Classification of Epileptic Seizures




Classification of Epileptic Seizures


Jerome Engel Jr.

Peter D. Williamson

Anne T. Berg

Peter Wolf



Introduction

Writings about epileptic seizures date back 3,000 years to Mesopotamia and India.18 In 400 BC, Hippocrates attributed epileptic seizures to disorders of the brain, rather than to supernatural forces and, 500 years later, Galen distinguished idiopathic seizures, which originated within the brain itself, from sympathetic seizures, which had external causes.22 Nevertheless, throughout this time until the 19th century, very little was understood about the causes of epileptic seizures or, indeed, the variety of their manifestations. Until this time, for all intents and purposes, only generalized tonic–clonic convulsions were considered to be epileptic seizures. Esquirol, in 1815, however, discriminated between grand mal and petit mal seizures12 and, in 1827, Bravais described focal motor seizures.5 Hughlings Jackson is credited with recognizing, in the 1860s, that a variety of focal symptomatology could be epileptic at a time when most workers considered only generalized convulsions—believed to originate in the medulla oblongata—to be manifestations of epilepsy.11,21 Jackson also recognized that it was easier to understand the mechanisms of epilepsy by studying focal ictal events, and his clinical pathologic correlations correctly established the cerebral cortex as the site of origin of focal epileptic seizures. This work helped define the location and function within the human cortex and led directly to the development of resective surgical therapy for epilepsy.11

With the advent of the electroencephalograph (EEG), characteristic electrographic ictal discharge patterns were identified to clearly distinguish among grand mal, petit mal, and psychomotor seizures.14 Because linked-ear references were used, however, all these patterns were believed to be generalized until so-called bipolar montages revealed that the location, and not the pattern, of the electrographic discharge differentiated various focal ictal events.16 Despite the description of hippocampal sclerosis in patients with epilepsy as early as 1826,4 and Hughlings Jackson’s observation that lesions in the hippocampal region occurred in patients with tasting movements and “dream state,”15 it wasn’t until the mid-1900s that epileptologists began to accept the fact that most “psychomotor” seizures originated in mesial temporal structures.17 This fact was further substantiated by the observation that psychomotor seizures could often be successfully treated by surgical resections of the temporal lobe.2,20

During this period, worldwide, multiple terminologies developed that made sensible discussions and communication increasingly difficult. In 1970, the International League Against Epilepsy (ILAE) created the first classifications of epileptic seizures and epilepsies.13 They clearly distinguished ictal events from the disorders with which they were associated, and ictal and interictal EEG patterns, anatomic substrate, etiology, and age were included in this definition of seizures. Seizures were broadly divided into partial, beginning in a part of one hemisphere, and generalized, which were bilaterally symmetrical without local onset (Table 1). Partial seizures were further divided into those with elementary symptomatology, referring to signs and symptoms mediated by eloquent areas of neocortex, and complex symptomatology, referring to signs and symptoms mediated predominantly by mesial temporal limbic structures. The term “complex partial seizure,” therefore became synonymous with the older terms, “psychomotor seizure” and “temporal lobe seizure.” This seizure classification was criticized because, at the time, insufficient anatomic and pathophysiologic information was available to provide a basis for classification, and there was controversy about some of the generalized seizure types. These perceived problems were rectified in 1981, with the second ILAE Classification of Epileptic Seizures (Table 2).6


1981 ILAE Classification of Epileptic Seizures

Despite persistent controversy, the 1981 Classification of Epileptic Seizures has gained general acceptance and is widely used. An ILAE Task Force has been reviewing this classification since 1997, but no new classification has yet been proposed.7,9,10 Although flawed, it has been agreed that this useful construct should not be abandoned until a clearly better version can be devised.

