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".