Effect of vagal nerve stimulation on interictal epileptiform discharges:: A scalp EEG study

Purpose: To investigate the effects of acute vagal nerve stimulation (VNS) on interictal epileptiform discharges (IEDs). Methods: Fifteen epilepsy patients, all of whom had been treated with VNS for >=6 months, entered the study. In each subject, the absolute number of IEDs was counted at the baseline period (BP), the stimulation period (SP), six interstimulation periods (IPs), and the prestimulation period (PP), by using an original paradigm. The number of IEDs at the BP and the PP was compared with the number of IEDs at the SP and IPs. The results were correlated with other variables (the duration of VNS, the value of the output current, the duration of epilepsy, the type of epilepsy, the effect of VNS, and the effect of extrastimulation). Results: We observed a significantly higher reduction in the number of IEDs in the SP and all the IPs as compared with the BP. We noticed a significantly higher reduction in the number of IEDs in the SP and in the first IP as compared with the PP. The reduction of IEDs was,greater in patients who responded to VNS (>50% reduction of all seizures) and in patients who responded positively to magnetic extrastimulation. There were no other significant results in the reduction of IEDs when comparing other variables. Conclusions: Short-term VNS reduces IEDs significantly. The reduction is most prominent during the SP (i.e., when the pulse generator is active). The value of reduction of IEDs is higher in patients who respond to VNS and in patients with positive experiences with magnetic extrastimulation. These results can be useful in predicting the effect of VNS.