Prospective Long‐Term Study of Vagus Nerve Stimulation for the Treatment of Refractory Seizures

Summary: Purpose: To determine the long‐term efficacy of vagus nerve stimulation (VNS) for refractory seizures. VNS is a new treatment for refractory epilepsy. Two short‐term double‐blind trials have demonstrated its safety and efficacy, and one long‐term study in 114 patients has demonstrated a cumulative improvement in efficacy at 1 year. We report the largest prospective long‐term study of VNS to date.

Methods: Patients with six or more complex partial or generalized tonic‐clonic seizures enrolled in the pivotal EOS study were prospectively evaluated for 12 months. The primary outcome variable was the percentage reduction in total seizure frequency at 3 and 12 months after completion of the acute EO5 trial, compared with the preimplantation baseline. Subjects originally randomized to low stimulation (active‐control group) were crossed over to therapeutic stimulation settings for the first time. Subjects initially randomized to high settings were maintained on high settings throughout the 12‐month study.

Results: The median reduction at 12 months after completion of the initial double‐blind study was 45%. At 12 months, 35% of 195 subjects had a >50% reduction in seizures, and 20% of 195 had a >75% reduction in seizures.

Conclusions: The efficacy of VNS improves during 12 months, and many subjects sustain >75% reductions in seizures.