Vagus nerve stimulation therapy for seizures.

Of the 3 million patients with seizures in North America approximately 70% have effective seizure control with medications. In the group refractory to medical treatment only a minority fit the criteria for surgical therapy. Vagus nerve stimulation therapy seems to be a suitable nonpharmacologic therapy for reducing seizure frequency in these cases. It is a simple device with 2 electrodes and an anchor loop implanted on the midcervical portion of left vagus nerve and the impulse generator is implanted subcutaneously in the left infraclavicular region. The left vagus is the preferred site as the right vagus innervates the sinoatrial node and influences the heart rate. Data from laboratory studies suggest that it most probably works by increasing the release of norepinephrine in the locus ceruleus, which in turn increases the seizure threshold. More than 32,000 devices have been implanted since it was approved in 1997. There is class I evidence that vagus nerve stimulator reduces the frequency of seizures. In addition it also elevates the patients' mood-independent of seizure control. In one of the studies 50% reduction in seizure frequency was 37% in the first year and 44% in the second and third year. The side effects commonly reported are constriction in the throat, change in voice, and throat pain which most patients are able to tolerate and continue the use of the device. In conclusion VNS seems to be an effective nonpharmacologic therapy for medically refractory partial onset seizures.