Differential Findings of Interictal and Ictal Scalp Electroencephalographic Pattern between Mesial and Neocortical Temporal Lobe Epilepsies

Choi, Seung Ho; Kim, Ji Eun; Yi, Sang Doe

Abstract

BACKGROUND: The clinical and electroencephalographic differentiation of the mesial temporal lobe epilepsy (MTLE) and neocortical temporal lobe epilepsy (NTLE) may have a practical value. Until now, a few comparative studies reported some relatively minor differences between the two groups. We investigated the clinical history, interictal and ictal electroencephalographic (EEG) patterns to differentiate NTLE from MTLE.
METHODS
Twenty two patients with medically refractory MTLE and fourteen patients with isolated neocortical lesions were recruited. The interictal and ictal scalp EEG patterns were compared in terms of the interictal EEG distribution patterns of epileptiform discharges, focal slow waves (ipsilateral/contralateral refers to side of pathology), and the frequencies of ictal discharges on EEG at seizure onset.
RESULTS
Interictal EEG patterns of epileptiform discharges and focal slow waves were recorded most often at the ipsilateral or bilateral sphenoidal electrodes in both groups without significant differences. Ictal EEG onset with rhythmic theta waves was significantly more frequent in MTLE (72.3%) than in NTLE (36.7%), but ictal EEG onset with rhythmic alpha waves and those with rhythmic beta waves were significantly more frequent in NTLE (33.3%, 20.0%, respectively) than in MTLE (10.8%, 1.2%, respectively). Initial ictal EEG patterns appeared more frequently at the sphenoidal electrodes in both groups (MTLE:73.5%, NTLE:60.0%). Initial ictal EEG patterns of the bilateral hemisphere, ipsilateral hemisphere or ipsilateral diffuse temporal area were seen only in NTLE (16.7%, 3.3%, 10% respectively), but not in MTLE.
CONCLUSIONS
This study showed that the initial ictal patterns and the frequency of ictal onset were significantly different in MTLE and NTLE. These differences could give a practical help in diagnosing MTLE and NTLE.