The 1981 Classification of Epileptic Seizures was based on expert consensus, analyzing video-recorded seizures and considering their semiology as a sequence of ictal events developing in time. In addition to the clinical phenomenology, the ictal and interictal EEG was considered, but it was decided that there was still insufficient information about pathophysiologic mechanisms and anatomic substrates to warrant a more diagnostic approach.6 The partial/generalized dichotomy was preserved, but the distinction between simple and complex partial seizures was based entirely on impairment of consciousness. Thus, the original intent of the concept of complex symptomatology indicating behaviors mediated predominantly by limbic structures was lost. Neocortical seizures with impaired consciousness became complex partial seizures, whereas limbic seizures without impaired consciousness became simple partial seizures. This was, and continues to be, a source of controversy and confusion. On the other hand, the 1981 classification acknowledged the evolution of partial signs and symptoms and recognized that simple partial seizures could evolve into complex partial seizures, and that both could evolve into secondarily generalized seizures. This classification also differed from the 1970 classification in that absences were divided into typical and atypical, infantile spasms were deleted because they were considered to be a syndrome and not a seizure type, and akinetic seizures were deleted because their existence was questioned.









Table 1 1970 ILAE CLASSIFICATION OF EPILEPTIC SEIZURES (defined by ictal + interictal EEG, anatomic substrate, etiology, and age)








  1. Partial

    1. With elementary symptomatology
    2. With complex symptomatology
    3. Secondarily generalized

  2. Generalized, bilaterally symmetrical or without local onset

    1. Absences
    2. Bilateral massive epileptic myoclonus
    3. Infantile spasms
    4. Clonic seizures
    5. Tonic seizures
    6. Tonic–clonic seizures
    7. Atonic seizures
    8. Akinetic seizures

  3. Unilateral or predominantly unilateral
From Gastaut H. Clinical and electroencephalographical classification of epileptic seizures. Epilepsia. 1970;11:102–113, with permission.








Table 2 1981 ILAE CLASSIFICATION OF EPILEPTIC SEIZURES




































































I. PARTIAL (FOCAL, LOCAL) SEIZURES
Partial seizures are those in which, in general, the first clinical and electroencephalographic changes indicate initial activation of a system of neurons limited to part of one cerebral hemisphere. A partial seizure is classified primarily on the basis of whether or not consciousness is impaired during the attack. When consciousness is not impaired, the seizure is classified as a simple partial seizure. When consciousness is impaired, the seizure is classified as a complex partial seizure. Impairment of consciousness may be the first clinical sign, or simple partial seizures may evolve into complex partial seizures. In patients with impaired consciousness, aberrations of behavior (automatisms) may occur. A partial seizure may not terminate, but instead progress to a generalized motor seizure. Impaired consciousness is defined as “the inability to respond normally to exogenous stimuli by virtue of altered awareness and/or responsiveness.”
There is considerable evidence that simple partial seizures usually have unilateral hemispheric involvement and only rarely have bilateral hemispheric involvement; complex partial seizures, however, frequently have bilateral hemispheric involvement.
Partial seizures can be classified into one of the following three fundamental groups:

  1. Simple partial seizures
  2. Complex partial seizures

    1. With impairment of consciousness at onset
    2. Simple partial onset followed by impairment of consciousness

  3. Partial seizures evolving to generalized tonic–clonic convulsions (GTC)

    1. Simple evolving to GTC
    2. Complex evolving to GTC (including those with simple partial onset)
Clinical seizure type EEG seizure type


  1. Simple partial seizures (consciousness not impaired)
Local contralateral discharge starting over the corresponding area of cortical representation (not always recorded on the scalp)


  1. With motor symptoms

    1. Focal motor without march
    2. Focal motor with march (Jacksonian)
    3. Versive
    4. Postural
    5. Phonatory (vocalization or arrest of speech)

  2. With somatosensory or special-sensory symptoms (simple hallucinations, e.g., tingling, light flashes, buzzing)

    1. Somatosensory
    2. Visual
    3. Auditory
    4. Olfactory
    5. Gustatory
    6. Vertiginous

  3. With autonomic symptoms or signs (including epigastric
    sensation, pallor, sweating, flushing, piloerection, and
    pupillary dilatation)
  4. With psychic symptoms (disturbance of higher cerebral function). These symptoms rarely occur without impairment of consciousness and are much more commonly experienced as complex partial seizures.

