Interim findings of a post-approval study of a responsive neurostimulation (RNS) system (Neuropace, Mountain View, CA) showing continued safety and efficacy were presented at the Annual American Epilepsy Society Meeting in Baltimore Maryland December 6-10, 2019. The RNS system was approved by the Food and Drug Administration (FDA) in 2013. In this 5-year safety and efficacy study, data was collected from 128 adults who had the RNS system implanted. Mean seizure reduction was higher than what was seen at the same timepoint in the initial pivotal trial.
Median seizure frequency reduction with the RNS system was 68% (interquartile range [IQR], 16.1–96) at 1 year compared with 44% in the pivotal trial. The responder rate was 61% (95% CI, 52.3–69.0) at the end of the first year. Of those with at least 1 year of follow-up, 34.4% had 1 or more 6-month seizure-free periods; 42.2% reported a 90% or greater reduction in seizures at their most recent 6-month follow-up visit.
The authors of the presentation suggested that experience gained from the pivotal trial, long-term open-label studies, and clinical experience may explain the increase in efficacy seen. There were no significant differences in demographic and seizure characteristics of participants in the post-approval trial. Mean age was 36.7 and mean duration of epilepsy was 16.9 years. At baseline, median seizure frequency was 5.7 (IQR, 2.7–16.7) seizures per month.
In 191 individuals treated to date, there were no unanticipated serious adverse events (AEs) related to the device. The infection rate was 2.0% per procedure (initial implant, replacement, explant or lead revision), in soft tissue only. Intracranial hemorrhage occurred in 4 people and was categorized as unassociated with seizure-related trauma. Single cases of mild right upper extremity weakness; transient headache and facial droop; transient confusion, seizures, and left visual field deficit; occurred. A cerebrospinal fluid leak occurred in 2 patients at 1 of 30 sites.
It has previously been reported that in a 9-year long-term study of the RNS system, 75% of patients had a 50% or more reduction in seizures, and approximately 33% experienced at least a 90% reduction in seizures. In that study, 28% of patients experienced seizure-free periods of 6 months or more, and 18% of patients had seizure-free periods of a year or more. The quality of life measures, including memory and cognition, persisted through the 9-year study period, with no chronic stimulation-related adverse effects.