Classification of epileptic seizures and syndromes.

SEMINARS IN NEUROLOGY-VOLUME

10, NO. 4 DECEMBER 1990

Classification of Epileptic Seizures and Syndromes

A variety of seizures and convulsive disorders has been recognized since antiquity. Attempts at classification have been based on descriptions of phenomena as well as underlying etiologies. Tissot (1770) described childhood absence epilepsy, and Esquirol (1815) called all minor seizures petit mal.' Reynolds2 (1861) distinguished between petit ma1 epilepsy and epilepsy with generalized convulsions, and also between idiopathic epilepsy and seizures due to other causes. The distinction between focal and generalized seizures was not, however, clearly established. Hughlings Jackson3 (1874), who was far ahead of his time in recognizing seizures to be a consequence of abnormal cortical discharge, believed all seizures to be of focal origin, differing only in location and extent. A few years later, Gowers4 (188 1) attempted a classification in which epilepsies due to focal cerebral lesions were separated from those caused by nonspecific brain abnormalities. With some modifications, this basic distinction still holds true. A seizure, by which we mean an abnormal electrical discharge in the brain, may be due to a variety of cerebral irritants. Epilepsy, which is the habitual occurrence of seizures, can therefore have various etiologies even though the resultant seizures may be clinically and electrically indistinguishable. Conversely, a particular etiology may produce a variety of seizure types, depending on whether the abnormal electrical discharge is focal or generalized. Generalized seizures are defined as those in which the clinical manifestations and electroencephalographic (EEG) patterns suggest bilateral cerebral involvement. Consciousness is always impaired, and tonic-clonic motor activity is common. In contrast, focal or partial seizures are characterized by clinical and EEG abnormalities that suggest initial involvement of only one cerebral region or hemisphere. By definition, in simple par-

tial seizures consciousness is always preserved, whereas in complex partial ones it is altered or lost. Partial seizures can become secondarily generalized when a focal electrical discharge spreads to both hemispheres. Often focal motor or sensory signs are evident for many seconds before generalization, but sometimes a brief subjective aura or brief focal motor activity is the only indication of a focal onset. In primary generalized seizures, in which the abnormal electrical discharge begins diffusely, an aura is almost never present. Because the types of epilepsy are not well correlated with the types of seizures, it is necessary to devise two independent systems of classification. The Commission on Classification and Terminology of the International League Against Epilepsy publishes classifications of seizures and epilepsies Such endeavors aim that are revised peri~dically.~,~ to improve communication among researchers and clinicians by establishing a generally accepted terminology. Classification of seizures and epilepsies also serves to clarify our thoughts regarding disease entities and their etiologies, identifies fresh fields for research, and can lead to more precise therapy for particular diseases. In this article we will review the classification of epilepsy, and in that context discuss the clinical and electrographic manifestations of various seizure types.

PRINCIPLES OF CLASSIFICATION The present system of classification distinguishes first between epilepsies with generalized seizures (generalized epilepsies) and those with focal or partial seizures (localization-related, focal or partial epilepsies). Focal seizures may, however, become secondarily generalized. This distinction between generalized and focal epilepsies corresponds

Department of Neurology, Yale University School of Medicine, New Haven, and Veterans Administration Medical Center, West Haven, Connecticut Reprint requests: Dr. Thadani, Department of Neurology VA Medical Center, West Haven, C T 06516 Copyright O 1990 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.

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V M . Thadani, M.D., Ph.D., and P.D. Williamson, M .D.

CLASSIFICATION O F EPI1,EPTIC SEIZURES-THADANI,WILLIAMSON

syndrome, and single syndromes will be found to have more than one etiology. For example a glioma, depending on its location, may produce temporal or occipital lobe epilepsy; whereas an arteriovenous malformation, if it is in the temporal lobe, may result in a syndrome of temporal lobe epilepsy indistinguishable from that produced by a glioma in the same location.

CLASSIFICATION OF EPILEPSIES AND SEIZURE TYPES Adapted versions of the International Classification of Epilepsies and the International Classification of Seizures are presented in Tables 1 and 2. In this and subsequent sections we will discuss some of the more important categories. This is meant as an overview. Details about specific epilepsies will also be found in the articles dealing with epileptic syndromes and seizures in infants, children, and adults.


