving the posterior frontal (central) or parietal areas are less likely to present with well circumscribed delta focus but often produce PDA falsely localized to the temporal areas. Focal PDA associated with lesions of the frontal area often spread to homologous contralateral areas, where it has a lower amplitude and smaller field.5,20
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FIGURE 452. Polymorphic Delta Activity (PDA); Mild Malformation of Cortical Development m(MCD), Right Mesial Temporal Lobe. A 6-month-old right-handed boy with normal developmental milestones who developed his first seizure at 1 1/2 months of age. His seizure was described as a sudden onset of motionless, spacing out, lip smacking, and cyanosis with or without head and eyes deviating to the left side lasting for 1–4 minutes. Postictally, he was either lethargic or irritable. (A) Coronal T2-weighted image shows subtle thickened cortex with blurring of gray-white matter junction in the right mesial temporal region (black arrow). (B) Ictal SPECT shows hyperperfusion in the right mesial temporal region (large arrow). EEG demonstrates nearly continuous polymorphic delta activity (PDA) in the right mid and posterior temporal region. Resection of the epileptogenic zone in the right mesial temporal region after an invasive EEG-video monitoring leads to seizure freedom. Pathology revealed mMCD in the right hippocampus. PDA usually results from structural abnormalities affecting the white matter and is seen in half of the patient with focal cortical dysplasia. Focal cortical dysplasia must be in the differential diagnosis of localized PDA.42,43
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FIGURE 453. Polymorphic Delta Activity (PDA); Hemiplegic Migraine. An 8-year-old girl with hemiplegic migraine. EEG performed 8 hours after an acute onset of left hemiparesis when she continued having mild weakness of her left arm shows widely diffuse distribution of polymorphic delta activity over the right cerebral hemisphere, maximal in the temporal region. Suppression of alpha rhythm is also noted in the right occipital region. EEG done 2 weeks later (not shown) was within normal limits.
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FIGURE 454. Focal Polymorphic Delta Slowing; Acute Disseminated Encephalomyelitis (ADEM). An 8-year-old boy with a history of ADEM in remission. He presented 3 years later after ADEM with intermittent gait disturbance and dysarthria. MRI shows hyperintense signal abnormality in the right parietal region. EEG few days prior to the MRI demonstrates polymorphic delta slowing in the right parietal and suppression of alpha rhythm in the right occipital region. Polymorphic delta activity results primarily from lesions affecting white matter and involvement of superficial cortex is not essential. The localizing value of focal polymorphic delta activity is greatest and is associated with underlying structural abnormalities when it is discrete and associated with depression of superimposed faster background frequencies. These are associated with a number of structural abnormalities.5
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FIGURE 455. Polymorphic Delta Activity (PDA); Acquired HIV infection with Toxoplasmosis. A 21 year old man with a history of HIV infection and toxoplasmosis diagnosed 5 months prior to this EEG when he presented with a new-onset generalized tonic-clonic seizure. He then presented again with headache and intermittent right hand and foot numbness lasting for approximately 1 minute. Cranial MRI shows multiple ring enhancement lesions with surrounding brain edema in the left frontal, parietal, and temporal regions with an old lytic lesion in the left parietal from a previous stereotactic biopsy. EEG demonstrates diffuse polymorphic delta slowing in the left hemisphere with temporal predominance. The other pages of this EEG recording (not shown) also showed epileptiform activity in the left temporo-parietal region. The causes of new-onset seizures in 26 patients with AIDS were idiopathic (8), HIV encephalopathy (8), CNS toxoplasmosis (5), alcohol withdrawal (2), progressive multifocal leukoencephalopathy (2), and CNS lymphoma (1). The authors suggest a neuroimaging study with a lumbar puncture, if indicated, in all patients with AIDS or suspected AIDS presenting with new-onset generalized seizures.44 EEG from 47 patients with the acquired HIV infection were reviewed.45 Among 27 patients (57%) with abnormal EEGs, there were 9 patients with dementia, 10 with opportunistic infections of the CNS, and 6 with no apparent neurologic disease. AIDS dementia was associated with intermittent or continuous slowing, often most prominent anteriorly. Focal slowing or sharp activity was usually found in patients who had focal CNS processes, such as cerebral toxoplasmosis and CNS lymphoma. These findings suggest the EEG can be a useful diagnostic test for evaluating patients with acquired HIV infection, particularly when these patients present with seizures, psychiatric symptoms, or cognitive dysfunction.
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FIGURE 456. Classic Migraine Headache; Intermittent Polymorphic Delta Activity. A 17-year-old girl with a last classic migraine attack 5 hours prior to the EEG. Her headaches were describes as intermittent left-sided throbbing associated with visual aura, nausea, photophobia and phonophobia and numbness on the right side of her body. Headaches occurred daily in the past 1 week. EEG during drowsiness without headache shows intermittently polymorphic delta activity (PDA) in the left temporal region. Intermittent PDA may occur during drowsiness, light sleep, and hyperventilation and fail to persist into sleep. PDA is attenuated with eye opening and other alerting procedures. It has been seen in reversible causes such as migraine, mild TBI, postictal state, mild viral encephalitis, hypertension, metabolic condition, and some cases of TIA and lacuna infarction.
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FIGURE 457. Diffuse Delta Slowing with Occipital Predominance; Left Cerebral Hemiatrophy Due to Intraventricular Hemorrhage. A 20-month-old-boy with developmental delay, spastic diplegia and right hemiparesis, stable hydrocephalus, and focal epilepsy caused by grade 4 intraventricular hemorrhages in newborn. Cranial CT shows left cerebral hemiatrophy with VP shunt insertion in the left frontal region. EEG performed 12 hours after a secondarily GTCS showed asymmetrically diffuse delta slowing with occipital predominance, greater on the left. Posterior accentuated diffuse delta activity are usually seen after generalized seizure, febrile seizure, and head injury and rarely seen in white matter degenerative diseases such as metachromatic leukodystrophy or metachromatic leukodystrophy.46,47
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FIGURE 458. Metachromatic Leukodystrophy (MLD); Posteriorly Accentuated Diffuse Delta Activity. A 20-month-old boy with developmental regression. The major neurologic symptoms were poor balance, spasticity and depressed deep tendon reflexes. MRI (not shown) revealed diffuse white matter abnormality in the periventricular regions and centrum semiovale in the posterior quadrants. Leukocyte arysulfatase-A activity was reduced. EEG demonstrates nearly continuous polymorphic delta activity in the posterior head regions. At the beginning of the genetic leukodystrophies (GLs), the EEGs were normal or showed mild slowing of background activity.49–50 However, Baslev et al. reported that recurrent seizures associated with epileptiform discharges on EEG are common in MLD at any stage of disease.51 Clinical seizures with progressive slowing and epileptiform discharges on EEGs, usually appeared during the later stages of all types of GLs such as metachromatic leukodystrophy, X-linked childhood adrenoleukodystrophy, and classic Pelizaeus-Merzbacher disease. Although cerebral involvement in GLs is mainly white matter, gray matter is eventually involved as well. In all types of GLs, there is good correlation between the severity of EEG changes, the severity of the diseases, and the clinical state of the patient. Serial EEGs are also helpful in separating GLs from static encephalopathy such as cerebral palsy.49
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FIGURE 459. High-voltage, Frontal-Dominant, Generalized Slow Wave Transient Symptomatic West syndrome and Asymmetric Epileptic Spasm. A 3 1/2-yearold boy with asymmetric epileptic spasms caused by left mesial fronto-parietal focal cortical dysplasia (FCD). A: Axial inversion recovery MRI shows blurring of gray-white matter junction and thickened cortex in the left mesial parietal region (arrow). B: Interictal FDG-PET shows subtle hypometabolism in the same area as the FCD (open arrow). EEG during a cluster of asymmetric epileptic spasms described as brief asymmetric tonic stiffening of arms and legs with left-sided predominance (arrow head) reveals lateralized highvoltage delta slow activity in the left hemisphere with positive polarity of delta slowing maximum at the P3 electrode (open arrow).
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FIGURE 460. Intermittent Focal Polymorphic Delta Activity (PDA); Nonfamilial Hemiplegic Migraine. A 10-year-old girl with intermittent episodes of right hemiparesis and/or aphasia accompanied by left-sided throbbing headaches. She has had a strong family history of migraines. The workup including cranial MRI/MRA and coagulation study was unremarkable. The EEG performed during one of her typical episodes demonstrates polymorphic delta activity (PDA) in the left occipital region and asymmetric alpha rhythm with lower amplitude in the left hemisphere. Focal PDA is exaggerated during hyperventilation. During the attacks of hemiplegic migraine, PDA can be seen in the hemisphere contralateral to hemiparesis.52 However, in patients with mild hemiparesis or dysphasia, EEG may remain normal.53
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FIGURE 461. Familial Hemiplegic Migraine; Focal Polymorphic Delta Activity. A 5-year-old boy who presented with a sudden onset of left-sided throbbing headache with right hemiparesis lasting for approximately 15 minutes. Cranial MRI/MRA with DWI and hypercoagulation study was unremarkable. His father had similar episodes when he was 10–15 years of age. EEG performed approximately 20 hours after the episode shows continuous polymorphic delta slowing in the left temporo-occipital region. The most definitely abnormal EEGs with unilateral or bilateral delta activity have been recorded during attacks of hemiplegic migraine, and during attacks of migraine with disturbed consciousness.54 However, Gastaut reported 2 patients with hemiplegic migraine whose EEG recording during the attacks were characterized by pseudoperiodic slow sharp waves over the hemisphere contralateral to the hemiplegia. Between attacks the interictal EEGs were normal.55
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FIGURE 462. Focal Polymorphic Delta Activity (PDA); Common Migraine. EEG of a 12-year-old girl with lamotrigine toxicity and exacerbation of migraine. There is background slow activity with the main posterior activity of 5–6 Hz. In addition, polymorphic delta activity maximally expressed in the left temporal region is noted. EEGs vary from normal to mildly abnormal (loss of alpha rhythm, intermittent focal delta activity) during visual auras and common migraine attacks.54,56,57 Although EEGs were reported to be almost always normal during classic and common migraine attacks by some authors,58 Niedermeyer disagreed and noted the statement was slightly exaggerated.59
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FIGURE 463. Periodic Lateralized Epileptiform Discharges (PLEDs); Hemiplegic Migraine. A 9-year-old girl with migraine who presented with acute headache, lethargy, aphasia, left eye gaze preference, right hemineglect, and profound right hemiparesis. The mother has a history of severe migraine but never had hemiplegic migraine. The first MRI performed few hours after the admission was unremarkable. MRI performed 2 days later shows subtle diffusion abnormality in the left MCA distribution (open arrow). MRA (not shown) shows small distal left ICA without cutoff or thrombus. CT angiogram done 1 day later was normal. MRI performed 3 months later was normal. EEG performed few hours after the admission shows: (1) diffuse alpha activity over the right hemisphere with depression in the left hemisphere, (2) periodic lateralized epileptiform discharges (PLEDs) in the left frontal-anterior temporal region (arrows), (3) diffuse polymorphic delta activity over the left hemisphere. The patient continued having neurologic deficits for 1 week before recovery and had lower cognitive ability during the neuropsychological evaluation. The diagnosis of hemiplegic migraine was entertained. She was fully recovery at a 3-month visit. She was found to have elevation of factor 8. The genetic testing for familial hemiplegic migraine is still pending. PLEDs have very rarely been reported in hemiplegic migraine/familial hemiplegic migraines.62,68,69 More commonly, EEG shows diffuse and/or focal delta slowing opposite to hemiparesis.70–73
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FIGURE 464. Lateralized Background Suppression; Hemiplegic Migraine. (Five hours after the EEG in Figure.4-63) EEG performed after the sedation with lorazepam for MRI shows depression of background activity over the left hemisphere and disappearance of the PLEDs. This EEG evolution supports the transient nature of her hemiplegic migraine. She showed significant improvement in her mental status and headache but remained having the same degree of the right hemiparesis and hemineglect.
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FIGURE 465. Lateralized Polymorphic Delta Activity (PDA); Hemiplegic Migraine. (Seventeen hours after the EEG in Figure 4-63) EEG show diffuse polymorphic delta activity (PDA) and suppression of spindles and vertex waves in the left hemisphere. The patient remained having right hemiparesis and hemineglect. EEG commonly shows focal delta slowing opposite to the hemiparesis or, at times, diffuse delta slowing during the attack of hemiplegic migraine.60–63
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FIGURE 466. Transient Unilateral Attenuation of Background Activity During Sleep. A 41-week CA newborn with recurrent apneic episodes associated with cyanosis. The neurologic examination was normal. Head CT was unremarkable. A routine EEG during slow sleep shows intermittent attenuation of background activity over the left hemisphere lasting for 1–2 minutes. Transient unilateral attenuation of background activity during quiet sleep is seen in 3–4% of newborn and consisted of a sudden flattening of the EEG activity occurring on one hemisphere, The asymmetry is transient, lasting from 1 to 5 minutes (less than 1.5 minutes in 75% of cases). It occurs at the beginning of quiet sleep. The EEG activity before and after the asymmetry is almost always normal. This EEG pattern may reflect the unusual functioning of mechanisms underlying the normal process of change from the low-voltage continuous EEG in REM sleep to the higher voltage discontinuous pattern of quiet sleep. This EEG phenomenon is of uncertain significance and must be differentiated from asymmetric background activity associated with structural abnormalities. The latter is usually shorter in duration, occurs in all states and is associated with other EEG abnormalities such as sharp waves or delta slowing.64–66
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FIGURE 467. Volume Conduction; Left Functional Hemispherectomy. A 2-year-old-left-handed boy with a history of life-threatening seizures resulting from left hemimegalencephaly associated with linear sebaceous nevus syndrome. He underwent emergency left functional hemispherectomy at 7 days of age and has been free of disabling seizures since. MRI shows postoperative change. EEG shows nearly continuous sharp waves in the left frontal-temporal region superimposed on marked background suppression in the left hemisphere. Background EEG activity is normal in the right hemisphere. There are periodic sharp waves of lower amplitude in the right frontal-temporal (arrows) timed-locked with the homologous sharp waves in the left hemisphere. These sharp waves are most likely due to volume conduction of electrical discharges from the homologous region in the left hemisphere passing through the skin to the right frontal-temporal region as the propagating pathway through the corpus callosum has been eliminated by the surgery. This is another example of EEG application of volume conduction theory.67
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FIGURE 468. Hemispheric Background Depression; Diffuse Left hemispheric Encephalomalacia Due to Nonaccidental Trauma. A 7-year-old boy with a history of nonaccidental trauma (NAT) at 1 month of age who subsequently developed severe mental retardation, spastic quadriparesis/right hemiparesis, and intractable epilepsy. EEG shows diffuse background depression of all EEG frequencies and continuously diffuse low-voltage polymorphic delta activity (PDA) over the entire left hemisphere and continuously diffuse medium-voltage PDA over the right hemisphere. A: Brain CT at the age of 1 month (1 day after the NAT) shows massive cerebral edema in the left hemisphere with midline shift to the right side (open arrow). B: Brain CT at 7 years of age reveals severe encephalomalacia over the left hemisphere and mild right cerebral atrophy with mild subdural hematoma (double arrows) in the frontal region. Hemispheric voltage attenuation is caused by either loss of normal cortical activity or attenuation of EEG activity by fluid collection (e.g., subdural hematoma) or skull thickening. Loss of normal EEG activity of all frequencies with low-voltage PDA is usually due to congenital or acguired (chronic) encephalomalacia caused by stroke, encephalitis, HHE or head injury, and Sturge-Weber syndrome.5
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FIGURE 469. Hydranencephaly; Symptomatic Focal Epilepsy. A 2 1/2-year-old girl with global developmental delay and spastic quadriplegia due to hydranencephaly who presented with recurrent episodes of staring, cyanosis, and apnea followed by postictal lethargy. Cranial CT shows absence of most of the cerebral hemispheres except small portion of the right temporal lobe (arrow head). The thalami are preserved (arrows). EEG during wakefulness shows nearly continuous dysrhythmic delta activity intermixed with spikes and sharp waves in the right temporal region. Flat EEG pattern is noted in all other brain regions in both hemispheres. In hydranencephaly, most of the cortical plate and hemispheric white matter is destroyed and resorbed. The cerebral hemispheres are largely replaced by thin-walled sacs containing CSF. A vascular etiology is highly likely the cause, although congenital infections, especially CMV and toxoplasmosis, have been reported. The distinction of hydranencephaly from severe hydrocephalus is important as children with severe hydrocephalus typically respond well to CSF diversion procedures.69 The typical EEG of hydranencephaly shows a flat pattern but the EEG of severe hydrocephalus does not demonstrate a flat pattern. Visual evoked potential (VEP) of severe hydrocephalus showed a normal pattern, while that of hydranencephaly showed no response.70 Short-latency somatosensory evoked potentials (SSEPs) showed absence of cortical activity with the preservation of waves of the thalamus.71,72 Therefore, EEG, SSEP, and VEP are useful for differentiation of hydranencephaly and severe hydrocephalus in cases whose CT scans do not provide clear differentiation. Lennox-Gastaut syndrome and infantile spasms reported in hydranencephaly support the important role of brainstem in generating seizures in these epileptic syndromes.73–75
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FIGURE 470. Focal Voltage Attenuation; Encephalomalacia Secondary to Neonatal Bacterial Meningitis. EEG of a 20-month-old-left-handed girl with a history of streptococcal meningitis during neonatal period. She subsequently developed spastic right hemiparesis, developmental delay, and intractable epilepsy. There is diffuse voltage attenuation over the entire left hemisphere and nearly continuous spike-wave discharges in the right hemisphere, maximal in the central-temporal region. MRI shows massive encephalomalacia in the left hemisphere and lesser degree in the right hemisphere with bilateral ventricular dilatation, greater on the left. Hemispheric voltage attenuation is due to either decreased cortical electrical activity production or increased impedance between the cortex and the recording electrodes (e.g., subdural hematoma, subgaliel hematoma). Reduction in cortical EEG generator of all activity is due to congenital lesions such as porencephaly and Sturge-Weber syndrome or acquired lesions such as meningitis, encephalitis, HHE, and stroke. EEG alone cannot differentiate between these causes.5,20
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FIGURE 471. Periodic Lateralized Epileptiform Discharges (PLEDs) in Epilepsia Partialis Continua (EPC); Hydrocephalus Secondary to Grade 4 Intraventricular Hemorrhage (IVH). A 2-year-old boy born 34 weeks GA with grade 4 intraventricular hemorrhage (IVH). He subsequently developed hydrocephalus requiring multiple VP shunt revisions, severely developmental delay, spastic quadriparesis, and intractable epilepsy. His seizure was described as continuous clonic jerking of his left arm (EPC) accompanied by horizontal nystagmus. Cranial CT shows severe hydrocephalus in both hemispheres, greater in the right hemisphere with VP shunt insertion in the right lateral ventricle. EEG demonstrates PLEDs in the right temporal-parietal-occipital regions with relative preservation of background activity in the left hemisphere. Sharp waves in the right hemisphere either were time-locked with clonic jerking or occurred independently without clinical accompaniment. PLEDs were first described by Chatrian et al.76 to define an EEG pattern consisting of sharp waves, spikes (alone or associated with slow waves), or more complex waveforms occurring at periodic intervals. PLEDs usually occur at the rate of 1–2/sec and are commonly seen in posterior head region, especially in the parietal areas. It is sometimes associated with EPC.77 This EEG pattern is usually related to an acute or subacute focal brain lesion involving gray matter.78 Chronic PLEDs were also reported in 9% of patients with intractable epilepsy who had structural abnormalities such as cortical dysplasia or severe remote cerebral injury.79,80 In a recent review of 96 patients with PLEDs,81 acute stroke, tumor, and CNS infection were the most common etiologies. Others included acute hemorrhage, TBI, PRES, familial hemiplegic migraine, and cerebral amyloidosis. PLEDs were more periodic when they were associated with acute viral encephalitis than with other etiologies.82 Seizure activity occurred in 85% of patients with mortality rate of 27%. However, 50% of patients with PLEDs never developed clinical seizure.83
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FIGURE 472. Periodic Lateralized Epileptiform Discharges (PLEDs); Hydrocephalus with Ventriculoperitoneal Shunt Infection. A 2 1/2-year-old-ex-premie boy with a history of grade 4 intraventricular hemorrhage with subsequent hydrocephalus. The ventriculoperitoneal shunt was inserted on the left side. One day prior to this EEG recording, the patient developed prolonged right-sided clonic seizures followed by GTCS. He was found to have VP shunt infection. EEG shows periodic sharp waves occurring every 2 sec in the left anterior/midtemporal region. The incidence of epilepsy in children with hydrocephalus is approximately 30%. Myelomeningocele carries a low risk at approximately 7%, cerebral malformations and intraventricular hemorrhage a moderate risk of approximately 30%, and infection a high risk of approximately 50%. There is a higher incidence of epilepsy among children who had shunt malfunctions, infection, or a combination of both.10 Mental retardation or CNS malformations are poor predictors of seizure control.84 Focal epileptiform discharges and slow waves found in the area of the ventricular catheter may indicate that shunt insertion is responsible for a cortical injury.85,86 Focal abnormalities were found in all children and in 95% of cases they were on the same side as the shunt; in 65% of cases they had amplitude of 300 mV or more. During sleep there was activation of abnormalities in all subjects, and in 33% we found continuous spikes and waves during slow sleep (CSWS).87 CSWS may partly be responsible for neuropsychological disturbances in these patients. Although ventriculoextracranial shunts have been the standard treatment for hydrocephalus, the long-term morbidity, especially postshunt epilepsy and cognitive dysfunction, has to be taken seriously.88 However, the relation of epilepsy to the shunting procedure remains to be a controversial topic.89
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FIGURE 473. Unilateral Attenuation of Background Activity; Sturge-Weber Syndrome. A 12-month-old-left-handed girl with port-wine stain (nevus flammeus) on both sides of her face, glaucoma, developmental delay, and intractable epilepsy. Her seizures are stereotyped and described as hypomotor followed by apnea, cyanosis, and destauration requiring oxygenation supplement. Her T1-weighted images with GAD show leptomeningeal enhancement over the entire left hemisphere. EEG shows marked attenuation of normal sleep architecture including sleep spindles and medium-voltage occipital slowing in the left hemisphere. Note spikes and sharp waves in the left occipital region. The most consistent interictal EEG finding was depression of activity over the ipsilateral hemisphere or part of one hemisphere that involved the side of the pial angioma and intracranial calcifications (18/20 patients). Interictal epileptiform activity were found in 16/20 patients and frequently recorded over the contralateral side. Six (6/20) patients had bilaterally synchronous spike/polyspike-wave discharges. Partial seizures were recorded in 7/20 patients.90
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FIGURE 474. Lateralized Electrodecrement; Intrauterine Stroke. A 14-year-old right-handed girl with severe mental retardation, left hemiparesis, and medically intractable epilepsy due to prenatal stroke caused by intrauterine cocaine exposure. She started having the first seizure at 4 months of age described as left arm clonic jerking. Subsequently, she developed multiple types of seizures including drop attacks, clonic jerking of left arm, staring episodes, and secondarily GTCS. This interictal EEG shows diffuse spike-wave activity followed by electrodecrement over the right hemisphere (<--->). The patient has been free of seizures since the right functional hemispherectomy.
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FIGURE 475. Lateralized Delta Slowing and Background Suppression; Postictal State. A 10-year-old girl with medically intractable epilepsy due to dual pathology, right frontal cortical dysplasia with secondary hippocampal sclerosis. (A and B) Axial FLAIR and coronal T2-weighted image through the hippocampal body shows definite atrophy and high intensity signal of the right hippocampus. EEG 1 minute after the seizure originating from the right mesial temporal lobe that was stopped by intravenous administration of benzodiazepine demonstrates marked diffuse polymorphic delta slowing and suppression of beta activity over the right hemisphere. Excessive beta activity in the left hemisphere is caused by the effect of benzodiazepine. Asymmetrical beta activity should be considered abnormal if there is a persistent voltage difference of 35% or more between homologous areas of the two sides. Polymorphic delta activity results primarily from lesions affecting white matter and involvement of superficial cortex is not essential. The localizing value of focal polymorphic delta activity is greatest when it is discrete and associated with depression of superimposed faster background frequencies. These are associated with a number of structural abnormalities.5 Lateralized polymorphic delta slowing during postictal state is highly predictive of the side of temporal lobe epilepsy.91
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FIGURE 476. Postictal Encephalopathy. A 14-year-old boy with static encephalopathy and infrequent focal motor seizures. This EEG was performed 1 week after the last seizure that was described as right Jacksonian march with secondarily generalized tonic-clonic seizure lasting for approximately 45 minutes. Postictally, the patient had Todd paralysis on the right side and global aphasia for 5 hours. One week later, the patient continued to be encephalopathy. Neurologic examination revealed mild right facial weakness and probable right homonymous hemianopsia. The MRI scan was within normal limit.
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FIGURE 477. Focal Polymorphic Delta Activity (PDA); Traumatic Brain Injury. An 8-year-old right-handed boy with traumatic brain injury. He was unconsciousness for 15 minutes and was aphasic for 4 days before recovering. He was found to have mild fright facial weakness and hemiparesis. Axial FLAIR image shows hyperintensity in the left temporal lobe (arrows) including mesial temporal region (open arrow). EEG reveals continuously diffuse polymorphic delta activity (PDA) and background attenuation in the left hemisphere, maximally expressed in the posterior head region. The combination of PDA and background attenuation is indicative of both gray and white matter lesion caused by head injury. Severe and acute focal processes are associated with greater variability (irregularity), longer duration of waves (slower frequency), and greater persistence of PDA. Slow waves at the center of the focus of PDA are usually more persistent and of lower frequency than slow waves at the periphery. PDA is often surrounded by theta waves (Fp1-F3 and C3-P3). Smooth PDA (flat polymorphism or flat PDA), concomitant loss of faster frequencies is very significant and indicative of both gray and white matter involvement.
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FIGURE 478. Improvement of Polymorphic Delta Activity; Associated with Clinical Improvement. (Same patient as in Figure 4-77) EEG performed 4 days later shows marked improvement in the left hemispheric PDA and disappearance of the right OIRDA consistent with resolution of the patient’s aphasia. Note reappearance of alpha rhythm, greater on the right.
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FIGURE 479. Polymorphic Delta Activity (PDA) and Background Asymmetry; Nanaccidental Trauma (NAT). EEG of an 8 weeks old girl with nonaccidental trauma (NAT). Diffuse low-voltage background activity is noted. There is depression of background activity over the right hemisphere with polymorphic delta activity (PDA) in the right temporal region. Brain CT with contrast enhancement shows acute hemorrhage with surrounding cerebral edema in the right temporal region. Also note slight midline shift to the left with brain edema in the left posterior quadrant. PDA is indicative of cerebral dysfunction affecting white matter tracts, which causes deafferent of the overlying cortex from its underlying white matter input. It is more prominent in acute than chronic lesions and in young children than in older patients, especially less than 5 years old. More severe and acute focal process is associated with greater variability (irregularity), longer duration of waves (slower frequency), and greater persistence. PDA near lesion is the slowest, least reactive, and has no superimposed beta activity. PDA at the center of the focus of slow wave activity is usually more persistent and of lower frequency than slow waves at the periphery. Smooth PDA (Flat polymorphism or Flat PDA; concomitant loss of faster frequencies) is indicative of involvement of both gray and white matter. Brain edema alone, even when extensive, does not appear to make a substantial contribution to the production of PDA unless it causes a functionally significant compression of midline structures.
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FIGURE 480. Focal Polymorphic Delta Activity (PDA) and Background Suppression; Sturge-Weber Syndrome. A 10-year-old girl with mental retardation, left hemiparesis, homonymous hemianopsia, glaucoma and medically intractable epilepsy (Jacksonian march) caused by Sturge-Weber syndrome. She had port-wine nevus on both sides of her face but much more prominent on the right side. Her left leg was 2 cm shorter than her right leg. She also had Klippel-Trenaunay syndrome (cutaneous vascular nevi on the right side of her body and extremities, hypertrophy of the right limbs). CT shows characteristic “tram line” calcification along the cortical gyri (arrow) with cerebral atrophy of the posterior aspect of the right hemisphere. She underwent right functional hemispherectomy and has been seizure free since. Leptomeningeal angiomatosis with enlarged regional veins, a hallmark of Sturge-Weber, was noted (Courtesy of Dr. M. Handler, Neurosurgery, The Children’s Hospital, Aurora, CO). EEG shows nearly continuous polymorphic delta slowing with a phase reversal in the right frontal temporal band background suppression in the right posterior regions. This finding is strongly supportive of underlying structural abnormality that is most likely caused by hypoxic change due to both obstruction of angiomatosis and lack of leptomeningeal vessels. These hemispheric EEG abnormalities are seen in infancy prior to development of intracranial calcification.23,92
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FIGURE 481. Sturge-Weber Syndrome; Decreased Benzodiazepine-Enhanced Beta Activity. (Same patient as in Figure 4-80) EEG after the treatment with intravenous benzodiazepine (lorazepam) to control the seizure shows suppression of beta activity and diffuse delta slowing in the right hemisphere that is ipsilateral to the facial nevus. Decreased diazepam-enhanced beta activity in the EEG is a sensitive criterion of functional abnormality. In patients with subtle structural abnormalities diazepam-enhanced EEG may have added value in diagnosing functional involvement and in monitoring disease progression in patients.34
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FIGURE 482. Lateralized Monorhythmic/Polymorphic Delta Activity; Acute Herpes Simplex Encephalitis Involving Left Mesial Temporal Region. A 7-year-old previously healthy boy who presented with high fever, lethargy, aphasia, right hemiparesis, and a new-onset secondarily GTCS. CSF examination showed mild lymphocytic pleocytosis with normal protein but slightly low glucose. Brain CT was unremarkable. EEG performed 2 hours after the lumbar puncture shows continuously diffuse monorhythmic and polymorphic delta activity over the left hemisphere with no evolving pattern. Brain MRI performed 18 hours later shows hyperintensity in the left mesial temporal region in an axial FLAIR sequence and hypointensity in the left mesial temporal in a coronal T1-weighted image (open arrow). The patient was treated with Acyclovir immediately in the ED. CSF PCR for HSV came back positive the next day after the MRI. During the earlier stages of the disease, the background activity is disorganized and localized or lateralized polymorphic delta activity develops with predominance over the involved temporal areas. Between 2 and 5 days after the onset of the disease, unilateral or bilateral periodic complexes (PLEDs or BiPLEDs), occurring every 1–3 sec develops. The periodic complexes last only 3–4 days, and almost always disappear in a week no matter what the clinical features are. On Occasion, the periodic complexes has been observed up to 24 and 30 days after the onset of the disease. EEG changes usually lag behind the clinical changes. MRI together with EEG was abnormal early in the disease stressing their significant role in any suspected case of HSE.93–95 The sensitivity of the EEG is approximately 84%, but the specificity is only 32.5 %. PCR detection of HSV DNA in the CSF has become the diagnostic method of choice. The sensitivity and specificity are 94% and 98%, respectively. The CSF remains PCR-positive for HSV DNA in more than 80% of cases even 1 week after the initiation of antiviral therapy in cases of HSE.96,97
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FIGURE 483. Unilateral Attenuation of Background Activity, PDA, and Sharp Wave; Acute Meningoencephalitis. A 15-year-old boy with an acute onset of low-grade fever, altered mental status, and inability to speak or walk. Neurological examination revealed signs of meningeal irritation, hyperreflexia of lower extremities, and aphasia. He developed a newonset seizure described as tonic stiffening with head and eyes deviating to the right side, choking, and cyanosis associated with desaturation. CSF showed mild lymphocytic pleocytosis. (A) Axial FLAIR shows signal abnormalities in the left lateral temporal and insula regions (open arrow). (B) Coronal T1-weighted image with GAD shows prominent enhancement of the left frontal-temporal region (arrows) compared to the homologous areas in the right hemisphere. EEG shows lateralized polymorphic delta activity (PDA) and monorhythmic delta activity (open arrow) in the left hemisphere, depression of alpha rhythm in the left occipital, depression of beta activity in the left frontal (double arrows at the right anterior beta), and sharp waves in the left frontal temporal regions (*). Also note diffuse low-voltage PDA in the anterior head region with preservation of alpha rhythm in the right hemisphere. The presence of PDA and depression of beta and alpha activities is supportive of underlying structural abnormalities (both gray and white matter) in the entire left hemisphere. In addition, the presence of sharp waves is consistent with active epileptiform activity in the left frontotemporal region. Low-voltage PDA over the right anterior head region may be caused by spreading of the PDA from the left homologous frontal region.
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FIGURE 484. Beta Suppression and Polymorphic Delta Activity (PDA); Right Mesial Temporal Sclerosis Due to Viral Encephalitis in Infancy. A 2-year-old girl with global developmental delay, right hemiparesis, and intractable epilepsy caused by viral encephalitis at the age of 1 year. Her typical seizure was described as spacing out and orofacial/hand automatisms. She presented to the ED with nonconvulsive status epilepticus. Coronal T2-weighted images show diffuse cerebral atrophy with increased signal abnormality in the right temporal region with right hippocampal atrophy (open arrow). EEG after the treatment with lorazepam and fosphenytoin shows significant suppression of beta activity over the right hemisphere but maximally expressed in the temporal lobe. In addition, there are polymorphic delta activity (PDA) and sharp waves in the in the right temporal lobe. The localizing value of PDA is greatest when it is topographically discrete and associated with depression of superimposed faster background activity.5,20,98 Superficial lesions produce more restricted EEG changes, whereas deep cerebral lesions result in hemispheric or even bilateral PDA.5
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FIGURE 485. Unilateral Background Attenuation & Low-Voltage Polymorphic Delta Activity; Severe Right Hemispheric Encephalomalacia. A 13-year-old girl with a history of severe traumatic brain injury at the age of 2 years. She has had mental retardation, profound left hemiparesis, and intractable epilepsy as consequences of the injury. MRIs reveal extensive encephalomalacia over the right hemisphere. EEG shows diffuse background EEG attenuation over the right hemisphere with low-voltage polymorphic delta activity (PDA) in the right central-temporal region. Characteristic findings of chronic lesions include marked attenuation and often total absence of rhythmic activities with or without subtle PDA over the involved hemisphere.
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FIGURE 486. Diffuse Delta Slowing with Occipital Predominance; Left Cerebral Hemiatrophy Due to Intraventricular Hemorrhage. A 20-month-old-boy with developmental delay, spastic diplegia and right hemiparesis, stable hydrocephalus, and focal epilepsy caused by grade 4 intraventricular hemorrhages in newborn. Cranial CT shows left cerebral hemiatrophy with VP shunt insertion in the left frontal region. EEG performed 12 hours after a secondarily GTCS showed asymmetrically diffuse delta slowing with occipital predominance, greater on the left. Posteriorly accentuated diffuse delta activity are usually seen after generalized seizure, febrile seizure, and head injury and rarely seen in white matter degenerative diseases such as metachromatic leukodystrophy or metachromatic leukodystrophy.46,47
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FIGURE 487. Occipital Intermittent Rhythmic Delta Activity (OIRDA) and Polymorphic Delta Activity (PDA); Subcortical Focal Cortical Dysplasia. A 4-year-old girl with medically intractable epilepsy due to focal cortical dysplasia. Her seizure was described as stiffening and clonic jerking of her left arm and leg. Cranial MRI reveals a large focal cortical dysplasia in the right temporal region causing dilatation of a temporal horn of left lateral ventricle (arrows). EEG during drowsiness shows constant rhythmic, high-voltage, 2.5–3.5-Hz delta activity (double arrows), intermixed with PDA (open arrow) in the right occipital region corresponding to the location of a subcortical focal cortical dysplasia. Focal PDA is seen in half of the patients with focal cortical dysplasia.100 Although the mechanisms remain unclear, it was hypothesized that focal PDA recorded over neocortical lesions is probably due to underlying white matter abnormalities rather than the lesion itself.101 Malformation of cortical development must be in the differential diagnosis of localized PDA.43 Intermittent rhythmic delta activity (IRDA) is generated by either cortex or deep gray matter. Persistent unilateral IRDA is usually associated with deep lesion. When present in association with focal cerebral lesion, it is usually indicative of the process that begins to produce an active widespread encephalopathy. Although frontal predominance is typical in adults, occipital predominance is more common in children less than 10–15 years; this is likely to be related to maturation rather than to any morphological abnormality. Although frequently bilateral, IRDA may occur predominantly unilaterally. Even when it occurs unilaterally in association with lateralized supratentorial lesion, the lateralization of the IRDA, although usually ipsilateral, may even be contralateral to the focal lesion. Therefore, when IRDA is present, determining whether it is due to a focal lesion will depend on persistent localizing signs, and not on the morphology or even the laterality of IRDA.102
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FIGURE 488. Temporal Intermittent Rhythmic Delta Activity (TIRDA); Subcortical Focal Cortical Dysplasia. (Same patient as in Figures 4-35 and 7-75) EEG shows rhythmic 2-Hz delta activity in the right posterior temporal region consistent with TIRDA. TIRDA is a unique EEG pattern that is highly pathognomonic for temporal lobe epilepsy. It is seen in drowsiness and light sleep in runs lasting 3–20 sec and often associated with ipsilateral interictal epileptiform discharges. TIRDA is considered an EEG marker of an epileptogenesis that involves the mesial structures of the temporal lobe and seen in approximately one fourth of patients undergoing presurgical workup for temporal lobe epilepsy.108,110–112
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FIGURE 489. Focal Spike-Wave Discharges & Intermittent Rhythmic Delta Activity; Right Precuneus Ganglioglioma. An 11-year-old boy with intractable epilepsy caused by a low-grade tumor. His seizures were stereotyped and described as vertigo, rotation of body counterclockwise, stiffening of the left arm with head and eyes deviating to the left side with or without secondarily GTCS. Interictal EEG during Laplacian run shows rhythmic delta activity intermingled with low-voltage spikes in the right centralparietal region. Coronal and axial MRIs show a lesion in the medial aspect of the right precuneus (arrow). Ictal SPECT shows maximal hyperperfusion in the area concordant with the lesion seen in the MRIs with some spreading to the right lateral parietal region. Pathology showed ganglioglioma grade 1. Intermittent rhythmic delta activity (IRDA) seen in the temporal region (TIRDA) is a hallmark EEG of mesial temporal lobe epilepsy, especially caused by mesial temporal sclerosis. IRDA seen in parietal lobe is not well established. In this patient, IRDA in the right central-parietal region, similar to TIRDA, is concordant with the most active epileptiform activity seen in the right central-parietal region.
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FIGURE 490. Asymmetric Frontal Intermittent Rhythmic Delta Activity (FIRDA); Intrauterine Stroke. A 15-year-old girl with mental retardation, right spastic hemiparesis, and intractable epilepsy due to intrauterine stroke. MRI reveals atrophy of left cerebral cortex, thalamus and midbrain. EEG shows asymmetric FIRDA with right hemispheric predominance and depression of background activity over the left hemisphere. Although frequently bilateral, IRDA may occur predominantly unilaterally. Even when it occurs unilaterally in association with lateralized supratentorial lesion, the lateralization of the IRDA, although usually ipsilateral, may even be contralateral to the focal lesion. Therefore, when IRDA is present, determining whether it is due to a focal lesion is bested on persistent localizing signs, and not on the morphology or even the laterality of IRDA.
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FIGURE 491. Ictal Aphasia; Intracranial Hemorhage Secondary to Malignant Hypertension. A 9-year-old girl with a sudden onset of altered mental status and right hemiparesis caused by malignant hypertension secondary to chronic renal failure associated with hemolytic uremic syndrome. Fifteen hours later, she was aphasic and developed intermittent clonic jerking of her right arm. MRI shows large hemorrhage in the left frontal-parietal region with mass effect. EEG demonstrates continuously diffuse semirhythmic delta activity in the left hemisphere with posterior predominance. After the treatment with intravenous lorazepam, the patient showed dramatic improvement in her clinical symptoms accompanied by resolution of the semirhythmic delta activity in the left hemisphere. This electroclinical feature confirmed the diagnosis of seizure as a cause of aphasia and right arm clonic jerking.
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FIGURE 492. Temporal Intermittent Rhythmic Delta Activity (TIRDA); Dual Pathology (Ganglioglioma with Secondary Mesial Temporal Sclerosis). A 7-year-old girl with medically intractable epilepsy caused by ganglioglioma. (A) Sagittal T1-weighted MRI shows mixed cystic and hyperintense lesions in the left mesial temporal lobe (arrow). (B) Coronal T2-weighted MRI showed left hippocampal atrophy with increased signal intensity (double arrows).These MRI findings are compatible with dual pathology and ganglioglioma with secondary hippocampal sclerosis. Interictal EEG showed semirhythmic delta activity intermixed with low-amplitude spikes with phase reversal in the left midtemporal region. Temporal intermittent rhythmic delta activity (TIRDA) is an EEG pattern characterized by sinusoidal trains of activity, ranging from 1 to 3.5 Hz, and well localized over the temporal regions. It is often associated with temporal spikes or sharp waves. TIRDA represents an important epileptogenic abnormality and is associated with temporal lobe epilepsy. TIRDA can be differentiated from polymorphic delta activity, in which frequencies and amplitudes are more variable.103–106
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FIGURE 493. Temporal Intermittent Rhythmic Delta Activity (TIRDA); Temporal Lobe Epilepsy. (Same patient as in Figure 9-71) A 12-year-old boy with medically intractable focal epilepsy due to focal cortical dysplasia (FCD) in the right hippocampus. His seizure is described as spacing out with orofacial and/or hand automatisms with or without GTCS. EEG shows rhythmic 2.5 Hz delta activity intermingled with spikes (asterisk) in the right midtemporal region consistent with TIRDA (temporal intermittent rhythmic delta activity). TIRDA represents an important epileptogenic abnormality. TIRDA was observed in 52 out of the 129 (40.3%) patients with temporal lobe epilepsy.105 Significant correlations were found between TIRDA and (1) mesial and mesiolateral TLE, (2) mesial temporal sclerosis, (3) interictal epileptiform discharge localized over the anterior temporal regions, and (4) 5–9 Hz temporal ictal discharge. TIRDA plays a role in localizing the epileptogenic zone, suggesting that this pattern might be considered as an EEG marker of an epileptogenesis that involves the mesial structures of the temporal lobe.
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FIGURE 494. Temporal Intermittent Rhythmic Delta Activity (TIRDA); Right Occipital Ganglioglioma with Dual Pathology (Hippocampal Sclerosis). A 9-year-old right-handed boy with medically intractable epilepsy caused by right occipital ganglioglioma with dual pathology (secondary mesial temporal sclerosis). His typical seizure was described as orofacial automatisms without altered mental status that is a characteristic semiology of nondominant mesial temporal seizure. (A) Axial FLAIR sequence reveals increased signal intensity and decreased volume in the right hippocampus (open arrow). (B) Coronal T1-weighted MRI shows enhanced lesion with dural sign in the right occipital region (double arrows). EEG during Laplacian run shows semirhythmic 1.5–2 Hz delta activity in the right midtemporal region consistent with TIRDA pattern (arrows). TIRDA is an EEG marker of epileptogenic zone localizing in the mesial temporal lobe and strongly supportive of the diagnosis of mesial temporal sclerosis as a cause of seizures.103,105
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FIGURE 495. Breach Rhythm; Prominent Mu Rhythm. A 9-year-old boy with a history of right occipital ganglioglioma resection. T1-weighted coronal and sagittal MRIs with GAD reveal skull defects and an area of previous surgical resection (arrow head). EEG during wakefulness with eye opening shows frequent runs of asymmetrical rhythmic 9 Hz arc-like activity in the central regions that is higher in amplitude on the right side.
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FIGURE 496. Breach Rhythm; Prominent Mu Rhythm. (Next EEG page of the same patient as in Figure 4-95) The arc-like activity in the central regions is attenuated by left hand movement. This is consistent with mu rhythm that can become very prominent beneath a skull defect. Sometimes, mu rhythm can simulate ictal EEG activity, especially in patients with skull defects; therefore, activating procedures, especially limb movement, is very important to differentiate mu rhythm from epileptiform activity.
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FIGURE 497. Breach Rhythm; Asymmetric Lambda Waves: EEG of a 16-year-old boy who had had a right frontal-temporal resection for intractable epilepsy. A waking EEG shows a breach rhythm (enhancement of lambda waves) (*) in the right occipital region and focal polymorphic delta and theta activity.
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FIGURE 498. Breach Rhythm; Focal Enhancement of Beta Activity; Polymorphic Delta Activity (PDA). (Same patient as in Figure 9-46 to 9-51) EEG of a 15-year-old girl who underwent two-step epilepsy surgery of the epileptogenic zone in the left parietal region. There is enhancement of beta activity in the F3 electrode (arrow head) and polymorphic delta activity (PDA) in the left parietal region (open arrow). Enhancement of beta activity is maximal nearest a margin of a skull defect with a board voltage distribution and can be as much as threefold of normal beta activity.5,107,108 PDA reflects structural abnormality of the white matter underneath the resective area.
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FIGURE 499. Focal Enhancement of Beta Activity; Focal Cortical Dysplasia. A 20-month-old boy with global developmental delay and a new-onset seizure described as prolonged clonic jerking of his left arm with secondarily GTCS. MRI showed a focal cortical dysplasia in the right superior temporal gyrus adjacent to posterior sylvian fissure. EEG shows very frequent runs of medium voltage beta activity in the right posterior temporal region. Contrary to localized attenuation of beta activity, focal enhancement of beta activity without skull defect is rare. It has been described in structural abnormalities including brain abscess, stroke, arteriovenous malformations, tumors, and focal cortical dysplasia.5
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FIGURE 4100. Focal Enhancement of Rhythmic Beta and Alpha Activities; Focal Cortical Dysplasia. A 3-year-old boy with intractable epilepsy described as left focal motor or hypermotor seizures with or without GTCS and drop attack. Coronal and axial MRIs show thickened and smooth cortex with blurred gray-white matter junction in the right frontal region. EEG reveals enhancement of rhythmic alpha and beta activities and spikes at the F4 electrode. Also note diffuse polymorphic delta activity (PDA) over the right hemisphere, maximally expressed in the midtemporal region. Rarely, the amplitude of the background activity, especially beta activity, is seen higher on the side of focal cerebral lesions without a skull defect.109 These conditions include focal cortical dysplasia, abscess, stroke, AVM, and tumor. Continuous, near continuous, or long trains of localized spikes or rhythmic sharp waves occur in 44% of patients with focal cortical dysplasia.110 Eighty-six percent of patients with focal cortical dysplasia had localized PDA, suggesting a structural lesion.43 Localized PDA recorded over neocortical lesions is due to underlying white matter abnormalities rather than the lesion itself. Developmental abnormalities affecting gyri may be associated with underlying changes in the white matter.111 Malformations of cortical development must be in the differential diagnosis of localized PDA.100
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FIGURE 4101. Ipsilateral Enhancement of Beta Activity; Polymicrogyria with Closed-lip Schizencephaly. EEG of a 13-year-old girl with focal epilepsy and mental retardation due to polymicrogyria (double arrows) with closed-lip schizencephaly (open arrow). EEG shows a run of focal enhancement of beta activity in the Fp2-F4 channel (arrow head). Rarely, the amplitude of the background activity, especially beta activity, is seen higher on the side of focal cerebral lesions without a skull defect.109 These conditions include focal cortical dysplasia,43,112 abscess,114,.115 stroke, AVM, and tumor.108,113,114
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FIGURE 4102. Focal Enhancement of Beta Activity; Low Voltage Fast Activity; Focal Transmantle Dysplasia. A 9-month-old boy with medically intractable epilepsy due to focal transmantle dysplasia in the right frontal region (arrow). Interictal EEG during Laplacian montage run demonstrates focal attenuation of background activity with superimposed low-voltage 18/sec beta activity in the right frontal-anterior temporal region (arrows). The epileptic foci are compatible with the location of the cortical dysplasia. This focal low-voltage fast activity is similar to the activity during subdural EEG recording. It is more commonly seen in infant due to thinner skull and scalp. Focal transmantle dysplasia is a malformation of cortical development that extends through the entire cerebral mantle, from the ventricular surface to the cerebral cortex. The presence of balloon cells suggests that these malformations are associated with maldifferentiation of the stem cells generated in the germinal zone.115
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FIGURE 4103. Ipsilateral Enhancement of Beta Activity and Polymorphic Delta Activity; Periventricular Leukomalacia with Focal Cortical Dysplasia. A 2-year-old righthanded boy who was born 24-week GA with grade 4 intraventricular hemorrhage (IVH). He subsequently developed hydrocephalus and required VP shunt that was inserted through the right frontal region. He also had global developmental delay and left hemiparesis. His typical seizure was described as head and eyes deviation to the left side and tonic stiffening of upper and lower extremities with left arm extension and right arm flexion. MRI shows periventricular leukomalacia with diffuse cerebral atrophy, greater in the right hemisphere. Also note thickening of the gray matter in the right frontal region that is consistent with focal cortical dysplasia (open arrow). EEG shows enhancement of low-voltage beta activity in the right frontal region (double arrows) that is concordant with the lesion seen in the MRI scan (open arrow). In addition, constant polymorphic delta activity is noted in the right prefrontal region (Fp2). Rarely, the amplitude of the background activity, especially beta activity, is seen higher on the side of focal cerebral lesions without a skull defect.109 These conditions include focal cortical dysplasia, abscess, stroke, AVM, and tumor.5 Eighty-six percent of patients with focal cortical dysplasia had localized PDA, suggesting a structural lesion.43 Localized PDA recorded over neocortical lesions is due to underlying white matter abnormalities rather than the lesion itself. Developmental abnormalities affecting gyri may be associated with underlying changes in the white matter.111 Malformations of cortical development must be in the differential diagnosis for localized PDA.100
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FIGURE 4104. Enhancement of Alpha and Beta Activity; Intrinsic Epileptogenicity of Focal Cortical Dysplasia (FCD). A 4-week-old boy with very frequent seizures described as epileptic nystagmus and versive seizures. MRI demonstrates thickened cortex and decreased normal cortical gyration over the left occipital region (arrow). EEG shows very frequent runs of rhythmic sharply contoured/sinusoidal 12-13/sec activity with phase reversal at P3. FCD has intrinsic epileptogenicity with unique EEG patterns including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.116 The incidence of intrinsic epileptogenicity in FCD was 11–20% in different series.43,100,110,117
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FIGURE 4105. Ipsilateral Diffuse Rhythmic Alpha Activity; Polymicrogyria and Close-Lip Schizencephaly. (Same patient as in Figure 4-101) EEG of a 13-year-old girl with focal epilepsy and mental retardation due to polymicrogyria (double arrows) with closed-lip schizencephaly (open arrow). There is consistently diffuse rhythmic 12 Hz alpha activity in the right hemisphere with some spreading to the anterior head region of the left hemisphere. Persistent focal rhythmic alpha or theta activity is indicative of focal structural abnormalities.
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FIGURE 4106. Asymmetric Epileptic Spasms; Aicardi’s Syndrome with Focal Cortical Dysplasia. A 14-month-old right-handed girl with asymmetric infantile spasms with spasms predominantly on the right side associated with Aicardi syndrome. MRI shows focal cortical dysplasia (FCD) in the right posterior head region (arrow). Interictal and ictal SPECT demonstrate hypoperfusion (solid arrow) and hyperperfusion (double arrows), respectively, in the same region as FCD seen in the MRI. Interictal EEG shows hemispheric asynchrony due to agenesis of corpus callosum, background suppression with superimposed low-voltage fast activity in the right temporaloccipital region, and temporal sharp waves in the right temporal region. The patient was free of disabling seizure after the resection of epileptogenic zone in the right temporal occipital region.
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5
389
General principle 䡲
䊳
Poor prognosis 앫 Triphasic waves (TWs). 앫 Alpha coma (AC) patterns in patients with anoxic encephalopathy nonreactive to noxious stimuli. 앫 Continuously diffuse polymorphic delta activity (unless due to a toxic/metabolic disturbance) typically bodes poorly for the patient, when these patterns are low voltage. 앫 Marked bilateral suppression coma. 앫 Burst-suppression (B-S) patterns.
䊳
Better prognosis: 앫 Spindle coma (SC) patterns
The EEG is unable to distinguish between different etiologies. The major usage of the EEG is to determine the severity of encephalopathy, prognosis, and response of treatment.
䡲
Common etiology: 䊳 Metabolic, toxic, inflammation, anoxic, and degenerative diseases 䡲 Few EEG patterns associated with more specific etiologies for the encephalopathy: 䊳 Periodic pattern: 앫 Anoxic encephalopathy 앫 Certain encephalitis 䊳
Generalized Nonepileptiform Activity
䡲
Triphasic waves (TWs) or 14- and 6-Hz positive spike bursts: 앫 Metabolic encephalopathy Lithium and ifosphamide toxicity
䊳
High-voltage beta activity: 앫 Benzodiazepine or barbiturate intoxication
䊳
Low-voltage fast patterns: 앫 Alcohol withdrawal
䊳
Bursts of high-voltage delta activity interspersed with mixed frequencies: 앫 PCP (angel dust) intoxication
Prognosis in most EEG patterns is usually correlated with underlying diseases and reactivity of EEG to external stimuli. 䊳
䡲
앫 Spontaneous variability 앫 Evidence of EEG reactivity to painful stimulation ⽧ Reduction
䊳
of amplitude, increase in frequency, and reduction in the slow activity ⽧ Paradoxical activation, which is a period of more severe delta slowing following painful stimuli Severe encephalopathy: 앫 Invariant EEG—no spontaneous variability or
reactivity to external stimuli 䡲
Ischemic strokes and anoxic ischemia after cardiorespiratory arrest are almost completely irreversible.
Brain injury produced by head trauma, subdural hemorrhages, and some intracranial hemorrhages, in the absence of raised intracranial pressure, may be partially, moderately, or occasionally wholly reversible. 䊳 Electrical disturbances with seizures and status epilepticus (SE), metabolic, and some toxic encephalopathies may be completely reversible. 䡲 Some particular patterns have been identified that may have some prognostic significance:
앫 Beta coma Severity: 䊳 Milder encephalopathy:
Combination of diffuse and focal EEG abnormalities: 䊳 Associated focal process such as old infarction or tumor 䊳 Nonketotic hyperosmolar coma 䊳
䊳
䊳
Focal seizure Herpes simplex encephalitis and Creutzfeldt-Jakob disease (CJD)
Selected specific conditions Drug intoxication 䡲
Generalized theta-delta activity with superimposed beta frequency activity is highly characteristic of sedative drug intoxication.
390
䡲
䡲
䡲
앫 Extremely poor prognosis.
With more severe intoxication, the fast activity shows a slower frequency (10–13 Hz), widespread distribution, but anterior predominance.
䡲
䡲
In the absence of prominent slow activity, the anterior-dominant generalized fast activity caused by sedative drug intoxication produces an alpha and SC pattern in the EEG that is indistinguishable from that seen with severe anoxic encephalopathy.
(without significant slower frequencies) 앫 EEG resembles that of an “awake” person except: ⽧ More
widespread ⽧ More prominent over the anterior head regions ⽧ No
앫 Prognosis is extremely poor in anoxic
encephalopathy 앫 Also present in other conditions besides anoxic
encephalopathy: ⽧ Sedative/hypnotic drug intoxication (best prognosis) ⽧ Intrinsic brainstem lesions
B-S pattern or electrocerebral silence (ECS) does not carry as ominous prognosis as when they occur in the setting of cardiopulmonary resuscitation. Common EEG patterns: 䊳 Delta coma pattern 䊳 Periodic discharges
䊳
앫
앫 앫
䡲
High-amplitude periodic complexes that are bilateral, usually synchronous, and symmetrical. 䡲 Remarkably stereotyped and consists of two or more delta waves with or without sharp waves. 䡲 Repeatedly every 4–10 sec. 䡲
One-to-one relationship with myoclonic jerks, when present. 䡲 May be seen only in sleep. 䡲
In early stages, there is asymmetry of the periodic complexes.
EEG pattern in diffuse nonepileptiform abnormalities
앫 At times, B-S associated with eye opening with
䡲
release phenomenon remains unknown. This movement may sometimes cause doubt about the patient’s state of consciousness, as they may mimic volitional motor activity 䊳
Subacute Sclerosing Panencephalitis (SSPE)
Excessive beta activity (Figures 5-1 to 5-8, 5-53)
앫 Whether this is an epileptic event or a brainstem
앫 Although involvement of cortical gray matter
Although PLEDs are not diagnostic of HSE, they are strongly suggestive of HSE in association with an acute febrile episode focal seizures, and CSF pleocytosis.
B-S pattern brief body movement
PLEDs or BiPLEDs (periodic lateralized epileptiform discharges or bilateral independent lateralized epileptiform discharges):
앫
reactivity
앫 Prognosis is mainly based on etiology
EEG should be done at least 5–6 hours after resuscitation.
may play a role in generalized periodic patterns, cortical isolation is not critical or not only mechanism for these EEG patterns. A recent stroke was the most frequent cause of PLEDs (33%), while anoxic encephalopathy (28%) and CNS infection (28%) accounted for the majority of BiPLEDs. Focal neurologic deficits, focal seizures, and focal computed tomographic scan abnormalities were frequent in those with PLEDs, while coma predominated in the group with BiPLEDs (72% vs. 24%). Mortality was also higher in patients with BiPLEDs—61% versus 29% compared to PLEDs. Often associated with myoclonic seizure.
Alpha coma pattern 앫 Coma associated with alpha frequency activity
Phencyclidine (PCP) or ketamine is associated with a distinctive EEG pattern similar to that of subacute sclerosing panencephalitis (SSPE).
䊳
䡲
앫 No treatment. 䊳
Anoxic encephalopathy 䡲
5
Generalized Nonepileptiform Activity
Suppression
Amplitude exceeding 20 μV is seen in only 1% of normal children. 䡲 Beta activity is predominant in anterior head regions in children older than 6 years of age and is maximum posteriorly in younger children. 䡲
Excessive beta activity, in the absence of medication (phenobarbital/benzodiazepine): 䊳 Seen in chronic, diffuse encephalopathy. 䊳
Encephalitis Herpes Simplex Encephalitis (HSE) 䡲 PLEDs—focal or unilateral quasiperiodic pattern with regular intervals of 1–3 sec 䡲 Large-amplitude sharp-wave complexes 䡲
䊳
䊳
Maximum over involved temporal lobe
䡲
Occurs 2–15 days after the onset of illness 䡲 BiPLEDs—with bilateral involvement, periodic complexes may occur over both hemispheres, either synchronously or independently.
䊳
Diffuse cerebral atrophy is seen in 75% of patients whose EEGs contained beta activity exceeding 20 μV but only 5% of children without excessive beta activity had cerebral atrophy. Mental retardation and behavioral disturbances were greater among those with excessive beta. Runs of 16- to 24-Hz, 20- to 50-μV waves also occurs in association with degenerative diseases of white matter. Diffuse excessive beta bands along with theta and alpha bands are characteristic of lissencephaly, especially type 1.
5 Background slow activity (Figures 5-9, 5-11 to 5-20, and 5-49 to 5-52) 䡲
Slowing of posterior background activity. 䡲 Very sensitive index of mildly nonspecific or mildly to moderately diffuse encephalopathy.
Generalized Nonepileptiform Activity
activity of fixed frequency (close to 2.5 Hz) with more rapid ascending than descending phase 䡲 Pathogenesis/pathophysiology:
Abnormal sleep architecture 䡲
Suppression of sleep architecture: 䊳
䡲
Extreme spindles: 䊳 70–80% are found in cognitively subnormal patients 䊳 Higher voltage (100–400 μV) 䊳 䊳
䡲
In patients with a static encephalopathy, suppressed V waves and spindles were most severe in quadriparetic children and asymmetric among hemiparetic children.
More persistent and more widespread Peak at 3 years and decline at 6 years
Frequency-amplitude gradient (FAG): 䊳
䊳 䊳
Sharp decline in voltage of delta from occipital to frontal regions in normal children in stage 2–4 sleep Not fully develop until 3–4 months Absence of the gradient seen in moderate to marked neurological disease
Diffuse intermittent slow activity 䡲
Delta activity in the awake tracing is rarely seen after the age of 5 years. 䡲 Mild, diffuse, nonspecific cortical/subcortical dysfunction.
Diffuse intermittent rhythmic delta activity (IRDA) (Figures 5-21 to 5-31) FIRDA/OIRDA 䡲 Definition: 䊳 Bursts/runs of high-voltage, bisynchronous (sinusoidal or sawtooth wave), rhythmic delta
391
䊳
Only partially understood.
䊳
Associated with diffuse gray matter disease both in cortical and in subcortical locations.
䊳
Dysfunction (but not complete disruption) of the thalamocortical circuit (especially dorsal-medial thalamus): 1. Overactive thalamocortical circuits
2. Some degree of cortical pathology Clinical correlation: 䊳 Widespread brain dysfunction. 䊳 Mild to moderate degree of encephalopathy. 䊳 Earliest symptoms—fluctuating levels of alertness and attention. 䊳 Represents active fluctuating, progressing, or resolving widespread brain dysfunction. As the condition progresses, often leading to more persistent, bilateral abnormalities, frank alteration in consciousness appropriate to the degree of persistent bilateral abnormalities is seen. 䊳 Less likely to be associated with chronic, stable brain dysfunction. 䡲 Etiology: 䊳 Abnormal interaction between cortical and subcortical neuronal systems. 䊳 Nonspecific in etiology with a wide variety of pathologic processes. 䊳 Seen in normal individuals during hyperventilation. 䊳 Found in diverse systemic and intracranial processes varying from systemic, toxic, and metabolic disturbances to focal intracranial lesions. Even when associated with a focal lesion, IRDA by itself is nonlocalizing. 䊳 With focal lesions, the mechanism may be sufficiently distort of the brain to produce secondary disturbances at both the subcortical and cortical levels. With primary intracranial 䡲
䊳
䊳
encephalopathy, it appears to be due to widespread involvement of the gray matter at subcortical and cortical levels. Ipsilateral IRDA is not only associated with an ipsilateral deep lesion but also can be contralateral to the focal lesion. Therefore, when IRDA is present, lateralization of the lesion should not be based on morphology or even the laterality of the IRDA. Typically occur with structural brain disease, midline abnormalities, obstructive hydrocephalus in posterior fossa lesion, or bihemispheric disease.
Increased ICP alone (such as pseudotumor cerebri), unless severe enough to produce secondary disturbance in cerebral circulation, does not produce IRDA. 䊳 When background activity is present and there is reactivity, the prognosis is good. 앫 No longer conceptionalized as “projected rhythm,” caused by deep midline lesions 䡲 Age: 䊳
䊳 䊳 䊳
䡲
Under 10–15 years: OIRDA. Adult: always FIRDA. The difference in the location of OIRDA and FIRDA is more likely due to “maturation-related spatial EEG features” rather than etiology.
Activation: 䊳 IRDA is accentuated by eye closure, hyperventilation, or drowsiness, disappears in stage 2 and deeper sleep stages, and reappears again in REM. 䊳
Attenuated with eye opening and alerting.
Diffuse continuous slow activity (Figures 5-35 to 5-43, 5-54, 6-1 to 6-4, 6-30) 䡲
Continuous, nonrhythmic, irregular slow activity. Severe diffuse encephalopathy. Patients are always in stupor or coma. 䡲 Nonreactive to external stimuli. 䡲 Caused by disturbance of interneuronal connections. 䡲
392
䡲
Cortical in origin and due to disruption of corticocortical and thalamocortical relationships. 䡲 White matter is always involved and causes cortical deafferentation.
䡲
Sharp waves, spikes (alone or associated with slow waves), or more complex wave forms occurring at periodic intervals.
䡲
PLEDs are associated with acute processes and occur transiently, typically between 2 and 20 days following the insult, and often occur with recent seizures from the surrounding structural abnormality. The prognosis depends on the underlying etiology.
䡲
Bilateral mesencephalic reticular formation and bilateral hypothalamic lesions in cats produce continuous PDA. This PDA is similar to focal polymorphic delta activity (PDA). produced by white matter lesions. 䡲 Disease processes that extensively involved hemispheric white matter or white and gray matter. 䡲 The generalized monomorphic slow complexes are considered a more severe manifestation of cerebral damage than polymorphic delta activity (PDA). 䡲
A defect in cholinergic pathways may play a role in pathological slow waves.
Posterior or Posteriorly Accentuated Diffuse Delta Activity 䡲
Bilateral delta involving the occipital and adjacent regions, with at least some preservation of background rhythms: 䊳
䊳
䊳
Usually does not imply a posterior structural lesion in children Appears several days after generalized tonic-clonic seizure Any process producing a diffuse encephalopathy
䊳
Metabolic and electrolyte derangements in a child with possible full resolution During the first week of febrile convulsions
䊳
First day after TBI
䊳
White matter degenerative disorders such as metachromatic leukodystrophy
䊳
Periodic pattern Periodic Lateralized Epileptiform Discharges (PLEDs) (Figures 6-8 to 6-11) 䡲 PLEDs are usually seen in acute, large, destructive, and widespread cortical processes and represent a confluent, although heterogeneous, area of cortical dysfunction.
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Generalized Nonepileptiform Activity
䡲
Mesial temporal sclerosis and familial hemiplegic migraine are rare causes of PLEDs.
䡲
The correlation between findings on neuroimages and PLEDs localization was excellent.
䡲
Patients lacking an acute structural lesion included the chronic PLED group and the alcohol-related group, as well as the cases of CJD, adenoviral encephalitis, hypertensive encephalopathy, familial hemiplegic migraine, Hashimoto’s encephalopathy, and two cases in which an acute anoxic or metabolic insult “triggered” PLED formation ipsilateral to a remote cerebral lesion.
䡲
PLEDs are usually associated with seizures (80–90%), mostly partial motor seizures; therefore, all patients with PLEDs should be treated with anticonvulsants.
䡲
“PLEDs Plus,, characterized by PLEDs admixed with high-frequency, low-voltage “polyspike” rhythms, is a rarer pattern associated with rapid, rhythmic, predominantly frontal discharges. This pattern is highly associated with seizures. Rhythmic buildup of PLEDs-plus is thought to precede seizures.
䡲
PLEDs are generally considered an interictal pattern, but this issue remains debatable.
䡲
Seventy-three percent of children found to have PLEDs on continuous EEG monitoring in the ICU experienced NCSE, despite what was clinically felt to be adequate anticonvulsant treatment. Absence of EEG reactivity increases the risk of NCSE.
䡲
Variations of PLEDs that can be seen in the same EEG as PLEDs, include:
䡲
Periodic lateralized epileptiform discharges are almost exclusively transient in nature, rarely persisting for more than a few weeks. They evolve and abate over an average 2-week time frame, with wave forms becoming progressively less complex and frequent over time. Rare chronic PLEDs, persisting for a period of 3 months to more than 20 years, have been reported in patients with chronic brain lesions and associated partial seizure disorders. 䡲 PLEDs could be the EEG manifestation of an abnormal response of neurons, which changes their excitatory neurotransmission in cases of acute brain lesion. The cells would either recover and respond normally or die after a period of time, no longer responding, and thereby leading to the disappearance of PLEDs in the EEG. Thus, they could be considered a nonspecific result of acute partial and transient functional denervation in a localized area of the cortex. 䡲 While an acute cortical lesion is the most common structural substrate of PLEDs, subcortical lesions, chronic lesions, and nonlesional scans are not uncommon in these patients. 䡲
䡲
Chronic PLEDs have also been reported in patients with chronic epilepsy, although most of them had chronic brain lesions. An acute structural lesion was evident in 71%. Acute ischemic stroke is the most frequent pathology, followed by tumor and central nervous system (CNS) infection, particularly acute herpes simplex virus (HSV) encephalitis. Periodic lateralized epileptiform discharges are reportedly frequent with hemorrhagic transformation of a cerebral infarct and with embolic infarcts.
䊳
BiPLEDs.
䊳
TriPLEDs.
䊳
Multifocal PLEDs.
䊳
Midline distribution (periodic epileptiform discharges in the midline: PEDIMs)
䊳
MEG-SPECT study showed that PLEDs originated from the hypoperfused cortex surrounding the lesion.
5 䊳
Most commonly caused by multifocal or diffuse cerebral injury, such as anoxic encephalopathy and CNS infection, having a poorer prognosis with a mortality of 52%, twice that of PLED patients.
䊳
䊳
䡲
䡲
May be classified as periodic short-interval diffuse discharges (PSIDDs) and suppression-burst pattern. Periodic long-interval diffuse discharges (PLIDDs) are the discharges with the interval duration 4–30 sec. 䡲 PSIDDs are discharges with an interval duration 0.5–4 sec. They occur in hypoxic or hepatic encephalopathy, drug toxicity, and degenerative disorders such as CJD. Generalized Periodic Epileptiform Discharges (GPEDs) (Figure 5-67, 6-19 to 6-21) 䡲 Definition: generalized, synchronous, periodic, or near-periodic complexes that occupied at least 50% of a standard 20-minute EEG. They may be spikes, polyspikes, sharp waves, sharply contoured slow waves, or a mixture of spikes and slow waves. The waves may be monophasic, biphasic, or triphasic. Typically, they are of high amplitude (100–300 μV) and occur at intervals of 0.3 sec to several seconds. Periodicity may be metronomic or almost periodic (pseudoperiodic). Morphology of GPEDs in the SE was variable and consisted of sharp/spike and slowwave complexes, triphasic-like waves, and slow-wave complexes. 䡲 Pathology and pathophysiology: 䊳 Cortical and subcortical gray matter and white matter lesions (5 out of 9 patients), cortical and
393
subcortical gray matter lesions (3/9), and a cortical gray matter lesion (1/9); none had only white matter lesions alone.
Despite advances in neurocritical care, the morbidity and mortality associated with PLEDs has changed little since their recognition four decades ago. This was even more striking in the BiPLED group, where the mortality rate was 52%.
Bilateral Independent Periodic Lateralized Epileptiform Discharges (BiPLEDs) (Figures 6-12 to 6-16) 䡲 PLEDs that are bilateral, generally asynchronous, and usually differ in amplitude, morphology, repetitive rate, and the site of maximum involvement. 䡲
Generalized Nonepileptiform Activity
Cortical involvement is necessary in the pathogenesis in both BiPLEDs and GPEDs in patients with hypoxic encephalopathy. Abnormal interactions between the ‘‘deranged cortex’’ and deeper ‘‘triggering’’ structures to increased local cortical irritability, possibly with involvement of normal and abnormal intracortical circuits.
䡲
An abnormal functional state in the CNS permitting rapid generalization of neuronal discharges.
䡲
Brainstem structures were suggested to act as a pacemaker in SSPE. GPEDs may arise from a subcortical source in CJD.
䡲
Although GPEDs cannot be used in isolation to make decisions regarding treatment and prognosis, when associated with suppression-burst pattern, they are indicative of poor prognosis.
Cause: 䊳
A wide variety of cerebral insults, and there is no generalization regarding etiology, treatment, and prognosis.
䊳
Toxic/metabolic encephalopathy (28%).
䊳
Anoxic with toxic/metabolic encephalopathy (40%).
䊳
䊳
Triphasic Waves (TWs) (Figures 5-32 to 5-34, 6-49) 䡲
Primary neurologic disorders—seizures, ICH, dementia, stroke with seizures, TBI and seizures (32%).
High-voltage positive sharp transients that are preceded and followed by negative waves of relatively lower voltage with repetitive rate of 1–2 Hz.
䡲
When GPEDs are seen in the EEG, the patient should carefully be checked for metabolic abnormalities and/or infectious diseases and intracranial lesions. Consciousness was impaired and clinical conditions were poor in all of the patients with GPEDs.
Many of the morphologies in typical patterns of “triphasic wave encephalopathy” may be biphasic with surface positively of the initial phase of the biphasic waveform.
䡲
Rarely seen in <20 years old.
䡲
Anterior predominance with anterior-posterior lag of the positive component of the TWs from the anterior to the posterior region (progressive time lag of 20–140 msec). However, occasionally, they may show posterior-anterior lag and even be relatively unilateral.
䡲
The frequency of these repeating patterns is 1–2 Hz, and they may vary from appearing as single TWs occasionally during the recording, to pairs, triples, brief runs of the activity, or all the way to continuous patterns.
䡲
Although earlier reports emphasized the TWs were highly specific for hepatic encephalopathy, this EEG pattern has been found to correlate best with any metabolic types of encephalopathy such as hepatic, renal, and anoxic etiologies, which account for over 75% of the EEGs with TWs.
䊳
SE was noted in 32%.
䊳
Structural lesions were found in most patients with GPEDs, but concurrent metabolic abnormalities and/or infectious diseases were also detected.
䡲
Whether GPEDs represent an EEG pattern of SE is debated. It may be a terminal EEG pattern in anoxic encephalopathy and represent severe brain damage rather than SE.
䡲
GPEDs have been described in NCSE:
䡲
be necessary, especially when GPEDs with very low inter-GPED amplitude are seen. On the other hand, 43% of patients with toxic/metabolic encephalopathy and 64% with primary neurologic process with GPEDs survived.
䊳
GPEDs with SE have higher amplitude, longer duration, and less inter-GPED amplitude.
䊳
GPEDs are associated with SE in 32%.
GPEDs after an anoxic encephalopathy carried a poor prognosis for survival. Aggressive treatment may not
394
䊳
䊳
䊳
䊳
TWs are also seen in lithium, ifosfamide, tricyclic, and baclofen toxicity, neuroleptic malignant syndrome, and serotonin syndrome. Prognosis is dependent on etiology, although TWs show overall poor prognosis (in one series, more than two-thirds of patients died). Occasionally, TWs are very difficult to differentiate from NCSE, especially when they appear with a frequency exceeding 1.0/sec. They may therefore straddle the border zone between epilepsy and encephalopathy. When background activity is present and when reactivity to external stimuli can be demonstrated, the prognosis is usually good, especially with reversible toxic/metabolic dysfunction. When seen in the setting of closed head trauma or anoxia, the prognosis is poor.
comatose children. There was a clinically significant better outcome with reactive rhythmic coma patterns. 䡲 Comatose children with reactive electroencephalographic patterns have better clinical outcome in terms of morbidity and mortality. Alpha Frequency Pattern (Alpha Coma) 䡲 Seen diffusely in comatose patients. 䡲 When coma arises from a brainstem lesion, the alpha activity is seen more posteriorly and varies often with external painful stimuli; the prognosis is poor. 䡲
When alpha frequency patterns are seen with anoxia after CRA, alpha frequencies appear more diffusely on EEG and are usually less reactive to external stimuli. Such patients also have a poor prognosis with mortality exceeding 90%.
䡲
Outcome of AC pattern depends on the underlying cause of coma. Reactive AC usually occurs after drug overdoses and lead to recovery in 90% of patients. At the opposite end of the spectrum, survival after CRA is 12% or less.
Rare but unique finding. 䡲 First described in rare patients with Reye syndrome. 䡲
䡲
One type of rhythmic pattern changed to another. 䡲 Reactive rhythmic coma is associated with favorable outcome in 67%. 䡲 Sixty percent with nonreactive pattern were associated with unfavorable outcome. 䡲 Rhythmic coma patterns in comatose children are not uncommon. The etiology, reactivity, and outcome of individual patterns are similar and thus make the rhythmic coma patterns distinct EEG signatures in
䡲
These patterns are usually seen with more advanced states of encephalopathy, either predominating over the anterior head regions or appearing diffusely with progression to deeper stages of coma. 䡲 In early stages of coma, delta activity may attenuate with external stimuli, but for the most part, it is usually unreactive. Many polymorphic delta comas are due to structural abnormalities involving subcortical white matter, but some profound metabolic comas can produce a similar pattern.
䡲
䡲
Hepatic or anoxic encephalopathy in children.
Etiology and outcome of alpha coma (AC) patterns and other rhythmic coma patterns were similar.
Delta pattern comas may show polymorphic morphology or more rhythmic or stereotyped blunted TWs.
䡲
Theta Frequency Pattern
Rhythmic coma pattern (alpha, theta, beta, delta coma, spindle) (Figures 5-53 to 5-56, 6-25 to 6-37) 䡲
䡲
䡲
Seen in comatose patients.
䡲
Delta Frequency Pattern
Spindle Coma (SC) Predominantly over the fronto-central regions, often with vertex sharp waves, and remitting only briefly with stimuli. 䡲 EEG pattern of “sleeplike” activity characterized by spindles in the 9- to 14-Hz range, often with vertex sharp waves and K-complexes occurring in patients with unconsciousness or coma. 䡲 Metabolic, infectious, and hypoxic encephalopathies are the most common etiologies; there was no case of CNS trauma. It is assumed that SC represents a coexistence of true sleep and coma, the latter accounting for the failure of arousal that is attributed to impairment of the activating ascending reticular formation at the midbrain level. The presence of spindles, vertex waves, and K-complexes indicates relative integrity of the cerebral hemispheres.
Fourteen- and six-hertz positive spikes with continuous delta slowing (Figures 5-44 to 5-48, 6-44) 䡲
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Generalized Nonepileptiform Activity
Diffuse theta patterns may occur on their own or may be mixed with other frequencies such as alpha or delta in coma. This mixed pattern in coma may occur after CRA where theta activity (although diffuse) is more prominent anteriorly, is usually unreactive to external stimuli, and usually carries a poor prognosis similar to AC.
Beta Frequency Pattern Predominance of high-voltage beta activity. Drug overdoses or even sedative withdrawal, especially benzodiazepines and barbiturates, result in more diffuse and higher voltage EEG beta activity, occasionally with sleeplike spindle activity, and diffuse high-voltage delta slowing. 䡲 In lesser degrees of encephalopathy, the EEG patterns are usually reactive to external stimuli. Coma is largely reversible and has a good prognosis.
䡲
The specific frequency of the EEG pattern such as alpha, beta, spindle, or theta did not influence the outcome. The clinical outcome appeared to depend on the primary disease process rather than the electroencephalographic finding. 䡲 The prognosis of rhythmic coma, in general, was better in children than in adults. The pathophysiology in children may be similar
5 (interruption of reticulothalamocortical pathways by metabolic or structural abnormalities, but the expression of this deafferentation may be more varied in the developing brain).93 䡲 Often with multiple concurrent pathologies, including head injury; cerebral, thalamic, midbrain, and brainstem infarctions and hemorrhages; encephalopathy; hypoxia; drug intoxication; eclampsia; and seizures. 䡲
There is controversy surrounding the prognostic significance of SC. 䡲 Prognosis is usually poor in other EEG patterns associated with coma such as diffuse suppression, B-S after CRA, generalized periodic pattern, intermittent attenuating, and AC of diverse etiologies, with mortalities exceeding 65%. However, the overall mortality in SC is only 23%. 䡲 In both SC and AC, there is a strong association between coma etiology and outcome. The marked difference in prognosis between AC and SC may be due to the differences in the etiologies producing the two EEG patterns. Whereas in AC, CRA accounts for most of the cases, carrying with it a correspondingly poor prognosis (83% mortality). CRA accounts for only 3/227 patients with SC. This suggests that the more “benign” nature of SC compared to AC is largely related to the lesser severity or extent of cerebral damage occurring with SC.
Generalized Nonepileptiform Activity
395
thalamocortical neurons account for the cyclic EEG wave bursts.
Burst-suppression pattern (Figures 5-57 to 5-66, 6-38 to 6-41) 䡲
Complex wave forms alternating with complete attenuated background activity (<10 mV). 䡲 Indicative of severe diffuse encephalopathy. 䡲 Immediately precedes ECI. 䡲
Always seen in coma except in severe epileptic encephalopathies, including: 䊳 䊳 䊳
Ohtahara Early myoclonic encephalopathy Infantile spasm variant
Nonketotic hyperglycinemia (NKH) 䡲 Experimental study of B-S showed that almost all (95%) cortical neurons become electrically silent during flat EEG epochs. 䊳
䊳
䊳
䊳
Hyperpolarization of cortical neurons precedes EEG flattening. The hyperpolarization is due to increased K+ conductance, which in turn is secondary to increased GABAergic inhibition at cortical synapses. This inhibition leads to functional disconnection from thalamic input, but 30–40% of thalamic cells continue firing while the cortex is silent. This is due to the intrinsic pacemaking properties of the thalamic neurons at modest levels of hyperpolarization. Volleys from these
Diffuse background attenuation (Figure 5-69 to 5-71, 6-42) 䡲
Voltage <10 μV. Also seen in normal individual. 䡲 In some adults, alpha rhythm may be absent (7–10% of adults >20 years but less common in children). The background may consist of irregular mixture of low-amplitude (<20 μV) activities without dominant frequency. The EEG is reactive to various physiologic stimuli. In more than 50% of these EEGs, HPV may bring out an alpha rhythm. During sleep, architecture may be generalized. 䡲
䡲
In unconscious patients, a persistent low-voltage pattern of less than 20 μV is indicative of poor prognosis.
Electrocerebral inactivity (ECI) (Figure 5-68 , 6-5, 6-43) 䡲
No electrical cerebral activity >2 μV.
䡲
With few exceptions, it is an expression of brain death. 䡲 Also seen in other conditions, including: 䊳 䊳
Thalamic involvement Drug effect and toxic encephalopathy
396
Generalized Nonepileptiform Activity
5
FIGURE 51. Excessive Beta Activity Due to Benzodiazepine. EEG of a 12-year-old boy with epilepsy who was treated with clonazepam. There is excessively high-voltage, 18- to 22-Hz, beta activity with anterior predominance. “Beating” appearance caused by waxing and waning in amplitude of beta activity is noted. Rhythmic 15- to 25-Hz beta activity increases with therapeutic doses of benzodiazepines (BZP) and phenobarbital and is most prominent during drowsiness. BZP produce a decrease in alpha activity and general voltage and a slight increase of 4- to 7-Hz theta activity. Beta activity is more pronounced and acute in children. In adults, it is more common in chronic treatment. Generalized slowing related to the decreased level of consciousness occurs with a higher dose of BZP. Paroxysmal rhythmic slow waves have been reported in chronic treatment.1–3
5
Generalized Nonepileptiform Activity
397
FIGURE 52. Excessive Beta Activity; Benzodiazepine & Phenobarbital. EEG of a 7-year-old boy with mental retardation and generalized epilepsy caused by traumatic brain injury who was on chronic phenobarbital and clonazepam. There is persistently high-voltage (>20 μV), 20- to 25-Hz beta activity with anterior predominance. Beta activity in normal children and adults always has a voltage less than 20 μV. Benzodiazepines and barbiturates most prominently and commonly produce this effect. Other agents or medications causing excessive beta activity but with lower voltage include cocaine, amphetamines, methylphenidates, and tricyclic antidepressants.2 Excess beta is also seen in rare normal individuals, chronic encephalopathy, hyperthyroidism, anxiety, and alcohol or barbiturate withdrawal. The effect is more prominent in children than in adults.
398
Generalized Nonepileptiform Activity
5
FIGURE 53. Type 1 Lissencephaly (Miller-Dieker Syndrome); Generalized High-Amplitude Fast Activity (Beta Frequency Band). A 6-year-old boy with spastic quadriparesis, severe mental retardation, and medically intractable epilepsy (atonic, atypical absence, and generalized tonic-clonic seizures) resulting from Miller-Dieker syndrome. Deletion of the short arm of chromosome 17 (p13.3) containing lissencephaly type 1 gene (LIS1) was found. MRI reveals a nearly smooth cerebral surface with abnormally thick cortex (typically 10–20 mm) and primitive sylvian fissures giving the “hourglass” configuration.4,5 EEG shows diffuse high-amplitude fast activity in alpha and beta frequency bands. The EEG in type 1 lissencephaly is characterized by generalized high-amplitude fast activity in alpha and beta frequency bands (8–18/sec), burst of slow spike-wave complexes, high-amplitude slow rhythms, hypsarrhythmia-like pattern, and alternating patterns consisting of bursts of sharp/spike waves alternating with periods of electrocerebral depression. The EEG does not react to sleep or medication.6–9
5
Generalized Nonepileptiform Activity
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FIGURE 54. Lissencephaly-Pachygyria Associated with Congenital CMV Infection; Excessive Beta Activity. EEG of a 7-year-old girl with lissencephaly-pachygyria associated with congenital CMV infection. Brain CT shows smooth, flat gyri with thickened cortex and calcification (open arrow) adjacent to the right frontal horn of lateral ventricle. The EEG shows excessively diffuse, medium-voltage beta activity with posterior predominance. The patient did not take any sedative medication. Patients with lissencephaly suffer injury before 16 or 18 weeks gestational age, whereas those with polymicrogyria are injured between approximately 18 and 24 weeks gestational age. Those with normal gyral patterns are probably injured during the third trimester. Cerebella hypoplasia and myelination delay in association with diffuse lissencephaly or cortical dysplasia should suggest the diagnosis of congenital cytomegalovirus infection.10 Excessive and high-voltage beta activity (amplitude > 20 μV) with no history of sedative drug usage is a nonspecific finding but can be seen in patients with mental retardation and also lissencephaly.7
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Generalized Nonepileptiform Activity
5
FIGURE 55. Type 1 Lissencephaly (Miller-Dieker Syndrome); Generalized High-Amplitude Fast Activity (Alpha Frequency Band). A 6-year-old boy with spastic quadriparesis, severe mental retardation, and medically intractable epilepsy (atonic, atypical absence, and generalized tonic-clonic seizures) resulting from Miller-Dieker syndrome. Deletion of the short arm of chromosome 17 (p13.3) containing lissencephaly type 1 gene (LIS1) was found. MRI reveals a nearly smooth cerebral surface with abnormally thick cortex (typically 10–20 mm) and primitive sylvian fissures giving the “hourglass” configuration.4,5 EEG shows generalized high-amplitude fast activity in the alpha frequency band. The EEG in type 1 lissencephaly is characterized by generalized high-amplitude fast activity in alpha and beta frequency bands (8–18/sec), burst of slow spike-wave complexes, high-amplitude slow rhythms, hypsarrhythmia-like pattern, and alternating patterns consisting of bursts of sharp/spike waves alternating with periods of electrocerebral depression. The EEG does not react to sleep or medication.6–9
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Generalized Nonepileptiform Activity
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FIGURE 56. Hypsarrhythmia; Lissencephaly Type 1 (Classical LIS). EEG of a 15-month-old with infantile spasm and global developmental delay due to Lissencephaly type 1 (LIS 1). Hypsarrhythmic pattern is noted. Classical lissencephaly (LIS) is a neuronal migration disorder resulting in brain malformation, epilepsy and mental retardation. Deletions or mutations of LIS1 on 17p13.3 and mutations in XLIS (also called DCX ) on Xq22.3-q23 produce LIS. Whereas the brain malformation due to LIS1 mutations was more severe over the parietal and occipital regions (posterior-to-anterior gradient), XLIS mutations produced the reverse gradient, which was more severe over the frontal cortex (anterior-to-posterior gradient). The distinct LIS patterns suggest that LIS1 and XLIS may be part of overlapping, but distinct, signaling pathways that promote promote neuronal migration. Hypoplasia of the cerebellar vermis is seen more common with XLIS mutations.11,12 Most children with LIS1 mutation have severe developmental delay and infantile spasms. DCX mutations usually cause lissencephaly in males and SBH in female patients. Mutations of DCX have also been found in male patients with anterior SBH and in female relatives with normal brain MRI. Autosomal recessive lissencephaly with cerebellar hypoplasia, accompanied by severe delay, hypotonia, and seizures, has been associated with mutations of the reelin (RELN) gene. X-linked lissencephaly with corpus callosum agenesis and ambiguous genitalia in genotypic males is associated with mutations of the ARX gene. Affected boys have severe delay and seizures with suppression-burst EEG. Carrier female patients can have isolated corpus callosum agenesis.13
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Generalized Nonepileptiform Activity
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FIGURE 57. Generalized High-Voltage Fast Activity (Alpha Band); Type 1 Lissencephaly. EEG of a 3-year-old boy with mental retardation and intractable epilepsy due to lissencephaly. There is generalized high-voltage 8- to 10-Hz rhythmic alpha activity with frontal-central predominance. MRI is compatible with lissencephaly type 1. The typical EEG in lissencephaly is characterized by abnormally high-voltage rhythmic EEG activity, predominantly in the alpha and beta frequency bands (8–18 Hz). This pattern is seen in the waking period with high-amplitude slow rhythms and simulates slow spike-wave complexes or hypsarrhythmia. It has been suggested that this is associated with the unusual orientation of the anomalous neuronal columns.7 This high-amplitude rhythmic EEG activity associated with lissencephaly has high specificity. Typical features of this EEG pattern include high voltage increasing with age, missing topographic structuring, no reactivity to sleep or medication, and unusually high-voltage, sharp, slow-wave complexes.8,14,15 They correlate with the severity of the brain malformation and the epilepsy.16 On sleep EEG, 14-Hz sleep spindles are found from early infancy but poorly observed after 1 year of age. Fourteen-hertz sleep spindles are replaced with high-amplitude rhythmic activity (HARA). The frequency of HARA is in the 5- to 11-Hz bands, and its amplitude is abnormally high. HARA may represent the extreme spindles reported in patients with central nervous system disorders.17 In an experimental study of lissencephaly, the extent of the extreme spindle activity, longer epileptiform after discharges, and seizure duration are dependent on the degree of cerebellar dysplasia, whereas the EEG focal abnormalities were related to lesions in the cerebral hemispheres.18 The above-described EEG pattern is not seen in type II lissencephaly. In type II lissencephaly, initially theta or delta waves of somewhat lower amplitude are initially observed. Sharp- and slow-wave complexes of very high amplitude are found more often in type I lissencephaly. They seem to correlate with the severity of the brain malformation and the epilepsy.16,19 The EEGs in the lissencephaly patients showed the following patterns: (a) generalized fast activity (8–18/sec) with an amplitude higher than 50 mV, (b) sharp- and slow-wave complexes with an amplitude higher than 500 μV, (c) an alternating pattern consisting of bursts of sharp waves alternating with periods of electrocerebral depression. Ninety-five percent show patterns (a) or (b) or both compared to only 5% of the patients with an atypical cortical dysplasia and 0.4% in the controls. EEG appears to be valuable in the diagnosis of lissencephaly type I.20 The EEG features and their evolution change with age. In early or middle infancy when infantile spasms begin, the EEG shows very high-amplitude (more than 400 mV) slow waves mixed with sharp theta waves. In late infancy, the EEG shows extreme spindles and a tendency toward bilaterally synchronous discharges of high-amplitude sharp and slow waves. The very high voltage of hypsarrhythmic patterns and the very low frequency of sharp-wave discharges seem to be typical in the most severe cases of lissencephaly or agyria.21
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Generalized Nonepileptiform Activity
FIGURE 58. Type 1 Lissencephaly; Infantile Spasm in Remission. (Same patient as in Figure 5-6) The patient was in remission after the treatment with antiseizure medications. EEG shows very frequent sharp waves, maximally expressed in the left midtemporal region without hypsarrhythmia.
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Generalized Nonepileptiform Activity
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FIGURE 59. Glossokinetic Artifact. Glossokinetic artifact is caused by movement of the tongue, which produces a DC potential. The tip of the tongue has a negative electrical charge with respect to the root. The activity can be either unilateral or bilateral, depending on the direction of tongue movement. The electrical field can be widely distributed, although it is most often noted in the temporal electrodes. Sometimes it can simulate cerebral slow-wave activity, especially when the mouth remains closed during tongue movements.
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Generalized Nonepileptiform Activity
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FIGURE 510. Excessive Photic Response at High Frequency Stimulation (H response); Migraine. The “H-response” is a prominent photic driving response at flash rates beyond 20 Hz. In a critical review of the literature, the reported sensitivity of the H-response varied from 25% to 100%, and the specificity from 80% to 91%. Although the relatively high sensitivities and specificities reported suggest that the H-response may be effective in distinguishing migraine patients from controls, and possibly migraineurs from tension headache sufferers, the Quality Standards Subcommittee (QSS) of the American Academy of Neurology concluded that the H-response was not more effective than the neurological history and examination in diagnosing headaches and was not recommended in clinical practice. However, in the presence of complex or prolonged aura, visual hallucinations, disorders of consciousness, history of recent trauma, and in infants vomiting with ocular and head deviation, the EEG may be useful for clinical diagnosis and help to monitor therapeutic response.22,23
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Generalized Nonepileptiform Activity
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FIGURE 511. Anterior Slow Dysrhythmia & Frontal Sharp Transients. A 38-week CA girl with hypoxic-ischemic encephalopathy and generalized clonic seizures on the first day of life. She received a loading dose of intravenous phenobarbital a few hours prior to this EEG. The EEG shows bilaterally synchronous and symmetric, rhythmic 1.5-Hz delta activity with frontal predominance, admixed with board frontal sharp transients. Excessive degree of anterior dysrhythmia is indicative of diffuse encephalopathy.
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Generalized Nonepileptiform Activity
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FIGURE 512. Excessive Anterior Slow Dysrhythmia & Frontal Sharp Transients. (Same patient as in Figure 5-11) EEG is similar to that on the previous page except that the frontal sharp transients and anterior slow dysrhythmia are more continuous. Excessive degree of anterior dysrhythmia is indicative of diffuse encephalopathy.
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Generalized Nonepileptiform Activity
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FIGURE 513. Hyperventilation Effect; Sobbing Artifact. EEG of a 17-month-old boy with a history of febrile convulsions. There is diffuse rhythmic 5-Hz theta slowing with posterior predominance noted during sobbing. The rest of the EEG was unremarkable. Diffuse theta slowing caused by hyperventilation effect from sobbing should not be interpreted as mild diffuse encephalopathy.
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Generalized Nonepileptiform Activity
FIGURE 514. Diffuse Theta Slowing With Central-Parietal Predominance; Myoclonic Astatic Epilepsy (MAE). EEG during wakefulness of a 5-year-old boy with myoclonic astatic epilepsy (MAE) showing diffuse monorhythmic 5- to 6-Hz theta activity with frontal-central-parietal predominance. Monorhythmic 4- to 7-Hz rhythm is a characteristic background EEG activity seen in almost all instances early in the course of MAE. This rhythm is usually parietally predominant. This EEG pattern is falsely attributed to drowsiness. During active seizures, the rhythm is more irregular and slower, than in a period of remission.24,25
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FIGURE 515. Diffuse Monomorphic Theta Rhythm; Myoclonic Astatic Epilepsy. Background EEG during wakefulness of a 6-year-old girl with myoclonic astatic epilepsy (MAE) showing monorhythmic 5- to 6-Hz theta activity. The prolonged video-EEG over a 3-day period showed rare bursts of generalized epileptiform activity, activated by sleep. Monorhythmic 4- to 7-Hz rhythm is a characteristic background EEG activity seen in almost all instances early in the course of MAE. This rhythm is usually parietally predominant. This EEG pattern is falsely attributed to drowsiness. During active seizures, the rhythm is more irregular and slower, than in a period of remission.24,25
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FIGURE 516. Slow Background Activity & Diffuse Theta Slowing; Lamotrigine Toxicity. A 12-year-old girl with juvenile myoclonic epilepsy (JME) who had been treated with lamotrigine. She developed acute sinusitis and was treated with azithromycin. One day after the treatment, she developed alteration of mental status and exacerbation of migraine. She showed marked improvement of her seizures and a decrease in EEG epileptiform activity. EEG during wakefulness shows slow background activity, diffuse theta activity, and occasional epileptiform activity. She returned back to normal within a few days, and EEG was normalized (not shown) within 1 week after stopping azithromycin. Therapeutic doses of lamotrigine did not affect the background EEG activity in patients with Lennox-Gastaut syndrome and partial epilepsies with secondary bilateral synchrony.26 There is only little information available about the effect of new AEDs on the EEG record.2
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FIGURE 517. Diffuse Rhythmic Theta Activity; Rett Syndrome. A 12-year-old girl with Rett syndrome. EEG in Rett syndrome is invariably abnormal when recorded during clinical stage II (regression) after age 2 years. The changes in the EEG parallel the clinical course of Rett syndrome. Three characteristic EEG changes have been reported: (1) loss of expected developmental features during wakefulness and NREM sleep and generalized background slowing; (2) epileptiform abnormalities, initially, characterized by central-temporal spike- and/or sharp-wave discharges activated by sleep and, later, multifocal spikes and/or sharp waves and generalized spike- and slow-wave discharges; and (3) rhythmic theta activity in the central or frontal-central regions during clinical stages III (post-regression) and IV (late motor regression). Less frequent EEG patterns, including periodic patterns and hypsarrhythmia, can also be seen. For some older female individuals and adults in clinical stages III and IV, the EEG can be minimally slow, with expected awake and sleep developmental features and an absence of epileptiform abnormalities.27
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FIGURE 518. Diffuse Rhythmic 4-Hertz Delta Activity With Fronto-Central and Vertex Predominance; Rett Syndrome. A 10-year-old girl who presented at 14 months with developmental delay and hypotonia. The first EEG done at 16 months was normal. Subsequently, she developed typical features of Rett syndrome, and the diagnosis was confirmed by the gene test. EEG shows diffuse rhythmic 4-Hz delta activity with frontal-central and frontal vertex predominance. Rhythmical 3- to 5-Hz theta or delta slowing is the most common EEG abnormality (30/44 patients) in patients with Rett syndrome. Diffuse/bisynchronous spikes or sharp waves or slow spike-wave complexes were found in 22/44 and 9/44 patients, respectively. With advancing age, the EEG abnormalities improve and a low-voltage EEG may develop. These changes parallel the clinical course of Rett syndrome.28
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FIGURE 519. Electroretinogram (ERG). The amplitude of ERG is usually low and obscured by normal EEG activity in Fp1 and Fp2. ERG can be confused with an electrode artifact generated by an exposed silver metal of chipped EEG electrode during photic stimulation. These physiological and art factual potentials can be differentiated by using a high photic stimulus frequency. With 30-Hz photic stimulus frequency, the amplitude of ERG diminishes but the amplitude of electrode artifact is constant.
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FIGURE 520. Sobbing: Hyperventilation Effect. EEG of a 9-year-old boy with mental retardation who sobbed during most of this EEG recording. There is diffuse rhythmic 3-Hz delta activity with posterior predominance noted. Occipital intermittent rhythmic delta activity (OIRDA) is a physiologic finding seen during hyperventilation.
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FIGURE 521. Migraine; Frontal Intermittent Rhythmic Delta Activity (FIRDA). A 17-year-old girl with migraine and a transient episode of confusion, aphasia, and right hemiparesis, followed by her typical migraine headache. EEG during the headache and mild confusion (2 hrs after the resolution of aphasia and right hemiparesis) shows bursts of bisynchronous high-voltage 2.5-Hz rhythmic delta activity with frontal predominance (FIRDA). MRI/MRA, CT angiography, and hypercoagulation study were unremarkable. EEG during or shortly after the episodes of basilar migraine showed FIRDA, which appears to be a sign of the rostral basilar artery ischemia. EEG gradually normalizes within 1–3 days after the acute stage.29–31 Recurrent prolonged episodes of coma, varying from 3 to 14 days, due to basilar artery migraine have been reported. Severe spasm of the basilar artery was demonstrated by arteriography. EEGs during the comatose episodes showed suppression-burst, marked generalized slow-wave delta activity or FIRDA patterns.32, 33 Both the EEG and clinical findings subsided within the following weeks. Chronic ischemic structural brain lesions may predispose FIRDA during acute metabolic derangement.34 The EEG changes during hyperventilation in migraine patients include theta activity and FIRDA.35
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FIGURE 522. Confusional Migraine; Frontal Intermittent Rhythmic Delta Activity (FIRDA). The ictal EEG during the prolonged video-EEG monitoring in a 9-year-old boy with confusional migraine. There is bisynchronous rhythmic delta activity, intermixed with low-amplitude spikes, with frontal predominance consistent with FIRDA (frontal intermittent rhythmic delta activity). EEG during or shortly after the basilar migraine episodes showed FIRDA, which appears to be a sign of ischemia of the rostral basilar artery region. The EEG gradually normalizes after the acute stage, usually within 1–3 days.29–31 FIRDA may have a slight notch on the descending phase of the delta waves (arrow) and should not be misinterpreted as spikewave activity.36
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FIGURE 523. Occipital Intermittent Rhythmic Delta Activity (OIRDA); Chronic Renal Failure with Chronic Dialysis. EEG of a 12-year-old boy with chronic renal failure requiring intermittent dialysis. He developed his first GTCS. There are trains of bisynchronous high-amplitude 3-Hz delta activity with a maximum in the occipital regions. Intermittent rhythmic delta activity (IRDA) is a burst or run of high-voltage, bisynchronous (sinusoidal or sawtooth wave), and rhythmic delta activity of fixed frequency (close to 2.5 Hz) with more rapid ascending than descending phase. It may have a slight notch on the descending phase of the wave form (in this EEG page, the small notches are noted during the ascending phase of the OIRDA). OIRDA is seen in children less than 10–15 years, and FIRDA is always seen in older children or adults. This is a maturation-related spatial EEG feature. The main association of IRDA is diffuse gray matter disease (both cortical and subcortical) or overactive thalamocortical circuits. It is indicative of mild to moderate encephalopathy and is usually seen in active fluctuating, progressing, or resolving diffuse brain dysfunction. It is nonspecific in etiology and is also seen in normal individuals during hyperventilation.
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FIGURE 524. HIV Meningoencephalitis; Frontal Intermittent Rhythmic Delta Activity (FIRDA). An 18-year-old boy with HIV infection due to blood transfusion and a recent episode of recurrent HIV meningoencephalitis. Cranial CT shows bilateral frontal and basal ganglia calcifications. Also note metallic artifact from cochlear implantation. EEG during lethargic state shows frequent bursts of frontal intermittent rhythmic delta activity (FIRDA). This EEG pattern is indicative of diffuse encephalopathy but is nonspecific for etiology. FIRDA can be seen in association with a wide variety of pathologic processes varying from systemic, toxic, or metabolic disturbances to focal intracranial lesions. Even when associated with focal lesions, FIRDA by itself is nonfocal.37
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FIGURE 525. HIV Meningoencephalitis; Occipital Intermittent Rhythmic Delta Activity (OIRDA). (Same patient as in Figure 5-24) EEG shows asymmetrical, bilateral synchronous, rhythmic 2-Hz delta activity with occipital and left-hemispheric predominance. OIRDA occurs almost exclusively in children and is associated with idiopathic generalized epilepsy and, less commonly, focal epilepsy. Occasionally, it can also be seen in patients with diffuse encephalopathy, as in this patient.38–41
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FIGURE 526. Frontal Intermittent Rhythmic Delta Activity (FIRDA); Postictal State. EEG of a 20-year-old boy with intractable epilepsy caused by a low-grade tumor in the right occipital region. There is a run of frontal intermittent rhythmic delta activity (FIRDA) appearing immediately after his typical seizure, which is described as a secondarily generalized tonic-clonic seizure. FIRDA is indicative of a mild to moderate degree of encephalopathy. It is seen in active fluctuating, progressing, or resolving widespread brain dysfunction and is less likely to be associated with chronic, stable brain dysfunction. It is nonspecific in etiology and can be seen in postictal state. OIRDA is seen in children under 10–15 years of age, and FIRDA is always seen in older children and adults. This represents a maturation-related spatial EEG feature.
