Epileptiform Activity, Seizures, and Epilepsy Syndromes
Linda M. Selwa
Identification of interictal epileptiform activity (IEA), seizures, and the specific EEG patterns that accompany epilepsy syndromes remains an electroencephalographer’s most critical task. Fortunately, IEA and seizures are also often easily distinguished and stand out in sharp contrast from background EEG frequencies. This chapter will focus on providing practical guidance in recognizing these patterns and understanding their significance in clinical application.
The definition of epileptiform activity is given in Chatrian’s glossary of terms as “distinctive waves or complexes, distinguished from background activity and resembling those recorded in a proportion of human subjects suffering from epileptic disorders.”1 These waves or complexes can appear as isolated focal spikes or sharp waves, generalized polyspike, spike-and-wave, or paroxysmal fast activity and sometimes as abrupt rhythmic evolution of the background that heralds seizures.
To recognize a wave as epileptiform, the pattern must include a wave that stands out from the background in frequency, amplitude, and/or field. Most often, epileptiform activity is distinguishable by all of these characteristics. Often, the sharpness of the wave at its maximum amplitude provides the first clue to its differentiation from the background. If there is an isolated wave with a peak that is sharper than the baseline background, the next helpful criteria are whether the amplitude is also distinctive and whether there is a field of distribution that suggests a focal or more diffuse surrounding area of positivity or negativity.2 An after-going slow wave with the same field of distribution is also very helpful in identifying epileptiform activity (see Fig. 9.1). To classify the epileptiform activity as a spike, the duration of the waveform is, by convention, between 20 and 70 ms. Epileptiform activity that lasts from 70 to 200 ms is referred to as a sharp wave (or sharp and slow-wave complex if followed by a delta frequency wave).3 The terms generalized polyspike-and-wave and spike-and-wave activity refer to discharges with a diffuse field of distribution and after-going delta wave that are often repetitive. These are usually also described by identifying the rate of the frequency of repetition, for example, 3.5-Hz generalized spike-and-wave or fast (4 or more Hz spike-andwave) or slow (2.5 or less Hz spike-and-wave).
More recently, a number of other patterns seen in intracranial recordings have been associated with possible localizing value for the ictal epileptogenic zone, but their importance and relevance are not clearly understood.4 High-frequency oscillations (HFO) and fast (FR) or very fast ripples (VFR) are designations for 80- to 250-Hz, 250- to 500-Hz, or 500- to 1000-Hz activity, respectively, that are seen at the cortical surface in patients with epilepsy but have also been seen in other physiologic conditions (including memory retrieval) and seem to shift location dependent on cortical activity in a way that gives them only equivocal usefulness in patients with epilepsy.5,6 Further studies may soon elucidate the hallmarks that distinguish normal from epileptiform HFOs and FRs, but it seems VFR are more closely associated with seizure onset than slower-frequency discharges.7
Many patterns of traditionally defined epileptiform activity are associated with a specific epilepsy syndrome, however, not all activity that meets the criteria to be considered epileptiform is associated with epilepsy or indeed any clinical abnormality.
EPILEPTIFORM ACTIVITY IN NORMAL EEGS (BENIGN VARIANTS)
Vertex Sharp Waves in Children
The onset of sleep is generally heralded by the appearance of vertex sharp waves (see Chapter 18, Sleep and Polysomnography). Vertex waves are generally diphasic sharply contoured activity with a maximum amplitude at C3 and C4, lasting up to 200 ms. The highest amplitude (150-250 µV) initial deflection is surface negative and is followed by a generally slower and lower-voltage surface-positive wave with the same distribution. In young children, vertex waves appear by 8 weeks of age and often have a slightly larger field through early childhood,
involving both frontocentral areas. Particularly in children aged 2 to 5, these waves can become quite sharp, occur repetitively, and can appear in more than a single morphology (see Fig. 9.2). Careful evaluation of the field, which will always be symmetric and synchronous, can be helpful in identifying the transients as vertex activity.
involving both frontocentral areas. Particularly in children aged 2 to 5, these waves can become quite sharp, occur repetitively, and can appear in more than a single morphology (see Fig. 9.2). Careful evaluation of the field, which will always be symmetric and synchronous, can be helpful in identifying the transients as vertex activity.
