Excerpt from EEG Atlas: Localization-related Epilepsies

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The International Classification of Epileptic Syndromes and Epilepsies (International League Against Epilepsy [ILAE], 1989) classifies the epilepsies along 2 dichotomies: partial (ie, localization-related) versus generalized, and idiopathic versus cryptogenic or symptomatic. This double dichotomy conveniently allows presentation of the epilepsy classification in a simple table, as follows:

Classification of the Epilepsies*

	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

*Adapted from Nguyen et al (1999)

**ADNFLE - Autosomal dominant nocturnal frontal lobe epilepsy

The term "idiopathic" often is misunderstood in this setting and requires clarification. Whereas the term idiopathic usually means "of unknown cause," idiopathic epilepsies are not truly of "unknown cause" (this confusing terminology will most likely be corrected in the upcoming ILAE classification system [Engel, 1998]). Idiopathic epilepsies are determined genetically and have no apparent structural cause, with seizures as the only manifestation of the condition. Findings of the neurologic examination and imaging studies are normal, and EEG is normal other than the epileptiform abnormalities. In some syndromes, the genetic substrate has even been identified.

Most idiopathic epilepsies are generalized, but a few are focal. Nonidiopathic epilepsies are by definition not genetic, although some may be associated with a minor genetic predisposition; they 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 is subtle: symptomatic means that the etiology is known, while cryptogenic means that an underlying etiology is apparent but cannot be documented objectively. Thus, the boundary between the two is largely dependent on the capabilities of our diagnostic and imaging techniques.

This review discusses EEG findings in the localization-related (also known as focal or partial) epilepsies.

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Please click here to view the full topic text: EEG Atlas: Localization-related Epilepsies