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FIGURE 527. Occipital Intermittent Rhythmic Delta Activity (OIRDA); Diffuse Encephalopathy Caused by Moyamoya Disease. An 8-year-old boy with a new right frontal infarction resulting in slurred speech and mild left hemiparesis. MRI/MRA shows bilateral supraclinoid carotid occlusion with lenticulostriate collateral vessels reconstituting bilateral middle cerebral and anterior cerebral arteries. These findings are supportive of the diagnosis of moyamoya disease. Hypercoagulation study was positive for heterozygote PT 20210 mutation. EEG shows bilateral synchronous, rhythmic delta activity with peak amplitude localized over the occipital area, which is consistent with an occipital intermittent rhythmic delta activity (OIRDA) pattern. OIRDA was first described in 1983.42 It was concluded that it was only seen in children and was not found to be helpful. in diagnosing a seizure disorder or structural abnormality. Subsequent publications show that OIRDA is seen almost exclusively in children with epilepsy and is rarely seen in children with diffuse encephalopathy.38–41
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FIGURE 528. Occipital Intermittent Rhythmic Delta Activity (OIRDA); Acute Viral Encephalopathy. A 4-year-old girl with congenital blindness due to congenital CMV infection who developed acute encephalopathy due to enteroviral infection (hand-foot-mouth syndrome). EEG shows asymmetric, bilateral synchronous, rhythmic 2-Hz delta activity with occipital and left-hemispheric predominance. OIRDA occurs almost exclusively in children and is associated with idiopathic generalized epilepsy and, less commonly, focal epilepsy. Occasionally, it can also be seen in patients with diffuse encephalopathy, as in this patient.38–41
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FIGURE 529. Occipital Intermittent Rhythmic Delta Activity (OIRDA); Idiopathic Generalized Epilepsy. A 13-year-old boy with a history of idiopathic generalized epilepsy. EEG shows bilateral synchronous, rhythmic delta activity with peak amplitude localized over the occipital area, consistent with the OIRDA pattern. OIRDA occurs almost exclusively in children and is associated with idiopathic generalized epilepsy and, less commonly, focal epilepsy. Occasionally, it can also be seen in patients with diffuse encephalopathy.38,39,41,43
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FIGURE 530. Notch Delta Pattern in Angelman Syndrome. An 11-month-old boy with a new-onset myoclonic seizure. His clinical phenotype was not definitely suggestive of Angelman syndrome (AS). MRI was normal. EEG shows frequent bursts of diffuse rhythmic notched delta with posterior predominance. The diagnosis was subsequently confirmed by a genetic test, which showed a deletion of chromosome 15. The notched delta pattern is the hallmark EEG feature in AS. It was described in AS children as young as 12–14 months.44,45 It often precedes the seizures and the suggestive phenotype for AS, and therefore allows an early detection of these patients.44–48 Majority (78%) of the notched delta patients had a clinical phenotype consistent with AS,49 and 88% of patients with AS had the notched delta EEG.45
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FIGURE 531. Notched Delta Pattern in Angelman Syndrome. A 12-year-old girl with Angelman syndrome (AS) with intractable epilepsy and multiple seizure types, including myoclonic, generalized tonic-clonic, absence, and atonic seizures. Interictal EEG shows frequent bursts of diffuse high-voltage notched delta pattern with frontal predominance. The notched delta pattern is the hallmark EEG feature in AS. It was described in AS children as young as 12–14 months.44,45 It often precedes the seizures and the suggestive phenotype for AS, and therefore allows an early detection of these patients.44–48 Majority (78%) of the notched delta patients had a clinical phenotype consistent with AS,49 and 88% of patients with AS had the notched delta EEG.45,50 This EEG pattern is also seen in other genetic conditions such as Rett syndrome45,51–53 and 4p(−) syndrome.54 At times, AS can be very difficult to distinguish from LGS. Absence of paroxysmal fast activity (PFA) during sleep in AS can help differentiate these two conditions. PFA is not seen in AS.
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FIGURE 532. Triphasic Waves (TWs); Hepatic Encephalopathy. EEG of a 28-year-old man with hepatic encephalopathy caused by hepatitis. EEG shows bursts of diffuse moderate amplitude 2-Hz TWs. TWs are high-voltage positive sharp transients (open arrow) that are preceded and followed by negative waves of lower voltage (double arrows). Anterior-posterior lag (20–140 msec) is inconsistently seen (<--->). TWS predominate in the anterior head regions but can be seen posteriorly, more diffusely, or in mixed dominance. TWs are etiologically nonspecific and are associated with a wide variety of etiologies with hepatic, renal, and anoxic accounting for over 75%. Other conditions such as hyperosmolarity; hyponatremia; Hashimoto thyroiditis; ifosfamide, metrizamide, lithium, tricyclic, baclofen toxicity; CJD; neuroleptic malignant syndrome; serotonin syndrome; Lyme disease; and West Nile disease have been reported. When occur at a frequency faster than 1 Hz, they are very difficult to differentiate from NCSE. The prognosis is mainly dependent on the etiology. TWs can also be seen in patients with cerebral atrophy and diffuse white matter disease. They are rarely seen in patients less than 20 years old.55–59
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FIGURE 533. Triphasic Waves; Dialysis Encephalopathy. EEG of a 20-year-old male with acute encephalopathy due to chronic renal failure and dialysis. EEG shows intermittently diffuse triphasic waves (TWs) (open arrow). The patient recovered after symptomatic treatment. The most characteristic EEG feature in dialysis encephalopathy is paroxysmal high-voltage delta activity with anterior predominance, and TWs consist of bursts of moderateto high-amplitude complexes, usually at 1.5–2.5 Hz, with three (but sometimes two or four) negative-positive-negative phases, usually occurring in runs at 1.5–3/sec or more continuously. A fronto-occipital lag (brought out by using a bipolar montage) is unique but not a constant finding. TWs have been considered as a pathognomonic sign in severe hepatic encephalopathy, but they are also seen in encephalopathies associated with renal failure or electrolyte imbalance, as well as anoxia and intoxications (such as lithium, metrizamide, and levodopa). In pre-coma, TWs do not predict outcome.59,61–63 TWs occur most often in patients with metabolic encephalopathies but cannot be used to distinguish different causes.64 They are rarely reported in patients below the age of 20 years.64
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FIGURE 534. Nonconvulsive Status Epilepticus (NCSE) with Triphasic Wave Configuration; Ifosfamide Toxicity. An 18-year-old boy with altered mental status and mutism during the treatment of metastatic germ cell tumor with ifosfamide. EEG shows continuously diffuse sharp-contoured triphasic wave configuration. Immediate improvement of his mental status and EEG following intravenous administration of diazepam supported the diagnosis of NCSE. Trial of benzodiazepines is recommended in patients with ifosfamide encephalopathy with rhythmic electroencephalogic patterns.65–67 Differentiating triphasic waves and NCSE may at times be very difficult. Both may disappear with benzodiazepines.58,59,68,69 Certain EEG morphological criteria may be helpful in distinguishing these two features. NCSE is associated with higher frequency, shorter duration of phase 1, extra-spikes components, and less generalized background slowing. Triphasic waves are associated with amplitude predominance of phase 2 and augmentation with noxious or auditory stimuli.55
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FIGURE 535. Intermittent Polymorphic Delta Activity (PDA); Acute Viral Meningoencephalitis. EEG of a 5-year-old girl with acute enteroviral meningoencephalitis demonstrates intermittent polymorphic delta activity (PDA) intermingled with theta activity, activated by eye closure (open arrow). The patient returned back to her baseline mental status 2 days after the EEG recording. Contrary to continuous PDA, the clinical correlation of intermittent PDA is less well defined and usually associated with a variety of reversible causes, including migraine, mild TBI, mild viral encephalitis, postictal state, TIA, hypertension, toxic/metabolic conditions, and lacunar infarction. Electroencephalographic findings of intermittent PDA include (1) attenuation with eye opening or other alerting procedures; (2) augmentation with eye closure ; (3) failure to persist into sleep; (4) occurring only in drowsiness, light sleep, and hyperventilation; and (5) mixing with substantial amount of theta or alpha activity.
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FIGURE 536. Metachromatic Leukodystrophy (MLD). A 20-month-old boy with developmental regression. The major neurologic symptoms were poor balance, spasticity, and depressed deep tendon reflexes. MRI (not shown) revealed diffuse white matter abnormality in the periventricular regions and centrum semiovale in the posterior quadrants. Leukocyte arylsulfatase-A activity was reduced. EEG demonstrates nearly continuous polymorphic delta activity in the posterior head regions. At the beginning of the genetic leukodystrophies (GLs), the EEGs were normal or showed mild slowing of background activity.70–72 However, Balslev et al. reported that recurrent seizures associated with epileptiform discharges on EEG are common in MLD at any stage of disease.73 Clinical seizures with progressive slowing and epileptiform discharges on EEGs usually appeared during the later stages of all types of GLs such as metachromatic leukodystrophy, X-linked childhood adrenoleukodystrophy, and classic Pelizaeus-Merzbacher disease. Although cerebral involvement in GLs is mainly white matter, gray matter is eventually involved as well. In all types of GLs, there is good correlation between the severity of EEG changes, the severity of the diseases, and the clinical state of the patient. Serial EEGs are also helpful in separating GLs from static encephalopathies such as cerebral palsy.72
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FIGURE 537. Combination of FIRDA and Continuous Polymorphic Delta Activity (PDA); HHE Syndrome (Hemiconvulsions Hemiplegia Epilepsy); Impending Cerebral Herniation. A 3-year-old boy with high fever, persistent left hemiclonic seizure, and lethargy. T2-weighted MRI shows diffusely increased signal intensity over the entire right hemisphere, maximal in the mesial temporal region. Ictal EEG during the left hemiclonic seizure demonstrates bilateral, high-voltage rhythmic slow waves, intermixed with spikes and polyspikes with higher amplitude in the right hemisphere. There is preservation of physiologic sleep spindles in the left frontal region (arrow). A combination of continuously diffuse PDA and FIRDA is noted. Note very low-voltage EEG activity in C3-P3 channel caused by salt bridge from excessive smearing of the gel. The combination of FIRDA and continuous PDA is the classic EEG sign of impending cerebral herniation.36
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FIGURE 538. Delta Coma; Near Drowning: Hypoxic-Ischemic Encephalopathy. A 6-year-old boy with near drowning, cardiac arrest, requiring cardiopulmonary resuscitation in the ER 30 minutes after the rescue. He was in comatose state and subsequently developed absent brainstem reflexes, diabetes insipitus, and decerebrate rigidity. Cranial CT scans showed progressively diffuse brain edema (A, B - same day as the near drowning; C and D - 2 days later). EEG performed 3 days after the near drowning demonstrates diffuse polymorphic delta slowing. The patient died 2 days after this EEG recording. None of the patients who was still comatose 15-30 minutes after the rescue survied without major neurologic deficits and 60% died (Snodgrass, 2006). Poor prognostic signs included 1) submersion more than 5 minutes; 2) serum pH below 7.0 in the ED; 3) delay resuscitation; 4) poor initial neurologic evaluation on resuscitation (Fields, 1992). Delta coma is an EEG pattern seen in comatose patients with severely diffuse encephalopathy from various causes. Cortical deafferentiation plays a major role in generating diffuse polymorphic delta activity.74,76,77,78 It is characterized by continuously or nearly continuously diffuse high-voltage polymorphic 1- to 2-Hertz delta activity without remaining rhythmic background activity. In early stages of coma, delta coma may be attenuated by external stimuli. Reactivity to external stimuli is lost in deeper coma.79,80 Delta coma is a poor prognostic indicator but nonspecific for etiology.81
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FIGURE 539. Combination of Continuous PDA & FIRDA; Bilateral Frontal, Basal Ganglion, and Cerebellar Infarction. A 4-year-old girl with a sudden onset of progressive deterioration of consciousness. MRIs with DWI show bilateral frontal, basal ganglia, and cerebellar infarction. The etiology was unknown. EEG shows frontal intermittent rhythmic delta activity (FIRDA) (open arrow) superimposed on continuously diffuse polymorphic delta activity (PDA) and diffuse alpha activity (double arrows). The patient died 3 days after this EEG recording. Widespread continuous PDA occurs mostly in deafferentation of the cortex caused by subcortical white matter lesions or, less commonly, in bilateral thalamic, hypothalamic, and upper mesencephalic lesions.76,78 IRDA (FIRDA or OIRDA) occurs in a wide variety of conditions involving both subcortical and cortical gray matter.82 A recent study showed that FIRDA may reflect a pathologic type of increased excitation of cortical and subcortical gray matter disease.83 The combination of IRDA (FIRDA or OIRDA) and continuous focal PDA is a classic sign of impending cerebral herniation from a focal structural lesion, but it is also seen in a wide variety of diffuse encephalopathies such as toxic or metabolic encephalopathies.36
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FIGURE 540. Combination of Continuous Polymorphic Delta Activity and FIRDA; Massive Brain Edema with Central Herniation Syndrome. EEG of a 28-month-old girl with a history of biliary atresia, status post-Kasai operation at 2 months of age. She developed multiorgan failure caused by septicemia 1 week after the liver transplantation. She was in a comatose state requiring cardiorespiratory support and later intracranial pressure monitoring. Her cranial CT shows severely diffuse hypodensity in both hemispheres (double arrows) and thalamus (open arrow). These findings and clinical features were consistent with central herniation syndrome. EEG reveals a combination of nonreactive, continuously diffuse polymorphic delta activity (PDA) and frontal intermittent rhythmic delta activity (FIRDA), maximally expressed at Fz-Cz. Widespread continuous PDA occurs mostly in cortical deafferentiation caused by subcortical white matter lesions or, less commonly, in bilateral thalamic, hypothalamic, and upper mesencephalic lesions.76,78 IRDA (FIRDA or OIRDA) occurs in a wide variety of conditions involving both subcortical and cortical gray matter.82 A recent study showed that FIRDA may reflect a pathologic type of increased excitation of cortical and subcortical gray matter disease.83 The combination of IRDA (FIRDA or OIRDA) and continuous focal PDA is a classic sign of impending cerebral herniation from a focal structural lesion, but it is also seen in a wide variety of diffuse encephalopathies such as toxic or metabolic encephalopathy.36 The EEG, CT, and clinical features in this patient are consistent with impending central herniation syndrome caused by diffuse massive brain edema.
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FIGURE 541. Combination of Continuous Polymorphic Delta Activity and FIRDA; Massive Brain Edema with Central Herniation Syndrome. (Same patient as in Figure 5-40) The EEG during the comatose state 18 hours after the EEG on the previous page (Figure 5-40) shows diffuse voltage attenuation with lower voltage and more prominent FIRDA compared to the EEG on the previous page. The patient subsequently developed intermittent high fever, bradycardia, and hypotension. She died 2 days after this EEG.
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FIGURE 542. Paradoxical Activation; Hypoxic Encephalopathy. EEG of a 13-month-old girl with near drowning after being left unattended in the bathtub. There is a period of background attenuation and more severe delta slowing following stimulation. This EEG reactivity is called “paradoxical activation.” In severe encephalopathy, the EEG does not show reactivity to any stimulation and is called “invariant EEG.” In milder encephalopathy, the EEG shows spontaneous variability, evidence of EEG reactivity to stimulation, typically attenuation of amplitude, reduction of delta activity, and increase in frequency. Paradoxical activation is a period of more severe delta slowing following painful stimulation. It is seen less commonly than a typical response to stimuli but is associated with a milder degree of encephalopathy than the invariant EEG.84
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FIGURE 543. Paradoxical Activation. EEG of a 4-year-old girl who was in comatose state due to bilateral frontal and basal ganglia infarction of uncertain etiology. There is an abrupt increase in the degree of diffuse delta slowing following stimulation (arrow head). This EEG reactivity is called “paradoxical activation.” It was performed on the first day of admission when the patient still responded to painful stimuli. The patient deteriorated over the next 24 hours. The MRI scan performed 1 day later showed signs of central herniation caused by bilateral frontal and basal ganglia infarction. In severe encephalopathy, the EEG does not show reactivity to any stimulation and is called “invariant EEG.” In milder encephalopathy, the EEG shows spontaneous variability, evidence of EEG reactivity to stimulation, typically attenuation of amplitude, reduction of delta activity, and increase in frequency. Paradoxical activation is a period of more severe delta slowing following painful stimulation. It is seen less commonly than a typical response to stimuli but is associated with a milder degree of encephalopathy compared to the invariant EEG.84
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FIGURE 544. 14 and 6/sec Positive Spike Discharge. This EEG pattern is defined as bursts of arch-shaped waves at 13–17 Hz and/or 5–7 Hz, most commonly at 14 and/ or 6 Hz, seen generally over the posterior temporal and adjacent areas of one or both sides of the head during deep drowsiness and very light sleep. The sharp peaks of its components are positive with respect to other regions. This pattern occurs in children aged between 3 and young adulthood with a peak at age 13–14 years. This pattern is a benign variant of no clinical significance.85
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FIGURE 545. 14-and-6-Hertz Positive Spikes; Diffuse Encephalopathy. A 7-year-old boy with refractory status epilepticus of unknown etiology. This EEG performed during continuous IV drip of midazolam shows the “14- and 6-Hz positive spikes” pattern (mainly 14 Hz) superimposed on diffuse background attenuation from physical stimulation. The background activity revealed a continuous low-voltage polymorphic delta activity (PDA). The patient died 4 days after this EEG. Fourteen- and six-hertz positive spikes in a background of diffuse PDA were initially reported in Reye syndrome.86,87 These were later reported in diverse encephalopathies of childhood including toxic/metabolic and primary cerebral insults, especially hepatic or anoxic encephalopathy. The 14- and 6-Hz positive spikes pattern shows a similar incidence and morphology and topography in healthy children. It was concluded that this EEG pattern is a normal wave form that is selectively preserved and more resistant to underlying processes than other background features of drowsiness and sleep.88, 84 Sometimes, 14- and 6-Hz positive spikes were provoked by auditory and somatosensory stimuli.89
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FIGURE 546. 14-and-6-Hertz Positive Spikes; Diffuse Encephalopathy. (Same EEG page as in Figure 5-45) EEG with referential ear montage, especially contralateral ear reference, enhances 14- and 6-Hz positive spikes and shows dipole characteristic with positive polarity in the posterior temporal-occipital and negative polarity in frontal-central regions.
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FIGURE 547. 14-and-6-Hertz Positive Spikes; Diffuse Encephalopathy. This is an 11-year-old boy with Lennox-Gastaut syndrome who developed NCSE, requiring continuous infusion of midazolam. EEG with contralateral ear reference montage shows “14- and 6-Hz positive spikes” pattern (mainly 14 Hz) superimposed on diffuse polymorphic delta activity (PDA) background activity. Note the characteristic dipole of the 14- and 6-Hz positive spikes, with positive and negative polarity in the posterior temporal-occipital and frontal regions, respectively. Fourteen- and six-hertz positive spikes in a background of diffuse PDA were initially reported in Reye syndrome.86,87 but later reported in diverse encephalopathies of childhood including toxic/ metabolic and primary cerebral insult, especially hepatic or anoxic encephalopathy. This EEG pattern may be a normal wave form that is selectively preserved and more resistant to underlying processes than other background features of drowsiness and sleep.88, 84 The positive spike bursts with continuous PDA in comatose children are a rare but unique EEG pattern associated with hepatic or anoxic encephalopathy.84 Fourteen- and six-hertz positive spikes are best seen in contralateral ear referential montage.
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FIGURE 548. 14-and-6-Hertz Positive Spikes; Encephalopathy Associated with Sepsis and Stroke. This is a 6-year-old girl with multiple embolic strokes in both hemispheres with largest involvement in the left MCA. EEG with an anterior-posterior bipolar montage run shows “14- and 6-Hz positive spikes” pattern (mainly 14 Hz) superimposed on continuously diffuse low-voltage polymorphic delta activity (PDA), greater on the left side. Fourteen- and six-hertz positive spikes in a background of diffuse delta waves were initially reported in patients with Reye syndrome.86,87 These were later reported in diverse encephalopathies of childhood, not just Reye syndrome, including toxic/metabolic and primary cerebral insult. The 14- and 6-Hz positive spikes pattern shows a similar incidence and morphology and topography to that seen in healthy children. It was concluded that the 14- and 6-Hz positive spikes are a normal wave form that is selectively preserved and more resistant to underlying structural or metabolic processes than other background features of drowsiness and sleep.88 The positive spike bursts with continuous delta activity in comatose children are a rare but unique EEG pattern associated with hepatic or anoxic encephalopathy.84
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FIGURE 549. Prolonged Runs of Spindles; Normal Sleep Spindles (3-6 Months CA). Between the ages of 3 and 6 months, sleep spindles appear to be biphasic and as prolonged runs, up to 10–15 sec.90,91 The prolonged run of spindles is a very useful developmental marker and is rarely seen beyond this age range.
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FIGURE 550. Extreme Sleep Spindles; Viral Meningoencephalitis. A 6-week-old boy with an acute onset of fever, lethargy, and generalized tonic seizures. His CSF examination showed mild lymphocytic pleocytosis with slightly high protein but negative PCR and viral culture. Cranial MRI with GAD was unremarkable. He recovered within a few days after hospitalization. EEG during sleep demonstrates extreme sleep spindles for age. Sleep spindles that last more than 10 sec are a hallmark of EEG in 3- to 6-month infants. At 3 months, the spindles are very long in duration and can last more than 10 sec, and are biphasic in appearance. By 5 months of age, the spindles are usually shorter in duration but asynchronous and monophasic, occurring only on one side at a time.92 Extreme spindles had been reported in acute mycoplasma encephalitis. These extreme spindles were in parallel with the degree of delirium.93,94 The mechanism may be explained by a transient involvement of the spindle generator in the thalamus.
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FIGURE 551. Acute Meningoencephalitis; Extreme Sleep Spindles. (Same EEG recording as in Figure 5-50) EEG with paper speed of 30 mm/sec shows sleep spindles with mixed biphasic and monophasic configurations lasting for a very long period, more than 10 sec.
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FIGURE 552. Asynchronous Spindles After 2 Years of Age (Pathologic); Chromosome 46 XX, Inv (2) (p23.3p25.3). A 29-month-old female with a chromosomal disorder and hypoplasia of the corpus callosum. EEG during sleep shows consistently asynchronous sleep spindles with monophasic appearance. Asynchronous spindles are less common after 12 months and disappear after 2 years of age when the commissural pathway connecting both cerebral hemispheres is mature. Constant spindle asynchrony after 2 years is considered abnormal.
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FIGURE 553. Extreme Spindles; Acute Mycoplasma Encephalitis with Reversible Focal Lesion in the Corpus Callosum. A 6-year-old girl with an acute onset of fever, cough, vomiting, and lethargy. CSF showed mild lymphocytic pleocytosis. Serology for mycoplasma IgM was positive. (A) An initial axial T2-weighted image shows hyperintense signal abnormality in the splenium of the corpus callosum (arrow). (B) A follow-up MRI performed 5 days later shows disappearance of abnormal signal intensity in the corpus callosum (arrow). EEG performed on the same day as the first MRI demonstrates excessively diffuse spindles. A repeated EEG performed 1 week later (not shown) was within normal limits. MRI of reversible focal lesions in the splenium of the corpus callosum (SCC) is hyperintense on T2-weighted sequences and iso- or hypointense on T1-weighted sequences, with no contrast enhancement. On DWI, SCC lesions are hyperintense with low ADC values, indicating cytotoxic edema. The common causes of reversible focal lesions of the SCC are viral encephalitis, antiepileptic drug toxicity/withdrawal, and hypoglycemic encephalopathy.95 Extreme spindles in acute mycoplasma encephalitis have been reported.93,94
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FIGURE 554. Diffuse Alpha Activity (Alpha Coma Pattern) & Delta Slowing (FIRDA and PDA); POLG1 Mutation (A467T). A 16-year-old girl with intractable epilepsy, peripheral neuropathy, ataxia, and mental deterioration. Her seizures include occipital lobe seizures and epilepsia partialis continua (EPC). She was lethargic, EEG is nonreactive, showing continuously diffuse alpha activity, developed multiple brainstem signs (ophthalmoplegia, facial weakness, and dysphagia), and died 4 days after this EEG. Blood DNA subsequently showed POLG1 mutation (A467T). EEG shows nonreactive, continuously diffuse alpha activity intermixed with polymorphic delta activity and FIRDA, indicating intrinsic brainstem dysfunction. An alpha frequency in an unresponsive patient (alpha coma, AC) was first described in a pontomesencephalic hemorrhage96 and subsequently in patients with cardiorespiratory arrest; brainstem lesions, including pontomesencephalic and thalamic tumors, infarctions, hemorrhages, and brainstem herniation; hypoxia; head trauma; Reye syndrome; encephalitis; drug and sedative overdoses; postictal state; and hyperglycemia. AC is described as an invariant and diffuse alpha rhythm, with frontal predominance. Sparing of at least half of the midbrain tegmentum appears to be sufficient to maintain an alpha pattern but insufficient to maintain full consciousness.97 AC after brain stem stroke or brain stem compromise carries a mortality of 90%. However, the etiology of AC is a more important prognostic indicator; patients with drug-induced coma survive in more than 90%. EEG reactivity is also a good prognostic indicator; EEG reactivity to noxious stimuli favors survival; without it, most patients die.98 Other authors debate whether or not AC lhas prognostic significance by itself.99
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FIGURE 555. Alpha Coma. A 15-year-old boy with a cerebellar infarction secondary to dissection of his right vertebral artery. He was in a coma and subsequently developed central herniation syndrome, and died 2 days after this EEG recording. Note broadly diffuse distribution of alpha activity without an anterior-posterior gradient that is nonreactive to external stimuli. This EEG pattern is called “alpha coma (AC).” AC is in the alpha frequency range that occurs with a generalized distribution in a comatose patient. It is monomorphic, does not change in response to sensory stimuli, and is most commonly predominant in the frontal region. AC is most frequently seen in anoxic encephalopathy caused by cardiorespiratory arrest (CRA) and is associated with a very poor prognosis. AC can also be seen in toxic encephalopathies, which are very similar to that seen with CRA, except with beta activity superimposed on the alpha activity. Other etiologies include head trauma, CJD, brainstem lesion, and encephalitis. Prognosis in AC depends on the underlying causes of coma. Etiology and outcome of AC and other rhythmic coma patterns (beta, theta, and spindle) were similar. One type of rhythmic pattern can change to another. Reactive rhythmic coma was associated with favorable outcome.57–59,100
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FIGURE 556. Asymmetric Spindle Coma; Acute Amoebic Meningoencephalitis with Herniation Syndrome. A 10-year-old boy with refractory status epilepticus and coma caused by the amoeba Balamuthia mandrillaris. Axial MRI with FLAIR sequence and coronal T1-weighted image with GAD show an infarction of the right basal ganglion and midbrain (arrow) and Kernohan phenomenon in the opposite hemisphere (open arrow). EEG reveals asymmetrically diffuse spindle and delta coma with less abundant spindles and more pronounced polymorphic delta activity in the right hemisphere. In this patient, spindle and delta coma is most likely due to the lesions in the midbrain and basal ganglia caused by infarction and brain herniation syndrome. The patient died a few days after this EEG. Rhythmic coma patterns were found in 30.2% of EEG recordings in coma. Etiology, reactivity, and outcome of spindle, beta, alpha, and theta coma patterns are similar. The reactive pattern was associated with favorable outcome (66.7%). The nonreactive rhythmic pattern was associated with unfavorable outcome (60%). Sequential EEG recordings are required to detect the evolution of rhythmic coma patterns during childhood.100 The prognosis depends mainly on the primary disease process rather than the EEG finding. The prognosis of rhythmic coma pattern is better in children than in adults. The rhythmic coma pattern is probably caused by interruption of reticulothalamocortical pathways by metabolic or structural abnormalities.101 An incomplete pattern has a better prognosis.98,102,103 More than 440 cases of severe central nervous system infections caused by Acanthamoeba spp., B. mandrillaris, and Naegleria fowleri have been reported.104 Balamuthia encephalitis may occur in any age group, may or may not be associated with immunosuppression, and usually has a subacute and fatal course from hematogenous dissemination of chronic skin or lung lesions.97 Common features that might be of value in the diagnosis of Balamuthia encephalitis are high CSF protein, hydrocephalus, and Hispanic ethnicity.106 When purulent CSF is obtained and when no bacteria are noted in a patient with meningoencephalitis, the CSF should be examined specifically for other organisms, including amoeba. PCR assay and specific antibodies to Balamuthia are available. Brain biopsy should be considered in patients with encephalitis of unknown etiology whose condition deteriorates despite treatment with acyclovir.107 Chronic necrotizing vasculitis and focal hemorrhages are typical findings in Balamuthia infections.108,109 The prognosis is very poor due to delayed diagnosis, difficulty in isolation/identification of the organism, and lack of well-established treatment.110
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FIGURE 557. Burst-Suppression Pattern; Central Pontine Myelinolysis (CPM). A 2-year-old boy with septo-optic dysplasia with panhypopituitarism who presented to the ED with lethargy, poor feeding, and generalized hypotonia. He developed diabetes insipidus with Na, HCO3, and glucose of 177 MMol/L, 10 MMol/L, and 33 Mg/DL, respectively. He developed generalized hypertonia with intermittent tonic stiffening. Axial T2-weighted images show hyperintense signal abnormalities in the pons (arrow), cerebellum, (open arrow), midbrain (double arrows), and cerebral white matter (arrow head). The diagnosis of CPM was made. EEG shows a burst-suppression (B-S) pattern. CPM and EPM (extrapontine myelinolysis) frequently coexist with other abnormalities, such as electrolyte, and other metabolic disturbances or structural cortical abnormalities. The EEGs (e.g., CPM in liver transplantation) may also show a variety of epileptiform abnormalities or triphasic waves, due to metabolic derangements. Although CPM and EPM do not involve cortical structures, involvement of white matter and subcortical nuclei can produce generalized slowing on the EEG.111,112 B-S has never been reported in CPM. B-S consists of bursts of high-voltage slow waves intermixed with sharp waves, alternating with periods of depressed background activity or complete electrographic suppression. It was first described in 1949.113 Most experts consider deafferentation of the cortex from thalamus as the pathogenesis of B-S.114 At variance with cortical neurons, only 60–70% of thalamic cells ceased firing before overt EEG B-S and was completely silent during flat periods of EEG activity. The remaining 30– 40% of thalamic cells discharged rhythmic (1–4 Hz) spike bursts during periods of EEG silence. This rhythm, within the frequency range of delta waves, is generated in thalamic cell hyperpolarization.115 B-S and periodic spikes indicate coma with dissolution of cerebral functions down to the midbrain level.116 This theory fits with this patient, whose MRI shows involvement of brainstem at the midbrain and pontine levels.
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FIGURE 558. Burst-Suppression Pattern; Central Pontine Myelinolysis. (Same EEG as in Figure 5-57) EEG of a 2-year-old boy with septo-optic dysplasia and panhypopituitarism who developed central pontine myelinolysis (CPM) secondary to hypernatremia. Note a burst-suppression EEG pattern. Axial T2-weighted image shows hyperintense lesions in the pons (arrow) and cerebellum (open arrow).
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FIGURE 559. Background Asynchrony; Diffuse Axonal Injury: Vasogenic Edema in Corpus Callosum. EEG of a 7-year-old boy with moderate traumatic brain injury (TBI) shows asynchronous background activity. Diffusion-weighted image shows hemorrhages in multiple areas, including the genu of the corpus callosum (CC) (open arrow), right hippocampus (arrow), white matter (double arrows), and white-gray matter junction (arrow head). Mild TBI is associated with diffusion tensor imaging (DTI) abnormalities in the genu. In more severe TBI, both the genu and the splenium are affected. DTI suggests a larger contribution of vasogenic edema in the genu than in the splenium in TBI.117 The CC may play a critical role in interhemispheric synchronization of cortical neuronal electrical activity. Disruption of CC may cause cortical areas to be released from such synchronization and act autonomously.118,119
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FIGURE 560. Background Asynchrony; Ohtahara Syndrome Associated with Dysgenesis of Corpus Callosum. EEG of a 7-month-old boy with Ohtahara syndrome who subsequently developed infantile spasm. (A, B) Cranial MRI and CT reveal dysgenesis of corpus callosum. EEG shows an asynchronous burst-suppression (B-S) pattern. Asynchronous B-S may be explained by the following: (1) the corpus callosum normally modulates interhemispheric synchronization of cortical inhibition; (2) B-S pattern is generated by cortical structures; (3) with corpus callosal disruption, cortical areas are released from such synchronization and act autonomously.118,119
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FIGURE 561. Nonketotic Hyperglycinemia (NKH); Burst-Suppression Pattern. A 10-year-old girl with progressive encephalopathy and medically intractable epilepsy resulting from nonketotic hyperglycinemia (NKH). (A) CT scans performed at 8 years of age, 7 months apart, show progressive brain atrophy. (B) MRI done at 9 years of age shows diffuse brain atrophy and mild thinning of corpus callosum. EEG during sleep demonstrates a burst-suppression pattern. EEGs were grossly abnormal in all patients with NKH. In the neonatal period, the “suppression-burst” pattern was observed. The EEG changed to hypsarrhythmia during early or mid-infancy. In the 2nd to 5th years of life, multifocal epileptiform discharges superimposed on diffuse slow background activity occurred during wakefulness, but more severe disorganization of the EEG occurred in sleep with the emerging of hypsarrhythmia.120 NKH must be in the differential diagnosis in all infants with infantile spasms who have a burst-suppression EEG pattern, as well as dysgenesis of the corpus callosum. The burst-suppression EEG pattern in this patient continues into older age, especially during sleep.
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FIGURE 562. Asynchronous Burst Suppression; Severely Diffuse Axonal Injury. A 15-year-old male with coma and frequent myoclonic jerks caused by severe head injury from a motor vehicle accident. Cranial MRI showed severely diffuse axonal injury, including hemorrhage in the corpus callosum. EEG demonstrates asynchronous burstsuppression (B-S) throughout the recording. The patient died a few days after this EEG tracing. Asynchronous B-S under pentobarbital anesthesia in patients with a corpus callosum hemorrhage has been reported. The corpus callosum may play a critical role in interhemispheric synchronization of cortical neuronal electrical activity. Asynchronous B-S associated with corpus callosum hemorrhage may be explained by the following: (1) the corpus callosum normally modulates interhemispheric synchronization of cortical inhibition; (2) the B-S pattern is generated by cortical structures; (3) with corpus callosal disruption, cortical areas are released from such synchronization and act autonomously.118,119
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FIGURE 563. Severe Anoxic Encephalopathy. An adult male with cardiac arrest due to myocardial infarction. The patient had frequent generalized myoclonic jerks that were time-locked with eye opening. He died 2 days after this EEG. The EEG shows a burst of generalized high-voltage polyspike-wave activity accompanied by a series of clinical symptoms, including eye opening, body jerking, and eye closing lasting for approximately 1–2 sec. This clinico-encephalographic finding is extremely rare and always indicative of a very poor prognosis for survival.121
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FIGURE 564. Severe Anoxic Encephalopathy. A 23-year-old man with severe traumatic brain injury and severe hypoxic encephalopathy who developed very frequent episodes of body jerking accompanied by eye opening and closing. He died 1 day after this EEG recording. The EEG shows a burst of generalized high-voltage spikes and sharp waves intermixed with alpha, theta, and delta activity against a very low-voltage background activity. This EEG activity is accompanied by eye opening, body jerking, and then eye closure. This clinico-encephalographic finding is indicative of a very poor prognosis for survival.121
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FIGURE 565. Burst-Suppression Pattern; Anoxic Encephalopathy. A 12-year-old boy with severe anoxic encephalopathy due to near drowning. The patient was in comatose state and had no brain stem reflexes on examination. He was not on any sedative medication. EEG shows bursts of generalized high-voltage spikes and sharp waves intermixed with irregular delta activity against a very low-voltage background. Periodically, rapid eyelid opening followed by a very brief body jerk and slow eyelid closure corresponding to the onset and termination of EEG suppression bursts are noted. The burst-suppression pattern in anoxic encephalopathy is usually associated with a very poor prognosis. Severe myoclonic jerks may accompany the bursts of EEG activity. Focal or multifocal intermittent jerks affecting only facial muscles, especially eyes and mouth, are rarely seen in association with bursts of EEG activity. These movements can mimic volitional movements in response to external stimuli and mislead the physician about the patient’s mental status. The presence of these movements does not change the poor prognosis associated with the burst-suppression EEG pattern. On rare occasions, these movements can be periodic. It is hypothesized that the myoclonus may arise from a brain stem generator because the cortex is severely damaged and unable to generate cerebral activity.121–122
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FIGURE 566. Evolution of EEG in Anoxic Encephalopathy: Burst-Suppression. An 18-year-old male who had cardiorespiratory arrest after severe head trauma from MVA. He was in a comatose state and subsequently developed frequent myoclonic jerks. Head CT showed diffuse, massive brain edema. The patient was not sedated. EEG performed on the 2nd day of admission shows a burst-suppression pattern.
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FIGURE 567. Evolution of EEG in Anoxic Encephalopathy: GPEDs. (Same patient as in Figure 5-66) EEG on day 3 shows bilateral synchronous spikes and sharp waves in all regions with frontal predominance, occurring every 0.5–1.5 sec. Generalized periodic epileptiform discharges (GPEDs) after an anoxic encephalopathy carries a poor prognosis for survival. Aggressive treatment may not be warranted, especially when GPEDs with very low inter-GPED amplitude are seen after anoxic brain injury. On the other hand, 43% of patients with toxic/metabolic disturbance and 64% with a primary neurologic process with GPEDs survived. Approximately 30% of GPEDs are associated with NCSE. GPEDs with SE have higher amplitude, longer duration, and lower inter-GPED amplitude.
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FIGURE 568. Evolution of Severe Anoxic Encephalopathy; Electrocerebral Inactivity (ECI). (Same patient as in Figure 5-66 and 5-67) EEG (note: sensitivity of 2 μV/mm) on day 5 shows no cerebral activity and is not reactive to noxious stimuli, consistent with electrocerebral inactivity (ECI). Cardiorespiratory support was discontinued shortly after this EEG and a negative apnea test. ECI indicates breakdown of neuronal electrical activity due to irreversible depolarization of the membrane potential. All patients with ECI die or survive with severe neurologic deficits. ECI can be helpful in confirming the diagnosis of brain death if the EEG is performed with all technical standards established by the American Clinical Neurophysiology Society.127
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FIGURE 569. Low-Voltage EEG; Bilateral Subdural Effusion. A 3½-month-old female with a history of nonaccidental trauma at 2 months of age. EEG during wakefulness demonstrates diffuse low-voltage activity with mild preservation of background activity in the left temporal region. Head CT performed 5 days later showed massive, bilateral subdural effusion. Signal attenuation in this EEG was caused by the effect of subdural fluid collection on scalp-recorded potentials rather than loss of cortical activity. Properties of the volume-conducting medium between intracranial generators and scalp electrodes can have a major effect on the recorded potentials. A regional increase in the thickness of the conducting medium (fluid collection) between intracranial generators and overlying electrodes may lead to significant focal attenuation of electrical activity, as in this case of a subdural fluid collection. This is an example of EEG application of volume conduction theory.128
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FIGURE 570. Scalp Edema and High Frequency Respirator Artifacts. An 18-day-old boy with diaphragmatic hernia, pulmonary hypoplasia, and generalized skin edema, including severe scalp edema due to hypoalbuminemia, who had been on ECMO since birth. Head CT showed significant extra-axial CSF space. His level of consciousness was improving. EEG demonstrates very low-voltage background activity throughout the recording probably caused by a combination of scalp edema, increased extra-axial CSF space, and hypoxic-ischemic encephalopathy. Note artifactual, low-voltage, rhythmic, 7-Hz theta activity due to the high-frequency respirator in the right occipital electrode (arrow).
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FIGURE 571. Severe Hypoxic Ischemic Encephalopathy (HIE); Electrocerebral Inactivity (ECI). A 2-day-old full term newborn with severe hypoxic ischemic encephalopathy. Axial T1W1 MR shows loss of signal in the posterioir limb of internal capsule (open arrow) and increased signal in posterior putamen, GP, lateral thalamus (arrow), and cortex and subcortical white matter. Sagittal T1W1 MR shows increased signal in basal ganglion (double arrows). EEG shows no cerebral activity with the EEG sensitivity of 2 μV/mm . ECI can be interpreted as a sign of brain death if there are absence of cortical and brainstem functions, evidence of intoxication, or hypothermia. Minimal technical standards for the EEG recording in brain death by The American Encephalographic Society (120) are required.
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5 74. Gloor P., Kalabay O, Giard, N. The electroencephalogram in diffuse encephalopathies: electroencephalographic correlates of grey and white matter lesions. Brain. 1968;91:779–802. 75. Singh R, Gardner RJM, Crossland, KM, et al. Chromosomal abnormalities and epilepsy: a review for clinicians and gene hunters. Epilepsia. 2002;43: 127–140. 76. Gloor P., Ball G. Schaul N. Brain lesions that produce delta waves in the EEG. Neurology. 1977;27:326–333. 77. Steriade M., Gloor P, Llinas R.R, Lopes da Silva, F.H, Mesulam M.M. Basic mechanisms of cerebral rhythmic activities. Electroencephalogr Clin Neurophysiol. 1998;106:11–107. 78. Schaul N. The fundamental mechanisms of electroencephalography. Electroenceph Clin Neurophysiol. 106, pp. 101–107. 79. Gibbs FA, Gibbs EL, Lennot WG. Effect on the electroencephalogram of certain drugs which influence nervous activity, Arch Intern Med. 1937;60:154–166. 80. Chatrian G-E, Turella G. Electrophysiological evaluation of coma and other states of diminished responsiveness and brain death. In: Ebersole JS, Pedley TA, eds. Practice of Clinical Electroencephalography. Philadelphia: Lippincott Williams and Wilkins; 2003:405–462. 81. Evans BM, Bartlett JR. Prediction of outcome in severe head injury based on recognition of sleep related activity in the polygraphic electroencephalogram. J Neurol Neurosurg Psychiatry. 1995;59:17–25. 82. Gloor P. Generalized cortico-reticular epilepsies. Some considerations on the pathophysiology of generalized bilaterally synchronous spike and wave discharge. Epilepsia. 1968;9(3):249–263. 83. Stam C, Pritchard W. Dynamics underlying rhythmic and non-rhythmic variants of abnormal, waking delta activity. Int J Psychophysiol. 1999;34(1):5–20. 84. Markand ON. Pearls, perils, and pitfalls in the use of the electroencephalogram. Semin Neurol. 2003;23(1):7–46. 85. Klass DW, Westmoreland BF. Nonepileptogenic epileptiform electroencephalographic activity. Ann Neurol. 1985;18(6):627–635. 86. Yamada T, Tucker RP, Kooi KA. Fourteen and six c/sec positive bursts in comatose patients. Electroencephalogr Clin Neurophysiol. 1976;40(6):645–653. 87. Yamada T, Young S, Kimura J. Significance of positive spike burst in Reye syndrome. Arch Neurol. 1977;34(6):376–380.
5 88. Drury I. 14-and-6 Hz positive bursts in childhood encephalopathies. Electroencephalogr Clin Neurophysiol. 1989;72(6):479. 89. Kooi K. Involutary movements associated with fourteenand six-per-second positive waves. Report of a case with electroencephalographic studies. Neurology. 1968;18(10):997. 90. Hughes JR. Sleep spindles revisited. J Clin Neurophysiol. 1985;2(1):37–44. 91. Dan B, Boyd SG. A neurophysiological perspective on sleep and its maturation. Dev Med Child Neurol. 2006;48(09):773–779. 92. Hughes JR. EEG in Clinical Practice. Boston: Butterworth-Heinemann. 1994. 93. Akaboshi S, Koeda T, Houdou S. Transient extreme spindles in a case of subacute Mycoplasma pneumoniae encephalitis. Pediatr Int. 1998;40(5):479–482. 94. Heatwole CR, Berg MJ, Henry JC, Hallman JL. Extreme spindles: a distinctive EEG pattern in Mycoplasma pneumoniae encephalitis. Neurology. 2005;64:1096–1097. 95. Gallucci M, Limbucci N, Paonessa A, Caranci F. Reversible focal splenial lesions. Neuroradiology. 2007;49:541–544. 96. Loeb C, Poggio G. Electroencephalograms in a case with ponto-mesencephalic haemorrhage. Electroencephalogr Clin Neurophysiol. 1953;5(2):295. 97. Westmoreland B, Klass DW, Sharbrough FW, Reagan TJ. “Alpha coma.” Electroencephalographic, clinical, pathologic and etiological correlations. Arch Neurol. 1975;32:713–718. 98. Kaplan PW, Genoud D, Ho TW, et al. Etiology, neurologic correlations, and prognosis in alpha coma. Clin Neurophysiol. 1999;110:205–213. 99. Austin EJ, Wilkus RJ, Longstreth WT, Jr. Etiology and prognosis of alpha coma. Neurology. 1988;38(5):773–777. 100. Ramachandrannair R, Sharma R, Weiss SK, et al: A reappraisal of rhythmic coma patterns in children. Can J Neurol Sci. 2005;32:518–523. 101. Horton EJ, Goldie WD, Baram TZ. Rhythmic coma in children. J Child Neurol. 1990;5(3):242–7. 102. Berkhoff M, Donati F, Bassetti C. Postanoxic alpha (theta) coma: a reappraisal of its prognostic significance. Clin Neurophysiol. 2000;111(2):297–304.
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103. Young GB, Blume WT, Campbell VM, Demelo JD, Leung LS, McKeown MJ, McLachlan RS, Ramsay DA, Schieven JR. Alpha, theta and alpha-theta coma: a clinical outcome study utilizing serial recordings. Electroencephalogr Clin Neurophysiol. 1994;91:93–99. 104. Qvarnstrom Y, Visvesvara GS, Sriram R & Da Silva AJ (2006) A multiplex real-time PCR assay for simultaneous detection of Acanthamoeba spp., Balamuthia mandrillaris and Naegleria fowleri. J Clin Microbiol. 2006;44:3589–3595. 105. Bodi I, Dutt N, Hampton T, Akbar N. Fatal granulomatous amoebic meningoencephalitis due to Balamuthia mandrillaris. Pathol Res Pract. 2008;204(12):925–928. 106. Bakardjiev A, Azimi PH, Ashouri N, Ascher DP, Janner D, Schuster FL, Visvesvara GS, Glaser C. Amebic encephalitis caused by Balamuthia mandrillaris: report of four cases. Pediatr Infect Dis. 2003;22:447–452. 107. Tunkel AR, Glaser CA, Bloch KC, et al. The management of encephalitis: clinical practice guidelines by the Infectious Diseases Society of America. Clin Infect Dis. 2008;47:303–327. 108. Griesemer DA, Barton LL, Reese CM, et al. Amebic meningoencephalitis caused by Balamuthia mandrillaris. Pediatr Neurol. 1994;10:249–254. 109. Healy JF. Balamuthia amebic encephalitis: radiographic and pathologic findings. Am J Neuroradiol 2002;23:486–489. 110. Perez M, Bush L. Balamuthia mandrillaris amebic encephalitis. Current Infect Dis Rep. 2007;9(4):323–328. 111. Steg R, Wszolek Z. Electroencephalographic abnormalities in liver transplant recipients: practical considerations and review. J Clin Neurophysiol. 1996;13(1):60. 112. Wszolek ZK, McComb RD, Pfeiffer RF, et al. Pontine and extrapontine myelinolysis following liver transplantation. Transplantation. 1989;48:1006–1012 113. Swank R, Watson C. Effects of barbiturates and ether on spontaneous electrical activity of dog brain. J Neurophysiol. 1949;12(2):137–160. 114. Savard M, Huot P. Asynchronous burst-suppression on EEG in severe, diffuse axonal injury. Can J Neurol Sci. 2008;35(4):526–527. 115. Steriade M, McCormick DA, Sejnowski TJ. Thalamocortical oscillations in the sleeping and aroused brain. Science. 1993;262(5134):679–685.
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116. Bauer G, Niedermeyer E. Acute convulsions. Clin EEG (Electroencephalogr). 1979;10(3):127. 117. Rutgers DR, Toulgoat F, Cazejust J, Fillard P, Lasjaunias P, Ducreux D. White matter abnormalities in mild traumatic brain injury: a diffusion tensor imaging study. Am J Neuroradiol. 2008;29:514–519. 118. Lazar LM, Milrod LM, Solomon GE, Labar DR. Asynchronous pentobarbital-induced burst suppression with corpus callosum hemorrhage. Clin Neurophysiol. 1999;110:1036–1040. 119. Lambrakis C, Lancman M, Romano C. Asynchronous and asymmetric burst-suppression in a patient with a corpus callosum lesion. Clin Neurophysiol. 1999;110(1):103–105. 120. Markand ON, Garg BP, Brandt IK. Nonketotic hyperglycinemia: electroencephalographic and evoked potential abnormalities. Neurology. 1982;32(2):151–156. 121. McCarty G, Marshall D. Transient eyelid opening associated with postanoxic EEG suppression-burst pattern. Arch Neurol. 1981;38(12):754–756. 122. Wolf P. Periodic synchronous and stereotyped myoclonus with postanoxic coma. J Neurol. 1977;215(1):39–47. 123. Jumao-as A, Brenner R. Myoclonic status epilepticus: a clinical and electroencephalographic study. Neurology. 1990;40(8):1199–1202. 124. Reeves A, Westmoreland B, Klass D. Clinical accompaniments of the burst-suppression EEG pattern. J Clin Neurophysiol. 1997;14(2):150. 125. Hallett M. Physiology of human posthypoxic myoclonus. Mov Disord. 2000;15:8–13. 126. Fernández-Torre J, Calleja J, Infante J. Periodic eye opening and swallowing movements associated with post-anoxic burst-suppression EEG pattern. Epileptic Disord. 2008;10(1):19. 127. American Electroencephalographic Society. Guideline three: minimum technical standards for EEG recording in suspected cerebral death. J Clin Neurophysiol. 1994;11(1):10–13. 128. Lagerlund TD, Daube JR, Rubin DI. Volume Conduction. In: Daube JRR, Devon I, eds. Clinical Neurophysiology. New York: Oxford University Press.2009:33–52.
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EEG pattern of encephalopathy
Nonspecific patterns 䡲
Alpha rhythm slowing → theta slowing → delta slowing → loss of alpha rhythm → loss of normal faster activity → loss/attenuation of sleep architectures, abnormal arousal patterns and presence of frontal intermittent rhythmic delta activity (FIRDA) → loss of normal variability and state changes → loss of reactivity to external stimuli, burst-suppression (B-S) → electrocerebral inactivity (ECI).
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In severe encephalopathy, the EEG does not show reactivity to any stimulation and is called invariant EEG.
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Bilateral but lateralized polymorphic delta activity (PDA) is characteristic of frontal lobe lesions. Functional or structural abnormal thalamocortical interactions, especially the dorsal medial nucleus of the thalamus, play a major role in IRDA.
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A combination of FIRDA or OIRDA and continuously focal PDA is the classic sign of impending cerebral herniation from a focal structural abnormality. However, the same combination of patterns can also be seen in patients with focal structural lesions and coexistent toxic or metabolic encephalopathies. Therefore, clinical correlation is required.
Specific patterns Generalized Periodic Epileptiform Discharges (GPEDs) 䡲 䡲
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Anoxic encephalopathy After status epilepticus (SE)
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Toxic encephalopathy 䡲 Creutzfeldt-Jakob disease (CJD; GPEDs at approximately 1 Hz) Triphasic Waves 䡲 Toxic/metabolic encephalopathy 䡲 NCSE Periodic Lateralized Epileptiform Discharges (PLEDs) 䡲 Acute or subacute unilateral lesions 䡲
EEG reactivity (Figures 6-6 and 6-7) 䡲
In milder encephalopathy, the EEG shows spontaneous variability, evidence of EEG reactivity to stimulation, typically attenuation of amplitude, reduction of delta activity, and increase in frequency. 䡲 Paradoxical activation is a period of more severe delta slowing following painful stimulation. It is seen less commonly than a typical response to stimuli but associated with a milder degree of encephalopathy compared to the invariant EEG.
Periodic lateralized epileptiform discharges (PLEDs) (Figures 6-8 and 6-9)
Most commonly seen in stroke and herpes simplex encephalitis
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Normal or Near-Normal EEG 䡲 Psychogenic process or brainstem disease ((locked-in syndrome)
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Diffuse polymorphic delta slowing (delta coma) (Figures 6-1 to 6-4, 6-30) 䡲
Advanced states of encephalopathy and coma. 䡲 Caused by structural abnormalities involving subcortical white matter or profound metabolic coma.
PLEDs is defined as an EEG pattern consisting of sharp waves, spikes (alone or associated with slow waves), or more complex wave forms occurring at periodic intervals.
Considered an interictal > ictal pattern. Transient phenomenon (disappear within days to weeks). 䡲 Clinical: lethargic, focal seizures, focal neurological signs. 䡲 Occur at the rate of 1–2/sec and are commonly seen in posterior head region, especially in the parietal areas. 䡲
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Sometimes associated with EPC. Related to an acute or subacute focal brain lesion involving gray matter. Chronic PLEDs were also reported in 9% of patients with intractable epilepsy who had structural abnormalities such as cortical dysplasia or severe remote cerebral injury. Etiology: 䊳 Acute stroke, tumor, and CNS infection were the most common etiologies. 䊳 Others included acute hemorrhage, TBI, PRES, familial hemiplegic migraine, and cerebral amyloidosis. PLEDs were more periodic when they were associated with acute viral encephalitis than with other etiologies. Most HSV encephalitides have PLEDs, maximal in the temporal region. Seizure activity occurred in 85%, with mortality rate of 27%. In one series, 50% of patients with PLEDs never developed clinical seizure.
Periodic epileptiform discharges in the midline (PEDIM) (Figures 6-10 and 6-11)
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Most commonly caused by multifocal or diffuse cerebral injury, such as anoxic encephalopathy and CNS infection, as well as strokes and epileptic seizure disorders (especially complex partial SE). 䡲 Mortality of 52%, twice of patients with PLEDs. 䡲
Higher incidence of seizures. 䡲 BiPLEDs and GPEDs after an anoxic insult carried a poor prognosis for survival. Aggressive treatment of patients may not be warranted when these EEG patterns are seen after anoxic brain injury.
Generalized periodic epileptiform discharges (GPEDs) (Figures 6-19 to 6-21) 䡲
Subcortically triggered cortical excitation alternating with prolonged inhibitory events.
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Periodic complexes that occur throughout the brain in a symmetric and synchronized manner.
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Not consistently associated with a specific etiology including:
Hypoxic encephalopathy (HE) (Figures 6-5 and 6-16)
Bilateral independent periodic lateralized epileptiform discharges (BiPLEDs) (Figures 6-12 to 6-16) 䡲
Bilateral and asynchronous, and differ in amplitude, morphology, repetitive rate, and the location.
Severe anoxic encephalopathy
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Post-SE
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Toxic encephalopathy 앫 High doses of almost any drugs depressing
central nervous system function.
Poor prognosis for HE 䡲 䡲 䡲
앫 Lithium, baclofen, ifosphamide, and cefepime
Suppression. Burst-suppression. Alpha- and theta-pattern coma.
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Generalized suppression to ≤20 μV.
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Burst-suppression patterns with generalized epileptiform activity.
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Generalized periodic complexes (GPEDs), especially on a flat background.
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Nonreactive EEG.
Hemiconvulsion hemiplegia epilepsy syndrome (HHE) (Figures 6-17 and 6-18)
Metabolic encephalopathy
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CJD
Whether GPEDs represent an EEG pattern of SE is debated. Many believe that the GPEDs represent brain damage rather than ongoing SE.
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GPEDs with high amplitude (mean, 110 μV) and longer duration (mean, 0.5 sec), with preserved interGPED amplitude (mean, 34 μV), were more likely to be associated with SE, although these differences could not be used clinically in isolation to differentiate between SE and non-SE.
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Patients with GPEDs whose clinical history and EEG are consistent with SE should be managed aggressively with antiepileptic drugs.
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Other characteristics that favor a more optimistic outlook include:
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Rare sequence comprising a sudden and prolonged hemiclonic seizure during febrile illness in an otherwise normal child, followed by permanent ipsilateral hemiplegia and focal epilepsy. 䡲 Caused by CNS infection and less commonly seen in TBI or cerebrovascular accident. 䡲 Ictal EEG shows high-voltage rhythmic slow waves intermingled with spikes, sharp waves, spike-wave complexes, or low-voltage fast activity. Higher amplitude and more abundant epileptiform activities with posterior predominance are noted in the affected hemisphere.
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Same characteristics as PLEDs, except for location in midline vertex. 䡲 All had acute onset of partial motor seizures involving the lower extremity and sustained a cerebrovascular insult. 䡲 Origin from the watershed area involving predominantly the parasagittal, midline parietal, or midline central areas. 䡲 The location of the PEDIM corresponded to the seizure type and focal neurologic deficits.
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Younger age
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Higher level of alertness at the time of the EEG
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History of seizures in the current illness
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Higher inter-GPED amplitude
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Independently associated with poor outcome in 90% of those with GPEDs versus 63% of those without.
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GPEDs and BiPLEDs after an anoxic insult carried a poor prognosis for survival. Aggressive treatment
6 of patients may not be warranted when these EEG patterns are seen after anoxic brain injury.
Stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs) (Figure 6-22)
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Most common human transmissible subacute spongiform encephalopathy (TSSE).
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Most CJD cases are sporadic (85%). The remaining 15% consist of genetic forms (genetic CJD, Gerstmann-Sträussler-Scheinker disease, fatal familial insomnia) and iatrogenic forms (cadaveric human growth hormone and dura mater, surgical or other invasive procedures, and transfusionassociated variant CJD infections). CJD has been reported in children.
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Periodic, rhythmic, or ictal-appearing discharges that were consistently induced by alerting stimuli. 䡲 Quasiperiodic discharges (sharp waves, spikes, polyspikes, or sharply contoured delta waves) recurring at regular intervals are noted. 䡲
At times, the pattern became continuous and rhythmic rather than periodic.
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The periodic or rhythmic nature of SIRPIDs may be a reflection of the oscillations generated by burst firing of the reticular thalamic nucleus. In the normal setting, the cortex inhibits thalamocortical bursting. In cortical dysfunction, disruption of this inhibitory feedback on the thalamus by cortical projections causes rhythmic activity.
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These EEG patterns often qualify as electrographic seizures but are consistently elicited by stimulation.
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Common in encephalopathy, critically ill patients, and particularly those with acute brain injury.
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The relation between clinical seizures and SIRPIDs is unclear; therefore, there is no consensus on how aggressively SIRPIDs should be treated.
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In patients with cortical and subcortical dysfunction, alerting stimuli activate the arousal circuitry and, when combined with hyperexcitable cortex, result in epileptiform activity or seizures. This activity can be focal or generalized, and is usually nonconvulsive.
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EEG in CJD usually starts with PLEDs with atypical short interdischarge intervals of 0.5–2 sec.
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It usually takes several months to evolve into BiPLEDs or periodic sharp wave complexes (PSWCs).
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In the terminal stage when myoclonus subsides, EEG shows low-voltage EEG or continuously diffuse PDA.
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Generalized periodic discharges at approximately 1 Hz, with rapidly progressive dementia and myoclonus.
All patients showed PSWCs if serial recordings are performed in different stages of the disease. In another series, at the fully developed stage of the disease, 94% of the EEGs showed PSWCs. The sensitivity, specificity, and positive and negative predictive values of PSWC were 64%, 91%, 95%, and 49%, respectively. Alzheimer’s disease and vascular dementia were the underlying diseases in the falsely positive cases.
Subacute sclerosing panencephalitis (SSPE) (Figure 6-24) 䡲
Periodic high-amplitude complexes in almost all cases.
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The periodic complexes consist of two to four high-amplitude delta waves, polyspikes, and sharpand-slow wave complexes of 0.5–2 sec in duration, and are usually bisynchronous and symmetric and repeated at irregular intervals once in 5–7 sec but can last up to 15 sec.
If the electrographic seizure activity is adequately synchronized in a specific region involving motor pathways, focal motor seizures can occur.
Creutzfeldt-Jakob disease (CJD) (Figure 6-23)
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When both the clinical myoclonic jerks and the periodic EEG complexes were present, a one-to-one relationship existed between the two phenomena.
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Other atypical EEG findings included:
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Frontal rhythmic delta activity in intervals between periodic complexes. Electrodecremental periods following EEG complexes. Paroxysm of bisynchronous spike-wave activity.
Random spikes over frontal regions. Focal abnormalities, such as spike- and slowwave foci. 䡲 In the terminal stage, the background activity is suppressed, and the periodic complexes disappear. 䊳 䊳
Rhythmic coma (Figures 6-25 to 6-37) 䡲
Invariant, nonreactive, diffuse cortical activity of a specific frequency, such as alpha, beta, spindle, or theta, is called a rhythmic coma.
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The clinical outcome in rhythmic coma pattern depended on the underlying cause rather than the EEG finding.
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Beta coma is generally caused by intoxication and, thus, is often a reversible EEG abnormality. It may also be caused by acute brain stem lesions.
Alpha coma 䡲
Alpha frequency range (8–13 Hz) that occurs with a generalized distribution in a comatose patient. 䡲 Alpha coma can be distinguished from physiologic alpha rhythm by: 䊳 Monotonous, monophasic, symmetric, and most commonly anterior predominance (except alpha coma caused by brain stem lesion, which is posterior predominance) 䊳 Widespread distribution Highly persistent and nonreactive to stimuli May be caused by interruption of reticulothalamocortical pathways by metabolic or structural abnormalities. 䡲 Etiology and outcome of alpha coma patterns and other rhythmic coma patterns (beta, theta, and spindle) are similar. 䊳
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One type of rhythmic pattern can change to another. Sequential EEG recordings are required to detect the evolution of rhythmic coma patterns during childhood. 䡲 Monomorphic and no change to sensory stimuli. 䡲
Most commonly predominant in frontal region. 䡲 Most frequently seen in anoxic encephalopathy caused by cardiorespiratory arrest hypoxia. 䡲 Also seen in drug overdose, which is very similar to that seen with cardiorespiratory arrest, except with beta activity superimposed on the alpha activity.
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Other etiologies include head trauma, CJD, pontomesencephalic lesions, and encephalitis. 䡲 Prognosis depends on the underlying causes of coma. 䡲
Reactive rhythmic coma was associated with favorable outcome. 䡲 Prognosis is very poor in anoxic encephalopathy, especially if it develops after 24 hours of coma. 䡲
Alpha coma is replaced within 5–10 days by delta coma. EEG reactivity in subsequent patterns is relatively favorable, while a B-S pattern without reactivity is unfavorable in anoxic-ischemic encephalopathy.
Burst-suppression (B-S) (Figures 6-38 to 6-41) 䡲
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Complex wave forms (amplitudes of the bursts, multiple sharps, and spikes or regular/irregular rhythmic activity from delta to beta range, varying from <20 to >100 μV) alternating with completely attenuated background activity (<10 mV).
Indicative of severe diffuse encephalopathy and immediately precedes ECI. 䡲 In the absence of a high level of sedative medications, severe metabolic disturbances, and hypothermia, B-S is indicative of irreversible severe encephalopathy and carries a very poor prognosis. 䡲 Experimental study of B-S showed that almost all (95%) cortical neurons become electrically silent during the flat EEG. Hyperpolarization of cortical
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neurons due to increased K+ conductance precedes EEG flattening, which in turn is secondary to increased GABAergic inhibition at cortical synapses. This inhibition leads to functional disconnection of cortex from thalamic input, but 30–40% of thalamic cells continue firing while the cortex is silent. This is due to the intrinsic pacemaking properties of the thalamic neurons at modest levels of hyperpolarization. Volleys from these thalamocortical neurons account for the cyclic EEG wave bursts. Spontaneous movements, especially myoclonic jerks associated with spontaneous eye opening and closing, during bursts of spike and sharp wave EEG activity are extremely rare and can be seen in deeply comatose patients after global anoxic or ischemic insult. They may be misread as signs of clinical improvement, although they apparently indicate grave prognosis similar to B-S EEG pattern without associated clinical symptoms. Generalized myoclonus in comatose survivors of CPR indicates a poor outcome despite advances in critical care medicine. AEDs are not effective. Amplitude of bursts in B-S: barbiturates higher > propofol > benzodiazepines. Common conditions: 䊳 Acute intoxication 䊳 Severe anoxic encephalopathy 䊳 Severe hypothermia 䊳 Anesthesia
Depression and lack of differentiation EEG (Figure 6-42)
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Electrocerebral inactivity (ECI) (Figures 6-43, 6-5) 䡲
Defined as “no cerebral activity over 2 μV when recording from scalp or referential electrode pairs, 10 or more centimeters apart with interelectrode resistances under 10,000 Ω (or impedances under 6000 Ω) but over 100 Ω.”
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Indicative of death only of the cortex, not the brain stem; therefore, a newborn can have prolonged survival despite having an EEG with ECI.
Fourteen- and 6-Hz positive spikes in encephalopathy (Figures 6-44, 5-44 to 5-48) 䡲
The 14- and 6-Hz positive spike pattern shows a similar incidence and morphology and topography to healthy children.
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The normal wave form is selectively preserved and more resistant to underlying structural or metabolic processes than other background features of drowsiness and sleep. 䡲 The positive spike bursts with continuous delta activity in comatose children are a rare but unique EEG pattern associated with hepatic, anoxic encephalopathy and other toxic/metabolic and primary cerebral insult. 䡲 In some subjects, 14- and 6-Hz positive spikes were provoked by auditory and somatosensory stimuli. 䡲
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Indicative of severe brain insult but is nonspecific in etiology and can be due to a wide variety of conditions, including severe HIE, severe metabolic disorders, meningitis or encephalitis, cerebral hemorrhage, and IVH. 䡲 A depressed and undifferentiated EEG within the first 24 hours after birth that persists indicates a poor prognosis.
All patients with HIE bilateral basal ganglia involvement have developmental delay.
Should not be misinterpreted as “paroxysmal fast activity (PFA).” The morphology, polarity, and distribution can differentiate between these two wave forms.
Refractory status epilepticus (RSE) (Figure 6-45 to 6-48) 䡲
Poor prognosis in children with mortality rate in one series of 32%.
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In seizures lasting >30 minutes, only 23% of the survivors were normal at follow-up; 34% showed developmental deterioration and 36% developed new-onset epilepsy.
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Mortality is related to etiology and is higher in younger children and with multifocal or generalized abnormalities on the initial EEG.
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RSE due to either an acute symptomatic etiology or a progressive encephalopathy were associated with highest mortality rates. Shorter duration of suppressive therapy, ultimately with the same outcome and possibly with fewer complications, was recommended. Continuous EEG monitoring detected seizure activity in 19% of patients, and the seizures were almost always NCSE. Coma, age <18 years, a history of epilepsy, and convulsive seizures prior to monitoring are risk factors for electrographic seizures. Comatose patients frequently require >24 hours of monitoring to detect the first electrographic seizure. TBI (18–28%), ischemic stroke (11–26%), and CNS infection (29–33%) are the most common causes of NCSE. Neuronal cell loss in HS occurs as the result of prolonged severe seizure activity in humans.
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MRI change in the early stage of SE, in as little as 24 hours, is manifest by either asymmetrical or bilateral T2 signal hyperintensity in the hippocampi (HC) caused by focal transient cytotoxic and vasogenic edema. 䡲 Significant volume loss in both hippocampi between weeks 4 and 10, most likely representing neuronal loss and astrogliosis as the correlate of the later histologically proven hippocampal sclerosis. 䡲 HS can develop within 2 months of SE and may further progress during the following 3–4 years.
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TWs have been considered as a pathognomonic sign in severe hepatic encephalopathy, but they are also seen in encephalopathies associated with renal failure or electrolyte imbalance, as well as anoxia and intoxications (such as lithium, metrizamide, and levodopa).
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Occur most often in patients with metabolic encephalopathies but cannot be used to distinguish different causes.
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The most characteristic EEG feature in dialysis encephalopathy was paroxysmal high-voltage delta activity with anterior predominance and, less commonly, spike-and-wave activity and triphasic waves.
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Causes: hepatic encephalopathy, uremia, valproic encephalopathy, severe electrolyte imbalance, hypercalcemia, anoxia, hypoglycemia, hyperthyroidism, myxedema, Hashimoto’s encephalopathy, hypothermia, toxic encephalopathy (baclofen, levodopa, pentobarbital, lithium, ifosphamide, and serotonin syndrome)
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Also seen in NCSE.
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Poor prognosis in severe anoxic and metabolic encephalopathy.
Triphasic waves (TWs) (Figure 6-49) 䡲 䡲 䡲
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Never been reported in children except in lithium and ifosphamide toxicity. Rarely reported below the age of 20 years. Bursts of moderate- to high-amplitude complexes, usually at 1.5–2.5 Hz, with three (but sometimes two or four) negative-positive-negative phases, usually occurring in runs at 1.5–3/sec or more continuously. Fronto-occipital lag of 25–140 msec (bipolar montage) is unique but not a constant finding. Anterior (60%) > diffuse or posterior (40%) predominance.
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FIGURE 61. Posterior Reversible Encephalopathy Syndrome (PRES); Diffuse Polymorphic Delta Activity with Posterior Predominance. A 10-year-old girl with microscopic polyangiitis and chronic renal failure developed visual hallucinations, lethargy, and new-onset seizures. She was on cyclophosphamide. After the visual hallucination, she was found to have elevation of her blood pressure. EEG shows continuously diffuse polymorphic delta activity (PDA) with occipital predominance. Head CT and MRI show diffuse white matter involvement, maximally expressed in the watershed areas in the two hemispheres. The patient recovered after cyclophosphamide was stopped, and the blood pressure was well controlled. Diffuse slowing is the most common finding on the EEGs in posterior reversible leukoencephalopathy syndrome (PRES).1 The delta coma EEG pattern is usually seen with more advanced states of encephalopathy and coma. With progression to deeper stages of coma, it appears diffuse and is usually unreactive. Polymorphic delta comas are due to structural abnormalities involving subcortical white matter or profound metabolic coma.2–4 Posterior-predominant delta activity in this case is probably due to the predominant involvement of posterior head region in PRES.
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FIGURE 62. Posterior Reversible Encephalopathy Syndrome (PRES); Occipital Lobe Seizure. (Same patient as in Figure 6-1) The patient developed a new-onset seizure described as head and eyes deviating to the right side, associated with unconsciousness lasting for approximately 3 minutes. EEG shows ictal activity arising from the left occipital lobe during the seizure. Occipital lobe seizures have been described as a major clinical manifestation of PRES. This suggests that occipital lobe seizures may play a significant role in the anatomical location of the signal changes, offering an alternative explanation for the posterior location of the lesions, instead of the hypothesis that a paucity of sympathetic innervation in that region is the reason for this location.4 Status epilepticus (SE) can be the initial presenting symptom of PRES. Ictal EEG was obtained in six patients with SE in one series. Seizure focus was parieto-occipital in four patients and temporal in two. Seizures in PRES are often occipital in origin, which correlates well with imaging findings of predominant occipitoparietal involvement.6
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FIGURE 63. Cerebral Herniation Syndrome; Continuous Polymorphic Delta Activity and FIRDA. A 7-year-old comatose girl with severe TBI causing intraparenchymal hemorrhage required brain decompression. Cranial CT shows bilateral intraparenchymal hemorrhage, much greater in the left fronto-temporal region (open arrow and double arrows), with compression of midline structure and probable bilateral cerebellar infarction/edema (arrow), signs of cerebral herniation syndrome. EEG shows asymmetrically and continuously diffuse mono- and polymorphic delta activity (PDA) with superimposed frontal intermittent rhythmic delta activity (FIRDA). Note a persistent focal suppression of the left fronto-temporal region. Bilateral but lateralized PDA is characteristic of frontal lobe lesions. Functionally or structurally abnormal thalamocortical interactions, especially involving the dorsal medial nucleus of the thalamus, play a major role in IRDA.7–9 A combination of FIRDA or OIRDA and continuously focal PDA is the classic sign of impending cerebral herniation from a focal structural abnormality. However, the same combination of patterns can also be seen in patients with focal structural lesions and coexistent toxic or metabolic encephalopathies.10,11 Therefore, clinical correlation is required.
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FIGURE 64. Improvement of Right Hemispheric FIRDA and PDA; After Resection of Necrotic Tissues, Left Hemisphere. (Same patient as in Figure 6-3) The patient developed signs of cerebral herniation. He underwent another cerebral decompression with resection of necrotic tissues in the left fronto-temporal region. EEG performed after the surgery shows continuous high-voltage polymorphic delta activity (PDA) in the left hemisphere, caused by the surgery. In addition, there is improvement of PDA and FIRDA in the frontal central midline and the right hemisphere. Unfortunately, despite subsequent treatment with pentobarbital coma, the patient deteriorated and died 4 days after the surgery. Improvement of FIRDA and PDA in the right hemisphere may be due to decreased intracranial pressure after the surgery, which can affect the thalamocortical interactions.
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FIGURE 65. Electrocerebral Inactivity (ECI); Pulse Artifact. (Same patient as in Figure 6-3 and 6-4) The EEG shows electrocerebral inactivity before the cardiorespiratory support was discontinued. Note rhythmic delta activity, mainly at F3, time-locked with ECG indicating pulse artifact. Electrocerebral inactivity is defined as “no cerebral activity over 2 μV when recording from scalp or referential electrode pairs, 10 or more centimeters apart with interelectrode resistances under 10,000 Ω (or impedances under 6000 Ω) but over 100 Ω.”12
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FIGURE 66. Paradoxical Activation. EEG of a 20-month-old girl with nonaccidental trauma (NAT). There is a period of background attenuation more severe delta slowing following stimulation. This EEG reactivity is called “paradoxical activation.” In severe encephalopathy, the EEG does not show reactivity to any stimulation and is called “invariant EEG.” In milder encephalopathy, the EEG shows spontaneous variability, evidence of EEG reactivity to stimulation, typically attenuation of amplitude, reduction of delta activity, and increase in frequency. Paradoxical activation is a period of more severe delta slowing following painful stimulation. It is seen less commonly than a typical response to stimuli but is associated with a milder degree of encephalopathy compared to the invariant EEG.13
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FIGURE 67. EEG Reactivity in Coma; Diffuse Voltage Attenuation. (Same patient as in Figure 6-6) EEG of a 20-month-old girl with nonaccidental trauma (NAT). There is a period of background attenuation without delta slowing following stimulation. In severe encephalopathy, the EEG does not show reactivity to any stimulation and is called “invariant EEG.” In milder encephalopathy, the EEG shows spontaneous variability, evidence of EEG reactivity to stimulation, typically attenuation of amplitude, reduction of delta activity, and increase in frequency.13
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FIGURE 68. PLEDs (Periodic Lateralized Epileptiform Discharges); Ischemic Stroke Due to Cardiac Transplantation. A 2-year-old boy with bilateral parietal strokes, maximal in the right hemisphere (arrow) occurring after cardiac transplantation. He developed frequent seizures described as head and eyes deviating to the left side, followed by generalized tonic-clonic seizures. MRI shows bilateral watershed infarctions in the frontal parietal regions, much greater in the right hemisphere. EEG shows periodic lateralized epileptiform discharges (PLEDs) in the right parietal temporal region and polymorphic delta slowing in parietal temporal regions, greater on the right, corresponding to the strokes. Note pacemaker rhythm in the ECG channel. PLEDs usually occur at the rate of 1–2/sec and are commonly seen in the posterior head region, especially in the parietal areas.14 Seizures occurred in 85% of patients with a mortality rate of 27%.15 Acute stroke, tumor, and central nervous system infection were the most common etiologies of PLEDs.16
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FIGURE 69. Periodic Lateralized Epileptiform Discharges (PLEDs); Posterior Reversible Encephalopathy Syndrome (PRES). A 14-year-old boy with ALL s/p bone marrow transplantation who developed posterior reversible leukoencephalopathy syndrome (PRES). He developed a new-onset seizure described as left arm and facial clonic jerking with head and eyes deviating to the left side, followed by a generalized tonic clinic seizure. EEG shows periodic lateralized epileptiform discharges in the right centrotemporal region. PLEDs were first described by Chatrian et al. (1964) to define an EEG pattern consisting of sharp waves, spikes (alone or associated with slow waves), or more complex wave forms occurring at periodic intervals. They usually occur at the rate of 1–2/sec and are commonly seen in the posterior head region, especially in the parietal areas. It is sometimes associated with EPC.14 This EEG pattern is usually related to an acute or subacute focal brain lesion involving gray matter.17 Chronic PLEDs were also reported in 9% of patients with intractable epilepsy who had structural abnormalities such as cortical dysplasia or severe remote cerebral injury.15,16 In a recent review of 96 patients with PLEDs,19 acute stroke, tumor, and CNS infection were the most common etiologies. Others included acute hemorrhage, TBI, PRES, familial hemiplegic migraine, and cerebral amyloidosis. PLEDs were more periodic when they were associated with acute viral encephalitis than with other etiologies.20 Seizure activity occurred in 85% of patients, with mortality rate of 27%. However, 50% of patients with PLEDs never developed clinical seizures.15
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FIGURE 610. Periodic Epileptiform Discharges in the Mideline (PEDIM). A 2-month-old boy with anoxic encephalopathy due to SIDS. He had multifocal clonic seizures. MRI shows bilateral watershed infarction (arrows) as typically seen in anoxic encephalopathy. EEG shows quasiperiodic spikes and sharp waves the Cz electrode. This activity has the same characteristics as periodic lateralized epileptiform discharges (PLEDs) except for its location in midline vertex. All five patients had acute onset of partial motor seizures involving the lower extremity. All patients had sustained a cerebrovascular insult, either old or new. The PEDIM and seizures suggested an origin from the watershed area between the anterior, middle, and posterior cerebral arteries, involving predominantly the parasagittal region of the cerebral hemisphere. The location of the PEDIM corresponded to the seizure type and focal neurologic deficits.21
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FIGURE 611. Periodic Epileptiform Discharges in the Midline (PEDIM); Bilateral Mesial Frontal Infarction. A 9-month-old boy with fever, left facial twitching, and then generalized tonic clonic seizure. CSF findings showed 90 WBCs with 30 PMN, 69 lymphocytes, 1 monocyte; 46 glucose; 15 total protein; and 1000 RBCs. PCR for HSV type 2 was positive. MRI showed bilateral watershed infarction in the mesial frontal regions (arrows). EEG shows quasiperiodic spikes at the central vertex electrode consistent with the PEDIM. The PEDIM has the same characteristics as periodic lateralized epileptiform discharges (PLEDs) except the location. In one series, all five patients had acute onset of partial motor seizures involving the lower extremity. All patients had strokes. The PEDIM and seizures suggested an origin from the watershed area, involving predominantly the parasagittal, midline parietal, or midline central areas. The patients had partial motor seizures involving predominantly the leg, and EPC with continuous clonic jerks of the legs time-locked with the PEDIM in the EEG. The seizures and PEDIM resolved after initiation of treatment with antiepileptic drugs and treatment of the underlying disorder. The EEG characteristics of PEDIM, other than being in the midline, are similar to those of PLEDs. Similar to PLEDs, the PEDIM carries a poor prognosis, three out of five patients died and two were left with significant neurologic deficits.21
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FIGURE 612. Bilateral Independent Periodic Lateralized Epileptiform Discharges (BiPLEDs); Acute Herpes Simplex Encephalitis. A previously healthy 4-year-old girl who presented with high fever, lethargy, vomiting, and a new-onset seizure described as head and eyes deviating to the right side, followed by cyanosis. Initial CSF showed 22 WBCs (lymphocyte predominante) and 6 RBCs with normal glucose and protein. The CSF for HSV PCR was negative on three separated occasions. Brain biopsy was performed over the left occipital region. Pathology revealed numerous histocytes and inflammatory cells with early capillary proliferation scattered throughout the molecular layer. Leptomeninges showed histocytes and chronic inflammatory cells but no evidence of vasculitis. Brain tissue for herpes simplex type 1 DNA PCR was positive. (A) MRI with FLAIR sequence demonstrates hyperintense signal in bilateral temporo-occipital regions, greater on the left (arrow and open arrow). (B) Axial T1-weighted image with GAD shows increased enhancement in the left parieto-occipital regions (double arrows). EEG shows bilateral independent spikes and sharp wave complexes in the posterior temporal region with diffuse delta slowing (arrow head and asterisk). At the last follow-up 1 year later, the patient had moderate global developmental delay, visual anogsia, and well-controlled seizures. BiPLEDs are PLEDs that are bilateral, generally asynchronous, and differ in amplitude, morphology, repetitive rate, and location. They are most commonly caused by multifocal or diffuse cerebral injury, such as anoxic encephalopathy and CNS infection, and have a poorer prognosis with a mortality of 52%, twice that of patients with PLEDs. It may be classified as periodic short-interval diffuse discharges (PLIDDs).
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FIGURE 613. Bilateral Periodic Lateralized Epileptiform Discharges (BiPLEDs); Pneumococcal Meningitis. A 5-month-old boy with pneumococcal meningitis who was in a comatose state and developed seizures. DWI MRIs are compatible with multifocal ischemic infarctions. EEG performed 4 hours after the seizure described as tonic posturing and nystagmus shows bilateral independent pseudoperiodic polymorphic sharp waves and spikes in the left temporal and right parieto-temporal regions. This finding is consistent with BiPLEDs. The patient subsequently developed NCSE. At 7 months of age, he started having infantile spasms. At a 26-month follow-up, he had severe developmental delay, microcephaly, intractable CPS, and left hemiparesis. BiPLEDs are PLEDs that are bilateral, generally asynchronous, and differ in amplitude, morphology, repetitive rate, and location. They are most commonly caused by multifocal or diffuse cerebral injury seen in patients with coma due to anoxic encephalopathy, strokes, epileptic seizure disorders, especially complex partial status epilepticus, and encephalitis.22,23 Stroke was the most frequent cause of PLEDs, while anoxic encephalopathy and CNS infection accounted for the majority of BiPLEDs.22 Patients with BiPLEDs have a poorer prognosis with a mortality of 52%, twice that of patients with PLEDs. BiPLEDs and GPEDs after an anoxic insult carried a poor prognosis for survival. Aggressive treatment of patients may not be warranted when these EEG patterns are seen after anoxic brain injury.24 BiPLEDs may be classified as periodic short-interval diffuse discharges (PLIDDs).
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FIGURE 614. Bilateral Independent Periodic Lateralized Epileptiform Discharges (BIPLEDs); Watershed Infarction Associated with Cardiomyopathy. A 9-yearold boy with dilated cardiomyopathy caused by viral myocarditis. He developed rhythmic shaking of his right arm and leg with eyes deviating to the right side as well as staring off with mouth movement. Examination and CXR were compatible with congestive heart failure. Axial FLAIR MR shows bilateral watershed infarction caused by hypoxic encephalopathy from poor cardiac function. EEG shows bilateral independent pseudoperiodic spikes and polymorphic sharp waves, maximum over the posterior head regions, consistent with BiPLEDs. There was no evolving pattern as seen in his electrographic seizures. The BiPLEDs persisted throughout the prolonged recording. BiPLEDs are PLEDs that are bilateral, generally asynchronous, and differ in amplitude, morphology, repetitive rate, and location. They are most commonly caused by multifocal or diffuse cerebral injury seen in patients with coma due to anoxic encephalopathy, strokes, epileptic seizure disorders, especially complex partial status epilepticus, and encephalitis.23,25 Stroke was the most frequent cause of PLEDs, while anoxic encephalopathy and CNS infection accounted for the majority of BiPLEDs.25 Patients with BiPLEDs have a poorer prognosis with a mortality of 52%, twice that of patients with PLEDs. BiPLEDs and GPEDs after an anoxic insult carried a poor prognosis for survival. Aggressive treatment of patients may not be warranted when these EEG patterns are seen after anoxic brain injury.24
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FIGURE 615. BIPLEDs; Bilateral Subdural Hematoma (Non-Accidental Trauma). A 4-month-old boy with a prolonged generalized tonic-clonic seizures due to nonaccidental trauma. Cranial CT and MRI show bilateral subdural hematoma and diffuse intracerebral hemorrhage. EEG during the comatose stage shows bilateral independent periodic lateralized epileptiform discharges in the bitemporal regions (BiPLEDS) (arrow and asterisk). This EEG pattern is commonly seen in patients with coma due to anoxic encephalopathy, strokes, epileptic seizure disorders, especially complex partial status epilepticus, and encephalitis.23,25
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FIGURE 616. Bilateral Independent Periodic Lateralized Epileptiform Discharges (BIPLEDs); Watershed Infarction Associated with Near Drowning. A 6-year-old boy with hypoplastic left ventricle with cardiac transplantation who developed anoxic encephalopathy due to near drowning. MRI shows a bilateral watershed infarction. EEG demonstrates BiPLEDs. The following EEG findings are associated with poor outcome in hypoxic encephalopathy (HE): (1) suppression; (2) burst-suppression; (3) alpha- and theta-pattern coma; (4) generalized combined periodic complexes; (4) generalized suppression to ≤20 μV; (5) burst-suppression patterns with generalized epileptiform activity; and (6) generalized periodic complexes on a flat background. BiPLEDs are usually caused by hypoxic encephalopathy or CNS infections and are typically associated with a poorer prognosis than PLEDs with a mortality of 52%, twice that of PLEDs patients. MRI in patients with BiPLEDs showed injury to the hippocampus bilaterally, bilateral infarction in the ACA territory or gray and white matter. Cortical involvement may be necessary in the pathogenesis in both BiPLEDs and GPEDs in patients with HE. Pathophysiology of PLEDs range from abnormal interactions between the “deranged cortex” and deeper “triggering” structures to increased local cortical irritability, possibly with involvement of normal and abnormal intracortical circuits.26 However, the pathophysiological mechanism responsible for periodicity in the EEG is unknown. GPEDs and BiPLEDs after an anoxic insult carried a poor prognosis for survival. Thus aggressive treatment of patients may not be warranted when these EEG patterns are seen after anoxic brain injury.24
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FIGURE 617. Hemiconvulsion Hemiplegia Epilepsy Syndrome (HHE); Refractory Nonconvulsive Status Epilepticus (NCSE). A 3-year-old boy with high fever, prolonged left hemiconvulsion, eye and head deviation to the left, and lethargy. Cranial CT shows diffuse hypodensity in the entire right hemisphere s/p decompression. EEG shows continuous ictal activity in the right hemisphere, maximally expressed in the fronto-central region. At times, the sharp waves are time-locked with the clonic jerks on the left side. He underwent surgical decompression and, subsequently, removal of necrotic tissue over the right hemisphere. A small focal cortical dysplasia was identified. The patient survived but was left with permanent left hemiparesis and intractable epilepsy. HHE is a rare sequence comprising a sudden and prolonged hemiclonic seizure during febrile illness in an otherwise normal child, followed by permanent ipsilateral hemiplegia and focal epilepsy. It is often due to CNS infection and less commonly seen in TBI or vascular. Ictal EEG shows high-voltage rhythmic slow waves intermingled with spikes, sharp waves, spike-wave complexes, or low-voltage fast activity. Higher-amplitude and more abundant epileptiform activity with posterior predominance is noted in the affected hemisphere.27
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FIGURE 618. Hemiconvulsion-Hemiplegia Epilepsy (HHE) Syndrome. (Same patient as in Figure 6-17) The EEG shows spike/polyspike-wave complexes time-locked with contralateral hemiclonic seizures of arm and face. Note muscle artifact, maximum in the left temporal region during the left facial twitching (open arrow). Axial and coronal T2 WI MRI shows increased signal intensity in the entire right hemisphere. The ictal EEG is characterized by bilaterally rhythmic slow waves, with higher amplitude on the hemisphere contralateral to the clinical seizure. The spike-wave complexes are periodically interrupted by a 1- to 2-sec background attenuation.28
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FIGURE 619. Generalized Periodic Epileptiform Discharges (GPEDs); Status Post Cardiopulmonary Resuscitation (CPR). A 4-year-old boy with cardiac arrest after rupture of coarctation of the aorta. Head CT shows bilateral massive cerebral edema. CXR shows congestive heart failure. EEG demonstrates generalized symmetric and synchronous periodic complexes consistent with GPEDs. Generalized periodic epileptiform discharges (GPEDs) are periodic complexes that occur throughout the brain in a symmetric and synchronized manner. They were not consistently associated with a specific etiology. Whether GPEDs represent an EEG pattern of SE is debated.29,30 Many believe that GPEDs represent brain damage rather than ongoing SE.31,32 GPEDs with high amplitude (mean, 110 μV) and longer duration (mean, 0.5 sec) with a preserved inter-GPED amplitude (mean, 34 μV) were more likely to be associated with SE, although these differences could not be used clinically to differentiate between SE and non-SE. Patients whose clinical history and EEG are consistent with SE should be managed aggressively with antiepileptic medications, despite GPEDs. Other characteristics that favor a more optimistic outlook include younger age, higher level of alertness at the time of the EEG, history of seizures in the current illness, and higher inter-GPED amplitude.33,34 Presence of any GPEDs was independently associated with poor outcome in 90% of those with PEDs versus 63% of those without.35 GPEDs and BiPLEDs after an anoxic insult carried a poor prognosis for survival than PLEDs. Aggressive treatment of patients may not be warranted when these EEG patterns are seen after anoxic brain injury.24
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FIGURE 620. Generalized Periodic Epileptiform Discharges (GPEDs); Refractory Status Epilepticus (RSE). A 9-year-old boy with refractory status epilepticus (RSE) of unknown etiology who was treated with pentobarbital coma but developed cardiorespiratory complications. He developed clinical seizures described as facial twitching and nystagmus while his pentobarbital dosage was decreased. EEG shows generalized periodic polyspikes and polyphasic sharp waves consistent with GPEDs superimposed on low-voltage background activity. The patient died after the cardiorespiratory support was withdrawn 3 days after this EEG.
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FIGURE 621. Asymmetrical Generalized Periodic Epileptiform Discharges (GPEDs); Refractory Status Epilepticus (RSE). (Same recording as in Figure 6-20) EEG consistently shows asymmetric GPEDs with no clinical accompaniment. At times, there are only periodic discharges in the right hemisphere, which simulate PLEDs (not shown).
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FIGURE 622. Stimulus-Induced Rhythmic, Periodic, or lctal Discharges (SIRPIDs); Refractory Status Epilepticus (RSE). (Same recording as in Figure 6-19 and 6-20) Phone ring induced a long burst of generalized polyspikes/sharp-wave and slow-wave activity in the EEG. SIRPIDs were defined as periodic, rhythmic, or ictal-appearing discharges that were consistently induced by alerting stimuli. Quasiperiodic discharges (sharp waves, spikes, polyspikes, or sharply contoured delta waves) recurring at regular intervals are noted. At times, the pattern became continuous and rhythmic rather than periodic.36 The periodic or rhythmic nature of SIRPIDs may be a reflection of the oscillations generated by burst firing of the reticular thalamic nucleus. In the normal setting, the cortex inhibits thalamocortical bursting. In cortical dysfunction, disruption of this inhibitory feedback on the thalamus by cortical projections causes rhythmic activity.37 The EEG patterns often qualify as electrographic seizures but are consistently elicited by stimulation. SIRPIDs are common in encephalopathic, critically ill patients, particularly those with acute brain injury. The relationship between clinical seizures and SIRPIDs is unclear; therefore, there is no consensus on how aggressively SIRPIDs should be treated.36 In patients with cortical and subcortical dysfunction, alerting stimuli activate the arousal circuitry and, when combined with hyperexcitable cortex, result in epileptiform activity or seizures. This activity can be focal or generalized, and is usually nonconvulsive. If the electrographic seizure activity is adequately synchronized in a specific region involving motor pathways, focal motor seizures can occur.38
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FIGURE 623. Periodic Sharp Wave Complexes (PSWCs); Creutzfeldt-Jakob Disease (CJD). A 75-year-old female with subacute progressive dementia and myoclonic jerks who was diagnosed with Creutzfeldt-Jakob disease (CJD) by postmortem examination. EEG shows bilateral synchronous periodic sharp waves occurring every 1.5–2 sec. CJD is the most common human transmissible subacute spongiform encephalopathy (TSSE). Most CJD cases are sporadic (85%). The remaining 15% consist of genetic forms (genetic CJD, Gerstmann-Sträussler-Scheinker disease, fatal familial insomnia) and iatrogenic forms (cadaveric human growth hormone and dura mater, surgical or other invasive procedures, and transfusion-associated variant CJD infections). CJD has been reported in children.39,40 EEG in CJD usually starts with PLEDs41 with atypical short interdischarge intervals of 0.5–2 sec. It usually takes several months to evolve into BiPLEDs or PSWCs. In the terminal stage when myoclonus subsides, EEG shows low-voltage or continuously diffuse polymorphic delta activity.42,43 All patients show PSWCs if serial recordings are performed in different stages of the disease.44 In another series, at the fully developed stage of the disease, 94% of the EEGs showed PSWCs.45 The sensitivity, specificity, and positive and negative predictive values of PSWCs were 64%, 91%, 95%, and 49%, respectively. Alzheimer’s disease and vascular dementia were the underlying diseases in the falsely positive cases.46
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FIGURE 624. Subacute Sclerosing Panencephalitis (SSPE). A 10-year-old boy with subacute deterioration of cognitive function and frequent myoclonus. He was diagnosed with SSPE. EEG shows bilateral synchronous pseudoperiodic sharp-wave complexes with interdischarge intervals of 3–4 sec. EEG in SSPE shows periodic high-amplitude complexes in almost all cases. The periodic complexes consist of two to four high-amplitude delta waves and polyspike-, sharp-, and slow-wave complexes of 0.5–2 sec in duration, are usually bisynchronous and symmetric, and repeated at irregular intervals once in 5–7 sec but can last up to 15 sec. When both the clinical myoclonic jerks and the periodic EEG complexes were present, a one-to-one relationship existed between the two phenomena. Besides periodic complexes, several atypical EEG findings were also noted that included frontal rhythmic delta activity in intervals between periodic complexes, electrodecremental periods following EEG complexes, paroxysms of bisynchronous spike-wave activity, random spikes over frontal regions, and focal abnormalities, such as spike- and slow-wave foci. In the terminal stage, the background activity is suppressed and the periodic complexes disappear.26,47 (Courtesy of Dr. Sorawit Viravan, Pediatric Neurology, Siriraj Hospital, Bangkok, Thailand.)
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FIGURE 625. Alpha Coma (AC); Hypoxic Encephalopathy During Midazolam Infusion. EEG of a 7-year-old boy with traumatic brain injury (TBI) who was on midazolam infusion for sedation. EEG shows continuously diffuse 10- to 12-Hz alpha activity, maximal anteriorly, throughout the whole recording. The EEG shows mild reactivity to external stimuli. The patient returned back to his baseline few days later. AC is an EEG pattern in the alpha frequency range (8–13 Hz) that occurs with a generalized distribution in a comatose patient. It is monomorphic and does not change in response to sensory stimuli and is predominant in the frontal region. The AC is most frequently seen in anoxic encephalopathy caused by cardiorespiratory arrest (CRA) 48,49 and associated with a very poor prognosis. AC can also be seen in drug overdose,50 which is very similar to that seen with CRA, except with beta activity superimposed on the alpha activity. Other etiologies include TBI, CJD, pontomesencephalic lesions,51 and encephalitis. The prognosis of AC depends on the underlying causes of coma. Etiology and outcome of AC and other rhythmic coma patterns (beta, theta, and spindle) were similar. One type of rhythmic pattern can change to another. Reactive rhythmic coma was associated with favorable outcome.5,34,52 Prognosis is very poor in anoxic encephalopathy, especially if it develops after 24 hours of coma.53
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FIGURE 626. Alpha Coma; Pontine Stroke. A 10-year-old boy with pontine stroke. He was in coma and died 4 days after this EEG recording. EEG shows broadly distributed alpha activity with anterior predominance and is nonreactive to external stimuli. This EEG pattern is termed “alpha coma.” Alpha coma is an EEG pattern in the alpha frequency range (8–13 Hz) that occurs with a generalized distribution in a comatose patient. It is monomorphic and does not change in response to sensory stimuli and is, most commonly, predominant in the frontal region. The alpha coma pattern is most frequently seen in anoxic encephalopathy caused by cardiorespiratory arrest and associated with a very poor prognosis. Alpha coma can also be seen in toxic encephalopathies that are very similar to that seen with cardiorespiratory arrest, except with beta activity superimposed on the alpha activity. Other etiologies include head trauma, CJD, brain stem lesions, especially pontomesencephalic, and encephalitis. Prognosis of alpha coma pattern depends on the underlying causes of coma. Etiology and outcome of alpha coma patterns and other rhythmic coma patterns (beta, theta, and spindle) were similar. One type of rhythmic pattern can change to another. Reactive rhythmic coma was associated with favorable outcome.5,52,54,55
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FIGURE 627. Alpha Coma. “Alpha coma” EEG pattern in an 18-year-old man who suffered from cardiac arrest after a severe motor vehicle accident occurring approximately 36 hours after the cardiopulmonary resuscitation. EEG shows continuously diffuse 10- to 11-Hz alpha activity, maximal posteriorly, throughout the whole recording. The EEG shows no reactivity to noxious stimuli. The alpha coma pattern has been reported in pontomesencephalic lesions,56 hypoxia,57,58 and drug overdose.50 The prognosis of alpha coma depends on the etiology. It is very poor in anoxic encephalopathy, especially if it develops after 24 hours of coma.53
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FIGURE 628. Comparison Between Alpha Coma and Physiological Alpha Rhythm. Alpha coma (B) can be distinguished from physiologic alpha rhythm (A) by (1) monotonous, monophasic, symmetric, and most commonly anterior predominance (except alpha coma caused by brain stem lesion, which is posterior predominance); (2) widespread distribution; and (3) highly persistent and nonreactive to stimuli.43 The clinical outcome in alpha coma depended on the underlying cause rather than the EEG finding. The prognosis of alpha coma as well as of rhythmic coma was better in children than in adults. Alpha coma may be caused by interruption of reticulothalamocortical pathways by metabolic or structural abnormalities.59 Alpha coma is replaced within 10 days by delta coma.60 In another study, alpha or theta coma change to a more definitive pattern by 5 days from coma onset. EEG reactivity in subsequent patterns is relatively favorable, while a burst-suppression pattern without reactivity is unfavorable in anoxicischemic encephalopathy.61
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FIGURE 629. Alpha-Theta Coma Pattern; Hypoxic Encephalopathy. EEG in a 5-year-old comatose boy with hypoxic ischemic encephalopathy due to near drowning shows widely distributed nonreactive alpha and theta activity with anterior predominance. This EEG is consistent with “alpha-theta coma.”
