Modifications of sleep EEG induced by chronic vagus nerve stimulation in patients affected by refractory epilepsy

Objective: The aim of this study was to evaluate the impact of chronic vagus nerve stimulation (VNS) on sleep/wake background EEG and interictal epileptiform activity (IEA) of patients with medically refractory epilepsy. Methods: From a broader sample of 10 patients subjected to baseline and treatment polysonmographies, spectral analysis and IEA count have been performed on 6 subjects' recordings, comparing the results by means of statistical analysis. Results: An overall increase in EEG total power after VNS has been observed, more marked in NREM sleep, collapsing EEG power spectra into 5 frequency bands, we have found a statistically significant increase in delta and theta in NREM sleep, and of alpha in wakefulness and REM sleep. The incidence of IEA is diminished, although not significantly only the duration of discharges is significantly diminished. Conclusions and significance: Long-term VNS produces an enhancement in sleep EEG power of medically refractory epileptic patients. These results may be related to a better Structured composition of EEG, and it is possible that chronic VNS may have a major role in enhancin,, the brain's ability to generate an electrical activity. (C) 2003 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.