Vagus nerve stimulation for partial seizures

Vagus nerve stimulation (VNS) has recently been introduced as an adjunct for treating patients with seizures. The aim of this systematic review was to overview the current evidence for the effects of vagus nerve stimulation, when used as an adjunctive treatment for patients with drug-resistant partial epilepsy.

To determine the effects of VNS high-level stimulation compared to low-level (presumed subtherapeutic dose) stimulation.

We searched the Cochrane Epilepsy Group trials register, MEDLINE (January 1966 to October 2000) and The Cochrane Controlled Trials Register (Cochrane Library Issue 4, 2000).

Randomized, double-blind controlled trials of VNS comparing high and low stimulation paradigms. Studies in adults or children with drug-resistant partial seizures.

Two reviewers independently selected trials for inclusion and extracted data. The following outcomes were assessed: (a) 50% or greater reduction in total seizure frequency; (b) treatment withdrawal (any reason); (c) side effects. Primary analyses were intention to treat. Sensitivity best and worst case analyses were also undertaken. Summary odds ratios (ORs) were estimated for each outcome.

Results of the overall efficacy analysis show that VNS stimulation using the high stimulation paradigm was significantly better than low stimulation. The overall OR (95% Confidence Interval (CI)) for 50% responders across all studies is 1.93 (1.1,3.3). This effect did not vary substantially and remained statistically significant for both the best and worst case scenarios. Results for the outcome "withdrawal of allocated treatment" suggest that VNS is well tolerated as no significant difference was found between the high and low stimulation groups, and withdrawals were rare. Statistically significant adverse effects associated with implantation (low versus baseline) were hoarseness, cough, pain and paresthesia. Statistically significant adverse effects associated with stimulation (high versus low) were hoarseness and dyspnea, suggesting the implantation is associated with hoarseness, but the stimulation produces additional hoarseness.

VNS for partial seizures appears to be an effective and well tolerated treatment. Adverse effects of hoarseness, cough, pain, paresthesias and dyspnea are associated with the treatment but appear to be reasonably well tolerated as dropouts were rare. Typical central nervous system adverse effects of antiepileptic drugs such as ataxia, dizziness, fatigue, nausea and somnolence were not statistically significantly associated with VNS treatment.