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.
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.
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.
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.