roughly to the one made by Gowers, although not all focal epilepsies, in the modern classification, have an underlying focal lesion. A second major distinction in the modern classification of epilepsy separates idiopathic (primary) epilepsies from those that are symptomatic (secondary) or cryptogenic. In idiopathic (primary) epilepsy no underlying cause is found, and usually the patient is asymptomatic except for seizures. A hereditary predisposition often exists, and different syndromes are defined by age of onset, clinical characteristics of the seizures, and typical EEG abnormalities. In symptomatic (secondary) epilepsy the seizures are believed to be secondary to an underlying brain disease. This may be a congenital malformation, inborn error of metabolism, trauma, anoxic injury, tumor, or any of the known causes of epilepsy. The terms primary and secondary, although used synonymously with idiopathic and symptomatic, should be avoided in the classification of epilepsy. 'They are more appropriate for generalized seizures, in which primary describes an electrical onset involving the whole brain and secondary describes an onset that begins focally but spreads diffusely. Primary generalized seizures are seen in both idiopathic and symptomatic epilepsies, and the same is true for secondarily. generalized ones. Cryptogenic epilepsies are similar to symptomatic epilepsies, except that the underlying cause is not known. As it becomes known, a cryptogenic epilepsy is reclassified as symptomatic. T h e distinction between idiopathic and symptomatic epilepsies cannot he sustained indefinitely. As the genetic basis of the idiopathic epilepsies is elucidated at a molecular level, subtle biochemical defects will doubtless become apparent. Once such defects are recognized, the distinction will not be between idiopathic and symptomatic epilepsies but between those that have a biochemical basis (with grossly normal brain structure) and those that are caused by structural lesions. Within each of these two groups, there will be some epilepsies that are inherited and others that are acquired. Similarly, the distinction between epilepsies and epileptic syndromes is unlikely to survive. At present, an epilepsy, for example childhood absence epilepsy, is regarded as a single disease with a single cause, even if the cause is not known. An epileptic syndrome, for example temporal lobe epilepsy, is a disorder characterized by seizures and a cluster of signs and symptoms that distinguish it from other syndromes. A single etiology is not implied for each syndrome. As our understanding advances, we will certainly find etiologies that may in varying circumstances produce more than one

LOCALIZATION-RELATED EPILEPSIES As shown in Table 1, localization-related epilepsies are divided into the idiopathic and the symptomatic. Most localization-related epilepsies are symptomatic, and at present only two syndromes clearly belong in the idiopathic category. These are benign rolandic epilepsy and childhood epilepsy with occipital paroxysms. IDIOPATHIC LOCALIZATION-RELATED EPILEPSIES

Benign Rolandic Epilepsy Benign rolandic epilepsy has an onset between the ages of 3 and 13 years. There is a hereditary disposition and a male predominance. Seizures are usually simple partial seizures with motor involvement of the face and arm and are often accompanied by sensory symptoms. By definition of simple partial seizures, consciousness is preserved. These seizures tend, however, to evolve into generalized tonic-clonic seizures with loss of consciousness. 'The EEG shows centrotemporal spikes and slow waves, which may alternate between hemispheres. No structural abnormality is found. T h e prognosis is good, and most cases resolve without treatment by the late teenage years7

Childhood Epilepsy with Occipital Paroxysms This syndrome is similar to benign rolandic epilepsy, except that the EEG abnormality is par-

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SEMINARS I N NEUROLOGY VOLUME 10, NUMBER 4 DECEMBER 1990 Table 1. Classification of Epilepsies* Localization-related (focal, local, partial) epilepsies and syndromes ldiopathic epilepsies a. Benign childhood epilepsy with centrotemporal spike (benign rolandic epilepsy) b. Childhood epilepsy with occipital paroxysms 1.2. Symptomatic epilepsies and epileptic syndromes a. Temporal lobe epilepsy b. Frontal lobe epilepsy c. Parietal lobe epilepsy d. Occipital lobe epilepsy e. Chronic progressive epilepsia partialis continua of childhood (Rasmussen syndrome, Kojewnikow syndrome) 1.3. Cryptogenic epilepsies (identical to the symptomatic epilepsies except that their causes are not known) II. Generalized epilepsies and syndromes 11.1. ldiopathic epilepsies a. Benign neonatal familial convulsions b. Benign neonatal convulsions c. Benign myoclonic epilepsy in infancy d. Childhood absence epilepsy e. Juvenile absence epilepsy f. Juvenile myoclonic epilepsy g. Epilepsy with generalized tonic-clonic seizures on awakening h. Other idiopathic generalized epilepsies 11.2 & 3. Symptomatic and cryptogenic epilepsies a. Infantile spasms (West syndrome) b. Lennox-Gastaut syndrome c. Myoclonic epilepsies of infancy and childhood d. Metabolic and other diseases with seizures as a predominant symptom Ill. Epilepsies not clearly focal or generalized 111.1. Epilepsies with both focal and generalized seizures a. Neonatal seizures (various etiologies) b. Severe myoclonic epilepsy in infancy c. Epilepsy with spike-wave during sleep d. Acquired epileptic aphasia (Landau-Kleffner syndrome) e. Other undetermined epilepsies 111.2. Epilepsies with seizures not clearly focal or generalized a. Epilepsy with generalized seizures originating in sleep IV. Special syndromes with situation-related seizures a. Febrile seizures b. Alcohol-related seizures c. Seizures associated with metabolic derangement (eclampsia, hyponatremia, hyperglycemia, etc) Special syndromes with seizures produced by specific stimuli (reading, music, etc) V. *Adapted from the International Classification of Epilepsies and Epileptic syndrome^.^

