Vagus nerve stimulation: current status and clinical applications

Despite the recent introduction of new anti-epileptic drugs (AEDs), many patients with epilepsy, especially those with partial-onset seizures, continue to have seizures that are refractory to pharmacotherapy. Other patients are unable to tolerate the side-effects of AEDs given singly or in combination. Cerebral resective surgery may be an option for a sub-group of these patients; however, many patients with refractory partial epilepsy are not optimal candidates for epilepsy surgery. Consequently, the introduction of left vagus nerve stimulation (VNS) for those patients who have been afflicted by seizures or medication side-effects has opened up a new, non-pharmacological approach to epilepsy treatment. The mechanism of action of VNS is uncertain. VNS exerts an anticonvulsant effect in a variety of animal seizure models; has no effect on hepatic metabolic processes, serum concentrations of AEDS, or laboratory values; and has no clinically significant effect on vagally-mediated physiological processes. VNS is safe and well-tolerated in patients with long-standing, medically-refractory, partial-onset epilepsy. Adverse effects are usually mild to moderate in severity and related to stimulation, and almost always resolve with adjustment in stimulation settings. Controlled studies of patients on AED therapy show that adjunctive VNS is effective for partial-onset seizures when given every 5 min for 30 s intervals. Results of studies in paediatric patients are encouraging.