Abstracts

Rationale: Epileptiform activity contralateral to the Hippocampal Sclerosis (HS) side occurs in up to 30% of patients with unilateral mesial temporal lobe epilepsy (MTLE), and may be associated with worse memory and postoperative seizure control (Passarelli, V. et al. 2015. J Neurol Sci. 359, 241–6). Paradoxically, successful epilepsy surgery in unilateral MTLE with contralateral epileptiform activity may be associated with contralateral epileptiform abnormalities resolution and improved memory (Castro, L. et al. 2008. Epilepsia. 49, 1324–32). We compared postoperative memory outcome in unilateral HS patients with and without bilateral electrographic ictal involvement to test the hypothesis that patients with bilateral ictal involvement present less pronounced memory decline compared to patients with exclusive ipsilateral ictal involvement. Methods: We evaluated medically refractory unilateral MTLE patients, aged 18 to 55 years; eight or more education years; no significant comorbidity and IQ>=70. Patients who declined surgery served as a control group. Surgical groups: left(L) and right(R) HS patients underwent noninvasive video-EEG monitoring and Wada testing. Patients were classified as Ipsilateral (Ip) if ictal EEG showed exclusive ipsilateral onset, or Bilateral (Bi), if at least one seizure onset occurred contralaterally to the HS, or if ictal discharge evolved to the contralateral HS side.  Memory was evaluated on two occasions. Verbal Memory was evaluated with the Rey Auditory Verbal Learning Test (RAVLT), and nonverbal memory was tested with the Rey Visual Design Learning Test (RVDLT). Baseline test scores, gender, age, epilepsy duration, seizure frequency, AED load, and mean difference between post and preoperative scores were compared with one-way ANOVA, followed by post-hoc analysis (Bonferoni/Games-Howell) if p1.645 as memory improvement, and Z<-1.645 as decline. Results were compared using Fisher’s exact test. Results: Seventy-one patients were studied (36 LHS). Twenty-one patients (9 LHS) declined surgery (Control). Patients with atypical language representation or who did not undergo Wada testing (2L, 2R) were excluded. Final analysis included 65 patients (34L). Patients were classified as L-Ip(10), L-Bi(15), L-Control(9), R-Ip(10), R-Bi(9), R-Control(12). Memory performance did not differ among surgical groups on preoperative evaluation. L-Ip presented significant post-op decline on immediate and delayed verbal recall (RAVLT-6 and 7) compared to controls, while L-Bi remained stable. L-Ip presented a significant delayed verbal memory decline compared to L-Bi (p=0.02). On individual performance (RCI Z-scores) on RVLT-7, three L-Ip and no L-Bi patients declined (p=0.05). There were no differences on nonverbal memory decline between L-Ip and L-Bi. RHS groups did not differ, except in one nonverbal memory score (RVDLT-T), where R-Ip declined more than R-Control (p=0.03). Conclusions: Dominant HS patients with bilateral ictal involvement presented less pronounced verbal memory decline compared to patients with exclusive ipsilateral ictal activity. Bilateral epileptiform activity is not associated with a higher risk of postoperative memory decline in unilateral HS patients.  Funding: CInAPCe (Inter-institutional Cooperation to Support Brain Research) Fapesp 2005/56464-9.