Vagus nerve stimulation for refractory epilepsy: A Belgian multicenter study

Abstract

Introduction Vagus nerve stimulation (VNS) is a symptomatic add-on treatment for patients with medically refractory epilepsy. It consists of continuous electrical stimulation of the left vagus nerve by means of a helical electrode and an implantable, programmable pulse generator. Currently, over 50,000 patients are treated with VNS worldwide. Aim This uncontrolled, open-label retrospective study evaluates long-term outcome in patients treated with VNS for refractory epilepsy in seven different epilepsy centres in Belgium. Methods For the purpose of this study, a minimum of essential inclusion criteria were defined to collect relevant data. This limited the results to basic findings with regards to efficacy on the long term. Inclusion criteria were a follow-up of at least 12 months and a documented seizure diary before implantation and at maximum follow-up. Primary outcome measures were the reduction in mean monthly seizure frequency and the percentage of patients with a seizure reduction of at least 50% (responder rate). Results About 138 patients (67M/71F) had a mean age of 30 years (range 4–59) at time of implantation and a mean post-implantation follow-up of 44 months (range 12–120). The mean number of AEDs before implantation was 3 (range 1–5). About 117/138 patients had focal epilepsy, 21 patients had symptomatic generalised epilepsy. About 117/138 patients were older than 16 years, 21 patients were 16 or younger. At maximum follow-up, mean stimulation output current was 1.84 mA (range 0–3.25). Mean number of AEDs at maximum follow-up remained unchanged. The overall reduction in mean monthly seizure frequency was 51%. Mean seizure frequency before implantation was 41 seizures/month (SD=61; range 1–300), mean seizure frequency after implantation at maximum follow-up was 7 seizures/month (SD=25; range 0–120). Responder rate was 59%. 13% of patients had a seizure frequency decrease between 30% and 50%. About 28% had a seizure frequency decrease of<30%. Seizure freedom was obtained in 12/138 patients (9%). Conclusions The long-term experience with VNS in Belgium confirms that VNS is an efficacious adjunctive antiepileptic treatment for patients with refractory epilepsy.