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FIGURE 630. Delta Coma. (Same patient as in Figure 6-29) EEG performed 6 days after the last EEG that showed “rhythmic coma” EEG pattern reveals continuously diffuse delta activity with suppression of sleep spindles. The patient developed moderate global developmental delay and focal epilepsy at 1-year follow-up after the near drowning. Alpha coma is replaced within 10 days by delta coma.60 In another study, alpha or theta coma changes to a more definitive pattern by 5 days from coma onset. EEG reactivity in subsequent patterns is relatively favorable, while a burst-suppression pattern without reactivity is unfavorable in anoxic-ischemic encephalopathy.5
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FIGURE 631. Beta Coma Pattern. (Same patient as in Figure 6-29 and 6-30) Prolonged EEG on the same day shows predominantly diffuse beta activity with anterior predominance. The patient received a low dose of midazolam for sedation. Invariant, nonreactive, diffuse cortical activity of a specific frequency, such as alpha, beta, spindle, or theta, is called “rhythmic coma.” The clinical outcome in a rhythmic coma pattern depended on the underlying cause rather than the EEG finding. The prognosis of alpha coma as well as of rhythmic coma was better in children than in adults. Alpha coma may be caused by interruption of reticulothalamocortical pathways by metabolic or structural abnormalities.59 Alpha coma is replaced within 10 days by delta coma.60 In another study, alpha or theta coma changes to a more definitive pattern by 5 days from coma onset. EEG reactivity in subsequent patterns is relatively favorable, while a burst-suppression pattern without reactivity is unfavorable in anoxic-ischemic encephalopathy.61
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FIGURE 632. Theta Coma (Reversible); Sedative Medication After NCSE. A 9-year-old boy with NCSE who received midazolam infusion. EEG shows anteriorly predominant theta activity intermixed with delta and beta activity. The patient was recovering after the treatment. Alpha or theta coma can also be seen in toxic encephalopathy. The EEG pattern is very similar to that seen with cardiorespiratory arrest, except that there is superimposed beta activity.62–64 Overdoses of many different drugs can produce this pattern.3 The outcome depends on the underlying causes. The prognosis of alpha-theta rhythmic coma as well as of other rhythmic coma is better in children than in adults.65
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FIGURE 633. Theta Coma (Irreversible) 15 Minutes Before the Patient Died; Anoxic Encephalopathy. A 9-year-old boy with anoxic encephalopathy after hanging. He underwent 45-minutes of CPR. Continuous EEG 15 minutes before he passed away shows nonreactive anteriorly dominant rhythmic 5-Hz theta activity. Diffuse theta patterns may occur on their own, or may be mixed with other frequencies such as alpha or delta in coma66,61 and may occur after cadiorespiratory arrest where theta activity is more prominent anteriorly, is nonreactive to external stimuli, and carries a poor prognosis similar to alpha coma.4,5 The prognosis of alpha coma (AC), theta coma (TC), or alpha-theta coma (ATC) patterns is poor in adults but better in children, especially if they are an incomplete (reactive) AC pattern. Based on the observation that etiology and outcome were similar in alpha, theta, spindle, and beta comas (“rhythmic coma” pattern), the pathophysiology of these patterns in children might be the same as AC in adults, interruption of the reticulothalamocortical pathways by structural or metabolic derangement and deafferentation. EEG patterns may be more variable in children (alpha, theta, spindle, and beta frequencies), possibly because of the difference in the response of the immature brain to such deafferentation.55 Whereas complete ATC is invariably associated with a poor outcome, full recovery is possible in patients with incomplete ATC.56 EEG in neonates may take longer to recover. Therefore, the first EEG should be waited until 24 hours after the CPR, unless seizures are suspected.68
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FIGURE 634. Evolving EEG Patterns in Anoxic Encephalopathy After Cardiopulmonary Resuscitation (CPR). A 9-year-old boy with anoxic encephalopathy from hanging. He underwent CPR 15 minutes after the incident when he was pulseless for 5 minutes. CPR was performed over 45 minutes. He was not noted to have hypothermia and severe metabolic disturbances, and was not on sedation. EEG evolves from electrocerebral inactivity to burst-suppression, GPEDs, and eventually theta coma before he passed away 15 minutes after the evidence of theta coma EEG pattern. EEG may evolve from one rhythmic pattern during a series of tests or may even occur in the same recording. The pathophysiology of rhythmic coma patterns (alpha, theta, spindle) in children might be the same as in adults, interruption of the reticulothalamocortical pathways by structural or metabolic derangement and deafferentation.65 In this patient, the theta coma pattern was most likely caused by the effect of central herniation syndrome on the brainstem. The risks of severe neurologic deficits or death are high among patients with alpha, theta, and alpha-theta coma patterns while in postanoxic coma. Seventy-three percent of patients with alpha coma after CPR died.3,64
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FIGURE 635. Asymmetric Spindle Coma During Midazolam Infusion; Embolic Stroke. A 6-year-old girl with acute lymphoblastic leukemia with febrile neutropenia complicated by left MCA stroke and small ischemia in the right occipital region. EEG during intubation and comatose state under midazolam IV infusion shows asymmetric 10- to 11-Hz spindle-like activity with suppression in the left hemisphere. Anterior predominance of spindle activity is noted. This finding is consistent with asymmetric spindle coma. Rhythmic coma patterns were found in 30.2% of recordings. Etiology, reactivity, and outcome of spindle, beta, alpha, and theta coma patterns are similar. The reactive pattern was associated with favorable outcome in 67%. The nonreactive rhythmic pattern was associated with unfavorable outcome in 60%. Sequential EEG recordings are required to detect the evolution of rhythmic coma patterns during childhood.55 The prognosis depends mainly on the primary disease process rather than the EEG finding. The prognosis of rhythmic coma pattern is better in children than in adults. The rhythmic coma pattern is probably caused by the interruption of reticulothalamocortical pathways by metabolic or structural abnormalities.59 An incomplete pattern has a better prognosis.64,61,67
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FIGURE 636. Asymmetric Spindle Coma; Acute Amoebic Meningoencephalitis with Herniation Syndrome. A 10-year-old boy with refractory status epilepticus and coma caused by amoeba Balamuthia mandrillaris. Axial MRI with FLAIR sequence and coronal T1-weighted image with GAD show an infarction of the right basal ganglion and midbrain (arrow) and Kernohan phenomenon in the opposite hemisphere (open arrow). EEG reveals asymmetrically diffuse spindle and delta coma with less abundant spindles and more pronounced polymorphic delta activity in the right hemisphere. In this patient, spindle and delta coma is most likely due to the lesions in the midbrain and basal ganglion caused by infarction and brain herniation syndrome. The patient died a few days after this EEG. Rhythmic coma patterns were found in 30.2% of recordings. Etiology, reactivity, and outcome of spindle, beta, alpha, and theta coma patterns are similar. The reactive pattern was associated with favorable outcome in 67%. The nonreactive rhythmic pattern was associated with unfavorable outcome in 60%. Sequential EEG recordings are required to detect the evolution of rhythmic coma patterns during childhood.52,55 The prognosis depends mainly on the primary disease process rather than the EEG finding. The prognosis of rhythmic coma pattern is better in children than in adults. The rhythmic coma pattern is probably caused by the interruption of reticulothalamocortical pathways by metabolic or structural abnormalities.65 Incomplete pattern has a better prognosis.4,61,67,69 More than 440 cases of severe central nervous system infections caused by Acanthamoeba spp., B. mandrillaris, and Naegleria fowleri have been reported.70 Balamuthia encephalitis may occur in any age group, may or may not be associated with immunosuppression, and usually has a subacute and fatal course from hematogenous dissemination of chronic skin or lung lesions. Common features that might be of value in diagnosis of Balamuthia encephalitis are high CSF protein, hydrocephalus, and Hispanic ethnicity.71 When purulent CSF is obtained and when no bacteria are noted in a patient with meningoencephalitis, the CSF should be examined specifically for other organisms, including amoeba. PCR assay and specific antibodies to Balamuthia are available. Brain biopsy should be considered in patients with encephalitis of unknown etiology whose condition deteriorates despite treatment with acyclovir.72 Chronic necrotizing vasculitis and focal hemorrhages are typical findings in Balamuthia infections.73,74 The prognosis is very poor due to delayed diagnosis, difficulty in isolation/identification of the organism, and lack of well-established treatment.75
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FIGURE 637. Beta Coma. A 10-year-old comatose boy following the treatment of convulsive status epilepticus with phenobarbital, fosphenytoin, and midazolam. Beta coma is generally caused by intoxication and thus is often a reversible EEG abnormality.50 It may also be caused by acute brain stem lesions.76
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FIGURE 638. Burst-Suppression Pattern; Cardiopulponary Arrest. A 15-month-old boy with anoxic encephalopathy caused by a complication of anesthesia. EEG shows very low-voltage background activity alternating with medium-voltage diffuse delta activity. The burst-suppression is characterized by their contrasting adjacent amplitude. The amplitudes of the bursts vary from <20 to >100 μV. Bursts contain multiple sharps and spikes or regular/irregular rhythmic activity from delta to beta range.43
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FIGURE 639. Burst-Suppression Pattern; Pentobarbital Coma. (Continue...) The EEG shows a burst-suppression (B-S) pattern with pentobarbital coma. A B-S pattern is a complex wave form alternating with complete attenuated background activity (<10 mV). It is indicative of severe diffuse encephalopathy and immediately precedes electrocerebral inactivity. In the absence of a high level of sedative medications, severe metabolic disturbances, and hypothermia, B-S is indicative of an irreversible severe encephalopathy and very poor prognosis. Experimental study of B-S showed that almost all (95%) cortical neurons become electrically silent during the flat EEG. Hyperpolarization of cortical neurons due to increased K+ conductance precedes EEG flattening, which in turn is secondary to increased GABAergic inhibition at cortical synapses. This inhibition leads to functional disconnection from thalamic input, but 30–40% of thalamic cells continue firing while the cortex is silent. This is due to the intrinsic pacemaking properties of the thalamic neurons at modest levels of hyperpolarization. Volleys from these thalamocortical neurons account for the cyclic EEG wave bursts.77,78
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FIGURE 640. Severe Hypoxic Encephalopathy; Associated with Myoclonic Jerks and Spontaneous Movement. A 22-year-old male with severe hypoxic ischemic encephalopathy after cardiac arrest due to a severe motor vehicle accident. He was in a comatose state with absent brain stem reflexes. He developed frequent body jerks (arrow) accompanied by eye opening and eye closing (arrow heads) before being declared brain dead and withdrawn from life support 1 day after this EEG recording. EEG during one of his typical episodes of jerking, associated with eye opening and closing, shows a burst of generalized high-voltage spikes and sharp waves intermingled with mixed frequency activities against a very low-voltage background activity. Spontaneous movements, especially myoclonic jerks associated with spontaneous eye opening and closing during bursts of spike- and sharp-wave EEG activity, are extremely rare and can be seen in deeply comatose patients after global anoxic or ischemic insult. They may be misled as signs of clinical improvement, although they actually indicate a grave prognosis similar to that of a suppression-burst EEG pattern without associated clinical symptoms.79,80
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FIGURE 641. Burst-Suppression Pattern; Associated with Myoclonic Seizures and Eye Opening/Closure. A 4-year-old girl with severe anoxic encephalopathy after cardiac arrest due to choking on corns. She was in a comatose state with absent brain stem reflexes, except for shallow irregular breathing. She developed frequent body jerks accompanied by eye opening and eye closing. She was withdrawn from life support after the apneic test and a repeated EEG, which showed electrocerebral silence. EEG during one of her typical episodes shows a burst of generalized high-voltage spikes and sharp waves intermingled with mixed frequency activities against, an extremely low-voltage background activity. Spontaneous movements, most commonly myoclonic jerks associated with spontaneous eye opening and closing during bursts of spike- and sharp-wave EEG activity, are extremely rare and can be seen in deeply comatose patients after global anoxic or ischemic insult. They may be misinterpreted as signs of clinical improvement, although their appearances indicate a grave prognosis similar to that of a suppression-burst EEG pattern without associated clinical symptoms.79,80 Generalized myoclonus in comatose survivors of CPR indicates a poor outcome despite advances in critical care medicine. AEDs are not effective.81
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FIGURE 642. Very Low-Voltage Background Activity; Hypoxic-Ischemic Encephalopathy (HIE). A 6-day-old infant who was born at term with Apgar scores of 0, 0, 0, 3, 4, 6, and 7 at 1, 5, 10, 15, 20, 25 and 30 minutes of life, respectively. The infant was cyanotic, depressed, and floppy at delivery and received intubation, chest compressions, and epinephrine. He underwent head cooling. MRI performed on day of life (DOL) 5 shows restricted diffusion in the basal ganglia (arrow) and medial temporal lobes bilaterally (double arrows). EEG performed on DOL 6 shows low-voltage background activity and lack of differentiation. Note frequent positive sharp waves in multifocal areas (open arrows). All patients with HIE with bilateral basal ganglia involvement have developmental delay. “Depression and lack of differentiation” EEG is indicative of severe brain insult, but is nonspecific in etiology and can be due to a wide variety of conditions, including severe HIE, severe metabolic disorders, meningitis or encephalitis, cerebral hemorrhage, and IVH. A depressed and undifferentiated EEG within the first 24 hours after birth that persists indicates a poor prognosis.82 Positive sharp waves in full-term infants are seen in structural cerebral lesions, including periventricular leukomalacia, intracerebral hemorrhages, HIE, and infarctions.14,66,83,84
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FIGURE 643. Electrocerebral Inactivity (ECI); Severe Hypoxic Ischemic Encephalopathy (HIE) with Central Herniation Syndrome. A 4-day-old girl who was born full term with Apgar scores of 0, 3, 3, and 5. Cord arterial gas was 6.91/66/-20. Initial blood gas was 7.15/13/123/9/-22. She had a seizure described as tonic posturing. She was placed in a head-cooling device. She developed another clinical seizure with rhythmic head twitching and tongue thrusting lasting 10 minutes. She received treatment with phenobarbital and levetriacetam. No EEG was performed until the 4th day of life. MRI performed on the 4th day of life shows severe global abnormality involving cerebellum, brain stem, thalamus, basal ganglia, deep white matter, and cortical gray matter. DWI shows markedly increased signal intensity, which suggests severe injury with liquefaction. Cardiorespiratory support was withdrawn 1 day after the EEG. EEG shows no cerebral activity (potentials < 2 μV when reviewed at a sensitivity of 2 μV/mm) consistent with electrocerebral inactivity (ECI). ECG artifact was noted with a dipole.85 ECI is indicative of death only of the cortex, not the brain stem; therefore, a newborn can have prolonged survival despite having an EEG showing ECI.86
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FIGURE 644. 14-and-6 Hertz Positive Spikes; Severely Diffuse Encephalopathy. An 8-year-old boy with refractory status epilepticus (RSE) of unknown etiology. Despite being treated with a pentobarbital coma for over 1 month, he continued having seizures. MRI scan 6 weeks after the onset of SE shows severe bilateral hippocampal atrophy, diffuse cortical atrophy, and severely diffuse white matter involvement. EEG shows markedly diffuse polymorphic delta slowing with superimposed 14- and 6-Hz positive spikes. Fourteen- and six-hertz positive spikes in a background of diffuse delta waves were initially reported in patients with Reye syndrome.87,88 It was later reported in diverse encephalopathies of childhood, including toxic/metabolic and primary cerebral insult, not just Reye syndrome. The 14- and 6-Hz positive spike patterns show a similar incidence, morphology, and topography to that seen in healthy children. It was concluded that the 14- and 6-Hz positive spikes are a normal wave form that is selectively preserved and more resistant to underlying structural or metabolic processes than other background features of drowsiness and sleep.89 The positive spike bursts with continuous delta activity in comatose children is a rare but unique EEG pattern associated with hepatic or anoxic encephalopathy.90 In some subjects, 14- and 6-Hz positive spikes were provoked by auditory and somatosensory stimuli as in this patient.91 Fourteen- and six-hertz positive spikes should not be misinterpreted as “paroxysmal fast activity (PFA).” The morphology, polarity, and distribution can differentiate between these two wave forms.
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FIGURE 645. Acute Viral Meningoencephalitis; Refractory Nonconvulsive Status Epilepticus (NCSE). An 11-month-old boy with high fever, lethargy, and prolonged generalized tonic-clonic seizures (GTCS) of unknown etiology. GTCS resolved after IV fosphenytoin and lorazepam treatment. However, he continued having constant eye blinking and facial and limb twitching. Video-EEG monitoring showed continuously bisynchronous slow (poly)spike-wave discharges with posterior predominance consistent with NCSE. He was treated with pentobarbital coma for 7 days until the NCSE stopped. Although survived , he developed severe neurologic deficits including global developmental delay, left hemiparesis, and behavioral disturbances. RSE in children is associated with poor prognosis. The mortality rate of RSE in one series was 32%,92 which was much higher than the overall mortality rate in pediatric SE (0–10%).93–98 Only 23% of the survivors were normal at follow-up; 34% showed developmental deterioration, and 36% developed new-onset epilepsy.98 Mortality is related to etiology and is higher in younger children and with multifocal or generalized abnormalities on the initial EEG. RSE due to either an acute symptomatic etiology or a progressive encephalopathy was associated with highest mortality rates. Almost all survivors had active epilepsy. A shorter duration of suppressive therapy, ultimately with the same outcome and possibly fewer complications, was recommended.92
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FIGURE 646. Nonconvulsive Status Epilepticus (NCSE). A 13-year-old boy with high fever and convulsive status epilepticus whose generalized tonic-clonic seizures were stopped by fosphenytoin and lorazepam in the ED. The patient was intubated and transferred to the PICU, where he had no clinical seizures except intermittent facial and limb twitching. Bedside video-EEG shows nonconvulsive status epilepticus (NCSE). The etiology of NCSE was not found. The patient developed refractory status epilepticus and was put in pentobarbital coma. CEEG monitoring detected seizure activity in 19% of patients, and the seizures were almost always nonconvulsive. Coma, age <18 years, a history of epilepsy, and convulsive seizures prior to monitoring were risk factors for electrographic seizures. Comatose patients frequently required >24 hours of monitoring to detect the first electrographic seizure. TBI (18–28%), ischemic stroke (11–26%), and CNS infection (29–33%) are the most common cause of NCSE.99
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FIGURE 647. Nonconvulsive Status Epilepticus (NCSE): Bisynchronous Temporal Discharges; Secondary Bilateral Hippocampal Atrophy. (Same patient as in Figure 6-46) A 13-year-old girl with prolonged generalized tonic-clonic seizures followed by refractory nonconvulsive status epilepticus despite treatment with fosphenytoin, phenobarbital, and midazolam. The EEG after treatment with fosphenytoin, phenobarbital, and midazolam shows generalized periodic sharp waves. Clinically, the patient was in a comatose state and had intermittent eye blinking and mouth movement. Subsequently, she was put in a pentobarbital coma for over 4 weeks. Repeated MRI 4 weeks later showed progressively diffuse cortical and bilateral hippocampal atrophy/increased T2/FLAIR signal intensity in both hippocampi (arrows).The patient was withdrawn from the life support a few days after the second MRI. Pathology showed diffuse laminar necrosis and severe bilateral mesial temporal sclerosis. EEG performed 1 month after the onset of SE when the patient had bilateral hippocampal sclerosis shows bisynchronous temporal discharges. These may indicate temporal lobe epilepsy caused by bilateral hippocampal sclerosis secondary to RSE.
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FIGURE 648. Generalized Periodic Epileptiform Discharges (GPED) in Refractory Nonconvulsive Status Epilepticus; Status Epilepticus-induced Diffuse Cortical Atrophy and Hippocampal Sclerosis. Same patient as in Figure 6-46 and 6-47). The EEG after the treatment with fosphenytoin, phenobarbital, and midazolam shows generalized periodic sharp waves. Clinically, the patient was in a comatose state and had intermittent eye blinking and mouth movement. Subsequently, she was put in a pentobarbital coma for over 4 weeks. Repeated MRI 4 weeks later showed progressively diffuse cortical and bilateral hippocampal atrophy/increased T2/FLAIR signal intensity in both hippocampi (arrows).The patient was withdrawn from the life support a few days after the second MRI. Pathology showed diffuse laminar necrosis and severe bilateral mesial temporal sclerosis. This case supports prior evidence that neuronal cell loss in HS occurs as the result of prolonged severe seizure activity in humans.100 In humans, MRI change in the early stage of SE, as little as 24 hours, is either asymmetrical or bilateral T2 signal hyperintensity in the hippocampi (HC) caused by focal transient cytotoxic and vasogenic edema.101 Associated early swelling of the affected HC was also shown.102–104 Serial coronal MRIs showed significant volume loss in both hippocampi between weeks 4 and 10, most likely representing neuronal loss and astrogliosis as the correlate of the later histologically proven HS.100 HS can develop within 2 months of SE and may further progress during the following 3–4 years.103,105
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FIGURE 649. Triphasic Waves; Dialysis Encephalopathy. EEG of a 20-year-old male with acute encephalopathy due to chronic renal failure and dialysis. EEG shows intermittently diffuse triphasic waves (TWs) (open arrow). The patient was recovered after symptomatic treatment. The most characteristic EEG feature in dialysis encephalopathy was paroxysmal high-voltage delta activity with anterior predominance, and, less commonly, spike-and-wave activity and TWs.106 TWs consist of bursts of moderate- to high-amplitude complexes, usually at 1.5–2.5 Hz, with three (but sometimes two or four) negative-positive-negative phases, usually occurring runs of 1.5–3/sec or more continuously. A fronto-occipital lag (brought out by using a bipolar montage) is unique but not a constant finding. TWs have been considered as a pathognomonic sign in severe hepatic encephalopathy, but they are also seen in encephalopathies associated with renal failure or electrolyte imbalance, as well as anoxia and intoxications (such as lithium, metrizamide, and levodopa). In pre-coma, TWs do not predict outcome.4,5,107–109 TWs occur most often in patients with metabolic encephalopathies but cannot be used to distinguish different causes.107 They are rarely reported below the age of 20 years.110
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59. Horton E, Goldie W, Baram T. Rhythmic coma in children. J Child Neurol. 1990;5(3):242. 60. Grindal A, Suter C, Martinez A. Alpha-pattern coma. High voltage electrical injury. Electroencephalogr Clin Neurophysiol. 1975;38(5):521–526. 61. Young GB, Blume WT, Campbell VM, Demelo JD, Leung LS, McKeown MJ, McLachlan RS, Ramsay DA, Schieven JR. Alpha, theta and alpha-theta coma: a clinical outcome study utilizing serial recordings. Electroencephalogr Clin Neurophysiol. 1994;91:93–99. 62. Austin EJ, Wilkus RJ, Longstreth WT, Jr. Etiology and prognosis of alpha coma. Neurology. 1988;38(5): 773–777. 63. Carroll WM, Mastaglia FL. Alpha and beta coma in drug intoxication uncomplicated by cerebral hypoxia. Electroencephalogr Clin Neurophysiol. 1979;46(1):95–105. 64. Kaplan PW, Genoud D, Ho TW, et al. Etiology, neurologic correlations, and prognosis in alpha coma. Clin Neurophysiol. 1999;110:205–213 . 65. Horton EJ, Goldie WD, Baram TZ. Rhythmic coma in children. J Child Neurol. 1990;5(3):242–247. 66. Nowack W, Janati A, Angtuaco T. Positive temporal sharp waves in neonatal EEG. Clin EEG (Electroencephalogr). 1989;20(3):196. 67. Berkhoff M, Donati F, Bassetti C. Postanoxic alpha (theta) coma: a reappraisal of its prognostic significance. Clin Neurophysiol. 2000;111(2):297–304. 68. Young GB. The EEG in coma. J Clin Neurophysiol. 2000;17(5):473–485. 69. Kaplan P. The EEG in metabolic encephalopathy and coma. J Clin Neurophysiol. 2004;21(5):307. 70. Qvarnstrom Y, Visvesvara GS, Sriram R, da Silva AJ. Multiplex real-time PCR assay for simultaneous detection of Acanthamoeba spp., Balamuthia mandrillaris, and Naegleria fowleri. J Clin Microbiol. 2006;44:3589–3595. 71. Bakardjiev A, Azimi PH, Ashouri N, Ascher DP, Janner D, Schuster FL, Visvesvara GS, Glaser C. Amebic encephalitis caused by Balamuthia mandrillaris: report of four cases. Pediatr Infect Dis. 2003;22:447–452. 72. Tunkel A, Glaser C, Bloch K, et al. Management of encephalitis: clinical practice guidelines of the Infectious Diseases Society of America. Clin Infect Dis. 2008;47:303–327. 73. Griesemer DA, Barton LL, Reese CM, Johnson PC, Gabrielsen JAB, Talwar D, Visvesvara GS Amebic meningoencephalitis caused by Balamuthia mandrillaris. Pediatr Neurol. 1994;10:249–254.
6 74. Healy J. Balamuthia amebic encephalitis: radiographic and pathologic findings. Am Soc Neuroradiol. 2002;486–489. 75. Perez M, Bush L. Balamuthia mandrillaris amebic encephalitis. Curr Infect Dis Rep. 2007. 9(4):323–328. 76. Otomo E. Beta wave activity in the electroencephalogram in cases of coma due to acute brain-stem lesions. J Neurol Neurosurg Psychiatry. 1966;29(5):383. 77. Steriade M, Amzica F, Contreras D. Cortical and thalamic cellular correlates of electroencephalographic burst-suppression. Electroencephalogr Clin Neurophysiol. 1994;90(1):1. 78. Schaul N. Pathogenesis and significance of abnormal nonepileptiform rhythms in the EEG. J Clin Neurophysiol. 1990;7(2):229–248. 79. McCarty G, Marshall D. Transient eyelid opening associated with postanoxic EEG suppression-burst pattern. Arch Neurol. 1981;38(12):754. 80. Reeves AL, Westmoreland BF, Klass DW. Clinical accompaniments of the burst-suppression EEG pattern. J Clin Neurophysiol. 1997;14(2):150–153. 81. Thömke F, et al. Observations on comatose survivors of cardiopulmonary resuscitation with generalized myoclonus. BMC Neurol. 2005;5(1):14. 82. Mizrahi E, Hrachovy R, Kellaway P. Atlas of Neonatal Electroencephalography. Philadelphia: Lippincott Williams & Wilkins. 2004. 83. Chung H, Clancy R. Significance of positive temporal sharp waves in the neonatal electroencephalogram. Electroencephalogr Clin Neurophysiol. 1991;79(4):256. 84. Clancy R, et al. Current Practice of Clinical Electroencephalography. 3rd ed. New York: Lippincott Williams & Wilkins. 2003. 85. Blume W, Kaibara M. Atlas of Adult Electroencephalography. Philadelphia: Lippincott Williams & Wilkins. 2002. 86. Mizrahi E, Pollack M, Kellaway P. Neocortical death in infants: behavioral, neurologic, and electroencephalographic characteristics. Pediatr Neurol. 1985;1(5):302. 87. Yamada T, Tucker RP, Kooi KA. Fourteen and six c/sec positive bursts in comatose patients. Electroencephalogr Clin Neurophysiol. 1976;40(6):645–653. 88. Yamada T, Young S, Kimura J. Significance of positive spike bursts in Reye syndrome. Arch Neurol. 1977;34(6):376. 89. Drury I. 14-and-6 Hz positive bursts in childhood encephalopathies. Electroencephalogr Clin Neurophysiol. 1989;72(6):479.
6 90. Markand ON. Pearls, perils, and pitfalls in the use of the electroencephalogram. Semin Neurol. 2003;23:7–46. 91. Kooi K, et al. Electroencephalographic patterns of the temporal region in normal adults. Neurology. 1964;14(11):1029–1035. 92. Sahin M, et al. Outcome of severe refractory status epilepticus in children. Epilepsia. 2001;42(11):1461–1467. 93. Aicardi J, Chevrie J. Convulsive status epilepticus in infants and children. A study of 239 cases. Epilepsia. 1970;11(2):187. 94. Yager J, Cheang M, Seshia S. Status epilepticus in children. Can J Neurol Sci. 1988;15(4):402. 95. Maytal J, Shinnar S, Moshe SL, Alvarez LA. Low morbidity and mortality of status epilepticus in children. Pediatrics. 1989;83:323–331. 96. Lacroix J, Deal C, Gauthier M, Rousseau E, Farrell CA. Admissions to a pediatric intensive care unit for status epilepticus: a 10-year experience. Crit Care Med. 1994;22:827–832. 97. Eriksson K, Koivikko M. Status epilepticus in children: aetiology, treatment, and outcome. Dev Med Child Neurol. 1997;39(10):652. 98. Barnard C, Wirrell E. Does status epilepticus in children cause developmental deterioration and exacerbation of epilepsy? J Child Neurol. 1999;14(12):787.
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99. Claassen J, Mayer SA, Kowalski RG, Emerson RG, Hirsch LJ. Detection of electrographic seizures with continuous EEG monitoring in critically ill patients. Neurology. 2004;62:1743–1748. 100. Pohlmann-Eden B, Gass A, Peters CAN, Wennberg R, Blumcke I. Evolution of MRI changes and development of bilateral hippocampal sclerosis during long lasting generalized status epilepticus. J Neurol Neurosurg Psychiatry. 2004;75:898–900. 101. Nohria V, Lee N, Tien RD, et al. Magnetic resonance imaging evidence of hippocampal sclerosis in progression: a case report. Epilepsia. 1994;35:1332–1336. 102. Scott RC, Gadian DG, King MD, Chong WK, Cox TC, Neville BG, et al. Magnetic resonance imaging findings within 5 days of status epilepticus in childhood. Brain. 2002;125:1951–1959. 103. Wieshmann UC, Woermann FG, Lemieux L, Free SL, Bartlett PA, Smith SJ, et al. Development of hippocampal atrophy: a serial magnetic resonance imaging study in a patient who developed epilepsy after generalized status epilepticus. Epilepsia. 1997;38:1238–1241. 104. VanLandingham KE, Heinz ER, Cavazos JE, Lewis DV. Magnetic resonance imaging evidence of hippocampal injury after prolonged focal febrile convulsions. Ann Neurol. 1998; 43: 413–426.
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Severe neonatal epilepsy with suppression-burst pattern (Figures 7-1 to 7-6)
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Epileptic Encephalopathy
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OS commonly transitions to West syndrome. EME transition to West syndrome is transient, if there is any transition at all.
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The EEG course of S-B in OS is that it turns into hypsarrhythmia in 3–6 months. The EME S-B course is long lasting. However, the distinction between these two conditions may be difficult because brief spasms are difficult to distinguish from myoclonus.
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The distinction between S-B and hypsarrhythmia with extreme fragmentation in sleep also is difficult in many cases, because in OS, the S-B evolves into the more continuous asynchronous spike and slow-wave activity of hypsarrhythmia.
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Pyridoxine dependency was reported in one patient with EME who had complete recovery after treatment with pyridoxine.
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Partial seizures are an almost constant feature in EME and tend to appear shortly after the erratic myoclonus. Epileptic spasms are rarely seen early in the course of EME.
Consist of two epileptic syndromes: 䊳 Ohtahara syndrome (OS) Early myoclonic encephalopathy (EME) The EEG shows bursts, lasting several seconds, of polyspikes alternating with very low-voltage activity, this combination being called “suppression bursts (S-B).” 䊳
The S-B pattern may be asymmetric, affecting mainly the side of following: 䊳 Malformation of cortical development 䊳 䊳 䊳 䊳
Hemimegalencephaly Focal cortical dysplasia (FCD) Aicardi syndrome Olivary-dentate dysplasia
Schizencephaly Encephalomalacia 䡲 The onset of seizures in OS is within the first 2–3 months but most commonly within the first 10 days. 䡲 The main type of seizures in OS is tonic spasms. Myoclonic seizures and erratic myoclonus are rare. A majority of cases of OS are associated with a structural brain abnormality, including porencephaly, hydrocephalus, hemimegalencephaly, and lissencephaly. No familial case of OS has been reported. 䊳 䊳
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EME is characterized by early onset in the neonatal period with main seizure types of erratic and massive myoclonus and partial seizures. The most common cause of EME is metabolic disease. The most common of these is nonketotic hyperglycinemia.
The causes of OS are symptomatic or organic. The causes of EME can be genetic, metabolic, or entirely unknown. OS causes tonic spasms and partial seizures. 䡲 EME causes myoclonic and partial seizures. 䡲 The EEG of OS contains periodic S-B and occurs during both waking and sleeping, while EME may have S-B only during sleep.
West syndrome (Figures 7-7 to 7-39) 䡲
Incidence is 1 in 3225 live births.
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Male predominance. The highest incidence correlates with higher geographic latitudes.
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Age at onset varies from the first week of life to more than 3 years of age, with the average onset at 6 months. Most cases (94%) begin within the first year of life. 䡲 Positive family history for epilepsy in 1–7%. 䡲 Symptomatic in 80–90%: 䊳
Hypoxic-ischemic encephalopathy (HIE)
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Infection Trauma and intracranial hemorrhage Malformation of cortical development
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Neurocutaneous syndrome Chromosome or genetic disorder
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Inborn errors of metabolism
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Idiopathic or cryptogenic in 10–20%.
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Gibbs and Gibbs defined hypsarrhythmia as “… random high voltage slow waves and spikes. These spikes vary from moment to moment, both in duration and in location. At times they appear to be focal, and a few seconds later they seem to originate from multiple foci. Occasionally the spike discharge becomes generalized, but it never appears as a rhythmically repetitive and highly organized pattern that could be confused with a discharge of the petit mal or petit mal variant type. The abnormality is almost continuous, and in most cases it shows as clearly in the waking as in the sleeping record.”
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Hemimegalencephaly and Aicardi syndrome with asymmetrical suppression-burst pattern. 䊳 Tuberous sclerosis and porencephaly are associated with focal slow waves. 䡲 Transient alterations of the hypsarrhythmia occur throughout the day in relation to sleep states. 䊳 During non-rapid eye movement (NREM) sleep, the voltage of the background activity typically increases, and there is a tendency for grouping of the multifocal spike and sharp wave activity, often resulting in a periodic pattern. 䊳
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Five variants of hypsarrhythmia: 䊳 Hypsarrhythmia with increased interhemispheric synchronization (35%) 䊳 Asymmetric hypsarrhythmia (12%) 䊳
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Hypsarrhythmia with episodes of voltage attenuation (11%)
Hypsarrhythmia with little spike or sharp activity (7%) 䡲 Although hypsarrhythmia and its variants are the most common EEG patterns seen in infantile spasms (IS), other interictal patterns may occur singly or in various combinations: 䊳 Focal or multifocal spikes and sharp waves 䊳 Abnormally slow or fast rhythms, diffuse slowing 䊳 䊳 䊳 䊳
Focal slowing Focal depression Paroxysmal slow or fast bursts Slow spike and wave pattern
Continuous spindling Normal (rare) 䡲 Specific neuropathology: 䊳 Symptomatic West syndrome (WS) usually does not have typical hypsarrhythmia. 䊳 Agyria is associated with fast rhythm. 䊳
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Hypsarrhythmia with a consistent focus of abnormal discharge (26%)
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Epileptic Encephalopathy
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Electrodecremental episodes frequently occur during NREM sleep. Immediately after arousal from either rapid eye movement (REM) or NREM, there is a reduction in amplitude or complete disappearance of the hypsarrhythmic pattern that may persist for a few seconds to many minutes (pseudonormalization) before hypsarrhythmia reappears. Hypsarrythmia seems to disappear during REM sleep.
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Review of earlier video-EEG evaluation is extremely helpful to identify the epileptic focus. 䡲 Sleep spindles are commonly preserved. 䡲 䡲
Total REM is reduced. The hypsarrhythmic pattern may also disappear during a cluster of spasms but immediately returns after cessation of the spasms.
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As with the clinical spasms, hypsarrhythmia characteristically disappears with increasing age. 䡲 A variety of patterns may be seen when hypsarrhythmia disappears including: 䊳 Diffuse slowing 䊳 Focal or multifocal spikes and sharp waves 䊳 䊳 䊳 䊳
Monorhythmic background activity Focal slowing Asymmetric background activity Slow spike and slow-wave activity
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Diffuse high-voltage fast activity
Normal (rare) Spike-wave activity is seen predominantly in bilateral parietal-occipital regions. West syndrome is a common complication of severe periventricular leukomalacia (PVL) and correlates strongly with the finding of bilateral parietal-occipital dominant irregular polyspike-wave activity. 䡲 Asymmetric hypsarrhythmia (hemihypsarrhythmia or unilateral hypsarrhythmia) is characterized by hypsarrhythmia, with a consistent amplitude asymmetry between the two hemispheres. 䡲 Asymmetric hypsarrhythmia is always associated with an underlying structural abnormalities of the brain: 䊳
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Large cystic or atrophic defects of one hemisphere, such as porencephaly or encephalomalacia (most common)
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Tuberous sclerosis
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Aicardi syndrome Hemimegalencephaly Other malformations of cortical development
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Asymmetric hypsarrhythmia also occurs in bilateral structural lesions that were more abnormal in the area of the greater EEG abnormality.
Hypsarrhythmia may be maximal over either the more abnormal or the more normal hemisphere. 䡲 Asymmetric hypsarrhythmia and asymmetric ictal EEG changes during IS often occurred together: each always indicated the side of a focal or asymmetric structural cerebral lesion. 䡲 Spasms are rarely asymmetric. Consistent asymmetry of epileptic spasms, especially when associated with asymmetry of ictal/interictal EEG discharges, is a supportive evidence for underlying focal structural abnormality. Persistent asymmetric hypsarrhythmia is always associated with underlying structural brain abnormalities. 䡲 Hypsarrhythmia with increased interhemispheric synchronization was seen in 35% of hypsarrhythmia
7 variants. The classic hypsarrhythmia, multifocal spikes and sharp waves, and the diffuse asynchronous slow-wave activity are replaced or intermixed with activity that demonstrates a significant degree of interhemispheric synchrony and symmetry. 䡲 The EEG evolution can take place over weeks to months. This EEG pattern sometimes appears only intermittently with classic hypsarrhythmia. Most infants with hypsarrhythmia will have some degree of synchronization of the background activity if the condition persists for many months or years. This is particularly true of those infants who exhibit a transition to the Lennox-Gastaut syndrome. 䡲 Hypsarrhythmia with a consistent focus of abnormal discharge and asymmetric hypsarrhythmia are associated with focal or lateralized structural lesions.
Epileptic Encephalopathy
treatment seems to be able to prevent diffuse paroxysmal activity outside of the FCD, which causes secondary generalization such as IS, but the intrinsic epileptogenicity of the FCD is poorly affected by AED. 䡲
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Patients with IS caused by FCD frequently develop partial seizures that can precede, be simultaneous with, or follow the cluster of epileptic spasms.
Eleven different ictal patterns were identified:
2. Generalized sharp and slow-wave complex 3. Generalized sharp and slow-wave complex followed by a period of voltage attenuation 4. Period of voltage attenuation only 5. Generalized slow transient only 6. Period of attenuation with superimposed fast activity 7. Generalized slow-wave transient followed by a period of voltage attenuation with superimposed fast activity
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8. Period of attenuation with rhythmic slow activity 9. Fast activity only 10. Sharp and slow-wave complex followed by a period of voltage attenuation with superimposed fast activity 11. Period of voltage attenuation with superimposed fast activity followed by rhythmic slow activity The most common pattern observed was an episode of voltage attenuation (electrodecremental episode) seen in 72%. The duration of ictal events ranged from 0.5 to 106 sec, with the longer episodes being associated with the arrest phenomenon. However, there was no close correlation between specific ictal EEG patterns and specific types of clinical events. 䡲
Another study found medium- to high-voltage, positive slow waves maximal at the central and vertex regions with superimposed low-voltage fast activity (ictal), followed by electrodecremental event (postictal) to be the most common ictal EEG pattern in IS.
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No significant correlation was found between the various types of ictal EEG patterns and the underlying cause (cryptogenic versus symptomatic), subsequent
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Spasms can be easily controlled by ACTH or Vigabatrin. EEG epileptic foci tend to persist after spontaneous disappearance of the hypsarrhythmic pattern or after successful treatment. 䡲 When spasms disappear, patients are left with focal epilepsy that is intractable to medical treatment, in contrast with IS. Antiepileptic drug (AED)
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1. A high-voltage, frontal-dominant, generalized slow-wave transient followed by a period of attenuation
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Asymmetric ictal patterns frequently occurring in patients with asymmetric epileptic spasms and are correlated with focal or lateralized structural abnormalities. 䡲 Cerebral maturation begins in the central regions and then extends to the occipital regions before the frontal lobes. Theoretically, lesions in the central and occipital regions would produce seizures earlier than in the frontal region. 䡲 Developmental processes may play a role in clinical seizure expression and propagation of seizure activity. Cerebral lesions located in critical areas of brain maturation may have a role in the genesis of IS. Occipital lesions are found to be associated with the earliest onset of spasms, whereas frontal lesions are rare and associated with latest spasm onset.
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seizure control, or prognosis for developmental outcome. As with interictal EEG patterns, an asymmetric ictal pattern, regardless of type, does correlate with focal or lateralized structural brain lesions. The most common patterns noted were higher amplitude fast activity and/or more pronounced voltage attenuation on the side of the lesion. Asymmetric spasms frequently occur in patients with asymmetric ictal patterns. Persistence of hypsarrhythmia during a cluster of spasms indicates a good prognosis in idiopathic case. A high-voltage, frontal-dominant, generalized slowwave transient is a common ictal EEG onset seen in IS. ACTH leads to rapid normalization of the EEG and clinical spasms in 67–97%. Recurrent spasms were noted in 31–47% after several months of being seizure-free. Transition to Lennox-Gastaut syndrome occurs in approximately 50–70%. Profound mental retardation occurs in 50%.
Lennox-Gastaut syndrome (Figures 7-40 to 7-59) 䡲
Two to three percent of all cases of childhood epilepsies. 䡲 Onset between 3 and 10 years (peak 3–5 years). 䡲
Criteria for Lennox-Gastaut syndrome: 䊳 Multiple seizure types, mainly atypical absence, axial tonic, and atonic seizures. Tonic seizures during sleep is a constant feature; other seizures (myoclonic, generalized tonic-clonic, focal) can also occur.
Characteristic EEGs: 앫 Diffuse slow-spike-and-wave discharges 앫 Bursts of fast rhythms at 10–12 Hz during sleep (paroxysmal fast activity) 䊳 Permanent psychologic disturbances with psychomotor delay, personality disorders, or both 䡲 LGS can be symptomatic or cryptogenic. 䊳
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Etiology (selected): 䊳
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Perinatal anoxic ischemia; antenatal or perinatal vascular accident antenatal, perinatal, or postnatal cerebral and cerebromeningeal infection HHE (hemiconvulsion-hemiplegia-epilepsy) syndrome Both diffuse and lateralized or even focal brain malformation and migration disorders Tuberous sclerosis Down syndrome Hydrocephalus Head trauma Brain tumor and radiotherapy for brain tumor
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History of prior IS with hypsarrhythmia is reported in approximately 10–25% of all patients with LGS. 䡲 Because the causative factors are very similar in West syndrome and LGS and because West syndrome may evolve into LGS, these two syndromes have long been considered as age-related, nonspecific epileptic encephalopathies.
Typical EEG feature of LGS Slow Spike-Wave (SSW) Pattern 䡲 A spike or a sharp wave followed first by a positive deep “trough” and then by a negative wave (350–400 msec). Most often, it is a sharp wave followed by a slow wave and less often a spike or polyspikes followed by a slow wave.
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The abundance and the waxing and waning characteristics of SSWs commonly blur any distinction between ictal and interictal patterns.
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SSWs can be distinguished from 3-Hz spike-wave discharges, which are usually associated with a clinical change if their duration is longer than 3 sec.
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The duration of the paroxysms of SSW activity also varies widely, but they are distinguished from classic 3-Hz spike waves by their abundance; they often appear in prolonged sequences without clinical changes. Hence, the SSW activity of LGS is usually considered to be an interictal pattern. 䡲 Bursts, which can range from several seconds in duration to being almost continuous, are often associated with some clouding of consciousness, which may constitute an atypical absence or even absence status. 䡲 Although the SSW pattern is fairly symmetric over the two hemispheres, shifting asymmetry in different bursts is common. 䡲
Persistent focal or lateralized asymmetry of SSW activity may occur in as high as 25% of patients.
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Generalized paroxysmal fast activity (GPFA), grand mal discharge, fast paroxysmal rhythms, rhythmic spikes, or runs of rapid spikes.
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Electrodes placed over the paraspinous muscles frequently demonstrate subclinical tonic EMG activity.
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PFA is frequently not an interictal pattern but is rather an ictal manifestation of a tonic seizure, which may range from a very slight change (only detected by EMG electrodes placed in several axial muscles) to a definite clinical tonic seizure.
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Extremely rare during REM sleep.
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Frontal or fronto-central predominance in approximately 90%. 䡲 Occipital predominance <10%. 䡲
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The frequency of the SSW varies from 1 to 4 cps, commonly between 1.5 and 2.5 cps. 䡲 The SSW discharges of LGS, unlike the classic 3-cps spike waves of absence epilepsy, only rarely show a very regular repetition rate; their characteristic feature is irregularity in frequency, amplitude, and morphology and distribution.
Shifting asymmetries are common, but rarely the pattern may show persistent amplitude asymmetry and may be unilateral or even focal.
The most characteristic feature of PFA is that the rhythmic spikes show little or no change in frequency throughout the burst, in contrast to the ictal pattern associated with generalized convulsive seizures in which the spikes decrease in frequency during the course of ictus. 䡲 During waking state, the PFA is usually ictal and associated with tonic seizures. 䡲 During NREM sleep, when it is most commonly expressed (often repeating every few minutes), the EEG pattern is usually unaccompanied by obvious clinical signs. Subtle clinical changes such as opening of the eyes and jaw, upward deviation of the eyes, or slight change in breathing are noted.
Paroxysmal Fast Activity (PFA)
Seen only in NREM sleep and occurs in older children, adolescents, and younger adults. 䡲 Paroxysms of 1–9 sec in duration, of high-frequency (8- to 25-cps) rhythmic activity, voltage of 100–200 μV, usually generalized but maximum over frontal regions, preceded or followed by generalized sharp and slow-wave complexes.
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Epileptic Encephalopathy
Bursts of more than 5-sec duration are usually associated with tonic seizures. 䡲 Although this EEG pattern is a hallmark of LGS, it can be seen in other generalized epilepsies, especially 3-Hz spike waves that have better outcome than in LGS as well as focal epilepsy (frontal or temporal lobe).
Background Activity 䡲
The background activity is also abnormal with varying degrees of diffuse slowing in 70–90% of patients. 䡲 Focal and multifocal epileptiform discharges are seen in 14–18% of the patients. 䡲 Photic stimulation in patients with LGS typically fails to “activate” SSWs, which distinguishes LGS from some myoclonic epilepsies. Seizure types Ninety-five percent of LGS have multiple types of seizures, the three common seizure types being tonic seizures, atypical absences, and drop attacks.
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7 Tonic Seizures 䡲 Thought to be a characteristic sign of Lennox-Gastaut syndrome, they are not present at onset and the EEG features are not pathognomonic of the disorder. 䡲
Tonic seizures are the main feature of the syndrome and are reported in 74%. 䡲 The EEG during tonic seizures consists of either a bilateral discharge of fast rhythms, predominantly in the anterior areas and at the vertex, or a flattening of the background, or a combination of these two patterns, sometimes preceded by generalized spike waves, followed by diffuse slow waves and SSWs that last longer in patients with “tonic-automatic” seizures. There is no postictal silence. The fast discharges are particularly common during slow-wave sleep, when they can be nearly subclinical. 䡲
In a typical tonic seizure, the neck and the trunk are usually flexed, arms are raised in a semiflexed or extended position, the legs are extended, facial and masticatory muscles contract, and the eyes deviate upward.
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Autonomic changes are consistent during tonic seizures, and understandably, they may be referred to as tonic-autonomic seizures. Autonomic symptoms include loss of bladder control, respiratory changes (apnea or rapid respirations), change in the heart rate (usually tachycardia), facial flushing, and dilated pupils. 䡲 When a tonic seizure is prolonged (lasting more than 10 sec), it may end in a vibratory tremor-like shaking of the body (tonic vibratory seizures). Less often, the tonic phase is followed by gestural or ambulatory automatisms (tonic-automatic seizures). 䡲
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Loss of consciousness may be slightly delayed after the onset of the seizure, but the recovery usually coincides with the end of the EEG ictal discharge.
A brief, mild episode may be limited to a slight upward movement of the eyes (sursum vergens) associated with a brief change in the respiratory and heart rate. 䡲 The EEG correlates of a tonic seizure are desynchronization and/or paroxysmal fast rhythmic activity.
Epileptic Encephalopathy
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Four major types of ictal patterns are reported: 1. Simple flattening (desynchronization) of all activity throughout the seizure 2. Very rapid rhythmic activity of 15–25 cps, usually low in amplitude initially but increasing progressively in amplitude to 50–100 μV 3. Combination of (1) and (2), i.e., “flattening” followed by very rapid rhythmic activity 4. Rhythmic discharge at approximately 10–15 cps, which is high amplitude from the start 䡲 Typical ictal EEG seen in children with LGS during a generalized tonic seizure. 䊳 Slow spike or slow wave → brief (1 sec or less) “flattening” of the EEG → low voltage fast (18–25) activity or spikes → subsequently slowing → postictal period, last spikes are followed by slow waves
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be difficult to recognize, especially in a child with severe cognitive impairment. 䊳 Drooling, changes in postural tone, and irregular eyelid/perioral myoclonia are common accompaniments. 䊳 Atypical absences are usually not precipitated by hyperventilation or intermittent photic stimulation. 䡲 EEG in atypical absences is accompanied by bisynchronous, high-amplitude, usually symmetric, 1.5- to 2.5-cps SSW activity, similar to the interictal EEG pattern. 䡲 The ictal pattern tends to be higher in amplitude and more regular and sustained than interictal paroxysms. Occasionally, atypical absences are accompanied by a generalized 10- to 20-cps PFA. Drop Attack 䡲
Atypical Absence 䡲
Associated with often irregular, more or less symmetric discharge of diffuse slow spikes and waves at 2–2.5 Hz or with a burst of rapid rhythms, or with a mixed pattern. 䡲 Tonic seizures are divided into three types: 䊳 Axial (involvement of the head and trunk) 䊳 Axo-rhizomelic (involvement of the arms predominantly) 䊳 Global (involvement of the whole body) 䡲 Atypical absences are also characteristic seizures of LGS observed in more than 75%. 䡲 Although similar to typical absences of childhood absence epilepsy in having brief loss of awareness as the dominant feature, there are important differences between the typical and atypical absences. 䊳 During atypical absences, the impairment of consciousness is progressive; it is usually incomplete and recovers gradually at the end of the seizure. Some purposeful motor activity may continue during the seizure so that the seizure may
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Epileptic drop attacks, in which the loss of posture with sudden forward or backward fall takes place in a fraction of a second, constitute the third most common and one of the cardinal seizure types in patients with LGS. Approximately one-third to two-thirds of all patients with LGS are reported to have drop attacks. Brief motor events associated with a fall may represent any of the following four different seizure types: 䊳 Pure atonic 䊳 Myoclonic-atonic 䊳 Myoclonic 䊳 Tonic Most of the epileptic falls in patients with LGS represent tonic falls, which are associated with overt increase of muscle tone involving both agonist and antagonist muscles of part of the or the entire body. Most patients with axial spasms or flexor spasms in LGS have had a history of West syndrome. The ictal EEG associated with drop/falling attacks is heterogenous:
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Brief tonic seizures or spasms responsible for a drop attack may produce either no change in the EEG or slight flattening (desynchronization).
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Longer tonic seizures (more than 1 sec in duration) may be associated with a run of low-amplitude fast rhythm or high-amplitude spike-wave discharges.
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Myoclonic drop attacks may show a generalized spike wave, polyspike wave, or polyspikes corresponding to the myoclonic jerk.
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Atonic or myoclonic-atonic events produce generalized polyspike and wave with loss of tone, usually in association with the wave component of the spike-wave complex.
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Other types of seizures, such as generalized tonicclonic, massive myoclonic jerks, and focal seizures, are not uncommon, but these seizure types are not considered to be specific for LGS.
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Myoclonic variant of Lennox-Gastaut syndrome with myoclonic seizures as the major seizure type. 䊳
Tonic seizures are either absent or only nocturnal.
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Onset is later.
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Two-thirds are cryptogenic.
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The overall prognosis is better compared with a typical case of symptomatic LGS (mental development and neurologic/cognitive deficits).
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The EEG shows SSW activity but no PFA.
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Myoclonic variant of LGS accounted for 18% (debatable).
Status Epilepticus 䡲
Episodes of epileptic status are common, occurring in more than two-thirds of all patients with LGS, often facilitated by overmedication, especially with hypnotic/sedative AEDs. Although any seizure type may constitute the status, tonic status and atypical absence status are the two most common. 䡲 Tonic status, often encountered during sleep, may occur spontaneously or may be precipitated by intravenous administration of a benzodiazepine.
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Epileptic Encephalopathy
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Atypical absence status characterized by mild clouding of consciousness or a confusional state is a type of nonconvulsive status, which is often unrecognized and mistaken for medication effect or intercurrent illness. It may begin so insidiously that the health care provider may describe the child to be more lethargic, irritable, or weak. Such an episode may last several days. Intravenous benzodiazepines are usually effective but may precipitate a tonic status. 䡲 Commonly, an episode of status may have features both of atypical absences and tonic seizures. The child has an almost continuous period of decline in alertness interrupted by intermittent tonic seizures. Such episodes may also last several hours to several days. 䡲 The EEG during status epilepticus (SE) may not be much different from the interictal EEG. The generalized SSW activity may be more persistent, or the EEG may become more severely abnormal to the extent of showing an atypical hypsarrhythmic pattern. 䡲
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The presence of persistent focal epileptiform activity and polymorphic delta activity, asymmetric generalized SSW discharges, and PFA predominating in one hemisphere, especially if associated with underlying structural abnormalities, should prompt the neurologist to consider focal resective surgery.
Electrical status epilepticus during slow sleep (ESES) Continuous spikes and waves during slow sleep (CSWS) Landau-Kleffner syndrome (LKS) (Figures 7-60 to 7-61, and 7-66 to 7-72)
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CSWS (continuous spike wave during slow sleep) refers to both the EEG and clinical features (cognitive and behavior disorders), but practically, both ESES and CSWS terms are interchangeable. 䡲 The age at onset is 2–10 years of life. 䡲 This is an EEG sign of particularly severe epilepsy. ESES is seen in either normally developed children
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or retarded patients. The patients usually present with regression of psychomotor and language development and motor incoordination. Remission of the EEG findings usually occurs during puberty, although the patients are usually left with cognitive and language deficits. ESES and CSWS are defined in the classification of the ILAE (1989) as follows: “Epilepsy with CSWS results from the association of various seizure types, partial or generalized, occurring during sleep and atypical absences when awake. Tonic seizures do not occur. The characteristic EEG pattern consists of continuous diffuse spike-waves during slow wave sleep, which is noted after onset of seizures. Duration varies from months to years. Despite the usually benign evolution of seizures, prognosis is guarded, because of the appearance of neuropsychological disorders.” Similar condition called “encephalopathy with ESES” in a recent ILAE proposal is defined as an age-related and self-limited disorder, characterized by the following features: 1. Epilepsy with focal and generalized seizures 2. Neuropsychological impairment (excluding acquired aphasia) 3. Motor impairment (ataxia, apraxia, dystonia, or unilateral deficit) 4. Typical EEG findings with a pattern of diffuse SW (or more or less unilateral or focal) occurring in up to 85% of slow sleep over a period of at least 1 month. ESES is an electrographic pattern characterized by nearly continuous SSW discharges, usually diffuse or generalized in distribution during NREM sleep but focal during awake or REM states. The spike-wave discharges occur in >85% of the NREM sleep, although the spike-wave index under 85% has been used by some authors. In the original series, the EEG pattern of ESES was described as consisting of “generalized” or “diffuse” SSW discharges at 1.5–2 Hz. However,
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Epileptic Encephalopathy
cases displaying slow spikes devoid of the wave component, sharp waves or relatively focal, albeit continuous, mainly involving the temporal or frontal regions, or markedly asymmetrical spike-wave activity over the two hemispheres, have been observed. 䡲 Interictal EEG abnormalities may have a role in cognitive impairment. Congenital stroke was seen in 10%. Early thalamic injuries have been reported to be a facilitating factor in provoking ESES. 䡲 Children with unilateral brain lesions, intractable seizures, and cognitive dysfunction with ESES may become seizure-free, show resolution of ESES, and improve cognitive function after epilepsy surgery, mainly hemispherectomy.
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Myoclonic jerks Atypical absences 䊳 Complex focal seizures 䡲 Seizures begin before 1 year of age in all cases.
Interictal epileptiform activity is more frequent and diffuse during NREM sleep due to better synchronization of EEG, but less frequent and more focal during REM sleep and wakefulness. 䡲 Interictal epileptiform discharges in focal epilepsy occur more frequently during sleep, especially stage 3/4 sleep (slow-wave sleep). The discharges have a greater propensity to spread during sleep and, thus, are often seen over a wider field than discharges occurring during wakefulness and REM sleep. Therefore, EEG during REM sleep may have greater localizing value in focal epilepsy than NREM sleep. 䡲 ESES may be the result of secondary bilateral synchrony. Focal motor seizure is a common type of seizure, and focal epileptiform activity is usually seen during wakefulness and REM sleep. 䡲
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EEG can sometimes simulate benign focal epilepsy syndrome such as epilepsy with centro-temporal spikes. The duration of ESES and the localization of focal epileptiform activity play major roles in cognitive dysfunction, suggesting that the clinical features in ESES result from a localized disruption of EEG activity caused by focal epileptic activity during slow sleep. Spike-wave activity below 85% during NREM sleep was correlated with less cognitive impairment.
Epileptiform activity in the patients with LKS is variable, but eventually, almost all of them have bilateral spike-and-wave activity during more than 85% of NREM sleep (ESES). At the earlier stage, the epileptic foci are usually located in the temporal region (>50%) or in the parieto-occipital regions (30%). Bilateral temporal (mainly posterior) spikes and generalized spike-and-wave discharges have also been observed.
Dravet syndrome (Figures 7-62 to 7-65) 䡲
Tetrad of seizures including: 䊳 Early infantile febrile clonic seizures (mainly unilateral) 䊳 䊳
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Twenty-five percent present with non-febrile seizure, and 20% have no myoclonic jerks.
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Febrile seizures in Dravet syndrome (DS): 䊳 Prolonged >15–30 minutes 䊳 Unilateral 䊳 䊳 䊳 䊳 䊳
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Mainly clonic Frequent Precipitated by low-grade fever, often <38 c Early onset before 1 year Concurrent with non-febrile seizures
Precipitating factors: 䊳 Hyperthermia
Photic or pattern stimulation, movement, and eye closure 䡲 Focal seizures, simple partial seizure (SPS) of motor type (versive or clonic), and complex partial seizures (CPS) occur in 43–78% of patients. They can appear early, from 4 months to 4 years. CPS are characterized by autonomic phenomena (pallor, cyanosis, rube faction, respiratory changes, drooling, sweating),
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oral automatisms, hypotonia, stiffness (rare), and sometimes with eyelid or distal myoclonia. The seizure focus was noted in the frontal, temporal, and occipital regions. 䡲
Only 25% of the patients with DS demonstrated abnormalities on initial EEG. On evolution, most patients demonstrated diffuse or generalized interictal epileptiform discharges and, less commonly, a combination of generalized and focal abnormalities.
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The lack of definite, typical EEG abnormalities on follow-up EEG makes the diagnosis of DS more difficult.
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Patients with DS have multiple types of seizures, including generalized tonic-clonic or clonic seizures, alternating unilateral clonic, myoclonic, focal seizures, and atypical absence seizures with an obtunded state. Tonic seizures are exceptional. Atypical absence seizures are associated with generalized irregular 2- to 3.5-Hz spike-wave discharges. 䡲 Rare typical absence seizures have been reported. 䡲 NCSE was observed in approximately 40% of patients with DS. Characteristic clinical findings during NCSE are erratic myoclonus associated with unsteadiness and frank ataxia. Sensory stimulations can interrupt but never definitely stop NCSE. EEG is characterized by diffuse slow wave dysrhythmia intermixed with focal, multifocal, or diffuse spikes, sharp waves, and spike-wave activity. Rhythmic spike-wave activity associated with absence SE is not seen, but complex partial SE has been reported.
EEG 䡲
EEG becomes very abnormal in 2/3 within 1 year. 䊳 Diffuse theta and delta slowing 䊳 Brief asymmetrical paroxysms of polyspike/spike slow-wave discharges 䊳 Focal or multifocal epileptiform activity 䊳 SSW discharges
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Photoparoxysmal response (40%) and eye closure and pattern stimulation.
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FIGURE 71. Severe Neonatal Epilepsy with Suppression-Burst Pattern (Early Epileptic Encephalopathy); Erratic Myoclonus. A 5-day-old boy born full term without complications who presented with hypotonia, apnea, irritability, and jitteriness. He was found to have frequent erratic myoclonus and myoclonic seizures. MRI was unremarkable. EEG shows suppression-burst (S-B) pattern and subclinical electrographic focal seizures (not shown). It also shows no significant changes during erratic myoclonus (open arrow). An extensive metabolic work-up was negative. There are two severe neonatal epilepsies with S-B pattern, Ohtahara syndrome (OS) and early myoclonic encephalopathy (EME). The EEG shows bursts, lasting several seconds, of polyspikes alternating with very low-voltage activity, this combination being called "suppression bursts." The S-B pattern may be asymmetric, affecting mainly the side of the cortical malformation, hemimegalencephaly, focal cortical dysplasia, Aicardi syndrome, olivary-dentate dysplasia, or schizencephaly.1–3 The onset of seizures in OS is within the first 2–3 months but most commonly within the first 10 days. The main type of seizure in OS is the tonic spasm. Myoclonic seizures and erratic myoclonus are rare. A majority of cases of OS are associated with structural brain abnormalities, including porencephaly, hydrocephalus, hemimegalencephaly, and lissencephaly. No familial case of OS have been reported. EME is characterized by an early onset in the neonatal period with the main seizure types of erratic and massive myoclonus and partial seizures. The most common cause of EME is metabolic disease. The causes of OS are symptomatic or organic; the causes of EME can be genetic, metabolic, or entirely unknown. OS causes tonic spasms and partial seizures. EME causes myoclonic and partial seizures. The EEG of OS contains periodic S-B and is irrespective of waking and sleeping, while EME may have S-B only during sleep. OS commonly transitions to West syndrome. EME transition to West syndrome is transient, if there is any transition at all. The EEG course of S-B in OS is that they turn into hypsarrhythmia in 3–6 months. The EME S-B course is long lasting.4,5 However, the distinction between these two conditions may be difficult because brief spasms are difficult to distinguish from myoclonus. The distinction between S-B and hypsarrhythmia with extreme fragmentation in sleep also is difficult in many cases because in OS, the S-B evolves into the more continuous asynchronous spike- and slow-wave activity of hypsarrhythmia.3
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Epileptic Encephalopathy
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FIGURE 72. Severe Neonatal Epilepsy with Suppression-Burst Pattern; Ohtahara Syndrome. A 1-week-old boy with a history of frequent tonic spasms starting on the first day of life with subsequent developmental regression, spastic quadriparesis, and intractable infantile spasms. Serial neuroimaging studies showed progressive cerebral atrophy. (A) CT performed at 10 months of age. (B) Axial T1-weighted image performed at 2½ years of age. The patient died at 2½ years of age. After intensive investigation, including autopsy, no specific metabolic or degenerative disease was found. EEG performed at 1 week of age shows suppression-burst (S-B) pattern. (Courtesy of Dr. B. Miller, Department of Neurology, The Children’s Hospital, Denver, CO.) Ohtahara syndrome is a very rare and devastating form of epileptic encephalopathy of very early infancy. Onset of seizures is mainly by 1 month of age and often within the first 10 days of life, sometimes prenatally or during the first 2–3 months after birth. Characteristic clinico-EEG features are tonic spasms and, less commonly, erratic focal motor seizures and hemiconvulsion with S-B pattern in the EEG occurring in both sleep and waking states. Although the etiologies of Ohtahara syndrome are heterogeneous, prenatal brain pathology such as a malformation of cortical development is suspected in most cases and metabolic disorders are rare. Evolution into West syndrome is often observed in surviving cases.4,6
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Epileptic Encephalopathy
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FIGURE 73. Unilateral Suppression-Burst Pattern (Ohtahara Syndrome); Hemimegalencephaly. A 19-day-old boy born at 35 weeks GA who started having seizures in utero (hiccup and increased fetal movement) and developed postnatal seizure at 1 week of age, described as left facial twitching and eye deviation and epileptic nystagmus with fast component to the left side. The seizures, at times, were continuous. MRI shows right hemimegalencephaly. EEG demonstrates suppression-burst (S-B) pattern over the right hemisphere. She underwent right functional hemispherectomy at 2 months of age and has been seizure-free for 3 years. Out of 44 patients with hemimegalencephaly, 35% had neurocutaneous syndromes. Almost all patients had mental retardation and hemiparesis. Ninety-three percent had epileptic seizures, which first appeared within a month in 40%. Twenty-five percent underwent functional hemispherectomy, which resulted in fairly good seizure control and improved development. There is a correlation between the onset of epilepsy and the degree of clinical severity of motor deficit and intellectual level.7 The interictal EEG in hemimegalencephaly demonstrates many abnormalities, especially high-amplitude spikes and spike-wave complexes over the damaged hemisphere in the first weeks or months of life8,9 and unilateral suppression burst (S-B).8,10,11 Hoefer et al.12 first described hypsarrhythmia with S-B pattern. The association of this pattern with epileptic spasms justifies the diagnosis of Ohtahara syndrome.13 S-B pattern in Ohtahara syndrome is generated from the subcortical structures and caused by a subcorticalcortical regulation disorder, which is also influenced by cortical lesions.11 Asymmetric S-B pattern can also be seen in cortical malformations, focal cortical dysplasia, Aicardi syndrome, olivary-dentate dysplasia, and schizencephaly.1–3
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Epileptic Encephalopathy
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FIGURE 74. Early Myoclonic Encephalopathy (EME); Pyridoxine Dependency. A 7-day-old girl with intermittent irritability, jitteriness, lethargy, and myoclonic jerks. A subsequent gene test confirmed the diagnosis of pyridoxine dependency. Her MRI was unremarkable. Her initial EEG (as shown) demonstrates diffuse suppression-burst pattern. After an administration of intravenous pyridoxine, the patient showed dramatic improvement in both her clinical symptoms and EEG. During her subsequent neurology visits, she continued to have no seizure and had normal developmental milestones. Her EEGs performed at 1 and 3 months of age were appropriate for age. EME is a very rare epileptic syndrome characterized by myoclonus with onset of seizures in the neonatal period. The EEG shows suppression-burst pattern. Metabolic diseases, especially nonketotic hyperglycinemia, are usually the causes of EME. Malformation of cortical development is an uncommon etiology. Pyridoxine dependency was reported in one patient with EME who had complete recovery after treatment with pyridoxine. Almost all patients with EME have a very poor prognosis.4
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FIGURE 75. Early Myoclonic Encephalopathy (EME) due to Pyridoxine dependency; Focal Clonic Seizure. (Same patient as in Figure 7-4) EEG shows a run of spikes and sharp waves in the right parieto-temporal region. The patient had focal clonic jerks of his left hand time-locked with spikes and sharp waves. Focal clonic seizures in the newborn always show a close relationship to electrographic seizures. They can be seen in both structural abnormalities such as stroke or in a variety of metabolic diseases.14 Partial seizures are an almost constant feature in EME and tend to appear shortly after erratic myoclonus. Epileptic spasms are rarely seen early in the course of EME.4
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FIGURE 76. Early Myoclonic Encephalopathy (EME) due to Pyridoxine dependency; Response to Treatment. (Same patient as in Figure 7-4) This EEG was performed at 13 months of age. The patient continues to be on vitamin B6 supplementation for pyridoxine dependency and has done extremely well. He has had normal developmental milestones and has been seizure-free. The EEG shows bilateral synchronous and relatively symmetric sleep spindles, which is normal for 13 months. No epileptiform activity is noted.
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FIGURE 77. West Syndrome; Diffuse Cerebral Atrophy due to Severe Hypoxic Ischemic Encephalopathy (HIE). A 5-month-old boy born 27 weeks GA with severe HIE who developed West syndrome at 4 months of age. EEG during wakefulness shows typical hypsarrhythmia. The average incidence of infantile spasms is 1 in 3225 live births. The highest incidence correlates with higher geographic latitudes. The age of onset of infantile spasms varies from the first week of life to more than 3 years of age, with the average onset at 6 months. Most cases (94%) begin within the first year of life. Positive family history for epilepsy ranges from 1% to 7%.15 Gibbs and Gibbs16 defined the term hypsarrhythmia as follows: “…random high voltage slow waves and spikes. These spikes vary from moment to moment, both in duration and in location. At times they appear to be focal, and a few seconds later they seem to originate from multiple foci. Occasionally the spike discharge becomes generalized, but it never appears as a rhythmically repetitive and highly organized pattern that could be confused with a discharge of the petit mal or petit mal variant type. The abnormality is almost continuous, and in most cases it shows as clearly in the waking as in the sleeping record.” Five variants of hypsarrhythmia were defined as follows: (1) hypsarrhythmia with increased interhemispheric synchronization (35%); (2) asymmetric hypsarrhythmia (12%); (3) hypsarrhythmia with a consistent focus of abnormal discharge (26%); (4) hypsarrhythmia with episodes of voltage attenuation (11%); and (5) hypsarrhythmia with little spike or sharp activity (7%).17,18 Transient alterations of the hypsarrhythmia occur throughout the day in relation to the sleep state. During non-rapid eye movement (NREM) sleep, the voltage of the background activity typically increases, and there is a tendency for grouping of the multifocal spike- and sharp-wave activity, often resulting in a periodic pattern.19,20 Electrodecremental episodes frequently occur during NREM sleep. On arousal from NREM sleep, there is also typically a reduction in amplitude or complete disappearance of the hypsarrhythmic pattern that may persist for a few seconds to many minutes. The hypsarrhythmic pattern may also disappear during a cluster of spasms but immediately returns after cessation of the spasms.17 As with the clinical spasms, hypsarrhythmia characteristically disappears with increasing age.21 A variety of patterns may be seen when hypsarrhythmia disappears, including diffuse slowing, focal or multifocal spikes and sharp waves, monorhythmic background activity, focal slowing, asymmetric background activity, slow spike and slow-wave activity, and diffuse high-voltage fast activity.22 Rarely, the EEG may be normal. Although hypsarrhythmia and its variants are the most common EEG patterns seen in infantile spasms, other interictal patterns may occur, including focal or multifocal spikes and sharp waves, abnormally slow or fast rhythms, diffuse slowing, focal slowing, focal depression, paroxysmal slow or fast bursts, a slow spike and wave pattern, continuous spindling or, rarely a normal pattern. These patterns may occur singly or in various combinations.15
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FIGURE 78. Hypsarrhythmia; Infantile Spasms secondary to Periventricular Leukomalacia (PVL). A 7-month-old girl with infantile spasms caused by periventricular leukomalacia (PVL). The patient was born 30 weeks GA with severe HIE with subsequent moderately severe developmental delay and spastic diplegia. She had her first seizure at 3 months of age. MRI shows multiple small periventricular cysts (arrow), decreased white matter volume, thinning of the corpus callosum, and absence of the septum pellucidum, consistent with PVL. Interictal EEG activity demonstrates a chaotic mixture of asynchronous, very high-voltage polymorphic delta slowing and multifocal sharp waves, which is characteristic of hypsarrhythmia. Spike-wave activity is seen predominantly in bilateral parietal-occipital regions. West syndrome is a common complication of severe PVL and correlates strongly with the finding of bilateral parietal-occipital dominant irregular polyspike-wave activity.23
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FIGURE 79. Asymmetric Hypsarrhythmia; Cystic Encephalomalacia due to Intrauterine Stroke. A 9-month-old right-handed boy with a history of antithrombin 3 deficiency with resultant intrauterine right middle cerebral artery stroke. At 7 months of age, he developed clusters of spells with bilateral upper extremity extension and leftsided deviation of his head. EEG shows asymmetrical hypsarrhythmia characterized by voltage asymmetry with amplitude higher in the right hemisphere. Asymmetric hypsarrhythmia (hemihypsarrhythmia or unilateral hypsarrhythmia), first described by Ohtahara24 is characterized by hypsarrhythmia, with a consistent amplitude asymmetry between the two hemispheres. Asymmetric hypsarrhythmia is always associated with underlying structural abnormalities of the brain, most commonly seen in large cystic or atrophic defects of one hemisphere, such as porencephaly or encephalomalacia, tuberous sclerosis, Aicardi syndrome, hemimegalencephaly, and other malformations of cortical development.25–29 Asymmetric hypsarrhythmia can also occur in bilateral structural lesions that were more abnormal in the area of the greater EEG abnormality.30 Hypsarrhythmia may be maximal over either the more abnormal or the more normal hemisphere.31 Asymmetric hypsarrhythmia and asymmetric ictal EEG changes during infantile spasms often occurred together: each always indicated the side of a focal or asymmetric structural cerebral lesion.30
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FIGURE 710. Asymmetric Infantile Spasms; Asymmetric Hypsarrhythmia. A 4-month-old left-handed boy with normal developmental milestones who developed asymmetric infantile spasms characterized by clusters of brief tonic contractions of the muscles of the trunk, neck, and limbs, that gradually relaxed over 1–3 sec. Persistent asymmetric muscle contraction of limbs and neck, described as head turning to the right side with left arm extension and right arm flexion, was noted. Axial and coronal T2weighted MRIs show left hippocampal atrophy (arrows). An interictal EEG shows hypsarrhythmia with a consistent amplitude asymmetry between hemispheres, compatible with “asymmetric hypsarrhythmia” with consistent left parietal epileptiform discharges (large arrow). Interictal PET scan (not shown) demonstrated hypometabolism in the left temporal region. The patient was in remission after 4 days of ACTH treatment and had normal developmental milestones after that. In the series by Kellaway et al.,32 only 0.6% of spasms were asymmetric. Consistent asymmetry of epileptic spasms, especially when associated with asymmetry of ictal/interictal EEG discharges, is supportive evidence for an underlying focal structural abnormality.33 Persistent asymmetric hypsarrhythmia is always associated with underlying structural brain abnormalities. However, it should be noted that the hypsarrhythmia can be more prominent over either the more abnormal or the more normal hemisphere.15
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FIGURE 711. Hypsarrhythmia with Increased Interhemispheric Synchronization; Symptomatic Late onset Epileptic Spasm Associated with Trisomy 21. A 2-year-old boy with trisomy 21 (mosaic) and mild global developmental delay and hypotonia who recently developed clusters of symmetric epileptic spasms. He responded well to ACTH. EEG shows hypsarrhythmia with increased interhemispheric synchronization. Hypsarrhythmia with increased interhemispheric synchronization was seen in 35% of hypsarrhythmia variants.18 The classic hypsarrhythmia, multifocal spikes and sharp waves, and the diffuse asynchronous slow wave activity are replaced or intermixed with activity that demonstrates a significant degree of interhemispheric synchrony and symmetry. The EEG evolution can take place over weeks to months. This EEG pattern sometimes appears only intermittently with classic hypsarrhythmia.31,34 Most infants with hypsarrhythmia will have some degree of synchronization of the background activity if the condition persists for many months or years. This is particularly true of those infants who exhibit a transition to Lennox-Gastaut syndrome.31
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Epileptic Encephalopathy
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FIGURE 712. Asymmetric Infantile Spasms; Asymmetric Hypsarrhythmia with Increased Interhemispheric Synchronization. (Same patient as in Figure 7-11) EEG during sleep shows three variants of hypsarrhythmia, including suppression-burst pattern, asymmetric hypsarrhythmia, and consistent focus of abnormal discharges. Hrachovy et al. describe five hypsarrhythmia variants: hypsarrhythmia with increased interhemispheric synchronization, asymmetric hypsarrhythmia, hypsarrhythmia with a consistent focus of abnormal discharge, hypsarrhythmia with episodes of voltage attenuation, and hypsarrhythmia with little spikes or sharp activity. These patterns may occur in various combinations. Hypsarrhythmia with a consistent focus of abnormal discharge and asymmetric hypsarrhythmia are associated with focal or lateralized structural lesions.15,17
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Epileptic Encephalopathy
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FIGURE 713. Asymmetric Hypsarrhythmia with a Consistent Focus of Abnormal Discharge; Asymmetric Infantile Spasm. (Same patient as in Figure 7-11) An interictal EEG at 4 months of age shows consistent epileptiform activity in the left centro-parietal and centro-parietal vertex regions (arrow) and asymmetric hypsarrhythmia, maximal in the left hemisphere. These findings are highly supportive of an epileptic focus caused by a structural abnormality in the left centro-parietal vertex region, which is concordant with the MRI and PET scan finding performed at 4 years of age when the patient started having focal seizures. Review of earlier video-EEG evaluation is extremely helpful in the identification of epileptic focus.35
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FIGURE 714. Asymmetric Infantile Spasms; Diffuse Electrodecrement with Focal Onset. (Same patient as in Figure 7-11) Ictal EEG during a typical asymmetric epileptic spasm shows a burst of low-voltage beta activity in the left midtemporal (solid arrow) and a spike in the left centro-parietal region (arrow), immediately prior to bilateral synchronous sharp activity, diffuse electrodecremental event, and the epileptic spasm. Asymmetric ictal patterns frequently occurring in patients with asymmetric epileptic spasms are correlated with focal or lateralized structural abnormalities.15,30,36
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FIGURE 715. Asymmetric Epileptic Spasms; Focal Cortical Dysplasia (FCD). (Same patient as in Figure 7-11) After the remission of infantile spasms (IS), the patient had normal developmental milestones with minimal focal neurological deficits that included pathologic left handedness, mild atrophy of the right thumb, mild right optic apraxia, asymmetric tonic neck refl ex, and hyperrefl exia/ dorsifl exion of the right side. EEGs performed every 6 months were within normal limits. At 3. years of age, the patient developed epileptic spasms similar to the IS he had when he was 4 months old. (A) Axial inversion recovery MRI shows blurring of the gray-white matter junction and thickened cortex in the left mesial parietal region (arrow). (B) Coronal T2-weighted MRI shows thickened cortex in the left lateral/mesial parietal region (arrow). The MRI continued to show left hippocampal atrophy (not shown). Interictal EEG shows frequent and, at times, periodic sharp waves and frequent polymorphic delta slowing, maximal in the left parietal region. This finding is compatible with the hypsarrhythmia with consistent left parietal spikes seen at 4 months of age (Figure 7-12). Cerebral maturation begins in the central regions and then extends to the occipital regions before occurring in the frontal lobes.37,38. Theoretically, lesions in the central and occipital regions would produce seizures earlier than those in the frontal region. Developmental process may play a role in clinical seizure expression and propagation of seizure activity. Cerebral lesions located in critical areas of brain maturation may have a role in the genesis of IS. Occipital lesions are found to be associated with the earliest onset of spasms, whereas frontal lesions are rare and associated with latest spasm onset.39,40 Patients with IS caused by FCD frequently develop partial seizures that can precede, be simultaneous with, or follow the cluster of epileptic spasms. Spasms can be easily controlled by ACTH or Vigabatrin. EEG epileptic foci tend to persist after spontaneous disappearance of the hypsarrhythmic pattern or after successful treatment. When spasms disappear, patients are left with focal epilepsy that is intractable to medical treatment, in contrast with IS. Antiepileptic drug (AED) treatment seems to be able to prevent the diffuse paroxysmal activity outside of the FCD that causes secondary generalization such as in IS, but the intrinsic epileptogenicity of the FCD is poorly aff ected by the AED.15,41
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FIGURE 716. High-Voltage, Frontal-Dominant, Generalized Slow Wave Transient; Symptomatic West syndrome and Asymmetric Epileptic Spasm. (Same EEG tracing as in Figure 7-11) EEG during a cluster of asymmetric epileptic spasms described as brief asymmetric tonic stiffening of arms and legs with left-sided predominance (arrow head) reveals lateralized high-voltage delta slow activity in the left hemisphere with positive polarity delta slowing, maximal at the P3 electrode (arrow). Eleven different ictal patterns were identified: (1) a high-voltage, frontal-dominant, generalized slow-wave transient followed by a period of attenuation; (2) a generalized sharp- and slow-wave complex; (3) a generalized sharp- and slow-wave complex followed by a period of voltage attenuation; (4) a period of voltage attenuation only; (5) a generalized slow transient only; (6) a period of attenuation with superimposed fast activity; (7) a generalized slow-wave transient followed by a period of voltage attenuation with superimposed fast activity; (8) a period of attenuation with rhythmic slow activity; (9) fast activity only; (10) a sharp- and slow-wave complex followed by a period of voltage attenuation with superimposed fast activity; and (11) a period of voltage attenuation with superimposed fast activity followed by rhythmic slow activity. The most common pattern observed was an episode of voltage attenuation (electrodecremental episode). The duration of ictal events ranged from 0.5 to 106 sec, with the longer episodes being associated with the arrest phenomenon. However, there was no close correlation between specific ictal EEG patterns and specific types of clinical events.32 No significant correlation was found between the various types of ictal EEG patterns and underlying cause (cryptogenic versus symptomatic), subsequent seizure control, or prognosis for developmental outcome.42 As with interictal EEG patterns, an asymmetric ictal pattern, regardless of type, does correlate with focal or lateralized structural brain lesions.30,43 The most common patterns noted were higher amplitude fast activity and/or more pronounced voltage attenuation on the side of the lesion. Asymmetric spasms frequently occur in patients with asymmetric ictal patterns.15 A high-voltage, frontal-dominant, generalized slow-wave transient is a common ictal EEG onset seen in infantile spasm. In this patient, lateralized diffuse high-voltage biphasic delta activity in the left hemisphere indicates a lateralized epileptic focus/structural abnormality in the left hemisphere. The positive sharp wave at P3 indicates a deep epileptic focus corresponding to the focal cortical dysplasia seen in the left mesial parieto-frontal region (arrow).
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FIGURE 717. Subdural EEG During Asymmetric Epileptic Spasms; High-Frequency Oscillations (HFOs). (Same patient as in Figure 7-11) Subdural EEG recording during a cluster of similar asymmetric epileptic spasms as in Figure 7-16 (arrow head) shows high-voltage delta slow activity with a positive polarity at the PG55 electrode, which is approximately at the same location as the P3 electrode in scalp EEG. What is missing in the scalp EEG recording is a brief run of low-voltage 70- to 80-Hz gamma activity both preceding and superimposed on the delta slowing (open arrow). High-frequency oscillations (HFOs), characterized by very fast activity, ranging from 80 to 150 Hz, are noted at the epileptic focus in neocortical epilepsy during subdural EEG recordings.44 Similar gamma activity ranging from 50-100 Hz is also detected on the scalp EEG during epileptic spasms.45 Recent findings suggest that HFOs ranging between 100 and 500 Hz might be closely linked to epileptogenesis.46 In humans, physiologic oscillations generally showed a frequency range between 80 and 160 Hz (“ripples”) in hippocampus.47,48 Pathological ripples were also observed.49 The differentiation between pathological and physiological events remains unclear.50 HFOs between 250 and 500 Hz, called fast ripples, have been recorded from normal rodent and human brains.51–53 It was hypothesized that they are related to somatosensory stimulation and sensory information processing.54,55 Fast ripples in mesial temporal structures were more epileptogenic than ripples.56 Ripples and fast ripples (250–500 Hz) occur frequently during interictal epileptiform discharges (IEDs) and may reflect pathological hypersynchronous events. In general, these HFOs are seen more frequently during non-rapid eye movement (NREM) sleep compared to rapid eye movement (REM) sleep or wakefulness.48 Recently, it has been shown that HFOs may also be recorded from intracranial macroelectrodes.57,58 During ictal recordings, HFOs could be identified and occurred mostly in the region of primary epileptogenesis and less frequently in areas of secondary spread.57 The recent study showed that HFOs are an important electrophysiological manifestation of the epileptic tissue. They are partially correlated with the spiking region and with the seizure-onset zone (SOZ). Ripples and fast ripples behaved in parallel, increasing in the SOZ and spiking regions, but fast ripples were more specific to the SOZ region than ripples.46
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FIGURE 718. Symptomatic West Syndrome and Asymmetric Epileptic Spasm; Focal Cortical Dysplasia, Left Mesial Fronto-Parietal. (Same patient as in Figure 7-10 to 7-17) (A) MRI: blurred gray-white matter junction with cortical thickening in the left mesial fronto-parietal region. (B) Interictal PET: hypometabolism, left fronto-parietal region. (C) Resection of epileptogenic zone in the same area.
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FIGURE 719. West Syndrome caused by Type 1 Neurofibromatosis. A 5-month-old boy with a family history of neurofibromatosis who had normal developmental history and presented with 3 weeks of epileptic spasms. His EEG shows hypsarrhythmia. He responded well with ACTH. At a last follow-up visit at 3 years of age, he was seizure-free and had only mild developmental delay. Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant disorders with a prevalence of 1 in 4000. Seizures may be relatively uncommon in NF1 and are not always explained by underlying brain lesions. Infantile spasms (IS) are the most frequent cause of epilepsy in infancy, with incidence rates ranging from 2 to 5 per 10,000 live births. IS occurs in NF1 with a frequency (0.76%), 10- to 20-fold higher than that reported in the general population.59 The frequency of West syndrome (WS) in NF1 clearly exceeds the frequency of WS in the general population.60,61 Although the combination of IS and NF1 is not coincidental, it is an unusual event in NF1 compared to other neurocutaneous syndromes. Generally, the outcome is favorable.62 Most patients had normal psychomotor development before spasms (14 of 15).60 Predictors of a good outcome include the following: (1) symmetrical spasms without associated partial seizures; (2) typical hypsarrhythmia; (3) good response to corticoid therapy.60 Infantile spasms caused by NF1 have several characteristics similar to idiopathic WS in profile and evolution: symmetrical spasms without partial seizures and without intellectual deficit, but with good response to corticotherapy and good long-term outcome.60 Another report found the opposite outcome.63 Some studies showed intermediate outcome.59 MRIs of NF1 patients with IS showed high-signal foci in the brain, either subcortical or higher brainstem and central cerebral regions, after the age of 3 years.59
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FIGURE 720. Infantile Spasm; Diffuse Electrodecremental Pattern (EDP) with Low-Voltage Fast Activity. A 6-month-old girl with infantile spasms. The work-up was unremarkable. Interictal EEG shows hypsarrhythmia. Ictal EEG during her typical spasm demonstrates diffuse electrodecrement (*). Note diffuse attenuation of background activity at the onset of epileptic spasm. Four seconds later, during the tonic phase, diffuse low-voltage fast activity with posterior predominance (arrow) followed by more pronounced diffuse background attenuation is noted. At the end of electrodecrement (**), the patient starts to move and cry.
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FIGURE 721. West Syndrome with Asymmetric Epileptic Spasms; Focal Cortical Dysplasia Associated with Cobalamin C Deficiency. A 4-month-old boy with global developmental delay who presented with asymmetric epileptic spasms with tonic stiffening greater on the right side, with or without high-pitch cry. MRI shows possible focal cortical dysplasia (FCD) in the left frontal region (white arrow). EEG during one of his typical seizures demonstrates diffuse attenuation of background activity (electrodecrement) with superimposed low-voltage beta activity. After treatment with zonisamide, the patient developed hyperthermia and apnea. He was intubated and was admitted from the ED to the PICU. He developed very frequent asymmetric epileptic spasms with persistent epileptic focus in the left hemisphere. Emergency ictal SPECT showed hyperperfusion in the left frontal region concordant with the location of FCD seen in the MRI (black arrow). He underwent emergency invasive EEG monitoring followed by resection of the epileptogenic zone in the left frontal region. The patient has been free of disabling seizures since the resection of the FCD and surrounding epileptogenic zone. Pathology confirmed the diagnosis of mild FCD. Asymmetric epileptic spasms are correlated with structural abnormalities, especially FCD in over 90% of cases. Functional modalities such as interictal PET and ictal SPECT play important roles in identification of epileptic foci.64 Although FCD can be seen in rare neurometabolic diseases such as nonketotic hyperglycinemia or cerebrohepatorenal syndrome, it has never been reported in cobalamin c deficiency. Underlying neurometabolic disease is not an absolute contraindication for epilepsy surgery. Outcomes after surgery, cortical resection, or hemispherectomy in infants with catastrophic focal epilepsy are very good. About 75–78% are seizure-free or have at least a 90% seizure reduction.65,66 Life-saving epilepsy surgery for status epilepticus caused by cortical dysplasia has been reported.67
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FIGURE 722. Hypsarrhythmia Variant: Consistent Focus of Abnormal Discharge; Focal Cortical Dysplasia Due to Cobalamin c Deficiency. (Same patient as in Figure 7-21) EEG during sleep shows high-voltage delta slowing intermixed with multifocal spikes and sharp waves with a consistent focus of polyspikes in the left occipital region (arrow). Hypsarrhythmia with a consistent focus of abnormal discharge is seen in 26% of hypsarrhythmia variants18 and characterized by a distinct focus of spike, polyspike, or sharpwave activity superimposed on a typical hypsarrhythmic background, and in some cases, focal electrographic seizure discharges may occur. Such foci tend to persist after spontaneous disappearance of the hypsarrhythmic pattern or after successful treatment.15
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FIGURE 723. Hypsarrhythmia Variant: Consistent Focus of Abnormal Discharge; Focal Cortical Dysplasia Due to Cobalamin c Deficiency. (Same patient as in Figure 7-21) EEG performed during one of his typical asymmetric epileptic spasms described as rapid stiffening of the arms and legs, greater on the right side. The EEG shows a burst of diffuse biphasic delta activity (arrow) followed by a diffuse lateralized electrodecremental event with superimposed low-voltage beta activity in the left hemisphere with occipital predominance (double arrows). Three seconds later, there is a run of sharp waves in the left occipital region (open arrow). Hypsarrhythmia with a consistent focus of abnormal discharge is seen in 26% of hypsarrhythmia variants18 and characterized by a distinct focus of spike, polyspike, or sharpwave activity superimposed on a typical hypsarrhythmic background, and in some cases, focal electrographic seizure discharges may occur. Such foci tend to persist after spontaneous disappearance of the hypsarrhythmic pattern or after successful treatment.15
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FIGURE 724. West Syndrome with Asymmetric Epileptic Spasms; Focal Cortical Dysplasia Associated with Cobalamin c Deficiency. (Same patient as in Figure 7-21 to 7-23) A 4-monthold boy with asymmetric epileptic spasms associated with cobalamin c deficiency. He developed seizure, hyperthermia, and apnea and was intubated. He developed NCSE. Emergency ictal SPECT shows hyperperfusion in the left frontal region concordant with the MRI (black arrow). EEG during the SPECT injection (open arrow) showed ictal activity arising from the left frontal region during the versive seizure. He underwent emergency invasive EEG monitoring followed by resection of epileptogenic zone in the left frontal region. The patient has been free of disabling seizures since the surgery. Pathology confirmed the diagnosis of mild FCD. Epileptic spasms (ES) in some patients with West syndrome (WS) may be triggered by an epileptic focus in the neocortex. A leading spike can be used as a marker of the trigger zone for ES.68 However, a study of WS by ictal SPECT demonstrates that the origin of hypsarrhythmia and ES may be different. Hypsarrhythmia appears to originate from cortical lesions, whereas the subcortical structures may be primarily responsible for the ES.69 Lee et al. proposed a model in which the brainstem was implicated as the source of hypsarrhythmia and ES.70 Asymmetric epileptic spasms are correlated with structural abnormalities, especially FCD in over 90% of cases. Functional modalities such as interictal PET and ictal SPECT play important roles in identification of epileptic foci.64,71 Although focal cortical dysplasia can be seen in rare neurometabolic diseases such as nonketotic hyperglycinemia or cerebrohepatorenal syndrome, it has never been reported in cobalamin c deficiency. Underlying neurometabolic disease is not an absolute contraindication for epilepsy surgery. Outcomes after surgery, cortical resection, or hemispherectomy in infants with catastrophic focal epilepsy are very good. About 75–78% are seizure-free or have at least a 90% seizure reduction.65,66 Life-saving epilepsy surgery for status epilepticus caused by cortical dysplasia has been reported.67
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FIGURE 725. Asymmetric Hypsarrhythmia (Hemihypsarrhythmia) (Ipsilateral); Intraventricular Hemorrhage with Subsequent Left cerebral Hemiatrophy. A 9-month-old girl with a history of a new-onset asymmetric infantile spasm due to grade 4 IVH. Her seizures were described as clusters of subtle spells of head and eyes deviating to the right side without definite flexor or extensor spasms, lasting for approximately 1 sec. (A) CT image during an acute IVH shows dilatation of lateral ventricles, intraventricular hemorrhages with abnormally hypodense areas surrounding them (presumably infarct or edematous) with left-sided predominance, and intraparenchymal hemorrhage in the left occipital region. (B) CT image at 6 months of age shows diffuse cerebral atrophy, greater on the left, with VP shunt placement into the temporal horn of the left lateral ventricle. EEG demonstrates chaotic, very high-voltage polymorphic delta slowing intermixed with multifocal sharp waves in the left hemisphere, with relatively normal background activity in the right hemisphere. These findings are termed “asymmetric hypsarrhythmia.” Asymmetric hypsarrhythmia is also referred to as hemihypsarrhythmia or unilateral hypsarrhythmia and is characterized by the presence of hypsarrhythmia with a consistent amplitude asymmetry between hemispheres. Asymmetric hypsarrhythmia is always associated with underlying structural abnormalities of the brain. However, it should be noted that the hypsarrhythmic activity may be maximal over either the more abnormal or the more normal hemisphere.31 It is more commonly seen in patients with malformation of cortical development. The presence of asymmetric hypsarrhythmia and other variant hypsarrhythmic patterns is more common than previously thought and generally does not correlate with prognosis.71 In children with leukomalacia and in patients with localized porencephalic lesions, the outcome of epilepsy appears to be better than in patients with diffuse cerebral lesions or in children with extensive porencephalic cysts, particularly those involving the frontal lobe.73 Atrophy of midbrain and pons and the presence of bilateral parieto-occipital polyspike-wave discharges on follow-up EEGs were strongly correlated with the development of West syndrome.74,75
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FIGURE 726. Hemihypsatthythmia; Herpes Simplex Encephalitis. A 4-year-old boy with intractable epilepsy caused by herpes simplex encephalitis at 2 years of age. His seizure is described as “very frequent clusters of asymmetric tonic spasms with left-sided predominance accompanied by head and eye deviation to the left side, with or without horizontal nystagmus with fast component to the left side.” MRI showed severe encephalomalacia of the entire right hemisphere with mild left cerebral atrophy. Interictal EEG shows a hypsarrhythmic pattern over the left hemisphere with severe background suppression and multifocal sharp waves over the right hemisphere. This EEG pattern is compatible with left hemihypsarrhythmia. The patient showed significant improvement of seizures after the right functional hemispherectomy. Brain pathology can be lateralized to either ipsilateral or contralateral hemihypsarrhythmia.31 Infections are considered to be etiological factors in 10% of patients with infantile spasms (congenital or acquired cytomegalovirus (CMV), congenital rubella, herpes simplex virus, enterovirus, adenovirus, meningococcus, pneumococcus, pertussis, and unknown agents). The outcome of children with infectious etiology is poor.76 herpes simplex virus (HSV-1) and varicella-zoster virus (VZV) are the most common causes of sporadic encephalitis in adults and children, respectively.77 Sixty-one percent of children have early seizures and an associated poor outcome.78
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FIGURE 727. Unilateral Paroxysmal Fast Activity (PFA); Infantile Spasms. (Same patient as in Figure 7-26) A 4-year-old boy with intractable infantile spasms caused by herpes simplex encephalitis at 2 years of age. His seizures were described as very frequent clusters of asymmetric epileptic spasms with head and eyes deviating to the left side with nystagmus. EEG during sleep shows left hemihypsarrhythmia with bursts of diffuse high-voltage fast activity (20–24/sec), compatible with unilateral PFA (arrow) over the left hemisphere, with no clinical accompaniment except bradycardia noted in the ECG channel (double arrows). Absence of PFA in the right hemisphere may be due to severe damage to the neocortex, which is an important substrate in generating PFA. Although PFA is very common in the EEG of Lennox-Gastaut syndrome, it can also be seen in infantile spasms,15 progressive partial epilepsy, and atypical generalized epilepsy.79 The minimal substrate for the production of seizures consists of spike-wave/polyspike-wave complexes and runs of fast activity in the neocortex.80
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FIGURE 728. Hemihypsatthythmia; Herpes Simplex Encephalitis: EEG Normalization after Hemispherectomy. (Same patient as in Figure 7-26) EEG performed 1 month after the right hemispherectomy reveals resolution of hemihypsarrythmia in the left hemisphere. The patient was almost seizure-free for 6 months before developing recurrent epileptic spasms.
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FIGURE 729. Asymmetric Epileptic Spasms; Post right Hemispherectomy. (Same patient as in Figure 7-26) After the right hemispherectomy, at 5 years of age, the patient showed a significant decrease in epileptic spasms with seizure reduction greater than 90%. He continues having some daily epileptic spasms that no longer occur in clusters. His seizure is described as rapid jerking of both arms and legs, greater on the left side, with head and eyes deviating to the left side, lasting for 2–5 sec. EEG during the seizure demonstrates diffuse biphasic delta slowing followed by a diffuse electrodecremental event with superimposed low-voltage beta activity, more prominent in the left hemisphere. Clinical seizures were compatible with epileptic focus lateralizing to the right hemisphere, although the EEG shows the predominant electrodecremental event in the left hemisphere. Persistent postoperative seizures after the functional hemispherectomy could be associated with residual insular cortex. In selected cases, repeated surgery was required.81,82
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FIGURE 730. MRI in Aicardi Syndrome. Aicardi syndrome is a genetic disorder transmitted as an X-linked dominant trait with hemizygous lethality in males. It is characterized by a triad of infantile spasms, agenesis of the corpus callosum, and chorioretinal lacunae. Other features include malformations of cortical development (polymicrogyria, periventricular heterotopia, focal cortical dysplasia), intracranial/interhemispheric cysts, papillomas of the choroid plexuses, gross hemispheric asymmetry, coloboma of the optic disc, microphthalmia, and vertebral and costal anomalies.28 (A, B, C) Axial T2-weighted MRIs show microphthalmia (double arrows), periventricular heterotopia (arrow), polymicrogyria with schizencephaly (large arrow), and absence of corpus callosum (curved arrow). (D, E) Axial T1-weighted MRIs demonstrate interhemispheric and intraventricular cysts (arrow), focal cortical dysplasia (double arrows), and papilloma of chloroid plexus (large arrow). (F) Sagittal T1-weighted MRI shows focal cortical dysplasia (arrow) and a Dandy-Walker cyst (*).
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FIGURE 731. "Split Brain" EEG; Aicardi Syndrome. (Same patient as in Figure 7-30) A 4-month-old girl with Aicardi syndrome. Interictal EEG shows bursts of high-amplitude spikes, sharp and slow waves separated by intervals of low-amplitude EEG. This suppression-burst pattern is almost always asymmetric, and the paroxysmal bursts may be unilateral or, when bilateral, may arise independently from both hemispheres. This is called a “split brain” EEG, which suggests impaired interhemispheric connection caused by an absence of corpus callosum.28
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FIGURE 732. Focal Transmantle Dysplasia; Focal low Voltage Fast Activity and Slow Direct Current (DC) Shift. A 21-day-old male child who started having seizures described as eye deviation to the right and left-sided tonic-clonic seizures starting at 1 week of life. The seizures evolved into asymmetric epileptic spasms. MRI shows focal transmantle dysplasia in the left parietotemporal region. EEG during the asymmetric epileptic spasm (stronger on the right side), demonstrates low-voltage fast activity mixed with polyspikes during the spasm (arrow), followed by a negative “slow DC shift” at F7 (underline). An asymmetric paroxysmal fast activity discharge or a sharp transient was consistently associated with asymmetric spasms, and the side with the stronger spasm contractions is contralateral to structural lesions.33,83 An ictal slow DC shift is a slow and sustained change in EEG voltage resulting from a change in the function or interaction of neurons, glia, or both.84,85 Ictal slow baseline shifts could be recorded with DC amplifiers. They were not seen with conventional EEG systems. When the high-pass filter was opened to 0.01–0.1 Hz, ictal baseline shifts were present in the scalp and in intracranially recorded seizures and may have localizing value.86–89 Usually scalp-recorded ictal DC shifts are not successfully recorded because movements during clinical seizures could cause artifacts. They are highly specific but low in sensitivity. Ictal DC shifts were seen in 14–40% of recorded seizures and their sensitivity varied.86,90,91 Scalp-recorded DC shifts were detected when seizures were clinically intense, while no slow shifts were observed in small seizures.86 They were restricted to 1–2 electrodes, very closely related to the onset of low-voltage fast activity and electrodecrement.92
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FIGURE 733. Aicardi’s Syndrome with Focal Cortical Dysplasia. A 14-month-old right-handed girl with asymmetric infantile spasms resulting from Aicardi syndrome. MRI shows extensive focal cortical dysplasia in the right hemisphere, especially in the posterior quadrant (arrow head). Interictal EEG (left) shows asynchrony between both cerebral hemispheres, suppression of background EEG activity, and diffuse low-voltage beta activity in the right hemisphere (arrow). Ictal EEG (above) during one of her typical asymmetric epileptic spasms, which came in clusters, shows diffuse electrodecrement with no definite epileptic focus. Ictal SPECT during this seizure shows hyperperfusion in the right temporal region corresponded to the focal cortical dysplasia (double arrows). The patient underwent a partial right functional hemispherectomy and has been seizure-free. Asymmetric infantile spasms have been found to be more frequent than previously considered.33,93 They were seen in 25% in the study performed at the UCLA, and it was suggested that the spasms are generated by a cortical epileptogenic region that involves the primary sensorimotor area.
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FIGURE 734. Hemihypsarrhythmia (Contralateral). A 6-month-old-boy who is an ex-38-week twin with a past history of left subdural hemorrhage at 5 days of age. He was found to have a remote left middle cerebral artery (MCA) stroke at that time. He developed global developmental delay and right hemiparesis. At 5 months of age, he started having clusters of asymmetric epileptic spasms with more intense jerking on the right side and with occasional head deviation to the right side. He failed very high dose of topiramate. (A) Axial T2-weighted MRI at 7 days of age shows extensive subdural hematoma (SDH) over the left hemisphere with mass effect and focal encephalomalacia in the left temporal region. (B) Axial T2-weighted MRI at 6 months of age shows resolution of SDH, which is transformed to a subdural hygroma, left temporal encephalomalacia, and left cerebral atrophy, especially in the posterior region. Interictal EEG shows hypsarrythmia over the right hemisphere, marked background suppression over the left hemisphere, and frequent bursts of low-voltage beta activity in the left posterior temporal region (arrow). Asymmetric hypsarrhythmia is also referred to as hemihypsarrhythmia or unilateral hypsarrhythmia and is characterized by hypsarrhythmia with a consistent amplitude asymmetry between both hemispheres. Asymmetric hypsarrhythmia is always associated with focal or lateralized structural abnormalities. Hypsarrhythmia can be maximal over either the more abnormal or the more normal hemisphere.15 Consistent low-voltage beta activity may represent intrinsic epileptogenicity in the left posterior temporal region.
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FIGURE 735. Neuroimages Before Functional Hemispherectomy. (A) Interictal FDG (2-dehydroxy-fluoro-D-glucose)-PET images show hypometabolism in the left parieto-temporo-occipital region. FDG-PET provides a measure of regional cerebral glucose utilization. Interictal PET and ictal PET (or frequent interictal spiking during tracer uptake period) will show decreased and increased utilization of glucose, respectively. These findings are correspond to epileptic foci. (B) Axial T2-weighted MRI after the left functional hemispherectomy.
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FIGURE 736. Asymmetric Infantile Spasms; Normalization of the Contralateral EEG After Left Functional Hemispherectomy. (Same patient as in Figure 7-34) The patient has done extremely well after the left functional hemispherectomy. He has been seizure-free and shown significant improvement of his developmental milestones. EEG shows disappearance of the right hemihypsarrhythmia and focal epileptic focus in the left temporal region. The background EEG activity in the right hemisphere is appropriate for maturation age. Compared to the EEG performed before the surgery (Figure 7-34), this EEG shows dramatic improvement.
