Long-Term Outcome of Vagus Nerve Stimulation for Refractory Epilepsy: A Longitudinal 4 year Follow-up Study in Korea

Background and Purpose: We evaluated the long-term outcome of patients with refractory epilepsy who were treated with vagus nerve stimulation (VNS). Methods: This investigation is designed as an uncontrolled, open-label, retrospective and long-term study. From June 1999 to October 2009, 20 patients were suitable for inclusion criteria: 4-year follow-up and documented seizure frequency before and after implantation. Seizure frequency was collected by clinical recording and interview. Primary outcome measures were the reduction in mean seizure frequency and responder rate (seizure frequency reduction of>50%). Results: In 20 patients (M:F=16:4), mean age at the time of implantation was 22.3 years (range 8-44) and mean disease duration was 13.9 years (range 1-37). Mean maximum stimulation output current was 1.90 mA (range 0.25-3.5). Overall mean seizure frequency reduction rate was 61.8 % at 4 year follow-up comparison with baseline (p<0.001). Proposition of responder (> 50 % seizure frequency reduction) o