 FIGURE 9.1. A. Left anterior temporal spike in a 25-year-old with epilepsy. Note the duration of 60 ms. B. Left temporal sharp wave in a 25-year-old with temporal lobe epilepsy. Note the duration of over 100 ms. Sensitivity 70 µV/cm. |
 FIGURE 9.2. Sharp vertex waves in a 7-year-old with ADD and headaches. Note multiple different vertex morphologies, which is normal for this age. |
Sharp Transients in Neonates
During gestational and neonatal developmental maturation, scattered sharp transients occur in the normal EEG tracing during quiet sleep (see also Chapter 7, Normal EEG in Newborn). These transients begin to appear at about 34 weeks of gestation and are often most common in both frontal regions independently. They are usually negative in surface polarity and have a duration of 150-200 ms and a low amplitude (50-100 µV); they occur most often in frontal distributions but are seen occasionally over other areas. These sharp transients reach a maximum between 35 and 36 weeks of gestation and should be dissipating by term, with occasional sharp transients persisting up to the 4th week of life during quiet sleep.8
Lambda Waves
While a normal subject is visually scanning a pattern, a train of occipital biposterior sharp waves can occur called lambda waves. These waves are usually biphasic, with an early positive component, followed by an occipital negativity (Fig. 9.3). Lambda waves are usually repetitive but can be attenuated by changes in illumination changes in fixation or eye closure. They are more common in older children and adolescents than in adults and are occasionally seen unilaterally, depending on the level of asymmetry in stimulation. They can be most easily distinguished from epileptiform activity by demonstrating their dependence on visual scanning.
 FIGURE 9.3. Lambda waves in occipital derivations in a 21-year-old during reading. Note the large voltage transient associated with eye closure followed by the alpha “squeak” effect. |
POSTS and BETS in Sleep
During light nonrapid eye movement (NREM) sleep, positive occipital sharp transients of sleep (POSTS) are often seen and can appear quite sharp in children and adolescents (Fig. 9.4). These waves are triangular with maximum positivity at the occipital electrode and usually repeat intermittently with a frequency of between 0.5 and 5 Hz. They can occur synchronously or independently over the two hemispheres and are usually moderate to high amplitude (70-150 µV).
 FIGURE 9.4. POSTS (positive occipital sharp transients of sleep) recorded during stage 2 NREM sleep in a 52-year-old with spells. Sensitivity 70 µV/cm. |
Another epileptiform pattern commonly seen in drowsiness and light sleep, most commonly in adults, are the 50-µV spikes referred to as benign epileptiform transients of sleep (BETS) or small sharp spikes (SSS, Fig. 9.5). They are usually quite brief and rarely longer than 50 ms and usually consist of an abrupt diphasic spike with a broad sloping potential field that can involve both hemispheres. In the largest study of benign variants to date, these were by far the most common discharges, seen in 1.85% of over 35,000 records.9 They usually recur during sleep in several morphologies and distributions and are best seen in montages with large
interelectrode distances. They can be distinguished from epileptiform activity because of the absence of after-going slow waves, absence of background disruption, and tendency to disappear in deeper stages of sleep. BETS may occur in up to 20% of the normal population.10 A low-resolution electromagnetic topography study localized BETS to a transhemispheric scalp distribution in the insula and the posterior quadrant, which helps to explain the diffuse hemispheric field usually seen at the scalp.11
interelectrode distances. They can be distinguished from epileptiform activity because of the absence of after-going slow waves, absence of background disruption, and tendency to disappear in deeper stages of sleep. BETS may occur in up to 20% of the normal population.10 A low-resolution electromagnetic topography study localized BETS to a transhemispheric scalp distribution in the insula and the posterior quadrant, which helps to explain the diffuse hemispheric field usually seen at the scalp.11
 FIGURE 9.5. BETS (benign epileptiform transients of sleep) in a 54-year-old. Note the diffuse field and rapid small spike in drowsiness. |
Wicket Spikes
In the mid temporal regions, the most common normal pattern that must be differentiated from focal sharp waves generated by an epileptogenic zone are wicket spikes (Fig. 9.6). These sharp waves are usually midtemporal, archiform, or wicket-shaped and often occur in short trains or clusters. They repeat at frequencies of 6-11 Hz; are