oxysmal spike and wave with an occipital or posterior temporal predominance. T h e seizures begin as partial seizures with visual symptoms, but may progress to hemibody motor seizures or complex partial seizures with impaired consciousness and

automat ism^.^ SYMPTOMATIC AND CRYPTOGENIC LOCALIZATION-RELATED EPILEPSIES

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Symptomatic epilepsies are frequently focal, although the seizures may secondarily generalize. Among the many etiologies are congenital structural anomalies, tumors, trauma, infection, and stroke. (The symptomatic epilepsies due to metabolic diseases are usually generalized and will be considered in subsequent sections). T h e symptomatic focal epilepsies are usually classified on the basis of anatomic localization and the predominant type of seizure. We will consider the various syndromes below.

Temporal Lobe Epilepsy T h e seizures of temporal lobe epilepsy are the archetypal complex partial (psychomotor) seizures, although complex partial seizures may have extratemporal origin. Complex partial seizures, as noted in Table 2, are defined as focal (partial) seizures during which consciousness is impaired. Typically, a seizure in temporal lobe epilepsy begins with an aura. Auras with a gastric sensation, emotional content, deja vu, and visual disturbances are common, but other sensory and autonomic symptoms may also be present. T h e seizure itself may begin with a motor arrest or motionless stare. This is ofsten followed by oro-alimentary automatisms such as lip-smacking and swallowing. Consciousness is often not initially impaired, but becomes so when the seizure spreads. More complex automatisms such as walking, drinking, and undressing may occur later in the seizure. Some temporal lobe seizures, of course, remain simple par-


I. 1.1.

CLASSIFICATION O F EPILEPTIC SEIZURES-THADANI. WILLIAMSON

Seizure T v ~ e I. Partial (focal, local) seizures A. Simple partial seizures (consciousness not impaired) 1. Seizures with motor signs (focal motor, jacksonian, postural, phonatory, etc) 2. Seizures with sensory symptoms (somatosensory, visual, auditory, olfactory, etc) 3. Seizures with autonomic symptoms or signs (epigastric sensation, diaphoresis, flushing, piloeiection, pupillary dilation) 4. Seizures with psychic symptoms (These more commonly occur with impaired consciousness and thus often belong in the complex partial category. Symptoms include dysphasia, dejavu, fear, illusions, and formed hallucinations) B. Complex partial seizures (consciousness always impaired) 1. Seizures with simple partial onset, followed by impairment of consciousness, sometimes with automatisms. 2. Seizures with consciousness impaired at the start, sometimes with automatisms. C. Partial seizures, simple or complex, which evolve to secondarily generalized seizures II. Generalized seizures (convulsive or nonconvulsive) A. Absence seizures 1. Typical absence seizures (impaired consciousness, minor tonic, clonic or atonic features, minor automatisms) 2. Atypical absence seizures (more variable tone, and less abrupt onset or cessation, than the typical absence seizures) B. Myoclonic seizures

C. Clonic seizures D. Tonic seizures

E. Tonic-clonic seizures F. Atonic (astatic) seizures

Classification of Seizures* EEG lctal

lnterictal EEG

Local discharge without spread

Localized spikes and sharp waves







Unilateral discharge with frequent bilateral spread, more commonly temporal or frontal

Unilateral spikes and sharp waves, sometimes bilateral and synchronous

Unilateral discharge with frequent bilateral spread, more commonly temporal or frontal Unilateral discharge which becomes secondarily generalized


3 Hz spike and slow-wave complexes, usually regular

Background usually normal

Heterogeneous 2-4 Hz spike and slow wave complexes, irregular fast and sharp activity

Background often abnormal, with slowing, sharp waves, and sharp and slow wave complexes

Polyspike and wave, spike and wave, or sharp and slow wave Fast ( > I 0 Hz) sharp activity and slow waves. Occasional spike wave Fast, low amplitude sharp activity, usually slower toward end of seizure Fast and sharp activity, turning to sharp and slow waves at end of seizure Low voltage fast activity, or polyspike and wave, or electrodecremental pattern

Similar to seizure


Table 2.


Spike or polyspike and wave Sharp and slow waves Spikes, sharp and slow waves Polyspikes and slow waves

Ill. Otherwise unclassified seizures 'Adapted from the International Classification of Seizures.=

tial, without impairment of consciousness. Others may secondarily generalize and become generalized tonic-clonic seizures.%otor activity in temporal lobe epilepsy is usually focal and may be tonic or dystonic. Automatisms may be unilateral or bilateral, and lateralized features of the clinical seizure can sometimes be correlated with lateralized EEG abnormalities.

