Abstracts

RATIONALE: Ictal EEG and MRI findings are considered the most important information to localize the epileptic focus and predict surgical outcome in patients with temporal lobe epilepsy. The role of interictal EEG abnormalities is less clear. METHODS: We studied 32 patients with mesial temporal lobe epilepsy who underwent anterior temporal lobectomy between 1994 and 1997. All had video-EEG monitoring and quantitative MRI. Scalp-recorded ictal EEG onset was lateralized to one temporal region in all. Interictal abnormalities were analyzed using a routine EEG on the day of admission to the Epilepsy Monitoring Unit and a 2-hour sleep-deprived EEG on day 3. Seizure outcome was categorized using Engel's classification. Only patients in Class I (seizure-free) were considered to have a favorable outcome. RESULTS: Of the 23 patients with a favorable outcome, 14 (61%) had unilateral temporal spikes, 3 had bitemporal independent spikes predominantly (67-95%) on the side corresponding to the ictal onset, 1 had additional frontal spikes and 5 had no recorded spikes. Of the 9 patients with an unfavorable outcome, 3 (33%) had unilateral temporal spikes, 2 had bitemporal independent spikes (88-92% on the side of ictal onset), 2 had additional ipsilateral frontal spikes and 2 had rare or no spikes. MRI showed unilateral hippocampal atrophy in 19 (83%) of the 23 patients with a favorable outcome and 7 (78%) of the 9 patients with an unfavorable outcome. Unilateral temporal interictal spikes were concordant with the temporal lobe of ictal EEG onset and MRI results in all patients. All patients in both outcome groups with rare or no interictal spikes had hippocampal atrophy on MRI. CONCLUSIONS: The presence of unilateral temporal spikes on routine and prolonged, sleep deprived EEGs is a predictor of favorable seizure outcome following surgery in patients with mesial temporal lobe epilepsy. In patients with unilateral hippocampal atrophy on quantitative MRI, interictal EEG may be sufficient to identify the epileptic focus but ictal EEG would still be required in patients with rare or no interictal spikes, bitemporal spikes and/or normal MRI.