Possible relationship between vagus nerve stimulation and ictal discharges revealed by long-term electroencephalographic and electrocorticographic monitoring in a non-responsive patient

Background: Vagus nerve stimulation (VNS) is a well-known palliative therapy for refractory epilepsy. However, some non-responsive patients experience persistent epileptic seizures after VNS. Aiming to identify the factors affecting response to VNS, we retrospectively analyzed the temporal relationship between VNS and ictal discharges through electroencephalographic and electrocorticographic monitoring in a non-responsive patient. Case description: We performed VNS in an 8-year-old boy suffering from posttraumatic epilepsy after the first presurgical evaluation. However, no therapeutic effect of VNS was noted. At age 14, we conducted the second presurgical evaluation. Electroencephalographic monitoring showed that 42% of ictal events originating in the right occipital region had a temporal relationship between the onset of ictal discharges and VNS. Electrocorticographic monitoring with implanted subdural electrodes showed that 50% of the ictal events originating from the medial site of the occipital tentorial surface had a temporal relationship between onset and VNS. Conclusion: Our results suggest a possible relationship between VNS and the ictal discharges.