monophasic, 50-200 µV; and may actually be a fragment of temporal alpha activity in adults. Wicket spikes occur most frequently in drowsiness or sleep and can be seen in each temporal region independently. When they occur singly, the most reliable way to distinguish wicket spikes from the epileptiform activity associated with temporal lobe epilepsy (TLE) is that wicket spikes are not associated with an after-going slow wave and do not disrupt the normal background activity present in this region.12
monophasic, 50-200 µV; and may actually be a fragment of temporal alpha activity in adults. Wicket spikes occur most frequently in drowsiness or sleep and can be seen in each temporal region independently. When they occur singly, the most reliable way to distinguish wicket spikes from the epileptiform activity associated with temporal lobe epilepsy (TLE) is that wicket spikes are not associated with an after-going slow wave and do not disrupt the normal background activity present in this region.12
 FIGURE 9.6. A. Wicket spikes and rhythmic midtemporal theta of drowsiness (RMTD, also known as psychomotor variant) in a normal 9-year-old with headaches. |
 FIGURE 9.6. (Continued) B. More subtle wicket spikes in a 22-year-old with headaches. Sensitivity 70 µV/cm. |
14- and 6-Hz Positive Bursts and 6-Hz (Phantom) Spike-and-Wave
During stage 2 sleep in adolescents, trains of 14- or 6-Hz activity can occasionally be seen over the posterior temporal regions lasting from 0.5 to 1 second. These bursts are arch-shaped with alternating positive spiky waveforms that can occur synchronously or independently. Recognition of the characteristic combination of frequencies establishes this as the previously defined benign variant.
A 6-Hz low-amplitude spike-and-wave activity (also referred to as phantom spike-and-wave) also occurs most commonly in light sleep in adolescents but is also seen in adults. The spike is very low amplitude and followed by a more prominent diffuse slow-wave component. Bursts can be asymmetric or anteriorly or posteriorly dominant. Similar morphologies occurring in males in wakefulness, sometimes at slightly lower frequencies, have been associated in some cases with epilepsy, but the low-amplitude discharges occurring in sleep have no clear clinical significance. Two acronyms are sometimes used to describe this distinction: WHAM (waking, high-amplitude spike [>45 µV], anterior, male), which is associated with epilepsy, especially when the discharge involves high-amplitude spikes and slightly slower spike frequency below 5-6 Hz and persists during deep sleep, and FOLD (female, occipital, low-amplitude spike, drowsy), which is not associated with epilepsy.
REVIEW
9.1: Posteriorly dominant positive triangular sharp waves that occur during visual scanning in normal patients are called:
a. POSTS
b. BETS
c. Lambda waves
d. Wicket spikes
View Answer
9.1: c. Lambda waves are triangular and occur in awake patients associated with visual fixation. POSTS are similar in morphology but occur in light sleep. BETS are brief, spiky with a broad electric field, seen in sleep, and wicket spikes are a sharply contoured temporal rhythm. None of these waveforms is associated with seizures.
9.2: Sharp transients during sleep in neonates should disappear by:
a. One year
b. Six months
c. Term
d. One month
GENERAL CLINICAL SIGNIFICANCE OF IDENTIFICATION OF IEA
Defining the Epilepsy Syndrome
Between 12% and 50% of EEGs show epileptiform activity after a single seizure.13 This yield is substantially increased (51%) if the first EEG can be done within 24 hours of the event compared with later studies (34%).14 Serial EEGs in patients might also increase the yield: in patients with defined epilepsy syndromes, the incidence of IEA can increase from 50% after one EEG to as much as 84% overall after three EEGs.15 The duration of the recording may also be important: in 46 patients with established epilepsy, 37% had IEA within the first 20 minutes, but 89% had positive findings after 24 hours of recording.16,17 The occurrence of epileptiform activity also seems to be age-dependent—older patients seem to have less focal and generalized epileptiform activity than children.18,19,20 In nearly all studies, IEA on EEG after a first seizure predicts a significantly higher risk of seizure recurrence.21 Some authors also feel that the frequency of focal IEA in early EEGs may be somewhat helpful in determining which patients will ultimately have refractory epilepsy.22
In a few syndromes, the EEG is almost always diagnostic—absence epilepsy, benign epilepsy with centrotemporal spikes (BECTS, formerly known as rolandic epilepsy), and juvenile myoclonic epilepsy (JME)—the likelihood of a normal EEG is <10%. West syndrome and Landau-Kleffner syndrome (see later discussion) are typically defined by their EEG pattern at presentation. Activation procedures are particularly helpful to elicit IEA in the primary generalized epilepsies. Hyperventilation activates generalized spike-and-wave in absence in 50%-80% of cases, and photic stimulation increases its incidence by 18%. Photic stimulation is most likely to activate the polyspike-and-wave patterns of JME, with a photosensitivity rate of about 30%.
