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Generalized Epilepsies on EEG

Overview

The International Classification of Epileptic Syndromes and Epilepsies
classifies the epilepsies along 2 dichotomies: (1) partial (ie, localization-related) versus generalized and (2) idiopathic versus cryptogenic or symptomatic. This double dichotomy conveniently allows the epilepsy classification system to be presented in a simple and clear manner (see the Table below).

Table. Classification of the Epilepsies (Adapted from Tich and Pereon, 1999
) (Open Table in a new window)

 

Generalized

Localization-related

Idiopathic

(genetic)

Childhood absence epilepsy

Juvenile absence epilepsy

Juvenile myoclonic epilepsy

Epilepsy with grand-mal seizures on awakening

Other idiopathic generalized epilepsies

Benign focal epilepsy of childhood (2 types)

ADNFLE*

Primary reading epilepsy

Symptomatic

or cryptogenic

West syndrome

Lennox-Gastaut syndrome

Other symptomatic generalized epilepsies

Mesiotemporal lobe epilepsy

Neocortical focal epilepsy

*ADNFLE – Autosomal dominant nocturnal frontal lobe epilepsy

The term idiopathic often is misunderstood in this setting and requires clarification. Whereas the term idiopathic in medicine usually means “of unknown cause,” idiopathic epilepsies are not truly of unknown cause; this confusing terminology will most likely be corrected in the upcoming International League Against Epilepsy (ILAE) classification system.

In epilepsy, idiopathic seizures are genetically determined and have no apparent structural cause, with seizures as the only manifestation of the condition. Findings of the neurologic examination and neuroimaging studies are normal, and electroencephalographic (EEG) findings also are normal, aside from the epileptiform abnormalities. In some syndromes, the genetic substrate has even been identified. Most idiopathic epilepsies are generalized, but a few genetic epilepsies are focal.

Nonidiopathic epilepsies, by definition, are not genetic (though some may be associated with a minor genetic predisposition) but are the result of a brain insult or lesion. If the damage is focal, it results in a localization-related epilepsy; if it is diffuse, it results in a generalized epilepsy.

The difference between symptomatic and cryptogenic in this context is subtle: to say that an epilepsy is symptomatic means that the etiology is known, whereas to say that it is cryptogenic means that an underlying etiology is apparent but cannot be documented objectively. Thus, the boundary between the 2 is largely dependent on our diagnostic and imaging techniques.

This review discusses EEG findings in the generalized epilepsies.
Go to Epilepsy and Seizures for an overview of this topic.

For patient education resources, see the Brain and Nervous System Center.

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