Prospective long-term study of vagus nerve stimulation for the treatment of refractory seizures

Purpose: To determine the long-term efficacy of vagus nerve stimulation (VN S) for refractory seizures. VNS is a new treatment for refractory epilepsy. Two short-term double-blind trials have demonstrated its safety and effica cy, and one long-term study in 114 patients has demonstrated a cumulative i mprovement in efficacy at 1 year. We report the largest prospective long-te rm study of VNS to date. Methods: Patients with six or more complex partial or generalized tonic-clo nic seizures enrolled in the pivotal EO5 study were prospectively evaluated for 12 months. The primary outcome variable was the percentage reduction i n 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 t herapeutic stimulation settings for the first time. Subjects initially rand omized 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% re duction in seizures, and 20% of 195 had a >75% reduction in seizures. Conclusions: The efficacy of VNS improves during 12 months, and many subjec ts sustain >75% reductions in seizures.