Abstracts

Rationale: To evaluate EEG predictors of seizure reccurrence after anteromesial temporal lobectomy (ATL) for medically-refractory epilepsy associated with unilateral medial temporal sclerosis (MTS). Methods: We prospectively evaluated 49 patients with medically-refractory epilepsy associated with unilateral MTS (25 women; 27 left MTS), who underwent prolonged noninvasive video-EEG monitoring and anteromesial temporal lobectomy (ATL). Endpoint was considered postsurgical seizure recurrence with at least two-year follow-up for seizure-free patients. All patients underwent noninvasive video-EEG monitoring with a minimum two-day duration (mean 5.72.8 days). We evaluated interictal epileptiform discharge frequency (IED/hour) in the first and last monitoring days, and occurrence of IEDS contralateral to the MTS side in the first and last monitoring days. Ictal EEG was classified as ipsilateral to MTS side or bilateral/contralateral. No patients with extratemporal IED were observed. We also analyzed possible clinical predictors of seizure-free outcome (age, age at epilepsy onset, epilepsy duration, generalized seizures occurrence, and presence of an initial precipitant insult). Results: Median postoperative follow-up was four years (range: one to seven years). 34 (69.4%) patients were seizure-free and 45 patients (91.8%) had Engel Class I outcome. Higher IED rates (median > 20.5 IED/hour) in the first monitoring day and contralateral IED occurrence in the first monitoring day were predictors of seizures recurrence on univariate analysis (Kaplan-Meyer survival analysis). Mean survival IED > median: 4.2 years; 95%CI 3.3-5.0; IED < median: 6.2 years; 95%CI: 5.4-6.9; p=0.03. Survival mean for contralateral IED occurrence: 3.5 years; 95%CI 2.5-4.5; exclusively ipsilateral IED: 5.9 years; 95%CI: 5.2-6.6; p=0.02. First day IED score, defined as: zero - lower IED frequency and no contralateral IED, one - higher IED frequency or contralateral IED occurrence or two - higher IED frequency and contralateral IED occurrence was a powerful predictor of seizure recurrence. Survival mean: score 2 - 2.8 years; 95% CI 1.6- 4.1; zero or one ?" 6.0 years; 95%CI 5.4 - 6.6; p=0.0003. Clinical, demographic and other EEG factors did not predict outcome. On multivariate analysis (Cox proportional-hazards regression), first day IED score of two points was a predictor of seizure recurrence (relative risk: 5.0 - 95%CI 1.8-14.3; p=0.0017). Conclusions: Patients with unilateral MTS without extratemporal epileptiform activity on VEEG monitoring generally have good postoperative seizure outcome. First day monitoring IED score was a powerful predictor of seizure recurrence in this patient population. Funding: This work was funded by FAPESP (Cinapce Program grant number 2005/56464-9).