Vagus Nerve Stimulation for Epilepsy: An Evidence-Based Approach

Abstract

Medical treatment of seizures yields a satisfactory response in 75-80% of the patients; resective epilepsy surgery is a therapeutic option for those patients who are refractory to drug therapy, but there is still a considerable portion (20-30%) of patients who are ineligible for surgery or failed surgery. Vagus nerve stimulation (VNS) might be an option for these very refractory patients. We carried out an evidence-based search to identify the best evidence presently available related to the use of VNS. We used multiple searchable databases (primary: PubMed-MEDLINE, EMBASE, LILACS, and SciELO; secondary: Cochrane Library) and a standard structured approach know as the PICO scheme: P (patient), I (intervention), C (comparison), and O (outcome). Publications were selected based on study design, PICO components, language, and availability of full text. For study design, we included papers designed as 'randomized controlled trials'; these trials were evaluated according to the Jadad score; the type II error was not used while selecting studies to avoid further limitations. Twenty-eight papers were selected, all from PubMed-MEDLINE. The search results showed that patients older than 12 years with refractory partial seizures (with or without generalization) may benefit from VNS. Children might also benefit, but might need different stimulation parameters. We also noted that higher stimulation settings are associated with increased occurrence of hoarseness, throat pain, cough, and dyspnea. The available randomized controlled trials and cohorts made it clear that VNS is a useful palliative procedure in adult patients with partial epilepsy, and a 50-60% reduction in seizure frequency might be expected in at least 50% of the patients. VNS is a useful palliative procedure in patients with refractory epilepsy. As our practical experience and understanding of the mechanism of action of VNS increase, more homogeneous patient populations that might respond better to VNS are being recognized, such as children with secondary generalized epilepsy and some types of reflex epilepsy.