Abstracts

Rationale: To examine the hypothesis that the main effect of Vagus Nerve Stimulation (VNS)is to act as a placebo. Methods: The published trials of VNS in epilepsy have been examined specifically to determine the rate of seizure freedom (SF), and this rate is compared with the placebo rate from placebo treated patients. The timing of the onset of SF and progression over time has been evaluated. Results: SF with VNS varies between 2% and 27% with a mean of 9%. SF rate is similar for different populations, e.g children and adults; those with or without learning disability. SF is greater in patients who have not undergone previous resective surgery; in those implanted earlier rather than later in their epilepsy history; and who have certain pre-implantation EEG patterns. No relationship to VNS stimulus parameters or concomitant AED prescriptions are noted. The SF rate increases over time in longer term follow up studies.Conclusions: SF with VNS is in the same range to that noted in trials of several newer AEDs. Determining the profile of patients most likely to be SF is important for clinical practice and the profile is presented in this communication. The SF rate reported in these studies argues against VNS acting as a placebo.