Vagus Nerve Stimulation for the Treatment of Medically Intractable Seizures

Background: Chronic vagus nerve stimulation (VNS) continues to be evaluated as an adjunctive treatment for medically intractable seizures. A previous randomized controlled trial of 114 patients demonstrated a significant decrease in seizure frequency during 3 months of VNS at effective stimulation levels. Objective: To evaluate the efficacy of 1 year of VNS therapy for the treatment of medically refractory partial seizures and the relationship between initial and longterm response. Patients and Methods: All patients exiting the randomized controlled study of VNS for treatment of medically refractory partial seizures were offered indefinite treatment extension as part of an open-label trial. One hundred (88%) of 114 patients completed 12 months of VNS treatment at effective stimulation levels. Fourteen patients discontinued VNS treatment prior to 1 year, principally because of the treatment's lack of efficacy. These 14 patients were retained in the present analysis using an intent-to-treat approach. Antiepileptic drug use was monitored throughout the trial. Seizure frequency was analyzed in 4 sequential 3-month treatment periods. Results: Compared with pretreatment baseline, there was a significant decrease in seizure frequency during each of the 3-month treatment periods. Seizure frequency was reduced by a median of 20% during the first 3 months of VNS treatment and by 32% during stimulation months 10 through 12. Response during the first 3 months of VNS treatment was a statistically significant predictor of response at months 10 through 12. The observed reduction in seizure frequency was not explained by overall changes in antiepileptic drug use. Conclusions: The results indicate that VNS remains an effective adjunctive therapy for medically refractory partial seizures over a period of at least 1 year. Response during the first 3 months of treatment is predictive of longterm response.