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Localization-Related Epilepsies on EEG


The International League Against Epilepsy (ILAE) 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 shown in Table 1, below.

Table. Classification of the Epilepsies (Open Table in a new window)






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)


Primary reading epilepsy


or cryptogenic

West syndrome

Lennox-Gastaut syndrome

Other symptomatic generalized epilepsies

Mesial temporal lobe epilepsy

Neocortical focal epilepsy

Adapted from Tich and Pereon, 1999.

ADNFLE = Autosomal dominant nocturnal frontal lobe epilepsy

The term idiopathic is often misunderstood in this setting and requires clarification. Although “idiopathic” usually means “of unknown cause,” idiopathic epilepsies are not truly of unknown cause (This confusing terminology was raised in the 1998 ILAE classification and is discussed in the 2010 ILAE report.
). 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 electroencephalography (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, whereas cryptogenic means that an underlying etiology is apparent but cannot be documented objectively. Thus, the boundary between the 2 conditions is largely dependent on the capabilities of our diagnostic and imaging techniques.

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

For patient education information, see the Procedures Center and Brain and Nervous System Center, as well as Electroencephalography (EEG) and Epilepsy.

For more information, see the following:

Epilepsy and Seizures

EEG in Status Epilepticus

Epileptiform Normal Variants on EEG

EEG in Common Epilepsy Syndromes

Generalized Epilepsies on EEG

EEG Video Monitoring

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