Closed-Loop Stimulation in the Control of Focal Epilepsy

This chapter describes the results of a multicenter study of a closed-loop neurostimulation system called the responsive neurostimulator (RNS) system undertaken by the NeuroPace, Inc. The institution performed nine implants and all cases involved more than one year follow-up. One of these nine (the only case without preoperative invasive monitoring) cases was an insulin dependent juvenile diabetic who was subsequently found to have anti-GAD antibody. This patient never responded to the neurostimulator system and her initial IPG was not replaced when the battery depleted. Follow-up on the other eight cases ranged from 19 to 32 months. All of these eight cases underwent preimplant invasive monitoring with discrete seizure focus localization. The median seizure frequency reduction was 56% and the mean reduction was 65%. The range in seizure frequency reduction was 43–100%. Seven cases required replacement of IPGs due to battery depletion and the time to IPG replacement ranged from 12 to 26 months with a median of 22 months and a mean of 21 months. There has been only one infection requiring explantation of the system. This infection occurred 16 months after implantation of a new IPG and 28 months after the original implantation. No adverse neurological events were reported in these cases. Observation of this study also support the ability of this automated seizure detection/therapeutic stimulation device to positively influence electrographic seizure activity. However, the study is still in a preliminary phase and more data is required to define optimal stimulation parameters as well as patient candidacy for seizure control.