Classification of seizures

Overview

The International League Against Epilepsy (2011-2013) classified seizures into three groups:

  • Generalised
  • Focal
  • Unknown

Classification amendments 2017

The following document provides detailed information on the revised classification of seizure types by the ILAE  in 2017:

 

References

  • Scheffer et al. ILAE classification of the epilepsies: Position paper of the ILAE Commission for Classification and Terminology. Epilepsia, 2017:58(4): 512-521.
  • Fisher et al. Operational classification of seizure types by the International League Against Epilepsy: Position Paper of the ILAE Commission for Classification and Terminology. Epilepsia, 2017:58(4): 522-530.
  • Fisher et al. Instruction manual for the ILAE 2017 operational classification of seizure types. Epilepsia, 2017:58(4): 531-542.

Generalised seizures

Generalised seizures include:

  • Generalised tonic clonic
  • Absence
  • Clonic
  • Tonic
  • Atonic
  • Myoclonic

Generalised Tonic Clonic seizures

  • There is an initial tonic phase in which there is brief tonic flexion of axial muscles then longer tonic extension. 
  • This is followed by an intermediary phase of vibratory tremor. 
  • The clonic phase consists of alternating contraction and atonia or inhibition. Expiratory grunts and tongue biting may occur in this phase. 
  • Finally, there is a second brief tonic phase in which again tongue biting may occur.
  • In the postictal phase the patient may be unconscious for a period and respiration compromised.
  • During a generalised tonic clonic seizure, there may be marked autonomic features.

Tonic seizures

  • May be subtle with only eyelid opening and upward eye deviation. 
  • In an axial tonic seizure, there is rigidity of posterior neck, paraspinal and abdominal muscles. 
  • The tonic activity may involve limb contraction leading to falls. Consciousness is abolished during attacks but the events may be very brief from seconds or last approximately a minute. 
  • The average length is about 10 seconds. 
  • Tonic seizures are activated by non-REM sleep.

Myoclonic seizures

  • There is a sudden involuntary shock-like muscle contraction. The seizure may be focal or regional.
  • Jerks may be single, repetitive, rhythmical or arrythmical.
  • An inhibitory form of myoclonus has been described known as epileptic negative myoclonus. 
  • Myoclonic seizures may originate at any level of the nervous system, cortex, cerebellum, brainstem or spinal cord.

Absence seizures

  • Classically there is impairment of consciousness.
  • There may be subtle other features including mild clonic components, tonic components, atonic components, automatisms or autonomic components. 
  • Absence seizures are characteristically seen in genetic generalised epilepsies. 

Focal seizures

  • Focal seizures originate within networks limited to one hemisphere.
  • In focal seizures, symptoms and signs may arise from limited involvement of the cortex. Examples are somatosensory, autonomic, psychic and motor focal seizures.
  • The revised ILAE terminology describes focal seizures according to one or more specific features: level of awareness/responsiveness, motor, autonomic, or subjective features (i.e. auras).
  • Previously, the term ‘simple partial’ seizure was used when consciousness was preserved, and the term ‘complex partial’ seizure was employed when awareness and responsiveness were altered.
  • A focal seizure may evolve to a bilateral convulsive seizure.

New terminology example: Under the revised ILAE classification, a "complex partial seizure with secondary generalization" would now be described as: "a focal seizure with loss of awareness, evolving to a bilateral convulsive seizure".

The doctor is initially presented with a description of a seizure type. It is important to identify the seizure type and collect information such as its time of occurrence, frequency, age of onset.

Using this information together with the EEG, a diagnosis of a particular childhood epilepsy syndrome should be reached upon which management can be based. For example, myoclonic seizures soon after waking in the young teenager are classical of the epileptic syndrome Juvenile Myoclonic Epilepsy.This syndrome carries implications and unique features important to the presiding physician and to the patient.

The aetiology of the epilepsy is critical. The terminology 'Idiopathic' has been replaced by 'Genetic', and the terminology 'Symptomatic' is replaced by ‘structural’, ‘metabolic’, ‘immune’, ‘infectious’, as required.

The importance of the interictal EEG is emphasized in syndrome classification. An MRI is the imaging  test of choice and is important in  epilepsies where a structural abnormality is suspected. The yield in genetic epilepsy is low.

Learning Resource

LEARNING RESOURCE - CONCEPTS OF CLASSIFICATION 2018

Please click on the link to access a new learning resource on: Concepts of Classification (2018).