Postictally there is confusion and sometimes dysphasia. Although simple partial seizures are recalled well, amnesia is usual for complex partial seizures. However, even in complex partial seizures, the aura may be recalled even though the seizure itself is not. Seizures of temporal lobe origin have been classified in a variety of ways, but the most basic

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distinction, based on depth EEG recording, is epilepsies can also produce rolandic seizures charprobably between those that have mesial temporal acterized by focal motor activity, with or without or amygdalo-hippocampal onset and those that jacksonian march. have lateral temporal onset. T h e former are more Supplementary motor area seizures are also common and comprise about 80% of all temporal quite characteristic. Contraversive head and eye lobe seizures. They usually have an epigastric deviation is typical, with posturing of the contraaura and early motor arrest. T h e latter are more lateral arm so that it is externally rotated and likely to have auditory or perhaps complex visual flexed at the elbow. Speech arrest or forced vocalauras. Auditory hallucinations suggest an onset in ization may occur, as well as elaborate coordinated Heschl's gyrus, whereas visual hallucinations are movements. Consciousrless is usually preserved, associated with a posterior temporal onset.1° Sei- but may be affected in complex partial seizures. zures with lateral temporal onset usually spread to Cingulate gyrus seizures are less stereotypic involve mesial temporal structures, so that, even- and less well characterized, but may include comtually, both types of seizures look quite similar. plex automatisms, including sexual ones, and are T h e interictal scalp EEG in temporal lobe sometimes accompanied by urinary incontinence. epilepsy may be normal or show background slow- Orbital frontal and dorsolateral frontal seizures ing on the affected side. Temporal spikes, sharp are even less well characterized, but generalized waves, and slow waves are common and may be seizures, absence-type seizures, and seizures with seen on the affected side only or both sides indep- prominent automatisms have all been described. endently. Ictally, the scalp EEG may show one of sevIn spite of their variability, complex partial seieral patterns, including disruption of background zures of frontal origin appear to share certain rhythms unilaterally or bilaterally with residual low characteristics. This association of characteristics is amplitude activity; unilateral rhythmic temporal definite enough to comprise a frontal lobe seizure spikes, sharp waves, or slow waves; and bilateral syndrome.12 Such seizures tend to occur frequently rhythmic sharp and or slow waves. Postictally, and in clusters. They are usually brief, lasting there is generalized slowing that is often more about 30 seconds. They begin and end abruptly prominent on the side of seizure origin. and postictal confusion is rare. T h e associated auWhen the scalp EEG abnormalities are bilat- tomatisms are complex and often appear to be eral at the time of clinical seizure onset, presum- semipurposeful. Sexual automatisms and forced ably the initial focal temporal seizure discharge is vocalization may be present in bizarre combinanot propagated to the surface. This view is con- tions that are hard to distinguish from psychogenic firmed by depth EEG studies where electrodes are (hysterical) seizures. Complex partial status epilepplaced within the temporal lobe. In the mesial tem- ticus has also been reported.13 poral type of seizure, depth EEG usually shows a T h e EEG in frontal lobe epilepsy is often unfast, low-amplitude discharge that begins in the revealing. Interictal and ictal scalp EEGs may be hippocampus and spreads to the ipsilateral neocor- quite normal, and even depth EEGs may fail to retex and often to the contralateral hippocampus veal the seizure focus. Seizures spread rapidly to and neocortex. In the lateral temporal type of sei- the contralateral frontal lobe and sometimes the zure, depth EEG shows an extra-hippocampal ori- first observed EEG abnormality is a high ampligin with spread to the ipsilateral hippocampus and tude bilateral spike-wave or polyspike discharge. then bilaterally.'O Onset and cessation, as already noted, are rapid, but if there is secondary generalization with a tonic-clonic convulsion, then postictal slowing is Frontal Lobe Epilepsy commonly seen.

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Epilepsies and epileptic syndromes of frontal lobe origin can produce a very wide range of seizure types1' This includes minor motor seizures, complex partial seizures, asymmetric tonic or clonic seizures, absence-type seizures, and generalized tonic-clonic seizures. Since the frontal lobes are large and by no means homogeneous structures, it is not surprising that seizures originating in different regions may be clinically quite different. Rolandic seizures were discussed earlier among the idiopathic epilepsies. Symptomatic frontal lobe

Occipital Lobe Epilepsy Seizures originating in the occipital lobes are characterized by an aura o r onset that includes elementary visual sensations, such as flashing lights, dark spots, and often loss of vision. Contralateral head deviation and rapid forced eye movements are also common. T h e electrical abnormality, by definition, begins in one or the other occipital lobe, but the remarkable feature of occipital lobe seizures is that patterns of spread can vary among in-


