Vagus Nerve Stimulation for Seizures

Abstract

It is agreed that 1% of the general population is afflicted with epilepsy and close to 30% of epilepsy patients are intractable to medications. In spite of a recent increase in the number of new medications that are available on the market, many patients continue to have seizures or their seizures are controlled at the expense of intolerable side effects. Resection epilepsy surgery is an alternative; however, not every intractable patient is a good candidate for this surgery. Additionally, it is only offered to a small fraction of these patients due to the lack of an adequate number of comprehensive epilepsy programs and financial support for such surgeries. Vagus nerve stimulation (VNS) is a novel adjunctive therapy that has recently become commercially available for intractable epilepsy. It is indicated as an add-on treatment for seizures of partial onset with or without secondary generalization in patients 12 years of age or older. The VNS system is comprised of a battery generator that delivers regular intermittent electrical stimuli programmed via menu-driven software and an interrogating wand. The generator is implanted in the left upper chest and connected to the left cervical vagus nerve via a pair of semi-circular helical electrodes wound around the vagus nerve and wires tunneled under the skin. Surgery is normally completed within 2 h under general anesthesia and the patient can go home within a few hours postoperatively. Experiments in humans began in 1988 with two single-blind pilot studies that demonstrated the feasibility and safety of this unconventional therapy. Following these studies, two multicenter, active-control, parallel, double-blind protocols showed a statistically significant reduction in partial onset seizures with reasonable and well-tolerated side effects. Adverse events related to VNS included voice alteration and a tingling sensation in the throat during stimulation only and a decrease in intensity over several weeks. Coughing during stimulation occurred normally when therapy was initiated and shortness of breath occurred mainly during exertion. Long-term follow-up suggests that reduction in seizure frequency and intensity is maintained over time. VNS is a novel adjunctive anti-epilepsy therapy that offers patients a better-tolerated option than medications in general and that is less invasive and extensive than resection surgery. Its efficacy may compare to novel potent anti-epilepsy drugs; however, VNS does not replace resection epilepsy surgery in selected patients in whom chances of seizure-free results are high (70–90%).