During sleep, the prevalence of slow spike-and-wave in Lennox-Gastaut syndrome (LGS) increases, as does the number of polyspike discharges and fragments, while absence epilepsy discharges occur less often and become slow and irregular in most cases. BECTS discharges occur much more frequently in drowsiness; indeed up to 30% of patients have their IEA only in light sleep. Childhood occipital epilepsy is also activated by both eye closure and NREM sleep.
In general, the most effective strategy for capturing IEA after a first seizure is to record as soon as possible after the event, use activation procedures, encourage sleep, and perform a longer or repeated recording in cases where the information about IEA would be most likely to be clinically useful (eg, those without structural lesions, without precipitating factors, or with possible prior seizures).
Specificity of IEA in Diagnosis of Epilepsy
Another way to examine the clinical relevance of IEA during an EEG is to look at the predictive value of finding IEA for the subsequent diagnosis of epilepsy.
Patterns of IEA most likely to be associated with seizures regardless of the chief complaint are 3-Hz spike-and-wave, focal anterior and midtemporal spikes, localized frontal spikes, and pseudoperiodic epileptiform discharges.23 The likelihood that seizures will occur in patients with anterior temporal spikes is over 90% in several series, and temporal intermittent rhythmic theta activity is associated with seizures in nearly 80%. Midline spikes in children have an 83% correlation with epileptic seizures.24 A frontal lobe spike carries a likelihood of epilepsy of about 75%.
Patterns of IEA most likely to be associated with seizures regardless of the chief complaint are 3-Hz spike-and-wave, focal anterior and midtemporal spikes, localized frontal spikes, and pseudoperiodic epileptiform discharges.23 The likelihood that seizures will occur in patients with anterior temporal spikes is over 90% in several series, and temporal intermittent rhythmic theta activity is associated with seizures in nearly 80%. Midline spikes in children have an 83% correlation with epileptic seizures.24 A frontal lobe spike carries a likelihood of epilepsy of about 75%.
Between 0.5% and 2% of the population may have IEA without ever developing seizures, with the higher end of the range often representing those hospitalized for psychiatric or neurologic illnesses.25 In one series of patients with IEA without previous seizures or diagnosis of epilepsy, 73% had acute or progressive cerebral disorders at the time of the abnormal EEG.26 The types of IEA patterns least associated with epilepsy include a photoparoxysmal response, occipital generalized spike-and-wave, BECTS, and occipital spikes. If centrotemporal spike complexes are seen, the incidence of the full-blown disorder with clinical seizures is 40%.27 The frequency of epilepsy in those with occipital spikes is <50% in most series.
Prognosis of Epilepsy Based on EEG
In patients with known epilepsy syndromes, EEG has value in predicting long-term seizure remission. In mesial TLE, unilateral IEA is clearly correlated with better outcome after surgery than bilateral IEA, and to some extent, the frequency of IEA before surgery may also correlate with likelihood of remission after surgery.28 More importantly, the persistence of mesial temporal IEA on postoperative recordings at 3 months and 1 year are predictive of seizure recurrence after anterior temporal lobectomy. In patients in whom some medications were withdrawn after a seizurefree interval, persistence of temporal IEA at 1 year postsurgery increased the likelihood of seizure recurrence by 2.6 times.29 This predictive value may be increased further by repeated studies at 2 and 3 years.