SEMINARS I N NEUROLOGY

CI.ASSIFICATION OF EPILEPTIC SEIZURES-'I'HADANI,WILLIAMSON

GENERALIZED EPILEPSIES Generalized epilepsies and epileptic syndromes are by definition those with primarily generalized seizures. Such seizures involve the whole brain diffusely, and the EEG shows a bilateral onset. Primarily generalized seizures must be distinguished from the secondarily generalized seizures that occur in the localization-related epilepsies. T h e latter have a focal onset and only later spread to involve the whole brain. In some cases, however, secondary generalization is so rapid that it cannot be distinguished clearly from a primary generalized seizure. Generalized epilepsies, like localization-related epilepsies, are divided into the idiopathic and the symptomatic. For want of a better organizing principle, the idiopathic generalized epilepsies are listed in the order of age at onset.


dividuals and between seizures in the same individual. This has been documented by depth electrode studies.I4 Below the sylvian fissure, if the pattern of spread is first more lateral and only later to mesial temporal structures, then complex visual phenomena will be followed after some delay by the confusion and oral automatisms characteristic of temporal lobe epilepsy. If the pattern of spread is mesial from the start, then apart from a visual aura, occipital lobe epilepsy may be indistinguishable from amygdalo-hippocampal temporal lobe epilepsy. Above the sylvian fissure, lateral spread will involve the parietal lobes and thus produce focal sensory and motor phenomena, whereas mesial spread will more likely affect the supplementary motor area and result in a variety of tonic posturing.

IDIOPATHIC GENERALIZED EPILEPSIES

Parietal Lobe Epilepsy

Benign Neonatal Familial Convulsions

Seizures with parietal lobe onset appear to be relatively rare. Somatosensory auras and vertiginous auras may be characteristic of parietal lobe epilepsy, but, apart from the sensory cortex, the parietal lobe may be clinically "silent" with regard to seizure onset.15~"'Patterns of electrical spread for parietal lobe seizures may be variable, as for occipital lobe seizures, so that even though the origin is parietal, such seizures may evolve into patterns indistinguishable from the other lobar epilepsies.

This is a rare disease. It appears to be dominantly inherited and produces "third day fits." Seizures are clonic or apneic, and EEG abnormalities are nonspecific.'Vhe prognosis is excellent, but a small percentage of patients develop generalized epilepsy as adults.

Epilepsia Partialis Continua of Childhood (Kojewnikow Syndrome) This is one of the rarer localization-related epileptic syndromes." It is characterized by focal motor seizures and the subsequent development of myoclonus. T h e EEG shows a rolandic abnormality with spikes and waves against a background that is often quite normal. One variant, which is relatively nonprogressive, has been associated with a number of causes, including encephalitis, tumors, and vascular malformations. Another variant, also known as Kasmussen syndrome, begins in childhood and produces refractory focal motor seizures. Mental retardation and hemiparesis may also develop. T h e disease is progressive, and pathologic examination of the affected hemisphere reveals a chronic inflammatory response. It is unclear whether a single etiology is responsible.

Benign Neonatal Convulsions This syndrome, also known as "fifth day fits," does not appear to be inherited and has no discernible metabolic cause. Seizures are clonic or apneic and do not recur. T h e interictal EEG shows sharp theta waves.'"

Benign Myoclonic Epilepsy in Infancy This epileptic syndrome is characterized by brief bursts of myoclonus starting between the age of 1 and 2 years. A family history of seizures is usual, and the EEG shows spike-wave during sleep. T h e prognosis is good, although generalized seizures may develop later. Intelligence is slightly affe~ted.~~

Childhood Absence Epilepsy (Petit Mal, Pyknolepsy) Childhood absence epilepsy begins most frequently at 6 to 7 years of age. It is a heritable disease with dominant or polygenic transmission but

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Juvenile Absence Epilepsy This entity is similar to childhood absence epilepsy, but absence seizures are less frequent, and generalized tonic-clonic seizures as well as myoclonic seizures occur more frequently than in the childhood illness. The characteristic EEG abnormality of absence seizures is generalized spikewave, but in juvenile absence epilepsy the frequency is often greater than the exact 3 Hz seen in childhood absence epilepsy.22

sleep deprivation, and photic stimulation. As in other epilepsies, anticonvulsant drugs reduce the seizure frequency and also affect the stages of sleep.25

Other Idiopathic Generalized Epilepsies A number of patients have epilepsy with primary generalized seizures, but no other syndromic features. They cannot be fitted into any of the categories already described and probably represent a heterogeneous group of as-yet-uncharacterized epilepsies. SYMPTOMATIC AND CRYPTOGENIC GENERALIZED EPILEPSIES

This is a very broad category and includes a variety of diffuse brain diseases in which seizures are a prominent feature. In the discussion to follow, organization is based partly on the clinical syndrome and partly on the known or presumed etiology.

