Using electrocorticogram baseline seizure frequency to assess the efficacy of responsive neurostimulation.

Background: The effect of direct brain responsive neurostimulation on the frequency of electrographic seizures in patients with medically refractory focal epilepsy has not been evaluated by chronic ambulatory electrocorticographic monitoring.

Methods: This was a retrospective study of 9 patients who underwent implantation of the responsive neurostimulator (RNS) system from 2015 to 2017 at the University of California, Irvine. Leads were placed at the ictal onset zone as determined by intracranial electroencephalography (EEG). The neurostimulator was programmed to detect and deliver stimulation following identification of the individual's epileptiform patterns. Electrographic seizures were determined by review of all detections. The electrocorticography (ECoG) seizure frequency baseline was the average of the first 2 months postimplantation. The patient-reported seizure frequency baseline was the average of the 2 most recent months prior to RNS implantation. Seizure control was assessed at 3 months, 6 months, and 12 months.

Results: Nine patients were included in the study. All 9 patients have been treated with responsive stimulation for at least 3 months, 7/9 for 6 months, and 4/9 for 12 months. The mean change in seizure frequency was -10%, -19%, and -56% at 3, 6, and 12 months, respectively, using a self-reported seizure frequency baseline compared with -85%, -71%, and -56% at 3, 6, and 12 months, respectively, using the ECoG seizure frequency baseline.

Conclusion: Chronic ECoG may provide a more accurate estimate of seizure frequency and provide additional insight into the true efficacy of the RNS system.