Vagus nerve stimulation for the treatment of medically intractable seizures. Results of a 1-year open-extension trial. Vagus Nerve Stimulation Study Group
M. C. Salinsky, B. M. Uthman, R. K. Ristanovic, J. F. Wernicke and W. B. Tarver
Oregon Health Sciences University Epilepsy Center, Portland, USA.
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 long-term 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 long-term response.