Vagus nerve stimulation in drug-resistant epilepsies. Analysis of potential prognostic factors in a cohort of patients with long-term follow-up

Abstract

The results of vagus nerve stimulation (VNS) for the treatment of drug-resistant epilepsies are highly variable due to the lack of defined patient's selection criteria and a follow-up of published studies being generally too short. Here we report the outcome of VNS in a series with long-term follow-up and try to identify subgroups of patients who could be better candidates for this procedure. We studied 53 patients (33 male, 20 female) with a prospectively recorded follow-up (mean, 55.96 ± 43.53 months). The monthly average seizure frequency for each patient at baseline, 3, 6, 12 months, and each year until the latest follow-up after implant was measured and the percentage of "responders" and response time (RT) were calculated. We investigated the following potential prognostic role of these factors: age of onset of epilepsy, pre-implant epilepsy duration, etiology, and age at implant. Globally, 40 % of patients responded to VNS (mean RT, 14.85 ± 16.85 months). Lesional etiology (p = 0.0179, logrank test), particularly ischemia (p = 0.011, Fisher exact test) and tuberous sclerosis (p = 0.0229, Fisher exact test), and age at implant <18 years (p = 0.0242, logrank test) were associated to better response to VNS. In the lesional subgroup the best results were observed in patients with a pre-implant epilepsy duration <15 years (p = 0.0204, logrank test) and an age at implant <18 years (p = 0.0187 logrank test). The best candidate to VNS seems to be a patient with lesional etiology epilepsy (particularly post-ischemic and tuberous sclerosis) and a short duration of epilepsy who undergo VNS younger than 18 years.