Infantile Spasms (West Syndrome)

This is the most common and devastating infantile epilepsy.26It is characterized by a triad of spasms (these may be flexor, extensor, head nodding, or a mixture), arrested mental development, and a diffusely abnormal EEG with high-ampliJuvenile Myoclonic Epilepsy tude complex sharp and slow waves (hypsarrhythmia). Onset is usually after 3 months and before 1 This epilepsy manifests itself at puberty and is year of age, and the prognosis is poor. In more characterized by a mixed seizure pattern, includ- than half the cases a particular etiology is known ing absence, generalized tonic-clonic, and myo- or suspected, for example, a congenital malforclonic seizures.23 The latter are most prominent mation, intrauterine infection, error of metaboand consist of sudden bilateral single or repetitive lism, or hypoxia at birth. However, in a substantial muscle jerks. These affect mainly the arms, but minority of cases (which could be regarded as idmay also involve the legs and cause the patient to iopathic) there is no obvious etiology. fall. It is noteworthy that myoclonic seizures are T h e syndromes of early infantile epileptic enoften not associated with loss of consciousness. The cephalopathy with tonic seizures, and early myointerictal and ictal EEG shows generalized irregu- clonic encephalopathy, in which the EEG shows a lar polyspike and spike-wave complexes. Recently, burst-suppression pattern, are probably variants of the gene responsible for this epilepsy has been West ~yndrorne.~'.'~ The burst-suppression EEG mapped to chromosome 6.24 often evolves to hypsarrhythmia.

Epilepsy with Generalized Tonic-Clonic Seizures on Awakening

334

This epilepsy begins in adolescence and has a mixed seizure pattern, but the most characteristic seizures are tonic-clonic. They occur in the morning on awakening. There is a hereditary predisposition, and seizures may be precipitated by stress,

Lennox-Gastaut Syndrome This syndrome appears between the ages of 1 and 10 years, sometimes de novo and sometimes following one of the other infantile epilepsy syndromes. West syndrome may, for example, evolve into Lennox-Gastaut syndrome. As in West syndrome there is no single etiology. Children with


limited penetrance. The characteristic EEG abnormality of 3 Hz spike and wave may be inherited without the clinical seizures o~curring.'.~' Seizures are brief, typically lasting from 30 seconds to 1 minute, and are characterized by sudden loss of contact and staring into space. Motor components are rare but may include retropulsion; falling; and tonic, clonic, and atonic activity. Blinking is common and oral automatisms may also occur. The latter sometimes cause absence seizures to be confused with temporal lobe seizures, but the EEG is invariably diagnostic. Both the electrographic abnormality and seizures may be elicited by hyperventilation and photic stimulation. Patients with childhood absence epilepsy may also develop generalized tonic-clonic seizures in adolescence.

CLASSIFICATION O F EPILEPTIC SEIZURES-THADANI,WILLIAMSON

Myoclonic Epilepsies of Infancy and Childhood Several overlapping and poorly characterized syndromes are grouped here. They are placed in

the symptomatic category and separated from the idiopathic benign myoclonic epilepsy in infancy because their relatively poor prognosis, sometimes progressive character, and association with mental retardation all suggest some underlying brain disease. We will consider them in order of age at onset: la. Early myoclonic encephalopathy. Severe myoclonic seizures, partial seizures, and tonic seizures may all be present, starting a few days after birth. The EEG shows burst suppression, but may evolve into hypsarrhythmia. T h e relationship of this syndrome to West syndrome is unclear, but familial groupings suggest underlying metabolic defects. Severe retardation and early death are common.28 lb. Early infantile encephalopathy with tonic seizures. Tonic seizures predominate here, but onset, EEG patterns, and outcome are similar to early myoclonic encephal~pathy.~' 2. Epilepsy with myoclonic-astatic seizures. Seizures begin between 1 and 5 years of age. Multiple seizure types may be present, but myoclonic seizures predominate. T h e interictal EEG may be normal early in the course of this disease, but later polyspike abnormalities are seen. Development also may be normal until the onset of seizures, but affected children may become retarded later.30 3. Epilepsy with myoclonic absences. Seizures begin at about 7 years of age and are characterized by severe bilateral myoclonus with preserved consciousness. T h e EEG is remarkable for 3 Hz spike and wave activity, which resembles that seen in absence epilepsy. Mental retardation is common, and seizures are hard to contr01.~'


Lennox-Gastaut syndrome usually Decome retarded, and the background EEG, which may be normal earlier, becomes quite abnormal with generalized slow (2 to 3 Hz) spike and wave discharges and sometimes focal abnormalities. During sleep bursts of fast (more than 10 Hz) sharp activity are comm ~ n . ~ ~ A key feature of the Lennox-Gastaut syndrome is the presence of multiple seizure types, each with its own characteristic EEG pattern. Some of these are described: 1. Absence seizures. These are similar to the seizures of absence epilepsy but in the Lennox-Gastaut syndrome they may have more atypical motor features, and the EEG may be less regular than the classic 3 Hz pattern. 2. Generalized tonic-clonic seizures. These are identical to the generalized seizures seen in other epilepsies. 3. Myoclonic seizures. These again are indistinguishable from the seizures of myoclonic epilepsy. 4. Clonic seizures. These are relatively rare and are characterized by clonic movements in the relative absence of increased tone. T h e ictal EEG can show a variety of generalized spikes and sharp and slow waves, and the postictal phase is relatively short. 5. Tonic seizures. These are very common and characterized by sustained rather than alternating muscle contraction. They may involve a part or, more likely, the whole of the body. T h e ictal EEG shows prolonged, fast, sharp spike activity, and fewer of the slow waves that are seen in other seizure types. 6. Atonic (astatic) seizures. These seizures are characterized by sudden loss of tone in various muscle groups and frequently result in falls (drop attacks). Consciousness is lost briefly or not at all. T h e ictal EEG may show a variety of generalized abnormalities, including an electrodecremental pattern, polyspike and wave, and low voltage fast activity. 7. Complex partial seizures. Since the EEG in ~ennoxI~astau syndrome t may have focal as well as generalized abnormalities, it is not surprising that complex partial seizures can occur that are clinically similar to those described in the localization-related epilepsies. Status epilepticus, with a variety of seizure types, is common.