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FIGURE 737. Ipsilateral Rhythmic Theta Activity (Intrinsic Epileptogenicity); Malformation of Cortical Development (MCD), Left Hemisphere. A 3-year-old left-handed girl with intractable epilepsy, severe global developmental delay associated with malformation of cortical development in the left hemisphere. She had a history of infantile spasms at 4 months of age. She presented with daily episodes of asymmetric epileptic spasms. MRI demonstrates left frontal cortical dysplasia (open arrow) and left frontal periventricular nodular heterotopia (PNH) (small arrows). Interictal PET shows diffuse hypometabolism in the left hemisphere, maximally expressed in the frontal region (arrow). EEG demonstrates very frequent runs of rhythmic theta and alpha activity in the left fronto-central region, with spreading to the midline and, to a lesser degree, to the right centro-parietal region. In a series of 132 patients with cortical dysgenesis, 15% had nodular heterotopias.1 Nodule formation may be the result of (1) failure of a stop signal in the germinal periventricular region, leading to cell overproduction, and (2) early transformation of radial glial cells into astrocytes, resulting in defective neuronal migration. The intrinsic interictal epileptiform activity of nodules may be due to an impaired intranodular GABAergic system.94 Two electroclinical patterns of PNH emerged: (1) simple PNH, characterized by normal intelligence and seizures, usually partial, that begin during the second decade of life—the seizures never become frequent and tend to disappear or become very rare, and the EEG shows focal abnormalities—and (2) PNH plus, characterized by mental retardation and seizures that begin during the first decade of life. The seizures were very frequent in most cases with drop attacks. Seizures were often medically refractory. The EEG showed focal and bisynchronous abnormalities.95 The interictal EEG abnormalities were always focal and consistent with the location of the PNH in focal PNH, often bilateral asynchronous foci in the patients with bilateral and symmetrical PNH, and the posterior epileptiform abnormalities in those with unilateral or asymmetrical bilateral PNH, the side always being the same as that of the anatomic malformation.96,97 Recurrent seizures were described in 82%, mainly partial seizures with temporo-parieto-occipital auras.97 The best predictor of surgical outcome is the presence of a focal epileptic generator that may or may not include the PNH. Invasive recording is required in patients with PNH to improve localization and is the key to better outcome.97 Good outcomes can be achieved for unilateral heterotopia when the surgery is guided by a careful invasive presurgical study. The overlying cortex is usually part of the epileptogenic zone and should be resected. In some cases, part of the nodular formation was left in situ, yet outcomes were excellent. Outcome in bilateral heterotopia was less positive, although seizure reduction was noted.94
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FIGURE 738. Comparison of Subdural and Scalp EEG Recording; During Clusters of Epileptic Spasms. (Same patient as in Figure 7-37) The EEG findings during asymmetric epileptic spasms (arrows) described as tonic stiffening of both arms and legs with right-sided predominance are quite similar in both subdural (above) and scalp EEG recordings (below). Differences include lower spike amplitude and absence of low-voltage fast activity in the gamma range (70–80 Hz) (open arrow). High-frequency oscillations (HFOs) (open arrow) characterized by very fast activity in the gamma range are noted at the epileptic focus in neocortical epilepsy during a subdural EEG recording.44 Similar gamma activity is also detected on the scalp EEG during epileptic spasms.99
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FIGURE 739. Asymmetric Epileptic Spasms; Activation of Supplementary Sensorimotor Area (SSMA). Subdural EEG during a cluster of asymmetric epileptic spasms shows periodic bursts of low-voltage very fast activity (gamma wave) in the range of approximately 40–80 Hz at the PIH 11 electrode, which is located in the left mesial frontoparietal region. The first burst of low-voltage gamma activity (arrow head) shows no association with clinical seizures. The second burst of gamma activity (open arrow) is associated with an asymmetric epileptic spasm described as a brief episode of tonic stiffening of trunk, neck, and both upper and lower extremities, greater on the right side. Most investigators think that epileptic spasms originate in the brainstem, although there has been no definite evidence for that.100 Ictal EEGs do not show bilaterally synchronous generalized discharges even in cryptogenic West syndrome with symmetric spasms, but display a positive slow wave maximal at Fz/Pz in accordance with spasms. This may suggest the supplementary sensorimotor area (SSMA) as a generator of spasms.101 Cortical stimulation of this area produces proximal, segmental, unilateral, or bilateral tonic postural movements.102 Some frontal lobe seizures occur frequently in clusters, but this cannot explain all. The EEG finding in this patient may support the theory that epileptic spasms are caused by activation of the SSMA.
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FIGURE 740. Lennox-Gastaut Syndrome (LGS); Generalized Slow Spike-Wave Discharges (SSW). A 14-year-old girl with a triad of severe mental retardation, multiple types of seizures, with tonic seizures, atypical absences, and drop attacks being the three most common seizure types, and a typical EEG showing generalized slow spike-wave (SSW) discharges with anterior predominance. The classic EEG feature of LGS, the SSW pattern, consists of a spike or a sharp wave followed first by a positive deep “trough” and then by a negative wave (350–400 msec).103 Most often, it is a sharp wave followed by a slow wave and less often spikes or polyspikes followed by a slow wave.104 The amplitude of the SSW is usually higher over the frontal or fronto-central regions in approximately 90% of patients. Less than 10% of the SSW shows occipital predominance. The frequency of the SSW varies from 1 to 4 cps, commonly between 1.5 and 2.5 cps. The SSW discharges of LGS, unlike the classic 3-cps spike waves of absence epilepsy, only rarely show a very regular repetition rate; their characteristic feature is irregularity in frequency, amplitude, morphology and distribution.105,106 The abundance and the waxing and waning characteristics of SSWs commonly blur any distinction between ictal and interictal patterns. SSWs can therefore be distinguished from 3-Hz spike-wave discharges, which are usually associated with a clinical change if their duration is longer than 3 sec. The duration of the paroxysms of SSW activity also varies widely, but they are distinguished from classic 3-Hz spike waves by their abundance; they often appear in prolonged sequences without clinical changes. Hence, the SSW activity of LGS is usually considered to be an interictal pattern. Bursts, which last several seconds in duration and may be almost continuous, are often associated with some clouding of consciousness. As such thismay constitute an atypical absence or even absence status. Although the SSW pattern is fairly symmetric over the two hemispheres, shifting asymmetry in different bursts is common. Persistent focal or lateralized asymmetry of SSW activity may occur in as as many as 25% of patients.105 The background activity is also abnormal with varying degrees of diffuse slowing in 70–90% of patients. Focal and multifocal epileptiform discharges are seen in 14–18% of the patients.104–106 Photic stimulation in patients with LGS typically fails to “activate” SSWs, which distinguishes LGS from some myoclonic epilepsies. Tonic seizures, which are thought to be a characteristic sign of Lennox-Gastaut syndrome, are not present at onset, and the EEG features are not pathognomonic of the disorder.103
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FIGURE 741. Lennox-Gastaut Syndrome (LGS); Runs of Rapid Spikes or Paroxysmal Fast Activity (PFA). (Same patient as in Figure 7-40) The EEG during sleep shows “runs of rapid spikes” (arrow), which are also called grand mal discharge, fast paroxysmal rhythms, rhythmic spikes, generalized paroxysmal fast activity (GPFA), or paroxysmal fast activity (PFA). It is seen only in NREM sleep and occurs in older children, adolescents, and younger adults. It consists of bursts of spike discharges at a rate from 10 to 25/sec, with voltage of 100–200 μV, usually generalized but maximum over frontal regions, and lasting for 2–10 sec. Bursts of more than 5-sec duration are usually associated with tonic seizures.107 Although this EEG pattern is a hallmark of LGS, it can also be seen in other generalized epilepsies that have better outcome than in LGS.79
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Epileptic Encephalopathy
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FIGURE 742. Paoxysmal Fast Activity (PFA): Ictal Activity During Generalized Tonic Seizure. (Same patient as in Figure 7-40) Run of rapid spikes or paroxysmal fast activity (PFA), which lasts more than 5 sec in duration, is usually associated with a tonic seizure. “Runs of rapid spikes” (arrow) are also called grand mal discharges, fast paroxysmal rhythms, rhythmic spikes, generalized paroxysmal fast activity (GPFA), or PFA. This EEG pattern is seen only in NREM sleep and occurs in older children, adolescents, and younger adults. It consists of bursts of spike discharges at a rate of 10 to 25/sec, voltage of 100–200 μV, usually generalized but maximal over frontal regions, lasting for 2–10 sec. Bursts of more than 5-sec duration are usually associated with tonic seizures.106 Although this EEG pattern is a hallmark of LGS, it can also be seen in other generalized epilepsies that have better outcomes than in LGS.79
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Epileptic Encephalopathy
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FIGURE 743. Generalized Tonic Seizure; Lennox-Gastaut Syndrome (LGS) in Children. Typical ictal EEG seen in children with LGS during a generalized tonic seizure (adapted from Tassinari et al.108). (1) A slow spike or slow wave. (2) A brief (1 sec or less) “flattening” of the EEG. (3) Low-voltage fast (18–25) activity or spikes (3a) subsequent slowing (3b). (4) Postictal period; last spikes are followed by slow waves. Heart rates accelerate during (1) to (3), plateaus during (3a) and early to mid-(3b), and slightly increases again during the late (3b). Postictally, the heart rates declines. Irregular respiration is noted throughout (1) to (4).
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Epileptic Encephalopathy
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FIGURE 744. Paroxysmal Fast Activity (PFA); Lennox-Gastaut Syndrome (LGS). A 9-year-old boy with severe mental retardation and multiple seizure types, including tonic, atonic, atypical absence, and generalized tonic-clonic seizures. EEG during wakefulness showed generalized slow spike-wave discharges (not shown). EEG during slow sleep demonstrates frequent bursts of high-voltage rhythmic rapid spikes at around 14 Hz with no clinical accompaniment. This EEG pattern is called PFA and is an EEG hallmark of LGS during NREM sleep. Bursts of more than 5 sec are usually correlated with clinical tonic seizures.
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Epileptic Encephalopathy
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FIGURE 745. Paroxysmal Fast Activity (PFA); Juvenile Myoclonic Epilepsy (JME). Paroxysmal fast activity (PFA) is a characteristic EEG pattern of LGS occurring predominantly or exclusively during NREM sleep.109 It is characterized by paroxysms of 1–9 sec in duration, high-frequency (10- to 25-cps) rhythmic activity, preceded or followed by generalized sharp- and slow-wave complexes. The paroxysms are widespread in distribution and bilaterally synchronous over both hemispheres, with the highest amplitude over the frontal and central head regions. Shifting asymmetries are common, but rarely, the pattern may show persistent amplitude asymmetry and may be unilateral or even focal.106 The rhythmic spikes show little or no change in frequency throughout the burst, in contrast to the ictal pattern associated with generalized tonic-clonic seizures in which the spikes decrease in frequency during the course of seizure.110 In the waking state, the PFA is usually ictal and associated with tonic seizures. During NREM sleep, when it is most commonly occurred, PFA is usually associated with subtle clinical changes such as opening of the eyes and jaw, upward deviation of the eyes, or slight change in breathing.106 Paroxysms which are longer than 6 sec, are more commonly associated with discernible clinical change.111 Although the most common condition associated with PFA is LGS, it is occasionally seen in patients with focal epilepsy and those with 3-Hz spike and wave106,112 or generalized epilepsies without severe mental deficit or any progressive symptoms.113
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Epileptic Encephalopathy
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FIGURE 746. Bilateral Perisylvian Polymicrogyria; Lennox-Gastaut syndrome (LGS). A 15-year-old girl with bilateral perisylvian polymicrogyria (arrows), severe mental retardation, spastic quadriparesis, and multiple types of seizures, including partial, generalized tonic-clonic, absence, and tonic seizures. Background EEG activity shows generalized 1.5- to 2.5-Hz spike-wave activity with anterior predominance. The electroclinical features in this patient are consistent with the diagnosis of Lennox-Gastaut syndrome. A classic patient with LGS is characterized by a triad of electroclinical features: (1) interictal EEG showing generalized slow spike-wave activity (SSW in the range of 1.5–2.5 Hz) during awake and paroxysmal fast activity (PFA) with a frequency of approximately 10 Hz during sleep; (2) multiple types of seizures, including tonic seizures, atypical absences, and drop attacks; (3) mental retardation. In 60% of LGS, the children have had a previous encephalopathy.114
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FIGURE 747. Bilateral Perisylvian Polymicrogyria with Lennox-Gastaut Syndrome; Generalized Paroxysmal Fast Activity (PFA or GPFA). (Same recording as in Figure 7-46) EEG activity during slow sleep shows a burst of generalized fast activity (14–16/sec) accompanied by subtle clinical features of arousal from sleep with eye opening and upward deviation, increased heart rate, and changing of respiration. GPFA or PFA is a signature EEG finding of LGS, occurring almost exclusively during sleep and characterized by bursts of diffuse fast activity (10–25/sec), maximal in the frontalcentral regions, of varying duration (lasting a few seconds to a minute) with or without a clinical accompaniment. Without video-EEG monitoring, subtle seizures (e.g., arousal from sleep, eye opening with upward eye deviation, and changing of heart rate and respiration) as were noted in this patient may be easily missed.15,114–116
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Epileptic Encephalopathy
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FIGURE 748. Bilateral Perisylvian Syndrome; Nocturnal Generalized Tonic Seizure in Lennox-Gastaut syndrome (LGS). (Same recording as in Figure 7-46) During sleep, the patient developed a tonic seizure characterized by tonic stiffening of the body and arms with upward deviation of the eyes. Her neck and trunk were flexed, arms were raised in an extended position, and legs were extended. EEG during the seizure shows a burst of polyspike-wave activity followed by generalized electrodecrement with superimposed low-voltage beta activity. Nocturnal tonic seizures are a hallmark of LGS and occur in almost all patients with LGS who underwent prolonged video-EEG monitoring. Four major types of ictal EEG patterns are reported: (1) desynchronization of all activity; (2) very rapid rhythmic fast activity (15–25/sec), usually low amplitude initially but increasing progressively in amplitude; (3) combination of (1) and (2); and (4) rhythmic high-amplitude activity at approximately 10–15/sec. These ictal patterns can be preceded by brief, generalized slow spike-wave activity.113,117,118
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FIGURE 749. Symptomatic Lennox-Gastaut Syndrome (LGS); Focal Cortical Dysplasia (FCD). A 15-year-old girl with mental retardation and multiple types of seizures (atypical absences, complex partial seizures, drop attacks, and tonic seizures). Axial MRIs show a well-defined focal cortical dysplasia (FCD) in the right parietal region (white arrow). Her seizure was described as an ill-defined sensory symptom followed by an asymmetric tonic seizure with left-sided predominance. Interictal EEG (not shown) showed generalized slow spike-wave discharges with right-sided predominance consistent with the diagnosis of LGS. Ictal EEG as shown above during one of her typical seizures, demonstrates a burst of polyspike-wave discharges (arrow head) followed by a diffuse electrodecremental event (black arrow) with superimposed low-voltage beta activity lasting for 1–2 sec. After that, a long run of sharp waves is noted in the right centro-temporal regions (double arrows). Note interictal sharp waves in the same region prior to the ictal EEG activity (open arrow).The patient has been free of seizures since the resection of the FCD and surrounding epileptogenic zone after invasive video-EEG monitoring. Pathology confirmed the diagnosis of FCD (balloon cell type). The presence of persistent focal epileptiform activity and polymorphic delta activity, asymmetric generalized slow spike-wave discharges, and paroxysmal fast activity predominating in one hemisphere (shown in next page), especially if associated with underlying structural abnormalities, should prompt the neurologists to consider focal resective surgery.119–124
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Epileptic Encephalopathy
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FIGURE 750. Symptomatic Lennox-Gastaut Syndrome (LGS); Generalized Slow Spike-Wave Discharges. (Same patient as in Figure 7-49) Background EEG activity during both wakefulness and sleep shows generalized slow spike-wave discharges with anterior predominance, which is a hallmark EEG finding of LGS. This EEG page does not demonstrate any evidence of a focal abnormality caused by the FCD in the right parietal region.
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Epileptic Encephalopathy
7
FIGURE 751. Symptomatic Lennox-Gastaut Syndrome (LGS); Normalization of Background EEG Activity After Focal Resection of FCD and Epileptogenic Zone. (Same patient as in Figure 7-49) EEG performed 7 months after the surgery shows background asymmetry with decreased amplitude and reactivity over the right hemisphere. Generalized slow spike-wave discharges seen prior to the surgery as shown in the previous page disappeared completely after the surgery. The patient has been free of seizures since the resection of focal cortical dysplasia and surrounding epileptogenic zone. Pathology confirmed the diagnosis of focal cortical dysplasia (balloon cell type). The presence of persistent focal epileptiform activity and polymorphic delta activity, asymmetric generalized slow spike-wave discharges, and paroxysmal fast activity predominating in one hemisphere, especially if associated with underlying structural abnormalities, should prompt the neurologists to consider focal resective surgery.119–124
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Epileptic Encephalopathy
587
FIGURE 752. Generalized Slow Spike-Wave Discharges; Lennox-Gastaut Syndrome (LGS) Secondary to Intrauterine Stroke. A 13-year-old left-handed boy with moderately severe mental retardation and mild right hemiatrophy and hemiparesis. His first seizure occurred at 3 years of age with a staring episode. Subsequently, he developed multiple types of seizures, including an asymmetric tonic seizures with right-side stiffness, atypical absence seizures, drop attacks, GTCSs, and nocturnal tonic axial seizure. MRI showed encephalomalacia caused by intrauterine stroke in the left frontal-temporal and insula regions (arrow). EEG during sleep shows diffuse, slow spike-wave, and polyspikewave activities with mild left hemispheric predominance. Although LGS has long been established in the literature, there is no consensus on its precise definition. Most agree that LGS is defined as (1) multiple types of epileptic seizures, including tonic axial, atypical absence, and atonic seizures; (2) interictal EEG, with bilaterally synchronous slow (1.5- to 2.5-Hz) spike waves (SSWs) during wakefulness and runs of bilateral paroxysmal fast activity (PFA) at about 10 Hz during sleep; and 3) slow mental development and behavioral/ personality disorders.125–127
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Epileptic Encephalopathy
7
FIGURE 753. Asymmetric Paroxysmal Fast Activity (PFA); Lennox-Gastaut Syndrome (LGS). (Same patient as in Figure 7-52) EEG during NREM sleep shows 5–6 seconds of asymmetric 10-Hz rhythmic activity with higher voltage in the left hemisphere, maximal in the temporal region, followed by a generalized sharp- and slow-wave complex with no clinical accompaniment. Paroxysmal fast activity (PFA) or “fast run” is a characteristic EEG pattern of LGS occurring most often during NREM sleep and rarely during wakefulness or REM sleep. It is characterized by runs of 1–9 sec in duration, fast rhythmic waves or polyspikes, at 10–20 Hz, which show no change in frequency throughout the burst, preceded or followed by generalized sharp- and slow-wave complexes. PFA is usually widespread in distribution and bilaterally synchronous over both hemispheres, with the highest amplitude over the frontal and central head regions. Shifting asymmetries are not uncommon. Persistent amplitude asymmetry, unilateral or focal, may rarely be seen. It is often associated with tonic seizures, especially if it lasts longer than 6 sec or occurs during wakefulness. Some authors require both generalized slow spike-wave (SSW) activity and PFA during sleep for the diagnosis of LGS.106,109,111,125,128
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Epileptic Encephalopathy
589
FIGURE 754. Generalized Slow Spike-Wave Discharges (SSW); Lennox-Gastaut Syndrome (LGS). (Same patient as in Figure 7-52) EEG shows generalized 2- to 2.5-hertz spike-wave activity with anterior predominance. Slow spike-wave (SSW) pattern is a classic interictal EEG feature of LGS and was originally called “petit mal variant pattern.” The SSW complexes consist of a spike or, more frequently, a sharp wave, followed by a sinusoidal electronegative slow wave of 350–400 msec in duration. The SSW complexes can occur singly or in runs. Runs of spike-wave activity at 3 Hz occur commonly. Shifting asymmetries are frequently seen. SSW complexes are diffuse, but predominance over the anterior head region is usually noted. They have little or no response to photic stimulation or hyperventilation.129
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Epileptic Encephalopathy
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FIGURE 755. Paroxysmal Fast Activity (PFA); Lennox-Gastaut Syndrome (LGS). A 9-year-old boy with severe mental retardation and intractable epilepsy with multiple types of seizures, especially nocturnal generalized tonic seizures. EEG during arousal from slow sleep, immediately after the K-complex (open arrow), shows bursts of diffuse fast activity (14–15/sec), maximal in the fronto-central regions, lasting a few seconds with subtle clinical accompaniment (changing of respiration, heart rate, and arousal from sleep). PFA is a signature EEG finding in LGS, occurring almost exclusively during sleep and characterized by bursts of diff use fast activity (10–25/sec), maximal in the fronto-central regions, of varying duration (lasting a few seconds to a minute) with or without a clinical accompaniment. Without video-EEG monitoring, subtle seizures (e.g., arousal from sleep, eye opening with upward eye deviation, and changing of heart rate and respiration) such as those noted in this patient may be easily missed.111,130,131
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Epileptic Encephalopathy
591
FIGURE 756. Symptomatic Lennox-Gastaut Syndrome; Multiple Cerebral & Cerebellar Anomalies; Bilateral Hippocampal Anomalies. A 15-year-old female, an ex-32 weeker, with a history of grade 4 intraventricular hemorrhage with greater impact on the right hemisphere. She developed hydrocephalus and had a VP shunt placed at 1 month of age. She has multiple types of seizures, including asymmetric tonic seizures (left-arm stiffening with head and eye deviating to left side), absences, focal myoclonic seizures, and secondarily generalized tonic-clonic seizures. MRI shows VP shunt placement (open arrow), right cerebral hemiatrophy, and right mesial temporal abnormalities (hyperintense signal and atrophy) (arrow). EEG shows diffuse polymorphic delta activity (PDA) in the right hemisphere, maximal in the temporal region, and secondary bilateral synchrony with maximal epileptogenic focus in the right frontal-central-anterior temporal and frontal vertex areas. Her electroclinical findings are consistent with symptomatic Lennox-Gastaut syndrome. She underwent right functional hemispherectomy and has been seizure-free. The presence of persistent focal epileptiform activity and polymorphic delta activity, asymmetric generalized slow spike-wave discharges, and paroxysmal fast activity predominating in one hemisphere (shown in next page), especially if associated with underlying structural abnormalities, should prompt the neurologist to consider focal resective surgery.119–124
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Epileptic Encephalopathy
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FIGURE 757. Symptomatic Lennox-Gastaut Syndrome; Asymmetric Paroxysmal Fast Activity (PFA). (Same recording as in Figure 7-56) Axial FLAIR MRI shows right cerebral hemiatrophy and severe mesial temporal atrophy and hyperintensity (open arrow). Interictal PET scans reveal hypometabolism in the entire right temporal lobe and posterior temporal region. EEG shows bisynchronous slow spike-wave discharges intermingled with paroxysmal fast activity (PFA), maximally expressed over the right hemisphere.
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FIGURE 758. Focal Polymorphic Delta Activity (PDA) With Intermixed Spikes; Mesial Temporal Abnormality. (Same patient as in Figure 7-56) Axial FLAIR image shows atrophy and hyperintensity of the right amygdala (arrow) with decreased white matter volume of the right temporal lobe. EEG shows constant PDA with intermixed spikes in the right posterior temporal region.
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Epileptic Encephalopathy
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FIGURE 759. Symptomatic Lennox-Gastaut Syndrome; s/p Right Functional Hemispherectomy. (Same patient as in Figure 7-56) Since the right functional hemispherectomy, background EEG in the left hemisphere has normalized. In rare cases where a stable EEG focus exists, associated with asymmetric generalized slow spike-wave discharges and paroxysmal fast activity (shown in next page) predominating in one hemisphere, focal resective surgery should be considered.119–124
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FIGURE 760. Electrical Status Epilepticus During Slow Wave Sleep (ESES). A 6-year-old left-handed girl with a history of severe intraventricular hemorrhage due to prematurity (26 weeks GA) who subsequently developed hydrocephalus and required VP shunt insertion into the left lateral ventricle. She subsequently developed frequent complex partial seizures with or without GTCS and developmental regression. EEG during wakefulness shows sharp waves in the left centro-temporal region and occasional bursts of generalized atypical spike-wave discharges.
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FIGURE 761. Electrical Status Epilepticus During Slow Sleep (ESES). When the patient entered into NREM sleep, the EEG showed nearly continuous generalized 2.5-Hz sharp-and-wave activity with suppression of vertex waves and spindles. Doose described ESES as the EEG sign of particularly severe epilepsy. ESES is seen in either normally developed children or retarded patients. The age of onset is 2–10 years of life. The patients usually present with regression of psychomotor and language development and motor incoordination. Remission of the EEG findings usually occurs during puberty, although the patients are usually left with cognitive and language deficits.132 ESES was first described by Patry et al.133 ESES or continuous spikes and waves during slow sleep (CSWS) are defined in the classification of the ILAE (1989) as follows: “Epilepsy with CSWS results from the association of various seizure types, partial or generalized, occurring during sleep and atypical absences when awake. Tonic seizures do not occur. The characteristic EEG pattern consists of continuous diffuse spike-waves during slow wave sleep, which is noted after the onset of seizures. Duration varies from months to years. Despite the usually benign evolution of seizures, prognosis is guarded, because of the appearance of neuropsychological disorders.” A similar condition called “encephalopathy with ESES” in a recent ILAE proposal (Engel, 2001) is defined as an age-related and self-limited disorder, characterized by the following features: (1) epilepsy with focal and generalized seizures; (2) neuropsychological impairment (excluding acquired aphasia); (3) motor impairment (ataxia, apraxia, dystonia, or unilateral deficit); and (4) typical EEG findings with a pattern of diffuse SW (or more or less unilateral or focal) occurring in up to 85% of slow sleep over a period of at least 1 month.134
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FIGURE 762. Dravet Syndrome; Complex Partial Seizure. A 4-year-old boy with intractable epilepsy and global developmental delay who was admitted to the EMU for presurgical evaluation. He had a history of several febrile convulsions since 6 months of age, GTCS, and hemiconvulsion. His seizures increased in frequency and severity with topiramate, which caused hyperthermia. Cranial MRI is unremarkable (not shown). EEG shows ictal EEG onset in the left occipital region (arrow). Clinically the patient started to be confused, turned head and eyes to the right side, and rotated clockwise with right arm extension consistent with versive and rotatory seizures. During the same EMU admission, he was also found to have complex partial seizures arising from the right occipital lobe. SCN1A gene mutation was sent and was positive. Focal seizures, simple partial seizure (SPS) of the motor type (versive or clonic), and complex partial seizures (CPS) occur in 43–78% of patients. They can appear early, from 4 months to 4 years. CPS are characterized by autonomic phenomena (pallor, cyanosis, rubefaction, respiratory changes, drooling, sweating), oral automatisms, hypotonia, rarely stiff ness, and sometimes eyelid or distal myoclonia. Seizure foci were noted in the frontal, temporal, and occipital regions.135
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FIGURE 763. Dravet Syndrome; Complex Partial Seizure. (Same patient as in Figure 7-62) EEG shows ictal activity arising from the right occipital region (arrow) at the onset of versive seizures, hypotonia, and autonomic symptoms.
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FIGURE 764. Typical Absence Seizure; Dravet Syndrome. A 5-year-old boy with Dravet syndrome (DS). He had a history of several febrile convulsions since 6 months of age, GTCS, hemiconvulsion, and versive seizures. His seizures were aggravated by hyperthermia caused by topiramate. SCN1A gene mutation was positive. He was admitted to the EMU for evaluation of frequent staring episodes associated with unresponsiveness, eye blinking, and orofacial automatisms lasting 5–10 sec without postictal confusion. EEG shows generalized 3-Hz spike-and-wave discharges associated with a typical absence seizure. Dramatic response was noted after treatment with valproate. Only 25% of the patients with DS demonstrated abnormalities on initial EEG. On evolution, most patients demonstrated diffuse or generalized interictal epileptiform discharges and, less commonly, a combination of generalized and focal abnormalities. The lack of definite, typical EEG abnormalities on follow-up EEG makes the diagnosis of DS more difficult.136 Patients with DS have multiple types of seizures, including GTC & GC, alternating unilateral clonic, myoclonic, and focal seizures, and atypical absence seizures with obtunded state. Tonic seizures are exceptional.135 Atypical absence seizures are associated with generalized irregular 2- to 3.5-Hz spike-wave discharges. Rare typical absence seizures as noted in this patient were reported by Dulac and Arthuis (1982).135
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FIGURE 765. Dravet Syndrome; Nonconvulsive Status Spilepticus (NCSE). A 4-year-old girl with global developmental delay, hand tremor, and medically intractable epilepsy, including drop attacks, myoclonic, absence, tonic, and generalized tonic-clonic seizures. MRI (not shown) was unremarkable. During prolonged video-EEG monitoring, the patient developed a prolonged episode of altered mental status, orofacial and hand automatisms, truncal ataxia, and erratic myoclonus lasting for about 45 minutes. EEG during this episode showed nearly continuous bilateral synchronous spike-wave activity, multifocal epileptiform activity, and diffuse delta slowing. SCN1A gene was positive for Dravet syndrome. NCSE had been observed in approximately 40% of patients with Dravet syndrome. Characteristic clinical findings during NCSE are erratic myoclonus associated with unsteadiness and frank ataxia. Sensory stimulations can interrupt but never definitely stop NCSE. EEG is characterized by diffuse slow-wave dysrhythmia intermixed with focal, multifocal, or diffuse spikes, sharp waves, and spike-wave activity. Rhythmic spike-wave activity associated with absence status epilepticus (SE) is not seen, but complex partial SE has been reported.135,137
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FIGURE 766. Electrical Status Epilepticus During Slow Sleep (ESES); REM Sleep. (Same recording as in Figure 7-65) Although the prolonged video-EEG obtained during REM sleep shows much less prominent diffuse epileptiform activity, an epileptic focus in the right centrotemporal region is better seen. Interictal epileptiform activity is more frequent and diffuse during NREM sleep due to better synchronization of the EEG, but less frequent and more focal during REM sleep and wakefulness. Interictal epileptiform discharges in focal epilepsy occur more frequently during sleep, especially stage 3/4 sleep (slow-wave sleep). The discharges have a greater propensity to spread during sleep, and thus are often seen over a wider field than discharges occurring during wakefulness and REM sleep. Therefore, EEG during REM sleep may have greater localizing value in focal epilepsy than in NREM sleep.138
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FIGURE 767. Electrical Status Epilepticus During Slow Sleep (ESES) or; Continuous Spikes and Waves During Slow Sleep (CSWS). (Same patient as in Figure 7-65) This prolonged video-EEG was performed 7 months later. Although the patient no longer had focal motor seizure, she developed cognitive dysfunction and behavioral disturbances. EEG during slow sleep shows continuous diffuse slow spike-wave activity. EEG during wakefulness and REM sleep (not shown) only showed occasional right central temporal sharp waves. These electroclinical features are compatible with the diagnosis of epilepsy with ESES. ESES may be the result of a secondary bilateral synchrony. The focal motor seizure is a common type of seizure, and focal epileptiform activity is usually seen during wakefulness and REM sleep. This EEG can sometimes simulate benign focal epilepsy syndrome such as epilepsy with centro-temporal spikes. The duration of ESES and the localization of focal epileptiform activity play major roles in cognitive dysfunction, suggesting that the clinical features in ESES result from a localized disruption of EEG activity caused by focal epileptic activity during slow sleep. Spike-wave activity less than 85% during NREM sleep was correlated with a decrease in cognitive impairment.139,140
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FIGURE 768. Electrical Status Epilepticus During Slow Sleep (ESES); Intrauterine Stroke. A 7-year-old left-handed girl with right hemiparesis, medically intractable epilepsy, and developmental regression. MRI shows severe cystic encephalomalacia in the left hemisphere due to intrauterine stroke. Prolonged video-EEG during REM sleep (on the left side) demonstrates very frequent polyspikes and polymorphic delta activity in the left frontal-central regions. EEG during slow sleep (on the right side) shows bilateral synchronous spike/polyspike-wave activity. These EEG findings support the diagnosis of ESES. Epileptiform activity is more lateralized during wakefulness and REM sleep than during a slow-sleep state. The MRI and EEG in this patient support the hypothesis that ESES is the result of a secondary bilateral synchrony.134
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FIGURE 769. Landau-Kleffner Syndrome (LKS). A 14-year-old boy with LKS diagnosed at the age of 7 years who partially responded to the treatment with methylprednisolone and IVIG. Although he had only occasional seizures, he continued having moderate language impairment. The waking background EEG activity was normal (not shown). EEG during sleep shows frequent epileptiform activity in the left centro-temporal region. Epileptiform activity in the patients with LKS is variable, but eventually, almost all of them have bilateral spike-and-wave activity during more than 85% of NREM sleep (ESES). At earlier stage, the epileptic foci are usually located in the temporal region (>50%) or in the parieto-occipital regions (30%).133 Bilateral temporal (mainly posterior) spikes and generalized spike-and-wave discharges have also been observed.141,142
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FIGURE 770. Landau-Kleffner Syndrome; During Wakefulness. (Same EEG recording as in Figure 7-69) EEG during wakefulness is within normal limits.
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FIGURE 771. ESES (Electrical Status Epilepticus During Slow Sleep); Intrauterine Stroke. An 8-year-old left-handed boy with mild global developmental delay, medically intractable epilepsy, and right hemiparesis resulting from an intrauterine stroke. He recently developed cognitive decline and increased seizures. His seizures were stereotypical and described as a rising sensation in his stomach, spacing out, left-hand automatisms, and loss of awareness followed by postictal confusion. MRI shows evidence of remote left middle cerebral artery stroke with thalamic atrophy. Interictal EEG during slow sleep shows nearly continuous bisynchronous sharp waves, maximally expressed in the left centro-temporal region consistent with the diagnosis of ESES. The patient has been seizure-free and has shown significant improvement of language and cognitive function after the left functional hemispherectomy. EEG has normalized since the surgery. ESES is an electrographic pattern characterized by nearly continuous slow spike-wave discharges, usually diffuse or generalized in distribution during NREM sleep but focal during awake or REM states. The spike-wave discharges occur in >85% of NREM sleep, although a spike-wave index of less than 85% has been used by some authors. In the original series, the EEG pattern of ESES was described as consisting of “generalized” or “diffuse” slow spike-wave discharges at 1.5–2 Hz. However, cases displaying slow spikes devoid of the wave component, sharp waves or with relative focality, albeit continuous, mainly involving the temporal or frontal regions, or markedly asymmetrical spike-wave activity over the two hemispheres have been observed.134 CSWS (continuous spikewave during slow sleep) refers to both the EEG and clinical features (cognitive and behavior disorders), but practically, both ESES and CSWS terms are interchangeable. Interictal EEG abnormalities may have a role in cognitive impairment.143 Congenital stroke was seen in 10% of 67 patients with ESES pattern in one study.143 Early thalamic injuries have been reported to be a facilitating factor in provoking ESES.145–147
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FIGURE 772. Resolution of ESES; After Left Functional Hemispherectomy. (Same patient as in Figure 7-71) EEG during sleep performed 2 months after the left functional hemispherectomy shows disappearance of the ESES. Note suppression of background activity over the left hemisphere and normal sleep architecture over the right hemisphere. The patient has shown dramatic improvement of cognitive function and has been seizure-free since the surgery. Children with unilateral brain lesions, intractable seizures, and cognitive dysfunction with ESES may become seizure-free, show resolution of ESES, and improve cognitive function after epilepsy surgery, speciafically a hemispherectomy.148
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Antiepileptic drug (AED)-induced seizure worsening (Figure 8-1)
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Generalized Epilepsy
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Carbamazepine (CBZ) is the most common antiepileptic drug (AED). CBZ can both aggravate and induce new seizure types including absence, atonic, or myoclonic seizures (MS) in patients with generalized epilepsies. Vigabatrin and gabapentin have been found to induce absence and MS. Benzodiazepines have been reported to precipitate tonic seizures, especially when given intravenously in patients with Lennox-Gastaut syndrome. Lamotrigine has been reported in worsening myoclonic, clonic, and tonic-clonic seizures in the patients with Dravet syndrome. AED-induced seizure worsening must be considered in all patients whose seizures are worse with the introduction of the new AED.
Occipital intermittent rhythmic delta activity (OIRDA) (Figures 8-6, 8-7, 8-16, 8-18) 䡲
Seen almost exclusively in children and is associated with epilepsy, most commonly in idiopathic generalized epilepsy (IGE), especially absence epilepsy.
Generalized paroxysmal fast activity (GPFA) (Figures 8-8 and 8-42) 䡲
Occurring almost exclusively during sleep. It is generated in the neocortex. Activation of thalamic neurons in response to varying corticothalamic input patterns may be critical in setting the oscillation frequency of thalamocortical network interactions causing GPFA. 䡲 Seventy-five percent of patients had clinical seizures associated with this activity, mostly tonic. 䡲 Slow spike-and-wave complexes were present in half of the patients. Twenty-five percent of patients had normal background activity.
Eye closure sensitivity (ECS) (Figures 8-9 and 8-10) 䡲
More common in females.
䡲
It may overlap with but is independent from photosensitivity.
䡲
ECS can activate polyspike-wave (PSW) discharges and myoclonic jerks (MJ).
䡲
It can be seen in different epileptic syndromes including childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), eyelid myoclonia with absences (EMA), juvenile myoclonic epilepsy (JME), idiopathic generalized epilepsy (IGE with tonic-clonic seizure), generalized epilepsy with grand mal upon awakening (EGMA), and idiopathic occipital lobe epilepsy.
䡲
Rapid eye movement (REM) sleep, similarly to eye opening, plays a role in inhibiting EEG manifestations of JME with ECS.
Epilepsy with grand mal on awakening (EGMA) (Figures 8-2 to 8-5, 8-10, and 8-13) 䡲
Occurs exclusively shortly after awakening.
䡲
The second seizure peak is in the evening during the peak period of relaxation.
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Typical absences and MJ occur in 10% and 22% of EGMA, respectively. Majority of patients with EGMA have rare generalized tonic-clonic seizure (GTCS).
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Sleep deprivation is a major triggering factor.
EEG of patients with EGMA 䡲
Generalized (poly)spike-and-wave discharges on their first routine electroencephalography (EEG) in 44%.
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Normal routine EEG but generalized (poly)spike-andwave discharges on sleep EEG only in 32%.
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No EEG abnormality at all in 24%.
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About 70% of those with additional absences or MJs preceding GTCSs have generalized (poly)spike-andwave discharges.
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A 24-hour video-EEG should be considered in patients suspected of having GMA and should include sleep and awakening.
Ictal EEG in GTCS" 䡲
Tonic phase: Brief period of diffuse background attenuation with superimposed low-voltage fast activity or spikes. These activities become more synchronized, with increases in spiky configuration and decreases in frequency and amplitude (into 10 Hz activity called "Epileptic recruiting rhythm") 䡲 Clonic phase: Repetitive polyspike-slow-wave complexes interupt the 10-Hz fast activity in tonic phase. Subsequently, the amplitude increases and the polyspike-slow-wave complexes slow down to 1 Hz. The clonic jerks coreespond to the polyspikes, whereas the periodic atonia corresponds to the slow waves. 䡲 Postictal period: Diffuse background suppression, bursts suppression, or triphasic wave pattern followed by diffuse polymorphic delta activity. Higher amplitude, faster frequency, and more rhythmic activity are noted as the patients recovers. Normal background activity may not be observed for 30 minutes to 24 hours. In children less than 6 years of age, bilateral occipital delta slowing is commonly seen.
Juvenile myoclonic epilepsy (JME) (Figures 8-9, 8-11, 8-12 and 8-14) 䡲
JME is characterized by: 䊳 䊳
䡲
Typical absence in most patients Precipitating factors include sleep deprivation, fatigue, and alcohol intake.
EEG findings 䡲
inattention, suggesting that very short-lasting spells of a second or less may have a cognitive effect on the patient. 䡲 The typical ictal EEG in myoclonic seizure (MS) is a bilateral synchronous and symmetric PSW discharge, immediately preceding a MJ. The polyspike component contains 5–20 spikes, with a frequency between 12 and 16 Hz. The amplitude of spikes is typically increasing and maximal over the frontal leads where it reaches 200–300 μV. Slow waves of variable frequency (3–4 Hz) and amplitude (200–350 μV) often precede or follow the polyspikes, this results in a PSW complex that lasts much longer than the MJ (approximately 2–4 sec). The number of spikes is associated with the MJ intensity: there are few spikes and a more pronounced slow component when the MJ is mild. 䡲 Back averaging shows that the conduction time, between the apex of the spike and the onset of the MJ, is short (20–50 msec) and characteristic of a cortical myoclonus. 䡲
Ictal EEG during absence seizure in JME is different from CAE or JAE in that it consists of polyspike/ double/triple preceding or superimposed on the slow waves with a frequency varying from 2 to 10 Hz with a mean of 3–5 Hz.
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Photoparoxysmal response (PPR) is described as generalized irregular spike/polyspike-and-wave complexes during photic stimulation.
䡲
PPRs are seen in 30–40% in JME, compared to 18% in absence epilepsy. However, only 5% of patients suffer from clinical photosensitivity. Seventy-seven percent of patients with PPR have a history of epilepsy.
MJs on awakening GTCS in all states.
䊳
Generalized fast (4- to 6-Hz) PSW activity. 䡲 Focal epileptiform activity is seen in about one third causing “pseudolateralization.” 䡲 As early as 0.5 sec after the onset of (poly)spikewave discharges, the majority of patients will show
8
Generalized Epilepsy
䡲
In patients with seizures, a generalized PPR strongly suggests the diagnosis of primary generalized epilepsy.
Childhood absence epilepsy (CAE) (Figures 8-15 to 8-20) Inclusion criteria for CAE (Loiseau & Panayiotopoulos, 2000) 䡲
Age at onset between 4 and 10 years (peak at 5–7 years).
䡲
Normal neurological state and development.
䡲
Brief (4–20 sec) and frequent (tens per day) absence seizures with abrupt and severe impairment of consciousness.
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EEG ictal discharges of generalized high-voltage spike and double (maximum occasional 3 spikes are allowed) spike- and slow-wave complexes. They are rhythmic at around 3 Hz with a gradual and regular slow down from the initial to the terminal phase of the discharge.
Exclusion criteria for CAE 䡲
Other types of seizure, such as GTCS, or MJs, prior to or during the active stage of absences.
䡲
Eyelid myoclonia, perioral myoclonia, rhythmic massivelimb jerking, and single or arrhythmic MJs of the head, trunk, or limbs. However, mild myoclonic elements of the eyes, eyebrows, and eyelids may be featured, particularly in the first 3 sec of the absence seizure. 䡲 Mild or no impairment of consciousness during the 3 or 4 Hz discharges. 䡲 Brief EEG 3- or 4-Hz spike-wave paroxysms of less than 4 sec, polyspikes (more than 3) or ictal discharge fragmentations. 䡲
Visual (photic) and other sensory precipitation of clinical seizures.
EEG in Absence Epilepsy 䊳
OIRDA is seen almost exclusively in children with epilepsy and it is rarely seen in children with diffuse encephalopathy.
䊳
OIRDA is seen almost exclusively in children less than 10–15 years old and is associated with epilepsy, most commonly in IGE, especially absence epilepsy and, less commonly, focal epilepsy. The frequency of the occipital rhythmic discharges in children with absences was generally faster (3–4 Hz) than in localization-related epilepsy (2–3 Hz).24
䊳
䊳
Diffuse 3-Hz rhythmic delta activity without spike component is an exceptional ictal EEG finding during the absence seizure.
8 䊳
䊳
䊳
䊳
Alterations in normal thalamocortical reciprocal interactions are critical in the generation of the regular generalized spike-wave discharges characteristic of the IGEs. Most patients with unilateral thalamic lesion and epilepsy showed bilateral synchronous generalized spike-wave (GSW) discharges. Absence status with bilateral GSW discharges caused by ischemic lesion in the left thalamus was reported. Children with thalamic lesions should be monitored closely for ESES. Lesions of the inferior-medialposterior thalamic structures might have a role in the pathogenesis of bilateral SW discharges and ESES by the mechanism of disinhibition, possibly through the GABA-ergic system of the zona incerta and its projections. Jeavons syndrome refers to idiopathic reflex epilepsy with eyelid myoclonia, eye closure sensitive seizure, and photosensitivity. Seizures are brief (3–6 sec). Ictal EEG consists of generalized PSW at 3–6 Hz, usually occurring after eye closure. Eyelid myoclonia is resistant to treatment.
Generalized Epilepsy
Myoclonic astatic epilepsy (MAE) (Figures 8-23 to 8-27) 䡲
䡲 䡲
䡲
Benign myoclonic epilepsy of infancy (BMEI) (Figures 8-21 and 8-22) 䡲
All tests other than EEGs in BMEI are normal.
䡲
Background and interictal EEG is normal.
䡲
Spontaneous generalized PSW discharges without MS are rare.
䡲
The ictal EEG during jerks shows generalized PSW discharges. The discharges are brief (1–3 sec) and isolated. Frequently, ictal EEG activity is limited to the rolandic and vertex regions.
䡲
During drowsiness, there is enhancement of MJ or epileptiform discharges.
䡲
Photic stimulation, sudden noises, and contact stimulate epileptiform discharges in the EEG. No other type of seizure is observed. Clinical examination and MRI are normal.
䡲
Outcome is correlated with early diagnosis and treatment.
䡲
䡲
Monorhythmic 4- to 7-Hz rhythm is a characteristic background EEG activity that is seen in almost all instances early in the course of MAE. This rhythm is usually parietal predominant. This EEG pattern is falsely attributed to drowsiness. During active seizures, the rhythm is more irregular and slower, whereas it will be more regular and faster in a period of remission. MS and myoclonic-astatic seizures (MAS) are present in all children with MAE. MAE develops atonia immediately after a single or a series of 2–3 MJs. A sudden loss of tone causes either a drop attack or slight myatonia, head nodding or sagging at the knees (post-myoclonic myatonia or epileptic negative myoclonus). Ictal EEG during MS is similar to a pure atonic seizure (AS) and characterized by generalized (poly) spike-and-wave discharges that can be isolated or repeated rhythmically at 2–4 Hz, lasting 2–6 sec. MJs are time-locked to a spike-and-wave complex. The EMG correlation of each jerk is a burst lasting around 100 msec, followed by a longer (200- to 500-msec) post-myoclonic myatonia. The atonic component of seizures is characterized by a rhythmic discharge of (poly)spike-and-slow-wave complexes at 2–4 Hz, accompanied by EMG inhibition lasting 60–400 msec, synchronous in the recorded muscles and time-locked to the onset of the slow wave. This generalized post-myoclonic myatonia (negative epileptic myoclonus) has caused the fall. The number of spikes in the individual complexes is associated with the severity of MS. AS is usually associated with the slow wave of a PSW complex, and the intensity of atonia is proportionate to the amplitude of the slow wave. MS present as brief generalized jerks of the body, isolated or in short series of 2–3 seizures. Proximal muscles are more involved, producing a sudden flexion of the head and trunk with a possible fall to the ground. The duration of these episodes is very brief (0.3–1 sec).
615
䡲
Falls can be either the direct effect of massive MJs or from the post-myoclonic silent period or generalized post-myoclonic myatonia (atonia or epileptic negative myoclonus) that may sometimes be prominent in some children.
䡲
MS are also triggered by photic stimulation. Myoclonic status epilepticus is characterized by stupor, apathetic, and erratic myoclonus in distal, facial, and neck muscles (head drops) lasting several hours to days. NCSE usually occurs on awakening. The MJs are brief (30–100 msec) and are not time-locked to individual spikes. An increase in the background muscle tone with mild vibratory movements is sometimes visible. It is more commonly seen in myoclonic astatic epilepsy (36%) or Dravet syndrome (30–44%). EEG demonstrates long runs of irregular slow waves and spike-wave discharges that, sometimes simulate a hypsarrhythmic pattern. Some AEDs including lamotrigine in high doses, CBZ, phenytoin, and levetriacetam may exacerbate myoclonic status.
䡲
Angelman syndrome (AS) (Figures 8-28 to 8-30) 䡲
Three characteristic EEG patterns in AS are as follows: 䊳
䊳
䊳
䡲
Prolonged runs of high-amplitude rhythmic 2- to 3-Hz delta activity, maximal in the frontal regions with superimposed epileptiform discharges (most common in children and adults) Persistent rhythmic 4- to 6-Hz high-amplitude activity (under 12 years of age) Spikes and sharp waves, intermixed with high amplitude, 3- to 4-Hz delta activity, mainly posterior and facilitated by eye closure
The notched-delta pattern was observed in more than 80% of AS with a specificity of more than 38%. Therefore, a patient with the clinical phenotype of AS who exhibits this EEG pattern should undergo genetic evaluation for AS. 䡲 This EEG pattern can precede clinical features and/ or may not be correlated with overt clinical seizure events.
616
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Abnormal EEG findings are more pronounced in AS with a deletion but are no different in AS patients with or without epileptic seizures. The EEG abnormalities are not pathognomonic of AS and can be seen in different genetic syndromes, such as Rett syndrome and 4p(-) syndrome. 䡲 Epilepsy in AS has typical features including absence, MS, drop attacks, and nonconvulsive status epilepticus, especially myoclonic status that characterized by apathy or neurologic regression and MJs.
䡲
䡲
The changes in the EEG parallel the clinical course of Rett syndrome. Three characteristic EEG changes have been reported.
1. Loss of expected developmental features during wakefulness and NREM sleep and generalized background slowing. 2. Epileptiform abnormalities, initially, characterized by central-temporal spike- and/or -sharpwave discharges activated by sleep and, later, multifocal spikes and/or sharp waves and generalized slow spike-and-wave discharges. 3. Rhythmic theta activity in the central or frontal-central regions during clinical stages III (postregression) and IV (late motor regression). 䡲 Rhythmic 3- to 5-Hz theta or delta slowing is the most common EEG abnormality (30/44 patients) in patients with Rett syndrome. Diffuse/bisynchronous spikes or sharp waves or slow spike-wave complexes were found in 22/44 and 9/44 patients, respectively. With advancing age, the EEG abnormalities improve and low voltage EEG may develop. These changes parallel the clinical course of Rett syndrome.
Lissencephaly and subcortical band heterotopia (SBH) (Figures 8-33 and 8-39) 䡲
Patients with SBH may present with infantile spasms, Lennox-Gastaut syndrome, or focal epilepsy.
䡲
Seizure semiology and ictal EEG patterns in SBH are not different from those seen in other causes of symptomatic generalized epilepsies.
In atypical MERRF, quasiperiodic sharp waves with higher amplitude in the posterior regions enhanced by low-frequency photic stimulation were noted.
䡲
All patients were seizure free on B6 monotherapy in one series. Recurrence of seizures and of specific sequential EEG changes (background slowing, PPR, spontaneous discharges, stimulus-induced myoclonus, generalized seizures) occurred upon B6 withdrawal. Long-term prognosis correlated with the EEG. All patients who had normal EEGs had normal or near normal development. Treatment requires lifelong supplementation with vitamin B6.
Miller-Dieker syndrome. Deletion of the short arm of chromosome 17 (p13.3) containing lissencephaly type 1 gene (LIS1) was found. MRI reveals a nearly smooth cerebral surface with abnormally thick cortex (typically 10–20 mm) and primitive sylvian fissures giving the “hour-glass” configuration. EEG shows generalized high-amplitude fast activity in alphafrequency band.
䡲
The EEG in type 1 lissencephaly is characterized by generalized high-amplitude fast activity in alpha and beta frequency (8–18/sec), burst of slow spike-wave complexes, high-amplitude slow rhythms, hypsarrhythmia-like pattern, and alternating pattern consisting of bursts of sharp/spike waves alternating with periods of electrocerebral depression with periods of depression. The EEG does not react to sleep or medication.
䡲
The EEGs in the type 1 lissencephaly patients showed the following patterns:
EEG in Rett syndrome is invariably abnormal when recorded during clinical stage II (regression) after age 2 years. 䊳
EEG in SBH is characterized by multifocal epileptiform activity with frequent bilateral diffusion, and high-amplitude anterior fast activity, with bursts of repetitive spikes.
䡲
Rett syndrome (Figures 8-31 and 8-32) 䡲
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Generalized Epilepsy
EEG in various conditions (Figures 8-40 and 8-55)
䡲
A characteristic EEG pattern of bilateral synchronous, high-voltage occipital spikes on low-frequency photic stimulation (1–3 Hz), associated with myoclonus, is observed mainly in type 2 NCL (late infantile onset: Jansky-Bielschowsky), but not in juvenile or adult forms. 䡲 Differential diagnosis of drop attacks includes syncope, seizure, TIA, third ventricular and posterior fossa tumor, motor and sensory impairment of lower limbs, vestibular disorders, cryptogenic falls in middleage women, aged state, and cataplexy. 䡲
REM stage in healthy children does not occur within the first cycle but after one complete cycle (stage 1–4 and then back from 4 to 1), usually 90 minutes after sleep onset. If REM sleep appears at first near the onset of sleep (early REM), narcolepsy must be considered. However, early REM can be seen in individuals withdrawing from CNS depressants such as barbiturates or alcohol.
䡲
The “H-response” is a prominent photic driving response at flash rates beyond 20 Hz. In a critical review of the literature, the reported sensitivity of the H-response varied from 25% to 100%, and the specificity from 80% to 91%. Although the relatively high sensitivities and specificities reported suggest that the H-response may be effective in distinguishing migraine patients from controls, and possibly migraineurs from tension headache sufferers,
(a) Generalized fast activity (8–18/sec) with amplitude higher than 50 μV. (b) Sharp- and slow-wave complexes with amplitude higher than 500 μV. (c) An alternating pattern consisting of bursts of sharp waves alternating with periods of electrocerebral depression. (d) high-amplitude slow rhythms (e) hypsarrhythmia-like pattern 䡲
The EEG does not react to sleep or medication.
䡲
Ninety-five percent of the lissencephaly patients showed pattern (a) or (c) or both compared to only 5 % of the patients with an atypical cortical dysplasia and 0.4% in the controls.
8 the Quality Standards Subcommittee (QSS) of the American Academy of Neurology concluded that the H-response was not more effective than the neurological history and examination in diagnosing headaches and not recommended in clinical practice (QSS, 1995). However, in the presence of complex or prolonged aura, visual hallucinations, disorders of consciousness, history of recent trauma and in infants with vomiting and ocular and head deviation, the EEG may be useful for clinical diagnosis and help to monitor therapeutic response. 䡲 Breath holding spells (BHS) occur most commonly within the first 18 months of age and 90% or more of breath-holders have their initial spell by age 2 years. Virtually all breath-holders cease experiencing episodes by 7–8 years of age. 䡲 EEG in 129 children with BHS was examined. All these children but one had normal EEG. 䡲 Gastaut and Fischer-Williams studied 100 patients, and they used ocular pressure to induce syncope. In 71 patients, cardiac arrest was observed following ocular compression. With an arrest lasting 3–6 sec, there were no clinical or electrical abnormalities. However, with a longer cardiac arrest (7–13 sec) bisynchronous slow waves appeared. This was usually accompanied
Generalized Epilepsy
by clouding or loss of consciousness. When the arrest lasted more than 14 sec, one or two generalized clonic jerks appeared without affecting the EEG. This could be followed by a generalized tonic contraction resembling decerebrate rigidity and accompanied by complete flattening of the EEG. Thus, during a syncopal event the EEG initially shows mild generalized slowing. This is followed by high-voltage frontal delta activity. If the cerebral hypoperfusion persists, the EEG flattens. With recovery, the EEG normalizes in a reverse sequence. 䡲 Occasionally, patients may experience protracted seizures or status epilepticus following either a cyanotic or pallid BHS. Typically, interictal EEG findings in these patients are normal, although one such patient of the author’s acquaintance had vertex spikes on his interictal EEG. Stephenson termed such episodes anoxic-epileptic seizures. Administration of an AED frequently ablates the lengthy seizures, although BHS may continue to occur. 䡲 Patients with cyanotic BHS may follow this EEG evolution without significant bradycardia or asystole. 䡲 Prolonged QT syndrome is a rare, but potentially malignant, cause of anoxic seizure. It is recommended that an EKG to screen for prolonged QT syndrome be performed.
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There are numerous causes of decreased cardiac output that may result in syncope. 䡲 There are important differences between cardiac syncope and neurocardiogenic syncope. In the former, a mechanical or electrophysiologic cardiac abnormality caused by serious underlying cardiac disease results in a sudden critical reduction in cardiac output, leading to cerebral hypoperfusion and syncope. This condition carries an ominous prognosis, whereas neurocardiogenic syncope has a more favorable prognosis due to the absence of serious cardiovascular disease. 䡲
Decreased cardiac output can result from obstruction to flow. Other heart diseases include pump failure and cardiac tamponade, as well as arrhythmias, which can be either bradyarrhythmias or tachyarrhythmias. With cardiac arrhythmias inducing syncope, such as the Stokes-Adams syndrome or prolonged QT interval (Romano-Ward syndrome), patients may present with convulsive syncope and be mistakenly diagnosed as epileptic. In addition to spontaneously occurring cardiac arrhythmias, cardiac dysrhythmias resulting in cardiac circulatory arrest can be induced.
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Generalized Epilepsy
8
FIGURE 81. Carbamazepine-Induced Myoclonic Seizure. A 3-year-old boy with a history of GTCS who developed frequent myoclonic jerks and drop attacks 2 weeks after starting the treatment with carbamazepine (CBZ). Ictal EEG during one of his myoclonic seizures shows a burst of generalized polyspike-and-slow-wave discharge followed by a brief diffuse electrodecrement and 5-Hz theta slowing. Myoclonic seizures and drop attacks disappeared 2 days after stopping CBZ. CBZ is the most common antiepileptic drug (AED) causing AED-induced seizure worsening. CBZ can both aggravate and induce new seizure types including absence, atonic, or myoclonic seizures in patients with generalized epilepsies. Vigabatrin and gabapentin have been found to induce absence and myoclonic seizures. Benzodiazepines have been reported to precipitate tonic seizures in patients with Lennox–Gastaut syndrome. Lamotrigine has been reported to worsen myoclonic, clonic, and tonic-clonic seizures in the patients with Dravet syndrome.1–3 Therefore, “AED-induced seizure worsening” must be considered in all patients whose seizures are worse with the introduction of the new AED.
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Generalized Epilepsy
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FIGURE 82. Generalized Tonic-Clonic Seizure (GTCS). A 14-year-old girl with a history of idiopathic generalized epilepsy (IGE). EEG shows recruiting rhythm described as rhythmic generalized alpha and theta frequency activity. Approximately 22 sec into the seizure, the background activity becomes obscured by myogenic artifact (arrow head) during generalized tonic stiffening.
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Generalized Epilepsy
8
FIGURE 83. Generalized Tonic-Clonic Seizure (GTCS). (Continued) The fast spike activity characterizes the tonic phase of GTCS. However, the background EEG activity becomes almost completely obscured by myogenic artifact during the tonic posturing. Digital high-frequency filter of myogenic artifact or EEG performed during paralyzing with muscle relaxant allows visualization of the EEG activity.
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Generalized Epilepsy
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FIGURE 84. Generalized Tonic-Clonic Seizure (GTCS). (Continued) During the clonic phase of GTCS, the fast spike activity becomes discontinuous and is replaced by highvoltage generalized polyspike-wave activity with polyspikes corresponding with clonic jerks and brief relaxation with slow waves. Immediately after the seizure stops, markedly generalized background suppression is noted. Very irregular diffuse slow-wave activity then follows and may last for minutes. In patients with secondarily GTCS, asymmetric postictal slowing can be a very important lateralizing sign.
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Generalized Epilepsy
8
FIGURE 85. Tonic Phase of Generalized Tonic-Clonic Seizure; (Subdural EEG Recording). Subdural EEG allows visualization of the EEG activity during tonic phase of generalized tonic-clonic seizure without myogenic artifact. EEG shows 4-Hz spike-wave activity during tonic posturing. Tonic and clonic phase of GTCS share similar EEG finding of spike-wave activity but with different duration of relaxation (slow wave). Note myogenic artifact in the EKG channel that represents muscle contraction during the tonic phase of GTCS (lowest channel).
8
Generalized Epilepsy
FIGURE 86. Occipital Intermittent Rhythmic Delta Activity (OIRDA); Idiopathic Generalized Epilepsy. A 9-year-old girl with a history of GTCS whose seizures were aggravated by increasing dose of carbamazepine. EEG demonstrates intermittently bisynchronous rhythmic delta activity, maximally expressed in the posterior head regions, which are attenuated with eye opening (arrow). OIRDA is seen almost exclusively in children and is associated with epilepsy, most commonly in idiopathic generalized epilepsy, especially absence epilepsy.4,5
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Generalized Epilepsy
8
FIGURE 87. Occipital Intermittent Rhythmic Delta Activity (OIRDA); Idiopathic Generalized Epilepsy. (Same EEG recording as in Figure 8-6) The patient developed a staring episode with mild jerking of his body and upper extremities accompanied by generalized irregular 3-Hz spike-wave activity. This EEG confirms that OIRDA represents epileptiform activity.
8
Generalized Epilepsy
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FIGURE 88. Generalized Paroxysmal Fast Activity (GPFA); Idiopathic Generalized Epilepsy (IGE). A 10-year-old boy who started having his first seizure after TBI at 3 years of age. He did well until 9 years of age, when he started having breakthrough seizures consisting of GTCS and myoclonic seizures. He is otherwise normal. Brain MRI was normal. Interictal EEG 3 days after the last GTCS shows very frequent bursts of generalized paroxysmal fast activity (GPFA). GPFA, occurring almost exclusively during sleep, is generated in neocortex. Activation of thalamic neurons in response to varying corticothalamic input patterns may be critical in setting the oscillation frequency of thalamocortical network interactions causing GPFA.6,7 Seventy-five percent of patients had clinical seizures associated with this activity, mostly tonic. Slow spike-and-wave complexes were present in half of the patients. Twenty-five percent of patients had normal background activity.8
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Generalized Epilepsy
8
FIGURE 89. Eye Closure Sensitivity (ECS); Juvenile Myoclonic Epilepsy (JME). A 14-year-old girl with a history of multiple types of seizures including absence, myoclonic, and generalized tonic-clonic seizure (GTCS). GTCS occurs exclusively within the first 1 hour after awakening. She was seizure free with lamotrigine but developed recurrent seizures after medication withdrawal. EEG shows generalized 4-Hz spike-and-wave activity consistently activated by eye closure. ECS is more common in females. It may overlap with photosensitivity but is independent from photosensitivity. ECS can activate polyspike-wave discharges and myoclonic jerks. It can be seen in different epileptic syndromes including childhood absence epilepsy (CAE), juvenile absence epilepsy (JAE), eyelid myoclonia with absences (EMA), juvenile myoclonic epilepsy (JME), idiopathic generalized epilepsy (IGE with tonic-clonic seizure), generalized epilepsy with grand mal upon awakening GMA, and idiopathic occipital lobe epilepsy.9–11 REM sleep, similar to eye opening, plays a role in inhibiting EEG manifestations of JME with eye closure sensitivity.12
8
Generalized Epilepsy
627
FIGURE 810. Epilepsy with Grand Mal on Awakening (GMA); Eye Closure Sensitivity (ECS). A 17-year-old girl with a history of three GTCSs occurring exclusively within the first 1 hour after awakening at ages 13, 15, and 17. There were no other types of seizures. She was seizure free with lamotrigine for 2 years but developed recurrent seizures after medication withdrawal. EEG shows generalized 4 Hz (poly)spike-and-wave discharges activated by eye closure. GTCS of epilepsy with grand mal on awakening (EGMA) occurs exclusively shortly after awakening. The second seizure peak is in the evening corresponding to the peak period of relaxation. Typical absences and myoclonic jerks occur in 10% and 22%, respectively. The majority of patients with EGMA have rare GTCS. Sleep deprivation is a major triggering factor. The EEG of patients with GMA shows generalized (poly)spike-and-wave discharges on their first routine EEG in 44%, normal routine EEG but generalized (poly)spike-and-wave discharges on sleep EEG only in 32%, and no EEG abnormality at all in 24%.13 About 70% of those with additional absences or myoclonic jerks preceding GTCSs have generalized (poly)spike-and-wave discharges.14 A 24-hour video-EEG should be considered in patients suspected to have GMA. It is necessary to include sleep and awakening in the record.
628
Generalized Epilepsy
8
FIGURE 811. Juvenile Myoclonic Epilepsy (JME). A 17-year-old girl with JME. The patient was asked by an EEG technologist to count during frequent bursts of generalized polyspike-wave discharges. She skipped counting the number “19” during the burst of generalized 4- to 4.5-Hz polyspike-wave activity that lasted for only 1–1.5 sec. No visible jerk was noted during the burst. As early as 0.5 sec after their onset of (poly)spike-wave discharges, the majority of patients will show inattention,15 suggesting that very short-lasting spells of a second or less may have a cognitive effect on the patient.16
8
Generalized Epilepsy
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FIGURE 812. Juvenile Myoclonic Epilepsy (JME); Myoclonic Seizures. A 15-year-old girl with JME. EEG during myoclonic jerks (MJ) of the right arm (*) shows symmetrically bilateral synchronous polyspike-wave discharges time-locked with the jerk followed by 2-sec bilateral synchronous, 3-Hz polyspike-wave discharges, and a subsequent diffuse electrodecremental event. A typical ictal EEG in myoclonic seizure is bilateral synchronous and symmetric polyspike-wave discharge, immediately preceding a myoclonic jerk. The polyspike component contains 5–20 spikes, with a frequency between 12 and 16 Hz. The amplitude of spikes is typically increasing and is maximal over the frontal leads where it reaches 200–300 μV. Slow waves of variable frequency (3–4 Hz) and amplitude (200–350 μV) often precede or follow the polyspikes that result in a polyspike-wave complex that lasts much longer than the MJ (approximately 2–4 sec). The number of spikes is associated with the MJ intensity: there are fewer spikes and a more pronounced slow component when the MJ is mild. Back averaging shows that the conduction time, between the apex of the spike and the onset of the MJ, is short (20–50 msec) and characteristic of a cortical myoclonus.17
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Generalized Epilepsy
8
FIGURE 813. Epilepsy with Grand Mal on Awakening (GMA); Photoparoxysmal Response (PPR). (Same recording as in Figure 8-12 ) EEG shows photoparoxysmal response during photic stimulation. GMA is positively correlated, and grand mal during sleep negatively correlated with photosensitivity.
8
Generalized Epilepsy
FIGURE 814. Juvenile Myoclonic Epilepsy (JME); Photoparoxysmal Response (PPR). EEG of a 15-year-old girl with JME. EEG during photic stimulation reveals photoparoxysmal response (PPR) with no clinical accompaniment. PPR is described as generalized irregular spike/polyspike-and-wave complexes during photic stimulation. PPRs are seen in 30–40% of JME patients, compared to 18% in absence epilepsy.9 However, only 5% of patients suffer from clinical photosensitivity.18 Seventy-seven percent of patients with PPR have a history of epilepsy.19 In patients with seizures, a generalized PPR strongly suggests the diagnosis of primary generalized epilepsy.20
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FIGURE 815. Childhood Absence Epilepsy (CAE). A 6-year-old boy with poor school performance and recurrent staring episodes. Inclusion criteria for CAE are (1) onset at 4 -10 years (peak at 5–7), (2) normal neurological condition, (3) brief (4–20 sec) and frequent (tens per day) absence seizures with abrupt and severe impairment of consciousness, (4) EEG ictal discharges of generalized high-voltage spike and double (occasionally triples are allowed) spike-and-slow-wave complexes. They are rhythmic at about 3 Hz with a gradual and regular slowdown from the initial to the terminal phase of the discharge. Exclusion criteria for CAE are: (1) other types of seizure prior to or during the active stage of absence; (2) eyelid myoclonia, perioral myoclonia, rhythmic massive limb jerking, and single or arrhythmic myoclonic jerks —however, mild myoclonic elements of the eyes, eyebrows, and eyelids may be featured, particularly in the first 3 sec of the absence seizure; (3) mild or no impairment of consciousness during the 3- or 4-Hz discharges; (4) brief EEG 3- or 4-Hz spike-wave paroxysms of <4 sec, polyspikes (more than three), or ictal discharge fragmentations; and (5) visual (photic) and other sensory precipitation of clinical seizures.21
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FIGURE 816. Occipital Intermittent Rhythmic Delta Activity (OIRDA) and Generalized 3/sec Spike-Wave Activity; Childhood Absence Epilepsy. A 7-year-old boy with a recent diagnosis of childhood absence epilepsy. EEG during hyperventilation demonstrates both occipital intermittent rhythmic delta activity (OIRDA) (open arrow) and generalized 3/sec spike-wave activity (double arrows) in the same recording. The patient has been seizure free with ethosuximide. OIRDA was first described in 1983 and was concluded to only be seen in children and not found to be helpful in diagnosing a seizure disorder or structural abnormality.22 Subsequent publications show that OIRDA is seen almost exclusively in children with epilepsy and it is rarely seen in children with diffuse encephalopathy. OIRDA is seen almost exclusively in children, less than 10–15 years old, and is associated with epilepsy, most commonly in idiopathic generalized epilepsy, especially absence epilepsy and, less commonly, in focal epilepsy.23–25
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FIGURE 817. Childhood Absence Epilepsy; Diffuse Rhythmic Delta Activity During Absence Seizure. A 12-year-old girl with a history of childhood absence epilepsy (CAE) in remission who presented with syncope. EEG during hyperventilation (HV) shows diffuse rhythmic 3-Hz delta activity with fronto-central predominance. Approximately 10 sec into the HV, the patient developed clinical absence seizures described as staring off, unresponsiveness, motionless, and lip smacking. The patient started moving immediately when the diffuse delta activity stopped. No postictal state is noted. Diffuse 3-Hz rhythmic delta activity without spike component is an exceptional ictal EEG finding during an absence seizure.
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FIGURE 818. Asymmetric OIRDA; Childhood Absence Epilepsy. An 8-year-old boy with recurrent absence seizures after stopping ethosuximide. EEG shows an asymmetric, bilateral synchronous occipital rhythmic 2.5- to 3.5-Hz delta activity with shifting predominance between left and right hemispheres. The patient was seizure free again after ethosuximide was reintroduced. OIRDA is found in children. Because it is age dependent, maturational factors probably play a role in the expression of OIRDA in children with epilepsy. OIRDA is not commonly associated with encephalopathy. It is more closely related to temporal intermittent rhythmic delta activity (TIRDA) than to FIRDA.4 OIRDA is seen during wakefulness and probably an epileptiform pattern. OIRDA is seen in absence and generalized tonic-clonic seizures. Its electrographic characteristics appear to differ between localization-related epilepsy and primary generalized epilepsy, particularly absence seizures. The frequency of the occipital rhythmic discharges in children with absences was generally faster (3–4 Hz) than in localization-related epilepsy (2–3 Hz).25
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FIGURE 819. Symptomatic Absence Seizure and ESES; Thalamic Heterotopia. A 6-year-old boy with intractable absence epilepsy and cognitive dysfunction caused by right thalamic heterotopia (arrow). Complete resection of heterotopia resulted in seizure freedom. Alterations in normal thalamocortical reciprocal interactions are critical in the generation of the regular generalized spike-wave discharges (GSWD).26 Most patients with unilateral thalamic lesion and epilepsy showed GSWD.27–31 Absence status with GSWD caused by ischemic lesion in the left thalamus have been reported.27 Lesions of the inferior-medial-posterior thalamic structures might have a role in the pathogenesis of GSWD and ESES.29 Gray matter heterotopia is caused by a halt in neuronal radial migration.32 Although gray matter heterotopia is commonly associated with refractory epilepsy, it is still uncertain what role heterotopic lesions play in seizure onset and propagation and whether they are epileptogenic. Intracranial EEG investigations showed that seizures are generated sometimes by heterotopias, sometimes by distant cortex, or sometimes by both. However, neither the removal of the lesion alone nor mesial temporal resections lead to a favorable outcome, suggesting a more widespread epileptogenic network in these patients. Seizure onset in a heterotopia is sometimes completely outside the lesion and sometimes has an overlap with the lesion. The heterotopia is part of more complex circuitry involving the surrounding and distant cerebral cortex.33,34 High-frequency oscillations (HFOs), especially fast ripples, are closely linked to seizure-onset areas. In focal cortical dysplasia and sometimes in heterotopia, HFOs occur in lesional areas that are not part of the seizure onset zone, and they may indicate potential epileptogenicity of these lesions.35–37
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FIGURE 820. Jeavons Syndrome (Eyelid Myoclonia with Absence). A 2-year-old boy who developed absence seizures at 18 months of age. He also had GTCS, myoclonic seizures, and tooth brushing-induced seizure. He was also noted to have “eyelid myoclonia” during prolonged video-EEG monitoring. EEG shows 3-Hz polyspike-wave (PSW) discharges associated with eyelid myoclonic and absence seizure. Jeavons syndrome is refers to idiopathic reflex epilepsy with eyelid myoclonia, eye-closure sensitive seizure, and photosensitivity. Seizures are brief (3–6 sec). Ictal EEG consists of generalized PSW at 3–6 Hz, usually occurring after eye closure. Eyelid myoclonia is resistant to treatment.38
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FIGURE 821. Benign Myoclonic Epilepsy of Infancy (BMEI). A 10-month-old boy who did well until 8 months when he developed recurrent myoclonic jerks with occasional drop attacks. Video-EEG captured his typical drop attack while sitting. There was increased muscle activity in the deltoid muscle corresponding to generalized polyspike-wave discharges during his drop. These findings confirmed the drop attack was a myoclonic seizure rather than atonic seizure. Background EEG was within normal limits. His development was normal. All tests other than EEGs in BMEI are normal. Background and interictal EEG is normal. Spontaneous generalized polyspike-wave discharges without myoclonic seizures are rare. The ictal EEG during jerks show generalized (poly)spike-wave discharges. The discharges are brief (1–3 sec) and isolated. Frequently, ictal EEG activity is limited to the rolandic and vertex regions. During drowsiness, there is enhancement of myoclonic jerks or epileptiform discharges. Photic stimulation, sudden noises and contact stimulate epileptiform discharges in the EEG. No other type of seizure is observed. Clinical examination and MRI are normal. Outcome is correlated with early diagnosis and treatment.14,39
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FIGURE 822. Benign Myoclonic Epilepsy of Infancy. A 22-month-old girl with recurrent myoclonic jerks of her arms, especially noticeable when something came in contact with her head. Cranial MRI was normal. Interictal EEG is normal. The patient had one typical episode of bilateral arm jerking associated with generalized spike/polyspikes-wave discharges (asterisk). All tests other than EEGs in BMEI are normal. Background and interictal EEG are normal. Spontaneous generalized polyspike-wave discharges without myoclonic seizures are rare. The ictal EEG during jerks show generalized (poly)spike-wave discharges. The discharges are brief (1–3 sec) and isolated. Frequently, ictal EEG activity is limited to the rolandic and vertex regions. During drowsiness, there is enhancement of myoclonic jerks or epileptiform discharges. Photic stimulation, sudden noises and contact stimulate epileptiform discharges in the EEG. No other type of seizure is observed. Clinical examination and MRI are normal. Outcome is correlated with early diagnosis and treatment.14,39
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FIGURE 823. Diffuse Theta Activity; Myoclonic Astatic Epilepsy (MAE). EEG during wakefulness of a 6-year-old boy with myoclonic astatic epilepsy (MAE) showing diffuse monorhythmic 5- to 6-Hz theta activity with centro-parietal predominance. A monorhythmic 4- to 7-Hz rhythm is a characteristic background EEG activity that is seen in almost all instances early in the course of MAE. This rhythm is usually parietal predominance. This EEG pattern is, falsely attributed to drowsiness. During active seizures, the rhythm is more irregular and slower, whereas it will be more regular and faster in a period of remission.40,41
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FIGURE 824. Myoclonic-Astatic Seizure (MAS - Myoclonic Seizure with Atonia); Myoclonic Astatic Epilepsy (MAE). EEG of a 7-year-old boy with MAE during his typical seizure described as myoclonic jerks of arms (open arrows) followed by head drop (double arrows). MAS develop atonia immediately after a single or a series of 2–3 myoclonic seizures (MS). A sudden loss of tone causes either a drop attack or slight myatonia, head nodding, or sagging at the knees (post-myoclonic myatonia or epileptic negative myoclonus).41,42 Ictal EEG during MS is similar to a pure atonic seizure (AS) and characterized by a generalized (poly) spike-and-wave discharges that can be isolated or repeated rhythmically at 2–4 Hz, lasting 2–6 sec. MS are time-locked to a spike-and-wave complex. The EMG correlation of each jerk is a burst lasting around 100 msec, followed by a longer (200–500 msec) post-myoclonic myatonia. The atonic component of seizures is characterized by a rhythmic discharge of (poly) spike-and-slow-wave complexes at 2–4 Hz, accompanied by EMG inhibition lasting 60–400 msec, synchronous in the recorded muscles and time-locked to the onset of the slow wave. This generalized post-myoclonic myatonia has caused the fall. The number of spikes in the individual complexes are associated with the severity of MS. AS is usually associated with the slow wave of a (poly)spike-wave complex, and the intensity of atonia is proportionate to the amplitude of the slow wave.14,41,43
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FIGURE 825. Myoclonic Astatic Epilepsy (MAE); Myoclonic Seizure (MS). EEG of a 6-year-old boy with myoclonic astatic epilepsy (MAE) during a myoclonic seizure. Myoclonic (MS) and MAS are present in all children with MAE. Clinically, MS presents as brief generalized jerks of the body, isolated or in a short series of 2–3 seizures. Proximal muscle is more involved, producing a sudden flexion of the head and trunk with a possible fall to the ground. The duration of these episodes is very brief (0.3–1 sec). Falls can be either the direct effect of massive myoclonic jerks or from the post-myoclonic silent period or generalized post-myoclonic myatonia (atonia or epileptic negative myoclonus) that may sometimes be prominent. In some children, MS is also triggered by photic stimulation. Ictal EEG during MS is similar to a pure atonic seizure (AS) and characterized by a generalized (poly)spike-and-wave discharge that can be isolated or repeated rhythmically at 2–4 Hz, lasting 2–6 sec. Myoclonic jerks are time-locked to a spike-and-wave complex.
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Generalized Epilepsy
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FIGURE 826. Myoclonic Astatic Epilepsy (MAE); Drop Attack. EEG of a 5-year-old boy with myoclonic astatic epilepsy (MAE) during an atonic seizure (AS). Myoclonic (MS) and MAS are present in all children with MAE. Clinically, MS present as brief generalized jerks of the body, isolated or in a short series of 2–3 seizures. Proximal muscles are more involved, producing a sudden flexion of the head and trunk with possible fall to the ground. The duration of these episodes is very brief (0.3–1 sec). Falls can be either the direct effect of massive myoclonic jerks or from the post-myoclonic silent period or generalized post-myoclonic myotonia (atonia or negative epileptic myoclonus) that may sometimes be prominent. In some children, MS is also triggered by photic stimulation. Ictal EEG during MS is similar to a pure AS. The number of spikes in the individual complexes is associated with the severity of MS. The intensity of atonia is proportionate to the amplitude of the slow wave.14,41,43
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FIGURE 827. Myoclonic Status Epilepticus; Myoclonic Astatic Epilepsy (MAE). Myoclonic status epilepticus is characterized by stupor, apathetic and erratic myoclonus in distal, facial, and neck muscles (head drops) lasting several hours to days. NCSE usually occurs on awakening. The myoclonic jerks are brief (30–100 msec) and are not time-locked to individual spikes. An increase in the background muscle tone with mild vibratory movements is sometimes visible. It is more commonly seen in myoclonic astatic epilepsy (36%) or Dravet syndrome (30–44%).44,45 EEG demonstrates long runs of irregular slow-wave and spike-wave discharges that, sometimes simulate a hypsarrhythmic pattern.46 Some antiepileptic drugs (AEDs) including lamotrigine in high doses. carbamazepine, phenytoin and levetriacetam may exacerbate myoclonic status.1,3
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Generalized Epilepsy
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FIGURE 828. Angelman Syndrome (AS); Notched-Delta Pattern. An 11-year-old girl with mental retardation and intractable epilepsy (absence and myoclonic) associated with AS. Interictal EEG shows frequent bursts of high voltage 2.5- to 3-Hz rhythmic delta activity with superimposed low-amplitude spikes, maximal in the occipital region. Three common EEG patterns in AS are (1) prolonged runs of high-amplitude rhythmic 2- to 3-Hz delta activity, maximal in the frontal regions with superimposed epileptiform discharges (most common in children and adults), (2) persistent rhythmic 4- to 6-Hz high-amplitude activity (under 12 years of age), and (3) spikes and sharp waves, intermixed with high-amplitude, 3- to 4-Hz delta activity, mainly posterior and facilitated by eye closure. The notched-delta pattern was observed in > 80% of AS with a specificity of > 38%. Therefore, a patient with the clinical phenotype of AS who exhibits this EEG pattern should undergo genetic evaluation for AS. This EEG pattern can precede clinical features and/ or may not be correlated with overt clinical seizure events. Abnormal EEG findings are more pronounced in AS with a deletion but are no different in AS patients with or without epileptic seizures. These EEG abnormalities can also be seen in different genetic syndromes, such as Rett syndrome and 4p(-) syndrome.47–49
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FIGURE 829. Bilateral Synchronous 3-4 Hz Spike-Wave Activity in the Occipital Region; Angelman Syndrome (AS). (Same patient as in Figure 8-28) EEG demonstrates a combination of bilateral synchronous 3- to 4-Hz spike-wave activity in the occipital regions and diffuse rhythmic 2.5- to 3-Hz, high-amplitude often-notched delta activity.
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Generalized Epilepsy
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FIGURE 830. Nonconvulsive Status Epilepticus (NCSE); Angelman Syndrome. EEG in an 8-year-old boy with Angelman syndrome. The patient developed nonconvulsive status epilepticus and died despite aggressive treatment. EEG shows continuously diffuse spike-wave and polyspike-wave activities. Epilepsy in Angelman syndrome has typical features including absence, myoclonic seizures, drop attacks, and nonconvulsive status epilepticus, especially myoclonic status that is characterized by apathy or neurologic regression and myoclonic jerks.50
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FIGURE 831. Rett Syndrome; Bisynchronous Sharp Waves. A 12-year-old girl with Rett syndrome. EEG in Rett syndrome is invariably abnormal when recorded during clinical stage II (Regression) after age 2 years. The changes in the EEG parallel the clinical course of Rett syndrome. Three characteristic EEG changes have been reported: (1) loss of expected developmental features during wakefulness and non-REM sleep and generalized background slowing; (2) epileptiform abnormalities, initially characterized by centraltemporal spike-and/or-sharp-wave discharges activated by sleep and, later, multifocal spikes and/or sharp waves and generalized slow spike-and-wave discharges; (3) rhythmic theta activity in the central or frontal-central regions during clinical stages III (post-regression) and IV (Late motor regression).51 Rhythmical 3- to 5-Hz theta or delta slowing is the most common EEG abnormality (30/44 patients) in the patients with Rett syndrome. Diffuse/bisynchronous spikes or sharp waves or slow spike-wave complexes were found in 22/44 and 9/44 patients, respectively. With advancing age, the EEG abnormalities improve and low-voltage EEG may develop. These changes parallel the clinical course of Rett syndrome.52
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FIGURE 832. Rett Syndrome; Bisynchronous Sharp Waves. A 9-year-old girl with Rett syndrome. EEG in Rett syndrome is invariably abnormal when recorded during clinical stage II (Regression) after age 2 years. The changes in the EEG parallel the clinical course of Rett syndrome. Three characteristic EEG changes have been reported: (1) loss of expected developmental features during wakefulness and non-REM sleep and generalized background slowing; (2) epileptiform abnormalities, initially, characterized by central-temporal spike-and/or-sharp-wave discharges activated by sleep and, later, multifocal spikes and/or sharp waves and generalized slow spike-and-wave discharges; (3) rhythmic theta activity in the central or frontal-central regions during clinical stages III (post-regression) and IV (Late motor regression).51 Rhythmic 3- to 5-Hz theta or delta slowing is the most common EEG abnormality (30/44 patients) in the patients with Rett syndrome. Diffuse/bisynchronous spikes or sharp waves or slow spike-wave complexes were found in 22/44 and 9/44 patients, respectively. With advancing age, the EEG abnormalities improve and low-voltage EEG may develop. These changes parallel the clinical course of Rett syndrome.52
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Generalized Epilepsy
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FIGURE 833. Subcortical Band Heterotopia (Double Cortex Syndrome). A 14-year-old girl with severe mental retardation, spastic quadriparesis, and medically intractable epilepsy resulting from subcortical band heterotopia (SBH). DCX gene located in chromosome Xp22.3-q23 was identified. MRI shows a thin layer of gray matter separated from the normal-appearing cortex by a layer of white matter. Also note the cortex in the right temporal lobe is smoother and thicker than in the left temporal lobe. EEG during sleep demonstrates generalized 2-Hz spike/polyspike-wave discharges intermixed with diffuse spindles with frontal predominance. Patients with SBH may present with infantile spasms, Lennox-Gastaut syndrome, or focal epilepsy. EEG in SBH is characterized by multifocal epileptiform activity with frequent bilateral diffusion, and high-amplitude anterior fast activity, with bursts of repetitive spikes.53,54 Seizure semiology and ictal EEG patterns in SBH are not different from those seen in other causes of symptomatic generalized epilepsies.55
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Generalized Epilepsy
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FIGURE 834. Type 1 Lissencephaly (Miller-Dieker Syndrome); Generalized High-Amplitude Fast Activity (Alpha-Frequency Band). A 6-year-old boy with spastic quadriparesis, severe mental retardation, and medically intractable epilepsy (atonic, atypical absence, and generalized tonic-clonic seizures) resulting from Miller-Dieker syndrome. Deletion of the short arm of chromosome 17 (p13.3) containing lissencephaly type 1 gene (LIS1) was found. MRI reveals a nearly smooth cerebral surface with abnormally thick cortex (typically 10–20 mm) and primitive sylvian fissures giving the “hour-glass” configuration.56 EEG shows generalized high-amplitude fast activity in alpha-frequency band. The EEG in type 1 lissencephaly is characterized by generalized high-amplitude fast activity in alpha and beta frequency (8–18/sec), burst of slow spike-wave complexes, highamplitude slow rhythms, hypsarrhythmia-like pattern, and alternating pattern consisting of bursts of sharp/spike waves alternating with periods of electrocerebral depression. The EEG does not react to sleep or medication.57–59
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Generalized Epilepsy
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FIGURE 835. Type 1 Lissencephaly (Miller-Dieker Syndrome); Generalized High-Amplitude Fast Activity & Polyspike-and Slow-Wave Complexes. (Same recording as in Figure 8-34) EEG shows generalized high-amplitude fast activity alternating with bursts of slow polyspike-wave complexes. The EEG in type 1 lissencephaly is characterized by generalized high-amplitude fast activity in alpha and beta frequency (8–18/sec), burst of slow spike-wave complexes, highamplitude slow rhythms, hypsarrhythmia-like pattern, and alternating pattern consisting of bursts of sharp/spike waves alternating with periods of electrocerebral depression. The EEG does not react to sleep or medication.57–59
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Generalized Epilepsy
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FIGURE 836. Type 1 Lissencephaly (Miller-Dieker Syndrome); Generalized High-Amplitude Fast Activity (Beta Frequency Band). (Same recording as in Figure 8-34 and 8-35) EEG shows abnormally generalized, very high-amplitude activity in the beta frequency band.57 The EEG in type 1 lissencephaly is characterized by generalized high-amplitude fast activity in alpha and beta frequency (8–18/sec), burst of slow spike-wave complexes, highamplitude slow rhythms, hypsarrhythmia-like pattern, and alternating pattern consisting of bursts of sharp/spike waves alternating with periods of electrocerebral depression. The EEG does not react to sleep or medication.57–59
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FIGURE 837. Type 1 Lissencephaly; High-Voltage Sharp-and-Slow-Wave Complexes. EEG of a 16-year-old girl with Lennox-Gastaut syndrome caused by type 1 lissencephaly. The EEGs in type 1 lissencephaly patients showed the following patterns: (a) generalized fast activity (8–18/sec) with amplitude higher than 50 μV; (b) sharp- and slow-wave complexes with amplitude higher than 500 μV; (c) an alternating pattern consisting of bursts of sharp waves alternating with periods of electrocerebral depression. Ninety-five percent of the lissencephaly patients showed pattern (a) or (c) or both compared to only 5 % of the patients with an atypical cortical dysplasia and 0.4% in controls.59
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FIGURE 838. Lissencephaly Type 2; Alternating Pattern (Bursts of Sharp Waves Alternating with Periods of Electrocerebral Depression). EEG of a 16-year-old girl with Lennox-Gastaut syndrome caused by type 1 lissencephaly. The EEGs in the type 1 lissencephaly patients showed the following patterns: (a) generalized fast activity (8–18/sec) with an amplitude higher than 50 μV; (b) sharp- and slow-wave complexes with an amplitude higher than 500 μV; (c) an alternating pattern consisting of bursts of sharp waves alternating with periods of electrocerebral depression. Ninety-five percent of the lissencephaly patients showed pattern (a) or (c) or both compared to only 5 % of the patients with an atypical cortical dysplasia and 0.4% in controls.59
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FIGURE 839. Type 1 Lissencephaly; Generalized Fast Activity (8-18/sec). EEG of a 16-year-old girl with Lennox-Gastaut syndrome caused by type 1 lissencephaly. The EEGs in the type 1 lissencephaly patients showed the following patterns: (a) generalized fast activity (8–18/sec) with amplitude higher than 50 μV; (b) sharp- and slow-wave complexes with amplitude higher than 500 μV; (c) an alternating pattern consisting of bursts of sharp waves alternating with periods of electrocerebral depression. Ninety-five percent of the lissencephaly patients showed pattern (a) or (c) or both compared to only 5 % of the patients with an atypical cortical dysplasia and 0.4% in controls.59
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FIGURE 840. Generalized Epileptiform Discharges with Diffuse Delta Slowing; End-stage Myoclonic Epilepsy with Ragged Red Fibres (MERRF). A 10-year-old girl with progressive myoclonic epilepsy caused by end-stage MERRF. EEG demonstrates continuously diffuse polymorphic delta activity and frequent bursts of generalized slow spike/polyspike-wave discharges. The patient expired a few weeks after this EEG recording. EEG in patients with MERRF shows diffuse background slowing with polyspike and wave complexes enhanced by photic stimulation and often related to generalize myoclonic jerks. In atypical MERRF, quasiperiodic sharp waves with higher amplitude in the posterior regions enhanced by low-frequency photic stimulation were noted.60,61
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FIGURE 841. Epileptic Encephalopathy; Generalized Clonic Seizure. A 13-year-old girl with severe developmental delay and medically intractable epilepsy. She developed more frequent generalized tonic-clonic seizures and increasing hand tremor-like episodes. EEG shows generalized 3- to 3.5-Hz (poly)spike-wave discharges with the spikes time-locked with her typical tremors. This finding indicates that her hand tremors were apparently generalized clonic seizures. A cranial MRI (not shown) and intensive metabolic work-up were unremarkable. Generalized clonic seizures are the result of either intermittent generalized activation of the motor cortex (Brodmann areas 4 and 6) or, rarely, epileptic seizures originating in the supplementary sensorimotor area. Generalized clonic seizures are frequently seen after generalized tonic-clonic seizures in GTCS. Isolated generalized clonic seizures are rare but may occur in patients with progressive myoclonic epilepsies.62
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FIGURE 842. Paroxysmal Fast Activity (PFA); Generalized Clonic Seizures. (Same recording as in Figure 8-41) EEG during one of her typical tremor-like episodes shows a run of 3 sec fast rhythmic spikes at 15 Hz, which shows no change in frequency throughout the burst, preceded and followed by generalized spike-wave activity. This EEG pattern is consistent with “paroxysmal fast activity (PFA)” commonly seen in Lennox-Gastaut syndrome. PFA can be either an interictal activity or ictal activity correlating with generalized tonic seizures. However, PFA can also be associated with other generalized or focal epilepsies. In this case, PFA is associated with generalized clonic seizures presenting as tremorlike episodes.
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FIGURE 843. Pyridoxine Dependency. A 4-week-full-term and previously healthy female with erratic myoclonus, poor feeding, irritability and apneic spells requiring mechanical ventilation. EEG shows burst-suppression pattern with multifocal epileptiform activity. EEG normalized 25 minutes after the B6 (pyridoxine) IV injection. The patient showed clinical improvement and was discharged 36 hours after that. At a follow-up visit at 20 months, the patient had normal developmental milestones and was seizure free for 11 months. Repeated EEG at 4 months of age was normal. At birth, patients were hypotonic, had decreased visual alertness, were agitated, irritable, jittery, hyperalert, and exhibited sleeplessness and a startle reaction to touch and sound. Age of onset of seizures varied from 30 minutes to 3 days. Seizures of various types include spasms, myoclonic seizures, partial clonic, and secondary generalized seizures. EEG showed burst-suppression patterns, continuous-discontinuous patterns, and bilateral high-voltage delta activity.63 Clinical seizures improved within minutes and paroxysmal discharges within hours after the IV pyridoxine. Treatment requires lifelong supplementation with pyridoxine (vitamin B6). All patients were seizure free on B6 monotherapy in one series. Recurrence of seizures and of specific sequential EEG changes (background slowing, photoparoxysmal response, spontaneous discharges, stimulus-induced myoclonus, and generalized seizures) occurred upon B6 withdrawal. Long-term prognosis correlated with the EEG. All patients who had normal EEGs had normal or near normal development.64
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FIGURE 844. Neuronal Ceroid Lipofuscinosis (NCL); Occipital Spikes Evoked by Low-Frequency Photic Stimulation. A 16-year-old boy with visual impairment, ataxia, myoclonus, cognitive decline, and medically intractable epilepsy, predominantly myoclonic seizures. He has been diagnosed with type 6 NCL. EEG shows occipital spikes on lowfrequency photic stimulation (1–3 Hz). A characteristic EEG pattern of bilateral synchronous, high-voltage occipital spikes on low-frequency photic stimulation (1–3 Hz), associated with myoclonus, is observed mainly in type 2 NCL (Late infantile onset: Jansky-Bielschowsky), but not in juvenile or adult forms.65
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FIGURE 845. Neuronal Ceroid Lipofuscinosis (NCL); Occipital Spikes Evoked by Low-Frequency Photic Stimulation. (Same patient as in Figure 8-34) A 16-year-old boy with visual impairment, ataxia, myoclonus, cognitive decline, and medically intractable epilepsy, predominantly myoclonic seizures. He has been diagnosed with type 6 NCL. EEG shows occipital spikes on low-frequency photic stimulation (1–3 Hz). A characteristic EEG pattern of bilateral synchronous, high-voltage occipital spikes on low-frequency photic stimulation (1–3 Hz), associated with myoclonus, is observed mainly in type 2 NCL (Late infantile onset: Jansky-Bielschowsky), but not in juvenile or adult forms.65
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Generalized Epilepsy
FIGURE 846. Neuronal Ceroid Lipofuscinosis (NCL); Diffuse Bisynchronous Epileptiform Paroxysms. (Same patient as in Figure 8-34) A 16-year-old boy with visual impairment, ataxia, myoclonus, cognitive decline, and medically intractable epilepsy, predominantly myoclonic seizures. He has been diagnosed with type 6 NCL. EEG shows diffuse bisynchronous polyspikes intermixed with diphasic delta activity. EEG in NCL shows markedly diffuse delta slowing with diffuse bisynchronous epileptiform discharges intermixed with the slow waves.66
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FIGURE 847. Drop Attack; Cataplexy. A 7-year-old boy with excessive daytime drowsiness, very difficult to wake in the morning, intermittent inability to move, and frequent fall to the ground while walking. Sleep study with MSLT confirmed the diagnosis of narcolepsy. Video-EEG captured multiple drop attacks. The EEG shows rapid eye movement (REM) approximately 1–1.5 sec prior to drop attack. No epileptiform activity is noted during the drop attack. With lateral eye movements, the eyes are moving to the side where positivity is noted. This is a result of the positivity of the cornea coming closer to the F7 or F8 electrode, making the one toward which the eyes are moving positive. If the eyes are moving to the left, then the positivity on the cornea is directed to the left side (F7 electrode), making F7 a positive polarity (pen separation) (arrow) and F8 a negative polarity (pen coming together) (arrow). REM stage in healthy children does not occur within the first cycle but after one complete cycle (stages 1 to 4 and then back from 4 to 1), usually 90 minutes after sleep onset. If REM sleep appears at first near the onset of sleep (early REM), narcolepsy and individuals withdrawing from CNS depressants such as barbiturates or alcohol.16 Differential diagnosis of drop attacks includes syncope, seizure, TIA, third ventricular and posterior fossa tumor, motor and sensory impairment of lower limbs, vestibular disorders, cryptogenic falls in middle-age women, aged state, and cataplexy.67
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FIGURE 848. Excessive Photic Response at High Frequency Stimulation (H Response); Migraine. The “H-response” is a prominent photic driving response at flash rates beyond 20 Hz. In a critical review of the literature, the reported sensitivity of the H-response varied from 25% to 100%, and the specificity from 80% to 91%. Although the relatively high sensitivities and specificities reported suggest that the H-response may be effective in distinguishing migraine patients from controls, and possibly migraineurs from tension headache sufferers, the Quality Standards Subcommittee (QSS) of the American Academy of Neurology concluded that the H-response was not more effective than the neurological history and examination in diagnosing headaches and not recommended in clinical practice (Quality Standard Subcommittee, 1995). However, in the presence of complex or prolonged aura, visual hallucinations, disorders of consciousness, history of recent trauma, and in infants with vomiting and ocular and head deviation, the EEG may be useful for clinical diagnosis and help to monitor therapeutic response.68
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FIGURE 849. Migraine with Excessive Periventricular Space; H-Response. EEG of a 10-year-old boy with severe migraine shows excessive photic response at flash rates of 21 Hz. Coronal T2 WI MRs show increased signal intensity at deep periventricular white matter. About 19% of the migraineurs had high signal white matter foci (WMF) on T2 weighted images strictly localized in the deep white matter (DF). No PVF were observed. These findings were not correlated with age, sex, disease duration, frequency of attacks, or different types of migraines. The presence in a subgroup of migraineurs of leukoaraiosis (DF) suggests that migraine could represent a cerebrovascular risk factor in these patients.69 The “H-response” is a prominent photic driving response at flash rates beyond 20 Hz. In a critical review of the literature, the reported sensitivity of the H-response varied from 25% to 100%, and the specificity from 80% to 91% for migraine headaches. Although the relatively high sensitivities and specificities reported suggest that the H-response may be effective in distinguishing migraine patients from controls, and possibly migraineurs from tension headache sufferers, the Quality Standards Subcommittee (QSS) of the American Academy of Neurology concluded that the H-response was not more effective than the neurological history and examination in diagnosing headaches and not recommended in clinical practice (Quality Standard Subcommittee, 1995). However, in the presence of complex or prolonged aura, visual hallucinations, disorders of consciousness, history of recent trauma, and in infants with vomiting and ocular and head deviation, the EEG may be useful for clinical diagnosis and for monitoring therapeutic response.68
8
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FIGURE 850. Anoxic Seizures; Pallid Breath Holding Spells. A 2-year-old boy with frequent tonic stiffening that always occurred after crying. The EEG when he holds his breath and stares off shows diffused rhythmic delta activity (arrow) followed by background attenuation during tonic stiffening (double arrows). EKG shows bradycardia. EEG returns back to normal in reverse fashion (open arrow) when the symptoms subside. The spells disappear after treatment with iron supplement for an iron deficiency anemia. BHS occur most commonly within the first 18 months of age. Virtually all breath-holders cease experiencing episodes by 7–8 years of age. 70 EEGs in 129 children with breath-holding spells were almost always normal.71 Cardiac arrest was observed following ocular compression. With an arrest lasting 3–6 sec, there were no clinical or electrical abnormalities. However, with a longer cardiac arrest (7–13 sec) bisynchronous slow waves appeared. This was usually accompanied by clouding or loss of consciousness. When the arrest lasted more than 14 sec, one or two generalized clonic jerks appeared without affecting the EEG. This could be followed by a generalized tonic contraction resembling decerebrate rigidity and accompanied by complete flattening of the EEG. Thus, during a syncopal event the EEG initially shows mild generalized slowing. This is followed by high-voltage frontal delta activity. If the cerebral hypoperfusion persists, the EEG flattens. With recovery, the EEG normalizes in a reverse sequence.71–73 Occasionally, patients may experience protracted seizures or status epilepticus following BHS.74,75 Typically, interictal EEG findings in these patients are normal or rarely vertex spikes. They were termed episodes anoxic-epileptic seizures. Administration of an AED frequently ablates the lengthy seizures, although BHS may continue to occur.76 Patients with cyanotic BHS may follow this EEG evolution without significant bradycardia or asystole. Prolonged QT syndrome is a rare, but potentially malignant, cause of anoxic seizure. It is recommended that an EKG to screen for prolonged QT syndrome be performed in all cases.77
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FIGURE 851. Cardiac Syncope. A 7-year-old boy s/p cardiac transplantation with frequent syncpoe. The EEG shows bisynchronous rhythmic delta activity (open arrow) after the ectopic beats in the EKG (asterisk) followed immediately by diffuse background suppression (double arrows). The EEG returns back to normal in reverse fashion (open arrow) when the symptoms subside. The patient died a few months after this EEG from heart failure. Cardiac arrest was observed following ocular compression. With an arrest lasting 3–6 sec, there were no clinical or electrical abnormalities. However, with a longer cardiac arrest (7–13 sec) bisynchronous slow waves appeared. This was usually accompanied by altered consciousness. When the arrest lasted > 14 sec, one or two generalized clonic jerks appeared without affecting the EEG. This could be followed by a generalized tonic contraction resembling decerebrate rigidity and accompanied by complete flattening of the EEG. With recovery, the EEG normalizes in a reverse sequence.72,73
8
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FIGURE 852. Cardiac Syncope. (Continued) There are numerous causes of decreased cardiac output that may result in syncope.78–80 There are important differences between cardiac syncope and neurocardiogenic syncope. In the former, a mechanical or electrophysiologic cardiac abnormality caused by serious underlying cardiac disease results in a sudden critical reduction in cardiac output leading to cerebral hypoperfusion and syncope. This condition carries an ominous prognosis, whereas neurocardiogenic syncope has a more favorable prognosis due to the absence of serious cardiovascular disease.81 Decreased cardiac output can result from obstruction to flow. Other heart diseases include pump failure and cardiac tamponade, as well as arrhythmias, which can be either bradyarrhythmias or tachyarrhythmias. With cardiac arrhythmias inducing syncope, such as the StokesAdams syndrome or prolonged QT interval (Romano-Ward syndrome), patients may present with convulsive syncope and be mistakenly diagnosed as epileptic.82–84 In addition to spontaneously occurring cardiac arrhythmias, cardiac dysrhythmias resulting in cardiac circulatory arrest can be induced.
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FIGURE 853. Cardiac Asystole; Anoxic Encephalopathy S/P Cardiac Arrest Due To Severe Traumatic Brain Injury. A 35-year-old male with anoxic encephalopathy after cardiac arrest due to severe TBI. His brainstem reflexes were absent. On day 4, the patient developed cardiac asystole. After cardiac asystole (open arrow), the EEG shows diffuse delta activity, which is followed by electrocerebral inactivity (ECI). Thirty seconds after the onset of cardiac asystole, the patient developed decerebrate rigidity with eye fluttering. The cardiac asystole lasts for approximately 75 sec. Four seconds after the first heart beat, the EEG changes from ECI to diffuse delta slowing. Six hundred and nine patients diagnosed clinically as brain dead were studied; 326 had final cardiac asystole while still being ventilated. The median time in hospital before the heart finally stopped was 3–4 days, with 30–40 hours on the ventilator.85 A singular ventricular escape beat occurring in the midst of prolonged asystole may prevent or delay both the tonic fit and the isoelectric pattern.86
8
Generalized Epilepsy
FIGURE 854. Cardiac Asystole; Anoxic Encephalopathy S/P Cardiac Arrest Due To Severe Traumatic Brain Injury. (Continued from Figure 8-53).
