When is a postoperative seizure equivalent to “epilepsy recurrence” after epilepsy surgery?

Abstract

Up to one-half of epilepsy surgery patients will have at least one seizure after surgery. We aim to characterize the prognosis following a first postoperative seizure, and provide criteria allowing early identification of recurrent refractory epilepsy. Analyzing 915 epilepsy surgery patients operated on between 1990 and 2007, we studied 276 who had >or=1 seizure beyond the immediate postoperative period. The probability of subsequent seizures was calculated using survival analysis. Patients were divided into seizure-free (no seizures for >or=1 year) and refractory (persistent seizures) and analyzed using multivariate regression analysis. After a first seizure, 50% had a recurrence within 1 month and 77% within a year before the risk slowed down to additional 2-3% increments every two subsequent years. After a second seizure, 50% had a recurrence within 2 weeks, 78% within 2 months, and 83% within 6 months. Having both the first and second seizures within six postoperative months [odds ratio (OR) 4.04; 95% confidence interval (CI) 2.05-8.40; p = 0.0001], an unprovoked initial recurrence (OR 3.92; 95% CI 2.13-7.30; p < 0.0001), and ipsilateral spikes on a 6-months postoperative electroencephalography (EEG) (OR 2.05; 95% CI 1.10-3.88; p = 0.025) predicted a poorer outcome, with 95% of patients who had all three risk factors becoming refractory. All patients with cryptogenic epilepsy and recurrent seizures developed refractoriness. Seizures will recur in most patients who present with their first postoperative event, with one-third eventually regaining seizure-freedom. Etiology and early and unprovoked postoperative seizures with epileptiform activity on EEG at six postoperative months may predict recurrent medical refractoriness.