    1. Dysphasic
    2. Dysmnesic (e.g., déjà-vu)
    3. Cognitive (e.g., dreamy states, distortions of time sense)
    4. Affective (fear, anger, etc.)
    5. Illusions (e.g., macropsia)
    6. Structured hallucinations (e.g., music, scenes)


  • B. Complex partial seizures (with impairment of consciousness: may sometimes begin with simple symptomatology)
Unilateral or, frequently, bilateral discharge, diffuse or focal in temporal or frontotemporal regions




    1. Simple partial onset followed by impairment of consciousness

      1. With simple partial features as in A.1–4 (followed by
        impaired consciousness)
      2. Without automatisms

    2. With impairment of consciousness at onset

      1. With impairment of consciousness only
      2. With automatisms


  • C. Partial seizures evolving to secondarily generalized seizures (This may be generalized tonic-clonic)
Above discharges become secondarily and rapidly generalized




    1. Simple partial seizures (A) evolving to generalized
      seizures
    2. Complex partial seizures (B) evolving to generalized
      seizures
    3. Simple partial seizures evolving to complex partial seizures evolving to generalized seizures
II. GENERALIZED SEIZURES (CONVULSIVE OR NONCONVULSIVE)
Generalized seizures are those in which the first clinical changes indicate initial involvement of both hemispheres. Consciousness may be impaired, and this impairment may be the initial manifestation. Motor manifestations are bilateral. The ictal electroencephalographic patterns initially are bilateral and presumably reflect neuronal discharge, which is widespread in both hemispheres.
Clinical seizure type EEG seizure type


  1. Absence seizures


  • 1. Typical absence
Usually regular and symmetrical 3-Hz but may be 2- to 4-Hz spike-and-slow- wave complexes and may have multiple spike-and- slow-wave complexes. Abnormalities are bilateral




    1. Impairment of consciousness onlya
    2. With mild clonic componentsa
    3. With atonic componentsa
    4. With tonic componentsa
    5. With automatismsa
    6. With autonomic componentsa


  • 2. Atypical absence
EEG more heterogeneous; may include irregular spike-and-slow-wave complexes, fast activity, or other paroxysmal activity. Abnormalities are bilateral but often irregular and asymmetrical.


  • May have:

    1. Changes in tone that are more pronounced than in A.1
    2. Onset and/or cessation that is not abrupt


  • B. Myoclonic seizures, myoclonic jerks (single or multiple)
Polyspike-and-wave or sometimes spike-and- wave or sharp and slow wavesb


  • C. Clonic seizures
Fast activity (10 c/sec or more) and slow waves; occasional spike-and- wave patternsb


  • D. Tonic seizures
Low voltage, fast activity or a fast rhythm of 9–10 c/sec or more, decreasing in frequency and increasing in amplitudeb


  • E. Tonic–clonic seizures
Rhythm at 10 or more c/sec, decreasing in frequency and increasing in ampli- tude during tonic phase, interrupted by slow waves during clonic phaseb


  • F. Atonic seizures (astatic)
Polyspike-and-wave or flattening or low-voltage fast activityb
III. UNCLASSIFIED EPILEPTIC SEIZURES
Includes all seizures that cannot be classified because of inadequate or incomplete data and some that defy classification in hitherto
described categories. This includes some neonatal seizures, e.g., rhythmic eye movements, chewing, and swimming movements.
IV. ADDENDUM
Repeated epileptic seizures occur under a variety of circumstances:

  1. As fortuitous attacks, coming unexpectedly and without any apparent provocation.
  2. As cyclic attacks, at more or less regular intervals (e.g., in relation to the menstrual cycle or to the sleep–waking cycle).
  3. As attacks provoked by:


    1. Nonsensory factors (fatigue, alcohol, emotion, etc.)
    2. Sensory factors, sometimes referred to as reflex seizures
Prolonged or repetitive seizures (status epilepticus). The term status epilepticus is used whenever a seizure persists for sufficient length of time or is repeated frequently enough that recovery between attacks does not occur. Status epilepticus may be divided into partial (e.g., Jacksonian), or generalized (e.g., absence status or tonic–clonic status). When very localized motor status occurs, it is referred to as epilepsia partialis continua.
aII.A.b–f may be used alone or in combination.
bCombinations of II.B–F, e.g., B and F, B and D.
From Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised clinical and electroencephalographic classification of epileptic seizures. Epilepsia. 1981;22:489–501, with permission.

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Aug 1, 2016 | Posted by in NEUROLOGY | Comments Off on Classification of Epileptic Seizures

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