Vagus nerve stimulation for epilepsy: a review

Vagus nerve stimulation is an empirically based method for treatment of epi lepsy by repeated stimulation of the left vagus nerve through implanted ele ctrodes. Despite studies in animals and man, which show changes in brain el ectrophysiology, metabolism and neurochemistry, the mode of action remains unknown. Clinical testing has presented methodological challenges, as it is difficul t to assess under double blind conditions a treatment which requires surger y and produces a sensation every time the stimulator comes on. This has nev ertheless been successfully addressed in parallel design, controlled trials comparing high and low stimulation schedules. These have been performed in adults with medically intractable partial seizures, and demonstrated effic acy, safety and good tolerability. Efficacy, both in the controlled trials and in numerous reports arising from the considerable post-marketing experi ence is modest. Some 30% of patients achieve a 50% seizure reduction after 3 months of treatment, but this proportion progressively increases to about 50% after 18 months. Side-effects comprise: discomfort in the face or neck when the stimulator i s activated, coughing, breathlessness on exertion and hoarseness of voice. All are related to intensity of stimulation and rapidly habituate in most s ubjects. Ln those patients who respond, a stimulus level can therefore gene rally be found which is acceptable to the subject. No indication other than refractory partial seizures in adults has been the subject of controlled trials, but post-marketing experience and uncontroll ed reports indicate comparable efficacy and safety in a wide range of epile psies, partial and generalized, idiopathic, cryptogenic, or symptomatic, in patients of all ages. (C) 2000 BEA Trading Ltd.