Ictal patterns can also predict not only the localization of the epileptogenic zone for surgery but also the likelihood of remission. For instance, after placement of stereo EEG electrodes, the presence of low-voltage fast activity in the ictal pattern seen at the onset zone predicts a better surgical outcome. Bursts of polyspikes followed by a low-voltage fast activity predicted an 83% seizure-free outcome, whereas sharply contoured alpha or theta patterns with intracranial electrodes predicted only a 38.5% seizure-free outcome.30 VFR, oscillations between 500 and 1000 Hz, may also have significant prognostic value in intracranial recordings.7
In generalized epilepsies, valproic acid (Depakote) reduces generalized IEA in 76% of patients and reduces the photoparoxysmal response in 25%. In absence epilepsy, differences in EEG findings can correlate with likelihood of initial seizure remission, likelihood of status epilepticus, and the rate of long-term need for medications, with more atypical findings having a significantly worse prognosis.31
REVIEW
9.3: After a single unprovoked seizure, EEG will be most helpful in defining a possible epilepsy syndrome if:
a. EEGs are recorded more than 2 weeks after the initial seizure.
b. Patients age is older than 60.
c. Recorded in children with probable absence seizures.
d. The recording does not include any sleep.
View Answer
9.3: c. Children with absence epilepsy have a high likelihood of a diagnostic EEG, particularly associated with hyperventilation.
9.4: Which IEA finding is most likely to be associated with clinical epilepsy?
a. Anterior temporal spikes
b. Generalized fragments of 3-Hz spike-and-wave
c. Centrotemporal transients in adolescents
d. Photoparoxysmal discharge
View Answer
9.4: a. Anterior temporal spikes are associated with clinical temporal lobe epilepsy in over 90% of cases. 3-Hz spike-and-wave is also highly predictive of absence epilepsy.
EPILEPTIFORM ACTIVITY AND SEIZURES IN SPECIFIC EPILEPSY SYNDROMES
Absence Epilepsy (Childhood and Juvenile)
The clinical syndrome defined by the International League Against Epilepsy (ILAE) as childhood absence epilepsy (also called pyknolepsy in the past) refers to a seizure disorder with only brief, frequent absence seizures (4 seconds to 1 minute, 10-100 per day) with an age of onset between 4 and 8 years.32,33 This syndrome generally remits in late adolescence and by definition does not include other seizure types, such as GTC or myoclonus. The incidence is clearly genetic, and in some families, calcium channel genes seem to play an important role.34 The incidence of this type of epilepsy is relatively low, comprising 2%-10% of epilepsy in children.35 Juvenile absence epilepsy, on the other hand, begins between 9 and 13 years, often includes morning GTC and sometimes myoclonus, and has a much lower remission rate, with 44%-55% persisting into adulthood.36 EEG findings also differ somewhat between the two types.
Interictal EEG
The interictal EEG of a patient with typical childhood absence epilepsy generally has a normal background rhythm, although some authors report mild diffuse slowing in a small fraction of cases. The classical finding in absence epilepsy is the interictal and ictal 3-Hz spike-and-wave discharge (Fig. 9.7A-C). This diffuse,
symmetric discharge begins abruptly, with a single or diphasic sharp wave, most often at a 3.5- to 4-Hz frequency, and slows to 2.5-3 Hz prior to its abrupt cessation.37 Typically, these discharges have a frontal maximum, but they may also appear centrally or bioccipitally. These discharges have been described as “egg and dart” and can be seen as a sharp column and high arch. There is no suppression of the background after the discharges. The most important feature to distinguish the typical spike-and-wave of absence from other generalized patterns is the very reliable frequency, the single or diphasic spike and the completely synchronous onset of the paroxysm.
symmetric discharge begins abruptly, with a single or diphasic sharp wave, most often at a 3.5- to 4-Hz frequency, and slows to 2.5-3 Hz prior to its abrupt cessation.37 Typically, these discharges have a frontal maximum, but they may also appear centrally or bioccipitally. These discharges have been described as “egg and dart” and can be seen as a sharp column and high arch. There is no suppression of the background after the discharges. The most important feature to distinguish the typical spike-and-wave of absence from other generalized patterns is the very reliable frequency, the single or diphasic spike and the completely synchronous onset of the paroxysm.
