Abstracts

Rationale: The RNS System is a brain-responsive neurostimulation system that is FDA-approved for adults with focal onset seizures based on safety and efficacy data from 256 patients treated in controlled clinical trials. The purpose of this study was to evaluate the safety and efficacy of the RNS System in the real world through retrospective assessments of patients at 7 Comprehensive Epilepsy Centers. Methods: A multicenter, retrospective chart review was performed on patients with the RNS System implanted for at least 1 year. Patients who did not meet the FDA indication or who were no longer being followed at their participating institutions were excluded. Data reported include the median percentage change in disabling seizures, responder rate (percentage of patients who experienced at least a 50% reduction in seizures) 1 year and 2 years after RNS implant, and serious adverse events (SAEs) related to implant site infection in three groups: RNS Only (RNS Neurostimulator and Leads were implanted as the sole procedure), RNS + ICM (RNS implanted concurrently with intracranial EEG diagnostic monitoring), and RNS + Surgery (RNS implanted concurrently with a resective surgery). Results: There were 128 patients followed for at least 1 year, with a mean follow-up of 2.3 years. Demographics and lead locations are provided in Table 1, and the median percent reduction in seizures and the responder rate after 1 and 2 years of treatment are provided in Table 2. Thirty-four percent experienced at least one >= 3 month period of seizure freedom, 22% at least one >= 6 month period, and 13% had >= 1 year of seizure freedom. Overall median seizure reductions were 67% at year one and 75% at year two. There were no appreciable differences in efficacy between mesial temporal and neocortical lead locations. The overall rate of implant-related infections was 3.1%. The rates were 2.6% for the RNS Only group (n=76), and 4.8% for the RNS + ICM group (n=42). The mean inpatient monitoring period for the RNS + ICM group was 11 days (range: 3-22 days). One of the RNS + ICM patients who experienced an infection also fell in the RNS + Surgery group. No other infections were seen in the RNS + Surgery group (n=10). Conclusions: Treatment of focal onset seizures with the RNS System in real-world settings is efficacious and safe. At 1 and 2 years post-implant, there were greater seizure reductions in this patient population compared to patients treated during the clinical trials. In the current study, median seizure reductions after 1 and 2 years were 67% and 75%, respectively. In previous clinical trials, similar seizure reductions were achieved much later-after 4 and 9 years, respectively1. There are several explanations for higher efficacy despite a shorter period. Patients treated outside of clinical trials may have less severe epilepsy, or the clinical benefit could be overestimated because seizure counts may be less accurate. Alternatively, efficacy could be higher because accumulated clinical experience has led to more effective seizure detection and stimulation programming. The implant site infection rate of 3.1% was similar to the 4.1% seen in the clinical trials, and comparable between those with concurrent ICM and those with resection. Treatment with the RNS System in the real world achieves benefits that exceed those demonstrated during early experience in the clinical trials. Funding: NeuroPace, Inc.