Abstracts

Rationale: Conventional assessment of seizure outcome after anterior temporal lobectomy (ATL) examines the effect of surgery on seizure frequency but not on seizure severity. However, for patients with persistent seizures after surgery, mitigation or intensification of seizure severity may have clinically meaningful impacts. Therefore, defining whether seizure type changes after surgery is important. We assessed whether seizure severity changes after ATL and determined whether any clinical features are associated with occurrence of secondarily generalized tonic-clonic seizures (GTCS) after surgery. Methods: Patients who had an ATL to treat medically refractory seizures were prospectively registered in a database from 1986 through 2008. Patients eligible for this study were followed for at least five years after surgery and had adequate documentation of preoperative and postoperative seizure types and frequency. Clinical data included age at surgery, gender, side of surgery, age at seizure onset, duration of epilepsy, febrile convulsion, IQ and seizure history including pre and post-operative seizure frequency and seizure type including GTCS, complex partial seizures (CPS) and simple partial seizures (SPS). Chi square, t- tests and the modified Wald statistic were used for data analysis. Results: 338 patients with a mean follow-up of 10.14 years (range 5-22 years) were eligible for inclusion. 173 were male, 165 were female, 178 had right ATL and 160 had left ATL, mean age at surgery was 34.7 10 years, average duration of epilepsy was 19.78 11 years and mean full scale IQ was 91.31 13. 179 patients (53.0%) had one or more CPS or GTCS after surgery; 159 had no recurrences. The data are summarized in the table. The chance of developing de novo GTCS after ATL was 6.2% (95% CI = 3.0-11.9%). Chance of GTCS remitting if present before surgery were 65.9% (95% CI = 59.2-72.0%). Among 8 patients who had not had GTCS before surgery and developed new onset GTCS after operation, 4 (50%) had one GTCS, 2 (25%) had two or three GTCS, and 2 (25%) had > 3 GTCS. Of the 8, one had GTCS acutely (? 1 month) and one had a seizure sub-acutely (? 6 months). The main risk factor for having GTCS after surgery was having GTCS in the year before surgery (p = 0.03). In contrast, age at seizure onset, age at surgery, FIQ, gender and history of febrile seizures in childhood were not associated with risk of GTCS occurrence after operation. Conclusions: In addition to improving seizure frequency, ATL substantially ameliorates seizure severity in patients. It infrequently leads to de novo GTCS; even when these first appear after surgery, they are usually rare. The most striking effect of surgery is the abolition of GTCS in most patients. The mechanism may be due to interruption of networks for seizure spread or reduction in the volume of epileptogenic cortex, which may then be less able to produce seizures that are potent enough to spread to subcortical structures needed for the clinical expression of GTCS.