We could predict good responders to vagus nerve stimulation: A surrogate marker by slow cortical potential shift

•Positive shifts of slow cortical potentials (SCPs) during the VNS period were observed in responders.•SCP shifts modulated by VNS were more effectively detected by EEGs with long enough time constant.•Positive polarity of SCP shift on scalp EEG could be an effective marker for response to VNS.

ObjectiveWe investigated whether vagus nerve stimulation (VNS) induces a positive shift of slow cortical potentials (SCPs) in patients with >50% seizure reduction (responders) but not in non-responders.MethodsWe analyzed routine clinical electroencephalograms (EEGs) from 24 patients who were undergoing seizure treatment by VNS. The patients were divided into 2 groups by hardware time constant (TC) of EEG: the TC 10-s group (10 patients) and TC 2-s group (14 patients). We compared SCPs at 5 electrodes (Cz and adjacent ones) between the 2 states of VNS: during stimulation and between stimulations. Seizure reduction was independently judged. Correlation between SCP (positivity or not) and seizure reduction (>50% or not) was estimated.ResultsIn the TC 10-s group, the correlation between SCP and seizure reduction was significant (p < 0.05) (i.e., both good results in 4 and both negative results in 5). In TC 2-s group, the correlation between SCP and seizure reduction was not significant (p = 0.209).ConclusionsA positive shift of SCP recorded by using a TC of 10 s could be a surrogate marker for VNS response.SignificanceSCP could be a biomarker of good responders to VNS.