Prognostic importance of serial postoperative EEGs after anterior temporal lobectomy

Objective: To assess the value of postoperative EEG in predicting seizure outcome and seizure recurrence following antiepileptic drug (AED) withdrawal in patients with mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS).

Methods: We studied 262 consecutive patients with MTLE-HS with serial EEGs at 3 months, and at 1, 2, and 3 years after anterior temporal lobectomy (ATL), and considered the presence of interictal epileptiform discharges (IED) as abnormal. We attempted AED withdrawal in all seizure-free patients. We defined favorable outcome as freedom from seizures/auras during the entire follow-up period (outcome 1) and during terminal 1-year follow-up (outcome 2).

Results: During mean follow-up period of 7.6 (range 5–12) years, 129 (49.2%) patients had favorable outcome 1 and 218 (83.2%) had favorable outcome 2. Of 225 (85.9%) patients in whom AED withdrawal was attempted, 61 (27.1%) had seizure recurrence. Compared to patients with normal EEG, those with IED on 1-year post-ATL EEG had a 3-fold increased risk for unfavorable outcome 1 and 7-fold increased risk for unfavorable outcome 2. The patients in whom all the 4 EEGs were abnormal had 9-fold odds for unfavorable outcome 1 and 26-fold odds for unfavorable outcome 2. An abnormal EEG at 1 year increased the risk of seizure recurrence following AED withdrawal by 2.6-fold.

Conclusions: Post-ATL EEG predicts seizure outcome and seizure recurrence following AED withdrawal. Serial EEGs predict outcome better than single EEG. This information will be helpful in counseling of patients after ATL, and in making rational decisions on AED withdrawal.