The Clinical Usefulness of Ictal Surface EEG in Neocortical Epilepsy

Lee, Sang Kun; Kim, Joo Yong; Nam, Hyun Woo

Abstract

BACKGROUND: Localizable scalp ictal EEG appears to be rare in neocortical epilepsy. However, there have not been many studies based upon a large number of patients. This study aims to identify the characteristic patterns of variable neocortical epilepsies and to evaluate their clinical usefulness in the localization of epileptogenic foci.
METHODS
We retrospectively assessed 394 noninvasive ictal recordings from 86 patients who subsequently underwent invasive study and resective surgery. Ictal EEGs were recorded by video-EEG monitoring systems with electrodes placed according to the international 10-20 system including additional anterior temporal electrodes. Ictal recordings were analyzed accord-ing to the localizing accuracy and frequency characteristics. The durations of discrete or regional ictal rhythms were also measured.
RESULTS
The percentage of discrete or regional EEGs were respectively 26, 52, 70, and 10% in frontal lobe epilepsy (FLE), lateral temporal lobe epilepsy, occipital lobe epilepsy (OLE), and parietal lobe epilepsy (PLE). The ictal rhythms in the order of frequency were theta, delta, beta, alpha, and rhythmic spike-and-wave. The duration of discrete or regional ictal rhythms were significantly shorter in FLE and PLE than in other epilepsies. Ictal beta activ-ity was the most common rhythm in discrete-patterned EEGs. There were some tendencies of poor lateralization in the presence of structural lesion. Types of seizure were not related with the degree of localization except for simple partial seizure.
CONCLUSIONS
Ictal surface EEG was clinically helpful in the localization of epileptogenic foci especially in particular neocortical epileptic syndromes.