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

  • 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".