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FIGURE 855. Cardiac Asystole; Anoxic Encephalopathy S/P Cardiac Arrest Due To Severe Traumatic Brain Injury. (Continued from Figure 8-53).
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41. Doose H. EEG in Childhood Epilepsy. 1st ed. Montrouge, France; John Libbey; 2003 Eurotext. 42. Gastaut H, Regis H. On the subject of Lennox's" akinetic" petit mal. in memory of WG Lennox. Epilepsia. 1961;2:298. 43. Guerrini R, Parmeggiani L, Bonanni P, Kaminska A, Dulac O. Myoclonic astatic epilepsy. In: Roger J, Bureau M, Dravet C, Genton P, Tassinari CA, Wolf P, eds. Epilepsy Syndromes in Infancy, Childhood and Adolescence. Montrouge: John Libbey Eurotext Ltd; 2005:115–124. 44. Ohtahara S, Yamatogi Y. Epilepsy with myoclonic-astatic seizures. Epilepsies. 2000:223. 45. Dravet C, Bureau M, Oguni H, Fukuyama Y, Cokar O. (2005) Severe myoclonic epilepsy in infancy (Dravet syndrome). In: Roger J, Bureau M, Dravet C, Genton P, Tassinari CA, Wolf P, eds. Epileptic Syndromes In Infancy, Childhood and AdolescenceMountrouge: John Libbey Eurotext Ltd; 2005:89–113. 46. Guerrini R, Aicardi J. Epileptic encephalopathies with myoclonic seizures in infants and children (severe myoclonic epilepsy and myoclonic-astatic epilepsy). J Clin Neurophysiol. 2003;20(6):449. 47. Laan LA, Vein AA. Angelman syndrome: is there a characteristic EEG? Brain Dev. 2005;27(2):80–87. 48. Williams CA., Beaudet AL, Clayton-Smith J, Knoll JH, Kyllerman M, Laan LA, Magenis RE, Moncla A, Schinzel AA, Summers JA, et al. Angelman syndrome 2005: updated consensus for diagnostic criteria. Am J Med Genet A. 2006;140:413–418. 49. Korff C, Kelley K, Nordli Jr D. Notched delta, phenotype, and Angelman syndrome. J Clin Neurophysiol. 2005;22(4):238. 50. Guerrini R, Carrozzo R, Rinaldi R, Bonanni P. Angelman syndrome: etiology, clinical features, diagnosis, and management of symptoms. Pediatr Drugs. 2003;5:647–661. 51. Glaze DG. Neurophysiology of Rett syndrome. J Child Neurol. 2005;20(9):740–746. 52. Niedermeyer E, Rett A, Renner H, Murphy M, Naidu S Rett syndrome and the electroencephalogram. Am J Med Genet Suppl. 1986;1:195–199. 53. Palmini A, Andermann F, Olivier A, Tampieri D, Robitaille Y. Focal neuronal migration disorders and intractable partial epilepsy: results of surgical treatment. Ann Neurol. 1991;30:750–757.
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54. Granata T, Battaglia G, D'Incerti L, et al. Double cortex syndrome: electroclinical study of three cases. Ital J Neurol Sci. 1994;15(1):15–23. 55. Grant AC, Rho JM. Ictal EEG patterns in band heterotopia. Epilepsia. 2002;43(4):403–407. 56. Kato M, Dobyns W. Lissencephaly and the molecular basis of neuronal migration. Hum Mol Genet. 2003;12(Rev 1):R89. 57. Gastaut H, Pinsard M, Raybaud O, et al. Lissencephaly (agyria-pachygyria): clinical fi ndings and serial EEG studies. Dev Med Child Neurol. 1987;29(2): 167–180. 58. Worle H, Keimer R, Kohler B. [Miller-Dieker syndrome (type I lissencephaly) with specific EEG changes]. Monatsschr Kinderheilkd. 1990;138(9):615–618. 59. De Rijk-van Andel J, Arts W, De Weerd A. EEG and evoked potentials in a series of 21 patients with lissencephaly type I. Neuropediatrics. 1992;23(1):4–9. 60. Canafoglia L, Franceschetti S, Antozzi C, Carrara F, Farina L, Granata T, et al. Epileptic phenotypes associated with mitochondrial disorders. Neurology. 2001;56:1340–1346. 61. Acharya J, Satishchandra P, Shankar S. Familial progressive myoclonus epilepsy: clinical and electrophysiologic observations. Epilepsia. 1995;36(5):429–434. 62. Noachtar S, Arnold S eds. Clonic seizures. In: Lüders H, Noachtar S, eds. Epileptic Seizures: Pathophysiology and Clinical Semiology. Churchill Livingstone Philadelphia: Saunders; 2000. 63. Nabbout R, Soufflet C, Plouin P, Dulac O. Pyridoxine dependent-epilepsy: a suggestive electroclinical pattern. Arch Dis Child Fetal Neonatal Ed. 1999;81:F125–F129. 64. Mikati M, Trevathan E, Krishnamoorthy K, et al. Pyridoxine dependent epilepsy: EEG investigations and long-term follow-up. EEG Clin Neurophysiol. 1991;78:215–221. 65. Pampiglione G, Harden A. So-called neuronal ceroid lipofuscinosis. Neurophysiological studies in 60 children. J Neurol Neurosurg Psychiatry. 1977;40(4):323–330. 66. Blume W, Kaibara M. Atlas of Pediatric Encephalography. Philadelphia, PA: Lippincott-Raven; 1999. 67. Remler, Bradley W. Falls and drop attacks. In: Bradley W, ed. Neurology in Clinical Practice. Churchill Livingstone Philadelphia: Taylor & Francis; 1996.
8 68. Raieli V, Puma D, Brighina F. Role of neurophysiology in the clinical practice of primary pediatric headaches. Drug Dev Res. 2007;68(7). 69. Pavese N, Canapicchi R, Nuti A, et al. White matter MRI hyperintensities in a hundred and twenty-nine consecutive migraine patients. Cephalalgia. 1994;14: 312–345. 70. DiMario Jr F. Breath-holding spells in childhood. Arch Pediatr Adolesc Med. 1992;146(1):125. 71. Low N, Gibbs E, Gibbs F. Electroencephalographic findings in breath holding spells. Pediatrics. 1955;15(5):595. 72. Gastaut H, Fischer-Williams M. Electroencephalographic study of syncope; its differentiation from epilepsy. Lancet. 1957;273(7004):1018. 73. Brenner R. Electroencephalography in syncope. J Clin Neurophysiol. 1997;14(3):197. 74. Emery ES. Status epilepticus secondary to breath-holding and pallid syncopal spells. Neurology. 1990;40:859. 75. Moorjani B, Rothner A, Kotagal P. Breath-holding spells and prolonged seizures. Ann Neurol. 1995;38:512–513. 76. Stephenson JBP. Fits and Faints. London: Mac Keith Press; 1990. 77. Breningstall G. Breath-holding spells. Pediatr Neurol. 1996;14(2):91–97. 78. Fogoros R. Cardiac arrhythmias. Syncope and stroke. Neurologic Clinics. 1993;11(2):375. 79. Kapoor W, Hanusa B. Is syncope a risk factor for poor outcomes? Comparison of patients with and without syncope. Am J Med. 1996;100(6):646–655. 80. Morrell M. Differential diagnosis of seizures. Neurologic Clinics. 1993;11(4):737. 81. Abboud F. Neurocardiogenic syncope. N Engl J Med. 1993;328(15):1117. 82. Schott G, McLeod A, Jewitt D. Cardiac arrhythmias that masquerade as epilepsy. BMJ. 1977;1(6074):1454. 83. Ballardie F, Murphy R, Davis J. Epilepsy: a presentation of the Romano-Ward syndrome. BMJ. 1983;287(6396):896. 84. Blumhardt L. Ambulatory ECG and EEG monitoring of patients with blackouts. Br J Hosp Med. 1986;36(5):354. 85. Jennett B, Gleave J, Wilson P. Brain death in three neurosurgical units. BMJ. 1981;282(6263):533. 86. Maulsby R, Kellaway P. Transient hypoxic crises in children. In: Neurological and Electroencephalographic Correlative Studies in Infancy. 1964:349–360.
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Interictal epileptiform discharges (IEDs) associated with epilepsy 䡲
With clinical correlation, the high sensitivity and the specificity of IEDs for seizure disorders support the use of IEDs as the electrophysiological signature of an epileptogenic brain. 䡲 IEDs represent the macroscopic field created by the summation of potentials from pathologically synchronized bursting neurons.
Common types of IEDs
䡲
The epileptiform discharge should have a physiologic field and not be confined to a single electrode except in newborn.
䡲
Besides interictal epileptiform spikes and sharp waves, intermittent rhythmic delta activity over the temporal region (TIRDA) has similar specificity for temporal lobe epilepsy. 䡲 There are also localized, periodic patterns of IEDs that are associated with seizures. These periodic patterns of IEDs can be lateralized to one hemisphere, as seen in periodic lateralized epileptiform discharges (PLEDs), or can be bilateral or multifocal (BiPLEDs).
䡲
Spikes, polyspikes, sharp waves, and spike-andslow-wave complexes, which can be either focal or generalized. 䡲 The main types of generalized IED patterns are: 䊳 3-Hz spike and slow wave 䊳 Sharp and slow wave 䊳
Atypical repetitive spike and slow wave Multiple spike and slow wave
䊳
Paroxysmal fast activity (PFA)
䊳
Definition of IEDs and features 䡲
The epileptiform sharp waves and spikes are: 䊳 Transient waveforms that may repeat, and arise abruptly out of the EEG background activity. 䊳 The waveforms are asymmetric with more than one phase (usually two or three). In contrast, nonepileptiform, sharply contoured transients such as wicket waves are often approximately symmetric. 䡲 The epileptiform spikes and sharp waves are often followed by a smoothly contoured slow wave (spike-and-slow-wave complexes), which disrupts the ongoing EEG background rhythm. 䡲 The sharp wave or spike is produced by an abrupt change in voltage polarity that occurs over several milliseconds. The duration of an epileptiform sharp wave is between 70 and 200 msec, and the duration of spikes is less than 70 msec, although the distinction is of unclear clinical importance.
Types of interictal EEG patterns 䡲
Spikes, spike-wave discharges, polyspikes, or sharp waves (interictal epileptiform discharges [IEDs]). 䡲 Broad sharp or polyphasic sharp waves (duration > 200 msec). 䡲
Periodic lateralized epileptiform activity (PLEDs) or bilateral independent periodic lateralized epileptiform activity (BiPLEDs) in an acute/subacute cerebral insult. 䡲 Paroxysmal fast activity (PFA)—most commonly in Lennox-Gastaut syndrome. 䡲 䡲 䡲 䡲 䡲
䡲 䡲
Hypsarrhythmia in infantile spasm (hemihypsarrhythmia in focal, symptomatic infantile spasm). Temporal intermittent rhythmic delta activity (TIRDA) in mesial temporal epilepsy. Occipital intermittent rhythmic delta activity (OIRDA) in generalized epilepsy, especially absence epilepsy. Frontal intermittent rhythmic delta activity (FIRDA) rarely represents IED. Continuous, near-continuous, or long trains of localized spikes or rhythmic sharp waves (intrinsic epileptogenicity) in structural abnormalities, especially focal cortical dysplasia (FCD). Regional polyspikes (especially in extratemporal region) are highly associated with FCD (80%). Focal low-voltage fast activity or electrodecrement in scalp EEG corresponding to high-frequency oscillation (HFO) in intracranial EEG.
676
䡲
앫 Focal discharges that appear generalized on
Usually occur with focal slowing, especially polymorphic delta activity (PDA) and focal attenuation.
scalp EEG due to secondary bilateral synchrony (SBS) often can be detected by examining the discharges on an expanded timescale to detect if one hemisphere discharge precedes the other.
Interictal epileptiform discharges (IEDs) 䡲
䊳
IEDs can induce brief episodes of impaired cognitive function. 䡲 Six to 11 cm2 of synchronously discharging cortex are necessary to be detected by scalp electrodes. 䡲 The first EEG will uncover an IED in 30–50% of the patients with epilepsy, and the yield increases to 80–90% by the fourth EEG.
䡲 䡲
䡲 䡲
䡲 䡲 䡲
At least 0.5% in healthy young men. Twelve percent in all age groups and patients with progressive cerebral disorders. Majority of the reports could not establish the relationship between the AED level and the frequency of focal IEDs, although this issue remains controversial. Ten percent of patients with epilepsy extratemporal > temporal) show no IEDs. The yield of a single EEG is increased if: 䊳 EEG performed within 1–2 days after the seizure 䊳 Monthly seizures > seizure-free for a year: 䊳 NREM sleep—increased neuronal synchronization within thalamocortical projection neurons during NREM IEDs are most focal in REM and least in NREM. IEDs are most sensitive in NREM and least in REM. Wakefulness is between REM and NREM.
Usually is not difficult except in two relatively common situations: 䊳 Focal IEDs may manifest as secondary bilateral synchronous discharges:
䡲
Generalized IEDs in primary generalized epilepsy can have fragmentary expression: generalized epilepsy are typically maximal over the frontal head region with shifting lateralization and have morphologies similar to the generalized discharge 앫 Most common in JME (pseudolocalization)
Evidence for the importance of IEDs 䡲
Most studies evaluating the sensitivity and specificity of interictal EEG for the diagnosis of epilepsy have a number of methodological flaws: 䊳
䊳
䡲
䡲 䡲
Distinction between partial and generalized IEDs 䡲
proven epilepsy, 19% of patients had no IEDs after an average of 7 days of prolonged recording.
앫 The focal fragmentary discharges seen in primary
Frequency of IEDs 䡲
9
Focal Epilepsy
䡲
Epilepsy remains a clinical diagnosis, and some studies may include patients with incorrect diagnoses. Most studies are retrospective, originating at epilepsy centers and likely representing a significant referral bias toward patients with refractory epilepsy.
The specificity of IEDs as a marker for epilepsy depends strongly on the population studied. 䊳 Only 69 (0.5%) of 13,658 healthy men who were candidates for aircrew training had IEDs on a routine EEG. Between 5 and 29 years of clinical follow-up was available for 43 of the 69 patients with IEDs, and only 1 patient developed epilepsy.
In contrast, 12% of 521 nonepileptic patients residing in Rochester, MN, had IEDs on routine EEGs performed as part of a neurological evaluation. Seventy-three percent of the patients with IEDs had acute or progressive cerebral disorders. None of these patients had seizures during follow-up. 䡲 The results of interictal EEG should be interpreted within the clinical setting, especially in patients with neurological disorders, structural lesions, or previous craniotomy. 䊳
Continuous polymorphic delta activity (PDA) 䡲
Retrospective studies show that IEDs are demonstrated on the initial EEG in 30–50% of patients with the clinical diagnosis of epilepsy.
In scalp EEG, slow-wave activity was present in 62%. Its distribution was most commonly regional and then multiregional, or generalized respectively. The slow-wave activity was more commonly absent in temporal than extratemporal tumor groups.
䡲
The sensitivity can often be increased to 80–90% by the use of serial routine EEG up to four EEGs.
Highly correlated with a focal structural lesion, more prominent in acute than chronic processes.
䡲
In patients with infrequent seizures, the initial and subsequent EEGs are likely to show a lower sensitivity. In a study of patients who had a single seizure, only 12% had IEDs on their first EEG. A subsequent EEG showed IEDs in an additional 14% of these patients, for a cumulative sensitivity of 26% after two EEGs. There are also patients with refractory epilepsy and infrequent IEDs, e.g., patients with mesial frontal lobe seizure disorders. In a study that examined IEDs in the continuous long-term EEG records of patients with
PDA is often surrounded by theta waves and maximally expressed over the lesions. 䡲 Superficial lesions cause more restricted field, and deeper lesions cause hemispheric or even bilateral distribution. 䡲
A lower voltage of PDA is seen over the area of maximal cerebral involvement, but a higher voltage PDA is noted in the border of lesions. 䡲 More severe PDAs (closer to the lesion, more acute, higher association with underlying structural abnormality) consist of the following:
9 1. Greater variability (most irregular or least rhythmic) 2. Slower frequency 3. Greater persistence
Focal Epilepsy
Positive sharp waves (PSWs) 䡲
4. Less reactivity 5. No superimposed beta activity 6. Less intermixed activity above 4 Hz
Periodic lateralized epileptiform discharges (PLEDs) 䡲
䡲
䡲 䡲
䡲
䡲
䡲
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PLEDs define an EEG pattern consisting of sharp waves, spikes (alone or associated with slow waves), or more complex waveforms occurring at periodic intervals. PLEDs usually occur at the rate of 1–2/sec and are commonly seen in the posterior head region, especially in the parietal areas. They are sometimes associated with EPC. Usually related to an acute or subacute focal brain lesion involving gray matter. Chronic PLEDs were also reported in 9% of patients with intractable epilepsy who had structural abnormalities such as cortical dysplasia or severe remote cerebral injury. PLEDs usually represent acute or subacute cerebral insults. However, in a review of 96 patients with PLEDs, 9 cases of chronic PLEDs (6.2%) were seen in patients with symptomatic focal epilepsy caused by underlying FCD or severe remote cerebral injury. Acute stroke, tumor, and CNS infection were the most common etiologies. Others included acute hemorrhage, TBI, PRES, familial hemiplegic migraine, and cerebral amyloidosis. PLEDs were more periodic when they were associated with acute viral encephalitis than with other etiologies. Seizure activity occurred in 85% of patients with mortality rate of 27%. However, 50% of patients with PLEDs never developed clinical seizures.
Not epileptiform activity and not directly associated with neonatal seizures but rather with underlying structural abnormalities, especially in the deep cerebral white matter, and can be seen in a variety of conditions, including periventricular leukomalacia, hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or HIE.
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Benign EEG variants not associated with seizures 䡲
Can be mistaken for IEDs, including: 䊳 Wicket waves 䊳 Small sharp spikes (SSS) 䊳 Rhythmic temporal theta of drowsiness (RTTD) 䊳 䊳
Limitation of scalp EEG 䡲
Impedance of the CSF, meninges, skull, and scalp.
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Deep or midline epileptogenic foci.
Distribution of EEG 䡲
Affected by: 䊳 Conductive properties 䊳 Spatial characteristics of generator 䊳 䊳
Propagation pathway Spatial resolution of surface EEG
Falsely localizing temporal IEDs 䡲
Frontal.
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Parietal. Occipital.
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Insular-opercular. 䡲 Orbitofrontal.
Pitfalls encountered in identifying IEDs 䡲
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Common pitfalls in identifying IEDs include misinterpretation of noncerebral potentials, benign cerebral transients and patterns, and artifacts. The electrodes, the recording equipment, or other electrical devices can produce artifacts. Artifacts can be especially challenging to distinguish in the hospital or intensive-care setting. Artifacts arising from swallowing, eye movements, body movements, sweating, pulse, and an electrocardiogram can be seen. These can be overcome by reviewing simultaneous video recording and annotation by the EEG technologist.
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Subclinical electrographic discharge of adults (SREDA) 14- and 6-Hz positive bursts 6-Hz spike and slow wave Paroxysmal hypnogogic hypersynchrony
Midline theta rhythms 䡲 In practice, IEDs often lack some of the characteristic features listed previously, whereas some nonepileptiform discharges can demonstrate many of these characteristics. 䡲 It is often useful to review possible IEDs by using different electrode montages, e.g., bipolar, referential, and laplacian recording montages. This often allows a more accurate understanding of the cerebral potential. 䡲 The choice of montage can make discharges appear more focal or generalized; the Laplacian montage can make a generalized discharge appear more focal, whereas a referential montage, when the reference electrode is active, may make a focal discharge appear generalized. 䊳
Ictal EEG pattern in focal epilepsy Characteristics 䡲 䡲
Almost always stereotyped for an individual.
Evolving repetitive sharp waves/spikes. Infrequently, lack of evolution, regular repetitive spikes, desynchronization, or regular rhythmic slowing is noted. 䡲 Evolution of frequency, amplitude, topography, and morphology. 䡲 May have generalization at the onset such as slowing, attenuation, or high-amplitude sharp waves lasting only a few seconds.
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May cause secondary generalization.
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Postictal slowing or depression usually occurs in the ictal onset zone.
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Postictally increased focal epileptiform activity in the ictal onset zone.
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Surface ictal EEG was adequately localized in 72% of cases, more often in temporal than extratemporal epilepsy.
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Localized ictal onsets were seen in 57% of seizures and were most common in: 䊳
Mesial temporal lobe epilepsy (MTLE)
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Lateral frontal lobe epilepsy (LFLE)
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Parietal lobe epilepsy (PLE)
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Lateralized onset predominates in neocortical temporal lobe epilepsy.
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Generalized onset predominates in: 䊳
Mesial frontal lobe epilepsy (MFLE)
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Occipital lobe epilepsy (OLE)
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Approximately two-thirds of seizures were localized, 22% generalized, 4% lateralized, and 6% mislocalized/ lateralized.
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False localization/lateralization occurred in 28% of occipital and 16% of parietal seizures.
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Rhythmic temporal theta at ictal onset was seen exclusively in temporal lobe seizures.
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Localized repetitive epileptiform activity was highly predictive of LFLE.
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Seizures arising from the lateral convexity and mesial regions of frontal lobe were differentiated by a high incidence of repetitive epileptiform activity at ictal onset in the former and rhythmic theta activity in the latter.
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With the exception of MFLE, ictal recordings are very useful in the localization/lateralization of focal seizures. Some patterns are highly accurate in localizing the epileptogenic lobe.
One limitation of ictal EEG is the potential for false localization/lateralization in occipital and parietal lobe epilepsies.
Start-stop-start phenomenon 䡲
HFOs characterized by very fast activity, ranging from 80 to 150 Hz, are noted at the epileptic focus in neocortical epilepsy during subdural EEG recording. Recent findings suggest that HFOs ranging between 100 and 500 Hz might be closely linked to epileptogenesis. Ripples (80–160 Hz) and fast ripples (250–500 Hz) occur frequently during IEDs and may reflect pathological hypersynchronous events. During ictal recordings, HFOs could be identified and occurred mostly in the region of primary epileptogenesis and less frequently in areas of secondary spread. HFOs are an important electrophysiological manifestation of the epileptic tissue and are associated with the spiking region and somewhat with the seizure-onset zone (SOZ). Although ripples and fast ripples share some characteristics, increasing in the SOZ and spiking regions, fast ripples are more specific to the SOZ region than ripples.
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The start-stop-start (SSS) phenomenon is defined as a pair of sequential ictal potentials separated by complete or almost complete cessation of seizure activity; the SSS phenomenon was found on subdural recordings in 23% of 98 patients. The two phases were morphologically similar. The first “start” usually had a narrow field. Fifty-eight percent of SSS seizures showed a complete stop. Thirty-five percent of patients and seizures restarted in a different location than the first start. When in different locations, the start, not the restart, is correlated with non-SSS origin. SSS seizures arose in the same region as nonSSS seizures in almost all patients. Subsequently, the SSS phenomenon was also observed in scalp EEG, sphenoidal, and foramen ovale electrodes, and the recognition of the phenomenon may improve the accuracy of seizure localization.
Secondary bilateral synchrony 䡲
Generalized spike-wave (GSW) discharges are a hallmark of idiopathic generalized epilepsy (IGE). The reticular thalamic nucleus is the pacemaker structure for the rhythmic cortical oscillations in spindle frequency range, which transform into GSW activity in IGE. The nucleus anterior thalami and the zona incerta have an important role in SBS.
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GSW discharges were described in patients with shunted hydrocephalus and in hypothalamic lesions.
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In the generation of GSW, the cortex is considered to be the decisive factor, while the thalamus is involved secondarily.
General consideration 䡲
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Focal Epilepsy
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The primary role in the synchronized activity of the thalamus and cortex is attributed to the reticular nucleus. Zona incerta contains a GABAergic inhibitory effect on the higher order thalamic nuclei projecting to the neocortex and results in effective, statedependent gating of thalamocortical information. 䡲 A lesion of this system can lead to disinhibition and marked activation of the paroxysmal activity in sleep. 䡲
Alterations in normal thalamocortical reciprocal interactions are critical in the generation of the regular GSW discharges characteristic of the idiopathic generalized epilepsies. 䡲 Most patients with unilateral thalamic lesion and epilepsy showed bilateral synchronous GSW discharges. 䡲
Absence status with bilateral GSW discharges caused by an seizure lesion in the left thalamus was reported. 䡲 Children with thalamic lesion should be monitored closely for ESES. Lesions of the inferior-medialposterior thalamic structures might have a role in the pathogenesis of bilateral SW discharges and ESES by a mechanism of disinhibition, possibly through the GABAergic system of zona incerta and its projections.
Ictal slow DC shift 䡲
An ictal slow DC shift is a slow and sustained change in EEG voltage resulting from a change in the function or interaction of neurons, glia, or both.
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Ictal slow baseline shifts could be recorded with DC amplifiers. They were not seen with conventional EEG systems. When the high-pass filter was opened to 0.01–0.1 Hz, ictal baseline shifts were present in scalp and intracranially recorded seizures and could have localizing value. Usually scalp-recorded ictal DC shifts are not successfully recorded because movements during clinical seizures cause artifacts. They are highly specific but low in sensitivity. Ictal DC shifts were seen in 14–40% of recorded seizures with sensitivity varying. Scalp-recorded DC shifts were detected when seizures were clinically intense, while no slow shifts were observed in small seizures. They were restricted to one to two electrodes, very closely related to the onset of low-voltage fast activity and electrodecrement. Ikeda concluded that (1) ictal DC shifts were observed in 85% of all the recorded seizures in subdural EEG and in 23% of all the scalp EEG recordings, by using LFF of 0.016 Hz for the AC amplifier; (2) ictal DC shifts were mainly surface-negative in polarity; (3) they started 1–10 sec earlier than the conventional ictal EEG onset; (4) ictal DC shifts were seen in a more restricted area (one to two electrodes) compared with the dimension defined by the conventional ictal EEG changes; (5) ictal DC shifts often coincided with the electrodecremental pattern; (6) scalp-recorded ictal slow shifts have high specificity but low sensitivity; (7) a DC amplifier is not necessary to record slow DC shifts; instead, an AC amplifier with long time constant could be used.
Focal Epilepsy
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Closely spaced scalp electrodes can improve the yield of spike detection and localization over the standard 10-20 System.
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The advantages of using sphenoid electrodes, even implanted under fluoroscopic control, over T1 and T2 electrodes are unclear. Anterior temporal electrodes are able to detect nearly all IEDs recorded by the foramen ovale. Therefore, assuming that the location of the latter is analogous to that of sphenoidal electrodes optimally, the use of sphenoidal electrodes in routine interictal investigations is controversial.
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Additional electrodes 䡲
Can be used to supplement the standard 10-20 System. 䡲 Added sensitivity of additional anterior temporal region surface electrodes for recording IEDs—97% of spikes are detected using additional anterior temporal region surface electrodes, whereas 58% of spikes are detected using only 10-20 System electrodes.
Areas that sphenoidal electrodes may help: 䊳 Mesial temporal Lateral temporal Orbitofrontal
Epileptiform discharges in temporal lobe epilepsy tend to produce a stereotyped pattern on the scalp, with largest amplitudes at the anterior temporal electrodes, independent of the topographic distribution of corticographic discharges. All these findings can be explained by assuming that a significant proportion of the electrical signal reaches the scalp through high-conductivity holes in the skull, such as the foramen ovale, the optic foramen, or the superior orbital fissure. As the optic foramen, the superior orbital fissure, and the foramen ovale are located anteriorly, this hypothesis would also explain the higher sensitivity of T1 and T2 electrodes to detect discharges in comparison to A1/A2 or T3/T4 electrodes, which are situated, however, anatomically nearer to the temporal lobe.
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Photic stimulation can activate IEDs— photoparoxysmal response. 䡲 Between 70% and 77% of individuals with generalized IEDs activated by photic stimulation have epilepsy. 䡲
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The photoparoxysmal response must be distinguished from the photomyogenic response, a noncerebral myogenic and eye movement artifact that usually ceases when the stimulus is stopped. 䡲 In patients with nonepileptic seizures, provocative testing and suggestion can frequently elicit the patient’s spell, although some clinicians question the ethical and diagnostic merits of provocative testing in such patients.
Ambulatory EEG 䡲
Improved sensitivity of prolonged recordings for detecting IEDs and seizures, with a “clinically useful” result achieved in 74% of patients in a large outpatient study. 䡲 Of patients with previously normal or nonspecific routine EEGs, clinically useful findings were obtained in 67.5%. Clinically useful findings included recordings of habitual events (normal and abnormal) and detection of subclinical EEG abnormalities. 䡲
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Sleep deprivation before routine EEG can increase the yield of recorded IEDs in patients with epilepsy by 30–70%. 䡲 Hyperventilation can activate IEDs and ictal EEG discharges in patients with absence seizures and complex partial seizures.
Ambulatory EEG is a useful tool for determining seizure frequency and response to treatment.
Magnetoencephalogram (MEG) 䡲
Activation methods
The IEDs associated with photic stimulation frequently outlast the photic stimulus by seconds and can evolve into a seizure.
MEG has a similar sensitivity to detect IEDs as scalp EEG. 䡲 MEG identified IEDs in one-third of EEG-negative patients, especially in cases of lateral neocortical epilepsies and epilepsies due to FCD. 䡲 Surface ictal EEG was adequately localized in 72% of cases, more often in temporal than extratemporal epilepsy.
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Localized ictal onsets were seen in 57% of seizures and were most common in: 䊳 MTLE 䊳 LFLE 䊳 Parietal lobe epilepsy Lateralized onsets predominated in neocortical temporal lobe epilepsy. Generalized onsets in: 䊳 MFLE 䊳 Occipital lobe epilepsy Approximately two-thirds of seizures were localized, 22% generalized, 4% lateralized, and 6% mislocalized/ lateralized. False localization/lateralization occurred in 28% of occipital and 16% of parietal seizures. Rhythmic temporal theta at ictal onset was seen exclusively in temporal lobe seizures. Localized repetitive epileptiform activity was highly predictive of LFLE. Seizures arising from the lateral convexity and mesial regions were differentiated by a high incidence of repetitive epileptiform activity at ictal onset in the former and rhythmic theta activity in the latter. With the exception of mesial frontal lobe epilepsy, ictal recordings are very useful in the localization/ lateralization of focal seizures. Some patterns are highly accurate in localizing the epileptogenic lobe. One limitation of ictal EEG is the potential for false localization/lateralization in occipital and parietal lobe epilepsies.
EEG criteria of poor prognosis in focal epilepsies in children 䡲 䡲 䡲 䡲 䡲 䡲
Abnormal asymmetric background activity. Continuous focal slow waves. Multifocal or diffuse epileptiform discharges. Disappearance of changes in REM sleep. Localized background flattening. Generalized or focal PFA.
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Focal Epilepsy
Focal cortical dysplasia (FCD) and epilepsy 䡲
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Higher amplitude of the background activity, especially beta activity on the side of a focal cerebral lesion, is rarely seen in the following conditions: tumor, FCD, abscess, stroke, and arteriovenous malformation. FCD is often associated with severe focal epilepsy. Intraoperative electrocorticography (ECoG) showed one of the following patterns:
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1. Repetitive electrographic seizures 2. Repetitive bursting discharges 3. Continuous or quasicontinuous rhythmic spiking One or more of these patterns were present in 67% with intractable focal epilepsy associated with FCD, and in only 2.5% with intractable focal epilepsy associated with other types of structural lesions. 䡲 These ictal or continuous epileptogenic discharges (I/CEDs) were usually localized, which contrast with the more widespread interictal ECoG epileptic activity, and tended to correspond with the lesion seen in the MRI. 䡲 Complete resection of the FCD displaying I/CEDs correlated with good surgical outcome. Three-fourths of the patients in whom the FCD displaying I/CEDs was entirely excised had favorable surgical outcome. FCDs are highly and intrinsically epileptogenic, and intraoperative ECoG identification of the intrinsically epileptogenic dysplastic cortical tissue is critical to decide the extent of excision. 䡲
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Trains of continuous or very frequent rhythmic spikes or sharp waves and recurrent electrographic seizures on the scalp EEG were seen in up to 44% of FCD in one series. 䡲 Eighty-six percent of patients with FCD also had localized PDA suggesting a structural lesion. 䡲 Localized PDA recorded over neocortical lesions is due to underlying white matter abnormalities rather than the lesion itself. Developmental abnormalities affecting gyri are associated with underlying changes in the white matter. Malformations of cortical development
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must be in the differential diagnosis for localized PDA, especially when associated with epileptiform activity. Interictal low-voltage beta activity seen in FCD represents intrinsic epileptogenicity. Intrinsic epileptogenicity in FCD is caused by abnormal synaptic interconnectivity and neurotransmitter changes within the lesion. FCD has intrinsic epileptogenicity with unique EEG patterns including: 䊳 Continuous spikes or sharp waves 䊳 Abrupt runs of high-frequency spikes 䊳 Rhythmic sharp waves 䊳 Periodic spike complexes that occur during sleep The incidences of intrinsic epileptogencity in FCD were 11–20%. In all patients with FCD, the SOZ was located within the lesion. Lesional non-SOZ areas might not be directly involved in the seizure origin but might turn into a seizure focus after the removal of primary epileptogenic tissue; therefore, removal of the entire lesion and surrounding interictally active tissue is necessary. Removal of the FCD alone does not lead to a good outcome, suggesting a more widespread epileptogenic network. A strong relationship was observed between the presence of rhythmic epileptiform discharges (REDs) on the scalp EEGs and the occurrence of continuous epileptiform discharges (CEDs) recorded on ECoG. Eighty percent of patients with REDs had CEDs. Regional polyspikes, especially in extratemporal region, are highly associated with FCD (80%) and should lead the clinician to perform advanced MRI studies to detect FCD. FCD is associated with REDs.
Hemimegalencephaly and epilepsy 䡲
Interictal electroencephalograms revealed asymmetric suppression-burst patterns, frequent focal discharges, a nearly continuous burst-suppression pattern over the malformed hemisphere.
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As with interictal EEG patterns, an asymmetric ictal pattern correlates with focal or lateralized structural abnormality of the brain.
Three types of EEG abnormalities in hemimegalencephaly Triphasic Complexes of Very Large Amplitude 䡲 Consists of a small negative wave, followed by a largeamplitude, positive slow spike. This was followed by a very slow wave, of large amplitude sometimes, which formed a plateau, often associated with monomorphic, sharp theta activity of moderate amplitude. This pattern was observed in patients with partial seizures. 䡲
They are seen in patients with the earliest onset of seizures and were associated with the poorest prognosis.
Asymmetrical Suppression-Burst Pattern, with Bursts of “Alpha-Like” Activity 䡲 Interrupted by hypoactive phases on the affected side and, on the unaffected side, bursts of large-amplitude, polymorphic polyspikes of the type usually observed in suppression-burst tracings. This pattern was observed at birth or after a few months and coincided with Ohtahara syndrome. It can also be recorded until adult life in patients with epilepsia partialis continua.
Focal Epilepsy
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An “Alpha-Like” Activity 䡲 Consists of an asymmetrical and large-amplitude, sharp, nonreactive 7- to 12-Hz rhythm, little modified by waking state, apart from the association of slow waves during sleep, which tends to be focused in the abnormal hemisphere. This pattern was recorded in patients with seizures occurring after three months of age and associated with better outcome. Asymmetric hypsarrhythmia originating on the affected side is also noted.
Periventricular nodular heterotopia (PNH) and epilepsy IEDs in PNH 䡲
Focal interictal EEG abnormalities are always consistent with anatomic location of the PNH.
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In slow sleep, focal abnormalities frequently change in bilaterally diffuse bursts of polyspikes. Multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions. In a minority of patients, 3- to 4-Hz spike-wave discharges, mimicking primary generalized epilepsy, are noted. Ictal EEG abnormalities at the onset and immediately after the end of the seizures were always localized to the brain regions where PNH was located. These findings suggest that epileptic discharges may originate from abnormal circuitries located close to or involving the PNH. Epilepsy in PNH patients is generated by abnormal anatomic circuitries including the heterotopic nodules and adjacent archicortical and neocortical areas. In the patient with medically intractable epilepsy, the surgical outcome can be very favorable if the abnormal circuitry generating seizures is carefully assessed before and then removed with epilepsy surgery. Patients with PNH and epilepsy represent a heterogeneous group. Seizures result from complex interactions between PNH and allo- or neocortex. A reduction of GABA-mediated inhibitory activity was demonstrated in both the cortex and the heterotopic gray matter. Abnormalities of cortical architecture, and of cortical neuronal composition and connectivity, may allow the cortex to act as a primary epileptogenic substrate. Patients with nodular heterotopia have a high incidence of cortical abnormalities such as atrophy and polymicrogyria in addition to hippocampal atrophy. Fifty-four percent of patients with PNH have visually detectable cortical abnormalities. In most patients with bilateral and symmetric PNH, no neurologic deficits or mental retardation are present. However, the lower limits of normal IQ scores and learning disability were noted. Epilepsy is the main clinical symptom in PNH. In patients with bilateral PNH, epilepsy onset is in the second decade of life, preceded by infantile febrile convulsions. GTCS is rare
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and easily controlled. Focal seizures are observed in all patients and are intractable to medical treatment. Status epilepticus is never observed. 䡲 A close relationship exists between heterotopic nodules and cortical regions in bilateral PNH, with an epileptogenic network including both structures. This finding may explain why a limited surgical resection to the temporal lobe fails to stop the seizures in these patients. 䡲 Unilateral PNH is frequently located in the posterior paratrigonal region (i.e., a watershed area) of the lateral ventricles and may extend into the white matter to involve adjacent neocortical and archicortical areas. Epilepsy in PNH patients is generated by abnormal anatomic circuitries including the heterotopic nodules and adjacent archicortical and neocortical areas. 䡲
Regardless of the different MRI features, the main clinical problem in most PNH patients is the presence of focal drug-resistant epilepsy.
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The presence of risk factors for prenatal brain damage, the common location in the paratrigonal region, and the lack of familial cases all suggest that acquired factors, damaging a limited region of the developing brain, may provoke the genesis of unilateral nodules. The selective ablation of a subpopulation of dividing neuroblasts alter the migration and differentiation of subsequently generated neurons, which in turn set the base for the formation of heterotopia.
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The clinical picture is related to the amount of heterotopic tissue, the distribution of nodules, and the extension to the overlying cortex. Therefore, the outcome is much more favorable in patients with unilateral PNH, especially single-nodule PNH, compared to patients with PNH associated with periventricular and subcortical nodules extending to the neocortex.
Frontal epileptiform patterns 䡲
Next to temporal lobe-onset seizures, frontal lobeonset seizures are the most frequent type of focal seizures.
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Frontal seizures can occur at any age and are often caused by structural abnormalities, such as mass lesions, vascular lesions, trauma, or congenital abnormalities, that give rise to the seizures. 䡲 Limitations of scalp EEG recording in the frontal lobe: 䊳 Inherent risk of sampling error, since only a small portion of the frontal lobe is accessible: 앫 Mesial interhemispheric convexity 앫 Cingulate cortex 앫 Depth of the cerebral sulci 䊳 Trend of frontal lobe seizures to undergo rapid seizure spread within and outside the frontal lobe: 앫 Seizure propagation to the temporal lobe via the uncinate fasciculus or the cingulum may result in a constellation of clinical and electrographic features resembling a TLS. 䊳 Small epileptogenic lesions located in the depth of frontal lobe, beyond the resolution of scalp recording, which may be reflected as a widespread epileptic disturbance recorded over the fronto-parasagittal or fronto-temporal convexity, thus resembling a large epileptogenic zone, especially ipsilateral fronto-centro-temporal region. 䊳 Bifrontal or generalized interictal or ictal epileptic abnormalities are commonly recorded in patients with unilateral FLE: 앫 Mesial parasagittal convexity 앫 Orbitofrontal region 앫 Cingular region 앫 Anterofrontal convexity 䡲 Certain factors contribute to difficulty with localization: 䊳
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Focal onset obscured by the rapid spread to other areas. Brief duration of seizure. Little or no postictal change, and the discharge may be obscured by muscle artifact. Clinical seizure may occur before the ictal discharge is apparent on the EEG.
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Focal Epilepsy
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Ictal EEG discharge may occur without the patient being aware of the seizure (subclinical).
Frontal absence 䡲
Seen in frontal lobe epilepsy with epileptic foci in either mesial frontal or orbitofrontal regions. 䡲 Generalized absences and frontal absences may show similar clinical and EEG features and involve the same neuronal circuits.
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The neuronal system primarily involved in these seizures consists of a relatively limited cortico-thalamocortical circuit, including the reticular thalamic nucleus, the thalamocortical relay and the predominantly anterior and mesial frontal cerebral cortex, with the cortex probably acting as the primary driving site. 䡲 The anterior cingulate gyrus is involved in selfregulation of fronto-thalamic circuits and may play an important role in both maintenance of arousal and generalized epilepsy in human. 䡲
Absence seizures may not be truly generalized but rather involve selective cortical networks as described above. 䡲 Can be caused by epileptic discharges arising from several areas of frontal region, including SSMA, orbitofrontal region, and cingulate gyrus. 䡲
Compared with absences of childhood absence epilepsy, frontal lobe absences may have subtle repetitive vocalization, rocking movements, mild version, and brief postictal confusion. 䡲 The patient may report awareness of motor arrest without loss of consciousness. Staring may evolve into a secondarily GTCS with version of the head and eyes, and focal or bilateral tonic posturing of upper limb(s). 䡲 Frontal absences seem to have a more anterior epileptogenic zone than those with bilateral asymmetric tonic seizures. However, the clinical and EEG features can be very close to that of a typical or simple absence seizure.
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Interictal patterns in frontal lobe epilepsy 䡲
A variety of IEDs can be seen with frontal seizures: 䊳 Spikes
Sharp waves 䊳 Spike and wave 䊳 Multiple spikes or multiple spikes and waves 䊳 Periodic sharp- and slow-wave complexes 䊳 Low-voltage fast rhythms 䊳 PFA The interictal discharges can occur as: 䊳 Focal discharges 䊳 Unilateral discharges over one frontal lobe 䊳 Multifocal discharges over one frontal lobe 䊳 Lateralized hemispheric discharges 䊳 Bifrontal spike or spike-and-wave discharges that are symmetric or asymmetric 䊳 Bilaterally synchronous generalized spike and spike-and-wave discharges 䊳 SBS with a consistent focal onset in one region 䊳 On occasion, no epileptiform activity may be apparent: 앫 SSMA 앫 Orbitofrontal 앫 Ictal EEG activity in patients with SBS 앫 Epilepsia partialis continua False localization in temporal lobe foci: 䊳 Orbitofrontal lesion 䊳 Mesial frontal lesion—projection through limbic pathway Secondarily generalized discharges are a common occurrence with frontal lobe epilepsy. The EEG findings that suggest SBS include: 1. Focal spikes or sharp waves consistently occurring in one area 2. Focal spike discharges that precede or initiate more generalized bursts 3. Persistent lateralized abnormalities such as slowing or an asymmetry over the involved area Because bilateral synchronous discharges in primary generalized epilepsy are not always perfectly 䊳
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synchronous and symmetric, overinterpretation of SBS should be avoided. Persistent focal abnormality in one area and with consistent initiation of most of the bursts of bilateral synchrony throughout the recording is very important to avoid this error of overinterpretation. Epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity, which is most likely the result of a horizontal dipole located within the interhemispheric fissure. Prolonged interictal EEG in mesial frontal epilepsy showed normal findings in 9%, and focal sharp waves were increased or appeared exclusively during sleep in the remaining patients. Interictal sharp waves were over the vertex in 90% and over the ipsilateral frontal-central region in 10%. Vertex sharp waves were asymmetric with greater distribution over the ipsilateral parasagittal region on one side in 40%. Midline fronto-central IEDs were found in 38–50% of patients with SSMA seizures. Rhythmical midline theta (RMT) activity not related to drowsiness or mental activation is significantly more common in patients with frontal (48.1%) than with temporal (3.7%) lobe epilepsy.
The localizing value of RMT activity is even more important in those patients with FLE who do not have any IEDs (24%). RMT was observed in the majority of these patients with FLE (62%). 䡲 Interictal RMT activity is, thus, common and has a localizing value in patients with FLE, provided that conditions such as drowsiness and mental activation as confounding factors for RMT activity are excluded. 䡲 Midline IEDs can sometimes be difficult to differentiate from vertex waves. The clues to differentiate between these two are: 1. After-going slow waves in IEDs. 2 Narrower and more persistently asymmetric field in IEDs.
Focal Epilepsy
3. Presence of the same midline IEDs during wakefulness. Paradoxical lateralization of IEDs was seen in 25%. 䡲 Other nonepileptiform EEG abnormalities that may be present and may give a clue to the abnormal side are focal or lateralized slowing or an asymmetry of activity over the two hemispheres. 䡲 Special electrodes may be helpful in distinguishing temporal from frontal foci (sphenoid, T1/T2, closely spaced additional electrodes). 䡲 IEDs in orbitofrontal epilepsy, including (1) SBS; (2) anterior temporal IED; (3) central or frontro-central IED; (4) bifrontal IED caused by volume conduction; (5) contralateral frontal IED; (6) large or blunted bifrontal or fronto-polar sharp waves with or without additional temporal involvement; and (7) various multilobar locations. At times, EEG can be normal.
Ictal patterns in frontal lobe epilepsy 䡲
Ictal discharges can be complex and quite variable, including: 䊳 Low-voltage fast activity 䊳 Incrementing or recruiting rhythm 䊳 Repetitive spikes or spikes and slow waves 䊳 Rhythmic slow waves 䊳 High-voltage sharp waves 䊳 Focal or widespread attenuation 䊳 Flattening of the background 䡲 At times, the seizure may be “electrically silent,” with no apparent change evident in the EEG. 䡲 In contrast to seizures arising from the temporal lobe, spike-and-wave, paroxysmal fast, and poly-frequency discharges with rapid spread are more likely to be seen with extratemporal and, particularly, with frontal seizures. 䡲
As with interictal discharges, the ictal discharges may be focal, unilateral in onset, lateralized asymmetric, bilaterally synchronous, or secondarily generalized. 䡲 In contrast to temporal lobe seizures, the ictal discharges are frequently more widespread and may
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become evident later in the course of the clinical seizure. 䡲 Precise localization of frontal lobe epilepsy is often difficult and may be misleading, due to: 䊳 Limitations of scalp recordings because of the anatomy of the frontal lobe and the network of projection pathways that allow the rapid spread of seizure activity within the frontal lobes or outside the temporal lobes. 䊳 Widespread areas of epileptogenicity or multiple foci of seizure generators within the frontal lobe. 䊳 Missed epileptic focus with scalp recordings, which may not show the focal onset or may not even show the seizure activity itself because of the inaccessibility of certain areas of the frontal lobe to scalp electrode, including: 앫 Orbitofrontal lobe 앫 Mesial frontal lobe 앫 Cingulum 앫 SSMA 䊳 The focus may be too distant from the scalp electrodes. 䊳 Small localized foci may not be apparent on scalp recordings because a certain population size of neurons is required for a focus to be propagated to the surface. 䊳 The spike discharges that may be present may not represent the primary focus because the lesion could be projected from a buried focus within deep cortical areas. 䡲 In general, well-localized frontal foci are the exception. More often, the discharges occur in a regional or lateralized manner or as bilateral discharges with or without a lateralized predominance. 䡲 Bisynchronous frontal or generalized interictal and ictal discharges are often seen with seizures originating from: 䊳 Orbitofrontal lobe 䊳 Cingulate gyrus 䊳 SSMA
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Frontal lobe seizures are often manifested by widespread seizure discharges with poor localization or lateralization, because frontal lobe seizures commonly propagate to contralateral frontal regions and ipsilateral temporal regions, causing a false localization. 䡲 Secondarily generalized discharges are a common occurrence with frontal lobe epilepsy. The EEG findings that suggest secondary bilateral synchrony or secondary generalized discharges include: 䊳 Focal spikes or sharp waves consistently occurring in one area. 䊳 Focal spike discharges that precede or initiate more generalized bursts. 䊳 Persistent lateralized abnormalities such as slowing or an asymmetry over the involved area. 䊳 Seizures arising from the mesial frontal lobe are challenging to localize. 䊳 Rhythmic alpha, beta, or theta at or adjacent to the midline was observed in 45% of cases 䊳 PFA was observed at the onset of seizures arising from the inferior aspect of the SSMA and cingulate gyrus. 䡲 Only 25% of mesial frontal seizures showed a localized or lateralized ictal EEG. Ictal EEG showed no EEG change or EEG was obscured by muscle artifact in more than 50%. 䡲 Seizures from SSMA most commonly show PFA (33%) or electrodecrement (29%) as the initial ictal pattern, whereas seizures from lateral frontal lobe show repetitive epileptic discharges (36%) or rhythmic delta at onset (26%).
zone commonly extend beyond the SSMA to the primary motor cortex, premotor cortex, cingulate gyrus, and mesial parietal lobe. 䡲 Intracranial or depth recording may be helpful in patients who may be candidates for surgery for more accurate localization of the seizure focus.
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The discharges can occur singly or in brief clusters of two to four in a row.
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The spike discharges are maximal over the central midtemporal regions.
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If extra electrodes are placed over the lower rolandic area midway between the central and the midtemporal electrodes, the discharge is usually maximal in these electrodes.
Only 25% of SSMA epilepsy seizures showed correct localization or lateralization, and 75% showed no lateralization. Lateral frontal epilepsy showed correct localization in 60% and correct lateralization in an additional 27%. 䡲 Although ictal involvement of SSMA produces bilateral tonic stiffening, ictal onset exclusively in SSMA is rare. The ictal onset zone and epileptogenic
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Focal Epilepsy
Central midtemporal spikes 䡲
The central midtemporal spikes are characteristically present in children with benign epilepsy of childhood with centro-temporal spikes (BECTS). 䡲 Usually, the centro-temporal spike discharges are seen in children between 5 and 10 years of age. 䡲 BECTS are characterized by focal twitching or paresthesias involving the hand or face on one side, and during the seizure the patient is unable to speak and exhibits excessive drooling or salivation. The seizures may spread and become generalized. Often they occur at night. The seizures are easily controlled with antiepileptic drugs (AEDs) and resolve after childhood. The children are usually otherwise normal and have no underlying lesion.
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The discharge may occur unilaterally, bilaterally, asynchronously, or synchronously with an asymmetric amplitude.
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At times the EEG shows what appears to be generalized bursts, but these may merely represent a widespread reflection of the centro-temporal spike discharges.
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The discharges can shift from side to side and may vary in location.
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The centro-temporal spike often presents as a tangential dipole across the rolandic fissure, with a surface positivity over the frontal region and a surface negativity over the centro-temporal regions.
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The frequency of the spike discharges is significantly increased during drowsiness and sleep.
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The discharges are not significantly altered by hyperventilation or by photic stimulation.
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There is no correlation between the frequency and prominence of the spike discharge and the frequency of clinical seizures. The spike discharge can also be present in patients without seizures.
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The EEG background is usually otherwise normal. No anatomic or structural lesions are seen, and the child usually exhibits no abnormalities.
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The location of EEG foci can change over time.
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It is the morphology of the spike discharge rather than the location that is the distinctive factor in identifying this type of spike discharge in association with the benign epilepsy of childhood.
Interictal discharges 䡲
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The characteristic EEG features consist of slow diphasic spikes with an after-coming slow-wave component. The spike discharge is usually prominent and is high in amplitude. The spike discharges may vary in shape and amplitude, and at the other end of the spectrum, a small low-voltage spike discharge that is difficult to distinguish from background activity can be seen.
Ictal discharges 䡲
Ictal discharges of patients with benign epilepsy of childhood have rarely been seen. 䡲 When recorded, the ictal discharge consists of lowvoltage fast activity, which initially occurs over the centro-temporal region and then evolves into higher amplitude with slower frequencies over the temporal and centro-temporal regions. The seizure discharge may spread ipsilaterally or contralaterally and may secondarily generalize.
9 Centro-parietal spikes
Focal Epilepsy
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Ictal EEG in PLE is predominantly lateralized.
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The maximum ictal activity was over either the central-parietal or the posterior head region in most patients.
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Localized parietal seizure onset was noted in only 4 out of 36 patients.
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Surface EEG monitoring is often nonlocalizing and unreliable in the parietal lobe.
Centro-parietal spikes of childhood 䡲
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Centro-parietal spikes can be seen in childhood between the ages of 2 and 8 years, with a peak at 5 years of age. Occur with benign seizures of childhood and may have characteristics similar to those of the centrotemporal spikes of childhood.
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The benign centro-temporal spikes of childhood may not necessarily be associated with seizures but can also be associated with cerebral palsy or some type of motor dysfunction. 䡲 These can also occur in asymptomatic children without epilepsy.
False localization/lateralization is 16% in PLE. The low sensitivity of extracranial ictal EEG may be related to the predominance of simple partial seizures.
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Epileptogenic zone in the frontal, occipital, insular, parietal, and orbitofrontal regions may show falsely localizing IEDs. Closely spaced scalp electrodes can improve the yield of spike detection and localization over the standard 10-20 System.
Centro-parietal spikes seen with other conditions
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The most frequent anatomical localization of somatosensory auras (SSAs) was in the upper extremities, followed by lower extremities and then face. Foot involvement was found in about 13%; 48.7% had purely SSAs, whereas evolution of motor seizures occurred in 47.4%.
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Symptomatic epilepsies arising from the central and parietal regions are associated with focal spikes or sharpwave discharges over the central and parietal regions.
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The centro-parietal spikes that occur in association with symptomatic seizures, in contrast to those seen in benign epilepsy of childhood, often occur as brief or rapid spikes. These are usually more epileptogenic spike and often are associated with some underlying pathology or disturbance of cerebral function affecting the central regions. 䡲 As with other focal spikes, these also may have a more widespread reflection to adjacent areas.
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Parietal lobe epilepsy 䡲
Scalp EEG is frequently negative or maybe misleading. In general, IED is an unreliable finding in parietal lobe epilepsy. IEDs are usually widespread, multifocal, and bilateral. Secondary bilateral synchrony is recorded up to 30% of cases. 䡲 Furthermore, spread of epileptic discharges from the parietal and occipital lobes to frontal and temporal regions may obscure the seizure origin.
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Tingling was the most common symptom (76%) of SSAs. SSAs are highly correlated with an epileptogenic zone in the central parietal region, particularly if they are well localized in the distal extremity and are associated with a sensory march. It was found to have localizing value in 96% with central parietal epilepsy. Epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity. “Paradoxical lateralization” is most likely the result of a horizontal dipole located within the interhemispheric fissure. MEGs only detect dipoles parellel to the surface, and are more sensitive to generators lining the sulci than ones from gyral surfaces. Therefore, MEGs may be helpful in detecting epileptic focus in the mesial aspect of hemispheres.
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An prefrontal-occipital (Fp-O) EEG pattern is an age-dependent nonspecific EEG pattern reflecting the maturational process of the brain seen in both idiopathic (Panayiotopoulos syndrome) and symptomatic focal epilepsies.
Midline spikes 䡲
Highly epileptogenic.
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Most patients have different types of clinical seizures, most commonly generalized tonic-clonic or SSMA seizures (unilateral or bilateral).
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Over two-thirds of the patients were neurologically impaired. 䡲 Most of midline spikes originate from the mesial or paramedian region of the cerebral cortex (supplementary motor seizures or somatosensory seizures arising from the mesial surface of the brain). 䡲 They are more common in children than in adults and markedly activated with sleep. 䡲
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They must be distinguished from normal sleep transients. In the patients with SSMA seizures, routine EEG findings were usually normal, but prolonged EEG showed epileptiform discharges over the vertex. Typical seizures are either unilateral or bilateral tonic limb involvement with preserved consciousness. Interictal sharp waves, when present, are seen over the vertex or just adjacent to the midline in the fronto-central region in 50%. The distinction between epileptic and physiologic vertex sharp waves can be difficult. Characteristic waveforms indicating epileptiform discharges include: 1. The presence of prominent slow waves after the initial sharp transients 2. Morphology of short duration with a subsequent spike-like appearance 3. The appearance of sharp transients during wakefulness 4. Morphology of the sharp transients as polyspikes
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Distinguishing the midline spikes from vertex waves can be difficult. If the discharges are consistently confined to one or more midline electrodes, the distinction can be made by the following:
Ictal patterns 䡲
1. Different fields of distribution 2. The tendency for spikes to be lateralized to one side 3. Focal slowing in association with the spikes 4. Occurrence during wakefulness or drowsiness before V-waves are present 5. Secondary generalization of epileptiform activity 䡲
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Interictal and ictal scalp EEG findings may be absent, non-lateralizing, or misleading, due to paradoxical lateralization. None of patients had abnormal scalp recordings in one study, and they underlined that depth recordings were mandatory when surgery was contemplated. SSMA epilepsy cannot be excluded solely on the grounds of a normal EEG.
Occipital spikes can be seen at different ages and with young children without seizures but with some type of visual impairment.
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Benign epilepsy of childhood with occipital spikes. 䡲 Sturge-Weber syndrome. 䡲 䡲
Adults with midline spikes may represent a distinct entity with a worse prognosis. Midline spikes showed strong correlations with clinical seizures; 91% had epileptic seizures of diverse types. Over two-thirds of the patients were neurologically impaired.
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If bilateral or widespread spikes or spike-and-wave discharges are present, it may be difficult to tell whether there is a midline focus or the side or site of origin of the discharges. Simultaneous video EEG monitoring, as well as intracranial monitoring, may be helpful in documenting the seizures, indicating the site of origin and distinguishing the seizures from nonepileptic seizures.
The ictal patterns consist of trains of spikes, sharp waves, spike-and-wave discharges, or rhythmic, or activity occurring focally in the midline. At times there may be an initial attenuation of the background followed by low-amplitude fast activity or spike-andwave discharges. There may be spread to adjacent parasagittal regions or a more widespread and bisynchronous reflection of the ictal discharges. On the other hand, the ictal EEG may show no change or may be obscured by muscle artifact.
Occipital spikes 䡲
Midline spikes occur almost exclusively in children, are strongly associated with clinical seizures, and are activated by sleep. Cz is the most frequent spike location. Most patients without sleep activation had CNS disease.
Midline spikes most probably originate from discharging lesions of the mesial or paramedian region of the cerebral cortex. Epilepsy with midline spikes is not necessarily benign.
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Focal Epilepsy
Epilepsy with bilateral occipital calcification. Late infantile neuronal ceroid lipofuscinosis and other symptomatic lesions.
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Seen more commonly in patients with mental retardation and epilepsy. 䡲 Disappear during childhood or adolescence.
Idiopathic childhood occipital epilepsy of Gastaut 䡲
Clinical Manifestation 䡲 Elementary visual hallucination, such as scotomata, flashing lights, and amaurosis. 䡲 Complex visual hallucinations. 䡲 䡲
Eye deviation. Forced eyelid closure and blinking.
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Ictal blindness. 䡲 Ictal headache/postictal headache. Interictal EEG 䡲
Needlelike spikes of the blind (occipital spikes of blindness) Occipital or parietal regions in most patients with congenital blindness and retinopathy during early infancy.
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Prevalence of 75% in retrolental fibroplasia age 3–14 years and 35% in all causes of blindness. 䡲 Amplitude 50–250 μV.
Shows the following: 䊳 High-amplitude spike and spike-and-wave discharges over the occipital and adjacent head regions in a unilateral, bilaterally independent, or bilaterally synchronous manner. 䊳 The discharges can occur singly or in rhythmic trains of 1–3 Hz and are usually maximal over the occipital head regions. 䊳
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can be in isolation or in burst 䡲 Activated by sleep.
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Low amplitude at 10 months; typical features at 2.5 years; after-going slow waves in mid childhood; disappear by the end of adolescence. 䡲 Functional deafferentation of the visual cortex gives rise to an increase in its irritability (denervation hypersensitivity). 䡲 Not an epileptiform activity.
Onset is between 3 and 15 years.
They may also spread to the adjacent posterior temporal and parietal regions. The discharges are attenuated with eye opening and reoccur with eye closure. The epileptiform activity is increased during NREM sleep and decreased during REM sleep.
The Ictal Discharges 䡲
Consist of low-voltage fast activity or fast rhythms or fast spikes or both over one or both occipital regions, which can spread more widely. 䊳 There are also subclinical discharges that can occur during sleep. The EEG is otherwise normal. Usually,
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there is no demonstrable lesion, and the child is otherwise normal and outgrows the seizures and the spike discharges. The EEG pattern of occipital paroxysmal discharges suppressed by eye opening is not specific to benign epilepsy of childhood. It can also be seen with variants of the entity, including benign nocturnal occipital epilepsy, and in patients who have had basilar migraine associated with seizures.
Panayiotopoulos syndrome (PS) 䡲 䡲
䡲 䡲 䡲 䡲 䡲 䡲 䡲
One of the most common childhood seizure disorders. Characterized by prolonged, predominantly autonomic symptoms with EEG that shows shifting and/or multiple foci, often with occipital predominance. Three-quarters of patients have their first seizure between the ages of 3 and 6 years with peak at 5 years. Seizures in PS occur predominantly in sleep. Vomiting is the most common symptom. Versive seizure is seen in 60%, and progression to generalized convulsions is quite frequent. Headache may be described and is concurrent with other autonomic symptoms. Most patients will have between two and five seizures. Approximately one-third had partial status epilepticus.
Interictal EEG Normal background with high-amplitude sharp- and slow-wave complexes, similar in morphology to those seen in benign childhood epilepsy with centrotemporal spikes. 䡲 There is great variability in location. Occipital localization is the most common, but all other brain regions may be involved. 䡲 Frequently shift in location, this possibly being age related. 䡲
Focal Epilepsy
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Brief generalized discharges are occasionally encountered. 䡲 Sharp waves or sharp- and slow-wave complexes may repeat themselves regularly and propagate, especially to frontal regions (clone-like). Seen in 17%. 䡲 䡲
EEG abnormalities in PS are accentuated by sleep. Not expected to be photosensitive.
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Elimination of central vision and fixation. 䡲 Variants of the EEG that are uncommon, but compatible, with the diagnosis include mild background abnormalities and small or inconspicuous spikes. 䡲 Ten percent of patients with PS may have a normal awake EEG, but abnormalities are nearly always seen in sleep. 䡲
EEG or a series of EEGs. Consistently normal EEGs are exceptional.
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None of the interictal EEG abnormalities in PS appear to determine prognosis. 䡲 EEG foci in most patients with PS are frequently shifting location, multiplying, and propagating diffusely with age rather than persistently localizing in the occipital region. 䡲 The occipital EEG spikes appeared initially and then shifted to the Fp region or appeared at the same time as Fp spikes, forming an Fp-O EEG pattern resulting in secondary occipito-fronto-polar synchrony. This phenomenon is an age-dependent nonspecific EEG pattern reflecting the maturational process of the brain. Ictal EEG 䡲 Clinical features, including tachycardia, irregular breathing, emesis, or coughing, start long after the ictal EEG onset. This onset is characterized by rhythmic theta or delta activity mixed with small spikes in unilateral posterior head region. 䡲 MEG in most patients showed an epileptic focus in parieto-occipital sulcus (61.5%) or calcarine sulcus (30.8%). Despite Fp-O synchronization of spike discharges in EEG, no frontal focus was found.
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Sturge-Weber syndrome 䡲
Epileptiform activity and seizures arising from the occipital region or adjacent posterior head regions. 䡲 Depression of background activity on the side of the facial nevus and intracranial calcifications.
Epilepsy with bilateral occipital calcification 䡲
The EEG findings consist of posterior spike-and-wave discharges, which are attenuated with eye opening in the waking state, and posterior “fast” spikes and polyspikes during the sleep state. 䡲 As the disease progresses, the seizures become more frequent, and the EEG shows more diffuse spike and wave discharges and posterior dominant polyspike discharges. The ictal pattern consists of a diffuse recruiting rhythm that is maximal over the posterior head regions.
Late infantile neuronal ceroid lipofuscinosis 䡲
Spike discharges are present over the occipital regions in the earlier stages of the disease. Later, these become more widespread.
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The most specific and diagnostic findings are photicinduced spikes over the occipital head regions at low rates of flash stimuli.
Symptomatic occipital epilepsy 䡲
Various symptomatic conditions and structural lesions involving the posterior head regions can also be associated with occipital seizures and epileptiform abnormalities, including: 䊳 Head trauma 䊳 Birth injury 䊳 Porencephaly 䊳 Congenital defects 䊳 Cortical dysplasia 䊳 Tumors 䊳 Inflammatory processes 䊳 Vascular lesions or malformations
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Mitochondrial encephalopathies Hematoma Tuberous sclerosis
Interictal EEG 䡲 Focal spikes. 䡲 Sharp waves. 䡲 Spike-and-wave discharges. 䡲 Polyspike-and-wave discharges. 䡲 The discharges can occur focally over the occipital head regions or with a more widespread reflection over the posterior quadrant. Epileptiform discharges can also be seen over the temporal or centrotemporal region, or as wandering foci from one region to the other. The EEG may show other abnormalities, including slowing, asymmetry, or attenuation of activity over one or both occipital regions, in addition to the epileptiform abnormalities.
the origin from the occipital lobe. Muscle artifact can contaminate the recording, adding to the difficulty in detecting the onset of the seizure discharges. 䡲 The most common ictal EEG onset in occipital lobe seizures is regional involving the posterior temporal occipital region. Ictal onsets restricted to the occipital lobe were seen in only 17%. 䡲 The most common pattern of spread involved the ipsilateral mesial temporal structures. 䊳 Ictal onset was localized to the occipital lobe in 30%, temporal and occipito-temporal lobes in 27%, and was more diffuse in 43%. 䡲
False localization and lateralization occurred in 28% of occipital seizures.
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The homologous area in the contralateral hemisphere, especially in the frontal and occipital regions, may be associated with similar slow waves and sharp waves, usually of lower amplitude. These findings may be caused by compression, edema, ischemia in the opposite hemisphere, transmission through commissural fibers, or volume conduction.
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There may also be a problem in detecting occipital discharges on scalp recordings, particularly if the seizure focus originates from the meso-occipital region at a distance from scalp leads. Rapid spread of the discharges may also make it difficult to identify
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Ictal EEG Repetitive spikes, sharp waves, and spike-and-wave or rhythmic fast activity. 䡲 The ictal discharges from the occipital region have a lesser tendency to evolve into polymorphic seizure. 䡲 Ictal discharges that occur focally over the occipital regions are usually associated with elementary visual symptoms or nystagmus. Occipital seizures can also spread to the temporal, parietal, and frontal lobes, to produce secondarily complex partial seizures or focal motor or sensory seizures. 䡲 The ictal discharges that occur in a widespread manner over the posterior head regions with spread to the temporal and other regions may make it difficult to distinguish occipital from temporal or parietal lobe epilepsy.
9
Focal Epilepsy
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Temporal spikes 䡲
Removal of visible lesions seen in MRI alone may not lead to a favorable outcome, suggesting a more widespread epileptogenic network or multiple FCD in these patients. Subdural EEG covering adjacent cortex or remote cortex, especially mesial temporal, is necessary for a complete resection of the epileptogenic zone. 䡲 Patients with MTS have >90% of IEDs in the anterior temporal region. Therefore, frequent posterior or extratemporal sharp waves decrease the certainty of the diagnosis of MTS. 䡲 Rarely, IEDs can be seen in lateral temporal and frontal regions due to spreading of the discharges to the orbitofrontal or temporal neocortex via the limbic system. 䡲 In MTLE, concordance of abnormal MRI and IED is associated with good surgical outcome and is a
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better indicator than concordance of abnormal MRI and ictal EEG activity but non-lateralizing IED. Although bilateral IEDs decrease the chance of favorable postoperative outcome, patients with bitemporal IEDs but MRI hippocampal abnormalities concordant with the ictal-onset region still can have a good to excellent surgical outcome. Automatisms with preserved responsiveness were observed exclusively during seizures arising from the right nondominant temporal lobe. They were not observed during seizures arising from the left dominant temporal region. IEDs in MTLE show negative spikes and sharp waves in the sphenoidal, T1/T2, and F7/F8 electrodes. These IEDs are an expression of epileptiform activity in the parahippocampal cortex. Spikes in the hippocampus are usually not seen in scalp electrodes. Most IEDs are accompanied by a widespread positivity over the contralateral central-parietal region or vertex. Bilateral IEDs occur in one-third of patients, often during NREM sleep. IEDs recorded during wakefulness and REM sleep are more often lateralized and closely associated with the area of seizure onset. Seizure recording may not be necessary if serial routine EEGs are consistently concordant with MRIidentified unilateral hippocampal atrophy.
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In scalp EEG, slow-wave activity was present in 62%. Its distribution was most commonly regional and then multiregional, or generalized. The slow-wave activity was more commonly absent in temporal than extratemporal tumor groups.
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IEDs occurred in 32 of the 37 patients and were present in all of those with extratemporal epilepsy. They were most often multiregional (n = 15), or regional (n = 12), or multiregional and generalized (n = 5). They were usually found over the lobe with the tumor, but in three patients, they were predominantly contralateral.
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Another study of ganglioglioma in temporal lobe revealed scalp IEDs ipsilateral temporal in 71% of patients, bitemporal in 19%, and generalized in 19%.
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An interictal mirror focus was found in 26.9% of patients with temporal lobe epilepsy.
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IEDs recorded during wakefulness and REM sleep are more often lateralized and closely associated with the area of seizure onset.
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“Hypomotor” seizure is a signature of temporal lobe epilepsy.
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A bipolar antero-posterior montage using the Standard 10-20 electrode placement would incompletely record in only about 40–55% of anterior temporal spikes.
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Additional electrodes can be used to supplement the standard 10-20 electrode placement. Ninetyseven percent of spikes are detected using additional anterior temporal region surface electrodes (T1 and T2), whereas 58% of the spikes are detected using only standard 10-20 electrode placement
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Anterior temporal electrodes (T1 and T2) are able to detect nearly all IEDs recorded by the foramen ovale electrode. Therefore, assuming that the location of the foramen ovale electrode is analogous to that of sphenoidal electrodes optimally implanted under fluoroscope, the use of sphenoidal electrodes in routine interictal investigations appears not to be justified.
Focal Epilepsy
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TIRDA has the same clinical significance as anterior temporal spikes/sharp waves, a characterisctic EEG finding seen in MTLE and hippocampal sclerosis. 䡲
Epilepsia partialis continua (EPC) 䡲
EPC may occur in any location but is most often associated with spike discharges over the central regions. Often the discharges consist of lowamplitude rapid spikes. 䡲 The spike discharges can occur as continuous repetitive spikes, in bursts or clusters, or in an intermittent fashion. 䡲 Back-averaging from the clonic or myoclonic jerks may help to demonstrate the presence of
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an antecedent spike discharge. At times no spike discharges may be visible on surface recordings, and only a focal slow-wave abnormality or an asymmetry of activity may be present over the involved region. Corticography or intracranial recordings may be necessary to demonstrate the presence of the epileptiform discharges that are not apparent with scalp recordings. Rasmussen syndrome is the most common cause of EPC. The EEG abnormalities vary widely depending on the stage of the disease with lateralized abnormalities early in the course and bilateral abnormalities in later stages. PDA occurred in all 49 patients. This was unilateral in 19%, bilateral but with unilateral predominance in 68%, and symmetrical in both hemispheres in 13%. In 32 patients in whom seizures were recorded, a localized onset was found in only 16%. An early and striking EEG feature in all cases was the presence of focal PDA, mainly over the central and temporal regions. Other EEG features were early ictal and interictal multifocal epileptiform activity over a single hemisphere, presence of subclinical ictal EEG activity, and progressive unilateral suppression of background activity. These abnormal EEG findings correspond to typical clinical features, and an MRI indicating progressive disease is rarely observed in other conditions causing symptomatic focal epilepsy besides Rasmussen encephalitis. The scalp EEG in EPC is nonspecific and is determined by the underlying pathology. EEG can vary from normal, focal slowing with or without spikes or spike-wave complexes, especially over the central or centro-parietal regions. Focal epileptiform discharges may consist of spike, spike-and-wave, or polyspikeand-wave discharges. Focal periodic slow transients and PLEDs were reported. Bilateral, but with unilateral predominance, bursts of delta waves are the rule. Ictal SPECT and interictal PET are useful tools in presurgical workup for the localization of the epileptogenic focus in patients with epilepsia partialis
689
continua with no definite ictal EEG localization, especially in the early phase. 䡲
SPECT with 99mTc-HMPAO may be the only imaging study to suggest Rasmussen encephalitis and to localize an abnormality in a patient with worsening clinical course and normal MRI and CSF examination. Ictal SPECT shows focal hyperperfusion while EEG fails to show epileptic changes.
Insular epilepsy 䡲
Semiology of an insular seizure includes sensation of laryngeal constriction, paresthesias affecting large cutaneous territories, dysarthric speech, focal motor convulsive symptoms, dysgeusia and contralateral somatosensory phenomena. 䡲 Generally, interictal or ictal epileptiform discharges originating in the insular cortex are unlikely to be detected by scalp-EEG recordings, unless these discharges propagate to lateral neocortical regions.
Benign neonatal familial convulsion Interictal EEG 䡲
Normal.
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Discontinuous. 䡲 Focal or multifocal sharp waves. 䡲 䡲
Théta pointu alternant pattern. Seen during waking and sleep and up to 12 days after the seizures are stopped.
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Nonspecific EEG pattern seen in status epilepticus caused by a variety of conditions such as HIE, hypocalcemia, meningitis, SAH, and benign idiopathic neonatal seizure. 䡲 Described as bursts of an unreactive dominant theta activity intermixed with sharp waves with frequent interhemispheric asynchrony. 䡲
The théta pointu alternant pattern is associated with good prognosis. 䡲 The patterns suggesting poor prognosis, such as a paroxysmal, inactive, or burst-suppression, have never been reported in BNFC.
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Selected epilepsy syndromes Benign neonatal nonfamilial convulsion 䡲
Theta activity mixed with sharp waves alternating with relative background suppression.
An Interictal EEG in BFNC 䡲 Was normal (10%) and discontinuous; showed focal or multifocal sharp waves or “théta pointu alternant” pattern. The “théta pointu alternant” pattern seen in half the cases may be seen during waking and sleep and up to 12 days after the seizures are stopped.
Benign infantile seizure 䡲 䡲 䡲 䡲 䡲
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Age of onset was under 1 year and ranged from 3 to 20 months. Seizures occurred in clusters, 1–10 times a day for 1–3 days, possibly recurring 1–8 weeks later. The duration of seizures ranged from 30 to 217 sec. Seizures occurred either during wakefulness or during sleep. They were characterized by motion arrest, decreased responsiveness, staring or blank eyes mostly with automatisms, and mild convulsive movements. Convulsive movements consist of eye deviation or head rotation, mild clonic movements involving the face, eyelids, or limbs, and increased limb tone. Benign infantile seizures are characterized by: 䊳 Familial or nonfamilial occurrence.
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Normal development prior to onset. Onset mostly during the first year of life. No underlying disorders nor neurological abnormalities. Complex partial seizures or secondarily generalized seizures often occurring in clusters. Normal interictal EEG. Ictal EEG most often showing temporal focus.
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Excellent response to treatment.
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Focal Epilepsy
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Normal developmental outcome.
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Ictal EEGs and clinical seizure are not much different from those of infants with refractory seizures.
䡲
During the recording with referential montage, the centro-temporal spike shows a horizontal dipole configuration with a negative pole over the centrotemporal region and a positive pole over the frontal region. The clinical relevance of a dipole in BCTS has become a widely debated issue. MEG demonstrates that the spikes were generated by a single tangential dipole source located in the precentral gyrus, closer to hand SII than to SI cortex, with the positive pole directed frontally and the negative pole directed centro-temporally.
䡲
Characteristic spikes over the rolandic area are regarded as neurobiological markers of BECTS. However, rolandic (centro-temporal) spikes have been reported in normal children without clinical seizures or neurologic manifestations. They are seen in 1.2– 3.5% of normal healthy children in the community and 6–34% of siblings of patients affected by BECTS. The risk of epilepsy is higher if rolandic spikes remain unilateral during sleep, rolandic spikes continue during REM sleep, and there are GSW discharges.
䡲
The frequency of rolandic spikes in children with ADHD (3–5.6%) is significantly higher than expected from epidemiologic studies.
Atypical benign partial epilepsy (ABPE) or pseudo-Lennox syndrome (PLS) 䡲
Characterized by generalized minor seizures (i.e., atonic-astatic, myoclonic seizures and atypical absences).
䡲
Focal sharp slow waves and spikes (SHW) as observed in rolandic epilepsy (RE), but with exceptionally pronounced activation during sleep.
䡲
All patients have at least atonic and nocturnal rolandic seizures.
䡲
ABPE broadly overlaps with RE, electrical status epilepticus during sleep, and Landau-Kleffner syndrome. 䡲 Regarding the epilepsy, the prognosis is excellent; mental deficit, however, seems to be frequent. 䡲
ABPE needs to be differentiated from Lennox-Gastaut syndrome and myoclonic astatic epilepsy. 䡲 Interictal EEG during wake shows characteristic features of BECTS in all cases, at least transiently, as well as generalized 3-Hz spike-wave discharges. 䡲
Epileptiform activity can also be seen in parietal, temporal, occipital, and frontal regions. EEG during sleep is similar to ESES.
Benign epilepsy with centro-temporal spikes (BECTS) 䡲
䡲
The spike may have a phase reversal in the centrotemporal or parietal regions but less commonly in the frontal or the vertex areas.
A more posterior predominance is often observed in the youngest subjects. 䡲 The most striking finding of the centro-temporal spikes is their significant increase in frequency during light NREM sleep. 䡲 When the frequency of centro-temporal spikes decreases abruptly during sleep, an underlying structural abnormality needs to be excluded.
䡲
Benign focal epileptiform discharges, mostly rolandic spikes, were seen in 9% of childhood migraine. 䡲 Temporal-parietal spikes can occur with BECTS with or without epilepsy. 䡲 Malignant rolandic-sylvian epilepsy (MRSE) differs from BECTS and LKS in its refractoriness to medication, clusters of seizures, change in semiology, and secondarily generalized seizures. After careful observation over at least 5 years, surgery is considered to control refractory seizures. 䡲 The clinical and EEG features which point to symptomatic focal epilepsy are: 1. Presence of subtle neuropsychological deficit or oromotor apraxia 2. Seizures starting with symptoms supporting an onset outside the opercular region 3. Presence of atypical absences or focal hypomotor seizures
9 4. Background EEG abnormalities 5. Presence of unusual fast activity 6. Morphological modification of the centrotemporal spikes during sleep 7. Enhancement of slow waves following the spike/ recurrence of spikes in trains 8. Intermittent slow-wave focus 9. Frontalization of the spikes 10. Diffuse discharges of slow-spike-slow-wave complexes 11. Continuous spikes and waves during slow sleep (CSWS) 12. Polymorphisms of the ictal discharge 13. Severe postictal depression 䡲 Back-averaging revealed that a biphasic spike in the contralateral rolandic region precedes an EMG burst by 6–22 msec, depending on whether proximal or distal muscles of the arm are involved. This time lag characterizes “cortical myoclonus” passing rostrocaudally through the brain stem, spinal cord, and then activating muscle.
Focal Epilepsy
HHE syndrome (hemiconvulsions, hemiplegia, epilepsy) 䡲
䡲
䡲
䡲
䡲
The causes of the initial convulsions in HHE syndrome include meningitis, subdural effusions, stroke, and trauma, although in many patients, no cause is found. Rhythmic bilateral slow waves, with higher amplitude on the hemisphere contralateral to the clinical seizure, are seen in the initial phase of HHE syndrome. The ictal EEG is characterized by rhythmic bilateral slow waves, with higher amplitude on the hemisphere contralateral to the clinical seizure. In the early phase of HHE, pseudorhythmical spikeand-wave discharges, contralateral to the clinical seizures, periodically interrupted by a 1- to 2-sec electrical flattening can also be noted. Polygraphic recordings do not demonstrate any consistent relation between muscle jerks and EEG discharges.
Autism and epilepsy 䡲
Abnormal EEGs were found in 43-75% of children with autism.
691
䡲
Forty-six percent had clinical seizures.
䡲
Nearly all children with seizures had epileptiform activity. 䡲 Almost 20% of those with spike discharges did not have clinical seizures. 䡲 Slow-wave abnormalities were more frequent in individuals with autism. 䡲 Most epileptic discharges were localized spikes; some had multiple spike foci and, only on rare occasions, generalized spikes. 䡲
Seventy-five percent of the epileptic discharge foci were in the frontal region, 2.1% in the temporal region, 14.1% in the centro-parietal region, and 6.4% in the occipital region. 䡲 Fifty-five percent of the frontal spikes were at midline, approximately equal at Fz and Cz. The dipole of midline spikes was in the deep midline frontal region. These results suggest that frontal dysfunctions are important in the mechanism and symptoms of autism.
692
Focal Epilepsy
9
FIGURE 91. Théta Pointe Alternant Pattern; Benign Familial Neonatal Convulsion (BFNC). An EEG of a younger twin. He developed similar types of seizures on the same day as his older twin. EEG showed bursts of théta pointu alternant pattern. An interictal EEG in BFNC was normal and discontinuous, and showed focal or multifocal sharp waves or “théta pointu alternant” pattern. The théta pointu alternant” pattern may be seen during waking and sleep and up to 12 days after the seizures are stopped. The théta pointu alternant pattern is a nonspecific EEG pattern seen in status epilepticus caused by a variety of conditions such as HIE, hypocalcemia, meningitis, SAH, and benign idiopathic neonatal seizures. It is described as bursts of an unreactive dominant theta activity intermixed with sharp waves with frequent interhemispheric asynchrony. Patterns suggesting poor prognosis, such as a paroxysmal, inactive, or burst-suppression, have never been reported in BNFC. The théta pointu alternant pattern is associated with good prognosis.1
9
Focal Epilepsy
693
FIGURE 92. Théta Pointu Alternant Pattern; Benign Neonatal Convulsion (Non-Familial) or “Fifth Day Fits”. A 6-day-old boy born full term without complication. He developed the first seizure 6 days after birth. His seizure is described as either unilateral or bilateral clonic jerking, as well as apnea. Postictally, he cried for 30–45 sec and returned back to normal. He was otherwise normal. Neurological examination was normal. Workup including cranial CT and metabolic tests were negative. There was no family history of epilepsy or seizure. The seizures lasted for approximately 36 hours. Interictal EEG shows bursts of unreactive theta activity mixed with sharp waves alternating with relative background suppression. An interictal EEG in benign non-familial neonatal convulsion was normal (10%) and discontinuous, and showed focal or multifocal sharp waves or “théta pointu alternant” pattern. The “théta pointu alternant” pattern seen in half the cases may be seen during waking and sleep and up to 12 days after the seizures have stopped. The théta pointu alternant pattern is described as bursts of an unreactive dominant 4- to 7-Hz theta activity intermixed with sharp waves with frequent interhemispheric asynchrony and shifting predominance between the two hemispheres. It is a nonspecific EEG pattern seen in status epilepticus caused by a variety of conditions such as HIE, hypocalcemia, meningitis, SAH, and benign idiopathic neonatal seizure. The patterns suggesting poor prognosis, such as a paroxysmal, inactive, or burst-suppression, have never been reported in BNFC. The théta pointu alternant pattern is associated with a good prognosis.1
694
Focal Epilepsy
9
FIGURE 93. Benign Infantile Seizures (Benign Partial Epilepsy in Infancy). A 4-week-old boy who was born full term without complication. He started having recurrent apneas at 3 days of age. He was treated with phenobarbital and did well until 1 week prior to this EEG recording, when he started having his typical seizures described as eye deviation to the left with left arm and leg clonic jerking followed by apnea and cyanosis. Subsequently, clonic seizures also occurred on the right side with or without generalized tonic-clonic seizures. He had clusters of seizures up to 10/day for 4 days and had recurrent clusters of seizures at 3 and 9 months of age. Extensive metabolic workup was normal. The patient has been seizure-free for 13 months with low-dose levetriacetam. His development has been normal. No family history of seizures was noted. DWI MRI during active seizures shows cytotoxic edema in the right frontal region (open arrow), which subsequently disappeared in the repeated MRI. Ictal EEG onset (arrow) is described as diffuse background attenuation with superimposed low-voltage spikes intermixed with rhythmic alpha activity in the right hemisphere, maximal in Cz, C4, and T4. Three seconds later, a spike is noted in the T4 (double arrows).
9
Focal Epilepsy
695
FIGURE 94. Benign Infantile Seizures (Benign Partial Epilepsy in Infancy). (Continued) Twenty-two seconds after the ictal EEG onset, the EEG shows a train of spikes in the Cz corresponding to left-leg movement. Three seconds later, a train of spikes are noted in the central areas, greater in the C4, corresponding to both arms stiffening. Ictal EEG then evolves into rhythmic sharply-contoured theta activity in the same areas corresponding to clonic jerking of the left arm and leg with eye deviation to the left side. The age of onset was under 1 year and ranged from 3 to 20 months. Seizures occurred in clusters, 1–10 times a day for 1–3 days, sometimes recurring 1–8 weeks later. The duration of seizures ranged from 30 to 217 sec. Seizures could occur during wakefulness or during sleep. They were characterized by motion arrest, decreased responsiveness, staring or blank eyes mostly with automatisms, and mild convulsive movements. Convulsive movements consist of eye deviation or head rotation, mild clonic movements involving the face, eyelids, or limbs, and increased limb tone. Benign infantile seizures are characterized by (1) familial or nonfamilial occurrence; (2) normal development prior to onset; (3) onset mostly during the first year of life; (4) no underlying disorders nor neurological abnormalities; (5) complex partial seizures or secondarily generalized seizures often occurring in clusters; (6) normal interictal EEG; (7) ictal EEG most often showing a temporal focus; (8) excellent response to treatment; and (9) normal developmental outcome. Ictal EEGs and clinical seizures are not much different from those of infants with refractory seizures.2–6
696
Focal Epilepsy
9
FIGURE 95. Benign Infantile Seizures (Benign Partial Epilepsy in Infancy). A previously healthy 9-week-old boy developed clusters of 5–10 seizures per day for 3 days. Seizures began with twitching of the left upper and lower extremities and spread to the left side of the face and then to the right upper and lower extremities, lasting for 2–5 minutes. The seizures finally stopped after multiple AEDs, including lorazepam, topiramate, phenytoin, and levetriacetam were tried. Extensive workup for metabolic and infectious diseases was unremarkable. MRI reveals cytotoxic edema, probably secondary to seizures in bilateral frontal regions, greater on the left. At a 7-month clinic visit, the patient had normal developmental milestones and had no seizures. A repeat MRI showed disappearance of the previous cytotoxic edema. EEG was normal. The age of onset was under 1 year and ranged from 3 to 20 months. Seizures occurred in clusters, 1–10 times a day for 1–3 days, sometimes recurring every 1–8 weeks. The duration of seizures ranged from 30 to 217 sec. Seizures occurred either during wakefulness or during sleep. They were characterized by motion arrest, decreased responsiveness, staring or blank eyes mostly with automatisms, and mild convulsive movements. Convulsive movements consist of eye deviation or head rotation, mild clonic movements involving the face, eyelids, or limbs, and increased limb tone. Benign infantile seizures are characterized by (1) familial or nonfamilial occurrence; (2) normal development prior to onset; (3) onset mostly during the first year of life; (4) no underlying disorders nor neurological abnormalities; (5) complex partial seizures or secondarily generalized seizures often occurring in clusters; (6) normal interictal EEG; (7) ictal EEG most often showing a temporal focus; (8) excellent response to treatment; and (9) normal developmental outcome. Ictal EEGs and clinical seizures are not much different from those of infants with refractory seizures.2–6
9
Focal Epilepsy
697
FIGURE 96. Benign Infantile Seizures (Benign Partial Epilepsy in Infancy). (Continued) An ictal EEG shows seizure onset starting at O1, spreading to Cz and C3 when he started having hemiconvulsions on the right side. Later in the seizure, the ictal EEG activity occurs in both hemispheres when the patient develops multifocal clonic jerking. The seizure lasts for approximately 3 minutes. The patient cries afterward with only very brief postictal lethargy.
698
Focal Epilepsy
9
FIGURE 97. Atypical Benign Partial Epilepsy of Childhood; Pseudo-Lennox Syndrome. A 7-year-old boy with mild developmental delay before his first seizure at 3 years of age. He had multiple types of seizures, including drop attack, GTCS, hemiconvulsion especially involving the orofacial region, and nonconvulsive status epilepticus (absence). His past EEGs showed different types of epileptiform activity such as generalized slow spike-wave or focal epileptiform activity in various locations, including multifocal, occipital, centro-temporal, or central vertex regions. In the past 2 years, EEG showed a constant finding of centro-temporal spikes with continuous discharges during slow sleep. His seizures have been relatively well controlled, but he developed a moderate degree of language and cognitive impairment. Atypical benign partial epilepsy (ABPE) or pseudo-Lennox syndrome (PLS) is characterized by generalized minor seizures (i.e., atonic-astatic, myoclonic seizures and atypical absences) and focal sharp slow waves and spikes (SHW) as observed in rolandic epilepsy (RE), but with exceptionally pronounced activation during sleep. All patients have at least atonic and nocturnal rolandic seizures. ABPE broadly overlaps with RE, electrical status epilepticus during sleep, and Landau-Kleffner syndrome. Regarding the epilepsy, the prognosis is excellent; mental deficit, however, seems to be frequent. ABPE needs to be differentiated from Lennox-Gastaut syndrome and myoclonic astatic epilepsy. Interictal EEG during wake shows characteristic features of BECTS in all cases, at least transiently, as well as generalized 3-Hz spike-wave discharges. Epileptiform activity can also be seen in parietal, temporal, occipital, and frontal regions. EEG during sleep is similar to ESES.6–9
9
Focal Epilepsy
699
FIGURE 98. Lennox-Gastaut Syndrome; Remote Stroke and Hydrocephalus. A 9-year-old boy with a history of congenital heart disease status post surgical correction, hydrocephalus with VP shunt, remote left middle cerebral artery stroke, mental retardation, and medically intractable epilepsy. He had multiple types of seizures, consisting of complex partial, generalized tonic-clonic and atypical absence seizures. He was hospitalized for a mental status change. Cranial CT shows remote ischemic infarction of the left middle cerebral artery distribution with left lateral ventricular dilatation and VP shunt insertion. Compared to the previous CT, there has been no change. EEG demonstrates continuous generalized 2-Hz spike-and-wave discharges with anterior and right predominance.
700
Focal Epilepsy
9
FIGURE 99. Lennox-Gastaut Syndrome; Focal Myoclonic Seizure. EEG of an 8-year-old with cryptogenic Lennox-Gastaut syndrome. The patient developed a myoclonic jerk on the right arm (arrow) accompanied by a very brief run of rapid spikes in the left parietal and central vertex regions. This finding is supportive of the diagnosis of a focal seizure with left centro-parietal focus.
9
Focal Epilepsy
701
FIGURE 910. Panayiotopoulos Syndrome. A 5-year-old girl with nocturnal GTCS associated with clicking noises from her mouth. She went back to sleep and then woke up with a throbbing headache. EEG shows clone-like repetitive occipital spike-wave discharges. Brain MRI was normal. The patient has normal development and been seizure free for over 2 years. Panayiotopoulos syndrome (PS) is one of the most common childhood seizure disorders. It is characterized by prolonged, predominantly autonomic symptoms with EEG that shows shifting and/ or multiple foci, often with occipital predominance. Three-quarters of patients have their first seizure between the ages of 3 and 6 years with a peak at 5 years. Seizures in PS occur predominantly in sleep. Vomiting is the most common symptom. Versive seizure is seen in 60%, and progression to generalized convulsions is quite frequent. Headache may be described and is concurrent with other autonomic symptoms. Most patients will have between two and five seizures. Approximately one-third had partial status epilepticus. The interictal EEG of PS shows a normal background with high-amplitude sharp- and slow-wave complexes. These are similar in morphology to those seen in benign childhood epilepsy with centro-temporal spikes. However, in PS, there is great variability in location. Occipital localization is the most common, but all other brain regions may be involved. Moreover, the complexes frequently shift in location, this possibly being age related. Brief generalized discharges are occasionally encountered. The sharp waves or sharp- and slow-wave complexes may repeat themselves regularly and propagate, especially to frontal regions. The term “clone-like” has been used to describe this appearance. EEG abnormalities in PS are accentuated by sleep. Patients are not expected to be photosensitive. Variants of the EEG that are uncommon, but compatible, with the diagnosis include mild background abnormalities and small or inconspicuous spikes. EEG Similar patterns to the ones seen in PS occasionally occur randomly in other children. Ten percent of patients with PS may have a normal awake EEG, but abnormalities are nearly always seen in sleep EEG or a series of EEGs. Consistently normal EEGs are exceptional. None of the interictal EEG abnormalities in PS appear to determine prognosis.6,10,11 EEG foci in most patients with PS frequently shift locations, multiply, and propagate diffusely with age rather than persistently localizing in the occipital region. The occipital EEG spikes appeared initially and then shifted to the Fp region or appeared at the same time as Fp spikes, forming an Fp-O EEG pattern resulting in secondary occipitofrontopolar synchrony. This phenomenon is an age-dependent nonspecific EEG pattern reflecting the maturational process of the brain.12 MEG in most patients showed epileptic focus in the parieto-occipital sulcus (61.5%) or calcarine sulcus (30.8%). Despite Fp-O synchronization of spike discharges in the EEG, no frontal focus was found.13
702
Focal Epilepsy
9
FIGURE 911. Panayiotopoulos Syndrome. A 6-year-old girl with fever and URI. She had headache and vomiting. After the third episode of vomiting, she woke up and had staring episode, which was followed immediately by clonic jerking of the left side of her body lasting for 10 minutes. This was followed by headache and lethargy. She was fine the next morning when she woke up. EEG performed 2 days later revealed right occipital spike- and -slow-wave discharges. Cranial MRI was unremarkable. She did well with oxcarbazepine until 1 year later, when she developed three episodes of seeing “colors” without loss of consciousness. Interictal EEG shows a normal background with high-amplitude sharp- and slow-wave complexes, which are similar in morphology to those seen in benign childhood epilepsy with centrotemporal spikes. However, in PS, there is great variability in their location. Occipital localization is the most common (70%), but sharp waves may appear anywhere and often shift from one location to another. They are age related. Brief generalized discharges may occur. The sharp waves or sharp- and slow-wave complexes may repeat themselves regularly and propagate, especially to frontal regions. They are termed “clone-like,” which are seen in 19%. EEG abnormalities are activated by sleep and elimination of central vision and fixation.6,10,11
9
Focal Epilepsy
703
FIGURE 912. Panayiotopoulos Syndrome. A 6½-year-old girl with a single febrile GTCS at 5 years of age who developed an episode of waking up with vomiting. She was continuously chewing, and her tongue and lips were very swollen. She was alert at the time but was unable to talk. She was noted to have left facial weakness with her tongue deviating to the left; otherwise, her neurological exam was normal. She subsequently had two more episodes of vomiting followed by left arm and head jerking with no LOC or postictal confusion. EEG shows multifocal epileptiform activity but maximally over the left occipital region. Interictal EEG shows a normal background (slow background in 20%) with high-amplitude sharp- and slow-wave complexes, which are similar in morphology to those seen in benign childhood epilepsy with centro-temporal spikes. However, in PS, there is great variability in their location. Occipital localization is the most common (70%), but sharp waves may appear anywhere and often often shift from one location to another. They are age related. Brief generalized discharges may occur. The sharp waves or sharp- and slow-wave complexes may repeat themselves regularly and propagate, especially to frontal regions. They are termed “clone-like,” which are seen in 19% of PS cases. EEG abnormalities are activated by sleep and elimination of central vision and fixation.6,10,11
704
Focal Epilepsy
9
FIGURE 913. Benign Epilepsy with Centro-Temporal Spikes (BCTS). A 12-year-old boy with recurrent episodes of nocturnal seizures described as right facial numbness followed immediately by mouth twitching, speech arrest, and drooling without loss of consciousness. Background EEG activity was normal during wakefulness. EEG during drowsiness and sleep showed frequent bilateral synchronous/independent biphasic spikes followed by slow waves in the centro-temporal regions. During the recording with a bipolar montage, the spike may have a phase reversal in the centro-temporal or parietal regions but less commonly in the frontal or the vertex areas. A more posterior predominance is often observed in the youngest subjects. The most striking finding of the centro-temporal spikes is their significant increase in frequency during light NREM sleep. When the frequency of centro-temporal spikes decreases abruptly during sleep, an underlying structural abnormality needs to be excluded.14
9
Focal Epilepsy
705
FIGURE 914. Benign Epilepsy with Centro-Temporal Spikes (BECTS); Horizontal Dipole. During the recording with referential montage, the centro-temporal spike shows a horizontal dipole configuration with a negative pole over the centro-temporal region and a positive pole over the frontal region.15,16 The clinical relevance of a dipole in BECTS has become a widely debated issue. Magnetoencephalogram (MEG) demonstrates that the spikes were generated by a single tangential dipolar source located in the precentral gyrus, closer to hand SII than to SI cortex, with the positive pole directed frontally and the negative pole directed centro-temporally.17,18
706
Focal Epilepsy
9
FIGURE 915. Contralateral Parietal-Midtemporal Spikes; Symptomatic Focal Epilepsy Due to Hemorrhagic Infarction Caused by Streptococcal Infaction. A 6-year-old girl with focal epilepsy with secondarily generalized tonic-clonic seizures caused by streptococcal infection. Her MRI/MRA is compatible with the diagnosis of hemorrhagic infarction in the left temporal-occipital region. EEG shows consistently slower frequency and less reactivity of the alpha rhythm in the left hemisphere and polymorphic delta slowing and sharp waves (open arrow) in the left posterior temporal region. In addition, there are trains of sharp waves in the right parietal-midtemporal region with horizontal dipole (double arrows), activated by drowsiness and sleep. The background activity of the right hemisphere, otherwise, is unremarkable. There is a very strong family history of nocturnal seizures. Despite active epileptiform activity in the right rolandic region in the subsequent EEGs, the patient has done well without clinical seizures. This EEG represents two types of abnormalities caused by both left temporal hemorrhagic infarction and the genetic trait of benign epilepsy with centro-temporal spikes (BECTS). Temporal-parietal spikes can occur in BECTS with or without epilepsy.
9
Focal Epilepsy
707
FIGURE 916. Malformation of Cortical Development with Cerebral Atrophy; Congenital CMV Infection. A 12-year-old girl with spastic right hemiparesis, developmental delay, and medically intractable epilepsy with epilepsia partialis continua (EPC) as a main type of seizure associated with a history of congenital CMV infection. CT and MRI showed an extensive malformation of cortical development in the left cerebral hemisphere, consisting of diffuse cerebral atrophy, widespread polymicrogyria (double arrows), and gyral calcifications (arrow). Interictal EEG demonstrates occasional bursts of bilateral synchronous frontal spikes with left-sided predominance (white arrow head) and mild asymmetry with amplitude lower in the left hemisphere. Patients with CMV infection with polymicrogyria suffer injury between approximately 18 and 24 weeks, whereas those with lissencephaly are injured before 16 or 18 weeks.19 Ictal SPECT is a useful tool in presurgical workup for the localization of the epileptogenic focus in patients with EPC with no definite ictal EEG localization.20,21
708
Focal Epilepsy
9
FIGURE 917. Epilepsia Partialis Continua (EPC); Ictal SPECT During Focal Clonic Seizure. (Same patient as in Figure 9-16) Ictal SPECT injection (*) was performed approximately 20 sec from the onset of right focal clonic seizure. Although EEG during the injection demonstrates no definite ictal activity except lambda asymmetry (arrow head), the ictal SPECT shows definite hyperperfusion in the left frontal parietal region (arrow). EEG in the early phase of a focal motor seizure can be normal or only show subtle abnormality; therefore, ictal SPECT is invaluable in localizing the epileptic focus. Ictal SPECT is a useful tool in presurgical workup for the localization of the epileptogenic focus in patients with epilepsia partialis continua with no definite ictal EEG localization.20,21
9
Focal Epilepsy
709
FIGURE 918. Ictal EEG Activity During Focal Clonic Seizure. (Same seizure as in Figure 9-16 and 9-17) EEG findings during the same episode of focal clonic seizure can be variable. The above EEG pages show more prominent rhythmic theta activity in the left parietal temporal regions compared to the EEG activity seen in Figure 9-17.
