How are epileptic seizures defined?

Updated: Nov 30, 2017
  • Author: Eissa Ibrahim AlEissa, MD, MBBS; Chief Editor: Selim R Benbadis, MD  more...
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The definitions of the following terms come from the International League Against Epilepsy (ILAE) Guidelines. [3, 4, 5] In 2017, the ILAE proposed revisions to the terminology, classification, and concepts for seizures and epilepsies, but the ILAE indicates these are guiding principles rather than a presentation of new classification per se. [6, 7]

An epileptic seizure is a clinical event presumed to result from an abnormal and excessive neuronal discharge. The clinical symptoms are paroxysmal and may include impaired consciousness and motor, sensory, autonomic, or psychic events perceived by the subject or an observer.

Epilepsy occurs when 2 or more epileptic seizures occur unprovoked by any immediately identifiable cause. The seizures must occur more than 24 hours apart. In epidemiologic studies, an episode of status epilepticus is considered a single seizure. Febrile seizures and neonatal seizures are excluded from this category.

Idiopathic epilepsy describes epilepsy syndromes with specific age-related onset, specific clinical and electrographic characteristics, and a presumed genetic mechanism.

Epileptic seizures are classified as cryptogenic or symptomatic. A cryptogenic seizure is a seizure of unknown etiology, and it is not associated with a previous central nervous system (CNS) insult known to increase the risk of developing epilepsy. A cryptogenic seizure does not conform to the criteria for the idiopathic or symptomatic categories. Previous studies use the term idiopathic to describe a seizure of unknown etiology. However, the ILAE guidelines discourage use of the term idiopathic to describe a seizure of unknown etiology.

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