Interictal scalp EEG in intractable temporal lobe epilepsy

Kim, Ji Eun; Sohn, Eun Ik; Kim, Joon Sik; Yi, Sang Doe; Park, Young Choon

Abstract

BACKGROUNDS: The localization validity of interictal scalp EEG abnormalities in the patients with temporal lobe epilepsy(TLE) has been a subject of much debate. This study was an attempt to assess the general characteristics and the lateralization value of interictal scalp EEG abnormalities of TLE. We also examined the possible etiologic factors of bitemporal independent epileptiform discharges(BIED).
METHODS
We investigated the interictal scalp EEGs of 59 patients. All patients have been seizure free but might have had persistent auras (Engel's classification, class I) after anterior temporal lobectomy(ATL) with minimum follow-up of 1 year. Long term scalp EEG monitoring records were evaluated for interictal EEG abnormalities in all patients.
RESULTS
Scalp EEGs from 59 patients exhibited clear epileptiform discharges. Strictly unitemporal epileptiform discharge(UED) was present in 23 patients (39%). It was concordant with the side of seizure origin in 22 patients (95%), and discordant in 1 patient (5%). Thirty six patients (61%) had BIED. Twenty two patients with BIED showed lateralized preponderance which was defined as at least 80% laterality. It was concordant with the side of seizure origin in 21 patients (95%), and discordant in 1 patient (5%), and 14 patients were not lateralized. Bilateral synchronous epileptiform discharges were present in 4 patients (7%), and extratemporal spike in only 1 patient (2%). Localized temporal slow waves were shown in 33 patients (56%). It was concordant with the side of seizure origin in 28 patients, discordant in 1 patient. Four of 33 patients had bilateral temporal slow waves. There was no statistically significant difference in age at seizure onset, duration of epilepsy between the groups with UED and with BIED. Febrile seizures occurred similarly in both groups.
CONCLUSIONS
It seems obvious that patients with UED or lateralized interictal temporal spike or sharp waves have a strong likelihood of ictal onset from the ipsilateral temporal region.