710
Focal Epilepsy
9
FIGURE 919. Rasmussen’s Encephalitis; Epilepsia Partialis Continua. An 18-year-old girl with EPC caused by Rasmussen syndrome. Axial FLAIR and coronal T2 MRIs show left cerebral hemiatrophy with increased signal intensity in the left fronto-parietal region (open arrows). Sagittal T1 MRI shows focal gyral enlargement in the left fronto-parietal region (open arrows). Ictal single photon emission computed tomography (SPECT) during EPC demonstrates hyperperfusion in the left fronto-parietal region (black arrow) corresponding to the lesion seen in the MRI. A reduced uptake of HMPAO (hypoperfusion) in the left temporal region in the interictal SPECT despite normal MRI was noted 6 months before the abnormalities, including abnormal neurological signs and left hemispheric atrophy in the MRI, were noted in the patient with EPC.22 Burke et al. found that SPECT with 99mTc-HMPAO was the only imaging study to suggest Rasmussen encephalitis and to localize an abnormality in a patient with a worsening clinical course and normal MRI and CSF examination.23 High concordance among clinical, EEG, CT, and SPECT studies in localization of epileptogenic foci were noted.24 Ictal SPECT showed focal hyperperfusion while EEG failed to show epileptic changes.25
9
Focal Epilepsy
711
FIGURE 920. Epilepsia Partialis Continua (EPC); Rasmussen’s Syndrome. An 18-year-old girl with EPC secondary to Rasmussen syndrome. Axial MRI with FLAIR shows left cerebral atrophy with increased signal intensity in the left frontal parietal region (white arrow). Ictal SPECT during EPC demonstrates hyperperfusion in the left parietal region corresponding to the lesion seen in the MRI (black arrow). Ictal EEG during continuous jerking of her right hand shows nearly continuous sharp waves and spikes in the left frontal-temporal region time-locked with right hand jerking (*). Intermixed polymorphic delta activity is also noted over the left hemisphere. Rasmussen syndrome is the most common cause of EPC. The EEG abnormalities vary widely depending on the stage of the disease with lateralized abnormalities early in the course and bilateral abnormalities in later stages. Polymorphic delta activity (PDA) occurred in all 49 patients studied at the Montreal Neurology Institute. PDA was unilateral in 19%, bilateral but with unilateral predominance in 68%, and symmetrical in 13%. In 32 patients in whom seizures were recorded, a localized onset was found in only 16%.26,27 An early and striking EEG feature in all cases was the presence of focal PDA, mainly over the central and temporal regions. Other EEG features were early ictal and interictal multifocal epileptiform activity over a single hemisphere, presence of subclinical ictal EEG activity, and progressive unilateral suppression of background activity. These abnormal EEG findings correspond to typical clinical features and an MRI indicating progressive disease is rarely observed in other conditions causing symptomatic focal epilepsy.28
712
Focal Epilepsy
9
FIGURE 921. Rasmussen Encephalitis; Periodic Lateralized Epileptiform Discharges (PLEDs). (Same patient as in Figure 9-19) An 18-year-old girl with Rasmussen encephalitis and epilepsia partialis continua (EPC). MRI shows a focal cerebral atrophy with increased signal intensity in the right fronto-parietal region (double arrows). Ictal SPECT demonstrates hyperperfusion in the same area as the abnormal MRI (open arrow). The scalp EEG in EPC is nonspecific and is determined by the underlying pathology. EEG can vary from normal to focal slowing with or without spikes or spike-wave complexes, especially over the central or centro-parietal regions. Focal epileptiform discharges may consist of spike, spike-and-wave, or polyspike-and-wave discharges.29 Focal periodic slow transients and PLEDs have been reported.30,31 Bilateral, but with unilateral predominant bursts of delta waves are the rule.26
9
Focal Epilepsy
713
FIGURE 922. HHE (Hemiconvulsions, Hemiplegia, Epilepsy) Syndrome. A 3-year-old boy with high fever, persistent left hemiclonic seizure, and lethargy. T2-weighted MRI shows diffusely increased signal intensity over the entire right hemisphere, maximal in the mesial temporal region. Ictal EEG during the left hemiclonic seizure demonstrates bilateral high-voltage rhythmic, slow waves, intermixed with spikes and polyspikes with amplitudes higher in the right hemisphere. Note the preservation of physiologic sleep spindles in the left frontal region (arrow). Note very low-voltage EEG activity in the C3-P3 channel caused by a salt bridge from excessive smearing of the gel. Rhythmic bilateral slow waves, with higher amplitude on the hemisphere contralateral to the clinical seizure, are seen in the initial phase of HHE syndrome.32
714
Focal Epilepsy
9
FIGURE 923. Hemiconvulsion-Hemiplegia Epilepsy (HHE) Syndrome. (Same patient as in Figure 9-22) EEG shows spike/polyspike-wave complexes time-locked with contralateral hemiclonic seizures of arm and face. Note muscle artifact, maximum in the left temporal region during the left facial twitching (open arrow). Axial and coronal T2 WI MRI shows increased signal intensity in the entire right hemisphere. The ictal EEG is characterized by rhythmic bilateral slow waves, with higher amplitude on the hemisphere contralateral to the clinical seizure. The spike-wave complexes are periodically interrupted by 1–2 sec of background attenuation.32
9
Focal Epilepsy
715
FIGURE 924. Hemiplegia Hemiconvulsion Epilepsy (HHE) Syndrome; Epilepsia Partialis Continua (EPC). (Same patient and EEG recording) The patient developed very frequent and, sometimes, continuous left hemiconvulsion with facial predominance, which led to left hemiparesis. During most of the EEG recordings, there was no consistent correlation between muscle jerks and EEG discharges. However, during some portions of the EEG (above), left facial twitching (*) was associated with spike/polyspike-wave discharges in the right hemisphere. Note muscle artifact, maximal at T5, caused by left facial twitching. Periodically diffuse flattening of the background EEG activity, maximally expressed in the right hemisphere (open arrow), was also noted. In the early phase of HHE, pseudorhythmic spike-and-wave discharges, contralateral to the clinical seizures, periodically interrupted by 1–2 sec of electrical flattening, can also be noted. Polygraphic recordings do not demonstrate any consistent relation between muscle jerks and EEG discharges.32 The causes of the initial convulsions in HHE syndrome include meningitis, subdural effusions, stroke, and trauma, although in many patients, no cause is found.33
716
Focal Epilepsy
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FIGURE 925. Orbitofrontal Seizure caused by Tuberous Sclerosis Complex (TSC); Secondary Bilateral Synchrony (SBS). A 15-year-old boy with TSC and gelastic seizures. The MRI shows prominent tuber (arrows) in the left orbitofrontal region. Ictal SPECT (double arrows) reveals hyperperfusion in the left lateral and basal frontal regions. Interictal EEG during sleep demonstrates generalized slow spike/polyspike-wave discharges. Frontal lobe seizures are often manifested by bisynchronous spike-wave discharges with poor localization or lateralization due to rapid spreading to contralateral frontal and ipsilateral temporal regions, causing no definite or even false localization or lateralization.34 Bisynchronous frontal or generalized interictal and ictal discharges are often seen with seizures originating from the mesial frontal region, cingulate gyrus, or orbitofrontal regions.35 Gelastic seizures can be a very rare manifestation of the seizure originating from the orbitofrontal region.36
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FIGURE 926. Tuberous Sclerosis Complex (TSC). A 12-year-old girl with tuberous sclerosis complex, mental retardation, and intractable epilepsy. Cranial MRI showed multiple cortical tubers in both hemispheres with the largest one in the right frontal region. Her EEG during the seizure shows an ictal onset zone described as a train of spikes in the right frontal-temporal region (open arrow). The patient underwent extraoperative subdural video-EEG monitoring with subsequent resection of the epileptogenic zone in the right frontal region. The ictal EEG activity during the invasive monitoring is somewhat similar to the scalp recording (see Figure 9-27). The patient had significant improvement of cognition and has been seizure-free since the surgery. Epilepsy surgery may be beneficial in select patients with TSC, despite multifocal interictal EEG and neuroimaging abnormalities.37 All patients in this study had ictal EEG foci corresponding to prominent neuroimaging abnormalities.
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FIGURE 927. Comparison of Ictal Scalp and Subdural EEG; Tuberous Sclerosis Complex. (Continued) Comparison of subdural EEG (A) and scalp EEG (B) during the patient’s typical seizures. The scalp and subdural EEG recordings show similarity of the ictal patterns with some loss of high-frequency activity in the scalp electrode due to volume conduction.
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FIGURE 928. Tuberous Sclerosis Complex (TSC). A 4-year-old girl with mental retardation and medically intractable epilepsy due to TSC. She had multiple types of seizures occurring in isolation or in combination. These included staring spells, head and eyes deviating to the right side, asymmetric tonic stiffening greater on the right side, myoclonic jerks, and drop attacks. (A) Axial FLAIR MRI shows multiple cortical tubers (white arrow) with subependymal nodules (arrow head). (B) Ictal SPECT scans show hyperperfusion in the left occipital region (large arrow). (C) Surface of the cortex illustrates cortical tubers (double black arrows), which are smooth, round, white, and firm to touch, and projected slightly above the surface of the surrounding cortex compared to normal cortex (black arrow). Ictal EEG during her typical seizure described as spacing out with head and eyes deviating to the right side demonstrates a run of spikes and sharp waves in the left occipital region. The patient was seizure-free for over 1 year after surgical resection of tubers and surrounding epileptogenic zone after invasive video-EEG monitoring. She then developed a new type of seizure described as a left focal motor seizure caused by a tuber in the right frontal region and required a second surgery that led to a greater than 95% seizure reduction and significant improvement of cognitive function. Epilepsy surgery in TSC can be performed safely. Good surgical outcome was related to concordance of seizure semiology, EEG, MRI, and ictal SPECT findings.37–39
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FIGURE 929. Tuberous Sclerosis Complex (TSC); Frontal Lobe Epilepsy with SSMA Seizure. (Same patient as in Figure 9-28) After the first epilepsy surgery in the left occipital region, the patient was seizure-free for more than 1 year and showed significant improvement of cognition. She then developed a new type of seizure. The seizure was described as an asymmetric epileptic spasm, greater on the left, followed by left arm and leg stiffening and clonic jerking of left hand. Prolonged video-EEG during the epileptic spasm shows bilateral synchronous spike-wave discharges followed by diffuse electrodecrement with superimposed beta activity (paroxysmal fast activity), maximal in the right fronto-central and fronto-central vertex regions, lasting for 3 sec. During asymmetric tonic stiffening, diffuse semi-rhythmic theta activity evolving into rhythmic 10-Hz alpha activity in the right centro-temporal region is noted. Ictal SPECT shows hyperperfusion in the right frontal region (black arrow), which is concordant with the EEG and MRI (white arrows). The patient has had greater than 90% seizure reduction and significant improvement of cognition since the second surgery (resection of epileptogenic zone and tuber in the right frontal region after invasive video-EEG monitoring). Seizures arising from the mesial frontal lobe are challenging to localize. Rhythmic alpha, beta, and theta at or adjacent to the midline were observed in 45% of cases.40 In another series, the ictal onset activity most commonly consisted of generalized paroxysmal fast activity, as seen in this patient.41 An epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity.42 Paradoxical lateralization is most likely the result of a horizontal dipole located within the interhemispheric fissure.43
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FIGURE 930. Apneic Spell: Cardiac Arrhythmia Associated with Cardiac Rhabdomyoma; Tuberous Sclerosis Complex (TSC). A 9-month-old boy who presented to the ED with recurrent apneic episodes. Physical examination revealed multiple hypopigmented patches over his body and limbs. MRI shows multiple cortical tubers and subependymal nodules. The diagnosis of TSC was made after the MRI. Although EEG recording shows no definite epileptiform activity, the ECG channel (box) shows a marked cardiac arrhythmia. Cardiology consultation revealed ventricular preexcitation syndrome with obstructive subaortic rhabdomyoma. Approximately 50–65% of patients with TSC have rhabdomyoma; most of the tumors usually regress with increasing age and are asymptomatic. Possible prevalence of Wolff-Parkinson-White syndrome WPW in TSC is 1.5%. The etiology of WPW in TSC is unknown. There was a hypothesis that some of the cells in the cardiac rhabdomyoma are structurally identical to normal Purkinje cells. Therefore, WPW may be caused by rhabdomyomatous tissue traversing the atrioventricular junction acting as the accessory pathway bypassing the atrioventricular node. Sudden unexpected death in infancy has been reported in TSC. It is possible that some of these cases may be caused by atrial arrhythmias, which, when associated with anterograde conduction down an accessory pathway, provoke ventricular fibrillation. Ten patients with concurrent diagnoses of WPW and TSC were reported by Callaghan.44 Nine cases were diagnosed during the first year of life. WPW was associated with supraventricular tachycardias in eight cases, and with cardiac rhabdomyoma in nine cases. One child died from cardiac failure secondary to obstruction of the left ventricular outflow tract by a rhabdomyoma. Therefore, cardiac arhythmia, most commonly, WPW and supraventricular tachycardia as well as cardiac rhabdomyomas must be considered in all patients with TSC. Infants diagnosed with tuberous sclerosis should always have an ECG and echocardiogram to exclude the possibility of pre-excitation and the presence of rhabdomyoma.44,45 Carbamazepine has been reported to induce cardiac arrhythmias in the patients with TSC who have cardiac rhabdomyomas and should be used with caution.46
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FIGURE 931. Symptomatic Focal Epilepsy Simulating Myoclonic Astatic Epilepsy (MAE); Focal Cortical Dysplasia (FCD). A 7-year-old girl with medically intractable epilepsy with multiple types of seizures, including myoclonic seizures, generalized tonic-clonic seizures, and drop attacks. Some of her myoclonic seizures involved predominantly or solely her right arm. (A) MRI with FLAIR sequence shows focal cortical dysplasia (FCD) in the left SSMA (arrow). (B) Interictal PET demonstrates diffuse hypometabolism in the left hemisphere but it is maximal in the left lateral frontal (open arrow) and SSMA (double arrows) regions. Hypometabolism in the left SSMA is concordant with the FCD seen in the MRI (arrow). EEG during one of her typical asymmetric myoclonic seizures, with right-sided predominance (*), shows low-voltage fast activity followed by a run of spikes in the left frontal region (open arrow) and then secondary bilateral synchronous slow spike-wave discharges with left frontal-temporal focus. Also note tachycardia (arrow head) during the burst of spike-wave activity. These findings are consistent with epileptic focus arising from the left SSMA and then propagating to the left motor area, causing asymmetric myoclonic seizure, maximally expressed on the right side. Patients presenting with clinical features compatible with MAE but with seizure semiology consistent with focal seizure or focal abnormality seen in the EEG or MRI should be further evaluated to rule out symptomatic focal epilepsy caused by a structural abnormality, especially FCD.
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FIGURE 932. Frontal Absence; Focal Cortical Dysplasia, Left Supplementary Sensorimotor Area (SSMA). (Same patient as in Figure 9-31) A 7-year-old girl with medically intractable epilepsy who had multiple types of seizures, including myoclonic seizure, generalized tonic-clonic seizure, and drop attack. At times, she had spacing out, subtle repetitive vocalization, rocking movement, and slight head and eyes turning to the right side with brief postictal confusion. (A) Axial MRIs with FLAIR and inversion recovery sequence show focal cortical dysplasia (FCD) in the left SSMA (arrow). EEG during one of her typical absence seizures shows generalized 2- to 2.5-Hz (poly) spike-and-wave discharges with higher amplitude over the left hemisphere. Frontal absences can be caused by epileptic discharges arising from several areas of the frontal region, including SSMA, orbitofrontal region, and cingulate gyrus. Compared with absences of childhood absence epilepsy, frontal lobe absences may have subtle repetitive vocalization, rocking movements, mild version, and brief postictal confusion. The patient may report awareness of motor arrest without loss of consciousness. The staring may evolve into a secondarily GTCS via version of the head and eyes, and focal or bilateral tonic posturing of upper limb(s). Frontal absences seem to have a more anterior epileptogenic zone than those with bilateral asymmetric tonic seizures. However, the clinical and EEG features can be very close to that of a typical or simple absence seizures.47,48 Secondarily generalized discharges are a common occurrence with frontal lobe epilepsy. The EEG findings that suggest secondary bilateral synchrony include (1) focal spikes or sharp waves consistently occurring in one area, (2) focal spike discharges that precede or initiate more generalized bursts, and (3) persistent lateralized abnormalities such as slowing or an asymmetry over the involved area.49,50
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FIGURE 933. Frontal Absence; Focal Cortical Dysplasia, Left Supplementary Sensorimotor Area (SSMA). (Same patient as in Figure 9-32) EEG recording in depth electrodes during her typical “frontal absence seizure” described as spacing out, unresponsiveness, and orofacial and hand automatisms demonstrates slow negative DC shifts (open arrow) at DC3 prior to diffuse low-voltage fast activity, maximally expressed at DC3 before the onset of generalized slow spike-wave discharges, which correspond to the clinical “absence seizure.” The scalp EEG recording captured only generalized spike-wave discharges but missed the low-voltage fast activity because the scalp and the skull act as a high-frequency filter and pass lower frequencies more than higher frequencies.51 Negative baseline shifts associated with seizure onset have been extensively studied in animals. Slow DC shifts during absence seizures has been reported.52–54
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FIGURE 934. Focal Myoclonic Seizure; Focal Cortical Dysplasia in Left Supplementary Sensorimotor Area (SSMA). (Same patient as in Figure 9-31) A 7-year-old girl with medically intractable epilepsy who had multiple types of seizures including myoclonic seizures, absence seizures, generalized tonic-clonic seizures and drop attacks. Axial MRIs with FLAIR and inversion recovery sequence show focal cortical dysplasia (FCD) in the left SSMA (open arrow). Sleep EEG during one of her myoclonic seizures (arrow) described as mild head jerking to the right side shows a positive sharp wave at F3.
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FIGURE 935. Focal Myoclonic Seizure; Focal Cortical Dysplasia in Left Supplementary Sensorimotor Area (SSMA). (Same patient as in Figure 9-31) A 7-year-old girl with medically intractable epilepsy who had multiple types of seizures including myoclonic seizures, absence seizures, generalized tonic-clonic seizures and drop attacks. Axial MRIs with FLAIR and inversion recovery sequence show focal cortical dysplasia (FCD) in the left SSMA (open arrow). Sleep EEG during one of her myoclonic seizures described as mild head jerking (arrow) to the right side shows a train of focal spike-wave discharges in the left frontal-central region. There is low-voltage fast activity overriding the last slow wave (arrow). The head jerking is slower than typical myoclonic seizure and may represent a very brief asymmetric tonic seizure.
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FIGURE 936. Bilateral Asymmetric Tonic Seizure; Supplementary Sensorimotor Area (SSMA) Seizure. (Same patient as in Figure 9-31) A 7-year-old girl with medically intractable epilepsy who had multiple types of seizures, including myoclonic seizures, absence seizures, generalized tonic-clonic seizures, and drop attacks. Axial MRIs with FLAIR and inversion recovery sequence show focal cortical dysplasia (FCD) in the left SSMA (arrow). Sleep EEG during one of her bilateral asymmetric tonic seizures described as head and eyes slightly turning to the right side with bilateral arm tonic posturing, right arm extension, and left arm flexion shows focal low-voltage fast activity (arrow) at C3 followed by generalized paroxysmal fast activity (double arrows). Although ictal involvement of SSMA produces bilateral tonic stiffening, ictal onset exclusively in the SSMA is rare. The ictal onset zone and the epileptogenic zone commonly extend beyond the SSMA to the primary motor cortex, premotor cortex, cingulate gyrus, and mesial parietal lobe.47,55 Paroxysmal fast activity was observed at the onset of seizures arising from the inferior aspect of the supplementary sensorimotor area and cingulate gyrus. Seizures from SSMA most commonly show paroxysmal fast activity (33%) or electrodecrements (29%) as the initial ictal pattern, whereas seizures from the lateral frontal lobe show repetitive epileptic discharges (36%) or rhythmic delta at onset (26%). Only 25% of SSMA epilepsy seizures showed correct localization or lateralization, and 75% showed no lateralization. Lateral frontal epilepsy showed correct localization in 60% and correct lateralization in additional 27%.56
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FIGURE 937. Focal Cortical Dysplasia; Intrinsic Epileptogenicity. A 2-year-old girl with an unusual seizure pattern. At 13 months of age, she had her first seizure described as “head and eye deviating to the right side with tonic stiffening of arms and legs (right arm extension and left arm flexion) without altered mental status” occurring 20–30 times daily. After treatment with carbamazepine, her seizures disappeared within 4 weeks but recurred at the age of 24 months. CT and MRI show focal cortical dysplasia (FCD) in the anterior-medial aspect of the left superior frontal gyrus (arrow). EEG demonstrates frequent bursts of polyspikes and low-voltage fast activity in the left fronto-central region (double arrows) compatible with intrinsic epileptogenicity of the FCD. During presurgical evaluation, her seizures improved. Subsequently, her carbamazepine was stopped by her parents. Since then, she has been seizure-free and had normal developmental milestones. Follow-up cranial MRIs showed no change of the FCD. Follow-up EEGs were unremarkable. Regional polyspikes, especially in the extratemporal location, are highly associated with focal cortical dysplasia (80%).57,58
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FIGURE 938. Focal Cortical Dysplasia (FCD); Subtle Epileptiform Activity. A 4-year-old right-handed girl with new-onset seizures described as “head and eyes deviating to the left side followed immediately by generalized tonic-clonic seizures.” She received treatment with intravenous lorazepam in the emergency department. (A) Axial MRI with FLAIR sequences exhibits increased signal intensity in the white matter underneath thickened cortex with blurred white and gray matter junction in the right frontal region (arrow). (B) Axial T2-weighted MRI shows focal cortical atrophy with increased subdural space adjacent to the focal cortical dysplasia (FCD) described in (A) (arrow). EEG done approximately 24 hours after the seizures demonstrates low-voltage spikes with polymorphic delta slowing in the right frontal region (small arrows) corresponding to the FCD. EEG can sometimes show only subtle abnormalities, especially after the treatment of seizures.
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FIGURE 939. Positive Spikes; Focal Transmantle Dysplasia, Right Frontal. (Same patient as in Figure 4-90 and 9-140) EEG shows positive and negative spikes in the right frontal area (box) with some spreading to the right anterior temporal area. Axial T2 WI MRI shows focal transmantle dysplasia in the right frontal region. Note board gyri (open arrow) with underneath subcortical hypointensity (double arrows) connecting to the ventricle (arrow). Focal transmantle dysplasia is a malformation of cortical development that extends through the entire cerebral mantle, from the ventricular surface to the cerebral cortex. The presence of balloon cells suggests that these malformations are associated with maldifferentiation of the stem cells generated in the germinal zone.59 The presence of positive spikes is indicative of deep epileptogenic focus caused by deep focal transmantle dysplasia.
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FIGURE 940. Dyke-Davidoff-Mason Syndrome; Left Frontal Spikes. (Same patient as in Figure 4-8 and 4-10) A 9-year-old left-handed girl with right hemiparesis and hemiatrophy due to intrauterine stroke who developed a new-onset right-sided focal motor seizure with secondarily generalized tonic-clonic seizure. Cranial MRI shows encephalomalacia in the left frontal-temporal region, left cerebral hemiatrophy, and thickening of the clavarium. These findings are compatible with Dyke-Davidoff-Mason syndrome. EEG during sleep shows spikes in the left frontal region (F3) with suppression of vertex waves in the left central region (C3). The epileptogenic focus is at the rim of the remote stroke, not within the lesion.
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FIGURE 941. Focal Clonic Seizures; Focal Cortical Dysplasia. A 13-month-old right-handed boy with medically intractable epilepsy due to focal cortical dysplasia (FCD) in the right parietal region. His typical seizure was described as “a sudden onset of irritability, left facial twitching, left arm stiffening, and eyes deviating to the left side.” This EEG was recorded during one of his typical seizures. He had facial twitching and head jerking time-locked with right frontal-anterior temporal spikes (X). MRI shows an FCD in the right parietal region (arrow). The patient has been seizure-free since the surgical resection of the FCD and surrounding epileptogenic zone after invasive video-EEG monitoring.
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FIGURE 942. Frontal Lobe Epilepsy; Interictal Psychosis. An 8-year-old girl with a long history of severe psychotic symptoms, including agitation, aggression, and hallucination, despite adequate treatment with antipsychotic drugs. She has not had a family history of psychosis. Her previous routine EEGs and MRIs were reported as normal. Axial FLAIR and coronal T2-weighted MRIs show thickened and smoothed cortex with mildly increased signal intensity in the right lateral frontal area (arrows) consistent with focal cortical dysplasia. Interictal EEG during prolonged video-EEG monitoring demonstrates very frequent bilateral synchronous spikes in bifrontal regions, which are compatible with “secondary bilateral synchrony”. Her psychotic symptoms completely disappeared within 1 week after the treatment with phenytoin. Antipsychotic drugs were stopped shortly after the diagnosis of interictal psychosis. She has done extremely well without psychiatric symptoms and been seizure-free without AEDs for over 4 years. Interictal psychosis is a very rare condition. It is seen in temporal lobe epilepsy, but rarely in frontal lobe epilepsy.60–62 The prevalence of interictal psychosis is approximately 3–7%.63 Interictal psychosis of epilepsy is characterized by the presence of psychotic symptoms not temporally related to seizure activity and lasting 6 months or more, and the presence of delusions, hallucinations in clear consciousness, bizarre or disorganized behavior, formal thought disorder of affective changes without any evidence of AED toxicity, EEG findings consistent with nonconvulsive status epilepticus, recent head trauma, and alcohol or drug intoxication or withdrawal. Diagnosis can be made by EEG.64
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FIGURE 943. Frontal Lobe Seizure; Interictal Psychosis in Frontal Lobe Epilepsy. (Same recording as in Figure 9-42) The ictal EEG onset (open arrow) during arousal from sleep shows bilateral synchronous frontal polyspikes, maximum on the right (arrow). It is followed by diffuse background attenuation with superimposed low-voltage fast activity. Subsequently, bilateral synchronous rhythmic delta activity with anterior predominance (arrow head) is noted. Postictally, FIRDA with right hemispheric predominance (double arrows) is noted. Clinically, she was awoken from sleep with excessive movement of her right upper and lower extremities and stiffening of her left upper and lower extremities. She was very agitated and had excessive vocalization. She went back to sleep after the seizure. Nocturnal hypermotor seizures are most commonly seen in frontal lobe epilepsy (FLE). Ictal vocalization is a potential lateralizing sign in patients with FLE. The mechanism is unclear, although either the dominant hemisphere from inhibition through the nondominant hemisphere or, alternatively, overexcitement of the nondominant hemisphere was supected.65 However, ictal vocalizations have also been observed after stimulation of the contralateral non-language-dominant anatomical Broca equivalent.66 Additionally, vocalizations have also been seen after stimulation of the SSMA, but more frequently in the language-dominant hemisphere.67
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FIGURE 944. Frontal Lobe Epilepsy; Focal Cortical Dysplasia (FCD). An 11-year-old boy with a history of intractable generalized tonic-clonic seizures (GTCS). Recently, the patient turned his head to the right side immediately prior to some of his GTCS. Five routine EEGs during wakefulness and sleep were within normal limits. He was admitted to an epilepsy monitoring unit. One seizure was described as “head and eyes deviating to the right side with right arm extension and left arm flexion followed by generalized tonic-clonic seizure.” The ictal EEG with laplacian montage shows a burst of spikes (black arrow), diffuse electrodecrement (black arrow head), and a run of spike-wave discharges (double arrows) followed by sharply-contoured rhythmic theta activity in the bifrontal region with left-sided predominance (big arrow). MRI shows subtle focal cortical dysplasia in the left frontal region (white arrow head). The patient with frontal lobe seizures can present with generalized tonic-clonic seizures. Routine EEGs can be normal or show generalized epileptiform activity. Prolonged video-EEG is the gold standard with which to identify epileptic focus if focal seizures are suspected. Limitations of scalp EEG recording in the frontal lobe include the following: only a small portion of the frontal lobe is accessible, rapid seizure spread within and outside the frontal lobe can occur, small epileptogenic lesions may be located deep in the frontal lobe beyond the resolution of scalp recording. There are common findings of bifrontal or generalized interictal or ictal epileptic abnormalities.68
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FIGURE 945. Six-Hertz-Spike-and-Wave Discharges; Remote Right Fronto-Temporal Stroke. A 9-year-old girl with a new-onset left focal clonic seizure. Head CT shows remote stroke in the right fronto-temporal-insular region. EEG shows asymmetric low-voltage bilateral synchronous 6-Hz spike-and-wave discharges with right hemispheric predominance. “ Six-hertz spike-and-wave discharges (phantom spikes)” are seen in adolescents and young adults. These are described as bursts of 1- to 2-sec-duration, diffuse, low-voltage, 5- to 7-Hz spike-and-wave discharges, commonly bifrontally or occipitally. This EEG pattern is regarded as a benign variant of uncertain significance.69 In this patient, the 6-Hz spike-and-wave discharges are most likely a pathologic finding caused by the remote right fronto-temporal stroke rather than a benign variant.
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FIGURE 946. Parietal Lobe Epilepsy; Focal Cortical Dysplasia. A 15-year-old right-handed girl with medically intractable focal epilepsy due to focal cortical dysplasia (FCD). Her seizure was described as “a tingling sensation in her right foot followed immediately by shaky feeling all over her body and limbs,” which was greater on the right side. Visible clonic limb jerking was noted on both sides, especially on the right side. She also had a nonspecific feeling of fear with palpitations in her chest and urinary urge during the seizure. The seizure lasted for approximately 20–50 sec without loss of consciousness. After some of her seizures, she could not move her right arm for 1–2 minutes. Axial MRI with inversion recovery sequence shows thickening of the cortex and blurring of the gray-white matter junction in the left mesial parietal lobe (arrow). Ictal SPECT shows hyperperfusion in the left superior parietal region adjacent to the lesion seen in the MRI (double arrows). EEG shows frequent and, at times, continuous spikes and polymorphic delta activity in the central vertex with some spreading to both parasagittal regions. The seizure semiology, EEG, MRI, and ictal SPECT are supportive of the diagnosis of left parietal epilepsy caused by FCD. Intrinsic epileptogenicity in focal cortical dysplasia (FCD) is caused by abnormal synaptic interconnectivity and neurotransmitter changes within the lesion.70,71 FCD has intrinsic epileptogenicity with unique EEG patterns, including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.72 The incidences of intrinsic epileptogencity in FCD were 11–20% in different series. Polymorphic delta activity indicative of white matter involvement is commonly seen in FCD.73–75 Trains of continuous or very frequent rhythmic spikes or sharp waves and recurrent electrographic seizures on the scalp EEG were seen in up to 44% of FCD in one series.73 In all patients with FCD, the seizure onset zone was located within the lesion. Lesional non-SOZ areas might not be directly involved in the seizure origin but might turn into a seizure focus after the removal of primary epileptogenic tissue; therefore, removal of the entire lesion and surrounding interictally active tissue is necessary.76 Removal of the FCD alone does not lead to a good outcome, suggesting a more widespread epileptogenic network.77,78 Midline spikes are highly epileptogenic. Most patients have different types of clinical seizures, most commonly generalized tonic-clonic or SSMA seizures. Over two-thirds of the patients were neurologically impaired. Most of midline spikes originate from the mesial or paramedian region of the cerebral cortex. They are more common in children than in adults and are markedly activated with sleep. They must be distinguished from normal sleep transients. In the patients with SSMA seizures, routine EEG findings were usually normal, but prolonged EEGs showed epileptiform discharges over the vertex. Typical seizures are either unilateral or bilateral tonic limb involvement with preserved consciousness.79–81
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FIGURE 947. Parietal Lobe Epilepsy (PLE). (Same patient as in Figure 9-46) AXIR MRI shows thickening of the cortex and blurring of gray-white matter junction in the left mesial parietal lobe (arrow). Ictal SPECT shows hyperperfusion in the left superior parietal region adjacent to the lesion seen in the MRI (double arrows). Ictal EEG activity during one of her typical seizure shows rhythmic 17- to 19-Hz beta activity in the central vertex with poorly defined lateralization. The scalp EEG is frequently negative or maybe misleading; furthermore, spread of epileptic discharges from the parietal and occipital lobes to frontal and temporal regions may obscure seizure origin.82 Ictal EEG in PLE is predominantly lateralized; the maximum ictal activity was over either the central-parietal or the posterior head region in most patients. Localized parietal seizure onset was noted in only 4 out of 36 patients.83 Surface EEG monitoring is often nonlocalizing and unreliable for parietal lobe seizures.84,85 Foldvary et al. reported false localization/lateralization in 16% of PLE.56 The low sensitivity of extracranial ictal EEG may have been related to the predominance of simple partial seizures.86
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FIGURE 948. Closely Spaced Scalp Electrodes; Mesial Parietal Lobe Epilepsy. (Same EEG page as in Figure 9-46) Adding extra electrodes (P1, P2, C1, C2) helps to define the epileptic focus in the P1 electrode (arrow), which is located between Pz and P3. This finding is invaluable to confirm the lateralization and localization of the epileptic focus, which will be invaluable in surgical planning. Epileptogenic zone in the frontal, occipital, insular, parietal, and orbitofrontal regions may show falsely localizing IEDs. Closely spaced scalp electrodes can improve the yield of spike detection and localization over the standard 10-20 System.68,87,88
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FIGURE 949. Simple Partial Seizure (Somatosensory). Subdural EEG (sEEG) recording during one of her typical “auras” described as “tingling of her right foot with rapid marching to the whole right side of the body.” The scalp EEG was unremarkable during most of these seizures. All ictal sEEGs show low-voltage fast activity in the left parietal area (circle) lasting for 4–5 sec (arrow). The most frequent anatomical localization of somatosensory auras (SSAs) was in the upper extremities, followed by lower extremities and then face. An aura involving the foot was found in about 13%; 48.7% had purely SSAs, whereas evolution of motor seizures occurred in 47.4%. Tingling was the most common symptom (76%) of SSAs. SSAs are highly correlated with an epileptogenic zone in the central parietal region, particularly if they are well localized in the distal extremity and are associated with a sensory march. It was found to have localizing value in 96% with central parietal epilepsy.89–91
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FIGURE 950. Comparison of Scalp and Subdural EEG recording in Simple Partial Seizure Due to Mesial Parietal Cortical Dysplasia. (Same patient as in Figure 9-46) MRI shows thickened cortex with blurring of the gray and white matter junction (arrow). During most of the patient’s simple partial seizures (SPS) described as right foot numbness with rapid spread to the right thigh, right side of the trunk, arm, and face, the scalp EEG recording showed no change from the baseline. However, approximately 15–20% of the scalp EEGs during these seizures (as shown on the left) demonstrate diffuse low-voltage spikes in the parasagittal area in both hemispheres without definite lateralization (arrow head). The characteristics of ictal EEG during scalp EEG recording (left) and subdural EEG recording (right) on separate episodes of SPS are quite similar, except for the difference in voltage that is lost during scalp EEG recording due to volume conduction when they pass through resistances, including the meninges, CSF, skull, and scalp.
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FIGURE 951. Paradoxical Lateralization; Focal Cortical Dysplasia: Left Parietal Lobe. (Same patient as in Figure 9-46) The extra electrodes (F3’, F4’, C3’, C4’, P3’, and P4’) were added between the frontal, central, and parietal electrodes in both hemispheres and the Fz, Cz, and Pz electrodes to precisely identify the epileptic focus. An interictal EEG shows a train of spikes in the Pz and P4’ electrodes (large arrow), which are opposite to the epileptic focus caused by a focal cortical dysplasia (FCD) in the left parietal region (arrow). The patient has been seizure-free since the resection of epileptogenic zone, which included the FCD and surrounding tissue in the left lateral and mesial parietal region. An epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity.42 “Paradoxical lateralization” is most likely the result of a horizontal dipole located within the interhemispheric fissure.43 Magnetoencephalogram (MEG) only detects dipoles horizontal to the surface, and is more sensitive to generators lining the sulci than ones from gyral surfaces. Therefore, MEGs may be helpful in detecting an epileptic focus in the mesial aspect of hemispheres.92
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FIGURE 952. Paradoxical Lateralization of Epileptic Focus. A 3-month-old girl with a hypoplastic left ventricle who developed a watershed infarction in the left mesial parietal region (arrow). The interictal EEG performed for focal clonic jerking of the right arm shows a train of board sharp waves in the right central-parietal region (*). Epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity. “Paradoxical lateralization” is most likely the result of a horizontal dipole located within the interhemispheric fissure.42,43,93 Magnetoencephalogram (MEG) may be helpful in detecting an epileptic focus in the mesial aspect of hemispheres as it detects only dipoles horizontal to the surface and is more sensitive in the detection of generators lining the sulci than ones from gyral surfaces.92
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FIGURE 953. Occipital Lobe Epilepsy; Intrinsic Epileptogenicity (Nearly Continuous Spikes) in Focal Cortical Dysplasia (FCD). A 4-year-old boy with medically intractable epilepsy secondary to focal cortical dysplasia (FCD) in the left occipital region. His seizures were stereotypic and were described as “head and eyes deviating to the right side and horizontal nystagmus with a fast component on the left side.” Axial and coronal MRI images show abnormal gyral pattern, blurring of the gray and white matter junction, and white matter hyperintensity in the left occipital region compatible with FCD (arrow). EEG shows nearly continuous epileptiform activity and polymorphic delta slowing in the left occipital region. Intrinsic epileptogenicity in focal cortical dysplasia (FCD) is caused by abnormal synaptic interconnectivity and neurotransmitter changes within the lesion.70,71 FCD has intrinsic epileptogenicity with unique EEG patterns, including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.72 The incidences of intrinsic epileptogencity in FCD were 11–20% in different series. Polymorphic delta activity indicative of white matter involvement is commonly seen in FCD.73–75 Trains of continuous or very frequent rhythmic spikes or sharp waves and recurrent electrographic seizures on the scalp EEG were seen in up to 44% of FCD in one series.73 In all patients with an FCD, the seizure onset zone was located within the lesion. Lesional non-SOZ areas might not be directly involved in the seizure origin but might turn into a seizure focus after the removal of primary epileptogenic tissue; therefore, removal of the entire lesion and surrounding interictally active tissue is necessary.76 Removal of the FCD alone does not lead to a good outcome, suggesting a more widespread epileptogenic network.77,78
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FIGURE 954. Ictal SPECT. (Continued from the previous EEG page) EEG shows evolving ictal activity in the left occipital region and postictal stage (third segment). Ictal SPECT injection was performed 13 sec after the ictal EEG onset in O1 (open arrow). Ictal SPECT shows hyperperfusion in the left occipital region (arrow). Note postictal delta slowing, maximally expressed in O1 and Fp1 (double arrows). An Fp-O EEG pattern is an age-dependent nonspecific EEG pattern reflecting the maturational process of the brain seen in both idiopathic (Panayiotopoulos syndrome) and symptomatic focal epilepsy.12
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FIGURE 955. Intrinsic Epileptogenicity; Focal Cortical Dysplasia (FCD). A 6-year-old boy with symptomatic focal epilepsy due to focal cortical dysplasia (FCD). Axial and coronal MRIs reveal FCD in the left occipital region (arrow). Interictal EEG shows continuous spike-wave activity in the left occipital region, which is concordant with the MRI finding. The presence of continuous spike-wave activity in the EEG is indicative of intrinsic epileptogenicity of the FCD. Long trains of nearly continuous or pseudoperiodic localized spikes are characteristics found in scalp EEGs in FCD and are seen in 22–44% of the patients.73,75
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FIGURE 956. Intrinsic Epileptogenicity; Focal Cortical Dysplasia (FCD). (Same patient as in Figure 9-55) FDG-PET scan during continuous left occipital spikes demonstrates hypometabolism in the left temporo-occipital region, which is much larger than the FCD and the area of intrinsic epileptogenicity. FDG-PET is very sensitive in localizing the area of seizure onset in patients with focal epilepsy, and includes areas outside the epileptogenic zone, and overestimates the extent of surgical resection needed to achieve seizure freedom. Glucose metabolism is nonspecific and can be seen in patients without seizures such as periventricular leukomalacia. The area of hypometabolism in FDG-PET does not necessarily correspond precisely to the seizure onset zone.94 Flumazenil (FMZ) PET scan detected at least the seizure onset zone in all patients, whereas FDG-PET failed to detect the seizure onset zone in 20%. Neither FMZ nor FDG PET was sensitive in identifying cortical areas of rapid seizure spread.95 In the patients with neocortical epilepsies, the cortical areas of decreased FMZ binding showed good correspondence and were smaller than the areas of glucose hypometabolism in FDG-PET.94
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FIGURE 957. Occipital Lobe Epilepsy; Focal Cortical Dysplasia. (Same patient as in Figure 9-55) Ictal EEG during the seizure characterized by visual hallucination (“figures look larger”), vertigo, imbalance, and head and eyes deviating to the right side demonstrates evolution of the frequency, amplitude, and shape of the waveforms with only mild spreading to the adjacent areas and opposite homologous hemisphere. The most common ictal EEG onset in occipital lobe seizures involving the posterior temporal occipital region. Ictal onsets restricted to the occipital lobe were seen in only 17%. The most common pattern of spread involved the ipsilateral mesial temporal structures.83 Ictal onset was localized to the occipital lobe in 30% and to the temporal and occipitotemporal region in 27%, and was more diffuse in 43%.96 False localization and lateralization occurred in 28% of occipital seizures.56
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FIGURE 958. Intrinsic Epileptogenicity; Occipital Lobe Epilepsy Caused By Focal Cortical Dysplasia (FCD). An 11-year-old girl with medically intractable epilepsy and right homonimous hemianopsia due to FCD in the left occipital region (open arrow). Her seizure was described as seeing different color spots in both eyes without alteration of awareness. Occasionally, she had generalized tonic-clonic seizures with headache and vomiting. EEG demonstrates continuous spikes and sharp waves and polymorphic delta activity in the left occipital region (double arrows) with some spread to the adjacent areas. Intrinsic epileptogenicity in focal cortical dysplasia (FCD) is caused by abnormal synaptic interconnectivity and neurotransmitter changes within the lesion.70,71 FCD has intrinsic epileptogenicity with unique EEG patterns, including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.72 The incidences of intrinsic epileptogencity in FCD were 11–20% in different series. Polymorphic delta activity indicative of white matter involvement is commonly seen in FCD.73–75 Trains of continuous or very frequent rhythmic spikes or sharp waves and recurrent electrographic seizures on the scalp EEG seen in up to 44% of FCD in one series.73 In all patients with FCD, the seizure onset zone was located within the lesion. Lesional non-SOZ areas might not be directly involved in the seizure origin but might turn into a seizure focus after the removal of primary epileptogenic tissue; therefore, removal of the entire lesion and surrounding interictally active tissue is necessary.76 Removal of the FCD alone does not lead to a good outcome, suggesting a more widespread epileptogenic network.77,78
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Focal Epilepsy
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FIGURE 959. Polymorphic Delta Activity & Sharp Wave; Left Temporal-Occipital Tumor. (Same patient as in Figure XXX) EEG with a laplacian montage shows a sharp wave and polymorphic delta activity in the left temporo-occipital region with some spread to the homologous area in the right hemisphere. Asymmetric photic driving response (previous page), in combination with lateralized polymorphic delta activity and sharp wave (arrow), supports the diagnosis of focal epilepsy caused by a structural abnormality in the left temporal-occipital area (open arrow). The homologous area in the contralateral hemisphere, especially in the frontal and occipital regions, may be associated with similar slow waves and sharp waves, usually of lower amplitude. These findings may be caused by compression, edema, ischemia in the opposite hemisphere, transmission through commissural fibers, or volume conduction.50,97
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FIGURE 960. Left Occipital and Mesial Temporal Cortical Dysplasia. (Same patient as in Figure 9-53) A 4-year-old boy with medically intractable epilepsy secondary to focal cortical dysplasia (FCD) in the left occipital region. His seizures were stereotypic and were described as head and eyes deviating to the right side and horizontal nystagmus with fast component to the left side. Brain MRIs show focal cortical dysplasia in the left occipital region (arrow) without hippocampal abnormality (not shown). (A) Subdural EEG shows ictal activity arising from the left lateral occipital region (double arrows) during his typical versive seizure and epileptic nystagmus. (B) Subdural EEG shows ictal activity arising from the left hippocampus (open arrow) approximately 45 sec before spreading to the left occipital electrodes (double arrows) when the patient starts having a typical versive seizure with epileptic nystagmus. Complete resection of the epileptogenic zone in the left occipital region as well as left anterior temporal lobectomy results in seizure freedom. Pathology revealed grade 2 focal cortical dysplasia in both the occipital lobe and the hippocampus without hippocampal sclerosis. Removal of the lesion seen in MRI alone may not lead to a favorable outcome, suggesting a more widespread epileptogenic network or multiple focal cortical dysplasia in these patients.98 Subdural EEG covering the adjacent cortex or remote cortex, especially mesial temporal, is necessary for a complete resection of epileptogenic zone.
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FIGURE 961. Mesial Temporal Lobe Epilepsy (mTLE); Mesial Temporal Sclerosis (MTS). A 15-year-old girl with a history of febrile convulsion who developed medically intractable epilepsy. Her typical seizure is described as an “epigastric sensation and orofacial and hand automatisms without loss of consciousness.” Occasionally, the automatisms were followed by GTCS. MRI with T2-weighted image shows right hippocampal atrophy with increased signal intensity consistent with mesial temporal sclerosis (open arrow). Interictal PET shows hypometabolism in the right mesial and lateral temporal regions (small arrows). The patient has been seizure-free for more than 3 years after the right temporal lobectomy. EEG during sleep shows frequent right anterior temporal spikes (arrow head) and polymorphic delta activity in the temporal region. No epileptiform activity is noted in the left temporal area. Patients with MTS have >90% of the IEDs in the anterior temporal region. Therefore, frequent posterior or extratemporal sharp waves make the diagnosis of MTS less certain. Rarely, IEDs can be seen in lateral temporal and frontal regions due to spreading of the discharges to the orbitofrontal or temporal neocortex via the limbic system. In MTLE, concordance of abnormal MRI and IED is associated with good surgical outcome and is a better indicator than concordance of abnormal MRI and ictal EEG activity but nonlateralizing IEDs.102 Although bilateral IEDs decrease the chance of favorable postoperative outcome, patients with bitemporal IED but with MRI hippocampal abnormalities concordant with the ictal-onset region still can have a good-to-excellent surgical outcome.68 Automatisms with preserved responsiveness were observed exclusively during seizures arising from the right nondominant temporal lobe. They were not observed during seizures arising from the left temporal region.99
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FIGURE 962. Mesio-Temporal Lobe Epilepsy (mTLE); Dual Pathology: Focal Cortical Dysplasia (FCD) and Hippocampal Sclerosis. A 12-year-old left-handed boy with a history of recurrent staring spells accompanied by hand and orofacial automatisms without altered mental status. Sometimes, he also had a feeling of “heart palpitation” immediately prior to or during the seizures. He had no past history of febrile seizure. Axial FLAIR and coronal T2-weighted MRIs reveal increased signal intensity and decreased volume of the right hippocampus (arrows). EEG shows periodic sharp waves in the right anterior temporal region (arrow heads). Clinical features, EEG and MRI scans support the diagnosis of right mesial temporal lobe epilepsy. WADA test was compatible with nondominant right temporal lobe. The patient has been seizure-free since the right temporal lobectomy. Pathology showed a mild malformation of cortical development in the inferior temporal region and severe hippocampal sclerosis (dual pathology). IEDs in MTLE show negative spikes and sharp waves in the sphenoidal, T1/T2, and F7/F8 electrodes. These IEDs are an expression of epileptiform activity in the parahippocampal cortex. Spikes in the hippocampus are usually not seen in scalp electrodes (So, 2001). Most IEDs are accompanied by a widespread positivity over the contralateral central-parietal region or vertex.100 Bilateral IEDs occur in one-third of patients, often during NREM sleep. IEDs recorded during wakefulness and REM sleep are more often lateralized and closely associated with the area of seizure onset.101 Patients with MTS have >90% of their IEDs in the anterior temporal region. Therefore, frequent posterior or extratemporal sharp waves are red flags for the diagnosis of hippocampal sclerosis. Rarely, IEDs can be seen in lateral temporal or frontal regions due to spreading of the discharges to the orbitofrontal or temporal neocortex via the limbic system. In MTLE, concordance of abnormal MRI and IEDs is associated with good surgical outcome and is a better indicator than concordance of abnormal MRI and ictal EEG activity but nonlateralizing IEDs.102 Although bilateral IEDs decrease the chance of favorable postoperative outcome, patients with bitemporal IEDs but MRI hippocampal abnormalities concordant with the ictal-onset region still can have a good to excellent surgical outcome.68 Seizure recording may not be necessary if serial routine EEGs are consistently concordant with MRI-identified unilateral hippocampal atrophy.103 Automatisms with preserved responsiveness were observed exclusively during seizures arising from the right nondominant temporal lobe. They were not observed during seizures arising from the left temporal region.99
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FIGURE 963. Temporal Lobe Epilepsy; Left Temporal Ganglioglioma. A 12-year-old boy with medically intractable epilepsy and deterioration of memory. His seizures were described as spacing out and loss of consciousness with orofacial and hand automatisms. Sagittal T1-weighted MRI shows a cystic cavity with a signal isointense to CSF in the left mesial temporal region. Note primary white matter involvement adjacent to the cyst. These findings are consistent with ganglioglioma. EEG shows rhythmic sinusoidal alpha activity intermixed with spikes and delta slowing in the left temporal region, maximally expressed at T3 (double arrows). Also note low-voltage polymorphic delta activity, maximally expressed at T3. In the scalp EEG, slow-wave activity was present in 62%. Its distribution was most commonly regional and then multiregional, or generalized. The slow-wave activity was more commonly absent in temporal than extratemporal tumor groups. Interictal epileptiform discharges occurred in 32 of the 37 patients and were present in all of those with extratemporal epilepsy. They were most often multiregional (n = 15), or regional (n = 12), or multiregional and generalized (n = 5). They were usually found over the lobe involved by the tumor, but in three patients, they were predominantly contralateral. An interictal mirror focus was found in 26.9% of patients with temporal lobe epilepsy.104 Another study of ganglioglioma in temporal lobe revealed scalp IEDs ipsilateral temporal in 71% of patients, bitemporal in 19%, and generalized in 19%.105
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FIGURE 964. Focal Polymorphic Delta Activity (PDA); Left Anterio-Mesial Temporal Ganglioglioma. (Same patient as in Figure 9-63) EEG shows continuous medium-voltage polymorphic delta activity (PDA) (double arrows) at T5 during laplacian run. Continuous PDA is highly correlated with a focal structural lesion, more prominent in acute than chronic processes. PDA is often surrounded by theta waves and maximally expressed over the lesions. Superficial lesions cause a more restricted field, and deeper lesions cause hemispheric or even bilateral distribution. A lower voltage of PDA is seen over the area of maximal cerebral involvement, but higher voltage PDA is noted in the border of lesions. More severe PDAs (closer to the lesion, more acute, higher association with underlying structural abnormality) consist of the following: (1) greater variability (most irregular or least rhythmic), (2) slower frequency, (3) greater persistence, (4) less reactivity, (5) no superimposed beta activity, and (6) less intermixed activity above 4 Hz. In the scalp EEG, slow-wave activity was present in 62%. Its distribution was most commonly regional and then multiregional, or generalized. The slow wave activity was more commonly absent in temporal than extratemporal tumor groups.104
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Focal Epilepsy
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FIGURE 965. Periodic Lateralized Epileptiform Discharges (PLEDs); Left Temporal Ganglioglioma. (Same patient as in Figure 9-63) EEG shows periodic sharp waves at T3 and T5 during the laplacian run. PLEDs were first described by Chatrian et al.106 as an EEG pattern consisting of sharp waves, spikes (alone or associated with slow waves), or more complex waveforms occurring at periodic intervals. They usually occur at the rate of 1–2/sec and are commonly seen in the posterior head region, especially in the parietal areas. It is sometimes associated with EPC.107 This EEG pattern is usually related to an acute or subacute focal brain lesion involving gray matter.108 Chronic PLEDs were also reported in 9% of patients with intractable epilepsy who had structural abnormalities such as cortical dysplasia or severe remote cerebral injury.109,110 In a recent review of 96 patients with PLEDs,111 acute stroke, tumor, and CNS infection were the most common etiologies. Others included acute hemorrhage, TBI, PRES, familial hemiplegic migraine, and cerebral amyloidosis. PLEDs were more periodic when they were associated with acute viral encephalitis than with other etiologies.112 Seizure activity occurred in 85% of patients with a mortality rate of 27%. However, 50% of patients with PLEDs never developed clinical seizures.110
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Focal Epilepsy
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FIGURE 966. Temporal Intermittent Rhythmic Delta Activity (TIRDA); Left Orbitofrontal–Mesial Temporal Tumor. A 13-year-old boy with a single episode of unprovoked seizure described as a mood change of “grumpiness” 30 minutes prior to the seizure followed by slumping over to the right and becoming unresponsive. During this time, he was drooling and had some upper body trembling that progressed to full-body shaking. The episode lasted 30 minutes altogether. After the seizure, he had slurred speech and a right Todd’s paralysis. He also has had aggressive behavior and depression. MRI shows a mass lesion that displaces the A1 segment superiorly and anteriorly, courses along the lateral wall of the cavernous sinus, and extends into the medial aspect of the left temporal fossa. EEG shows a brief run of monomorphic 1.5- to 2-Hz delta activity at F7-T3 consistent with TIRDA. TIRDA has the same clinical significance as anterior temporal spikes/sharp waves, a characterisctic EEG finding seen in MTLE and hippocampal sclerosis.113,114
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Focal Epilepsy
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FIGURE 967. Mesio-Temporal Lobe Epilepsy (mTLE); Right Anterior Temporal Spikes. An 18-year-old right-handed girl with autism and intractable complex partial seizures described as a “catatonic stare” with lip smacking and hand automatisms since 2 years of age. In the past 2 years, she started having secondarily generalized seizures. MRI shows right hippocampal atrophy. Interictal PET scan shows hypometabolism in the right temporal lobe. All routine EEGs were normal. Prolonged video-EEG shows subtle right anterior temporal spikes (*), best seen at the T1-T2 channel. IEDs in MTLE show negative spikes and sharp waves in the sphenoidal, T1/T2, and F7/F8 electrodes. These IEDs are an expression of epileptiform activity in the parahippocampal cortex. Spikes in the hippocampus are usually not seen in scalp electrodes (So, 2001). Most IEDs are accompanied by a widespread positivity over the contralateral central-parietal region or vertex.100 Bilateral IEDs occur in one-third of patients, often during NREM sleep. IEDs recorded during wakefulness and REM sleep are more often lateralized and closely associated with the area of seizure onset.101 Patients with MTS have >90% of their IEDs in the anterior temporal region. Therefore, frequent posterior or extratemporal sharp waves are red flags for the diagnosis of hippocampal sclerosis. Rarely, IEDs can be seen in lateral temporal or frontal regions due to spreading of the discharges to the orbitofrontal or temporal neocortex via the limbic system. In MTLE, concordance of abnormal MRI and IEDs is associated with good surgical outcome and is a better indicator than concordance of abnormal MRI and ictal EEG activity but nonlateralizing IEDs.102 Although bilateral IEDs decrease the chance of favorable postoperative outcome, patients with bitemporal IEDs but MRI hippocampal abnormalities concordant with the ictal-onset region still can have a good to excellent surgical outcome.68 Seizure recording may not be necessary if serial routine EEGs are consistently concordant with MRI-identified unilateral hippocampal atrophy.103
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FIGURE 968. Temporal Lobe Epilepsy; Low-Grade Tumor, Right Mesial-Posterior Temporal Lobe. A 17-year-old boy with medically intractable localization-related epilepsy. His seizure was described as staring off and orofacial and hand automatisms, followed by head and eye deviation to the left side with or without generalized tonic-clonic seizure. EEG shows occasional spikes and sharp waves in the right anterior- and midtemporal region (T2, T4) with maximal potential at the T1-T2 channel (double arrows). MRI with coronal FLAIR, axial FLAIR, and sagittal T1 sequences (open arrow) shows a cystic lesion most likely a low-grade tumor in the right mesial-posterior temporal region. The seizure semiology is compatible with “hypomotor” seizure, which is a signature of temporal lobe epilepsy. Additional electrodes can be used to supplement the standard 10-20 System.115 Ninety-seven percent of spikes are detected using additional anterior temporal region surface electrodes (T1 and T2), whereas 58% of the spikes are detected using only 10-20 System electrodes. Anterior temporal electrodes (T1 and T2) are able to detect nearly all interictal epileptiform discharges recorded by the foramen ovale electrode. Therefore, assuming that the location of the foramen ovale electrode is analogous to that of sphenoidal electrodes optimally implanted under fluoroscopy, the use of sphenoidal electrodes in routine interictal investigations appears not to be justified.116
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FIGURE 969. Mesio-Temporal Lobe Epilepsy (mTLE); Subtle Right Anterior Temporal Spikes at T1-T2 Channel. (Same recording as in Figure 9-67) EEG during NREM sleep shows a subtle spike at the T1-T2 channel. This spike would not be detected using a standard 10-20 international electrode system. A bipolar anteroposterior montage using the 10-20 electrode system would incompletely record about 40–55% of anterior temporal spikes.117
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FIGURE 970. Mesio-Temporal Epilepsy (mTLE); Temporal Intermittent Rhythmic Delta Activity (TIRDA). (Same recording as in Figure 9-67) EEG during wakefulness shows a brief run of monomorphic 1- to 1.5-Hz delta activity in the right anterior- and midtemporal region. This is termed temporal intermittent rhythmic delta activity (TIRDA). TIRDA has the same clinical significance as anterior temporal spikes/sharp waves, a characteristic EEG finding seen in MTLE and hippocampal sclerosis.113,114
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Focal Epilepsy
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FIGURE 971. Mesial Temporal Lobe Epilepsy; Focal Cortical Dysplasia. A 12-year-old boy with medically intractable focal epilepsy due to focal cortical dysplasia (FCD) in the right hippocampus. His seizure is described as “spacing out with orofacial and/or hand automatisms with or without GTCS.” Coronal T2-weighted MRI shows decreased volume and increased signal intensity in the right hippocampus (arrow). EEG demonstrates periodic sharp waves (PLEDs) and polymorphic delta slowing in the right temporal region. The patient underwent presurgical evaluation for epilepsy surgery. Interictal FDG PET shows extensive hypometabolism in the right mesial and lateral temporal region (arrow heads). There is significant neuronal loss in both the ipsilateral and contralateral thalami in TLE patients, with greater impairment in the anterior portions of the ipsilateral thalamus. The degree of loss in the ipsilateral and contralateral thalamus and putamen is directly correlated with that of the ipsilateral hippocampus. The damage associated with recurrent seizures results in injury in other subcortical structures. PET scan is highly sensitive in TLE, but its yield is low in extra-TLE.118 Regional hypometabolism in mesial TLE typically is diffuse, with graded demarcations from adjacent areas of normal metabolism and with a relatively large area of hypometabolism.119
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FIGURE 972. Right Mesio-Temporal Lobe Epilepsy (mTLE); Focal Cortical Dysplasia, Right Hippocampus. A 17-year-old right-handed girl with recurrent episodes of deja vu. Presurgical workup was consistent with right mesio-temporal epilepsy. EEG shows IEDs in the right anterior temporal region (open arrow). IEDs in MTLE show negative spikes and sharp waves in the sphenoidal, T1/T2, and F7/F8 electrodes. These IEDs are an expression of epileptiform activity in the parahippocampal cortex. Spikes in the hippocampus are usually not seen in scalp electrodes (So, 2001). Most IEDs are accompanied by a widespread positivity over the contralateral central-parietal region or vertex.100 Bilateral IEDs occur in one-third of patients, often during NREM sleep. IEDs recorded during wakefulness and REM sleep are more often lateralized and closely associated with the area of seizure onset.101 Patients with MTS have >90% of their IEDs in the anterior temporal region. Therefore, frequent posterior or extratemporal sharp waves are red flags for the diagnosis of hippocampal sclerosis. Rarely, IEDs can be seen in lateral temporal or frontal regions due to spreading of the discharges to the orbitofrontal or temporal neocortex via the limbic system. In MTLE, concordance of abnormal MRI and IEDs is associated with good surgical outcome and is a better indicator than concordance of abnormal MRI and ictal EEG activity but nonlateralizing IEDs.102 Although bilateral IEDs decrease the chance of favorable postoperative outcome, patients with bitemporal IEDs but MRI hippocampal abnormalities concordant with the ictal-onset region still can have a good to excellent surgical outcome.68 Seizure recording may not be necessary if serial routine EEGs are consistently concordant with MRI-identified unilateral hippocampal atrophy.103 Deja vu probably depends upon a neuronal network that engages both medial and lateral aspects of the temporal lobe, and that of the anterior hippocampus, amygdala, and superior temporal gyrus have relatively privileged access to this circuit. Autonomic and psychic auras were more frequently associated with right-sided temporal lobe lesions,120,121 although their use in lateralization has been questioned.122
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FIGURE 973. Interictal PET & Ictal SPECT. (Same patient as in Figure 9-72) Interictal PET (arrow) and ictal SPECT performed during the deja vu symptom (open arrow) are concordant with the MRI scan and show hypometabolism and hyperperfusion in the right temporal lobe, respectively. Pathology showed FCD grade 1. The patient has been seizure-free for over 18 months since the right temporal lobectomy.
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FIGURE 974. Focal Polymorphic Delta Activity (PDA) & Focal Enhancement of Beta Activity & Focal Spikes; Balloon Cell-Typed Focal Cortical Dysplasia. A 5-yearold boy with infrequent complex partial status epilepticus with left-sided focal clonic jerking and head and eyes deviating to the left side. His developmental milestones have been normal. Cranial CT (A) and axial T2-weighted image (B) demonstrate a focal cortical dysplasia (FCD) that is most likely to be balloon cell-typed FCD (open arrows). EEG shows bursts of low-voltage beta activity (double arrows), focal polymorphic delta activity (PDA), and spikes (arrow head) at the T4 electrode that are concordant with the location of the FCD seen in the CT and MRI. Higher amplitude of the background activity, especially beta activity on the side of a focal cerebral lesion, is rarely seen in the following conditions: tumor, FCD, abscess, stroke, and arteriovenous malformation. Interictal low-voltage beta activity seen in FCD represents intrinsic epileptogenicity. Continuous, near–continuous, or long trains of localized spikes or rhythmic sharp waves occur in 44% of patients with FCD.73 Eighty-six percent of patients with FCD also had localized PDA, suggesting a structural lesion.123 Localized PDA recorded over neocortical lesions is due to underlying white matter abnormalities rather than the lesion itself. Developmental abnormalities affecting gyri are associated with underlying changes in the white matter.124 Malformations of cortical development must be in the differential diagnosis for localized PDA,75 especially when associated with epileptiform activity.
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FIGURE 975. Ictal Slow Direct Current (DC) Shift; Gelastic Epilepsy caused by Right Mesial Temporal Cortical Dysplasia. A 3-year-old boy suffered his first seizure, which lasted over an hour, at 11 months of age. His eyes were open and unresponsive, and he was drooling. The twitching began on the left side and then generalized. He was found to be febrile. A left-sided Todd’s paralysis was noted for 3–4 hours. EEG showed slowing in the right temporal lobe. MRI showed edema of the right temporal lobe. He was started on oxcarbazepine and was seizure-free until 4 months ago, when he began experiencing frequent complex partial seizures and persistent left-side facial weakness. During the seizure, his breath became heavy, his eyes were glazed over, and he would look down and to the left. He will have a left-sided smile only before starting to laugh. Axial FLAIR and coronal T2 WI MRIs show signal hyperintensity and atrophy of the right mesial temporal lobe (open arrow). EEG with an LFF setting of 0.05 Hz during his typical gelastic seizures (in box) shows a burst of positive sharp waves at T4, followed immediately by a slow DC shift at T2 with overriding rhythmic activity in the same area. Note tachycardia at the seizure onset. An ictal slow DC shift is a slow and sustained change in EEG voltage resulting from a change in the function or interaction of neurons, glia, or both.125,126 Ictal slow baseline shifts can be recorded with DC amplifiers. They are not seen with conventional EEG systems. When the high-pass filter is opened to 0.01–0.1 Hz, ictal baseline shifts are present in scalp and intracranially recorded seizures and may have localizing value.127–130 Usually, scalp-recorded ictal DC shifts are not successfully recorded because movements during clinical seizures could cause artifacts. They are highly specific but low in sensitivity. Ictal DC shifts were seen in 14–40% of recorded seizures and their sensitivity varied.127,131,132 Scalp-recorded DC shifts were detected when seizures were clinically intense, while no slow shifts were observed in small seizures.127 They were restricted to 1–2 electrodes, very closely related to the onset of low-voltage fast activity and electrodecrement.133
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FIGURE 976. Emotion and Autonomic Nervous System (ANS); During Nondominant Temporal Lobe Seizure; Mesial Temporal Sclerosis (MTS). A 10-year-old righthanded girl with learning disability, behavioral outbursts, inattention, and medically intractable epilepsy due to a left mesial temporal lesion. She had a simple febrile convulsion at 4 years of age. Her seizure was described as a rising sensation from her stomach, fear feeling (mom called it a “panic attack”), and orofacial automatism followed by coughing, pupillary dilatation, and vomiting with no altered mental status. She answered questions appropriately throughout the seizure, which could last up to 30 minutes. Postictally, she was always alert and rubbed her nose with her left hand (postictal nosewiping). (A) Coronal MRI with FLAIR shows well-circumscribed increased signal intensity in the left mesial temporal region (arrow). (B) Interictal PET shows marked hypometabolism in the left mesial temporal region (arrow head). Neuropsychological testing revealed normal verbal but poor visual memory. WADA test exhibited language and verbal memory lateralization to both hemispheres, but greater on the right side. EEG during her typical seizure (10 sec after vomiting and coughing) shows significant cardiac arrhythmia in the ECG channel (solid arrow). Five seconds after this EEG page (not shown), the patient desaturated and required oxygen supplementation. The patient has been seizure-free after the left temporal lobectomy. Pathology confirmed the diagnosis of MTS. Seizure semiology, including automatisms without altered mental status, ictal vomitus, ictal coughing, and ictal panic attack, is strongly supportive of epileptic focus in the nondominant temporal lobe. This seizure semiology and pupillary dilatation or cardiac arrhythmia, occurring during the seizures, are caused by stimulation of Papez circuit, which controls both emotion and the autonomic nervous system (ANS). ANS changes are asymmetric and usually more prominent in the nondominant hemisphere. Ipsilateral postictal nosewiping is a very sensitive and specific seizure symptomatology for temporal lobe seizures.134 Forced lateralization of verbal memory to the opposite hemisphere usually jeopardizes visual memory and causes nonverbal memory impairment.135
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FIGURE 977. Orbitofrontal Lobe Epilepsy; Interictal Psychosis. A 6-year-old girl with psychotic symptoms, intermittent visual and auditory hallucination, and seizures caused by focal cortical dysplasia in the left orbitofrontal cortex (OFC). Axial and sagittal FLAIR images demonstrate high-intensity signal abnormality of the left OFC (arrow). Interictal EEG shows very active epileptiform activity and polymorphic delta activity in the left centro-temporal region, activated by sleep. Centro-temporal epileptiform activity in the EEG of this patient can simulate benign epilepsy with centro-temporal spikes (BECTS), although the presence of polymorphic delta slowing and atypical clinical manifestations is against the diagnosis. The prevalence of interictal psychosis of epilepsy is approximately 3–7%.63 Interictal psychosis is characterized by the presence of psychotic symptoms not temporally related to seizure activity and lasting 6 months or more, and the presence of delusions, hallucinations in clear consciousness, bizarre or disorganized behavior, formal thought disorder or affective changes without any evidence for AED toxicity, EEG findings consistent with nonconvulsive status epilepticus, recent head trauma, and alcohol or drug intoxication or withdrawal. Differential diagnosis can be made by EEG.64 The association of temporal lobe epilepsy and psychosis was well established.136–143 Hallucinations and psychosis can also rarely be associated with frontal lobe epilepsy.144,145 A case of OFC seizures that present with ictal visual hallucinations and interictal psychosis has been reported; the patient was seizure-free after the resection of the epileptogenic zone in OFC.60 It was speculated that epileptic activity in the OFC was connected to the association fiber pathways (uncinate fasciculus) and propagated to anteromedial temporal and associative areas causing interictal psychosis and hallucination. Functional connectivity between the hippocampus and the OFC has been recently established in humans.146
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FIGURE 978. Central Vertex Spikes; Orbitofrontal Lobe Region (OFR) Epilepsy. An 8-year-old right-handed boy who experienced his first seizure at 2 years of age, described as a sudden loss of awareness, body and eyes turning to his left, and left-sided clonic jerks and fall. One year later, he began to have brief staring spells with or without laughing. Significant behavioral disturbances including short attention span, mood swings, and repetitive behaviors were noted. At 7 years, he began having nightly episodes of screaming, inappropriate laughter, and hyperventilation. Axial FLAIR and coronal T2 WI MRIs show focal cortical dysplasia in the right orbitofrontal region. Interictal EEG demonstrates occasional central vertex spikes during sleep. In general, IEDs or ictal scalp EEGs are of limited value in the localization or lateralization of epileptogenic foci in the orbitofrontal lobe (basal frontal lobe) because of the hidden, distant location of this part of the cortex with relation to scalp electrodes. When detected on the scalp EEG, IEDs can be helpful in the diagnosis of epilepsy. Special electrodes may be helpful in distinguishing temporal from frontal foci (sphenoid, T1/T2, closely spaced additional electrodes). IEDs in OFR epilepsy include (1) secondary bilateral synchrony (SBS); (2) anterior temporal IEDs; (3) central or fronto-central IEDs; (4) bifrontal IEDs caused by volume conduction; (4) contralateral frontal IEDs; (5) large or blunted bifrontal or frontopolar sharp waves with or without additional temporal involvement; and (6) various multilobar located IEDs. At times, the EEG can be normal.147–150
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FIGURE 979. Secondary Bilateral Synchrony (SBS); Orbitofrontal Lobe Region (OFR) Epilepsy. (Same EEG recording as in Figure 9-78) Axial FLAIR shows focal cortical dysplasia in the right orbitofrontal region. Interictal EEG demonstrates consistent bisynchronous spikes and spike waves with right frontal predominance during sleep. In general, IEDs or ictal scalp EEGs are of limited value in the localization or lateralization of epileptogenic foci in the orbitofrontal lobe (basal frontal lobe) because of the hidden, distant location of this part of the cortex with relation to scalp electrodes. When detected on the scalp EEG, IEDs can be helpful in the diagnosis of epilepsy. Special electrodes may be helpful in distinguishing temporal from frontal foci (sphenoid, T1/T2, closely spaced additional electrodes). IEDs in OFR epilepsy include (1) secondary bilateral synchrony (SBS); (2) anterior temporal IEDs; (3) central or fronto-central IEDs; (4) bifrontal IEDs caused by volume conduction; (4) contralateral frontal IEDs; (5) large or blunted bifrontal or frontopolar sharp waves with or without additional temporal involvement; and (6) various multilobar located IEDs. At times, the EEG can be normal.147–150
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FIGURE 980. Orbitofrontal Lobe Region (OFR) Epilepsy. (Same patient as in Figure 9-78) Ictal EEG during sleep shows a burst of generalized polyspikes, followed by diffuse background attenuation, semi-rhythmic delta activity, and then a train of sharp waves in the bifrontal, and frontal vertex region. No lateralization or localization of ictal EEG activities is noted. In seven patients who were seizure-free after the resective surgery for OFR epilepsy, none had localized ictal EEG recording.151–153
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FIGURE 981. Periodic Lateralized Epileptiform Discharges (PLEDs); Left lnsula Epilepsy Caused by Focal Cortical Dysplasia. (Same EEG recording as in Figure 4-32 and 9-82) A 7-year-old left-handed girl with nocturnal hypermotor seizures and simple partial seizures described as “buzzing in her right ear”. EEG with laplacian montage during sleep shows periodic sharp waves in the left midtemporal region occurring approximately every 1 sec with no clinical accompaniment. PLEDs in this patient are indicative of very active epileptiform activity. Chronic PLEDs was reported in 9% of patients with intractable epilepsy who had chronic brain lesions such as focal cortical dysplasia or severe remote cerebral injury.154 Laplacian montage is a very useful montage to localize focal epileptiform activity.
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FIGURE 982. Secondary Bilateral Synchrony; Focal Cortical Dysplasia, Left lnsula. (Same EEG recording as in Figure 4-32 and 9-81) EEG during sleep shows frontally predominant bilateral synchronous spike-wave activity, which is consistently preceded by left centro-temporal spikes by 100–200 msec (arrow). This EEG pattern is consistent with secondary bilateral synchrony, which indicates localization-related epilepsy and the possibility of an underlying structural abnormality. Because bilateral synchronous discharges in primary generalized epilepsy are not always perfectly synchronous and symmetric, overinterpretation of secondary bilateral synchrony should be avoided. Persistent focal abnormality in one area and consistent unilateral initiation and preceding most of the bursts of bilateral synchrony throughout the recording are very important to avoid this error of overinterpretation.101
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FIGURE 983. Hypomelanosis of lto Associated with Hemimegalencephaly; Recurrent Seizures After Functional Hemispherectomy: lnsula Seizure. A pathologically left-handed 9-year-old boy with hypomelanosis of Ito associated with left hemimegalencephaly and intractable epilepsy. He underwent left functional hemispherectomy 9 months prior to this EEG. He did well for several months following the surgery but began having recurrent seizures that were much milder and limited to right facial twitching and posturing of the right hand. He was alert throughout. Sometimes, he had a feeling of choking. EEG during the seizure shows rhythmic theta activity in the left midtemporal region. Ictal SPECT demonstrates hyperperfusion in the left insular cortex (arrow). Thirty-eight to 88% of patients are seizure free after undergoing hemispherectomy. Factors affecting the surgical outcome include (1) the causes of the seizures, with patients having cortical dysplasia faring worse than those with Rasmussen encephalitis and infarction;155 (2) follow-up length; (3) duration of seizures prior to surgery; and (4) whether the basal ganglia, thalamus, or insular cortex are included in the resection/disconnection.156,157 The insular cortex has connections with the cerebral cortex, the amygdala, other limbic areas, the dorsal thalamus, and the basal ganglia. The proximity of the basal ganglia makes removal of the insular cortex challenging. The risk of complications is minimal in surgical resection of the insula.156 Repeat surgery should be considered in patients with incomplete disconnection or residual insular cortex, confirmed on postoperative MRIs, if they continue to have seizures after surgical treatment. Good results of seizure freedom after reoperation were reported.158–160 The semiology of insular seizures includes sensation of laryngeal constriction, paresthesias affecting large cutaneous territories, dysarthric speech, focal motor convulsive symptoms, dysgeusia, and contralateral somatosensory phenomena.161
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FIGURE 984. Intrinsic Epileptogenicity; Insular Epilepsy. A 16-year-old girl with medically intractable epilepsy. Her typical seizure was head deviation to the right side followed by GTCS. MRI shows thickening and hyperintensity of the left insular cortex (arrow). EEG shows nearly continuous rhythmic polyspike-and-wave discharges in the left frontal-anterior temporal region. A strong relationship was observed between the presence of rhythmic epileptiform discharges (REDs) on the scalp EEGs and the occurrence of continuous epileptiform discharges (CEDs) recorded on electrocorticography (ECoG). Eighty percent of patients with REDs had CEDs. Focal cortical dysplasia is associated with rhythmic epileptiform discharges.162 Although there is active epileptiform activity noted in this patient, generally, interictal or ictal epileptiform discharges originating in the insular cortex are unlikely to be detected by scalp EEG recording, unless these discharges propagate to lateral neocortical regions.163
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FIGURE 985. Asymmetric Tonic Seizure; Supplementary Sensorimotor Area (SSMA) Seizures. A 21-year-old boy who was born 24 weeks GA with right hemiparesis, developmental delay, and medically intractable epilepsy. His seizures are described as “asymmetric tonic seizures with head and eyes deviating to the right side” and “figure-offour” sign (right arm extension and left arm flexion) with or without GTCS. MRI shows left cerebral hemiatrophy with thickening of the cortex over the left frontal region (open arrow). Ictal SPECT shows hyperperfusion in the left lateral and mesial frontal region. Resective surgery results in seizure freedom. Pathology of the left frontal lesion revealed grade 1 focal cortical dysplasia. EEG with a laplacian run during his typical asymmetric tonic seizure demonstrates diffuse irregular slow waves followed by sharp waves at F3 and then a diffuse electrodecrement with superimposed low-voltage fast activity, best seen at Fz (double arrows), and muscle artifact. Generalized, frontally predominant, rhythmic fast activity is the most common ictal EEG accompaniment of generalized tonic seizures. Ictal EEG patterns in asymmetrical tonic seizures reveal initial high-amplitude slow-wave transients or midline sharp waves followed by bilateral fronto-central low-voltage fast activity or electrodecrement. Electrodecrement usually evolves into low-voltage fast activity and then bilateral fronto-central or generalized rhythmic theta slowing. Lateralization of these rhythms may be noted but is usually minimal.164
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FIGURE 986. Supplementary Sensorimotor Area (SSMA) Seizure; Focal Transmantle Dysplasia. A 5-year-old girl with global developmental delay, spastic right hemiparesis, and medically intractable epilepsy due to focal transmantle dysplasia. Axial T2-weighted and sagittal T1-weighted MRIs show thickened cortex and an abnormal gyral pattern with a cone-shaped abnormal hyper- and hypointensity extending from the depth of the affected sulcus to the ventricular margin in the left mesial frontal region (arrow head). Interictal EEG during a laplacian run demonstrates periodic lateralized epileptiform discharges (PLEDs) in the left frontal-central and frontal vertex regions. Her typical seizure was described as a brief asymmetric tonic posturing involving both extremities (greater on the right), vocalization, and versive head and eye movement to the right with or without evolving into a generalized tonic-clonic seizure. Vertex or midline epileptiform abnormalities can be seen with supplementary motor seizures or somatosensory seizures arising from the mesial surface of the brain.165 Interictal sharp waves, when present, are seen over the vertex or just adjacent to the midline in the fronto-central region in 50%. The distinction between epileptic and physiologic vertex sharp waves can be difficult.166 Characteristic waveforms indicating epileptiform discharges include (1) the presence of prominent slow waves after the initial sharp transients; (2) morphology of short duration with a subsequent spike-like appearance; (3) the appearance of sharp transients during wakefulness; and (4) morphology of the sharp transients as polyspikes.167 Interictal and ictal scalp EEG findings may be absent, nonlateralizing, or misleading, due to paradoxical lateralization.168,169 None of patients had abnormal scalp recordings in one study, and they emphasized that depth recordings were mandatory when surgery was contemplated. SSMA epilepsy cannot be excluded solely on the grounds of a normal EEG.170
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FIGURE 987. Secondary Absence Seizure (Frontal Absence); Supplementary Sensorimotor Area (SSMA) Seizure; Focal Transmantle Dysplasia. (Same patient as in Figure 9-86) Axial T2-weighted and sagittal T1-weighted MRIs (arrow head) show an abnormal gyral pattern with heterogeneous signal abnormality extending radially inward from the abnormal cortex to the ventricular margin of the slightly enlarged left lateral ventricle in the left frontal region. EEG during one of her absence-like episodes (altered mental status, staring, motionless, eye blinking, with no postictal confusion) shows bilateral synchronous 2.5- to 3-Hz spike-wave activity with fronto-central and left hemispheric predominance. Focal transmantle dysplasia is a malformation of cortical development that extends through the entire cerebral mantle, from the ventricular surface to the cerebral cortex. The presence of balloon cells suggests that these malformations are associated with maldifferentiation of the stem cells generated in the germinal zone.59 “Frontal absence” can be seen in frontal lobe epilepsy with epileptic foci in either the mesial frontal or orbitofrontal regions.48,55,120 Generalized absences and frontal absences may show similar clinical and EEG features and involve the same neuronal circuits. The neuronal system primarily involved in these seizures consists of a relatively limited cortico-thalamocortical circuit, including the reticular thalamic nucleus, the thalamocortical relay, and the predominantly anterior and mesial frontal cerebral cortex, with the cortex probably acting as the primary driving site.171 The anterior cingulate gyrus is involved in self-regulation of frontothalamic circuits and may play an important role in both maintenance of arousal and generalized epilepsy in humans. Absence seizures may not be truly generalized but rather involve selective cortical networks as described above.172
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FIGURE 988. Supplementary Sensorimotor Area (SSMA) Seizure; Focal Transmantle Dysplasia. A 5-year-old girl with global developmental delay, spastic right hemiparesis, and medically intractable epilepsy due to focal transmantle dysplasia. Axial T2-weighted and sagittal T1-weighted MRIs show thickened cortex and an abnormal gyral pattern with a cone-shaped abnormal hyper- and hypointensity extending from the depth of the affected sulcus to the ventricular margin in the left mesial frontal region (arrow head). Interictal EEG during a laplacian run demonstrates periodic lateralized epileptiform discharges (PLEDs) in the left frontal-central and frontal vertex regions. Her typical seizure was described as a brief asymmetric tonic posturing involving both extremities (greater on the right), vocalization, versive head and eye movement to the right with or without evolution into a generalized tonic-clonic seizure. Vertex or midline epileptiform abnormalities can be seen with supplementary motor seizures or somatosensory seizures arising from the mesial surface of the brain.165 Interictal sharp waves, when present, are seen over the vertex or just adjacent to the midline in the fronto-central region in 50%. The distinction between epileptic and physiologic vertex sharp waves can be difficult.166 Characteristic waveforms indicating epileptiform discharges include (1) the presence of prominent slow waves after the initial sharp transients; (2) morphology of short duration with a subsequent spike-like appearance; (3) the appearance of sharp transients during wakefulness; and (4) morphology of the sharp transients as polyspikes.167 Interictal and ictal scalp EEG findings may be absent, nonlateralizing, or misleading, due to paradoxical lateralization.168,169 None of patients had abnormal scalp recordings in one study, and they emphasized that depth recordings were mandatory when surgery was contemplated. SSMA epilepsy cannot be excluded solely on the grounds of a normal EEG.170
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Focal Epilepsy
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FIGURE 989. Supplementary Sensorimotor Area (SSMA) Seizure; Mild Malformation of Cortical Development (MCD), Right Mesial Frontal. A 7-year-old girl with medically intractable, non-lesional SSMA seizures. MRI (not shown) was unremarkable. Although the past routine EEGs were within normal limits, her interictal EEG during prolonged video-EEG monitoring shows frequent and, at times, periodic spikes (x) and polymorphic delta activity in the central vertex and right centro-parietal regions. She underwent extraoperative subdural video-EEG monitoring prior to the resection of epileptogenic zone in the right mesial frontal region. She has been free of seizures since the surgery. Neuropathology of the most active epileptic focus showed microdysgenesis. In a study of 11 pediatric patients with SSMA seizures at Cleveland Clinic, prolonged interictal EEG showed normal findings in 1 child, and focal sharp waves were increased or appeared exclusively during sleep in the remaining 10 patients. Interictal sharp waves were over the vertex in nine patients and over the ipsilateral frontal-central region in one patient. Vertex sharp waves were asymmetric with greater distribution over the ipsilateral parasagittal region on one side in four patients.79
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FIGURE 990. Mesial Frontal Stroke; Central Vertex Spikes. A 15-year-old right-handed boy with intrauterine right anterior cerebral artery stroke. MRI shows encephalomalacia in the right mesial frontal region. Sleep EEG during prolonged EEG monitoring shows runs of spikes in the central vertex region. Seizure semiology was compatible with localization of epileptic focus in the right SSMA. The patient underwent surgical resection of the lesion and surrounding epileptogenic zone and has been free of seizures since the surgery. Pathology showed focal cortical dysplasia in multiple areas adjacent to the encephalomalacia. Midline spikes are highly epileptogenic. Most patients have different types of clinical seizures, most commonly generalized tonic-clonic or SSMA seizures. Over two-thirds of the patients were neurologically impaired. Most of midline spikes originate from the mesial or paramedian region of the cerebral cortex. They are more common in children than in adults and markedly activated with sleep. They must be distinguished from normal sleep transients. In patients with SSMA seizures, routine EEG findings were usually normal, but prolonged EEG showed epileptiform discharges over the vertex. Typical seizures are either unilateral or bilateral tonic limb involvement with preserved consciousness.79–81
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FIGURE 991. Train of Near Continuous Localized Spikes; Small FCD Located at the Bottom of the Sulcus. A 4-year-old girl with two episodes of Jacksonian marches resulting from a focal cortical dysplasia (FCD) in the right frontal region (arrow). The seizure was described as clonic jerking starting in her left hand with gradual spreading to the left upper arm, face, and then leg. MRI shows a small FCD in the right frontal region (arrow). Interictal EEG demonstrates a train of pseudoperiodic spikes in the right central region (x). Also note polymorphic delta activity in the right centro-temporal regions. Focal clonic activity is caused by seizure discharges in the primary motor cortex. Long trains of near-continuous or pseudoperiodic localized spikes are a characteristic scalp EEG in focal cortical dysplasia and are seen in 22–44% of patients.73,75 Small FCD lesions are preferentially located at the bottom of an abnormally deep sulcus (18 out of 21 patients). Among them, 81% had been overlooked during initial radiological evaluation and were subsequently identified using image processing.173
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FIGURE 992. Malignant Rolandic Epilepsy (or Malignant Rolandic-Sylvian Epilepsy); Focal Transmantle Dysplasia. A 3-year-old right-handed boy with medically intractable focal epilepsy described as “left arm jerking occurring during both wakefulness and sleep.” He had no family history of seizure. Neurologic examination showed mild atrophy of his left thumb and soft neurological signs in the left upper and lower extremities. MRI with FLAIR shows increased signal intensity and thickened cortex in the right frontal region consistent with focal cortical dysplasia (arrow). EEG during wakefulness demonstrates polymorphic delta slowing and trains of sharp waves in the right centrotemporal region. Malignant rolandic-sylvian epilepsy (MRSE) differs from BECTS and LKS in its refractoriness to medication, clusters of seizures, change in semiology, and secondarily generalized seizures. After careful observation over at least 5 years, surgery is considered to control refractory seizures.174 The clinical and EEG features that point to symptomatic focal epilepsy are (1) presence of subtle neuropsychological deficit or oromotor apraxia, (2) seizures starting with symptoms evoking an onset outside the opercular region, (3) presence of atypical absences or focal hypomotor seizures, (4) background EEG abnormalities, (5) presence of unusual fast activity, (6) morphological modification of the centro-temporal spikes during sleep, (7) enhancement of slow waves following the spike/recurrence of spikes in trains, (8) intermittent slow-wave focus, (9) frontalization of the spikes, (10) diffuse discharges of slow-spike-slow-wave complexes, (11) continuous spike and waves during slow sleep (CSWS), (12) polymorphisms of the ictal discharge, and (13) severe postictal depression.175
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FIGURE 993. Focal Myoclonic Seizure. (Same patient as in Figure 9-5) Video-EEG recording during one of his typical myoclonic seizures, described as bilateral synchronous jerking of both upper extremities, greater on the left, shows a single spike discharge in the right rolandic region time-locked to the myoclonic jerk. The spike precedes the EMG (ECG channel) by approximately 10–20 msec. This finding is compatible with the study using evoked potentials of back-averaging the EEG from onset of myoclonic jerks (”jerklocked averaging”). Back-averaging revealed a biphasic spike in the contralateral rolandic region precedes an EMG burst by 6–22 msec, depending on whether proximal or distal muscles of the arm are involved. This time lag is due to “cortical myoclonus” passing rostrocaudally through the brain stem, spinal cord, and then activating muscle.176,177
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FIGURE 994. Asymmetric Epileptic Spasms; Postoperative Thalamic Astrocytoma. A 7-year-old girl with a history of left thalamic astrocytoma resection who developed very frequent asymmetric epileptic spasms described as a brief tonic stiffening with left arm extension, right arm flexion, and head and eyes deviating to the right side. Interictal EEG shows quasiperiodic bursts of spikes intermingled with high-voltage delta and theta activity, which are superimposed on nearly continuous low-voltage polymorphic delta activity over the left hemisphere (burst-suppression-like pattern). The EEG criteria of poor prognosis in focal epilepsies in children include abnormal asymmetric background activity, continuous focal slow waves, multifocal or diffuse epileptiform discharges, disappearance of changes in REM sleep, localized background flattening, and generalized or focal paroxysmal fast activity.178 Tumors are rare causes of epileptic spasms. Epileptic spasms secondary to a basal ganglian glioma spreading to the cortex have been reported. The appearance of symmetrical spasms preceded by partial seizures indicated that the epileptogenic cortex was the primary driver of the epileptic spasms.179 There was postulation that the pathogenesis of epileptic spasms results from dysfunction of cortical-subcortical circuit and cortical or hemispheric resection provided good seizure control.180 The epileptic spasms in West syndrome seem to be the final manifestation of various processes but are believed to start on a cortical level.181 Ictal cortical high-frequency oscillations (HFOs) preceding the EMG changes and sustained regional HFOs during epileptic spasms provided additional direct evidence that a subset of epileptic spasms in older pediatric patients represents focal-onset secondarily generalized seizures.182
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FIGURE 995. Asymmetric Epileptic Spasms; Post-Surgical Resection of Thalamic Astrocytoma. A 7-year-old girl with a history of left thalamic astrocytoma resection who developed very frequent asymmetric epileptic spasms described as a brief tonic stiffening with left arm extension, right arm flexion, and head and eyes deviating to the right side. Ictal EEG shows bursts of fast activity intermingled with spikes and high-voltage biphasic delta activity in the left hemisphere with mild spreading to the homologous areas in the right hemisphere during the epileptic spasms. Tumors are rare causes of epileptic spasms. Epileptic spasms secondary to a basal ganglia glioma spreading to the cortex have been reported. The appearance of symmetrical spasms preceded by partial seizures indicated that the epileptogenic cortex was the primary driver of the epileptic spasms.179 There was postulation that the pathogenesis of epileptic spasms results from dysfunction of a cortical-subcortical circuit and a cortical or hemispheric resection provided good seizure control.180 The epileptic spasms in West syndrome seem to be the final manifestation of various processes but are believed to start on a cortical level.181 Ictal cortical high-frequency oscillations (HFOs) preceding the EMG changes and sustained regional HFOs during epileptic spasms provided additional direct evidence that a subset of epileptic spasm in older pediatric patients represents focal-onset secondarily generalized seizures.182
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FIGURE 996. Left Thalamic Lesion; Secondary Bilateral Synchrony. Generalized spike-wave (GSW) discharges are a hallmark of idiopathic generalized epilepsy (IGE). The reticular thalamic nucleus is the pacemaker structure for the rhythmic cortical oscillations in spindle frequency range, which transform into GSW activity in IGE.183,184 The nucleus anterior thalami and the zona incerta have an important role in secondary bilateral synchrony.185–187 GSW discharges were described in patients with shunted hydrocephalus and in hypothalamic lesions.188–190 Most patients with unilateral thalamic lesions and epilepsy showed bilateral synchronous GSW discharges.191–195 In the generation of GSW, the cortex is considered to be the decisive factor, while the thalamus is involved secondarily.193 The primary role in the synchronized activity of the thalamus and cortex is attributed to the reticular nucleus.183,184 Zona incerta contains a GABAergic inhibitory effect on the higher order thalamic nuclei projecting to the neocortex, which results in effective, state-dependent gating of thalamocortical information.186 A lesion of this system can lead to disinhibition and marked activation of the paroxysmal activity in sleep.
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FIGURE 997. Symptomatic Absence Seizure and ESES; Thalamic Heterotopia. A 6-year-old boy with intractable symptomatic absence epilepsy and cognitive dysfunction caused by right thalamic heterotopia (arrow). Complete resection of the heterotopia results in seizure freedom. Alterations in normal thalamocortical reciprocal interactions are critical in the generation of the regular generalized spike-wave discharges characteristic of the idiopathic generalized epilepsies.196 Most patients with unilateral thalamic lesion and epilepsy showed bilateral synchronous GSW discharges.191–195 Absence status with bilateral GSW discharges caused by ischemic lesion in the left thalamus has been reported.192 Children with thalamic lesions should be monitored closely for ESES. Lesions of the inferior-medial-posterior thalamic structures might have a role in the pathogenesis of bilateral spike-wave (SW) discharges and ESES by the mechanism of disinhibition, possibly through the GABAergic system of zona incerta and its projections.193 Gray matter heterotopias are caused by a halt in neuronal radial migration and consist of clusters of neurons separated from the cortex by white matter and not organized in layers like the normal cortex.197 Although gray matter heterotopia is commonly associated with refractory epilepsy, it is still uncertain which role heterotopic lesions play for seizure onset and propagation and whether they are epileptogenic. Intracranial EEG investigations showed apparently contradictory results implying that seizures are generated sometimes by the heterotopias, sometimes by the distant cortex, and sometimes by both. However, neither the removal of the lesion alone nor mesial temporal resection leads to a favorable outcome, suggesting a more widespread epileptogenic network in these patients. Seizure onset in heterotopia is sometimes completely outside the lesion and sometimes has some overlap with the lesion. Heterotopia is part of a more complex circuitry involving the surrounding and distant cerebral cortex.98,198 High-frequency oscillations (HFOs), especially fast ripples, are closely linked to seizure onset areas. In focal cortical dysplasia and sometimes in heterotopia, HFOs occur in lesional areas that are not part of the seizure onset zone, and they may indicate potential epileptogenicity of these regions.77,78,199
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FIGURE 998. Midline Spikes; Focal Cortical Dysplasia, Right Mesial Parietal. A 7-year-old boy with three episodes of seizures. Two GTCS occurred during sleep. The third seizure occurred while walking. He fell back, with eyes deviating to the left before developing GTCS. MRI shows a focal cortical dysplasia in the right parietal lobe (arrow). EEG shows centro-parietal vertex spikes with slowing at C4>C3 (box A) and spreading of the spike to P4 (box B). These findings indicate an epileptogenic focus in the right parietal midline. Midline spikes occur almost exclusively in children, are strongly associated with clinical seizures, and are activated by sleep.80,200,201 Cz is the most frequent spike location. Most patients without sleep activation had CNS disease. Adults with midline spikes may represent a distinct entity with a worse prognosis. Midline spikes showed strong correlations with clinical seizures; 91% had epileptic seizures of diverse types. Over two-thirds of the patients were neurologically impaired. Midline spikes most probably originate from discharging lesions of the mesial or paramedian region of the cerebral cortex.80,202,203 Epilepsy with midline spikes is not necessarily benign.203 Distinguishing the midline spikes from vertex waves can be difficult. If the discharges are consistently confined to one or more midline electrodes, the distinction can be made by the following: (1) different fields of distribution; (2) the tendency for spikes to be lateralized to one side; (3) focal slowing in association with the spikes; (4) occurrence during wakefulness or drowsiness before V-waves are present; and (5) secondary generalization of epileptiform activity.204,205
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FIGURE 999. Paradoxical Lateralization of Epileptic Focus. A 7-year-old girl with medically intractable epilepsy. Her seizure was described as bilateral tonic posturing of arms and legs with head and eyes deviating to the left side with or without secondarily generalized tonic-clonic seizures. Axial FLAIR MRI shows increased signal abnormality in the right parietal region (double arrows). Coronal FLAIR MRI shows cortical thickening in the same area (open arrow). These findings are consistent with a focal cortical dysplasia. EEG demonstrates spikes in the parietal vertex with some spread to the left parietal region (box). In general, an interictal epileptiform discharge (IED) is an unreliable finding in parietal lobe epilepsy. IEDs are usually widespread, multifocal, and bilateral. Secondary bilateral synchrony is recorded in up to 30% of cases.68 An epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity.42 “Paradoxical lateralization” is most likely the result of a horizontal dipole located within the interhemispheric fissure.43 Magnetoencephalogram (MEG) detects only dipoles horizontal to the surface and is more sensitive to generators lining the sulci than ones from gyral surfaces. Therefore, it may be helpful in detecting an epileptic focus in the mesial aspect of hemispheres.92
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FIGURE 9100. Pervasive Developmental Disorder (PDD); Midline Sharp Waves. A 5-year-old boy with pervasive developmental disorder who never had definite clinical seizures. Cranial MRI was unremarkable. EEG with transverse bipolar run shows a train of sharp waves and isolated sharp waves with phase reversals at Pz and Cz. Abnormal EEGs were found in 43–75% of autistic children and 82% of their EEGs; 46% had clinical seizures. Nearly all children with seizures had epileptiform activity, but almost 20% of those with spike discharges did not have clinical seizures. Slow-wave abnormalities were more frequent in the autistic individuals. Most epileptic discharges were localized spikes; some had multiple spike foci and, only on rare occasions, generalized spikes; 76.6% of the epileptic discharge foci were in the frontal region, 2.1% in the temporal region, 14.1% in the centro-parietal region, and 6.4% in the occipital region; 55.6% of the frontal spikes were at midline, approximately equal at Fz and Cz. The dipole of midline spikes was in the deep midline frontal region. These results suggest that frontal dysfunction is important in the mechanism and symptoms in autism.206,207
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FIGURE 9101. Rett Syndrome; Central Vertex Sharp Waves. A 32-year-old female with Rett syndrome and a history of focal epilepsy who presented with intermittent beahavioral outbursts. This EEG was performed when the patient was asymptomatic. EEG shows very frequent central vertex sharp waves and rhythmic without clinical accompaniment. During the typical outbursts, EEG showed no changes from the baseline. The patient’s clinical symptoms resolved with pain treatment. Prominent rhythmical theta activity (4-5/sec or 5-6/sec) is an outstanding EEG feature in Rett syndrome. This pattern was present in waking state and/or sleep. During wakefulness, the localization (vertex and central region) and blocking responses to active or passive movements suggested a slow equivalent of Rolandic mu rhythm. During sleep, rhythmical theta activity was either rolandic or more diffuse, sometimes independently occurring with central spikes. The prominent rhythmical 4-5/sec or 5-6/sec activity and its relationship to Rolandic mu rhythm suggest a dysfunction of the motor cortex in Rett syndrome. This would be congruent with the frequent observation of central spikes.
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FIGURE 9102. Mesio-Temporal Lobe Epilepsy (mTLE); Temporal Intermittent Rhythmic Delta Activity (TIRDA). EEG of a 15-year-old boy with right mesio-temporal lobe epilepsy caused by hippocampal sclerosis. EEG shows a brief run of monomorphic 3.5-Hz delta activity at T7 consistent with TIRDA. TIRDA has the same clinical significance as anterior temporal spikes/sharp waves, a characterisctic EEG finding seen in MTLE and hippocampal sclerosis.113, 208
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FIGURE 9103. Wicket-Wave Like Waveform; Left Frontal-Temporal Infarction. A 4-month-old boy who developed a right-sided focal motor seizure after cardiac surgery for complex congenital heart defects. MRI with DWI shows cerebral infarction in the left frontal-temporal region. Interictal EEG shows trains of negative sharp arciform waves in the left posterior temporal region (double arrows) and suppression of background activity over the left hemisphere. The trains of sharp-wave configuration are similar to “wicket waves.” Wicket waves are most commonly seen in individuals older than 30 years of age. They are relatively rare with a prevalence of 0.9% in adults but unknown in children. They occur in clusters or trains, but also as single sharp transients, of midtemporal or anterior temporal 6- to 11-Hz negative sharp arciform waves with amplitudes of up to 200 μV. Wicket waves can be differentiated from temporal lobe epileptiform discharges based on the following criteria: (1) no slow wave component following wicket spikes; (2) occurring in trains or in isolation and not disrupting the background; and (3) having a similar morphology to the waveforms in the train when occurring as a single spike. In this EEG, the age and abnormal background activity are strongly against the diagnosis of wicket waves but supportive of epileptiform activities. In adults, wicket waves are more commonly seen in patients with cerebrovascular disease.209
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FIGURE 9104. Transmantle Cortical Dysplasia; Positive Sharp Waves. An 8-week-old boy with a 4-week history of frequent seizures described as head deviation to the left side and left clonic jerks. (A) Coronal T2 WI MRI at 18 months shows increased signal intensity in the subcortical white matter adjacent to the subependymal area in the right parieto-temporal region (open arrow). (B) Coronal T2 MRI at 2 months shows a transmantle cortical dysplasia in the right parieto-temporal region (arrow). EEG shows positive sharp waves (in box) in the right central region, indicating a deep white matter lesion. Also note negative spikes in the right central and temporal regions. Positive sharp waves (PSWs) are not epileptiform activity and are not directly associated with neonatal seizures but rather with underlying structural abnormalities, especially in the deep cerebral white matter, and can be seen in a variety of conditions, including periventricular leukomalacia, hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or HIE.210–213 Transmantle cortical dysplasia should also be in the differential diagnosis of PSWs in young infants.
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Focal Epilepsy
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FIGURE 9105. Positive Sharp Waves in Traumatic Brain Injury. A 4-week-old boy with nonaccidental trauma. Axial DWI MRI showed diffusion restriction in the periventricular, subcortical white matter and cortex of the right temporal lobe (open arrow). Sagittal T1 WI MRI shows subdural hematoma (arrow). CXR reveals old left 7th rib fracture (double arrows). EEG demonstrates positive sharp waves (PSWs) (*) and negative spikes (open arrow) at T6. PSWs are not epileptiform activity and are not directly associated with neonatal seizures but rather with underlying structural abnormalities, especially in the deep cerebral white matter, and can be seen in a variety of conditions, including periventricular leukomalacia, hydrocephalus, meningitis, inborn errors of metabolism, stroke, hemorrhages, or HIE.210–213
9
Focal Epilepsy
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FIGURE 9106. Rhythmic Sinusoidal Alpha Activity & Trains of Sharp Waves; Intrinsic Epileptogenicity in Focal Cortical Dysplasia. (Same patient as in Figure 4-28, 4-92 and 9-107) A 4-week-old infant with very frequent seizures described as versive seizures and epileptic nystagmus. EEG during sleep shows mixed findings of rhythmic sinusoidal alpha activity in the left parietal area and trains of spikes and sharp waves, mainly in the left occipital region with volume conduction of sharp waves to the right occipital region. Focal cortical dysplasia (FCD) has intrinsic epileptogenicity with unique EEG patterns, including continuous spikes or sharp waves, abrupt runs of high-frequency spikes, rhythmic sharp waves, and periodic spike complexes that occur during sleep.72 The incidences of intrinsic epileptogencity in FCD were 11–20% in different series.73,74
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Focal Epilepsy
9
FIGURE 9107. Focal Cortical Dysplasia; Intrinsic Epileptogenicity During Subdural EEG Monitoring. (Same patient as in Figure 9-106) During subdural EEG monitoring, periodic and, at times, nearly continuous spikes are noted in the H4 and I2 electrodes, which are located in the occipital region. This finding is compatible with the scalp EEG recording shown in the previous page. PVCs are also noted in the ECG channel.