Metabolic and Other Diseases with Seizures as a Prominent Symptom Many congenital malformations, errors of metabolism, and storage diseases have seizures as a major manifestation. A representative sample will be given. Among the diseases with obvious structural abnormalities, Aicardi syndrome and lissencephaly are associated with West ~yndrorne.~'Tuberous sclerosis may produce a similar picture, and the rare syndrome of gelastic seizures with mental retardation is associated with hypothalamic tum o r ~ . ~ ~ ~ ~ ~ Inborn errors of metabolism such as hyperglycinemia have been associated with early myoclonic encephalopathy, and phenylketonuria can inherbe a cause of West ~yndrome.~'.~%aternally

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EPILEPSIES NOT CLEARLY FOCAL OR GENERALIZED This is an unsatisfactory category, since it is based on lack of information rather than positive features. Failure to classify an epilepsy as generalized o r localization-related can occur in two ways. First, the patient may have both focal and generalized seirires, with clinical and EEG features such that one cannot tell whether the generalized seizures are primarily or secondarily generalized. Secand, the patient may have nOnfocal seizures and an unrevealing EEG. If the seizures Occur Out of sleep, the patient will not recall an aura, and it may remain unclear whether the seizures are primarily or secondarily generalized. Because of such problems, several syndromes remain unclassified as focal or generalized.

-

Neonatal Seizures

A variety of causes can produce seizures in the neonate. These include intraventricular hemorrhage, electrolyte abnormalities, hypoglycemia, hypoxic-ischemic injury, infections, and inborn errors of metabolism. Because the brain of the neonate is immature, seizures often appear different from those in the adult. Often, the manifestations are subtle and can appear as nonepileptic phenomena. These include eye deviations, blink-

ing, sucking, minor jerking of the arms and legs, decorticate posturing, and sometimes apnea. Tonic and myoclonic seizures can also occur, and the EEG often shows a burst-suppression pattern. At other times, seizures may be focal or follow a migratory focal pattern, and the EEG shows focal seizure activity against a diffusely abnormal background. It is likely that in the immature neonatal brain, in which excitatory and inhibitory mechanisms are both undeveloped, the distinction between focal and generalized epilepsies is less clear than in the adult.

Severe Myoclonic Epilepsy in Infancy This syndrome probably belongs among the symptomatic myoclonic epilepsies. There is usually a family history of seizures and the patient develops epilepsy before the age of 1 year. Seizures are generalized or focal and often occur with fever. Myoclonus develops later. The EEG shows spikewave as well as focal abnormalities and there may be photosensitivity. Mental retardation, spasticity, and ataxia may appear following the onset of seizures. The outlook is poor and the cause or causes are unknown.40

Epilepsy with Continuous Spike Waves during Slow-Wave Sleep

This syndrome usually begins in early childhood and is characterized by multiple seizure types that occur out of sleep, and absence-type seizures that occur out of wakefulness. The characteristic EEG abnormality is a continuous slow spike-wave and EEG abdischarge during sleep. ~h~ normality may remit in adolescence, but developmental abnormalities often persist.41

Acquired Epileptic Aphasia (Landau-Kleffner syndrome) In this childhood syndrome there is regression of language with receptive aphasia and reduced speech. Multiple seizure types may occur, and the EEG shows multifocal spike and slow-wave discharges, which often center around the speech areas. Prognosis is mixed, and the relationship of this syndrome to other progressive focal syndromes such as Rasmussen syndrome remains unclear.42


ited defects in mitochondrial respiration produce seizures and the mitochondrial encephalomyopathy and ragged red fibers ~yndrome.~' A variety of storage disease with known enzymatic defects such as Tay-Sachs disease and Sandhoff disease can present with myoclonus that develops into focal and generalized epilepsy.38T h e background EEG in these cases usually shows generalized slowing, and ictally several different seizure types may be seen. The progressive nature of these illnesses serves to distinguish them from the idiopathic and other symptomatic epilepsies. Progression may also occur in storage and degenerative diseases in which the metabolic defect is not known. T h e ceroid lipofuscinoses (infant, juvenile, and adult variants) all have myoclonic, astatic, or generalized tonic-clonic seizures as part of the syndrome, and the background EEG is diffusely abnormal. Lafora body disease, Unverricht-Lundborg disease, and the Ramsey Hunt syndrome all feature mental deterioration, myoclonus, and generalized seizures, with diffusely abnormal E E G S . ~ ~