 FIGURE 9.7. A. 3-Hz spike-and-wave discharge using AP bipolar montage in a 17-year-old with juvenile absence epilepsy, including occasional generalized seizures. This discharge occurred during photic stimulation (stimulus trace not shown). Sensitivity 300 µV/cm. |
 FIGURE 9.7. (Continued) B. Same 3-Hz spike-and-wave discharge as 7A, now seen in average reference montage. Sensitivity 300 µV/cm. |
 FIGURE 9.7. (Continued) C. A longer 3-Hz spike-and-wave discharge after hyperventilation in the same patient, now in ipsilateral ear reference montage. The patient was amnestic for an item presented during the discharge. Sensitivity 320 µV/cm. |
In 15%-30% of young patients with absence epilepsy, the interictal EEG may also contain occipital intermittent rhythmic delta activity (OIRDA) at 3-4 Hz,38,39 which is a high-amplitude 3-Hz paroxysmal synchronous bilateral discharge without sharp waves. OIRDA is correlated with increased sensitivity to hyperventilation. Some have even reported rare focal centrotemporal spikes, like those seen in BECTS in some patients.40 The typical 3-Hz discharges become fragmented and brief during sleep and are often suppressed during rapid eye movement (REM). Hyperventilation may increase the rate of discharges in up to 30% of patients and about 18% may be photosensitive.41 One-third to one-half of patients treated with antiepileptic drugs (AEDs) completely attenuate these discharges.41,42,43
In juvenile absence epilepsy, discharges are generally associated with an initial polyphasic sharp wave and a somewhat more rapid repetition of sharp and slow waves at 4-6 Hz (Fig. 9.8A and B). The frequency and distribution of the generalized discharges are more irregular, and there is a lower incidence of OIRDA and photosensitivity in this population.44 Prognosis of the syndrome can be monitored to some extent by the response of the generalized discharges to medications.45 In 5% of patients with absence epilepsy, generalized paroxysmal fast discharges can be seen in slow-wave sleep, usually brief, medium voltage, posterior predominance, and most often in girls. The presence of GPFA may be a marker of greater likelihood of lifelong need for medications.46
Ictal Findings
Defining an ictal event may be more difficult than in other syndromes, as it has been demonstrated that reaction time is delayed both in short and longer paroxysms of 3-Hz spike-and-wave.47 Clinically recognized typical absence events usually last longer than 3 seconds, with an average of 10 seconds, and as many as 92% demonstrate some type of retained slowed behavior, clonic movement, or automatisms.48 Normal behavior resumes quite abruptly after the ictal events end. In one study of pretreatment EEGs in 445 patients with absence epilepsy, the average duration of recorded seizures was 10.8 seconds. The authors found that the longer the baseline seizures, the higher the rate of response to medications. Patients with longer seizures (but not those with more seizures) clearly had more inattention during the EEG but unexpectedly had a significantly better seizure-free response to treatment.49
During generalized tonic-clonic seizures in those with juvenile absence, the seizure begins with a diffuse low-amplitude beta frequency activity and progresses to slower repetitive complexes of spike-and-wave activity during the clonic portion of the event. After the generalized seizure, all frequencies are symmetrically suppressed.
