Abstracts

Rationale: The Responsive Neurostimulation System (RNS®) was recently approved as an adjunctive therapy for drug-resistant focal onset epilepsy. It records electrocorticographic (ECoG) activity, detects epileptiform patterns, and delivers electrical stimulation to abort seizures. The efficacy of the pivotal trial and the Long-Term Treatment Study was based on a self-reported seizure frequency baseline. However, since subclinical seizures are not accounted for, the true seizure frequency baseline may be inaccurate. The aim of this study was to evaluate the effectiveness of RNS using an ECoG seizure frequency baseline.  Methods: A retrospective study identified 9 patients who underwent implantation of the RNS system from 2015 to 2016 at the University of California, Irvine. To be included in the study, subjects had to qualify for RNS implantation and have 2 or fewer seizure foci as determined by intracranial EEG. Subjects who had their RNS explanted for any reason and those who had concurrent RNS implantation and surgical resection were excluded. Leads were placed at the site of the ictal onset zone. The stimulator was programmed to detect and deliver treatment following identification of the individual epileptiform patterns. To avoid potential under reporting of seizures, the baseline seizure frequency was determined by the ECoG average of the first 2 months post implantation. Seizure control was assessed at 3 month, 6 months, and 12 months. Results: 2 of the 9 patients were excluded from this study. One patient had their RNS explanted for a presumed device-related infection and 1 patient underwent surgical resection and RNS implantation on the same day. All 7 patients have had their RNS® enabled for at least 3 months, 6/7 for 6 months, and 3/7 for 12 months. Using a self-reported seizure frequency baseline, the mean change in seizure frequency was +11%, -6% and -58% at 3, 6, and 12 months, respectively. In contrast, by using the ECoG seizure frequency baseline, the mean change in seizure frequency was -82%, -66% and -75% at 3, 6, and 12 months, respectively. Conclusions: The efficacy of RNS is influenced by the seizure frequency baseline. Our results compare favorably to the pivotal trial only when using the ECoG seizure frequency baseline. The reason for this discrepancy is due to underreporting of seizures by patients and consequently a falsely low seizure frequency. Therefore, determination of the true baseline seizure frequency by ECoG is likely a more accurate assessment of seizure outcome. Funding: N/A