From Seconds to Seasons: First-in-Human Insights from a Chronic Subscalp EEG System

Objective: Patient self-report is known to be an inaccurate reflection of true seizure frequency in persons with epilepsy. The current study aimed to assess the safety and performance of the Minder system, a bilateral subscalp electroencephalographic (EEG) acquisition system for continuous long-term EEG recording. Methods: This prospective, multicenter first-in-human study enrolled adult patients with focal or generalized epilepsy and at least 2 seizures per month. The primary outcome was adverse events (AEs) in the first 6 months of implantation. Secondary analyses determined whether normal neurophysiological signals, interictal discharges, and seizures seen on scalp video EEG monitoring were identifiable on subscalp recordings, and signals were rated for clarity on subscalp and 2-channel scalp EEG recordings (1 = not recognizable, 5 = clear). Subscalp data were reviewed in relation to events reported in 6-month seizure diaries. Results: Twenty-six subjects were implanted between November 2019 and July 2023. No serious device- or implant procedure-related AEs were reported. The most common device-related AEs were mild or moderate postsurgical pain, headache, or scalp pain/paresthesia (9/26, 35%). All sleep spindles, chewing artifacts, interictal discharges, and electrographic seizures observed on scalp recordings (25 seizures from 8 patients) were identified on subscalp recordings and given higher clarity ratings compared to 2-channel scalp recordings (median seizure clarity rating was 3 for both scalp and subscalp EEG, range = 1-5, P = .0025). Subscalp recordings captured seizures from diverse seizure focus locations, including frontal and mesial temporal seizure foci and hypothalamic hamartoma. Bilateral recording revealed clinically relevant findings not possible with unilateral recordings (6/26 patients, 23%). Findings of potential clinical utility were identified on manual review of 6-month recordings in most patients (23/26, 88%). Significance: This study demonstrates the safety and performance of the Minder bilateral subscalp EEG acquisition system for long-term seizure monitoring in patients with epilepsy. Bilateral hemisphere coverage captured seizures in a diverse patient group and permitted lateralization of events.