Benign Epilepsy With Centrotemporal Spikes
BECTS is one of the most common childhood epilepsy syndromes and has the best prognosis, with seizures disappearing before age 16-18 in virtually all patients.50,51
Clinically, the syndrome most often presents between ages 4 and 10, with infrequent nocturnal seizures, often characterized by clonic facial twitching, pharyngeal spasms, and interruption of speech with occasional generalization. Few patients have more than three seizures. In some patients, during the phase where the EEG is significantly active, there may be subtle language difficulties.52 The predisposition to the syndrome and to the interictal EEG findings is significantly genetically determined: up to 30% have relatives with similar EEG findings.53
Clinically, the syndrome most often presents between ages 4 and 10, with infrequent nocturnal seizures, often characterized by clonic facial twitching, pharyngeal spasms, and interruption of speech with occasional generalization. Few patients have more than three seizures. In some patients, during the phase where the EEG is significantly active, there may be subtle language difficulties.52 The predisposition to the syndrome and to the interictal EEG findings is significantly genetically determined: up to 30% have relatives with similar EEG findings.53
Interictal EEG
The background in patients with BECTS is normal for age. Particularly during drowsiness, the record is punctuated by frequent, repetitive, diphasic to triphasic sharp waves with the middle negative component having the largest amplitude. The sharp wave complex is almost always followed by a lower-amplitude negative delta frequency slow wave. These sharp waves are distributed roughly equally between central (C3-C5 and C4-C6) and midtemporal (T3 or T4) derivations54 and may be unilateral, bilateral, or sometimes synchronous (Fig. 9.9A and B). These discharges are usually very stereotyped and often have a frontal positive dipole when seen on a referential montage. In 30% of patients, these discharges are seen only during sleep recordings.55 Photic stimulation and hyperventilation have no effect. In up to 15% of cases, occipital spikes or generalized spike-and-wave discharges can also be seen in recording of patients with this syndrome.56,57
Ictal Findings
Very few seizures have been captured on EEG. Reports of events recorded describe a low-voltage centrotemporal fast activity that slows and spreads before generalizing. There was no postictal slowing or attenuation after the seizure, but spikes were suppressed.58
Benign Occipital Epilepsy
Benign occipital epilepsy (BOE) has been defined by the ILAE as an idiopathic localization-related syndrome. Clinically, BOE most often presents as a young onset variant, in ages 3-5, often (˜30%) with a genetic predisposition, sometimes also known as Panayiotopoulos syndrome.59 Infrequent partial seizures occur, often at night, and the most common semiology is tonic eye deviation accompanied by emesis, evolving at times to focal or generalized motor patterns. Imaging studies and development are normal, and the prognosis for response to medication and remission by age 12 is excellent. There is a later variant, with a peak age of onset of 7-9 years, in which seizures more often present with visual hallucinations, without loss of consciousness, lasting only a few seconds, but commonly with associated postictal headache.60 The outcome is generally favorable but worse than in the early-onset form.
Interictal EEG
Electrographically, the background rhythm is normal. With closed eyes, there are unilateral or bilateral, very frequent (up to 1-3 Hz), diphasic (surface negative, then positive), high-amplitude spikes in the occipital lobe.61 There is often, but not always, an after-going slow wave. The epileptiform activity can be suppressed by eye closure and is often suppressed by visual fixation.62 Hyperventilation and photic stimulation usually have no effect on the discharges, although some patients have inhibition of spikes at high flash rates. In many patients, the interictal activity can persist long past the time the patient is clinically asymptomatic. A significant proportion of those with BOE also have generalized spike-and-wave discharges or centrotemporal spikes in their interictal EEG studies.61
Ictal Findings
Seizures begin with an ictal spike pattern of increasing frequency, evolving to theta and delta rhythms that spread anteriorly, but these seizures have been infrequently recorded.63 In one case series, two seizures were recorded, one from the left and one from the right occipital lobe, both beginning with very focal repetitive activity and rapidly generalizing to involve both hemispheres.64
Juvenile Myoclonic Epilepsy
JME is the most common idiopathic generalized epilepsy syndrome, beginning between the ages of 12 and 15 years with significant genetic linkages to chromosomes 2, 3, 5, 6, and 15.65,66 The hallmark clinical characteristic is arrhythmic uni- or bilateral myoclonic jerks with retained consciousness. These jerks can affect any extremity, although the arms may be the most frequent site. Myoclonus is reliably most common in the hours after awakening. Most patients also suffer generalized tonicclonic seizures, and roughly one-third have absence seizures. Sleep deprivation or disruption or alcohol use also tends to bring on the jerks and seizures. Myoclonus and seizures can be triggered by photic stimuli or even eye closure. JME responds very well to medications, particularly valproic acid, but the medications usually need to be continued lifelong to avoid recurrence of the seizures.
