Abstracts

Rationale: Patients undergoing brain surgery for intractable epilepsy anticipate a “cure”. However, up to half will have at least one seizure after surgery. Some undergo expensive re-evaluations only to regain seizure-freedom without needing further interventions, while others have recurrent seizures for years before a reoperation is explored. No evidence-based guidelines exist for their management. We aim to characterize the prognosis following a first postoperative seizure, and to provide criteria allowing early identification of recurrent refractory epilepsy. Methods: Of 915 epilepsy surgery patients of all ages operated on between 1990- 2007 in a single comprehensive program, we reviewed those with at least 1 seizure beyond the immediate postoperative period, and one or more year of follow-up beyond the initial recurrence. The probability of subsequent seizures was calculated using survival analysis. Multivariate regression analysis was then used to compare seizure-free(no seizures for at least one year by last follow-up) and refractory(persistent seizures) patients. Results: Resections were temporal (73%), frontal (17%) or in the posterior quadrant (9%). 276 patients had at least one postoperative seizure. Of those, 49% were female and 56% had left-sided surgery. The mean overall follow-up duration after surgery was 6.6 years (range 1.1-19 yrs; standard deviation 4.3) and mean follow-up after the first postoperative seizure was 5.6 years (range1.1-18.6; standard deviation 4.1). The mean timing of the first postoperative seizure was 12.1 months (median 4.6; range 0.13-114.4 months). Forty patients (14%) did not have any further recurrences, 22 had a total of 2 seizures, and 17 a total of 3 seizures by last follow-up. Ninety five patients became seizure-free, with a mean duration of seizure-freedom of 4.9 ±0.4 years (range 1.1-16.4 years) by last follow-up, and a mean interval of 17.8 (±3.1) months to achieve seizure-freedom (time from first to last postoperative seizure). The remaining 181 cases were having persistent seizures with a mean frequency of 14.4 ± 2.6seizures/month. After a first seizure, 50% had a recurrence within one month, 77% within a year before the risk slowed down to additional 2-3% increments every 2 subsequent years. After a second seizure, 50% had a recurrence within 2 weeks, 78% within 2 months, and 83% within 6 months (figure 1). Having both the first and second seizure within 6 postoperative months (odds ratio 4.04; 95% C.I. 2.05-8.40; p< 0.001), an unprovoked initial recurrence (O.R. 3.92; 95% C.I. 2.13-7.30; p< 0.001), and ipsilateral spikes on a 6-months postoperative EEG (O.R. 2.05; 95% C.I. 1.10-3.88; p= 0.02) predicted a poorer outcome, with 95% of patients having all three risk factors becoming refractory versus 32% of those with none. Conclusions: Seizures will recur in most patients presenting with their first postoperative event. The period of highest risk is within the few subsequent months. A third will become seizure-free with the risk for refractoriness assessed by easily ascertainable measures at 6 postoperative months.