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FIGURE 9108. lctal Slow Direct Current (DC) Shift; Angiocentric Neuroepithelial Tumor (ANET), Right Occipital. A 20-year-old male with a history of medically intractable epilepsy and right parieto-occipital lesion. He experiences two types of seizures. The first type of seizure was blacking-out episodes where he made clicking noises, had activity arrest, picked at his clothing, and stared upward and to the left for about 2–4 minutes. He had dizziness and was tired afterward. The second type of seizure was seeing colors in periphery of his vision with blurring of central vision. MRI shows a discrete lesion in the right occipital region. EEG during the seizure with LFF setting of 0.1 Hz shows ictal onset in the right occipital region (open arrow). Ictal slow DC shift was noted immediately after the ictal onset (box). An ictal slow DC shift is a slow and sustained change in EEG voltage resulting from a change in the function or interaction of neurons, glia, or both.125,126 Ictal slow baseline shifts could be recorded with DC amplifiers. They were not seen with conventional EEG systems. When the high-pass filter was opened to 0.01–0.1 Hz, ictal baseline shifts were present in scalp and intracranially recorded seizures and could have localizing value.127–130 Usually, scalp-recorded ictal DC shifts are not successfully recorded because movements during clinical seizures could cause artifacts. They are highly specific but low in sensitivity. Ictal DC shifts were seen in 14–40% of recorded seizures and their sensitivity varied.127,131,132 Scalp-recorded DC shifts were detected when seizures were clinically intense, while no slow shifts were observed in small seizures. They were restricted to 1–2 electrodes, very closely related to the onset of low-voltage fast activity and electrodecrement.127,133
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Focal Epilepsy
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FIGURE 9109. lctal Slow Direct-Current (DC) Shift; Temporal Lobe Epilepsy Caused by Ganglioglioma. A 15-year-old boy with intractable epilepsy due to a right mesial temporal ganglioglioma. His seizure typesconsists of hypomotor and occasional gelastic seizure. Ictal EEG onset during arousal shows slow baseline shift, maximal at T4 and T6 (open arrow), followed by rhythmic delta activity in the right temporal region (arrow). LFF of 0.1 Hz was used. An ictal slow DC shift is a slow and sustained change in EEG voltage resulting from a change in the function or interaction of neurons, glia, or both.125,126 Ictal slow baseline shifts could be recorded with DC amplifiers. They were not seen with conventional EEG systems. When the high-pass filter was opened to 0.01–0.1 Hz, ictal baseline shifts were present in scalp and intracranially recorded seizures and could have localizing value.127–130 Usually, scalp-recorded ictal DC shifts are not successfully recorded because movements during clinical seizures cause artifacts. They are highly specific but low in sensitivity. Ictal DC shifts were seen in 14–40% of recorded seizures and their sensitivity varied.127,131,132 Scalp-recorded DC shifts were detected when seizures were clinically intense, while no slow shifts were observed in small seizures.127 They were restricted to 1–2 electrodes, very closely related to the onset of low-voltage fast activity and electrodecrement.133
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FIGURE 9110. Paradoxical Lateralization; Neurocysticercosis. An 11-year-old girl with a sudden onset of headache, vomiting, lethargy, and a new-onset generalized tonic-clonic seizure. Cranial CT shows a cystic lesion with surrounding cerebral edema in the left superior frontal gyrus (arrow). The patient was diagnosed with neurocysticercosis. Immediate clinical improvement was noted after an intravenous administration of dexamethasone. EEG shows polymorphic delta slowing in the left frontal-temporal region (box C) and sharp waves in the right central region (box A), which are contralateral to the lesion. Note asymmetric vertex waves with suppression in the left hemisphere (box B). An epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity.42 “Paradoxical lateralization” is most likely the result of a horizontal dipole located within the interhemispheric fissure.43 Magnetoencephalogram (MEG) detects only dipoles horizontal to the surface and is more sensitive to generators lining the sulci than ones from gyral surfaces. Therefore, MEG may be helpful in detecting an epileptic focus in the mesial aspect of hemispheres.92
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Focal Epilepsy
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FIGURE 9111. Paradoxical Lateralization of Epileptic Focus. A 13-year-old boy with well-controlled secondarily generalized tonic-clonic seizures. Axial FLAIR MRI (arrow) and coronal T2-weighted MRI show hyperintensity in the right dorsolateral-mesial frontal region. EEG shows bilateral synchronous sharp and slow waves with left frontal predominance (*). Epileptic focus on the mesial surface of one cerebral hemisphere can project epileptiform activity obliquely to the opposite hemisphere, leading to paradoxical lateralization of the epileptiform activity.42 “Paradoxical lateralization” is most likely the result of a horizontal dipole located within the interhemispheric fissure.43 Magnetoencephalogram (MEG) detects only dipoles horizontal to the surface and is more sensitive to generators lining the sulci than ones from gyral surfaces. Therefore, MEG may be helpful in detecting an epileptic focus in the mesial aspect of hemispheres.92
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Focal Epilepsy
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FIGURE 9112. Periodic Lateralized Epileptiform Discharges (PLEDs); Focal Transmantle Dysplasia. A 7-month-old right-handed boy born at 28 weeks GA due to abruptio placenta and PROM. He had a normal development until 5 months of age when he started having seizures described as “head and eyes deviating to the left with clonic jerking of the left arm and left side of the face.” He had developmental regression and preferred to use his right hand more after the onset of his very first seizures. (A) Axial T2weighted image shows heterogenous signal abnormality (white arrow) extending inward from the abnormal gyri to the surface of the frontal horn of the right lateral ventricle. (B) Sagittal T1-weighted image shows heterogenous signal abnormality (black arrow) over the surface of the right lateral ventricle. Interictal EEG demonstrates suppression of sleep spindles over the right central region and PLEDs (arrow head) in the right central midtemporal region. Focal transmantle dysplasia is a malformation of cortical development that extends through the entire cerebral mantle, from the ventricular surface to the cerebral cortex. The presence of balloon cells suggests that these malformations are associated with maldifferentiation of the stem cells generated in the germinal zone.214 PLEDs usually represent acute or subacute cerebral insults. However, in a review of 96 patients with PLEDs, 9 cases of chronic PLEDs (6.2%) were seen in patients with symptomatic focal epilepsy caused by underlying focal cortical dysplasia or severe remote cerebral injury.215
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Focal Epilepsy
9
FIGURE 9113. Enhancement of Anterior Beta Activity; Encephalomalacia Due to Severe Intraventricular Hemorrhage in the Newborn. This is a 5-year-old righthanded boy who was born 32 weeks GA with a grade 4 intraventricular hemorrhage. Subsequently, he developed hydrocephalus and required multiple VP shunt revisions. He has had global developmental delay, spastic diplegia, and left hemiparesis, and intractable epilepsy. He presented with a 45-minute seizure described as rhythmic left hand jerking with eyes deviating to the left side. This EEG was performed 4 hours after the seizure was stopped by intravenous fosphenytoin and lorazepam. MRI shows bilateral periventricular leukomalacia and focal encephalomalacia in the right frontal region. EEG demonstrates consistent low-voltage beta activity with frequent bursts of higher amplitude beta activity in the F4 electrode (boxes). Higher amplitude of the background activity, especially beta activity on the side of a focal cerebral lesion, is rarely seen in the following conditions: tumor, focal cortical dysplasia, abscess, stroke, and arteriovenous malformation. Low-voltage fast activity associated with focal cortical dysplasia (FCD) represents intrinsic epileptogenicity of the FCD. A similar phenomenon seen in intracranial EEG monitoring called “high-frequency oscillations (HFOs)” can precede or follow the seizure and can be used as a predictor of clinical and/or electrographic seizure. Low-voltage fast activity, also called “regional polyspikes,” especially in the extratemporal location, are highly associated with focal cortical dysplasia in 80%.57
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FIGURE 9114. Frontal Arousal Rhythm (FAR); Intrauterine Right Anterior Cerebral Artery Stroke. A 15-year-old boy with symptomatic focal epilepsy caused by intrauterine stroke (open arrow). EEG during arousal from sleep is compatible with the frontal arousal rhythm (FAR). The patient underwent epilepsy surgery and has been free of seizures. The FAR pattern completely disappeared after the surgery. The FAR is a rare EEG rhythm seen in the frontal regions during arousal from sleep in children. It is characterized by 30- to 150-uV predominantly monophasic negative waves occurring in bursts or runs lasting up to 13 sec (usually 1–5 sec) with a characteristic notching of the ascending or descending phase of each wave. The notched appearance may represent harmonics of the waveforms. The waxing and waning of the amplitude often leads to a spindle-like morphology. The FAR appears at the F3 and F4 electrodes with minimal spread to nearby scalp areas (White and Tharp, 1974). The incidence of the FAR in a normal population is unknown. Although it was first reported in children with minimal cerebral dysfunction or a seizure disorder, it was later considered to be a nonspecific EEG pattern of no clinical significance.69
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Focal Epilepsy
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FIGURE 9115. Supplementary Sensorimotor Area (SSMA) Seizure. A 15-year-old right-handed boy with intrauterine stroke involving right anterior cerebral artery. MRI shows encephalomalacia surrounding a cystic lesion (open arrows) in the right anterior medial and lateral frontal region (arrow and double arrows). Interictal EEG during sleep shows bisynchronous fronto-central polyspikes occurring simultaneously with fronto-central vertex polyspikes, with right hemispheric prominence. The patient underwent epilepsy surgery after extraoperative subdural EEG implantation. Pathology revealed grade 2 FCD surrounding the cystic encephalomalacia. The interictal EEG in patients with mesial FLE most commonly either shows frequent, nonlateralized IEDs or no IEDs at all.47 Focal IEDs at or adjacent to the midline have been reported.40,216 Bilateral synchronous discharges are characteristic but not specific.217,218 Midline fronto-central IEDs were found in 38–50% of patients with SSMA seizures.216,219 Midline IEDs can sometimes be difficult to differentiate from vertex waves. The clues to differentiate between these two are (1) after-going slow waves in IEDs; (2) narrower and more persistently asymmetric fields in IEDs; and (3) presence of the same midline IEDs during wakefulness. Paradoxical lateralization of IEDs was seen in 25%.219
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Focal Epilepsy
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FIGURE 9116. Supplementary Sensorimotor Area (SSMA) Seizure; Ictal Scalp EEG. (Same patient as in Figure 9-114) Ictal EEG onset (box A) shows low-voltage fast activity at the Fz and Cz electrodes with some spread to the F3 followed immediately by a burst of high-voltage polyspikes. Next, rhythmic alpha activity and low-voltage fast activity are noted at Cz with some spread to the right fronto-central region. Note tachycardia (open arrow) prior to the onset of the clinical seizure (arrow head), which appears 6–7 sec after the onset of ictal EEG. Ictal SPECT scan obtained approximately 10 sec into the ictal EEG seizure shows hyperperfusion in the right dorsolateral and mesial frontoparietal region (double arrows), which is concordant with the area of hypoperfusion in the interictal SPECT scan (open arrow) and encephalomalacia in the MRI (arrow). The onset of ictal EEG activity in a mesial frontal seizure showed paroxysmal fast activity (33%) or electrodecrement (29%) whereas in a lateral frontal seizure showed repetitive epileptic discharges (36%) or rhythmic delta activity (26%).47 Only 25% of mesial frontal seizures showed localized or lateralized ictal EEG. Ictal EEG showed no EEG change or EEG obscured by muscle artifact in more than 50%.41 Localized hyperperfusion was a surrogate for the epileptogenic zone, and complete resection was a predictor of an excellent outcome.220
808
Focal Epilepsy
9
FIGURE 9117. Photosensitive Myoclonic Seizure; Severe Encephalomalacia. A 15-year-old girl with a past history of a severe motor vehicle accident at 2 years of age. She had mild mental retardation, left hemiparesis, and medically intractable epilepsy. MRI shows severe encephalomalacia over the right hemisphere. EEG during photic stimulation demonstrates generalized polyspike activity obscured by excessive muscle artifact. Clinically, she had a very brief myoclonic jerk of her left arm, lasting less than 1 sec, with no altered mental status or postictal state. Photosensitivity represents cortical reflex sensitivity and is most likely seen in idiopathic generalized epilepsy and progressive myoclonic epilepsy.221
9
Focal Epilepsy
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FIGURE 9118. Hemimegalencephaly Associated with Linear Sebaceous Nevus Syndrome; Epileptic Nystagmus and Asymmetric Epileptic Spasms. A 4-week-old girl with right hemimegalencephaly associated with linear sebaceous nevus syndrome with asymmetric epileptic spasms and nearly continuous epileptic nystagmus. Interictal electroencephalograms revealed asymmetric suppression-burst patterns,222 frequent focal discharges, and a nearly continuous burst-suppression pattern over the malformed hemisphere.223 Triphasic complexes of large amplitude were observed in patients with the earliest onset of seizures and were associated with the most severe prognosis; unilateral, rhythmic “alpha-like” activity was recorded in patients with seizures occurring after 3 months of age and was associated with a relatively favorable outcome; asymmetric suppressionbursts characterized by “alpha-like” activity on the abnormal side were seen in patients with infantile spasms. The EEG pattern seems to make an important contribution to both diagnosis and prognosis.224 All EEGs performed in the first 10 days of life showed a suppression-burst pattern (video/EEG aspects of early-infantile epileptic encephalopathy with suppression-bursts).225
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Focal Epilepsy
9
FIGURE 9119. Linear Sebaceous Nevus Syndrome with Hemimegalencephaly; Asymmetric Infantile Spasms. (Same patient as in Figure 9-118) EEG during one of her typical seizures described as horizontal nystagmus with fast component to the left side with or without trunk, neck, and limb stiffening, maximal on the left side. Her clinical seizures were nearly continuous. EEG shows a burst of very high-voltage sharp-and-slow-wave activity over the right hemisphere (solid arrow) followed by a diffuse electrodecremental event with superimposed low-voltage fast beta activity (arrow), maximal in the right hemisphere, and then semi-rhythmic theta activity in the right occipital region (arrow head). As with interictal EEG patterns, an asymmetric ictal pattern correlates with a focal or lateralized structural abnormality of the brain.226
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FIGURE 9120. Right Hemimegalencephaly; Asymmetric Suppression-Burst Pattern. A 17-year-old girl with severe mental retardation and medically intractable epilepsy due to right hemimegalencephaly. EEG shows a suppression-burst pattern. Axial T2-weighted MRI shows enlargement of the right cerebral hemisphere, pachygyric appearance of the right frontal-temporal cortex, and increased signal intensity in the white matter surrounding the ventriculomegaly. These findings are compatible with the right hemimegalencephaly. An interictal SPECT scan shows hypoperfusion over the entire right cerebral hemisphere. Although asymmetric suppression-burst patterns are considered characteristic EEG findings in hemimegalencephaly, the duration of their appearance does not have definite prognostic significance.222
812
Focal Epilepsy
9
FIGURE 9121. Hemimegalencephaly; Rhythmic Alpha-Like Activity. (Same patient as in Figure 9-120) A 17-year-old with right hemimegalencephaly and intractable epilepsy. The interictal EEG activity is age related in patients with hemimegalencephaly. During the first few months of life, EEG shows asymmetric background activity and sporadic epileptiform activity confined to the malformed hemisphere. Two more specific patterns, ipsilateral suppression-burst (S-B) and asymmetric hypsarrhythmia, are seen. The S-B pattern is characterized by bursts of high-voltage paroxysmal activity alternating with periods of low-voltage activity during both wakefulness and sleep. When the S-B pattern occurrs during the first few months of life and is associated with epileptic spasms, the patients are classified as Ohtahara syndrome. Some patients present in the infancy period with West syndrome with a typical interictal EEG of hemihypsarrhythmia. After the first year of life, patients with hemimegalencephaly usually develop medically intractable focal epilepsy. EEG activity gets progressively worse over time and shows asymmetric spike/polyspike complexes, slow waves, and rhythmic alpha-frequency bands (arrow). Similar EEG patterns of rhythmic alpha-frequency bands are seen in type 1 lissencephaly, although they are evenly distributed, rather than asymmetrical. However, bilateral synchronous epileptiform activity is not uncommon in older children.227
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Focal Epilepsy
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FIGURE 9122. Secondary Bilateral Synchrony (SBS); Unilateral Polymicrogyria (PMG). A 10-year-old right-handed girl with mental retardation, behavioral disturbances, left hemiparesis, and frequent seizures, including generalized tonic-clonic, absence, and complex partial seizures (head and eyes deviating to the left side with asymmetric tonic stiffening), associated with unilateral polymicrogyria caused by congenital CMV infection. (A) Axial inversion recovery MRI shows multiple small undulating gyri in the right frontal region (large arrow) and thickened cortex with diffuse small irregular gyri in the frontal-temporal regions (small arrows). (B) Coronal T2 WI MRI shows diffuse small irregular gyri with indistinct gray-white interface in the right frontal-temporal region (small arrows). EEG demonstrates bilateral synchronous irregular spike-wave activity with frontal and right hemispheric predominance (secondary bilateral synchrony). Frontal lobe seizures can manifest as atypical absence seizures, with generalization based on SBS (Millan et al., 2001). MEG detected the sources of SBS in the medial frontal lobe (Tanaka et al., 2005). The thalamus plays an important role in the occurrence of bilateral discharges in patients with partial epilepsy (SBS). Spontaneous interictal epileptiform discharges in a penicillin-induced cortical epileptogenic focus are propagated antidromically into the thalamus. On the other hand, thalamic stimulation can induce epileptiform discharges in the hippocampus. The thalamus also regulates cortical excitability and synchronization of seizure activity in limbic structures and the neocortex. Thalamic lesions causing intractable partial epilepsy also suggest that the thalamus might have a role in seizure propagation.228,229
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Focal Epilepsy
9
FIGURE 9123. Simple Partial Seizure (Sensory). (Same patient as in Figure 4-27, 9-124, and 9-125 during the prolonged video-EEG monitoring) Ictal EEG during his typical simple partial seizure characterized by left arm numbness with preserved consciousness demonstrates a run of spikes in the right central region (arrow). Epileptiform discharges were recorded in only 10% of patients with scalp electrodes compared to 90% with subdural electrodes during simple partial seizures in one study.86
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FIGURE 9124. Simple Partial Seizure (Motor). (Continued) One of his typical seizures described as body and limb stiffening with left arm extension and right arm flexion accompanied by head turning to the left side (versive seizure). He remains conscious throughout the seizure. EEG demonstrates rhythmic, low-voltage alpha-beta activity in the right fronto-central region.
816
Focal Epilepsy
9
FIGURE 9125. Simple Partial Seizures; Focal Encephalomalacia Due to Viral Meningoencephalitis in Newborn. A 15-year-old boy with medically intractable epilepsy and severe left hemiparesis due to viral meningoencephalitis during the neonatal period. Almost all seizures were characterized by sensory or versive seizures with preserved consciousness. Coronal and axial T2-weighted and sagittal T1-weighted images show right cerebral hemiatrophy with abnormal intensity in the right insular, frontal, and parietal regions. Interictal EEG shows very frequent sharp waves in the right frontal-anterior temporal regions.
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Focal Epilepsy
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FIGURE 9126. History of Refractory Status Epilepticus. (Same patient as in Figure 6-45 and 9-127) At 3½ years of age, the patient has occasional seizures, mild right hemiparesis, right homonimous hemianopsia, ADHD and aggressive behavior, and global developmental delay, especially in the areas of language and cognition. He had only three to four words. Cranial MRI shows diffuse cerebral atrophy. EEG shows bilateral synchronous spike-wave activity with left posterior predominance. In patients with seizures lasting >30 minutes, only 23% of the survivors were normal at follow-up; 34% showed developmental deterioration and 36% developed newonset epilepsy.230 Mortality is related to etiology and is higher in younger children and with multifocal or generalized abnormalities on the initial EEG. RSE due to either an acute symptomatic etiology or a progressive encephalopathy was associated with the highest mortality. Only one survivor did not have active epilepsy. A shorter duration of suppressive therapy, ultimately with the same outcome and possibly fewer complications, was recommended.231
818
Focal Epilepsy
9
FIGURE 9127. Electrical Status Epilepticus During Slow Sleep (ESES); History of Refractory Status Epilepticus in Infancy. (Same patient as in Figure 9-126) At 6 years of age, the patient had worsening of seizures, especially GTCS, and also regression of language, learning, and behaviors. A 24-hour prolonged video-EEG revealed focal electrical status epilepticus during slow sleep, with maximal epileptic activity in the left fronto-centro-temporal region. Only 23% of the survivors of RSE were normal at follow-up; 34% showed developmental deterioration and 36% developed new-onset epilepsy.230 Mortality is related to etiology and is higher in younger children and with multifocal or generalized abnormalities on the initial EEG. RSE due to either an acute symptomatic etiology or a progressive encephalopathy was associated with highest mortality rates. Only one survivor did not have active epilepsy. A shorter duration of suppressive therapy, ultimately with the same outcome and possibly fewer complications, was recommended.231
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FIGURE 9128. Common Migraine; Parieto-Temporal Sharp Wave. EEG of an 8-year-old girl with common migraine and syncope shows occasional left parieto-temporal sharp waves (open arrow). Benign focal epileptiform discharges, mostly rolandic spikes, were seen in 9% of patients with childhood migraine.232
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Focal Epilepsy
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FIGURE 9129. Migraine; Temporal Sharp Wave. EEG of a 9-year-old boy with common migraine shows occasional left centro-temporal sharp waves (open arrow). Note small sharp spikes (arrow head), a benign variant of no clinical significance. Benign focal epileptiform discharges, mostly rolandic spikes, were seen in 9% of childhood migraine.232
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Focal Epilepsy
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FIGURE 9130. Hearing-Induced Seizure; Encephalomalacia Associated with Meningococcal Meningitis. A 5-year-old boy with severe bilateral frontal encephalomalacia due to acute meningococcal meningitis in infancy. He had severe developmental delay, spastic quadriparesis, and medically intractable epilepsy. During prolonged video-EEG monitoring, he had generalized tonic seizures induced by a noise from an ear thermometer. Axial and coronal T2 WI MRI shows severe bifrontal encephalomalacia. EEG during one of his typical seizures shows diffuse electrodecrement with subsequent bilateral spike-wave activity associated with generalized tonic seizure, which occurred immediately after an insertion of a thermometer into his left ear. Ictal SPECT scan showed multifocal hyperperfusion. Only a few specific sounds such as ones from an ear thermometer, dial-tone telephone, or opening of a soda can precipitate seizures. Hearing-induced seizures are very rare. The patients usually have automotor seizures, generalized tonic-clonic seizures, or temporal lobe epilepsy. The pathogenesis of auditoryinduced seizures probably involves activation of the temporal auditory areas and inferior colliculus. The following criteria should be met: (1) more than one seizure evoked by the stimulus recorded by EEG or video-EEG; (2) the seizure should follow stimulus onset within 5 minutes (usually 10 sec to 5 minutes); and (3) an EEG seizure pattern has to be present.233
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Focal Epilepsy
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FIGURE 9131. Rett Syndrome; Rhythmic Theta Activity in the Central Vertex with Low-Voltage Background. A 15-year-old girl with Rett syndrome. Rhythmic 3- to 5-Hz theta or delta slowing is the most common EEG abnormality (30/44 patients) in the patients with Rett syndrome. Diffuse/bisynchronous spikes or sharp waves or slow spikewave complexes were found in 22/44 and 9/44 patients, respectively. With advancing age, the EEG abnormalities improve and a low-voltage EEG may develop. These changes parallel the clinical course of Rett syndrome.234
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Focal Epilepsy
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FIGURE 9132. Symptomatic Occipital Lobe Epilepsy; Neonatal Western Equine Encephalitis. A 15-year-old girl with a history of neonatal Western equine enephalitis at 2 weeks of age who subsequently developed severe mental retardation, spastic quadriparesis, and medically intractable epilepsy. Her typical seizure was described as vomiting, orofacial automatisms, and altered mental status with or without GTCS. Cranial CT shows diffuse cerebral atrophy and multiple parenchymal calcifications in the basal ganglia bilaterally and white matter. EEG shows trains of bilateral synchronous occipital spikes with left-sided predominance. Visual hallucination and vomiting are the most common symptoms seen in occipital lobe seizures.6
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Focal Epilepsy
9
FIGURE 9133. Herpes Simplex Encephalitis; Simple Partial Seizure. A 2½-year-old boy with fever, intermittent episodes of right facial twitching, drooling, and dysarthria without altered mental status. CSF examination showed mild lymphocytosis with normal protein and glucose. PCR for HSV type 1 was positive. Cranial MRI shows bilateral rolandic involvement, left greater than right (arrow). EEG demonstrates semi-rhythmic sharply-contoured theta activity and sharp waves in the left midtemporal region.
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Focal Epilepsy
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FIGURE 9134. Viral Meningoencephalitis; Subclinical Electrographic Seizure. A 17-year-old girl with viral meningoencephalitis who presented with fever and recurrent spacing-out episodes. MRI with FLAIR sequence shows subtle increased signal intensity in the right frontal region (arrow). EEG demonstrates diffusely, frontally predominant, rhythmic 6- to 7-Hz theta activity that is sharply contoured.
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Focal Epilepsy
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FIGURE 9135. Rhythmic Sharply-Contoured Theta Activity; Herpes Simplex Encephalitis (HSE). A 2-year-old boy with acute onset of right facial twitching, and speech and swallowing difficulties associated with high fever. Cerebrospinal fluid (CSF) examination showed WBC of 20 cells/ml with lymphocyte predominance, protein of 27 mg/dl, and glucose of 87 mg%. PCR for HSV type 1 in the CSF was positive. Cranial MRI shows abnormal signal intensity in the operculum bilaterally, greater on the left (arrows). EEG demonstrates semi-rhythmic sharp-contoured theta activity in the midtemporal regions bilaterally, much greater in the left hemisphere. HSE must be considered in all children who present with acute onset of focal seizures, especially when associated with febrile illnesses. Acute onset of weakness of masseter, facial, pharyngeal, and glossal muscles, accompanied by fever, headache, and focal motor seizures of the face, should suggest HSE involving the bilateral frontal and parietal operculum (anterior opercula syndrome).235
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827
FIGURE 9136. Comparison of Ictal Activity Between Scalp and Subdural EEG Recording; Transmantle Cortical Dysplasia. (Same patient as in Figure 9-112) EEGs during scalp (left) and subdural (right) EEG recording in different seizures but similar characteristics. Onset of ictal EEG activity starts with a burst of bilateral synchronous polyspike-wave discharges (*) → diffuse electrodecrement (double arrows) → rhythmic 9-Hz alpha activity (arrow) → cardiac arrhythmia (arrow head). The scalp EEG findings in infants, especially in patients with epilepsy caused by focal cortical dysplasia, can be similar to subdural EEG findings due to less resistance to volume conduction of EEG activity propagating through the dura, CSF, scalp, and skin.236
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FIGURE 9137. High-Frequency Oscillations (HFOs); Start-Stop-Start Phenomenon. (Same patient as in Figure 9-136) Subdural EEG recording with a bipolar montage over the right hemisphere shows diffuse high-voltage spike-wave discharges (box A) followed by diffuse background attenuation for 7–8 sec, and then a run of sharp waves at A47 (box B). At the lower page and insert, the same incidence as box A with the reference run, EEG shows a brief burst of low-voltage fast activity (50–60 Hz) at A47, consistent with “high-frequency oscillations (HFOs).” This phenomenon is also called “start-stop-start” (SSS) phenomenon.237 HFOs characterize by very fast activity, ranging from 80–150 Hz, are noted at the epileptic focus in neocortical epilepsy during subdural EEG recording.238 Recent findings suggest that HFOs ranging between 100 and 500 Hz might be closely linked to epileptogenesis.239 Ripples (80–160 Hz) and fast ripples (250–500 Hz) occur frequently during IEDs and may reflect pathological hypersynchronous events. During ictal recordings, HFOs could be identified and occurred mostly in the region of primary epileptogenesis and less frequently in areas of secondary spread.240 HFOs are an important electrophysiological manifestation of epileptic tissue and are associated closely with the spiking region and partly with the seizure onset zone (SOZ). Although ripples and fast ripples share some characteristics, increasing in the SOZ and spiking regions, fast ripples were more specific to the SOZ region than ripples.239 The SSS phenomenon is defined as a pair of sequential ictal potentials separated by complete or almost complete cessation of seizure activity; the SSS phenomenon was found on subdural recordings in 23% of 98 patients.237 The two phases were morphologically similar. The first “start” usually had a narrow field.241 Fifty-eight percent of SSS seizures showed a complete stop. Thirty-five percent of patients and seizures restarted in a different location than the first start. When in different locations, the start, not the restart, is correlated with the non-SSS origin. SSS seizures arose in the same region as non-SSS seizures in almost all patients.237 Subsequently, the SSS phenomenon was also observed in scalp EEG, sphenoidal, and foramen ovale electrodes, and the recognition of the phenomenon may improve the accuracy of seizure localization.241,242
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FIGURE 9138. False Localization of Polymorphic Delta Activity (PDA) with Suppression of Sleep Spindles; Encephalomalacia Due to Acute Viral Meningoencephalitis. A 9 month-old right-handed boy with right fronto-parietal encephalomalacia (open arrow) due to hypoxic ischemic encephalopathy in the newborn. He developed his first seizure at 4 months of age, described as left arm clonic jerking with head deviation to either right or left side and, at times, with nystagmus. EEG shows consistent suppression of sleep spindles at C4 and sharp waves with polymorphic delta activity (PDA) at T4. Lesion in the parietal lobe or thalamus can attenuate sleep spindles.97,243,244 A more recent study demonstrates that sleep spindles are generated in the reticular nucleus of the thalamus, and through thalamocortical neurons, the cortex is triggered to generate spindle bursts.245 A study using magnetoencephalogram (MEG) suggests involvement of the pre- and post-central areas in the generation of MEG sleep spindles.246 Focality of the PDA depends on the lesion location. Lesions in the posterior frontal and parietal areas can be falsely localized to the temporal area.247
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FIGURE 9139. Epidermal Nevus Syndrome (ENS); Focal Cortical Dysplasia, Left Temporal Region. A 6-year-old left-handed girl with epidermal nevus syndrome who developed seizures at 18 days of life that evolved into West syndrome. Currently, the patient has daily seizures that consist of tonic spasms of arms and the trunk without drop attack. Coronal FLAIR MRI shows thickened and hyperintense cortex in the left temporal region (open arrow) with enlargement of the left temporal horn (double arrows). Ictal SPECT during the cluster of spasms displays hyperperfusion in the left temporal region (arrow). EEG shows a diffuse electrodecrement followed immediately by a train of spikes in the left frontal-anterior temporal region (box). The epidermal nevus syndrome (ENS) is a sporadic neurocutaneous disorder that consists of epidermal nevi and congenital anomalies involving the brain and other systems. Proteus syndrome, encephalocraniocutaneous lipomatosis, and epidermal nevus syndrome have several overlapping phenotypic features.248 The most common clinical neurologic symptom is epilepsy, which was seen in almost all cases. In addition to unilateral hemimegalencephaly with relatively preserved frontal lobes, which is the most commonly found CNS abnormality, other neuronal migration abnormalities (patchy macrogyria, microgyria, heterotopia, etc.), vascular malformations, agenesis of the corpus callosum, Dandy-Walker syndrome, myelomeningocele, Arnold-Chiari malformation, and tumors have been reported.249 These acquired brain lesions are best explained by prior ischemia or hemorrhage.250 All had ipsilateral epidermal nevi of the head, and several had ipsilateral facial hemihypertrophy.250 Hyperperfusion during ictal SPECT in the damaged hemisphere was helpful for hemispherectomy.249
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FIGURE 9140. Presurgical Evaluation; Resection of Epileptogenic Zone after Extraoperative Subdural EEG Monitoring. (A) Sagittal T1-weighted MRI shows focal cortical dysplasia (transmantle) in the right frontal region. (B) Interictal SPECT shows hypoperfusion in the right frontal region. (C) Ictal SPECT shows hyperperfusion in the same area as (B). (D) Subdural EEG (sEEG) electrodes were implanted over the right lateral frontal parietal regions and mesial frontal region. (E) AP and lateral skull x-ray were performed to look at the location of sEEG electrodes. (F) Video-sEEG monitoring was used to identify interictal activity and ictal epileptogenic zone and cortical mapping was used to identify functional cortex. (G) The results of (F) guides the surgical resection of the epileptogenic zone. The ideal goal is a complete resection of the epileptogenic zone without permanent neurologic deficits.
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Focal Epilepsy
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FIGURE 9141. Supplementary Sensorimotor Area (SSMA) Seizure; Absence-Like Seizure. A 14-year-old boy with frontal lobe epilepsy caused by extensive malformation of cortical development (MCD) in the right frontal region. He had multiple types of seizures, including secondarily GTCS, asymmetric tonic seizures, and absence-like seizures. Axial FLAIR MRI shows the patient has been seizure free since the surgery. Axial and sagittal FLAIR MRIs demonstrate a lipoma in the right sylvian fissure (open arrow) and extensive polymicrogyria (PMG) in the entire right frontal lobe (arrows), including the mesial frontal area. Interictal PET scan shows hypometabolism in the right lateral and mesial frontal regions (double arrows). Ictal EEG shows bilateral synchronous slow spikewave discharges with right frontal predominance. The patient has been seizure free since the surgery. Cerebral lipomas account for 0.1–1.3% of brain tumors, and only 20% of them cause epilepsy.251 Fourteen cases of sylvian fissure lipomas have been reported, and only a few cases underwent surgical resection.252 A variety of vascular abnormalities, including hypervascularization, venous angioma, dilatation and tortuosity of the feeding arteries, abnormal arterial branches, and saccular aneurysm, have been described in patients with cerebral lipoma. Thus, development of a lipoma may also involve vascular abnormalities.253 Perisylvian lipoma is also associated with malformations of cortical development (MCDs).254,255 Intracranial lipomas are due to persistence of the primitive meninx (mesenchymatous origin) followed by transformation into mature adipose cells during the first weeks of intrauterine life. Resorption of the rudimentary meninges should be complete by the 10th week. The presence of the lipoma could have secondary or concomitant effects on the development of adjacent cortical structures, which takes place between the 6th and 20th weeks: as an obstacle to migration of gray matter, gyration abnormalities, or vascular defects resulting from the lesion and/or its hypervascularization.254 Ischemia could account for the PMG observed in some patients. Therefore, the causes of epilepsy probably involve vascular abnormalities and MCDs. Due to the complexity of the lesion, hemispheric lipomas are better classified with localized cortical malformations rather than simple extracerebral malformations.254,256 Frontal absences can be caused by epileptic discharges arising from several areas of the frontal region, including SSMA, orbitofrontal region, and the cingulate gyrus. Compared with absences of childhood absence epilepsy, frontal lobe absences may have subtle repetitive vocalization, rocking movements, mild version, and brief postictal confusion. The patient may report awareness of motor arrest without loss of consciousness. The staring may evolve into a secondarily GTCS via version of the head and eyes, and focal or bilateral tonic posturing of the upper limb(s). Frontal absences seem to have a more anterior epileptogenic zone than those with bilateral asymmetric tonic seizures. However, the clinical and EEG features can be very close to that of a typical or simple absence seizure.47,48 Secondarily generalized discharges are a common occurrence with frontal lobe epilepsy. The EEG findings that suggest secondary bilateral synchrony include (1) focal spikes or sharp waves consistently occurring in one area, (2) focal spike discharges that precede or initiate more generalized bursts, and (3) persistent lateralized abnormalities such as slowing or an asymmetry over the involved area.49,50
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FIGURE 9142. Supplementary Sensorimotor Area (SSMA) Seizure; Subdural vs Scalp EEG Recording. A 14-year-old boy with frontal lobe epilepsy caused by an extensive malformation of cortical development (MCD) in the right frontal region who underwent invasive EEG monitoring. Subdural EEG during his typical simple partial seizure described as mild stiffening of the left arm with or without head turning to the left shows diffuse fast activity maximum in the mesial frontal electrodes (MIH and AIH) (open arrow) with some spreading to the lateral frontal region (LF electrodes in the box). Ictal tachycardia (double arrows) is observed at the onset of seizure. Note the similarity between the subdural and scalp EEG recordings in clinical features, and in EEG and ECG findings. The major difference between the subdural and scalp EEG recordings is the amplitude, which is lower in the scalp EEG recording due to volume conduction. The EEG pattern is consistent with asymmetric “paroxysmal fast activity (PFA).” Axial FLAIR MRI demonstrates a lipoma in the right sylvian fissure (arrow) and extensive polymicrogyria (PMG) in the entire right frontal lobe (open arrow). The patient has been seizure free since the surgery. All patients with SSMA seizures had preservation of consciousness during the seizure unless secondarily generalization occurred. Tonic posturing of the extremities was present in all patients, and in 63% it was present bilaterally. Adversive movements were not seen unless the seizure became secondarily generalized. Interictal and/or ictal abnormalities were present at or adjacent to the midline in almost all patients.40 In patients whose seizures began in the medial frontal region (anterior cingulate, supplementary motor region, medial perirolandic region), ictal patterns were significantly shorter than those of other groups and included, no rhythmic electrographic changes were seen, and rhythmic electrographic changes occurred after the onset of clinical seizures or generalized suppression or PFA. This is probably because the primary seizure generator is located some distance from the scalp electrodes and requires a greater amount of cortical involvement (implying propagation) before electrographic activity can be detected. In contrast, patients whose seizures were of dorsolateral origin had a high percentage (68%) of focal electrographic seizure activity (rhythmic fast activity, alpha or beta activity, or repetitive spikes) that preceded the onset of clinical symptoms and was thus distinguished from seizures that originated in the medial frontal region.41,257 The absence of focal electrographic seizure activity nearly excluded the possibility of seizures emanating from the dorsolateral frontal region.257 PFA may be a reflection of proximity of the epileptogenic zone to the recording electrodes. Seizures arising from the lateral frontal convexity began with repetitive epileptiform activity, whereas seizures of patients with mesial lesions more often began with rhythmic theta activity. PFA was observed at the onset of seizures arising from the inferior aspect of the supplementary sensorimotor area and cingulate gyrus, where the distance between the nearest scalp electrode and the generator is great. PFA was virtually never observed at the onset or during the course of MTLE seizures. Therefore, PFA is generated during neocortical ictal activation.41,258–260 Its presence is not primarily dependent on the proximity of the recording electrode to the epileptic generator. Rather, the presence of paroxysmal fast activity may be an expression of propagation from the epileptogenic zone to areas underlying the involved scalp electrodes, or may be influenced by other factors such as a pathologic substrate.41 Incomplete removal of epileptic activity as defined by subdural EEG is likely to result in seizure recurrence.261,262 Interictal and ictal paroxysmal fast activity is reported to be more specific for FCD than other pathologies.263–265 The localized burst, continuous, or nearly continuous pattern of epileptiform discharges on ECoG was associated with the FCD lesion.73 Interictal PFA and runs of repetitive spikes correlated with the ictal onset zone, whereas isolated spikes did not, and incomplete resection of interictal PFA correlated with seizure recurrence.261
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FIGURE 9143. Periventricular Nodular Heterotopia (PNH). A 4-year-old girl with intractable epilepsy and bilateral periventricular nodular heterotopia (PNH) with right hemispheric predominance. Seizures were described as behavioral arrest for several seconds followed by irritability and sleep. MRI shows bilateral PNH (left PNH is not shown) mainly in the right fronto-parietal (open arrow) and temporo-occipital regions (arrow and double arrows). EEG demonstrates spike-wave discharges in the right occipital region (box). Focal interictal EEG abnormalities are always consistent with the anatomic location of the PNH. In slow sleep, focal abnormalities frequently change to bilaterally diffuse bursts of polyspikes. In addition, EEG frequently demonstrates multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions.266 The EEG abnormalities at the onset and immediately after the end of the seizures were always localized to the brain regions where the PNH was located. These findings suggest that epileptic discharges may originate from abnormal circuitries located close to or involving the PNH. Epilepsy in PNH patients is generated by abnormal anatomic circuitries including the heterotopic nodules and adjacent archicortical and neocortical areas. In the patient with medically intractable epilepsy, the surgical outcome can be very favorable if the abnormal circuitry that generates seizures is carefully assessed before and then removed using epilepsy surgery.78,228,267
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FIGURE 9144. Periventricular Nodular Heterotopia (PNH); Secondary Bilateral Synchrony (SBS). (Same patient as in Figure 9-143) A 4-year-old girl with intractable epilepsy and bilateral periventricular nodular heterotopia (PNH) with right hemispheric predominance. MRI shows bilateral PNH (left PNH is not shown) mainly in the right fronto-parietal (open arrow) and temporo-occipital regions (arrow and double arrows). EEG demonstrates secondary bilateral synchrony with occipital predominance. Focal interictal EEG abnormalities are always consistent with anatomic location of the PNH. In slow sleep, focal abnormalities frequently change to bilaterally diffuse bursts of polyspikes. In addition, EEG frequently demonstrates multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions.266
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Focal Epilepsy
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FIGURE 9145. Perinodular Nodular Heterotopia (PNH); Low-Voltage Fast Activity. (Same patient as in Figure 9-143) EEG shows low-voltage fast activity overriding the spike-and-wave discharges in the right occipital region. The morphology of the waveform is similar to “high-frequency oscillations” recorded in intracranial EEG. Patients with PNH and epilepsy represent a heterogeneous group. Seizures result from complex interactions between PNH and allo- or neocortex. A reduction of GABA-mediated inhibitory activity was demonstrated in both the cortex and heterotopic gray matter.268 Abnormalities of cortical architecture, and of cortical neuronal composition and connectivity, may allow the cortex to act as a primary epileptogenic substrate.269–271 Patients with nodular heterotopia have a high incidence of cortical abnormalities such as atrophy and polymicrogyria in addition to hippocampal atrophy.272 Fifty-four percent of patients with PNH had visually detectable cortical abnormalities.
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FIGURE 9146. Periventricular Nodular Heterotopia; Symptomatic Focal Epilepsy. A 9-year-old previously healthy boy with five seizures in the past 3 years. Seizures were described as staring, stiffening, inability to talk, increased oral secretions, cyanosis, and unresponsiveness with or without secondarily GTCS. MRI shows a small heterotopia adjacent to the frontal horn of the left lateral ventricle (arrow). EEG demonstrates a run of central vertex spikes intermingled with polymorphic delta activity. Unilateral PNH is frequently located in the posterior paratrigonal region (i.e., a watershed area) of the lateral ventricles and may extend into the white matter to involve adjacent neocortical and archicortical areas.266 Epilepsy in PNH patients is generated by abnormal anatomic circuitries including the heterotopic nodules and adjacent archicortical and neocortical areas. Regardless of the different MRI features, the main clinical problem in most PNH patients is the presence of focal drug-resistant epilepsy. The presence of risk factors for prenatal brain damage, the common location in the paratrigonal region, and the lack of familial cases all suggest that acquired factors, damaging a limited region of the developing brain, may provoke the genesis of unilateral nodules. The selective ablation of a subpopulation of dividing neuroblasts alters the migration and differentiation of subsequently generated neurons, which in turn set the base for the formation of heterotopia.273,274 Focal interictal EEG abnormalities are always consistent with the anatomic location of the PNH. In slow sleep, focal abnormalities frequently change in bilaterally diffused bursts of polyspikes or multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions. In a minority of patients, 3- to 4-Hz spike-wave discharges, mimicking primary generalized epilepsy, are noted.232 The ictal EEG abnormalities at the onset and immediately after the end of the seizures were always recorded in brain regions where PNH was located. These findings suggest that epileptic discharges may take origin from abnormal circuitries located close to or involving the PNH.275 The clinical picture is related to the amount of heterotopic tissue, the distribution of nodules, and the extension to the overlying cortex. Therefore, the outcome is much more favorable in patients with unilateral PNH, especially single-nodule PNH, compared to patients with PNH associated with periventricular and subcortical nodules extending to the neocortex.266
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Focal Epilepsy
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FIGURE 9147. Asymmetric Frontal Intermittent Rhythmic Delta Activity (FIRDA); Periventricular Nodular Heterotopia (PNH). A 10-year-old girl with generalized tonic-clonic seizures and complex partial seizures. Axial FLAIR MRI shows periventricular nodular heterotopia (PNH) in the right fronto-parietal region (open arrow) and overlying focal cortical dysplasia in the right fronto-parietal region (double arrows). EEG demonstrates bilateral synchronous FIRDA with right hemispheric predominance. Widespread continuous PDA occurs mostly in deafferentation of the cortex caused by subcortical white matter lesions or, less commonly, by bilateral thalamic, hypothalamic, and upper mesencephalic lesions.276,277 IRDA (FIRDA or OIRDA) occurs in a wide variety of conditions involving both subcortical and cortical gray matter.278 A recent study showed that FIRDA may reflect a pathologic type of increased excitation of cortical and subcortical gray matter.279
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FIGURE 9148. Bilateral Periventricular Nodular Heterotopia (PNH); Mental Retardation and Cerebellar Hypoplasia. A 20-year-old male with cerebellar hypoplasia, mild left hemiparesis, mild ventriculomegaly, and seizures characterized by seeing a star burst, becoming frightened, spacing out, experiencing vertigo, and tremors of legs, drooling, and lip smacking. MRI shows PNH in the two hemispheres (arrow and open arrow), cerebellar hypoplasia, and ventricular dilatation. EEG demonstrates polyspike discharges in the right temporal region (box). Bilateral brain malformations and the associated cerebral abnormalities (mega cisterna magna, cerebellar hypoplasia, ventriculomegaly) suggest a widespread disorder of brain ontogenesis.275 Focal interictal EEG abnormalities are always consistent with the anatomic location of the PNH. In slow sleep, focal abnormalities frequently change to bilaterally diffuse bursts of polyspikes. In addition, EEG frequently demonstrates multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions.266
840
Focal Epilepsy
9
FIGURE 9149. Bilateral Periventricular Nodular Heterotopia. A 10-year-old boy with ADHD, bipolar disorder, essential tremor, learning disorder, and complex partial seizures. Axial T2 MRI demonstrates bilateral and symmetric PNH. EEG shows bilateral synchronous centro-temporal spikes or unilateral centro-temporal spikes. In most patients with bilateral and symmetric PNH, no neurologic deficits or mental retardation are present. However, the lower limits of normal IQ scores and learning disability were noted. Epilepsy is the main clinical symptom in PNH. In patients with bilateral PNH, epilepsy onset is in the second decade of life, preceded by infantile febrile convulsions. GTCS is rare and easily controlled. Focal seizures are observed in all patients and are intractable to medical treatment. Status epilepticus is never observed.266 Focal interictal EEG abnormalities are always consistent with the anatomic location of the PNH. In slow sleep, focal abnormalities frequently change to bilaterally diffuse bursts of polyspikes. In addition, EEG frequently demonstrates multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions. In a minority of patients, 3- to 4-Hz spike-wave discharges, mimicking primary generalized epilepsy, are noted.232 The ictal EEG abnormalities at the onset and immediately after the end of the seizures were always recorded on the EEG leads exploring the brain regions where PNH was located. These findings suggest that epileptic discharges may take origin from abnormal circuitries located close to or involving the PNH.275 A close relationship exists between heterotopic nodules and cortical regions in bilateral PNH, with an epileptogenic network including both structures. This finding may explain why a surgery limited to the temporal lobe fails to stop the seizures in these patients.280
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FIGURE 9150. Triphasic Complexes; Hemimegalencephaly Due to Linear Sebaceous Nevus Syndrome. A 7-day-old boy with left hemimegalencephaly caused by linear sebaceous nevus syndrome. He presented to the hospital with continuous right arm jerking. Examination revealed right thumb atrophy with constant horizontal nystagmus. MRI shows left ventricular dilatation, white matter signal abnormality, abnormal cortical gyration, and enlargement of the left hemisphere. EEG reveals nearly continuous periodic triphasic sharp waves in the left hemisphere, maximal over the centro-temporal region. There are three types of EEG abnormalities in hemimegalencephaly:281 1. Triphasic complexes of very large amplitude consisting of a small negative wave, followed by a large-amplitude, positive slow spike. This was followed by a very slow wave, of large amplitude sometimes, which formed a plateau, often associated with monomorphic, sharp theta activity of moderate amplitude. This pattern was observed in patients with partial seizures. 2. Asymmetrical suppression-burst pattern, with bursts of “alpha-like” activity interrupted by hypoactive phases on the affected side and, on the unaffected side, bursts of large amplitude, polymorphic polyspikes of the type usually observed in suppression-burst tracings. This pattern was observed at birth or after a few months and coincided with Ohtahara syndrome.282 It can also be recorded until adult life in patients with epilepsia partialis continua.222 3. An “alpha-like” activity consisted of an asymmetrical and large-amplitude, sharp, nonreactive 7- to 12-Hz rhythm, little modified by waking state, apart from the association of slow waves during sleep, which tended to be focused in the abnormal hemisphere. This pattern was associated with better outcome. Asymmetric hypsarrhythmia originating on the affected side is also noted.283,284
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Focal Epilepsy
9
FIGURE 9151. Unilateral Suppression-Burst Pattern (Ohtahara Syndrome); Hemimegalencephaly. A 19-day-old boy born at 35 weeks GA who started having seizures in utero (hiccup and increased fetal movement) and developed postnatal seizures at 1 week of age described as left facial twitching and eye deviation and epileptic nystagmus with fast component to the left. The seizures, at times, were continuous. MRI shows right hemimegalencephaly. EEG demonstrates a suppression-burst pattern over the right hemisphere. She underwent right functional hemispherectomy at 2 months of age and has been seizure free for 3 years since the surgery. There are three types of EEG abnormalities in hemimegalencephaly:281 1. Triphasic complexes of very large amplitude consisting of a small negative wave, followed by a large-amplitude, positive slow spike. This was followed by a very slow wave, of large amplitude sometimes, which formed a plateau, often associated with monomorphic, sharp theta activity of moderate amplitude. This pattern was observed in patients with partial seizures. 2. Asymmetrical suppression-burst pattern, with bursts of “alpha-like” activity interrupted by hypoactive phases on the affected side and, on the unaffected side, bursts of large amplitude, polymorphic polyspikes of the type usually observed in suppression-burst tracings. This pattern was observed at birth or after a few months and coincided with Ohtahara syndrome.282 It can also be recorded until adult life in patients with epilepsia partialis continua.222 3. An “alpha-like” activity consisting of an asymmetrical and large-amplitude, sharp, nonreactive 7- to 12-Hz rhythm, little modified by waking state, apart from the association of slow waves during sleep, which tended to be focused in the abnormal hemisphere. This pattern was observed to be associated with better outcome. Asymmetric hypsarrhythmia originating on the affected side is also noted.283,284
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FIGURE 9152. Hemimegalencephaly; "Alpha-Like" Activity. A 17-year-old girl with mental retardation, intractable epilepsy including epilepsia partialis continua caused by right hemimegalencephaly. Axial T2 MRI shows increased volume of white matter in the enlarged hemisphere. Interictal SPECT reveals diffuse hypoperfusion in the right hemisphere. EEG demonstrates asymmetric and large-amplitude, sharp, nonreactive 10- to 12-Hz rhythm in the right hemisphere. There are three types of EEG abnormalities in hemimegalencephaly:281 1. Triphasic complexes of very large amplitude consisting of a small negative wave, followed by a large-amplitude, positive slow spike. This is followed by a very slow wave, of large amplitude sometimes, which forms a plateau, often associated with monomorphic, sharp theta activity of moderate amplitude. This pattern is observed in patients with partial seizures. 2. Asymmetrical suppression-burst pattern, with bursts of “alpha-like” activity interrupted by hypoactive phases on the affected side and, on the unaffected side, bursts of large amplitude, polymorphic polyspikes of the type usually observed in suppression-burst tracings. This pattern is observed at birth or after a few months and coincides with Ohtahara syndrome.282 It can also be recorded until adult life in patients with epilepsia partialis continua.222 3. An “alpha-like” activity consisting of an asymmetrical and large-amplitude, sharp, nonreactive 7- to 12-Hz rhythm, little modified by waking state, apart from the association of slow waves during sleep, which tended to be focused in the abnormal hemisphere. This pattern was observed to be associated with better outcome. Asymmetric hypsarrhythmia originating on the affected side is also noted.283,284 Brain SPECT is useful in excluding seizure foci or other perfusion abnormalities in the contralateral side before surgery.285
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FIGURE 9153. Temporal Lobe Epilepsy Due to Right Hippocampal Sclerosis; Start-Stop-Start Phenomenon. (Same patient as in Figure 9-67) Coronal FLAIR MRI, interictal PET, and interictal EEG are concordant with the right mesial temporal lobe epilepsy caused by mesial temporal sclerosis. Ictal EEG during her typical seizure, characterized by rising sensation from the epigastrium, orofacial and hand automatism, and confusion, shows a burst of right temporal spikes (start) followed by diffuse background attenuation without definite rhythmic activity (stop) (box).
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FIGURE 9154. Temporal Lobe Epilepsy Due to Right Hippocampal Sclerosis; Start-Stop-Start Phenomenon. (Continued) Twenty seconds later, evolving rhythmic theta activity in the T2 electrode, which represents ictal activity in the right mesial temporal region, is noted (start). The start-stop-start (SSS) phenomenon is defined as a pair of sequential ictal potentials separated by complete or almost complete cessation of seizure activity, the SSS phenomenon was found on subdural recordings in 23% of 98 patients.237 The two phases were morphologically similar. The first “start” usually had a narrow field.241 Fifty-eight percent of SSS seizures showed a complete stop. Thirty-five percent of patients and seizures restarted in a different location than the first start. When in different locations, the start, not the restart, is correlated with non-SSS origin. SSS seizures arose in the same region as non-SSS seizures in almost all patients.237 Subsequently, the SSS phenomenon was also observed in scalp EEG, sphenoidal, and foramen ovale electrodes. Recognition of the phenomenon may improve the accuracy of seizure localization.241,242
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Focal Epilepsy
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FIGURE 9155. High-Frequency Oscillations (HFOs); Slow Direct-Current (DC) Shifts or Infraslow Activity (ISA). A 2-year-old right-handed boy with very frequent, brief seizures described as clusters of asymmetric tonic seizures, greater on the left side with head drops occurring 10–20 times daily. Brain MRI was normal. Interictal PET showed hypometabolism in the right frontal lobe. Interictal subdural EEG (sEEG) shows nearly continuous polyspike-wave discharges at FPG7 (box A). The ictal sEEG onset (box B) demonstrates disruption of interictal EEG activity at FPG7 and the presence of diffuse low-voltage fast activity consistent with high-frequency oscillations (HFOs), maximally expressed at FPG7. Immediately after that, slow negative direct-current (DC) shifts are noted at FPG7. Localized negative DC shifts were recorded during penicillin-induced seizures in animal models, and they occur in association with sustained paroxysmal activity, suggesting that these negative shifts are an expression of cellular depolarization.286 The DC shifts were of maximal voltage at the center of the focus and had narrower distribution than paroxysmal activity.287 There are only limited reports of subdurally recorded DC potentials in humans.288 Other elements than neurons are additionally involved, including glia, ionic changes, as well as those of the blood-brain barrier and of cerebral blood flow, have been implicated. Ictal DC shifts or infraslow activity (ISA) obtained from scalp recordings with standard EEG machines with a high-pass filter of 0.1 Hz might be able to differentiate between purely focal seizures versus those where there is an additional generalized component.129 Ictal onset baseline shifts are part of a marked increase of interictal DC shifts. The current digital EEG instruments that have a high-pass filter of 0.1 or at times even 0.01 Hz can record scalp and intracranial DC shifts and could have localizing value.127,289,290 Rodin and Funke have defined ISA (DC shifts) as the frequency band of 0.01–0.1 Hz rather than 0.5 Hz because respirations, which typically have a frequency of 0.2–0.4 Hz, can contaminate the tracings when a low-pass filter of 0.5 Hz is used.291 In contrast to the conventional EEG frequencies, it has a small electrical field, which is negative at the site of activity and positive at a distance.292 Ikeda concluded that (1) ictal DC shifts were observed in 85% of all the recorded seizures in subdural EEG and in 23% of all the scalp EEG recordings by using LFF of 0.016 Hz for the AC amplifier; (2) ictal DC shifts were mainly surface negative in polarity; (3) they started 1–10 sec earlier than the conventional ictal EEG onset; (4) ictal DC shifts were seen in a more restricted area (one to two electrodes) compared with the dimension defined by the conventional ictal EEG changes; (5) ictal DC shifts often coincided with the electrodecremental pattern; (6) scalp-recorded ictal slow shifts have high specificity but low sensitivity; and (7) a DC amplifier is not necessary to record slow DC shifts; instead, an AC amplifier with long time constant could be used.127,133,289 The subdurally recorded ictal DC shifts are clinically useful in strengthening the conventional ictal EEG findings and confirming the epileptogenic area. In neocortical seizures, even subdural recordings show widely distributed or ill-defined initial ictal change, especially when imaging studies did not reveal a clear focal lesion. In addition, it would be difficult to judge the area most attenuated in amplitude from the electrodecremental pattern, which is usually seen as the initial ictal EEG change in neocortical seizures. Ictal DC shifts, in contrast, are so prominent and transient that the areas that show the maximal changes of ictal DC shifts are easily recognized.127 After the seizure has been viewed using conventional frequencies and muscle activity has been removed, a search for baseline shifts should be performed by opening the highpass filter to at least 0.1 or 0.01 Hz. When intracranial recordings are performed the conventional frequency band, DC shifts and HFOs should be evaluated separately for seizure onset determination. HFOs can be ascertained by setting the high-pass filter at >60 Hz and leaving the low-pass filter open.292
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FIGURE 9156. Slow Direct Current (DC) Shifts; Supplementary Sensorimotor Area (SSMA) Seizure. A 7-year-old girl with medically intractable epilepsy caused by a focal cortical dysplasia (FCD) in the left SSMA (box). She presented with Doose syndrome-like epilepsy. She subsequently developed absence-like seizures and asymmetric/ unilateral tonic seizures. Subdural EEG using LFF of 0.05 Hz recorded one of her typical asymmetric tonic seizures described as slight head turning to the left side with left arm tonic stiffening. EEG shows a slow DC shifts (box A) at the DC3 depth electrode, which is located at the left SSMA. This occurs approximately 12 sec before the onset of HFOs, which are diffuse but maximally expressed at DC3. Ten seconds later, she develops her typical seizure, as described above, lasting for approximately 9 sec. Note ictal tachycardia (box B), which occurs 5 sec after the onset of HFOs. Ikeda concluded that (1) ictal DC shifts were observed in 85% of all the recorded seizures in subdural EEG and in 23% of all the scalp EEG recordings by using LFF of 0.016 Hz for the AC amplifier; (2) ictal DC shifts were mainly surface negative in polarity; (3) they started 1–10 sec earlier than the conventional ictal EEG onset; (4) ictal DC shifts were seen in a more restricted area (one to two electrodes) compared with the dimension defined by the conventional ictal EEG changes; (5) ictal DC shifts often coincided with the electrodecremental pattern; (6) scalp-recorded ictal slow shifts have high specificity but low sensitivity; (7) A DC amplifier is not necessary to record slow DC shifts; instead, an AC amplifier with a long time constant can be used.127,133,289 The subdurally recorded ictal DC shifts are clinically useful in strengthening the conventional ictal EEG finding and confirming the epileptogenic area. In neocortical seizures, even subdural recordings show widely distributed or ill-defined initial ictal change, especially when imaging studies do not reveal a clear focal. In addition, it would be difficult to judge the area most attenuated in amplitude from the electrodecremental pattern, which is usually seen as the initial ictal EEG changes in neocortical seizures. Ictal DC shifts, in contrast, are so prominent and transient that the areas that show the maximal changes of ictal DC shifts are easily recognized.127 Ictal slow DC shifts were also recorded by depth electrodes placed in the hippocampus in patients with MTLE.126
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FIGURE 9157. Electrocorticography (ECoG); Supplementary Sensorimotor Area (SSMA) Seizure Due to Severe Focal Cortical Dysplasia with Balloon Cells. A 14-year-old left-handed boy with a history of fever at 13 days of life and development of seizures 2 weeks later, diagnosed with encephalitis. He also has right hemiparesis and developmental delay. He had infantile spasms that evolved into LGS. His seizures occur mostly at night but may also occur during the day when he is fatigued. The seizures were described as clusters of right-sided stiffening and Todd’s paralysis consistent with epileptic spasms. MRI shows abnormal signal with volume loss in the left medial frontal white matter, consistent with gyriform calcification intermixed with cystic lesions. He underwent electrocorticography (ECoG), which shows repetitive spikes (box B) and continuous rhythmic spikes (box A) in the MIH 13 and MIH 14 (mid interhemispheric leads), respectively. Pathology after the resective surgery showed severe focal cortical dysplasia with balloon cells. The patient has been seizure free after the surgery. Focal cortical dysplasia (FCD) is often associated with severe focal epilepsy. Intraoperative ECoG showed one of the following patterns: (1) repetitive electrographic seizures, (2) repetitive bursting discharges, or (3) continuous or quasicontinuous rhythmic spiking. One or more of these patterns were present in 67% with intractable focal epilepsy associated with FCD and, in only 2.5% with intractable focal epilepsy, were associated with other types of structural lesions. These ictal or continuous epileptogenic discharges (I/CEDs) were usually localized, which contrast with the more widespread interictal ECoG epileptic activity, and tended to correspond with the lesion seen in the MRI. Complete resection of the FCD displaying I/CEDs correlated with good surgical outcome. Three-fourths of the patients in whom the FCD displaying I/CEDs was entirely excised had favorable surgical outcome. FCDs are highly and intrinsically epileptogenic, and intraoperative ECoG identification of this intrinsically epileptogenic dysplastic cortical tissue is critical to decide the extent of excision.73
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FIGURE 9158. Symptomatic Lennox-Gastaut Syndrome; Malformation of Cortical Development Due to Duplication of Chromosome 10p 15.3. A 4-year-old girl with duplication of chromosome 10p15.3. She had a history of infantile spasms that evolved into Lennox-Gastaut syndrome. She had developmental delay and multiple types of seizures, including GTCS, atypical absence, myoclonic, and asymmetric tonic seizures. MRI shows right mesial temporal cyst (arrow), left temporal cortical dysplasia (double arrows), and left parieto-temporal periventricular nodular heterotopia (PNH) (open arrow). Background EEG shows generalized slow spike-and-wave discharges consistent with the diagnosis of Lennox-Gastaut syndrome. EEG during asymmetric epileptic spasms with right-sided predominance reveals low-voltage fast activity superimposed on diffuse biphasic delta activity, maximally expressed in the left parasagittal region, which is followed immediately by diffuse electrodecrement (box). The patient has been seizure free for over 2 years since the left functional hemispherectomy over 2 years ago. There has been no report of focal cortical dysplasia associated with duplication of chromosome 10p15.3. Bilateral lesions should not preclude consideration for hemispherectomy. On the other hand, bilateral EEG abnormalities can be seen in unilateral hemispheric lesions, and these findings alone should not exclude the possibility of hemispherectomy. The etiology of the lesion plays a major role in determining the outcome.293 Unilateral PNH is frequently located in the posterior paratrigonal region (i.e., a watershed area) of the lateral ventricles and may extend into the white matter to involve adjacent neocortical and archicortical areas.266 Epilepsy in PNH patients is generated by abnormal anatomic circuitries including the heterotopic nodules and adjacent archicortical and neocortical areas. Regardless of the different MRI features, the main clinical problem in most PNH patients is the presence of focal drug-resistant epilepsy. The presence of risk factors for prenatal brain damage, the common location in the paratrigonal region, and the lack of familial cases all suggest that acquired factors, damaging a limited region of the developing brain, may provoke the genesis of unilateral nodules. The selective ablation of a subpopulation of dividing neuroblasts alters the migration and differentiation of subsequently generated neurons, which in turn set the base for the formation of the heterotopia.273,274 Focal interictal EEG abnormalities are always consistent with anatomic location of the PNH. In slow sleep, focal abnormalities frequently change in bilaterally diffused bursts of polyspikes or multifocal interictal EEG abnormalities. Spikes may be asynchronous (mostly independent) and occur in multifocal regions. In a minority of patients, 3- to 4-Hz spike-wave discharges, mimicking primary generalized epilepsy, are noted.232 The ictal EEG abnormalities at the onset and immediately after the end of the seizures were always recorded in brain regions where PNH was located. These findings suggest that epileptic discharges may take origin from abnormal circuitries located close to or involving the PNH.275 The clinical picture is related to the amount of heterotopic tissue, the distribution of nodules, and the extension to the overlying cortex. Therefore, the outcome is much more favorable in patients with unilateral PNH, especially single-nodule PNH, compared to patients with PNH associated with periventricular and subcortical nodules extending to the neocortex.266
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FIGURE 9159. Secondary Bilateral Synchrony with Secondary Epileptogenesis; Angiocentric Neuroepithelial Tumor (ANET), Right Occipital. A 20-year-old male with a history of medically intractable epilepsy and right parieto-occipital lesion. He experiences two types of seizures. The first type of seizure involved blacking-out episodes where he made clicking noises, had activity arrest, picked at his clothing, and stared upward and to the left for about 2–4 minutes. He had dizziness and was tired afterward. The second type of seizure involved seeing colors in the periphery of his vision with blurring of central vision. His seizures had been progressing with more frequent secondarily GTCS. Coronal FLAIR MRI shows a discrete lesion in the right parieto-occipital region (open arrow) with hyperintensity in the left homologous parieto-occipital region. EEG demonstrates bisynchronous slow spike-wave discharges with right hemispheric predominance. Presence of the hyperintensity in the left parieto-occipital region corresponding to the homologous brain tumor in the right parieto-occipital region supports the presence of secondary epileptogenesis in humans. Kindling has been referred to as a model of epileptogenesis. It is “the process by which repeatedly induced seizures result in an increasing seizure duration and enhanced behavior involvement of those induced seizures until a plateau is reached.” Kindling can result in spontaneous seizures if enough stimuli are given, suggesting that kindling can cause epilepsy.294
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FIGURE 9160. Epilepsia Partialis Continua (EPC); POLG1 Mutation. A 16-year-old girl with intractable epilepsy, peripheral neuropathy, ataxia, and mental deterioration. Her seizures include occipital lobe seizures and epilepsia partialis continua (EPC). Brain MRI shows multifocal increased signal intensity in the right fronto-temporal region and cerebellum. EEG during the left EPC demonstrates sharp waves in the right central/centro-temporal region time-locked with EMG activity. Subtle polymorphic delta activity is also noted in the right hemisphere. Ten months later, she developed liver failure, brain stem involvement (ophthalmoplegia, facial weakness, and dysphagia) and died shortly after that. POLG mutation produces a variety of neurological syndromes, including progressive external ophthalmoplegia, Alper’s syndrome, and mitochondrial spinocerebellar ataxia-epilepsy syndrome (MSCAE). Characteristic neurologic features of children with mutations in POLG1 were early-onset psychomotor regression, refractory seizures in the form of myoclonus and EPC,295,296 stroke-like episodes, and ataxia.296 Axonal neuropathies have been described, often causing profound sensory ataxia.297 Epilepsy is one of the most common manifestations of POLG1 disease. Epilepsy has an early predilection for the occipital lobes. Thereafter, patients develop simple partial motor seizures and complex partial seizures, myoclonus, and status epilepticus (SE). Repeated seizure activity, especially SE, contributes to worsening mitochondrial function, energy deficiency, and a fatal outcome.298 A wide variety of occipital symptoms were noted. Almost all patients had occipital seizures. In addition, frontal and generalized epileptic activity occurred in most patients during seizure spread or SE.298 POLG1 mutations should be considered in teenagers and young adults reporting episodic visual symptoms with migraine-like headaches and sudden-onset intractable seizures. Due to the risk of liver failure, valproic acid should be avoided when treating patients with POLG1 phenotypes.296,299
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FIGURE 9161. Occipital Lobe Epilepsy; POLG1 Mutation. (Same patient as in Figure 9-160) Seven months after the previous EEG in Figure 9-149. The patient showed deterioration of mental status. Her seizures got worse. She had multiple types of seizures, including GTCS, myoclonic seizures, hemiconvulsion, and occipital lobe seizures described as confusion, visual hallucination, and blindness. Visual hallucinations included simple hallucination, seeing lights and colors, and complex hallucinations, seeing people and ghosts. No auditory hallucinations were noted. Elevation of liver enzymes was noted. Axial FLAIR and coronal T2 WI MRIs show hyperintensity in the right occipital lobe (arrows). EEG demonstrates very frequent and, at times, nearly continuous occipital spikes with some extension to the parieto-temporal regions with right-sided predominance. Epilepsy is one of the most common manifestations of POLG1 disease. Epilepsy has an early predilection for the occipital lobes. Thereafter, patients develop simple partial motor seizures and complex partial seizures, myoclonus, and status epilepticus (SE). Repeated seizure activity, especially SE, contributes to worsening mitochondrial function, energy deficiency, and fatal outcome.298 A wide variety of occipital symptoms were noted. Almost all patients had occipital seizures. In addition, frontal and generalized epileptic activity occurred in most patients during seizure spread or SE.298 POLG1 mutations should be considered in teenagers and young adults reporting episodic visual symptoms with migraine-like headaches and sudden-onset intractable seizures. Due to the risk of liver failure, valproic acid should be avoided when treating patients with POLG1 phenotypes.296,299
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INDEX Page numbers followed by f indicate figures.
A Absence-like seizure, supplementary sensorimotor area in, 832f Absence seizure. See also specific types in Dravet syndrome, 599f in Lennox-Gastaut syndrome, 533 from right thalamic heterotopia, unilateral alpha attenuation in, 275, 294f secondary (See Frontal absence) Acanthamoeba CNS infection, 451f Acquired immunodeficiency syndrome (AIDS) EEG in, 334f new-onset seizures in, 334f Activation methods, in focal epilepsy, 679 Acute disseminated encephalomyelitis (ADEM), polymorphic delta activity slowing in, 333f Aicardi syndrome with focal cortical dysplasia, 568f with focal cortical dysplasia, asymmetric epileptic spasms in, 385f MRI in, 565f “split brain” EEG in, 566f Alcohol withdrawal, excessive beta activity with, 397f Alpha and beta enhancement, with focal cortical dysplasia, 378f, 379f, 383f Alpha asymmetry in Dyke-Davidoff-Mason syndrome from intrauterine stroke, 275, 287f in focal cortical dysplasia, 275, 304f in hemorrhagic stroke from streptococcal infection, 275, 293f Alpha attenuation ipsilateral, in focal cortical dysplasia and left supplementary sensorimotor area, 275, 296f with polymorphic delta activity, 275, 291f–292f focal, in acute focal axonal injury, 275, 295f thalamocortical circuit lesions in, 300f
unilateral, right thalamic heterotopia in, 275, 294f Alpha coma (AC), 394, 449f–450f, 473–474 after cardiac arrest and CPR, 502f in anoxic encephalopathy, 390 in cerebellar infarction, 450f with delta slowing (FIRDA & PDA) and POLG1 mutation, 449f with generalized nonepileptiform activity, 394 in hypoxic encephalopathy during midazolam infusion, 500f overview of, 501f vs. physiologic alpha rhythm, 503f in pontine stroke, 501f prognosis in, 389, 508f Alpha enhancement, focal, with focal cortical dysplasia, 379f Alpha power, fMRI signal and, 293f Alpha rhythm, 1–2, 8f–12f asymmetry in, 2 in Bancaud phenomenon, 2 beating in, 2, 10f distribution in, 2 frequency in, 1 high-amplitude, fast activity in, in lissencephaly type 1, 400f low-voltage background activity in, 18f mesencephalic-medial thalamic network in, 294f mu rhythm with, 11f, 12f normal, 2, 8f paradoxical, 2 physiologic, alpha coma vs., 503f regulation in, 1 slowing of, 275, 304f slow variant of, 275, 284f–286f with behavioral disturbance and headache, 286f with recurrent staring episodes, 285f with recurrent vertigo, 284f
squeak effect in, 2 in subdural EEG, 8f, 9f suppression of, in hemiplegic migraine, 332f from thalamus, 293f voltage attenuation abnormalities of, 275 voltage in, 1 Alpha rhythm focal abnormalities, 275, 280f–304f, 307f asymmetry in Dyke-Davidoff-Mason syndrome from intrauterine stroke, 275, 287f in focal cortical dysplasia, 275, 304f in hemorrhagic stroke from streptococcal infection, 275, 293f attenuation ipsilateral, in focal cortical dysplasia and left supplementary sensorimotor area, 275, 296f with polymorphic delta activity, 275, 291f–292f with polymorphic delta activity, in acute focal axonal injury, 275, 295f unilateral, in right thalamic heterotopia, 275, 294f in Bancaud phenomenon with Dyke-Davidoff-Mason syndrome, 275, 289f ipsilateral enhancement, in unilateral polymicrogyria, 275, 302f normal variations posterior slow wave of youth, 275, 280f–283f slow alpha variant, 275, 284f–286f fast alpha variant, 2, 15f–17f from right occipital tumor, 275, 288f slowing, 275 voltage accentuation, 275 Alpha seizure discharge in newborn, 203, 257f–260f in pyruvate dehydrogenase deficiency, 258f–260f Alpha-theta coma in hypoxic encephalopathy, 504f prognosis in, 508f
861
Ambulatory EEG, of focal epilepsy, 679 Amoebic meningoencephalitis with herniation syndrome, asymmetric spindle coma in, 450f, 511f Amphetamines, excessive beta activity with, 397f Angelman syndrome, 615–616, 645f–647f bilateral synchronous 3-4 Hz spike-wave activity in occipital region in, 646f nonconvulsive status epilepticus in, 647f notched-delta pattern in, 425f–426f, 645f Angiocentric neuroepithelial tumor (ANET), secondary bilateral synchrony with secondary epileptogenesis with, 850f Anoxic encephalopathy after CPR, evolving EEG patterns in rhythmic coma from, 509f alpha coma from, 390 bilateral independent lateralized epileptiform discharges in, 390 burst-suppression in, 460f evolution of EEG in, 461f myoclonic bursts with, 458f–460f from near drowning, 460f with severe encephalopathy, 458f, 459f evolution of EEG in, 462f with severe encephalopathy, 463f generalized nonepileptiform activity in, 390 generalized periodic epileptiform discharges in, 462f periodic epileptiform discharges in midline in, 485f theta coma in from hanging, 508f irreversible, 508f–509f theta in rhythmic coma in, 15 min before death, 508f–509f Anoxic seizures, pallid breath holding spells in, 667f Anterior cingulate gyrus, on fronto-thalamic circuits, 682 Anterior slow dysrhythmia, 406f–407f with frontal sharp transients, 228f, 231f, 232f in newborn, 202, 231f–233f Antiepileptic drugs (AEDs) new, on EEG, 411f seizure worsening from, 613, 618f Anxiety, excessive beta activity with, 397f Aphasia, ictal, in intracranial hemorrhage from malignant hypertension, 370f
862
Artifacts, 125–198. See also specific types characteristics of, 125 nonphysiological, 127–128 60-cycle, 127–128, 189f electrode (pop), 128, 192f, 197f, 198f ground electrode misplacement, 196f ground lead, 128, 194f–196f high-frequency jet respirator, 128, 191f high-frequency ventilator, 128, 190f, 266f photocell, 128, 193f positive sharp waves, 198f, 245f telephone ring, 127, 188f physiological, 125–127, 129f–153f electrocardiographic, 126, 145f–149f electromyographic, 126–127, 143f–144f, 150f, 187f eye movements, 125–126, 129f–142f galvanic skin response, 127, 153f glossokinetic, 127, 151f, 152f movements, 127 physiological movements, 127, 154f–186f body movement, rapid, 127, 184f breath holding, 186f chewing, 187f head movement, 127, 176f–177f hiccup, 127, 163f–168f limb movement, 127, 178f–179f patting, 127, 154f–162f respiration, 127, 181f, 182f, 184f–186f shivering, 127, 180f, 183f sobbing, 127, 169f–170f sucking, 127, 171f–173f tremor, 127, 174f–175f ventilator, 127, 182f Asymmetric infantile spasms, 568f Asymmetric alpha rhythm, 2, 22f Asymmetric beta attenuation, focal anterior, in left middle cerebral artery stroke, 308f with polymorphic delta activity from embolic stroke in pneumococcal septicemia, 309f with sleep spindles and vertex waves, in encephalomalacia from meningoencephalitis, 310f Asymmetric beta rhythm in left middle cerebral artery stroke, 308f
normal, 354f and polymorphic delta activity with embolic stroke in pneumococcal septicemia, 309f with sleep spindles and vertex waves, in encephalomalacia from meningoencephalitis in newborn, 310f Asymmetric epileptic spasms. See Epileptic spasms, asymmetric Asymmetric hypsarrhythmia. See Hypsarrhythmia, asymmetric Asymmetric ictal pattern, 551f Asymmetric infantile spasms. See Infantile spasms (IS), asymmetric Asymmetric lambda with breach rhythm, 376f in normal individuals, 307f Asymmetric spindle coma in acute amoebic meningoencephalitis with herniation syndrome, 450f, 511f during midazolam infusion, with embolic stroke, 510f Asymmetric tonic seizure, in supplementary sensorimotor area seizures, 776f Asynchrony background with diffuse axonal injury and vasogenic edema in corpus callosum, 454f in Ohtahara syndrome with corpus callosum dysgenesis, 455f gross interhemispheric, in newborn with severe hypoxic ischemic encephalopathy, 211f Asystole, cardiac, from anoxic encephalopathy S/P cardiac arrest with severe traumatic brain injury, 670f–672f Atypical absence seizures, in Lennox-Gastaut syndrome, 533 Atypical benign partial epilepsy (ABPE), 690, 698f vs. Lennox-Gastaut syndrome, 675, 698f Atypical MERRF, 616, 657f Autism, epilepsy and, 691 Axonal injury acute focal, focal polymorphic delta activity and alpha attenuation with, 275, 295f diffuse
asynchronous burst suppression in, 457f and vasogenic edema in corpus callosum, background asynchrony in, 454f
B B6 (pyridoxine) therapy, 616, 660f Back-averaging, 689 Background activity. See also specific types and disorders in Lennox-Gastaut syndrome, 532 low-voltage, 18f transient unilateral attenuation of, during sleep, 202, 235f, 236f very low-voltage, in hypoxic ischemic encephalopathy, 265f, 517f Background activity, focal enhancement of breach rhythm, 276, 374f–377f asymmetric lambda waves in, 376f beta activity focal enhancement with polymorphic delta activity in, 377f prominent mu rhythm in, 374f–375f higher amplitude, 276, 378f–385f alpha and beta enhancement in with focal cortical dysplasia, 378f, 379f with intrinsic epileptogenicity of focal cortical dysplasia, 383f asymmetric epileptic spasms in Aicardi syndrome with focal cortical dysplasia with, 385f beta enhancement in focal, with low-voltage fast activity in focal transmantle dysplasia, 381f ipsilateral, in polymicrogyria with closed-lip schizencephaly, 380f ipsilateral, with polymorphic delta activity in periventricular leukomalacia with FCD, 382f ipsilateral diffuse rhythmic alpha, in polymicrogyria and closed-lip schizencephaly, 384f localized polymorphic delta activity in, 379f Background asynchrony with diffuse axonal injury and vasogenic edema in corpus callosum, 454f in Ohtahara syndrome with corpus callosum dysgenesis, 455f Background attenuation beta, during drowsiness, 311f–312f
diffuse, 395, 464f–466f, 517f with low-voltage EEG with bilateral subdural effusion, 464f with scalp edema and high-frequency respirator artifacts, 465f with severe hypoxic encephalopathy and electrocerebral inactivity, 466f polymorphic delta activity with, 356f in Sturge-Weber syndrome, 352f unilateral with low-voltage polymorphic delta activity, in severe right hemispheric encephalomalacia, 364f with sharp wave and polymorphic delta activity, in meningoencephalitis, 362f Background suppression with lateralized delta slowing, in postictal state, 354f lateralized, in hemiplegic migraine, 343f with polymorphic delta activity, in Sturge-Weber syndrome, 359f Balamuthia mandrillaris CNS infections with, 450f meningoencephalitis and herniation syndrome from, asymmetric spindle coma in, 450f, 511f Ballistocardiographic artifact, 126, 149f Balloon cells, severe focal cortical dysplasia with, supplementary sensorimotor area seizure in, 848f focal polymorphic delta activity with focal enhancement of beta activity and focal spikes in, 765f Bancaud phenomenon, 2 alpha rhythm in, 2 in Dyke-Davidoff-Mason syndrome, 275, 289f in hemorrhagic infarction, 301f Barbiturate withdrawal, excessive beta activity in, 397f Basal ganglion infarction FIRDA and continuous polymorphic delta activity in, 434f paradoxical activation in, 438f Beating of alpha rhythm, 2, 10f in excessive beta activity, 396f
Benign EEG variants not associated with seizures, 677. See also specific variants Benign epilepsy with centro-temporal spikes (BECTS), 684, 690–691, 704f–706f Benign epileptiform transients of sleep (BETS), 6, 100f–103f in 16-year-old with migraine and recurrent passing out, 101f in 17-year-old with recurrent déjà vu episodes, 102f Benign familial neonatal convulsion (BFNC), 261f, 689, 692f théta pointe alternant in, 261f, 689, 692f Benign infantile seizures, 690, 694f–697f in 4-week-old with recurrent apnea and clonic seizures, 694f–695f in 9-week-old with clusters of seizures, 696f–697f characteristics of, 695f, 696f Benign myoclonic epilepsy of infancy (BMEI), 615 in 10-month-old, with recurrent myoclonic jerks and drop attacks, 638f in 22-month-old, with recurrent myoclonic jerks of arms, 639f drop attacks in, 638f Benign neonatal nonfamilial convulsion, 262f, 690 théta pointe alternant in, 262f, 690 Benign partial epilepsy in infancy, 690, 694f–697f. See also Benign infantile seizures Benign sporadic sleep spikes (BSSS), 6, 102f Benzodiazepine excessive beta activity with, 396f for ifosfamide encephalopathy, 429f with phenobarbital, excessive beta activity with, 397f Beta activity, 2 depressed, in focal cortical dysplasia, 324f normal, 397f Beta activity enhancement, focal with focal cortical dysplasia, 378f, 379f with focal spikes and focal polymorphic delta activity, in balloon cell-type focal cortical dysplasia, 765f ipsilateral in polymicrogyria with closed-lip schizencephaly, 380f and polymorphic delta activity, in periventricular leukomalacia with FCD, 382f
863
Beta activity enhancement, focal (continued) low-voltage fast activity with, in focal transmantle dysplasia, 381f near skull defect, 377f with polymorphic delta activity, 377f without skull defect, 378f, 379f Beta activity, excessive, 390, 396f–403f, 448f beating appearance in, 396f from benzodiazepines, 396f decreased, in Sturge-Weber syndrome, 360f and phenobarbital, 397f extreme spindles in, with acute mycoplasma encephalitis with reversible focal lesion in corpus callosum, 448f from lissencephaly-pachygyria with congenital CMV, 399f from lissencephaly, type 1 classical, hypsarrhythmia, 400f high-amplitude fast activity, alpha band, 400f high-amplitude fast activity, beta band, 398f high-voltage fast activity, alpha band, 402f infantile spasm in remission, 403f lower voltage, 397f Beta asymmetry in left middle cerebral artery stroke, 308f normal, 354f Beta attenuation, focal, 275–276, 362f–364f asymmetric anterior, in left middle cerebral artery stroke, 308f with sleep spindles and vertex waves, in encephalomalacia from meningoencephalitis in newborn, 310f background asymmetry and polymorphic delta activity with embolic stroke in pneumococcal septicemia, 309f decreased, from benzodiazepine in Sturge-Weber syndrome, 360f lateralized background suppression with hemiplegic migraine in, 343f transient unilateral attenuation of background activity in sleep in, 345f Beta attenuation, ipsilateral, with monorhythmic theta in right parietal focal cortical dysplasia, 324f
864
Beta coma, 389, 394, 473 after hypoxic encephalopathy, 506f after phenobarbital, fosphenytoin, and midazolam, 512f Beta-delta complexes, 201, 208f–211f, 216f, 217f. See also Delta brushes Beta enhancement with alpha enhancement, 378f, 379f, 383f anterior, from encephalomalacia with severe intraventricular hemorrhage, 804f focal, with low-voltage fast activity in focal transmantle dysplasia, 381f ipsilateral in polymicrogyria with closed-lip schizencephaly, 380f and polymorphic delta activity, in periventricular leukomalacia with focal cortical dysplasia, 382f Beta frequency patterns. See also specific disorders and patterns with generalized nonepileptiform activity, 394 high-amplitude and fast activity, in lissencephaly type 1, 398f Beta suppression anterior, 308f with polymorphic delta activity, from right mesial temporal sclerosis due to viral encephalitis in infancy, 363f in Sturge-Weber syndrome, 317f Bilateral independent lateralized epileptiform discharges (BiPLEDs), 393, 472, 487f–491f, 675 in acute herpes simplex encephalitis, 487f in bilateral subdural hematoma, 490f in Creutzfeldt-Jakob disease, 473 in herpes simplex encephalitis, 390 in pneumococcal meningitis, 488f in polymorphic delta activity anoxic encephalopathy, 390 in watershed infarction with cardiomyopathy, 489f Bilateral synchrony of 3-4 Hz spike-wave activity in occipital region, in Angelman syndrome, 646f of high-voltage occipital spikes on low-frequency photic stimulation, 616, 661f–662f secondary (See Secondary bilateral synchrony (SBS))
Blind, needle-like (occipital) spikes of, 4, 42f–44f, 686 Body movement artifacts, 127, 184f Brain dead patients, 670f Brain edema, with central herniation syndrome, FIRDA and continuous polymorpic delta activity in, 435f–436f Brain injury, traumatic. See Traumatic brain injury (TBI) Breach rhythm, 276, 374f–377f asymmetric lambda waves in, 376f beta activity focal enhancement with polymorphic delta activity in, 377f with prominent mu, 374f–375f after right occipital ganglioma resection, 116f–117f during photic stimulation, 115f Breath holding artifact, 186f Breath holding spells (BHS), 617, 667f Burst-suppression (B-S) pattern, 395, 452f–461f. See also Suppression-burst (S-B) pattern in anoxic encephalopathy, 390 evolution of EEG in, 461f from near drowning, 460f in anoxic encephalopathy, severe from cardiac arrest due to myocardial infarction, 458f from traumatic brain injury, 459f asynchronous, 455f in Ohtahara syndrome with corpus callosum dysgenesis, 455f with pentobarbital anesthesia and corpus callosum hemorrhage, 457f in severely diffuse axonal injury, 457f background asynchrony in with diffuse axonal injury and vasogenic edema in corpus callosum, 454f in Ohtahara syndrome with corpus callosum dysgenesis, 455f in central pontine myelinosis, 452f–453f in ICU, 474, 513f–517f in cardiopulmonary arrest, 513f in hypoxic encephalopathy, with myoclonic jerks and spontaneous movement, 515f in hypoxic ischemic encephalopathy, with very low-voltage background activity, 517f
with myoclonic seizures and eye opening/closure, 516f from pentobarbital coma, 514f in newborn, 202–203, 237f–239f with diffuse rhythmic alpha activity, 238f, 239f with severe hypoxic ischemic encephalopathy, 237f in nonketotic hyperglycinemia, 456f overview of, 395, 452f prognosis with, 389 unilateral, in Ohtahara syndrome with hemimegalencephaly, 842f
C Carbamazepine, myoclonic seizure from, 618f Cardiac arrest and CPR, alpha coma after, 502f from myocardial infarction, burst-suppression pattern in, 458f Cardiac asystole, from anoxic encephalopathy S/P cardiac arrest from severe traumatic brain injury, 670f–672f Cardiac output, decreased cardiac syncope from, 617, 669f from obstruction to flow, 617, 669f Cardiac rhabdomyoma, apneic spell from arrhythmia from, in tuberous sclerosis complex, 688, 721f Cardiac syncope, 617, 668f–669f from decreased cardiac output, 617, 669f vs. neurocardiogenic syncope, 617, 669f Cardiac transplantation, periodic lateralized epileptiform discharges in ischemic stroke from, 483f Cardiomyopathy, bilateral independent lateralized epileptiform discharges in watershed infarction with, 489f Cardiopulmonary arrest burst-suppression in, 513f generalized nonepileptiform activity after, 389 Cardiopulmonary resuscitation (CPR), generalized periodic epileptiform discharges after, 494f Central herniation syndrome electrocerebral inactivity from severe hypoxic ischemic encephalopathy in, 138f, 518f FIRDA and continuous polymorphic delta activity with massive brain edema in, 435f–436f
Central midtemporal spikes, 684 in focal epilepsy, 684 ictal discharges in, 684 interictal discharges in, 684 Central pontine myelinosis (CPM) burst-suppression pattern in, 452f–453f other abnormalities in, 452f Central vertex spikes in mesial frontal stroke, 781f in orbitofrontal lobe epilepsy, 769f Central vertex theta, rhythmic, with low-voltage background in Rett syndrome, 781f Centro-parietal spikes, 685 of childhood, 685 in focal cortical dysplasia, right mesial parietal, 789f in other conditions, 685 in parietal lobe epilepsy, 685, 737f–739f Cerebellar anomalies, in Lennox-Gastaut syndrome, 591f Cerebellar hypoplasia, mental retardation and bilateral periventricular nodular heterotopia with, 839f Cerebellar infarction alpha coma with, 450f FIRDA and continuous polymorphic delta activity with, 434f Cerebral contusion. See also Traumatic brain injury (TBI) late post-traumatic epilepsy with encephalomalacia from, 316f Cerebral hemiatrophy electrical status epilepticus during slow sleep in, with EKG artifacts, 146f left, diffuse delta slowing with occipital prominence from intraventricular hemorrhage in, 336f, 365f Cerebral herniation, impending, 278, 432f Cerebral herniation syndrome. See also Herniation syndrome frontal intermittent rhythmic delta activity and continuous polymorphic delta activity in, 478f–479f Cerebral lesions. See also Traumatic brain injury (TBI) focal, in voltage asymmetry of sleep spindles, 321f on sleep patterns, 314f Cerebral lipomas, 832f
Cerebral malformation, epilepsy with, 351f. See also specific malformations Cerebral maturation, 550f Cerebromeningeal scar, late post-traumatic epilepsy with encephalomalacia from, 316f Chewing artifact, 126, 187f Childhood absence epilepsy (CAE), 614–615, 632f–637f diffuse rhythmic delta activity in, 634f with electrical status epilepticus during slow sleep, from thalamic heterotopia, 636f with eyelid myoclonia, 637f inclusion criteria for, 632f Jeavons syndrome in, 637f occipital intermittent rhythmic delta activity in asymmetric, 635f with generalized 3/sec spike-wave activity, 633f overview of, 632f photomyogenic (photomyoclonic) response in, 112f Chromosome 46XX, Inv (2)(p23,3p25.3), asynchronous spindles in, 446f Ciganek rhythm, 5, 78f Clonazepam, excessive beta activity from, 396f Clonic limb movement artifact, 178f Clonic seizures. See specific types Cobalamin C deficiency, focal cortical dysplasia with asymmetric epileptic spasms in, 556f–559f hypsarrhythmia variant in, with consistent focus of abnormal discharge, 556f Cocaine, excessive beta activity from, 397f Coma. See also specific types EEG reactivity with diffuse voltage attenuation in, 482f Coma, rhythmic, 394–395, 448f–451f, 473, 500f–512f. See also specific types alpha, 394 after cardiac arrest and CPR, 502f with cerebellar infarction, 450f with delta slowing (FIRDA & PDA) from POLG1 mutation, 449f in hypoxic encephalopathy during midazolam infusion, 500f overview of, 501f vs. physiologic alpha rhythm, 503f in pontine stroke, 501f
865
Coma, rhythmic (continued) alpha-theta in hypoxic encephalopathy, 504f prognosis in, 508f in anoxic encephalopathy after CPR, 509f asymmetric spindle in acute amoebic meningoencephalitis with herniation syndrome, 511f during midazolam infusion, with embolic stroke, 510f beta, 394 after hypoxic encephalopathy, 506f after phenobarbital, fosphenytoin, and midazolam, 512f delta, 394 after hypoxic encephalopathy, 505f etiology of, 510f, 511f evolution of, 451f frequency of, 451f prognosis in, 451f, 508f, 510f, 511f reactive vs. nonreactive, 510f, 511f spindle, 394–395 asymmetric, with acute amoebic meningoencephalitis and herniation syndrome, 450f extreme, from acute mycoplasma encephalitis with reversible focal lesion in corpus callosum, 448f theta, 394 irreversible, from anoxic encephalopathy 15 min before death, 508f–509f reversible, from sedative after nonconvulsive status epilepticus, 507f Complex partial seizures, in Dravet syndrome, 597f–598f Congenital hydrocephalus with ventriculoperitoneal shunt, focal epilepsy from, 275, 290f Continuous epileptogenic discharges (CEDs), 680 Continuous spikes and waves during slow sleep (CSWS), 351f, 534, 595f, 596f, 601f–604f. See also Electrical status epilepticus (ESES) during slow sleep in 4-year-old with developmental delay, hand tremor, and medically intractable epilepsy, 601f–602f
866
Corpus callosum diffuse axonal injury and vasogenic edema in, background asynchrony with, 454f dysgenesis of, background asynchrony in Ohtahara syndrome from, 455f hemorrhage of, asynchronous burst-suppression pattern with pentobarbital anesthesia in, 457f in interhemispheric synchronization, 454f Cortical deafferentation, 392 diffuse polymorphic delta activity with, 433f, 434f Cortical dysgenesis. See also specific disorders and types nodular heterotopias in, 572f (See also specific types) Cortical EEG generator, in beta attenuation, 275–276 Creutzfeldt-Jakob disease (CJD), 473, 498f bilateral independent lateralized epileptiform discharges in, 473 periodic sharp wave complexes in, 498f Cystic encephalomalacia, from intrauterine stroke, asymmetric hypsarrhythmia in, 544f Cytomegalovirus (CMV) infection, congenital brain in, 399f encephalopathy with, occipital intermittent rhythmic delta activity in, 423f lissencephaly-pachygyria with, excessive beta activity in, 399f malformation of cortical development with cerebral atrophy from, epilepsia partialis continua in, 707f with polymicrogyria, 707f
D DC shifts scalp-recorded, 679 in focal transmantle dysplasia, 567f with high-frequency oscillations, 846f ictal, 678–679, 766f, 800f in supplementary sensorimotor area seizure, 567f Deafferentation, cortical, 392 diffuse polymorphic delta activity in, 433f, 434f Degenerative diseases of white matter, excessive beta activity in, 390 Déjà vu symptom in benign epileptiform transients of sleep, 102f
