Differential Findings of Ictal EEG Pattern between Mesial and Neocortical Temporal lobe Epilepsies

Kim, Yo Sik; Seo, Dea Won; Hong, Seung Bong

Abstract

BACKGROUND: Neocortical temporal lobe epilepsy (NTLE) appears to have different characteristics in clinical and electrophysiological aspects from mesial temporal lobe epilepsy (MTLE). Many semiological studies on TLE have been performed. We investigated ictal EEG patterns to differentiate NTLE from MTLE.
METHODS
One hundred twenty nine scalp ictal EEG recordings came from 27 pathologically proven TLE patients were analyzed by 1) frequency of ictal discharge at EEG seizure onset (alpha, beta, theta & delta), 2) distribution patterns of ictal EEG onset (diffuse, lateralized & regionalized), 3) electrode of maximum amplitude at initial regionalized portion of ictal EEG, and 4) mesial to lateral and anterior to posterior amplitude ratio of ictal discharges in temporal electrodes.
RESULTS
One hundred seven seizures came from MTLE (23 patients) and twenty-two seizures from NTLE (4 patients). Ictal EEG onset with delta wave was observed more frequently in MTLE (42.7%) than in NTLE (14.3%), but beta wave onset was noted more frequently in NTLE (14.3%) than MTLE (0%). Initial ictal EEG discharges were lateralized on ipsilateral hemisphere in 22.0% of MTLE and in 28.6% of NTLE, regionalized over ipsilateral temporal region in 36.6% and 23.8% respectively, and showed diffuse nonlateralized onset in 41.5% of MTLE and 47.6% of NTLE. Both TLE groups revealed most often their maximum negativity of ictal EEG onset at sphenoidal electrode (MTLE: 59.3%, NTLE: 42.8%). Mesial to lateral amplitude ratio of ictal EEG was significantly larger in MTLE group than NTLE group. The amplitude ratio of anterior to posterior temporal electrodes was greater in NTLE group than in MTLE group.
CONCLUSION
Delta frequency of ictal onset EEG is more suggestive of MTLE while beta frequency may suggest NTLE. Initial ictal EEG patterns with their maximum on sphenoidal electrode do not differentiate MTLE from NTLE. NTLE has wide vertical and narrow horizontal electrical field, but MTLE has wide horizontal and narrow vertical electrical field.