Optimal timing and differential significance of postoperative awake and sleep EEG to predict seizure outcome after temporal lobectomy.

Objective: To evaluate the prognostic value of postoperative EEGs to estimate post anterior temporal lobectomy (ATL) seizure outcome.

Methods: We studied postoperative EEGs in 325 consecutive patients who had minimum five years of post-ATL followup. Interictal epileptiform discharges (IEDs) present only during sleep were classified as sleep IEDs. We defined favorable final-year outcome as no seizures during the final one year and favorable absolute-postoperative outcome as no seizures during the entire postoperative period.

Results: At mean follow-up of 7.3 ± 1.8 years, 281 (86.5%) patients had favorable final-year outcome while 161 (49.5%) had favorable absolute-postoperative outcome. IEDs on three months and one year EEG were associated with unfavorable outcomes while IEDs at 7th day had no association with outcomes. Sleep record increased the yield of IEDs by 30% at each time-point without compromising predictive value. EEG at one year predicted the risk of seizure recurrence on drug withdrawal.

Conclusion: While EEG at three months and at one-year after ATL predicted seizure outcome, EEG at 7th day was not helpful. Sleep record increases the sensitivity of postoperative EEG without compromising specificity.

Significance: Both awake and sleep EEG provide useful information in postoperative period following ATL.