 FIGURE 9.8. A. Atypical spike-and-wave in a 12-year-old with new-onset brief seizures. Note the polyphasic components and variable frequency. Sensitivity 250 µV/cm. |
 FIGURE 9.8. (Continued) B. Atypical absence discharge in a 9-year-old with juvenile absence epilepsy. |
 FIGURE 9.9. A. Centrotemporal spikes in a 9-year-old girl with BECTS. She had two nocturnal seizures with drooling followed by secondary generalization. Sensitivity 170 µV/cm. |
 FIGURE 9.9. (Continued) B. Repetitive diphasic left centrotemporal spikes with after-going slow waves, typical for BECTS, in a normal 8-year-old girl with a single episode of ictal chewing followed by right-sided tingling and generalized tonic-clonic seizure activity. |
Interictal EEG
The background is normal. Discharges in JME are marked by polyspike-and-wave discharges, often at frequencies between 3 and 5 Hz (Fig. 9.10). In general, the frontocentrally dominant discharges are more brief and irregular than in absence and may be more fragmented with greater asymmetric emphasis. Polyspike discharges may occur without an aftercoming slow wave. Some JME patients demonstrate a more typical 3-Hz single spike-and-wave pattern, and absence seizures are more common in these patients.67
 FIGURE 9.10. Polyspike-and-wave discharge during photic stimulation and drowsiness in a 10-year-old with morning myoclonic seizures and generalized tonic-clonic seizures. Sensitivity 100 µV/cm. |
The polyspike-and-wave activity diminishes in deeper slow-wave sleep and is absent during REM sleep. Arousal from sleep is often a potent activator of discharges.
Hyperventilation also activates the spike bursts. Sensitivity to photic stimulation (spikes triggered by flashing lights) occurs in 30%-40% of JME patients, the highest rate of any epilepsy syndrome.68,69 Roughly half of patients have normalization of the EEG (disappearance of generalized spike-and-wave) on medication.70
Hyperventilation also activates the spike bursts. Sensitivity to photic stimulation (spikes triggered by flashing lights) occurs in 30%-40% of JME patients, the highest rate of any epilepsy syndrome.68,69 Roughly half of patients have normalization of the EEG (disappearance of generalized spike-and-wave) on medication.70
Ictal EEG
The EEG associated with myoclonus or atypical absence seizures usually consists of a fast spike-and-wave pattern, most often between 3.5 and 5 Hz. Myoclonic jerks occur concomitant with the polyspike discharges at a rate of 10-16 Hz,40 which are followed by a burst of 2.5- to 5-Hz spike-and-wave activity that can outlast the jerks. It is not uncommon for the jerks to recur with increasing frequency and lead up to a generalized seizure after minutes to hours.71 The mechanisms for these discharges may relate to dissociation of cortex from subcortical inhibitory structures.72
REVIEW
9.5: The syndrome with the best prognosis for remission by age 18 is:
a. Juvenile myoclonic epilepsy
b. Juvenile absence epilepsy
c. Late-onset benign occipital epilepsy
d. Benign epilepsy with centrotemporal spikes
View Answer
9.5: d. Remission of BECTS occurs in nearly all patients by the early to midteens. Late-onset BOE has slightly worse prognosis than early onset but still generally good. Juvenile absence can progress to generalized convulsive epilepsy, and JME, though often well controlled by medication, is a lifelong disorder.
9.6: Important electrographic features that define typical absence discharges include:
a. Activation during hyperventilation in over 2/3 of patients
b. Bilateral synchronous, frontally dominant 3-Hz spike-and-wave
c. Posteriorly dominant over 250-µV spike-and-wave discharges
d. Discharges that begin at 5 Hz and slow gradually to 3 Hz over 5 seconds
View Answer
9.6: b. Typical absence is marked by generalized, frontally dominant 3-Hz spike-and-wave discharges. Hyperventilation increases the rate of discharges in up to 30% of patients (not 2/3). They are not maximal posteriorly (though occipital rhythmic delta activity may be seen) and are moderate in amplitude. They may be slightly faster at onset (up to 4 Hz) and may gradually slow to 2.5 Hz.
9.7: The ictal EEG pattern in JME usually includes:
a. Progressively evolving occipital polyspikes
b. 10- to 16-Hz polyspikes followed by 2- to 5-Hz spike and slow waves
c. Unilateral posterior 3-Hz spike-and-wave that gradually generalizes
d. Generalized spike-and-wave that lasts 3-10 seconds and ends at 3 Hz
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