V O L U M E 10, NUMBER 4 DECEMBER 1990

SPECIAL SYNDROMES WITH SITUATIONRELATED SEIZURES Certain patients may have seizures only in the context of another acute illness or metabolic derangement. It is not clear whether such patients should be described as having epilepsy. They may, however, have a hereditary. predisposition for seizures, since the same metabolic stresses do not produce seizures in every patient.

reading epilepsy, the act of reading, no matter what the content, causes the patient to have a focal seizure involving the jaw muscles, or a generalized tonic-clonic seizure.46 T h e interictal EEG shows sharp waves in the temporoparietal region. Since the seizures and the EEG are sometimes focal, this epilepsy is also classified among the idiopathic localization-related epilepsies.

CONCLUSION Febrile Seizures

Seizures Associated with Metabolic Derangement A variety of metabolic disorders can produce seizures. Among these are alterations in sodium, calcium, and magnesium levels; hyperglycemia or hypoglycemia; eclampsia; uremia; and hepatic failure. T h e seizures are usually generalized, but can be focal, particularly in patients with prior focal brain injury. EEG abnormalities are nonspecific, but triphasic waves are common in uremia and hepatic fai1u1-e.45

SPECIAL SYNDROMES WITH SEIZURES PRODUCED BY SPECIFIC STIMULI In certain individuals, seizures are triggered -by specific stimuli. F~~ example, a particular sight, or a particular work of music, will trigger a seizure. Such seizures may be partial or generalized. In


A system of classification is only as good as the data upon which it is based. T h e present classifiThis is a disorder that usually begins in the cation of epilepsies and seizures is rich in phenomfirst year of life and by definition has an onset be- enologic description, but remarkably weak in the fore the age of 3 years. Generalized seizures (al- understanding of etiologies. It is likely, therefore, though sometimes they may have focal features) that those aspects of the classification that depend occur only in the context of a febrile illness. T h e on the description of seizures, for example the disbackground EEG is usually normal and the under- tinction between generalized and localization-relying cause is a genetically low seizure threshold. lated epilepsies, will survive for the foreseeable fuThis is a self-limited disorder, but prolonged sei- ture. On the other hand, those aspects that require zures and focal seizures are associated with the sub- an understanding of the causes of epilepsy, for exsequent development of temporal lobe epilep~y.~" ample, the classification of overlapping syndromes listed under the generalized symptomatic epilepsies, will surely require reorganization as soon as Alcohol-Related Seizures the causes of the various syndromes are better understood. Withdrawal from alcohol use can precipitate The goal of creating or studying a classificaseizures.44These seizures are almost always gener- tion of epileptic syndromes and seizures must be to alized tonic-clonic. T h e background EEG is nor- place the whole field in perspective. Then, by stepmal. This is probably a withdrawal rather than a ping back and seeing all the convulsive disorders toxic effect, since moderate alcohol consumption in a single pattern, one can hope to discern which does not increase the seizure frequency in known areas will best repay intensive study. epileptics.

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SEMINARS I N NEUROLOGY VOLUME 10, NUMBER 4 DECEMBER 1990

Epileptic seizures and syndromes.

Epileptic syndromes and seizures in infants.

Epileptic seizures and syndromes in adults.

Classification of epileptic seizures and the epilepsies.

Childhood epileptic syndromes.

Up-to-date Critical Review of the Classification of Epilepsies and Epileptic Seizures.

State of the Art Approach to the Classification of Epileptic Seizures and Epilepsies.

Epileptic seizures in thrombotic stroke.

Epileptic syndromes may be misleading.

Nonketotic hyperglycemia-related epileptic seizures.

Cardiorespiratory abnormalities during epileptic seizures.

Predicting epileptic seizures in advance.

KCC2 downregulation facilitates epileptic seizures.

Epileptic Seizures with Mirthful Laughter.

Epileptic seizures precipitated by atenolol.

Inhomogeneous cortical synchronization and partial epileptic seizures.

Epileptic syndromes and seizure types in children.

Cognitive functions, epileptic syndromes and antiepileptic drugs.

Analysis of epileptic seizures with complex network.

Association of RASgrf1 methylation with epileptic seizures.

Biopsychosocial predictors of psychogenic non-epileptic seizures.

Emergence of semiology in epileptic seizures.

Postictal serum creatine kinase for the differential diagnosis of epileptic seizures and psychogenic non-epileptic seizures: a systematic review.

Psychogenic non-epileptic seizures in Iran.