Vagus nerve stimulation for epilepsy

Abstract

In two prospective, double-blind, 3-month trials with 300 patients, chronic intermittent high intensity electrical stimulation of the cervical vagus nerve with a subcutaneous surgically implanted device (vagus nerve stimulation, VNS) reduced medication-resistant partial onset seizures by 24–28%, compared with seizure rate reductions of 6–15% in the low intensity control group. Side effects in the first 3 months of treatment were hoarseness (60%), cough (38%), parasthesias (20%) and dyspnea (20%); after 3 years of VNS, less than 5% of patients experience side effects. Seizure rates decline further with increasing VNS treatment durations (43% of patients have a 50% or more seizure rate reduction after 3 years); this seems independent of later antiepileptic drug (AED) and stimulation parameter changes. Antiepileptic effects of VNS may persist after termination of the therapy. The following clinical features are not predictive of seizure rate responsiveness to VNS: epilepsy duration, epilepsy syndrome, age, gender, epilepsy onset age, baseline seizure rate, prior epilepsy surgery, number and type of concomitant AEDs, number of prior AEDs, and number of seizure types. In one small study, increased thalamic blood flow seen on PET scans performed upon VNS initiation was predictive of later clinical responsiveness. Better methods to identify preoperatively probable VNS responders need to be developed.