in right mesio-temporal lobe epilepsy, 764f Delta activity frontal intermittent rhythmic (See Frontal intermittent rhythmic delta activity (FIRDA)) with generalized nonepileptiform activity, frequency patterns in, 394 notched, in Angelman syndrome, 425f–426f, 645 polymorphic (See Polymorphic delta activity (PDA)) posterior or posteriorly accentuated diffuse, 336f, 392 Delta brushes, 201, 208f–211f, 216f, 217f in 28-week-old with apnea, 208f excessive, 212f with markedly excessive discontinuity, gross interhemispheric asynchrony, and extremely low voltage, 211f with monorhythmic occipital delta activity, 217f and extremely low-voltage background activity, 209f, 216f occipital predominance in, 210f overview of, 208f with temporal theta bursts, 220f Delta coma, 394, 433f, 471, 476f–479f, 505f from anoxic encephalopathy, 390 from hypoxic encephalopathy, 505f from hypoxic-ischemic encephalopathy with near drowning, 433f Delta rhythm, diffuse during absence seizure, 634f with fronto-central and vertex predominance, in Rett syndrome, 413f Delta slowing with focal cortical dysplasia, right mesial temporal, 322f intermittent right occipital, 21f lateralized, with background suppression in postictal state, 354f Delta slowing, continuous FIRDA and polymorphic delta activity with diffuse alpha activity in, from POLG1 mutation, 449f 14- and 6-Hz positive spikes in, 394, 439f–443f bursts and arch-shaped waves in, 439f with diffuse encephalopathy and Lennox-Gastaut syndrome, 442f and refractory status epilepticus, 440f–441f
in encephalopathies of childhood, 440f, 442f, 443f in encephalopathy with sepsis and stroke, 443f in Reye syndrome, 394, 440f, 442 in severely diffuse encephalopathy, 519f Delta slowing, diffuse generalized epileptiform discharges in MERRF with, 616, 657f with occipital prominence, from left cerebral hemiatrophy due to intraventricular hemorrhage, 365f Depressed brain, seizures of, 203, 253f, 254f Depression and lack of differentiation EEG, 474, 517f in newborn, 204, 265f very low-voltage background activity and hypoxic ischemic encephalopathy in, 517f Dialysis, chronic, occipital intermittent rhythmic delta activity with, 418f Dialysis encephalopathy EEG in, 428f triphasic waves in, 428f, 524f Diffuse axonal injury (DAI) from head injury, asynchronous burst suppression in, 457f and vasogenic edema in corpus callosum, background asynchrony in, 454f Diffuse continuous slow activity. See Slow activity, diffuse continuous Discontinuity, markedly excessive, with gross interhemispheric asynchrony and extremely low-voltage, 211f Double cortex syndrome, 616, 650f Dravet syndrome, 535, 596f–600f complex partial seizures in, 597f–598f EEG in, 595 nonconvulsive status epilepticus in, 595, 600f seizures in, 595 typical absence seizure in, 599f Drop attacks in benign myoclonic epilepsy of infancy, 638f differential diagnosis of, 616 in Lennox-Gastaut syndrome, 533–534 in myoclonic-astatic seizure, 641f, 643f Drowsiness 14- and 6-Hz positive bursts in, 46f
in older children and adults, 45f slow eye movement in, 130f Dyke-Davidoff-Mason syndrome alpha defects in, 275, 287f with alpha asymmetry, 275, 287f wih Bancaud phenomenon, 275, 289f left frontal spikes in, 731f Dysrhythmia, anterior slow, 406f–407f with frontal sharp transients, 228f, 231f, 232f in newborn, 202, 231f–233f
E Early myoclonic encephalopathy (EME), 204, 263f, 529, 536f erratic myoclonus in, 179f with Ohtara syndrome, 529, 536f–541f pyridoxine dependency in, 263f, 529, 539f–541f EEG generator, cortical, in beta attenuation, 275–276 EEG reactivity, 481f in coma, with diffuse voltage attenuation, 482f paradoxical activation in, 481f EEG variants, benign. See also specific variants not associated with seizures, 677 EKG artifact, 126, 145f–146f Electrical status epilepticus (ESES) during slow sleep, 534–535 in 4-year-old with developmental delay, hand tremor, and medically intractable epilepsy, 601f–602f in 6-year-old with severe intraventricular hemorrhage, 595f in childhood absence epilepsy, with thalamic heterotopia, 636f epileptic focus in, 601f with intrauterine stroke, 603f, 606f with left cerebral hemiatrophy, EKG artifacts with, 146f in NREM sleep, 596f overview of, 596f with refractory status epilepticus, 818f in REM sleep, 601f resolution of, after left functional hemispherectomy, 607f Electrocardiographic artifacts, 126, 145f–149f
ballistocardiographic, 126, 149f EKG, 126, 145f–146f pulse, 126, 147f–148f Electrocerebral inactivity (ECI), 395, 463f, 474 artifact in, 518f definition of, 480f high-frequency ventilator artifact with, 190f, 266f in newborn, 204, 266f–268f pulse artifact in, 139f, 147f, 480f severe anoxic encephalopathy with, 463f severe hypoxic encephalopathy with, 466f severe hypoxic ischemic encephalopathy with, 267f, 268f and central herniation syndrome, 138f, 518f Electrocerebral silence (ECS), from anoxic encephalopathy, 390 Electrocorticography (ECoG), 848f Electrode (pop) artifact, 128, 192f, 197f, 198f Electrographic seizure, 247f patting artifact vs., 155f, 157f, 162f Electromyographic artifacts, 126–127, 143f–144f, 150f, 187f chewing, 126, 187f lateral rectus spike, 126, 143f, 144f Electroretinogram (ERG) artifact, 125, 135f, 414f Embolic stroke, asymmetric spindle coma during midazolam infusion in, 510f Encephalitis. See also specific types Acanthamoeba, 450f Balamuthia mandrillaris, 450f generalized nonepileptiform activity in, 389, 390 Naegleria fowleri, 450f viral, beta suppression and PDA in right mesial temporal sclerosis from, 363f western equine, occipital lobe epilepsy with, 823f Encephalitis, herpes simplex asymmetric hypsarrhythmia in, 561f–562f EEG normalization after hemispherectomy in, 563f bilateral independent lateralized epileptiform discharges in, 390 earlier stages of, 361f lateralized monorhythmic/polymorphic delta in, 361f rhythmic sharply contoured theta in, 826f simple partial seizure in, 824f
867
Encephalitis, mycoplasma, with reversible focal lesion in corpus callosum and extreme spindles, 448f Encephalitis, Rasmussen’s, 689, 710f–712f epilepsia partialis continua in, 689, 710f–711f periodic lateralized epileptiform discharges in, 712f Encephalomalacia cystic, from intrauterine stroke, asymmetric hypsarrhythmia in, 544f diffuse left hemispheric, hemispheric background depression in, 347f from earlier cerebral contusion, late post-traumatic epilepsy with, 316f from meningitis meningococcal, hearing-induce seizure in, 821f neonatal bacterial, focal voltage attenuation in, 349f viral, simple partial seizure in, 816f severe photosensitive myoclonic seizure in, 808f right hemispheric, unilateral background attenuation and low-voltage PDA in, 364f from severe intraventricular hemorrhage, anterior beta enhancement in, 804f Encephalomyelitis, acute disseminated, polymorphic delta activity slowing in, 333f Encephalopathy. See also specific types acute viral extreme sleep spindles in, 445f–446f occipital intermittent rhythmic delta activity in, 423f background slow activity in, 391 chronic, excessive beta activity in, 390, 397f diffuse anterior dysrhythmia in, excessive, 406f–407f background slow activity in, 391 chronic, excessive beta activity in, 390 14- and 6-Hz positive spike in, 94f 14- and 6-Hz positive spikes with continuous delta slowing in, with refractory status epilepticus, 440f–441f from moyamoya disease, occipital intermittent rhythmic delta activity in, 422f hepatic, triphasic waves in, 427f with sepsis and stroke, 14- and 6-Hz positive spikes with continuous delta slowing in, 443f
868
severe, invariant EEG in, 437f, 438f spontaneous variability in, 438f triphasic waves in, 428f Encephalopathy with ESES, 534 Encoches frontales, 202, 226f–230f, 232f. See also Frontal sharp transients (FSTs) Epidermal nevus syndrome (ENS), 830f Epilepsia partialis continua (EPC), 689, 707f–711f focal clonic seizure in ictal EEG during, 709f ictal SPECT during, 708f as focal epilepsy, 689, 707f–711f, 851f hemiconvulsion hemiplegia epilepsy syndrome with, 715f in malformation of cortical development with cerebral atrophy, from congenital CMV, 707f periodic lateralized epileptiform discharges in, from hydrocephalus with intraventricular hemorrhage, 350f POLG1 mutation in, 851f in Rasmussen’s encephalitis, 689, 710f–711f Epilepsy. See also specific types and topics with cerebral malformation, 351f with encephalomalacia from cerebral contusion, late post-traumatic, 316f focal (See Focal epilepsy) generalized (See Generalized epilepsy) with hydrocephalus, 351f with infection, 351f with intraventricular hemorrhage, 351f from left temporo-occipital tumor, asymmetric photic response in, 299f with myelomeningocele, 351f occipital intermittent rhythmic delta activity in, 422f–424f schizencephaly and, 318f Epilepsy with bilateral occipital calcification, 687 Epilepsy with grand mal on awakening (EGMA), 613–614 eye closure sensitivity in, 627f generalized tonic-clonic seizure in, 619f–622f photoparoxysmal response in, 630f Epileptic encephalopathy, 529–607. See also specific disorders
with continuous spikes and waves during slow sleep, 534, 595f, 596f, 601f–607f in Dravet syndrome, 535, 596f–600f with electrical status epilepticus during slow sleep, 534–535, 595f, 596f, 601f–607f with generalized clonic seizure, 658f in Landau-Kleffner syndrome, 535, 604f–605f in Lennox-Gastaut syndrome, 531–534, 575f–594f with severe neonatal epilepsy with suppression-burst pattern, 529, 536f–541f in West syndrome, 529–531, 542f–574f Epileptic spasms subdural vs. scalp EEG in, 573f symptomatic late onset, with hypsarrhythmia with increased interhemispheric synchronization, 546f triggers for, in West syndrome, 559f Epileptic spasms, asymmetric after right hemispherectomy, 564f in Aicardi syndrome with focal cortical dysplasia, 385f correlations of, 556f with focal cortical dysplasia, 550f from cobalamin C deficiency, 556f–559f left mesial fronto-parietal, 338f left mesial fronto-parietal, in West syndrome, 553f with high-frequency oscillations, subdural EEG in, 552f high-voltage, frontal-dominant generalized slow wave transient in West syndrome with, 551f supplementary sensorimotor area activation in, 574f, 776f Epileptiform discharges, interictal, 601f Epileptogenicity, intrinsic. See Intrinsic epileptogenicity Epileptogenic zone resection, presurgical evaluation for, after extraoperative subdural EEG, 831f Extraoperative subdural EEG, of epileptogenic zone, 831f Extrapontine myelinosis (EPM), 452f Extremely low-voltage background activity with markedly excessive discontinuity and gross interhemispheric asynchrony, 211f with monorhythmic occipital delta activity and delta brushes, 209f, 216f Eye blink artifact, 126, 136f–138f
Eye closure sensitivity (ECS), 613, 626f, 627f Eyelid flutter artifact, 126, 139f–142f Eyelid myoclonia, with childhood absence epilepsy, 637f Eye movement artifacts, 125–126, 129f–142f vs. brain waves, 136f electroretinogram, 125, 135f eye blink, 126, 136f–138f eyelid flutter, 126, 139f–142f vs. frontal sharp transients, 230f horizontal nystagmus, 125, 131f–134f in newborn, 230f photomyoclonic response, 126, 139f, 142f rapid eye movement, 125, 129f slow or roving eye movement, 125, 130f Eye movements, 125–126
F Falsely localizing temporal interictal epileptiform discharges, 677 Familial hemiplegic migraine, focal polymorphic delta activity in, 339f, 340f Fast alpha variant, 2, 15f–17f Fast paroxysmal rhythms. See Paroxysmal fast activity (PFA) Fast ripples, 552f Febrile convulsion, acute, MRI of, 329f Fifth day fits, with théta pointe alternant, 262f Focal clonic seizure in early myoclonic encephalopathy from pyridoxine dependency, 540f with focal cortical dysplasia, 732f left-sided, from right middle cerebral artery infarction, 249f with neonatal stroke from systemic infection, 256f in newborn, 203, 248f–250f, 253f, 256f with venous sinus thrombosis, 248f overview of, 248f–249f in schizencephaly with polymicrogyria from HSV encephalitis, 250f from stroke, 256f with zips, 253f Focal cortical dysplasia (FCD), 675 Aicardi syndrome with, 568f asymmetric epileptic spasms in, 385f
alpha asymmetry in, 275, 304f alpha enhancement in, focal, 378f, 379f asymmetric epileptic spasms in, 550f with balloon cells, supplementary sensorimotor area seizure in, 848f focal polymorphic delta activity with focal enhancement of beta activity and focal spikes in, 765f beta activity depression in, 324f beta activity voltage attenuation in, 275 beta attenuation during drowsiness with, 311f–312f beta enhancement in, focal, 378f, 379f with cobalamin C deficiency asymmetric epileptic spasms in, 556f–559f hypsarrhythmia variant in, with consistent focus of abnormal discharge, 556f EEG patterns in, 848f epileptogenicity of, 383f focal clonic seizures in, 732f focal epilepsy simulating myoclonic astatic epilepsy with, 690, 698f, 722f focal epilepsy with, 680 frontal epilepsy with, 735f intrinsic epileptogenicity in, 269f, 680 alpha and beta enhancement in, 383f left fronto-central region, 728f occipital lobe, 743f–749f parietal lobe, 737f left insula epilepsy from, periodic lateralized epileptiform discharges in, 772f left mesial fronto-parietal, 338f with asymmetric epileptic spasms in West syndrome, 553f left occipital, alpha attenuation and PDA in, 291f left occipital and mesial temporal, 751f left parietal, paradoxical lateralization in, 742f left temporal, with epidermal nevus syndrome, 830f left temporo-occipital, photic response attenuation in, 298f in Lennox-Gastaut syndrome, 584f, 586f low-voltage fast activity with, 804f in mesio-temporal lobe epilepsy, 753f, 762f–764f in parietal lobe epilepsy, 685, 737f
from periventricular leukomalacia, PDA and ipsilateral beta activity enhancement in, 382f polymorphic delta activity in, 382f localized, 379f right temporal sharp waves in, 327f resection of, background EEG normalization after, 586f right frontal, extraoperative subdural EEG of, 831f right mesial temporal, delta and theta slowing in, 322f right parietal, ipsilateral beta attenuation and monorhythmic theta activity in, 324f right posterior frontal, right temporal polymorphic delta activity in, 330f scalp EEG in infants with epilepsy from, 827f seizure onset zone in, 269f, 737f subcortical occipital intermittent rhythmic delta activity and polymorphic delta activity in, 366f temporal intermittent rhythmic delta activity in, 366f unilateral attenuation of hypnagogic hypersynchrony in, 314f subtle epileptiform activity in, 729f in supplementary sensorimotor area, 723f–727f bilateral asymmetric tonic seizure from, 727f focal myoclonic seizure from, 725f–726f frontal absence from, 723f–724f in supplementary sensorimotor area, left focal myoclonic seizure from, 725f frontal absence from, 723f–724f ipsilateral alpha attenuation from, 275, 296f symptomatic focal epilepsy from akinetic and extensor epileptic spasms in, 270f focal low-voltage fast activity in, 269f in newborn, 204, 269f–271f Focal epilepsy, 675–852. See also specific types activation methods in, 679 ambulatory EEG of, 679 atypical benign partial epilepsy, 690, 698f autism and, 691 benign epilepsy with centro-temporal spikes, 684, 690–691, 704f–706f benign familial neonatal convulsion, 261f, 689, 692f benign infantile seizure, 690, 694f–697f
869
Focal epilepsy (continued) benign neonatal nonfamilial convulsion, 262f, 690 bilateral synchrony, secondary, 678, 716f, 773f central midtemporal spikes in, 684 ictal discharges, 684 interictal discharges, 684 centro-parietal spikes in, 685 of childhood, 685 in other conditions, 685 in parietal lobe epilepsy, 685, 737f–739f distribution of EEG in, 677 electrodes for, additional, 679, 759f epilepsia partialis continua (EPC), 689, 707f–711f, 851f focal cortical dysplasia in, 680 focal clonic seizures in, 732f vs. myoclonic astatic epilepsy, 690, 698f, 722f frontal epileptiform patterns in, 681–684 focal myoclonic seizure, 725f–726f frontal absence, 682, 723f–724f ictal, 683–684 interictal, 682–683 hemimegalencephaly and, 680–681, 809f–812f, 841f–843f HHE syndrome (hemiconvulsions, hemiplegia, epilepsy), 691, 713f–715f high-frequency oscillations in, 675, 678, 828f, 846f ictal EEG pattern in, 677–678 ictal slow DC shift in, 678–679, 766f, 800f, 846f insular epilepsy, 689, 775f interictal EEG patterns in, types of, 675–676 interictal epileptiform discharges, 601f, 675, 676 common types of, 675 definitions of, 675 falsely localizing temporal, 677 features of, 675 frequency of, 676 importance of, 676 partial vs. generalized, 676 in periventricular nodular heterotopia, 681 pitfalls in identification of, 677 left frontal spikes in, with Dyke-Davidoff-Mason syndrome, 731f magnetoencephalogram (MEG) of, 679–680 midline spikes in, 685–686, 781f, 789f, 791f
870
epidemiology and etiology of, 685 ictal patterns of, 686 waveforms of epileptiform charges in, 685–686 occipital spikes in, 686–688 epilepsy with bilateral occipital calcification, 687 idiopathic childhood occipital epilepsy of Gastaut, 686–687 late infantile neuronal ceroid lipofuscinosis, 687 needle-like spikes of the blind, 4, 42f–44f, 686 Panayiotopoulos syndrome, 687, 701f–703f, 745f Sturge-Weber syndrome, 687 symptomatic occipital epilepsy, 687–688, 744f–745f, 823f, 852f periodic lateralized epileptiform discharges in, 675, 677, 772f, 803f periventricular nodular heterotopia and, 681, 834f–840f, 849f polymorphic delta activity in, continuous, 676–677, 750f poor prognosis in children with, EEG criteria for, 680 positive sharp waves in, 677 positive spikes in, with focal transmantle dysplasia, 730f pseudo-Lennox syndrome, 690, 698f scalp EEG limitations and, 677 start-stop-start phenomenon in, 678, 828f, 844f–845f symptomatic from congenital hydrocephalus with ventriculoperitoneal shunt, 275, 290f from hydranencephaly, 348f temporal intermittent rhythmic delta activity in, 5, 675, 757f temporal spikes in, 688–689 Focal myoclonic seizure with focal cortical dysplasia in left supplementary sensorimotor area, 725f–726f in Lennox-Gastaut syndrome, 700f Focal negative sharp waves, in newborn, 203, 248f–250f Focal nonepileptiform activity. See Nonepileptiform activity, focal Focal transmantle dysplasia, 321f, 381f, 778f, 803f ictal activity in scalp vs. subdural EEG in, 827f low-voltage fast activity in with focal beta activity enhancement, 381f with slow DC shift, 567f
malignant Rolandic epilepsy with, 783f periodic lateralized epileptiform discharges in, 803f right frontal, positive spikes in, 730f in supplementary sensorimotor area seizure, 731f, 777f–779f Fosphenytoin infusion, beta coma and, 512f 14- and 6-Hz positive spikes, 6, 90f–99f, 439f–443f, 519f in 12-year-old, 96f in 12-year-old with Lennox-Gastaut syndrome, 94f 13 Hz positive spike predominance in, 91f anterior-posterior bipolar, 92f contralateral ear reference with, 93f, 95f in diffuse encephalopathy, 94f diffuse, with right hemispheric predominance, 96f in encephalopathy, 439f–443f, 474, 519f overview of, 90f with polyspike-wave-like discharge, 97f in right neocortical temporal lobe epilepsy, 99f with sleep spindles, 98f subdural EEG monitoring of, 99f 14- and 6-Hz positive spikes, with continuous delta slowing, 394, 439f–443f bursts and arch-shaped waves in, 439f with diffuse encephalopathy and Lennox-Gastaut syndrome, 442f and refractory status epilepticus, 440f–441f in encephalopathies of childhood, 440f, 442f, 443f in encephalopathy with sepsis and stroke, 443f in Reye syndrome, 394, 440f, 442 in severely diffuse encephalopathy, 519f Frontal absence, 682, 723f–724f, 778f, 832f focal transmantle dysplasia with focal transmantle dysplasia in, 778f with supplementary sensorimotor area seizure and focal transmantle dysplasia, 778f Frontal arousal rhythm (FAR), 5, 79f–83f, 805f in 6-year-old, with frontal lobe epilepsy, 83f in 8-year-old, with GTCS history, 81f in 8-year-old, with idiopathic generalized epilepsy, 80f in 10-year-old, with idiopathic generalized epilepsy, 82f from intrauterine right anterior cerebral artery stroke, 805f overview of, 79f
Frontal epilepsy focal cortical dysplasia in, 735f with focal transmantle dysplasia, 321f, 381f, 803f malignant Rolandic epilepsy in, 783f periodic lateralized epileptiform discharges in, 803f right, positive spikes in, 730f supplementary sensorimotor area seizure in, 731f, 778f, 779f interictal psychosis in, 733f–734f, 768f nocturnal hypermotor seizures in, 734f Frontal epileptiform patterns, 681–684 epidemiology of, 681–682 focal myoclonic seizure with focal cortical dysplasia in left SSMA in, 725f–726f frontal absence in, 682, 723f–724f ictal, 683–684 interictal, 682–683 localization difficulties with, 682 scalp EEG limitations and, 682 Frontal infarction, 675 bilateral FIRDA and continuous polymorphic delta with, 434f paradoxical activation in, 438f Frontal intermittent rhythmic delta activity (FIRDA), 391. See also Intermittent rhythmic delta activity (IRDA) asymmetric in intrauterine stroke, 369f in periventricular nodular heterotopia, 838f clinical correlates of, 434f and continuous polymorphic delta, 278, 432f, 434f in cerebral herniation syndrome, 478f–479f with diffuse alpha activity and POLG1 mutation, 449f with frontal, basal ganglion and cerebellar infarctions, 434f with HHE syndrome and impending cerebral herniation, 432f with massive brain edema and central herniation syndrome, 435f–436f focal, 278–279 with HIV meningoencephalitis, 419f improvement of, after resection of left hemisphere necrotic tissue, 479f
with migraine, 416f, 417f with occipital intermittent rhythmic delta activity, 471 postictal state, 421f Frontal lobe epilepsy/seizures incidence of, 681 localization of, difficulty with, 681 manifestations of, 813f secondarily generalized discharges in, 723f Frontal lobe, scalp EEG limitations in, 681, 735f Frontal sharp transients (FSTs), 202, 226f–232f in 31-week CA infant, 229f in 39-week infant with apnea, 226f anterior slow dysrhythmia with, 228f, 231f, 232f overview of, 226f, 227f, 229f pathologic, 226f, 227f temporal sharp waves in, 226f Frontal sharp waves, in 2-day-old FT infant with intraventricular hemorrhage, 233f Frontal-temporal infarction, left, wicket-wave like waveform in, 108f Fronto-temporal stroke, remote right, 6-Hz spike-andwave bursts in, 736f
G Galvanic skin response artifacts, 127, 153f salt bridge, 127, 153f sweat (perspiration), 127 Ganglioglioma left temporal, temporal lobe epilepsy from, 754f temporal intermittent rhythmic delta activity with, 371f left anterio-mesial temporal, polymorphic delta activity with, 755f resection for, breach rhythm and prominent mu rhythm after, 374f–375f right occipital, temporal intermittent rhythmic delta activity in, 372f right precuneus, focal spike-wave discharges and temporal intermittent rhythmic delta activity in, 368f Gelastic seizures, 716f Generalized clonic seizure, 658f Generalized epilepsy, 613–672
Angelman syndrome, 615–616, 645f–647f antiepileptic drug–induced seizure worsening in, 613, 618f atypical MERRF, 616, 657f B6 (pyridoxine) therapy, 616, 660f benign myoclonic epilepsy of infancy, 615, 638f, 639f bilateral synchronous, high-voltage occipital spikes on low-frequency photic stimulation, 616, 661f–662f breath holding spells, 617, 667f cardiac asystole, from anoxic encephalopathy S/P cardiac arrest from severe traumatic brain injury, 670f–672f cardiac output, decreased, from obstruction to flow, 617, 669f cardiac syncope, 617, 668f–669f from decreased cardiac output, 617, 669f vs. neurocardiogenic syncope, 617, 669f childhood absence epilepsy, 614–615, 632f–637f drop attacks in benign myoclonic epilepsy of infancy, 638f differential diagnosis of, 616 in myoclonic-astatic seizure, 641f, 643f epilepsy with grand mal on awakening, 613–614, 619f–622f, 626f, 630f epileptic encephalopathy, with generalized clonic seizure, 658f eye closure sensitivity in, 613, 626f, 627f H-response in, migraine and, 616–617, 665f, 666f idiopathic frontal arousal rhythm in, 80f, 82f occipital intermittent rhythmic delta activity in, 424f photomyogenic (photomyoclonic) response in, 110f, 113f juvenile myoclonic epilepsy, 614, 626f, 628f, 629f, 631f lissencephaly, 616, 656f myoclonic astatic epilepsy, 615, 640f–644f vs. focal epilepsy, 690, 698f, 722f myoclonic astatic seizure with atonia, 641f myoclonic seizure, 642f neuronal ceroid lipofuscinosis, 616, 661f, 662f diffuse bisynchronous epileptiform paroxysms in, 663f drop attack and cataplexy in, 664f
871
Generalized epilepsy (continued) occipital spikes evoked by low-frequency photic stimulation in, 661f, 662f occipital intermittent rhythmic delta activity in, 613, 623f, 624f, 633f, 635f paroxysmal fast activity in, 659f generalized, 613, 625f with generalized clonic seizures, 659f prolonged QT syndrome, 617, 667f, 669f REM stage drop attack with cataplexy and, 664f in healthy children, 616, 664f on juvenile absence epilepsy, 613, 626f Rett syndrome, 616, 648f, 649f subcortical band heterotopia, 616, 650f Generalized nonepileptiform activity. See Nonepileptiform activity, generalized Generalized paroxysmal fast activity (GPFA). See Paroxysmal fast activity (PFA) Generalized periodic epileptiform discharges (GPEDs), 393, 462f, 471, 472–473, 494f–496f in anoxic encephalopathy, 462f asymmetrical, 496f overview of, 494f in refractory nonconvulsive status epilepticus, with diffuse cortical atrophy and hippocampal sclerosis, 523f in refractory status epilepticus, 495f in status post cardiopulmonary resuscitation, 494f Generalized spike-waves (GSW), in focal epilepsy, 678 Generalized tonic-clonic seizure (GTCS), 619f–621f subdural EEG of tonic phase of, 622f Generalized tonic seizures ictal EEG in, 776f in Lennox-Gastaut syndrome, 533, 578f, 581f, 583f Genetic leukodystrophies (GLs), 337f, 431f. See also specific types Glossokinetic artifact, 127, 151f, 152f, 404f Grand mal discharges. See Paroxysmal fast activity (PFA) Grand mal on awakening, 627f. See also Epilepsy with grand mal on awakening (EGMA) Gray matter heterotopia, 636f Ground electrode misplacement artifact, 196f Ground lead artifact, 128, 194f–196f
872
H Hand-foot-mouth syndrome, occipital intermittent rhythmic delta activity in encephalopathy from, 423f Hanging, theta coma with anoxic encephalopathy from, 508f Headache, migraine. See Migraine Head movement artifact, 127, 176f–177f Head trauma. See also Traumatic brain injury (TBI) focal cortical dysplasia seizures from, 327f Hearing-induce seizure, with encephalomalacia from meningococcal meningitis, 820f Hematoma, bilateral subdural, bilateral independent lateralized epileptiform discharges in, 490f Hemiconvulsion hemiplegia epilepsy syndrome (HHE), 472, 492f–493f, 691 in 3-year-old with high fever, left hemiclonic seizure and epilepsy, 713f–714f continuous polymorphic delta activity and FIRDA in, 432f epilepsia partialis continua with, 715f focal epilepsy in, 691, 713f–715f ictal EEG in, 493f refractory nonconvulsive status epilepticus with, 492f spike-wave complexes in, 493f Hemifacial spasm, artifactual spikes from, 126, 150f Hemihypsarrhythmia. See Hypsarrhythmia, asymmetric Hemimegalencephaly, 538f “alpha-like” activity in, 681, 841f, 843f asymmetric suppression-burst pattern with and bursts of “alpha-like” activity, 681, 841f, 842f in right hemimegalencephaly, 811f EEG abnormalities in, 841f focal epilepsy and, 680–681, 809f–812f, 841f–843f hypomelanosis of Ito with, recurrent insula seizures after functional hemispherectomy for, 774f with linear sebaceous nevus syndrome asymmetric infantile spasms in, 810f epileptic nystagmus and asymmetric epileptic spasms in, 809f triphasic complexes in, 809f, 841f Ohtahara syndrome and suppression-burst pattern with, 538f rhythmic alpha-like activity with, 812f, 841f
triphasic complexes of very large amplitude with, 681, 809f Hemiplegic migraine EEG in, 339f, 340f familial, focal polymorphic delta activity in, 339f, 340f lateralized background suppression in, 343f lateralized polymorphic delta activity in, 344f nonfamilial, intermittent focal polymorphic delta activity in, 339f periodic lateralized epileptiform discharges in, 342f with polymorphic delta activity, 332f Hemispherectomy EEG normalization after, with asymmetric hypsarrhythmia in herpes simplex encephalitis, 563f for electrical status epilepticus during slow sleep, 535, 607f functional neuroimages before, 570f recurrent insula seizures after, with hypomelanosis of Ito with hemimegalencephaly, 774f on seizures, 774f left functional for asymmetric infantile spasms, contralateral EEG normalization after, 571f on electrical status epilepticus during slow sleep, 607f volume conduction in, 346f right, asymmetric epileptic spasms after, 564f right functional, for Lennox-Gastaut syndrome, 594f Hemispheric background depression, from diffuse left hemispheric encephalomalacia, 347f Hemorrhagic infarction, alpha symmetry with decreased photic response in, 301f Hemorrhagic stroke, from streptococcal infection, alpha asymmetric reactivity in, 275, 293f Hepatic encephalopathy, triphasic waves in, 427f Herniation syndrome. See also Central herniation syndrome asymmetric spindle coma in, with acute amoebic meningoencephalitis, 450f, 511f central electrocerebral inactivity from hypoxic ischemic encephalopathy in, 138f, 518f
FIRDA and continuous PDA with massive brain edema in, 435f–436f cerebral, FIRDA and continuous PDA in, 478f–479f severe HIE and, seizures of depressed brain in, 254f Herpes simplex encephalitis bilateral independent lateralized epileptiform discharges in, 390, 487f generalized nonepileptiform activity in, 390 hypsarrhythmias from, asymmetric, 561f–564f after hemispherectomy, asymmetric epileptic spasms in, 564f after hemispherectomy, EEG normalization in, 563f baseline EEG in, 561f unilateral paroxysmal fast activity and infantile spasms in, 562f rhythmic sharply contoured theta in, 826f schizencephaly with polymicrogyria from, focal clonic seizures in, 250f simple partial seizures in, 824f HHE syndrome (hemiconvulsions, hemiplegia, epilepsy). See Hemiconvulsion hemiplegia epilepsy syndrome (HHE) Hiccup artifacts, 127, 163f–168f in 8-week-old with recurrent cyanotic episodes, 166f from epidural bupivacaine, 163f vs. epileptiform discharge, 167f movement artifacts in, 164f variable effects of, 168f High-amplitude rhythmic activity (HARA), in lissencephaly type 1, 402f High-frequency oscillations (HFOs), 552f, 573f asymmetric epileptic spasms with, subdural EEG in, 552f in focal epilepsy, 675, 678, 828f, 846f slow DC shifts or infraslow activity in, 846f start-stop-start phenomenon in, 678, 828f High-frequency (jet) respirator artifact, 128, 191f, 465f High-frequency ventilator artifact, 128, 190f, 266f High-voltage, frontal-dominant generalized slow wave transient, with asymmetric epileptic spasms, 551f
High-voltage, frontal-dominant polymorphic delta activity, with generalized slow wave transient symptomatic West syndrome and asymmetric epileptic spasm, 338f High-voltage occipital spikes, bilateral synchronous, on low-frequency photic stimulation, 616, 661f–662f High-voltage sharp- and slow-wave complexes, in lissencephaly, type 1, 654f Hippocampal anomalies, in Lennox-Gastaut syndrome, 591f Hippocampal atrophy, bisynchronous temporal discharges with, in nonconvulsive status epilepticus, 522f Hippocampal sclerosis with diffuse cortical atrophy, generalized periodic epileptiform discharges in refractory nonconvulsive status epilepticus in, 523f mesio-temporal lobe epilepsy with, 753f right, temporal lobe epilepsy with, 844f–845f temporal intermittent rhythmic delta activity in, 372f Hippocampus large volume, prolonged complex febrile convulsion with, 328f right, focal cortical dysplasia of, in mesio-temporal lobe epilepsy, 763f–764f HIV infection, with toxoplasmosis, polymorphic delta activity in, 334f HIV meningoencephalitis frontal intermittent rhythmic delta activity in, 419f occipital intermittent rhythmic delta activity in, 420f Holoprosencephalopathy, focal polymorphic delta activity in, 278 Holoprosencephaly, nystagmus artifact with, 131f Horizontal nystagmus artifact, 125, 131f–134f H-response, 4, 39f–41f, 665f, 666f migraine and, 39f, 40f, 405f, 616–617, 665f migraine with cyclic vomiting and, 41f migraine with excessive periventricular space and, 666f Human immunodeficiency virus. See HIV infection Hydranencephaly, 348f focal and frontal epilepsy with, 348f Hydrocephalus
congenital, with ventriculoperitoneal shunt frontal epilepsy with, 275, 290f symptomatic focal epilepsy with, 275, 290f epilepsy with, 351f from intraventricular hemorrhage, periodic lateralized epileptiform discharges in epilepsia partialis continua with, 350f remote stroke with, in Lennox-Gastaut syndrome, 699f with ventriculoperitoneal shunt infection, periodic lateralized epileptiform discharges in, 351f Hyperglycinemia, nonketotic, burst-suppression pattern in, 456f Hyperpolarization, cortical neuron, 395 Hyperthyroidism, excessive beta activity with, 397f Hyperventilation increased interictal epileptiform discharges with, 679 occipital intermittent rhythmic delta activity with, 415f Hyperventilation effect, from sobbing, background slow activity in, 408f, 415f Hypnagogic hypersynchrony, 5, 70f–73f in 4-year-old, 73f in 22-month-old, 71f asymmetric, at 25 months, 72f with focal cortical dysplasia subcortical, unilateral attenuation of, 314f suppression of, during drowsiness, 311f–313f overview of, 70f Hypnagogic jerks, 5, 74f–77f. See also Hypnic myoclonia (HM) Hypnic myoclonia (HM), 5, 74f–77f in 5-year-old, 74f, 77f asymptomatic centro-temporal spikes in, 76f 14- and 6-Hz positive spikes in, 75f Hypomelanosis of Ito, with hemimegalencephaly and recurrent insula seizures after functional hemispherectomy, 774f Hypoxic encephalopathy (HE), 472, 480f, 491f alpha-theta coma in, 504f beta coma in, 506f delta coma in, 505f during midazolam infusion, alpha coma in, 500f paradoxical activation in, 437f
873
Hypoxic encephalopathy (HE) (continued) poor outcome in, 491f severe electrocerebral inactivity with, 466f with myoclonic jerks and spontaneous movement, burst-suppression pattern in, 515f Hypoxic-ischemic encephalopathy (HIE) delta brushes with monorhythmic occipital delta activity in, 210f electrocerebral inactivity from with central herniation syndrome, 138f with high-frequency ventilator artifact, 190f, 266f moderate, burst-suppression with diffuse rhythmic alpha activity in newborn with, 238f, 239f from near drowning, delta coma in, 433f severe burst-suppression pattern in, 237f from central herniation syndrome, electrocerebral inactivity in, 518f diffuse cerebral atrophy from, West syndrome in, 542f electrocerebral inactivity in, 267f, 268f and herniation syndrome, seizures of depressed brain in, 254f monorhythmic occipital delta activity and delta brushes with extremely low-voltage background activity in, 209f sharp theta on occipitals of prematures with, 214f tracé discontinu with, 205f, 207f zips with, 251f sucking artifact in 5-day-old with, 172f–173f very low-voltage background activity in, 265f burst-suppression pattern in, 517f Hypsarrhythmia, 675 with consistent focus of abnormal discharge, 556f definition of, 530 with increased interhemispheric synchronization, and symptomatic late onset epileptic spasms, 546f infantile spasms from periventricular leukomalacia with, 543f in lissencephaly type 1, 401f, 402f in nonketotic hyperglycinemia, burst-suppression pattern in, 456f
874
vs. suppression-burst pattern, 529 unilateral (See Hypsarrhythmia, asymmetric) variants of, 530, 542f Hypsarrhythmia, asymmetric, 560f, 675 with asymmetric infantile spasms, 545f and consistent focus of abnormal discharge, 548f with increased interhemispheric synchronization, 547f contralateral, 569f with cystic encephalomalacia from intrauterine stroke, 544f from herpes simplex encephalitis, 561f–564f after hemispherectomy, asymmetric epileptic spasms in, 564f after hemispherectomy, EEG normalization in, 563f baseline EEG in, 561f unilateral paroxysmal fact activity and infantile spasms in, 562f Hypsarrhythmia variant, consistent focus of abnormal discharge in, with focal cortical dysplasia from cobalamin C deficiency, 557f
I Ictal aphasia, in intracranial hemorrhage from malignant hypertension, 370f Ictal/continuous epileptogenic discharges (I/CEDs), 680 Ictal EEG asymmetric, 551f in focal epilepsy, 677–678 in periventricular-intraventricular hemorrhage, 255f types of, 551f Ictal slow DC shift. See Slow DC shift, ictal ICU, 471–524. See also specific topics alpha coma in, 473–474 bilateral independent lateralized epileptiform discharges in, 472, 487f–491f burst-suppression in, 474, 513f–516f Creutzfeldt-Jakob disease in, 473, 498f diffuse polymorphic delta slowing in, 471, 476f–479f, 505f EEG depression and lack of differentiation in, 474, 517f EEG reactivity in, 471, 481f, 482f
electrocerebral inactivity in, 474, 480f, 518f encephalopathy in, 471 14- and 6-Hz positive spikes in encephalopathy in, 439f–443f, 474, 519f generalized periodic epileptiform discharges in, 472–473, 494f–496f hemiconvulsion hemiplegia epilepsy syndrome in, 472, 492f–493f hypoxic encephalopathy in, 472, 480f, 491f periodic epileptiform discharges in midline in, 472, 485f, 486f periodic lateralized epileptiform discharges in, 471–472, 483f, 484f refractory status epilepticus in, 474–475, 520f–523f rhythmic coma in, 473, 500f–512f stimulus-induced rhythmic, periodic, or ictal discharges in, 473, 497f subacute sclerosing panencephalitis in, 473, 499f triphasic waves in, 475, 524f Idiopathic childhood occipital epilepsy of Gastaut, 686–687 Ifosfamide generalized nonepileptiform activity from, 389 nonconvulsive status epilepticus from, triphasic waves in, 429f Independent temporal alphoid rhythm, 7, 107f Infantile seizure, benign, 690 Infantile spasms (IS) asymmetric, 568f with diffuse electrodecremental pattern and lowvoltage fast activity, 555f incidence of, 542f infections in, 561f with unilateral paroxysmal fast activity, 562f in West syndrome, 542f, 543f Infantile spasms (IS), asymmetric asymmetric hypsarrhythmia with, 545f and consistent focus of abnormal discharge, 548f and increased interhemispheric synchronization, 547f with diffuse electrodecrement and focal onset, 549f hemispherectomy for, contralateral EEG normalization after, 571f
incidence of, 545f in linear sebaceous nevus syndrome with hemimegalencephaly, 810f Infarction, hemorrhagic, alpha symmetry with decreased photic response in, 301f Infection. See also specific types congenital, vertex sharp wave and spindle suppression with, 305f epilepsy with, 351f Infraslow activity (ISA), with high-frequency oscillations, 846f Insula, in nocturnal hypermotor seizures, 315f Insular seizures/epilepsy, 689 after functional hemispherectomy, for hypomelanosis of Ito with hemimegalencephaly, 774f intrinsic epileptogenicity in, 775f with nocturnal hypermotor seizures, 315f Interhemispheric asynchrony, gross, in newborn with severe hypoxic ischmic encephalopathy, 211f Interhemispheric hypersynchrony, 206f Interhemispheric synchronization, increased hypsarrhythmia with, 546f–547f in West syndrome, 530–531 Interictal EEG patterns, 675–676. See also specific patterns and disorders Interictal epileptiform discharges (IEDs), 601f, 675, 676 activation methods for, 679 ambulatory EEG of, 679 common types of, 675 definitions of, 675 electrodes for, additional, 679 epilepsy and, 675 falsely localizing temporal, 677 features of, 675 focal, 676 frequency of, 676 generalized, 676 importance of, 676 magnetoencephalogram of, 679–680 in mesial temporal sclerosis, 752f, 753f in mesio-temporal lobe epilepsy, 753f, 758f, 763f partial vs. generalized, 676
in periventricular nodular heterotopia, 681 pitfalls in identification of, 677 Interictal psychosis, 733f frontal epilepsy in, 733f–734f, 768f orbitofrontal lobe epilepsy in, 768f prevalence of, 733f, 768f temporal lobe epilepsy in, 768f Intermittent rhythmic delta activity (IRDA). See also specific types clinical correlates of, 434f focal or lateralized, 278, 366f–373f focal spike-wave discharges and, with right precuneus ganglioma, 368f generation of, 366f lateralization of, 366f, 369f occipital, 391 chronic renal failure with chronic dialysis, 418f in hyperventilation, 415f persistent unilateral, 366f Intermittent rhythmic delta activity (IRDA), diffuse, 391, 416f–424f activation of, 391 age of, 391 clinical correlations of, 391, 418f definition, pathogenesis, and pathophysiology of, 391, 418f etiology of, 391 frontal HIV meningoencephalitis, 419f migraine, 416f migraine, confusional, 417f postictal state, 421f ipsilateral, 391 occipital acute viral encephalopathy, 423f chronic renal failure with chronic dialysis, 418f diffuse encephalopathy from moyamoya disease, 422f HIV meningoencephalitis, 420f idiopathic generalized epilepsy, 424f Intermittent right occipital delta slowing, 21f Intracerebral hemorrhage, from venous sinus thrombosis, positive temporal sharp waves in, 240f
Intracranial EEG, pathologic vs. physiologic waves in, 54f Intracranial hemorrhage (ICH), from malignant hypertension, ictal aphasia in, 370f Intrauterine stroke. See Stroke, intrauterine Intraventricular hemorrhage (IVH) from CMV and cardiomyopathy, frontal sharp waves in, 233f epilepsy with, 351f hydrocephalus from, periodic lateralized epileptiform discharges in epilepsia partialis continua from, 350f with left cerebral hemiatrophy asymmetric hypsarrhythmia in, 560f diffuse delta slowing with occipital prominence in, 336f, 365f positive temporal and Rolandic sharp waves in, 242f, 243f severe anterior beta enhancement from encephalomalacia with, 804f electrical status epilepticus during slow sleep in, 595f Intrinsic epileptogenicity alpha and beta enhancement in, 383f in focal cortical dysplasia, 269f, 680 left fronto-central, 728f occipital lobe, 743f–749f parietal lobe, 737f in insular epilepsy, 315f, 689, 775f in malformation of cortical development, left hemisphere, 572f in periventricular nodular heterotopia, 572f Invariant EEG, 389, 471, 481f, 482f in severe encephalopathy, 437f, 438f Ischemia. See also Hypoxic-ischemic encephalopathy (HIE) anoxic, generalized nonepileptiform activity in, 389 Ischemic stroke from cardiac transplantation, periodic lateralized epileptiform discharges in, 483f generalized nonepileptiform activity in, 389
875
J Jeavons syndrome, 637f Juvenile myoclonic epilepsy (JME), 614 eye closure sensitivity in, 626f inattention during bursts in, 628f myoclonic seizures in, 629f paroxysmal fast activity in, 580f photoparoxysmal response in, 631f
K K complexes, 4, 52f–55f during arousal, subdural EEG monitoring of, 53f early (16 week CA), 55f Kernohan phenomenon, 450f
L Lambda waves, 3, 24f–26f and alpha rhythm, 25f asymmetric breach rhythm of, 376f in normal individuals, 307f postresection of left pariental epileptogenic zone, 275, 307f Lamotrigine, slow background activity and diffuse theta slowing from, 411f Landau-Kleffner syndrome (LKS), 535, 604f–605f during sleep, 604f during wakefulness, 605f Late infantile neuronal ceroid lipofuscinosis, 687 Lateralized electrodecrement, from intrauterine stroke, 353f Lateral rectus spike, 126, 143f, 144f Left cerebral hemiatrophy, electrical status epilepticus during slow sleep in, with EKG artifacts, 146f Left frontal-temporal infarction, wicket-wave like waveform in, 108f Left hemispheric stroke, focal patting artifact with, 161f Left insula epilepsy, from focal cortical dysplasia, periodic lateralized epileptiform discharges in, 772f Lennox-Gastaut syndrome (LGS), 531–534, 575f–594f vs. atypical benign partial epilepsy, 675, 698f bilateral perisylvian polymicrogyria in, 581f–583f in children, 578f
876
criteria for, 531 EEG features of, 581f background activity, 532 generalized tonic seizure, 578f, 581f, 583f paroxysmal fast activity, 532, 576f, 577f, 579f–581f, 588f, 590f slow spike-wave (SSW) pattern in, 532, 575f, 581f, 585f, 587f, 589f epidemiology of, 531 etiology of, 532 focal myoclonic seizure in, 700f 14- and 6-Hz positive spikes in, 94f with continuous delta slowing and diffuse encephalopathy, 442f intrauterine stroke in, slow spike-wave pattern in, 587f paroxysmal fast activity in, 675 remote stroke and hydrocephalus in, 699f seizure types in atypical absence, 533 drop attack, 533–534 overview, 532 status epilepticus, 534 tonic, 533 symptomatic, 584f–585f background EEG normalization in, after focal resection of focal cortical dysplasia and epileptogenic zone, 586f cerebral and cerebellar anomalies in, 591f focal cortical dysplasia in, 584f focal polymorphic delta activity in, with intermixed spikes, 593f generalized slow spike-wave discharges in, 585f hippocampal anomalies in, 591f malformation of cortical development from chromosome 10p 15.3 duplication in, 849f mesial temporal abnormality in, 593f paroxysmal fast activity in, asymmetric, 588f, 592f right functional hemispherectomy in, 594f Leukodystrophies genetic, 337f (See also specific types) metachromatic, 337f, 431f Leukoencephalopathy, posterior reversible, right posterior temporal theta slowing in, 323f
Leukomalacia, periventricular with focal cortical dysplasia, polymorphic delta activity, and ipsilateral beta activity enhancement, 382f West syndrome with, 543f Limb movement artifact, 127, 178f–179f Linear sebaceous nevus syndrome, with hemimegalencephaly asymmetric infantile spasms in, 810f epileptic nystagmus and asymmetric epileptic spasms in, 809f triphasic complexes in, 809f, 841f Lipomas, 832f Lissencephaly-pachygyria, with congenital CMV, excessive beta activity with, 399f Lissencephaly, time of brain injury in, 399f Lissencephaly, type 1 age on EEG in, 402f beta activity in, excessive, with infantile spasm in remission, 403f classical, 401f general EEG characteristics in, 402f generalized fast activity (8-18/sec) in, 656f generalized high-amplitude fast activity in, 651f alpha frequency band, 400f, 651f beta frequency band, 398f, 653f high-voltage fast activity in, alpha band, 402f high-voltage sharp- and slow-wave complexes in, 654f hypsarrhythmia in, 401f, 402f Lissencephaly, type 2, 402f alternating pattern in, 655f Lithium toxicity, generalized nonepileptiform activity in, 389 Low impedance, increased products of, 276 Low-voltage background activity, 18f in Rett syndrome with rhythmic theta, 822f Low-voltage beta activity, excessive, 397f Low-voltage EEG, with bilateral subdural effusion, diffuse background attenuation in, 464f Low-voltage EKG, from scalp edema, 191f Low-voltage fast activity focal cortical dysplasia and, 804f in generalized nonepileptiform activity, 389
in infantile spasms with diffuse electrodecremental pattern, 555f in periventricular nodular heterotopia, 836f Low-voltage fast activity, focal beta activity enhancement with, in focal transmantle dysplasia, 381f with slow DC shift, in focal transmantle dysplasia, 567f in symptomatic focal epilepsy from focal cortical dysplasia, 269f Low-voltage polymorphic delta activity, unilateral background attenuation in, with severe right hemispheric encephalomalacia, 364f
M Magnetoencephalogram (MEG), 679–680 Malformation of cortical development (MCD) from chromosome 10p 15.3 duplication, in symptomatic Lennox-Gastaut syndrome, 849f from CMV infection, epilepsia partialis continua in, 707f frontal lobe epilepsy with, supplementary sensorimotor area seizure and absence-like seizure in, 832f hemispheric, ipsilateral attenuation of photic response in, 275, 297f left hemispheric, ipsilateral rhythmic theta activity in, 572f mild right mesial temporal lobe polymorphic delta activity with, 331f small sharp spikes in, 103f supplementary sensorimotor area seizure from with frontal lobe epilepsy, 832f with right mesial frontal MCD, 780f subdural vs. scalp EEG on, 833f Malignant hypertension, ictal aphasia in intracranial hemorrhage from, 370f Malignant Rolandic-sylvian epilepsy (MRSE), 783f Meningitis bacterial, focal voltage attenuation from encephalomalacia in neonates due to, 349f meningococcal, hearing-induce seizure with encephalomalacia from, 821f pneumococcal, bilateral independent lateralized epileptiform discharges in, 488f
viral, simple partical seizure in focal encephalomalacia from, 816f Meningoencephalitis unilateral attenuation of background activity, polymorphic delta activity, and sharp wave with, 362f viral sleep spindle runs in, extreme, 445f–446f sleep spindle suppression from, false localization of polymorphic delta activity in, 829f subclinical electrographic seizure in, 825f Meningoencephalitis, acute viral intermittent polymorphic delta activity in, 430f refractory nonconvulsive status epilepticus in, 520f Meningoencephalitis, HIV frontal intermittent rhythmic delta activity in, 419f occipital intermittent rhythmic delta activity in, 420f Meningoencephalitis with herniation syndrome, acute amoebic, asymmetric spindle coma in, 450f, 511f Mesencephalic-medial thalamic network, in alpha rhythm, 294f Mesial frontal infarction bilateral, periodic epileptiform discharges in midline in, 486f Mesial frontal lobe epilepsy, interictal EEG with, 806f, 807f Mesial frontal stroke, central vertex spikes in, 781f Mesial-posterior temporal lobe tumor, temporal lobe epilepsy from, 759f Mesial temporal abnormality, in Lennox-Gastaut syndrome, 593f Mesial temporal cortical dysplasia with left occipital cortical dysplasia, 751f right, ictal slow DC shift from gelastic epilepsy with, 766f Mesial temporal sclerosis (MTS) emotion and autonomic nervous system during nondominant temporal lobe seizure in, 767f interictal epileptiform discharges in, 752f, 753f mesio-temporal lobe epilepsy in, 752f prolonged febrile convulsion in, 329f temporal intermittent rhythmic delta activity in, 368f, 371f
temporal spikes in, 688, 752f–753 Mesio-temporal lobe epilepsy (mTLE) focal cortical dysplasia and hippocampal sclerosis with, 753f focal cortical dysplasia in, 762f interictal epileptiform discharges in, 753f, 758f, 763f mesial temporal sclerosis with, 752f right déjà vu symptom in, 764f focal cortical dysplasia of right hippocampus in, 763f–764f right anterior temporal spikes in, 758f subtle right anterior temporal spikes at T1-T2 in, 760f temporal intermittent rhythmic delta activity in, 368f, 761f temporal spikes in, 688, 752f–753 Metabolic encephalopathy, generalized nonepileptiform activity in, 389 Metachromatic leukodystrophy (MLD), 431f posteriorly accentuated diffuse delta activity in, 337f Methylphenidates, excessive beta activity with, 397f Midazolam infusion beta coma after, 512f with embolic stroke, asymmetric spindle coma in, 510f Middle cerebral artery (MCA) infarction, left-sided focal clonic seizure from, 249f Middle cerebral artery (MCA) stroke, left anterior beta asymmetry in, 308f sleep spindle suppression and focal polymorphic delta activity in, 320f Midline spikes, in focal epilepsy, 685–686, 781f, 789f, 791f epidemiology and etiology of, 685 ictal patterns of, 686 in parietal lobe epilepsy with focal cortical dysplasia, 737f waveforms of epileptiform charges in, 685–686 Midline theta rhythm, 5, 78f Migraine coma with, 416f common (classic) focal intermittent polymorphic delta activity in, 335f
877
Migraine (continued) focal polymorphic delta activity in, 341f complicated, glossokinetic artifact polymorphic delta activity from, 152f with cyclic vomiting, H-response in, 41f EEG in, 341f frontal intermittent rhythmic delta activity with, 416f, 417f hemiplegic EEG in, 339f, 340f familial, focal polymorphic delta activity in, 339f, 340f lateralized background suppression in, 343f lateralized polymorphic delta activity in, 344f nonfamilial, intermittent focal polymorphic delta activity in, 339f periodic lateralized epileptiform discharges in, 342f with polymorphic delta activity, 332f H-response and, 39f, 40f, 405f, 616–617, 665f, 666f with intermittent polymorphic delta activity, 335f parieto-temporal sharp wave in, 819f temporal sharp wave in, 820f Mild malformation of cortical development [m(MCD)] of right mesial temporal lobe, polymorphic delta activity in, 331f right mesio-temporal epilepsy from, small sharp spikes in, 103f Miller-Dieker syndrome, generalized high-amplitude fast activity in, 651f of alpha frequency band, 400f, 651f of beta frequency band, 398f, 653f with polyspike and slow-wave complexes, 652f Mitten patterns, 5, 66f–69f Monorhythmic occipital delta activity, 201, 209f–211f, 216f, 217f delta brushes with, 210f, 217f delta brushes with extremely low-voltage background and, 216f Movement artifacts, physiological, 127, 154f–186f. See also Physiological movement artifacts Movements, spontaneous, 515f Moyamoya disease, occipital intermittent rhythmic delta activity in diffuse encephalopathy from, 422f Mu rhythm, 7, 11f, 12f, 114f–122f
878
in 3-year-old after epilepsy surgery, 119f with alpha rhythm, 11f, 12f asymmetric slowing of, focal, 275 in depth EEG bipolar, 121f implantation during seizure, 122f intermittent photic stimulation activation of, 118f overview of, 114f prominent, breach rhythm with, 374f–375f after right occipital ganglioma resection, 116f–117f during photic stimulation, 115f in subdural EEG monitoring, 120f Mycoplasma encephalitis, with reversible focal lesion in corpus callosum, extreme spindles in, 448f Myelomeningocele, epilepsy with, 351f Myocardial infarction, burst-suppression pattern in cardiac arrest from, 458f Myoclonic astatic epilepsy (MAE), 615, 640f–644f diffuse monomorphic theta rhythm in, 410f diffuse theta activity in, 640f diffuse theta slowing with central-parietal predominance in, 409f drop attack in, 643f vs. focal epilepsy, 690, 698f, 722f focal epilepsy simulating, with focal cortical dysplasia, 690, 722f myoclonic astatic seizure in, 641f myoclonic seizure in, 642f myoclonic status epilepticus in, 644f Myoclonic astatic seizure (MAS) with atonia, 641f drop attacks in, 641f, 643f Myoclonic epilepsy with ragged red fibers (MERRF), generalized epileptiform discharges with diffuse delta slowing in, 616, 657f Myoclonic jerks and spontaneous movements, in severe hypoxic encephalopathy, 515f Myoclonic seizure (MS), 642f from carbamazepine, 618f and eye opening/closure, burst-suppression pattern in, 516f in juvenile myoclonic epilepsy, 629f photosensitive, with severe encephalomalacia, 808f
Myoclonic status epilepticus, in myoclonic astatic epilepsy, 644f Myoclonus, in early myoclonic encephalopathy, 179f
N Naegleria fowleri CNS infections, 450f Narcolepsy, rapid eye movement in, 129f Near drowning burst-suppression from anoxic encephalopathy with, 460f hypoxic encephalopathy from alpha-theta coma in, 504f beta coma in, 506f bilateral independent periodic lateralized epileptiform discharges in, 491f delta coma in, 433f, 505f paradoxical activation in hypoxic encephalopathy after, 437f Needle-like (occipital) spikes of blind, 4, 42f–44f, 686 Neurocysticercosis, paradoxical lateralization from, 801f Neurofibromatosis type 1 (NF1), 554f Neuronal ceroid lipfuscinosis (NCL) type 2, 616, 661f, 662f Neuronal ceroid lipofuscinosis (NCL) diffuse bisynchronous epileptiform paroxysms in, 663f drop attack and cataplexy in, 664f late infantile, 687 occipital spikes evoked by low-frequency photic stimulation in, 661f, 662f Newborn, 201–271. See also specific disorders alpha seizure discharge in, 203, 257f–260f anterior slow dysrhythmia in, 202, 231f–233f burst suppression in, 202–203, 237f–239f delta brushes in, 201, 208f–211f, 216f, 217f depression and lack of differentiation EEG in, 204, 265f early myoclonic encephalopathy in, 204, 263f electrocerebral inactivity in, 204, 266f–268f eye movement artifact in, 230f focal clonic seizure in, 203, 248f–250f, 253f, 256f focal negative sharp waves in, 203, 248f–250f frontal sharp transients (encoches frontales) in, 202, 226f–230f, 232f
ictal EEG activity in, from periventricularintraventricular hemorrhage, 255f monorhythmic occipital delta activity in, 201, 209f–211f, 216f, 217f Ohtahara syndrome in, 204, 264f positive sharp waves in, 203, 240f–247f pyruvate dehydrogenase deficiency in, 257f–260f rhythmic midline central theta bursts in, 202, 234f seizures of depressed brain in, 203, 253f, 254f sharp theta on occipitals of prematures in, 201–202, 212f–215f symptomatic focal epilepsy from focal cortical dysplasia in, 204, 269f–271f temporal alpha bursts in, 202, 223f temporal theta bursts in, 202, 215f, 218f–222f théta pointe alternant in, 203–204, 261f, 262f trace alternant in, 202, 224f–225f tracé discontinu in, 201, 205f–207f, 211f transient unilateral attenuation of background activity in, 202, 235f, 236f zip-like electrical discharges (zips) in, 203, 251f–253f Nocturnal tonic seizures, in Lennox-Gastaut syndrome, 583f Nodular heterotopias, in cortical dysgenesis, 572f Nonconvulsive status epilepticus (NCSE) in Angelman syndrome, 647f in Dravet syndrome, 600f from ifosfamide, triphasic waves in, 429f with Lennox-Gastaut syndrome, 14- and 6-Hz positive spikes with continuous delta slowing in, 442f with periodic lateralized epileptiform discharges, 392 refractory (See Refractory status epilepticus (RSE)) sedative after, reversible theta coma from, 507f triphasic waves vs., 429f Nonepileptiform activity, focal, 275–385 alpha rhythm abnormalities, 275, 280f–304f, 307f (See also Alpha rhythm focal abnormalities) photic response (See Photic response) voltage attenuation, 275 background activity, focal enhancement of breach rhythm, 276, 374f–377f higher amplitude, 276, 378f–385f
beta attenuation, focal, 275–276, 308f–310f, 343f, 362f–364f (See also Beta attenuation, focal) frontal intermittent rhythmic delta activity, 278–279 intermittent rhythmic delta activity, focal or lateralized, 278, 366f–373f (See also Intermittent rhythmic delta activity (IRDA), focal or lateralized) lambda asymmetry, postresection of epileptogenic zone, 275, 307f occipital intermittent rhythmic delta activity, 279 photic response (See Photic response) polymorphic delta activity, focal, 276–278, 306f, 322f–342f, 344f, 354f, 356f–365f (See also Polymorphic delta activity (PDA), focal) causes of, 276–277 continuous, 277–278 definition of, 276 intermittent, 277 lesion location in, 277 mechanisms of, 277 reactivity in, 277 sleep architecture attenuation, unilateral, 276, 305f, 310f–321f, 352f (See also Sleep architecture attenuation, unilateral) symptomatic focal epilepsy, congenital hydrocephalus with ventriculoperitoneal shunt, 275, 290f voltage attenuation, focal, 275–276, 345f–360f (See also Voltage attenuation, focal) Nonepileptiform activity, generalized, 389–466 in anoxic encephalopathy, 389, 390 diffuse, EEG patterns in, 390–395 beta activity, excessive, 390, 396f–403f, 448f (See also Beta activity, excessive) bilateral independent periodic lateralized epileptiform discharges, 393 burst-suppression pattern, 395, 452f–461f, 517f (See also Burst-suppression (B-S) pattern) delta activity, posterior or posteriorly accentuated, 392 diffuse background attenuation, 395, 464f–466f, 517f electrocerebral inactivity, 395, 463f, 480f, 518f
14- and 6-Hz positive spikes with continuous delta slowing, 394, 439f–443f, 519f generalized periodic epileptiform discharges, 393 intermittent rhythmic delta activity, diffuse, 391, 416f–424f (See also Intermittent rhythmic delta activity (IRDA)) notched delta pattern, 425f–426f, 645 periodic lateralized epileptiform discharges, 392–393 periodic patterns, 392–394 rhythmic coma patterns, 394 alpha, 394 beta, 394 delta, 394 spindle coma, 394–395 theta, 394 sleep architecture, abnormal, 391 slow activity background, 391, 404f, 406f–415f, 444f–447f (See also Slow activity, background) continuous, 391–392, 430f–438f, 476f–479f, 505f diffuse intermittent, 391 triphasic waves, 393–394, 427f–429f in drug intoxication, 389–390 EEG patterns in high-voltage beta activity, 389 high-voltage delta activity, 389 low-voltage fast patterns, 389 periodic pattern, 389 triphasic waves, 389 in encephalitis, 389, 390 etiology and EEG with, 389 general principles of, 389 in herpes simplex encephalitis, 390 in PCP intoxication, 389, 390 prognosis with, 389 in subacute sclerosing panencephalitis, 390 Nonketotic hyperglycinemia (NKH), burst-suppression pattern in, 456f Notched-delta pattern, in Angelman syndrome, 425f–426f, 645f Nystagmus artifact, 125, 131f–134f with holoprosencephaly, 131f horizontal
879
Nystagmus artifact (continued) constant, 133f with eye closure, 132f with fast component to left side, 134f Nystagmus, epileptic, and asymmetric epileptic spasms, 809f
O Occipital calcification, bilateral, epilepsy with, 687 Occipital cortex focal lesions, on alpha rhythm, 288f, 301f Occipital intermittent rhythmic delta activity (OIRDA), 391, 623f, 675. See also Intermittent rhythmic delta activity (IRDA) in childhood absence epilepsy asymmetric, 635f and generalized 3/sec spike-wave activity, 633f in children with epilepsy, 422f–424f in chronic renal failure with chronic dialysis, 418f clinical correlates of, 434f with continuous polymorphic delta activity, 278 in diffuse encephalopathy from moyamoya disease, 422f focal, 279 with focal intermittent rhythmic delta activity, 471 in generalized epilepsy, 613, 633f, 635f in generalized epilepsy, idiopathic, 623f, 624f historical perspective on, 422f in hyperventilation, 415f in idiopathic generalized epilepsy, 424f and polymorphic delta activity, in subcortical focal cortical dysplasia, 366f in viral encephalopathy, acute, 423f in V meningoencephalitis, 420f Occipital lobe epilepsy/seizures focal cortical dysplasia in intrinsic epileptogenicity of, 743f–749f response attenuation in, 298f from neonatal western equine encephalitis, 823f with POLG1 mutation, 852f in posterior reversible encephalopathy syndrome, 477f symptomatic, 687–688, 744f–745f, 823f, 852f Occipital sharp transients with eye movements, 32f–35f
880
Occipital slow transients, 3–4, 36f–38f cone wave and diphasic slow transient, 36f cone waves, 37f–38f Occipital spikes, in focal epilepsy, 686–688 epilepsy with bilateral occipital calcification, 687 idiopathic childhood occipital epilepsy of Gastaut, 686–687 late infantile neuronal ceroid lipofuscinosis, 687 needle-like spikes of the blind, 4, 42f–44f, 686 Panayiotopoulos syndrome, 687, 701f–703f, 745f Sturge-Weber syndrome, 687 symptomatic occipital epilepsy, 687–688, 744f–745f, 823f, 852f Occipital spikes of blindness, 4, 42f–44f, 686 Occipital tumor, right, on alpha rhythm, 288f Ohtahara syndrome, 264f, 529, 536f, 537f corpus callosum dysgenesis in, background asynchrony in, 455f with early myoclonic encephalopathy, 529, 536f–541f suppression-burst pattern in, 529, 536f–538f, 842f severe neonatal epilepsy with, 204, 264f unilateral, with hemimegalencephaly, 842f West syndrome from, 529, 537f Orbitofrontal lobe region (OFR) epilepsy central vertex spikes in, 769f interictal epileptiform discharges in, 769f, 770f interictal psychosis in, 768f polyspike burst in, 771f secondary bilateral synchrony in, 770f Orbitofrontal-mesial temporal tumor, temporal intermittent rhythmic delta activity in, 757f Orbitofrontal seizure, from tuberous sclerosis complex, with secondary bilateral synchrony, 715f
P Panayiotopoulos syndrome (PS), 687, 701f–703f, 745f Paradoxical activation, 389, 437f, 438f, 471, 481f, 683 with bilateral frontal and basal ganglia infarction, 438f in hypoxic encephalopathy, 437f Paradoxical hypersynchrony, 206f Paradoxical lateralization of epileptic focus, 743f–744f, 802f in focal cortical dysplasia of left parietal lobe, 742f from neurocysticercosis, 801f
Parietal cortex, sleep spindles from, 309f, 310f Parietal cortical dysplasia, mesial, scalp vs. subdural EEG in, 741f Parietal lobe epilepsy, 685, 737f–739f mesial, closely spaced scalp electrodes in, 738f midline spikes in, 737f paradoxical lateralization in focal cortical dysplasia of left parietal lobe in, 742f scalp EEG in, 738f Parietal lobe lesions on sleep patterns, 314f on sleep spindles, 305f Parieto-temporal sharp wave, in migraine, 819f Paroxysmal fast activity (PFA), 613, 625f, 675 asymmetrical, 588f epileptogenic zone proximity and, 832f vs. 14- and 6-Hz positive spikes, 519f generalized, 613, 625f with generalized clonic seizures, 659f with generalized epilepsy, 659f in idiopathic generalized epilepsy, 625f in juvenile myoclonic epilepsy, 580f in Lennox-Gastaut syndrome, 532, 576f, 577f, 579f–581f, 588f, 590f in Lennox-Gastaut syndrome, asymmetric, 588f, 592f unilateral, in infantile spasms, 562f Patting artifacts, 127, 154f–162f in 10-month-old being burped, 154f in 11-month-old with congenital CMV, 158f from electrode loosening, 160f vs. electrographic seizure, 155f, 157f, 162f focal, with left hemispheric stroke, 161f monomorphic and monophasic spike-like activity in, 159f unilateral, 156f Pentobarbital anesthesia, with corpus callosum hemorrhage, asynchronous burst-suppression pattern in, 457f Pentobarbital coma, burst-suppression in, 514f Periodic epileptiform discharges in midline (PEDIM), 472, 485f, 486f in 2-month-old with anoxic encephalopathy, 485f in 9-month-old with bilateral mesial frontal infarction, 486f
Periodic lateralized epileptiform discharges (PLEDs), 392–393, 471–472, 483f, 484f, 675 from anoxic encephalopathy, 390 clinical correlates of, 392 in epilepsia partialis continua, from hydrocephalus with intraventricular hemorrhage, 350f etiology of, 350f, 392 in focal epilepsy, 675, 677, 772f, 803f in focal transmantle dysplasia, 803f in herpes simplex encephalitis, 390 in ICU, 471–472, 483f, 484f in ischemic stroke from cardiac transplantation, 483f in left insula epilepsy from focal cortical dysplasia, 772f with left temporal ganglioglioma, 757f with migraine, hemiplegic, 342f in posterior reversible encephalopathy syndrome, 484f in Rasmussen’s encephalitis, 712f Periodic long-interval diffuse discharges (PLIDDs), 393 Periodic sharp wave complexes (PSWCs), in CreutzfeldtJakob disease, 473, 498f Periodic short-interval diffuse discharges (PSIDDs), 393 Perisylvian polymicrogyria, bilateral, in Lennox-Gastaut syndrome, 581f–583f Periventricular hemorrhage (PVH), from CMV and cardiomyopathy, frontal sharp waves in, 233f Periventricular-intraventricular hemorrhage (PVH-IVH) ictal EEG activity in, 255f positive temporal sharp waves in, 241f Periventricular leukomalacia (PVL) with focal cortical dysplasia, polymorphic delta activity and ipsilateral beta activity enhancement in, 382f West syndrome with, 543f Periventricular nodular heterotopia (PNH) asymmetric frontal intermittent rhythmic delta activity in, 838f bilateral, 839f, 840f epilepsy in, 681 focal epilepsy and, 681, 834f–840f, 849f focal interictal EEG abnormalities in, 834f, 835f, 837f, 839f–840f, 849f interictal epileptiform discharges in, 681
intrinsic epileptogenicity in, 572f in Lennox-Gastaut syndrome due to malformation of cortical development from chromosome 10p 15.3 duplication, 849f low-voltage fast activity in, 836f mental retardation and cerebellar hypoplasia in, 839f with right hemispheric predominance, 834f secondary bilateral synchrony in, 835f symptomatic focal epilepsy in, 837f unilateral, 681, 849f Persistent nonrhythmic delta activity (PNDA), 277–278 Perspiration artifact, 127 Phantom spikes (spike-waves), 6, 104f–105f, 736f Phencyclidine (PCP) intoxication, generalized nonepileptiform activity in, 389, 390 Phenobarbital benzodiazepine with, excessive beta activity from, 397f beta coma after, 512f Photic driving response asymmetry from focal lesions, 301f in normal individuals, 299f Photic response asymmetric, 297f with left temporo-occipital tumor, 275, 299f with left thalamic atrophy and calcification, 275, 300f attenuation of, with remote stroke, multiple calcification, and schizencephaly from congenital infection, 306f decreased, alpha symmetry with, in hemorrhagic infarction, 275, 301f excess, in ipsilateral cerebral hemisphere, 303f at high frequency stimulation, excessive, 405f ipsilateral attenuation of with hemispheric malformation of cortical development, 275, 297f with left temporo-occipital focal cortical dysplasia, 275, 298f ipsilateral enhancement of, with unilateral polymicrogyria, 275, 303f from thalamocortical circuit lesions, 300f Photic stimulation, increased interictal epileptiform discharges from, 679
Photocell artifact, 128, 193f Photomyoclonic response artifact, 126, 139f, 142f Photomyogenic (photomyoclonic) response, 7, 110f–113f in 9-year-old with childhood absence epilepsy, 112f in 13-year-old with controlled idiopathic generalized epilepsy, 113f in 14-year-old with controlled idiopathic generalized epilepsy, 110f eyelid artifacts with EMG potentials, 113f orbicularis oculi, frontalis, and temporalis muscles in, 111f vs. photoparoxysmal response, 679 Photoparoxysmal response in epilepsy with grand mal on awakening, 630f in juvenile myoclonic epilepsy, 631f vs. photomyogenic response, 679 Photosensitive myoclonic seizure, with severe encephalomalacia, 808f Photosensitivity, 808f Physiological movement artifacts, 127, 154f–186f body movement, rapid, 127, 184f chewing, 187f head movement, 127, 176f–177f hiccup, 127, 163f–168f limb movement, 127, 178f–179f patting, 127, 154f–162f respiration, 127, 181f, 182f, 184f–186f shivering, 127, 180f, 183f sobbing, 127, 169f–170f sucking, 127, 171f–173f tremor, 127, 174f–175f ventilator, 127, 182f PLEDs Plus, 392 Pneumococcal meningitis, bilateral independent lateralized epileptiform discharges in, 488f Pneumococcal septicemia, embolic stroke with, background asymmetry and polymorphic delta activity in, 309f POLG1 mutation alpha coma with delta slowing (FIRDA & PDA) with, 449f epilepsia partialis continua with, 851f occipital lobe epilepsy with, 852f
881
Polymicrogyria (PMG), 832f bilateral perisylvian, in Lennox-Gastaut syndrome, 581f–583f with closed-lip schizencephaly ipsilateral beta activity enhancement in, 380f ipsilateral diffuse rhythmic alpha in, 384f with schizencephaly from HSV encephalitis, focal clonic seizures in, 250f time of brain injury in, 399f unilateral ipsilateral alpha enhancement in, 302f ipsilateral photic response enhancement in, 303f secondary bilateral synchrony in, 813f Polymorphic delta activity (PDA), 392, 676 and alpha attenuation, with focal cortical dysplasia of left occipital lobe, 291f and background asymmetry, with embolic stroke and pneumococcal septicemia, 309f with background attenuation, 356f beta activity enhancement with, focal, 377f with beta and alpha depression, 362f bilateral, but lateralized, 471 in frontal lobe lesions, 478f–479f with focal cortical dysplasia, 382f glossokinetic artifact with, from complicated migraine, 152f improvement of, after resection of necrotic tissue, 479f with ipsilateral beta activity enhancement, in periventricular leukomalacia with focal cortical dysplasia, 382f localization of, 363f false, with sleep spindle suppression from viral meningoencephalitis, 829f with focal cortical dysplasia, 379f and occipital itermittent rhythmic delta activity, in subcortical focal cortical dysplasia, 366f pulse artifact vs., 148f and sharp wave, with left temporal-occipital tumor, 750f slowing of, diffuse, 471, 476f–479f, 505f smooth, 276 vs. temporal intermittent rhythmic delta activity, 371f with theta or alpha activity, 295f
882
Polymorphic delta activity (PDA), continuous clinical correlates of, 434f from diffuse left hemispheric encephalomalacia, 347f in focal epilepsy, 676–677, 750f with frontal intermittent rhythmic delpha activity, 432f, 434f in cerebral herniation syndrome, 478f–479f with diffuse alpha activity and POLG1 mutation, 449f with frontal, basal ganglion and cerebellar infarctions, 434f with HHE syndrome and impending cerebral herniation, 432f with massive brain edema and central herniation syndrome, 435f–436f Polymorphic delta activity (PDA), diffuse cortical deafferentation in, 433f, 434f with posterior predominance, in posterior reversible encephalopathy syndrome, 476f Polymorphic delta activity (PDA), focal, 276–278, 354f, 356f–365f in acquired HIV with toxoplasmosis, 334f alpha attenuation with, in acute focal axonal injury, 275, 295f with alpha slowing, 295f with background asymmetry, from nonaccidental trauma, 358f beta suppression and, in right mesial temporal sclerosis from encephalitis, 363f causes of, 276–277 at center of lesion, 358f continuous, 277–278 definition of, 276 delta and theta slowing in, with right mesial temporal focal cortical dysplasia, 322f diffuse delta slowing with occipital prominence in, from left cerebral hemiatrophy due to intraventricular hemorrhage, 336f, 365f flat, 358f with focal enhancement of beta activity and focal spikes, in balloon cell-type focal cortical dysplasia, 765f in hemiplegic migraine, 332f
high-voltage, frontal-dominant, with generalized slow wave transient symptomatic West syndrome and asymmetric epileptic spasm, 338f improvement of, with clinical improvement, 357f intermittent, 277 in classic migraine, 335f in nonfamilial hemiplegic migraine, 339f with intermixed spikes, in Lennox-Gastaut syndrome, 593f lateralized in hemiplegic migraine, 344f left hemisphere, during arousal, 306f monorhythmic/polymorphic, in acute herpes simplex encephalitis, 361f from left anterio-mesial temporal ganglioma, 755f lesion location in, 277 low-voltage, with unilateral background attenuation in severe right hemispheric encephalomalacia, 364f mechanisms of, 277 in migraine common, 341f familial hemiplegic migraine, 340f nonfamilial hemiplegic, 339f mild malformation of cortical development in, right mesial temporal lobe, 331f near lesion, 358f periodic lateralized epileptiform discharges in, with hemiplegic migraine, 342f posteriorly accentuated diffuse delta activity in, from metachromatic leukodystrophy, 337f with postictal state, lateralized delta slowing and background suppression, 354f prolonged febrile convulsion with large hippocampal volume and hyperintensity in, 328f mesial temporal sclerosis in, 329f from pulse artifact, 325f reactivity in, 277 right parietal focal cortical dysplasia in, ipsilateral beta attenuation and monorhythmic theta activity in, 324f right temporal, with focal cortical dysplasia, right posterior frontal, 330f
with sharp waves and epileptic focus from structural abnormality, 327f from left temporal-occipital tumor, 326f right temporal, and focal cortical dysplasia, 327f sleep spindle suppression with, in left middle cerebral artery stroke, 320f slowing of, in acute disseminated encephalomyelitis, 333f smooth, 358f in Sturge-Weber syndrome with background suppression, 359f decreased benzodiazepine-enhanced beta activity in, 360f theta slowing in, right posterior temporal, with posterior reversible leukoencephalopathy, 323f in traumatic brain injury, 356f unilateral attenuation of background activity and sharp wave with, in meningoencephalitis, 362f white matter lesions in, 330f, 331f, 333f, 358f Polymorphic delta activity (PDA), intermittent with alpha attenuation, in systemic lupus erythematosus, 292f focal with classic migraine headache, 335f with nonfamilial hemiplegic migraine, 339f with meningoencephalitis, acute viral, 430f Polyphasic waves, 19f–21f, 275, 280f–283f Polyspike, and slow-wave complexes, generalized highamplitude fast activity in, 652f Polyspike-wave-like discharge, 97f Pontine stroke, alpha coma in, 501f Positive occipital sharp transients of sleep (POSTs), 3, 27f–30f Positive Rolandic sharp waves (PRSs), 240f in intraventricular hemorrhage, 242f, 243f Positive sharp waves (PSWs) as artifact, 198f, 245f in focal epilepsy, 677 with hypoxic ischemic encephalopathy and very low-voltage background activity, 265f in newborn, 203, 240f–247f
Rolandic, with intracerebral hemorrhage from venous sinus thrombosis, 240f temporal, with periventricular-intraventricular hemorrhage, 241f temporal in congenital toxoplasmosis, 244f vs. electrode pop, 246f and Rolandic, 242f, 243f Positive temporal sharp waves (PTSs), 241f in congenital toxoplasmosis, 244f vs. electrode pop, 246f in intraventricular hemorrhage, 241f–243f Posterior dominant rhythm, 1–2, 8f–12f. See also Alpha rhythm Posterior reversible encephalopathy syndrome (PRES) diffuse polymorphic delta activity with posterior predominance in, 476f occipital lobe seizure in, 477f periodic lateralized epileptiform discharges in, 484f Posterior reversible leukoencephalopathy syndrome, right posterior temporal theta slowing in, 323f Posterior slow waves of youth, 3, 19f–21f, 275, 280f–283f activated with eye closure, 283f attenuated with eye opening, 20f, 282f intermittent right occipital delta slowing simulating, 21f Posterior slow-wave transients with eye movements, 3, 32f–35f Postictal encephalopathy, EEG in, 355f Postictal state frontal intermittent rhythmic delta activity in, 421f lateralized delta slowing and background suppression in, 354f Prefrontal-occipital EEG pattern, 685 Prolonged febrile convulsion (PFC) with large hippocampal volume and hyperintensity, 328f with mesial temporal sclerosis, 329f Prolonged QT syndrome, 617, 667f, 669f Pseudo-Lennox syndrome (PLS), 690, 698f Psychosis, temporal lobe epilepsy and, 733f, 768f Pulse artifact, 126, 147f–148f electrocerebral inactivity with, 147f, 480f
vs. polymorphic delta activity, 148f polymorphic delta activity from, 325f Pyridoxine dependency, 616, 660f in early myoclonic encephalopathy, 263f, 529, 539f–541f Pyridoxine therapy, 616, 660f Pyruvate dehydrogenase deficiency, 257f–260f in 4-week-old, 257f with alpha seizure discharge, 258f–260f overview of, 257f
Q QT syndrome, prolonged, 617, 667f, 669f
R Rapid eye movement (REM) artifact, 125, 129f Rapid spikes, runs of. See Paroxysmal fast activity (PFA) Rasmussen’s encephalitis, 689, 710f–712f epilepsia partialis continua in, 689, 710f–711f periodic lateralized epileptiform discharges in, 712f Refractory status epilepticus (RSE), 474–475, 520f–523f electrical status epilepticus during slow sleep in, 818f generalized periodic epileptiform discharges in, 495f, 496f hemiconvulsion hemiplegia epilepsy syndrome in, 492f history of, 817f nonconvulsive in 13-year-old with high fever, 521f in acute viral meningoencephalitis, 520f bisynchronous temporal discharges with bilateral hippocampal atrophy in, 522f generalized periodic epileptiform discharges in, with diffuse cortical atrophy and hippocampal sclerosis, 523f prognosis in, 520f prognosis of survivors of, 817f, 818f stimulus-induced rhythmic, periodic, or ictal discharges in, 497f REM sleep, 4, 51f, 129f drop attack with cataplexy and, 664f electrical status epilepticus in, 601f in healthy children, 616, 664f on juvenile absence epilepsy, 613, 626f
883
Renal failure, chronic, occipital intermittent rhythmic delta activity with, 418f Respiration artifacts, 127, 181f, 182f, 184f–186f with body movement, 181f, 182f, 185f breath holding, 186f plus movement artifact, 184f Respirator artifacts high-frequency, diffuse background attenuation with, 465f high-frequency jet, 128, 191f high-frequency ventilator, 128, 190f, 266f Rett syndrome, 616 bisynchronous sharp waves in, 648f, 649f diffuse rhythmic 4-Hz delta with fronto-central and vertex predominance in, 413f diffuse rhythmic theta in, 412f general EEG changes in, 412f–413f rhythmic theta activity in central vertex with lowvoltage background in, 822f Reye syndrome, 14- and 6-Hz positive spikes with continuous delta slowing in, 394, 440f, 442, 519f Rhabdomyoma, with tuberous sclerosis complex, 688, 721f Rhythmical midline theta (RMT), 683 Rhythmic coma. See Coma, rhythmic Rhythmic midline central theta bursts, 202, 234f Rhythmic midtemporal discharges (RMTD), psychomotor variant, 5–6, 84f Rhythmic spikes. See Paroxysmal fast activity (PFA) Rhythmic temporal rhythm (physiologic), 7, 107f Rhythmic temporal theta bursts of drowsiness (RTTD), 5–6, 84f–89f in 15-year-old, with recurrent passing out, 85f in 16-year-old, with recurrent vertigo, 86f in 17-year-old, with new-onset general tonic-clonic seizure, 88f in 17-year-old, with recurrent headache and right arm numbness, 87f monomorphic and monorhythmic notched theta runs in, 89f overview of, 84f Right middle cerebral artery infarction, left-sided focal clonic seizure with, 249f
884
Ripples, 552f Ripples of prematurity, 201, 208f–211f, 216f, 217f. See also Delta brushes Roving eye movement artifact, 125, 130f Runs of rapid spikes. See Paroxysmal fast activity (PFA)
S Salt bridge artifact, 127, 153f Scalp edema diffuse background attenuation with, 465f low-voltage EKG with, 191f Scalp EEG limitations, in focal epilepsy, 677 Scalp-recorded DC shifts, 679 Schizencephaly closed-lip, polymicrogyria with ipsilateral beta activity enhancement in, 380f ipsilateral diffuse rhythmic alpha in, 384f epilepsy and, 318f open-lip, ipsilateral vertex wave and spindle attenuation in, 318f with polymicrogyria from HSV encephalitis, focal clonic seizures in, 250f vertex sharp wave and spindle suppression with, 305f Secondary absence seizure. See Frontal absence Secondary bilateral synchrony (SBS), 678, 716f left insula focal cortical dysplasia with, 773f in orbitofrontal lobe region epilepsy, 770f with orbitofrontal seizure from tuberous sclerosis complex, 715f in periventricular nodular heterotopia, 835f with secondary epileptogenesis, and angiocentric neuroepithelial tumor, 850f in unilateral polymicrogyria, 813f Sedative. See also specific sedatives after nonconvulsive status epilepticus, reversible theta coma from, 507f generalized nonepileptiform activity from intoxication with, 389–390 Seizure onset zone (SOZ), 269f. See also specific disorders high-frequency oscillations and, 552f Seizures of depressed brain, 203, 253f, 254f with severe HIE and herniation syndrome, 254f Sensory simple partial seizure, 814f
Sepsis, encephalopathy with stroke and, 14- and 6-Hz positive spikes with continuous delta slowing in, 443f Severe neonatal epilepsy with suppression-burst pattern, 204, 264f, 529, 536f–541f in 1-week-old with tonic spasms, 537f in 5-day-old with erratic myoclonus, 536f in 19-day-old with hemimegalencephaly, 538f Sharp theta on occipitals of prematures (STOP), 201–202, 212f–215f in 39-week-old with severe HIE, 214f with excessive delta brushes, 212f overview of, 201–202, 212f–213f with temporal theta burst patterns, 215f Sharp waves, positive, as electrode artifact, 198f Shivering artifact, 127, 180f, 183f in 5-year-old with recurrent shivering and loss of consciousness, 180f vs. abnormal fast activity, 183f Short-latency somatosensory evoked potentials (SSEPs), in hydranencephaly, 348f Shunt, ventriculoperitoneal with congenital hydrocephalus, symptomatic focal epilepsy from, 275, 290f problems with, 290f Simple partial seizures from focal encephalomalacia with viral meningoencephalitis, 816f with herpes simplex encephalitis, 824f motor, 815f sensory, 814f somatosensory, 740f 6-Hz spike-and-wave bursts, 6, 104f–105f, 736f remote right fronto-temporal stroke with, 736f 60-cycle artifact, 127–128, 189f Sleep architecture, abnormal, 391 Sleep architecture attenuation, unilateral, 276, 305f, 310f–321f, 352f asymmetric beta with sleep spindles and vertex waves, in encephalomalacia from meningoencephalitis, 310f with focal cortical dysplasia background activity attenuation during drowsiness in, 311f–312f
hypnagogic hypersynchrony suppression during drowsiness in, 311f–313f insular epilepsy with nocturnal hypermotor seizures in, 315f subcortical, hypnagogic hypersynchrony in, unilateral attenuation of, 314f late post-traumatic epilepsy with, in encephalomalacia from cerebral contusion, 316f sleep spindle slowing in, unilateral, 321f sleep spindle with focal polymorphic delta activity in, from left middle cerebral artery stroke, 320f Sturge-Weber syndrome, sleep spindle, vertex wave, and beta activity suppression with, 317f suppression of, from uterine stroke, 319f vertex sharp wave and spindle suppression in, with congenital infection with remote stroke, multiple calcification, and schizencephaly, 305f vertex wave and spindle attenuation in, with openlip schizencephaly, 318f Sleep deprivation, increased interictal epileptiform discharges from, 679 Sleep spindles, 4–5, 56f–65f asynchronous, at 2+ years, 446f cerebral structure on, 305f extreme runs of, 391 in acute mycoplasma encephalitis with reversible focal lesion in corpus callosum, 448f in viral meningoencephalitis, 445f–446f 14 and 6/sec positive spikes with, 98f infant age and, 444f, 445f magnetoencephalogram of pre- and post-central areas in, 319f, 320f normal 8 weeks CA, harmonic of, 57f 10 weeks CA, 58f 16 weeks CA, 62f 2 months, 56f 3-6 months CA, 59f 9 months, asynchronous, 64f 14 months, synchronous, 64f parietal lobe lesions on, 305f prolonged
3-6 mos CA, 59f–61f with normal sleep spindles, 444f in subdural EEG, 48f with subharmonic, 63f suppression of, from viral meningoencephalitis, 829f thalamus in, 309f, 310f thalamus lesions on, 305f unilateral slowing of, 321f voltage asymmetry of, 321f Sleep stages drowsiness, 4, 45f–46f 14- and 6-Hz positive bursts in, 46f in older children and adults, 45f REM sleep, 4, 51f, 129f stage 2 sleep, 4, 47f–48f stage 3 sleep, 4, 49f stage 4 sleep, 4, 50f Sleep starts, 74f–77f. See also Hypnic myoclonia (HM) Sleep, transient unilateral attenuation of background activity in, 202, 235f, 236f, 345f Slow activity, background, 391, 404f, 406f–415f, 444f–447f with abnormal sleep architecture, 391 anterior slow dysrhythmia and frontal sharp transients in, 406f–407f with diffuse intermittent slow activity, 391 with diffuse theta slowing, from lamotrigine, 411f electroretinogram in, 414f general points on, 391 glossokinetic artifact in, 404f hyperventilation from sobbing in, 408f, 415f myoclonic astatic epilepsy in with diffuse monomorphic theta rhythm, 410f with diffuse theta slowing with central-parietal predominance, 409f in Rett syndrome with diffuse rhythmic 4-Hz delta with fronto-central and vertex predominance, 412f with diffuse rhythmic theta, 412f sleep spindle runs in, asynchronous, 2+ years, 446f sleep spindle runs in, extreme in acute meningoencephalitis, 446f in viral meningoencephalitis, 445f–446f
sleep spindle runs in, prolonged, with normal sleep spindles, 444f Slow activity, diffuse continuous, 391–392, 430f–438f, 476f–479f, 505f delta coma in, from hypoxic-ischemic encephalopathy with near drowning, 433f FIRDA and continuous polymorphic delta activity in with frontal, basal ganglion and cerebellar infarctions, 434f with HHE syndrome and impending cerebral herniation, 432f with massive brain edema with central herniation syndrome, 435f–436f intermittent polymorphic delta activity in, with acute viral meningoencephalitis, 430f with metachromatic leukodystrophy, 431f paradoxical activation in with bilateral frontal and basal ganglia infarction, 438f with hypoxic encephalopathy, 437f Slow activity, diffuse intermittent, 391 Slow alpha variant, 2, 13f–14f, 275, 284f–286f with behavioral disturbance and headache, 286f with recurrent staring episodes, 285f with recurrent vertigo, 284f Slow DC shift, 567f, 766f with focal low-voltage fast activity, in focal transmantle dysplasia, 567f with high-frequency oscillations, 846f ictal, 678–679, 766f, 800f, 846f, 847f in focal epilepsy, 678–679, 766f, 800f in gelastic epilepsy from right mesial temporal cortical dysplasia, 766f in temporal lobe epilepsy from ganglioma, 800f in supplementary sensorimotor area seizure, 567f Slow eye movement (SEM) artifact, 125, 130f Slow spike-wave (SSW) discharges, 575f in Lennox-Gastaut syndrome, 532, 575f, 581f, 589f after intrauterine stroke, 587f symptomatic, 585f Small sharp spikes (SSS), 6, 100f–103f in 16-year-old with migraine and recurrent passing out, 101f in 17-year-old with recurrent déjà vu episodes, 102f
885
Small sharp spikes (SSS) (continued) in normal adults, 100f with right mesio-temporal epilepsy from mild malformation of cortical development, 103f Sobbing artifact, 127, 169f–170f Sobbing, background slow activity in hyperventilation effect from, 408f, 415f Somatosensory auras (SSAs), 740f Somatosensory simple partial seizure, 740f Spike-and-slow wave complexes, 675 Spike-and-wave bursts/discharges 3-Hz, in absence epilepsy, 138f 6-Hz, 6, 104f–105f Spindle coma (SC), 394–395 asymmetric, in acute amoebic meningoencephalitis with herniation syndrome, 450f, 511f extreme, in acute mycoplasma encephalitis with reversible focal lesion in corpus callosum, 448f with generalized nonepileptiform activity, 389, 394–395 Spindle-delta bursts, 201, 208f–211f, 216f, 217f. See also Delta brushes Spindle-like fast waves, 201, 208f–211f, 216f, 217f. See also Delta brushes “Split brain” EEG, 566f Spontaneous movements, 515f Squeak effect, 2, 8f, 23f Stage 2 sleep, 4, 47f–48f Stage 3 sleep, 4, 49f Stage 4 sleep, 4, 50f Start-stop-start (SSS) phenomenon, 678, 828f with high-frequency oscillations, 828f in temporal lobe epilepsy from right hippocampal sclerosis, 844f–845f Status epilepticus (SE) generalized nonepileptiform activity in, 389 in Lennox-Gastaut syndrome, 534 myoclonic, in myoclonic astatic epilepsy, 644f in posterior reversible encephalopathy syndrome, 477f refractory, 14- and 6-Hz positive spikes with continuous delta slowing in, 440f–441f
886
Stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs), 473, 497f Streptococcal infection, alpha asymmetric reactivity in hemorrhagic stroke from, 275, 293f Stroke encephalopathy with sepsis and, 14- and 6-Hz positive spikes with continuous delta slowing in, 443f focal clonic seizure from, 256f hemorrhagic, from streptococcal infection, alpha asymmetric reactivity in, 275, 293f left hemispheric, focal patting artifact with, 161f left middle cerebral artery anterior beta asymmetry in, 308f sleep spindle suppression and focal polymorphic delta activity in, 320f mesial frontal, central vertex spikes in, 781f neonatal, from systemic infection, focal clonic seizure in, 256f pontine, alpha coma in, 501f remote, with hydrocephalus, in Lennox-Gastaut syndrome, 699f Stroke, embolic asymmetric spindle coma during midazolam infusion in, 510f with pneumococcal septicemia, background asymmetry and PDA in, 309f Stroke, intrauterine cystic encephalomalacia from, asymmetric hypsarrhythmia in, 544f Dyke-Davidoff-Mason syndrome from, alpha asymmetry in, 275, 287f electrical status epilepticus during slow sleep after, 603f, 606f frontal intermittent rhythmic delta activity in, asymmetric, 369f lateralized electrodecrement from, 353f right cerebral artery frontal arousal rhythm in, 805f supplementary sensorimotor area seizure in, 805f sleep architecture suppression by, 319f slow spike-wave discharges in Lennox-Gastaut syndrome after, 587f
Stroke, ischemic from cardiac transplantation, periodic lateralized epileptiform discharges in, 483f generalized nonepileptiform activity in, 389 Sturge-Weber syndrome decreased benzodiazepine-enhanced beta activity in, 360f EEG in, 317f occipital spikes in, 687 polymorphic delta activity with background suppression in, 359f sleep spindle, vertex wave, and beta activity suppression in, 317f unilateral attenuation of background activity in, 352f Subacute sclerosing panencephalitis (SSPE), 390, 473, 499f Subclinical electrographic seizure, in viral meningoencephalitis, 825f Subcortical band heterotopia (SBH), 616, 650f Subdural effusion, bilateral, low-voltage EEG with, 464f Subdural hematoma (SDH) asymmetric hypsarrhythmia after, contralateral, 569f bilateral, bilateral independent lateralized epileptiform discharges in, 490f Sucking artifact, 127, 171f–173f in 3-month-old with recurrent staring episodes, 171f in 5-day-old with hypoxic ischemic encephalopathy, 172f–173f Supplementary sensorimotor area (SSMA) alpha attenuation in, 275, 296f in asymmetric epileptic spasms, 574f, 776f asymmetric tonic seizures and, bilateral, 727f focal cortical dysplasia in, 723f–727f bilateral asymmetric tonic seizure from, 727f focal myoclonic seizure from, 725f–726f frontal absence from, 723f–724f ipsilateral alpha attenuation in, 275, 296f frontal lobe epilepsy with seizures from, 720f ictal involvement of, 684 seizures from, 684, 723f–727f tingling in, 685 Supplementary sensorimotor area (SSMA) seizure, 806f, 833f absence-like, 832f asymmetric tonic seizure in, 776f
bilateral asymmetric tonic, 727f focal transmantle dysplasia in, 731f, 777f–779f ictal scalp EEG in, 807f mild malformation of cortical development in, right mesial frontal, 780f with right anterior cerebral artery intrauterine stroke, 806f from severe focal cortical dysplasia with balloon cells, 848f slow DC shifts in, 847f subdural vs. scalp EEG on, 833f Suppression-burst (S-B) pattern in hemimegalencephaly, 812f asymmetric, 841f right, 811f unilateral, 842f vs. hypsarrhythmia, 529 in Ohtahara syndrome, 529, 536f–538f, 842f severe neonatal epilepsy with, 204, 264f, 529, 536f–541f Suppression coma, bilateral, prognosis in, 389 Sweat artifact, 127 Sylvian fissure lipoma, 832f Symptomatic focal epilepsy from focal cortical dysplasia, in newborn, 204, 269f–271f Synchrony. See specific disorders and types bilateral (See Bilateral synchrony) secondary bilateral (See Secondary bilateral synchrony (SBS)) Systemic lupus erythematosus (SLE) intermittent polymorphic delta activity and alpha attenuation with, 292f with seizures, EEG in, 292f
T Telephone ring artifact, 127, 188f Temporal alpha bursts, in newborn at 33 weeks CA, 202, 223f Temporal alphoid rhythm, independent, 7, 107f Temporal bisynchronous discharges with bilateral hippocampal atrophy, nonconvulsive status epilepticus with, 522f Temporal cortical dysplasia, left occipital and mesial, 751f
Temporal ganglioglioma, left periodic lateralized epileptiform discharges from, 757f temporal lobe epilepsy from, 754f–756f Temporal intermittent rhythmic delta activity (TIRDA), 279, 367f, 371f focal epilepsy with, 5, 675, 757f with ganglioglioma and mesial temporal sclerosis, 371f in mesio-temporal lobe epilepsy, 368f, 761f with orbitofrontal-mesial temporal tumor, 757f vs. polymorphic delta activity, 371f with right occipital ganglioma and hippocampal sclerosis, 372f with subcortical focal cortical dysplasia, 367f in temporal lobe epilepsy, 372f Temporal lobe epilepsy (TLE). See also Mesio-temporal lobe epilepsy (mTLE) epileptiform discharges in, 679 14- and 6-Hz positive spike discharge in, 99f from ganglioma ictal slow DC shift in, 800f left temporal, 754f–756f interictal psychosis and, 768f low-grade tumor of right mesial-posterior temporal lobe in, 759f neuronal loss in, 762f nondominant, emotion and autonomic nervous system during, with mesial temporal sclerosis, 767f psychosis and, 733f, 768f from right hippocampal sclerosis, 844f–845f right neocortical, 14- and 6-Hz positive spike discharge, 99f temporal intermittent rhythmic delta activity in, 372f Temporal lobe, in nocturnal hypermotor seizures, 315f Temporal lobe tumor ganglioglioma ictal slow DC shift in, 800f left temporal, 754f–756f orbitofrontal-mesial, temporal intermittent rhythmic delta activity in, 757f right mesial-posterior, in temporal lobe epilepsy, 759f Temporal occipital tumor, left
asymmetric photic response with, 299f polymorphic delta activity and sharp wave with, 326f, 750f Temporal sawtooth waves, temporal theta bursts with, 22f, 218f, 221f Temporal sharp wave, in migraine, 820f Temporal spikes in focal epilepsy, 688–689 in frontal epilepsy, 688–689 Temporal theta bursts, 202, 215f, 218f–222f delta brushes with, 220f overview of, 218f–219f with sharp theta on occipital of prematures, 215f with temporal sawtooth waves, 22f, 218f, 221f with temporal sharp transients, 218f Thalamic calcification, lateralized PDA during arousal in left hemisphere with, 306f Thalamic heterotopia childhood absence epilepsy with electrical status epilepticus during slow sleep with, 636f right, in unilateral alpha attenuation, 275, 294f Thalamocortical circuit lesions alpha attenuation from, 294f alpha rhythm attenuation and photic response with, 300f, 306f alpha rhythm with, 287f on sleep spindles, 309f Thalamocortical circuit, on alpha rhythms, 293f Thalamocortical neurons, spindle bursts from, 319f, 320f Thalamus alpha rhythm from, 293f atrophy and calcification of, asymmetric photic response with, 275, 300f sleep spindles from, 309f, 310f, 320f Thalamus lesions alpha attenuation from, 294f anteroventral on alpha rhythm, 301f focal, on alpha rhythm, 288f on sleep spindles, 305f Theta diffuse, in myoclonic astatic epilepsy, 410f, 640f with generalized nonepileptiform activity, 394 midline rhythm, 5, 78f
887
Theta (continued) rhythmic in herpes simplex encephalitis, sharply contoured, 826f monorhythmic with beta attenuation, in right parietal focal cortical dysplasia, 324f in Rett syndrome, diffuse, 412f in Rett syndrome, in central vertex with lowvoltage background, 822f Theta coma, 394 irreversible, 15 min before death, from anoxic encephalopathy, 508f–509f prognosis in, 508f reversible, from sedative after nonconvulsive status epilepticus, 507f rhythmic, 394 Théta pointe alternant, 203–204, 261f, 262f in benign familial neonatal convulsion, 261f, 689, 692f in benign neonatal nonfamilial convulsion, 262f, 690 Theta slowing diffuse with central-parietal predominance, 409f with slow background activity, from lamotrigine, 411f with focal cortical dysplasia, right mesial temporal, 322f right posterior temporal, with posterior reversible leukoencephalopathy, 323f Third rhythm, 7, 107f 3-Hz spike-and-wave discharges, in absence epilepsy, 138f Tonic seizures. See specific types Toxic encephalopathy, generalized nonepileptiform activity in, 389 Toxoplasmosis congenital, positive temporal sharp waves in, 244f HIV with, polymorphic delta activity in, 334f Trace alternant, 202, 224f–225f Tracé discontinu, 201, 205f–207f, 211f with interhemispheric hypersynchrony, 206f with severe hypoxic ischemic encephalopathy, 205f, 207f vs. trace alternant, 224f Transients. See specific types
888
Transient unilateral attenuation of background activity, during sleep, 202, 235f, 236f Transmantle dysplasia, focal. See Focal transmantle dysplasia Transmissible subacute spongiform encephalopathy (TSSE), 473 Traumatic brain injury (TBI) anoxic encephalopathy from, severe, burstsuppression in, 459f anoxic encephalopathy S/P cardiac arrest from, with cardiac asystole, 670f–672f focal polymorphic delta activity in, 356f genu abnormalities in, 454f splenium abnormalities in, 454f Todd paralysis from, focal PDA and alpha attenuation in, 275, 295f Tremor artifact, 127, 174f–175f in 9-year-old with whole-body shaking, 174f in 10-year-old with essential tremor, 175f Tricyclic antidepressants, excessive beta activity with, 397f Triphasic complexes of large amplitude, hemimegalencephaly from linear sebaceous nevus syndrome in, 809f, 841f Triphasic waves (TWs), 389, 393–394, 427f–429f, 471, 475, 524f clinical correlations of, 427f definition of, 427f in dialysis encephalopathy, 428f, 524f with generalized nonepileptiform activity, poor prognosis in, 389 in hepatic encephalopathy, 427f vs. nonconvulsive status epilepticus, 429f in nonconvulsive status epilepticus, from ifosfamide, 429f Trisomy 21, hypsarrhythmia with increased interhemispheric synchronization and symptomatic late onset epileptic spasm with, 546f Tuberous sclerosis complex (TSC), 688, 715f–721f in 4-year-old with mental retardation and intractable epilepsy, 719f–720f in 12-year-old with mental retardation and intractable epilepsy, 717f–718f
apneic spell in, from arrhythmia with cardiac rhabdomyoma, 721f frontal lobe epilepsy with supplementary sensorimotor area seizures in, 720f ictal scalp vs. subdural EEG in, 717f orbitofrontal seizure from, with secondary bilateral synchrony, 715f overview of, 716f Wolff-Parkinson-White syndrome with, 721f
V Variants, normal and benign, 1–122. See also specific variants 6-Hz spike-and-wave bursts (phantom spike-wave), 6, 104f–105f alpha rhythm or posterior dominant rhythm, 1–2, 8f–12f alpha and mu rhythm, 11f, 12f alpha in subdural EEG, 9f asymmetry in, 2, 22f in Bancaud phenomenon, 2 beating, 2, 10f distribution in, 2 frequency in, 1 low-voltage background activity, 18f paradoxical alpha rhythm in, 2 regulation in, 1 squeak effect in, 2, 8f, 23f in subdural EEG, 8f voltage in, 1 benign sporadic sleep spikes, 6, 102f beta activity, 2 fast alpha variant, 2, 15f–17f 14- and 6-Hz positive spike discharge, 6, 90f–99f, 439f–443f, 519f frontal arousal rhythm, 5, 79f–83f H-response, 4, 39f–41f hypnagogic hypersynchrony, 5, 70f–73f hypnic myoclonia (hypnagogic jerks), 5, 74f–77f K complexes, 4, 52f–55f during arousal, subdural EEG monitoring of, 53f early (16 week CA), 55f lambda waves, 3, 24f–26f midline theta rhythm, 5, 78f
mitten patterns, 5, 66f–69f mu rhythm, 7, 114f–122f needle-like spikes of blind, 4, 42f–44f, 686 occipital slow transients, 3–4, 36f–38f photomyogenic (photomyoclonic) response, 7, 110f–113f positive occipital sharp transients of sleep, 3, 27f–32f posterior slow waves of youth, 3, 19f–21f posterior slow-wave transients with eye movements, 3, 32f–35f rhythmic midtemporal discharges, psychomotor variant, 5–6, 84f rhythmic temporal rhythm (physiologic), 7, 107f rhythmic temporal theta bursts of drowsiness, 5–6, 84f–89f sleep spindles, 4–5, 56f–65f sleep stages drowsiness, 4, 45f–46f REM sleep, 4, 51f, 129f stage 2 sleep, 4, 47f–48f stage 3 sleep, 4, 49f stage 4 sleep, 4, 50f slow alpha variant, 2, 13f–14f small sharp spikes, 6, 103f small sharp spikes or benign epileptiform transients of sleep, 6, 100f–103f third rhythm (independent temporal alphoid rhythm), 7, 107f wicket waves, 6–7, 106f, 108f, 109f Vasogenic edema, in corpus callosum and diffuse axonal injury, background asynchrony with, 454f Venous sinus thrombosis focal clonic seizure with, in newborn, 248f intracerebral hemorrhage from, positive temporal sharp waves in, 240f Ventilator artifacts, 127, 182f high-frequency, 128, 190f, 266f Ventriculoperitoneal shunt with congenital hydrocephalus, symptomatic focal epilepsy from, 275, 290f epilepsy and, 351f problems with, 290f Vertex waves, cerebral structure on, 305f
Very low-voltage background activity, in hypoxic ischemic encephalopathy, 265f, 517f Visual evoked potential (VEP), in hydranencephaly, 348f Voltage asymmetry, 302f Voltage attenuation, diffuse, EEG reactivity in coma with, 482f Voltage attenuation, focal, 275–276, 345f–360f in encephalomalacia from neonatal bacterial meningitis, 349f hemispheric, 349f hemispheric background depression in, from traumatic diffuse left hemispheric encephalomalacia, 347f lateralized electrodecrement in, from intrauterine stroke, 353f periodic lateralized epileptiform discharges in and epilepsia partialis continua, from hydrocephalus due to intraventricular hemorrhage, 350f from hydrocephalus with ventriculoperitoneal shunt infection, 351f symptomatic focal epilepsy with, from hydranencephaly, 348f unilateral attenuation of background activity in, in Sturge-Weber syndrome, 352f volume conduction in, from left functional hemispherectomy, 346f Volume conduction, after left functional hemispherectomy, 346f Volume conduction theory, EEG application of, 346f, 464f
W Watershed infarction, with cardiomyopathy, bilateral independent lateralized epileptiform discharges in, 489f Western equine encephalitis, neonatal, occipital lobe epilepsy with, 823f West syndrome, 529–531, 542f–574f Aicardi syndrome and with focal cortical dysplasia, 568f MRI in, 565f “split brain” EEG in, 566f asymmetric epileptic spasms in
after right hemispherectomy, 564f focal cortical dysplasia from cobalamin C deficiency in, 556f–559f focal cortical dysplasia in, 550f cerebral maturation in, 531 development on seizure expression in, 531 EEG evolution in, 531 epidemiology of, 529 epileptic spasms in asymmetric, supplementary sensorimotor area activation in, 574f trigger for, 559f focal transmantle dysplasia in, focal low-voltage fast activity and slow DC shift in, 567f generalized slow wave transient in, 338f hemispherectomy for, neuroimages before, 570f hypsarrhythmia in, 530, 542f, 543f with consistent focus of abnormal discharge, 531 disappearance of, 530 with increased interhemispheric synchronization, 530–531 with increased interhemispheric synchronization and symptomatic late onset epileptic spasm, 546f and infantile spasms with diffuse cerebral atrophy from severe hypoxic ischemic encephalopathy, 542f with periventricular leukomalacia, 543f transient alterations of, 530 variants of, 530 hypsarrhythmia in, asymmetric, 530 with asymmetric infantile spasms, 545f with asymmetric infantile spasms, and consistent focus of abnormal discharge, 548f with asymmetric infantile spasms, and increased interhemispheric synchronization, 547f contralateral, 569f with cystic encephalomalacia from intrauterine stroke, 544f EEG normalization after hemispherectomy with, 563f with herpes simplex encephalitis, 561f–563f intraventricular hemorrhage and left cerebral hemiatrophy in, 560f
889
West syndrome (continued) hypsarrhythmia variant in consistent focus of abnormal discharge in, 557f with focal cortical dysplasia from cobalamin C deficiency, 556f–559f ictal patterns in, 531 asymmetric, 531 clinical events and, 531 infantile spasms in, 542f, 543f with diffuse electrodecremental pattern and lowvoltage fast activity, 555f from focal cortical dysplasia, 531 with unilateral paroxysmal fast activity, 562f infantile spasms in, asymmetric contralateral EEG normalization after left functional hemispherectomy in, 571f with diffuse electrodecrement and focal onset, 549f interictal patterns in, 530
890
ipsilateral rhythmic theta activity in, with left hemisphere malformation of cortical development, 572f from neurofibromatosis type 1, 554f neuropathology of, 530 from Ohtahara syndrome, 529, 537f spasm control in, 531 spasms in, 530 spike-wave activity in, 530 subdural EEG during asymmetric epileptic spasms in, with high-frequency oscillations, 552f subdural vs. scalp EEG during epileptic spasm clusters in, 573f symptomatic, 529–530 asymmetric epileptic spasm in, with left mesial fronto-parietal focal cortical dysplasia, 553f high-voltage, frontal-dominant generalized slow wave transient in, with asymmetric epileptic spasm, 551f
White matter degenerative diseases, excessive beta activity in, 390 Wicket-wave like waveform in left frontal-temporal infarction, 108f in nonaccidental trauma, 108f Wicket waves, 6–7, 106f, 108f, 109f
Y Youth waves, 19f–21f, 275, 280f–283f activated with eye closure, 283f attenuated with eye opening, 282f
Z Zip-like electrical discharges (zips), 203, 251f–253f in 30-day-old with pulmonary hypoplasia, diaphragmatic hernia, and severe HIE, 251f–252f with focal clonic seizure, 253f ictal EEG activity in, 252f
