Real-world epilepsy monitoring with ultra long-term subcutaneous EEG: a 15-month prospective study

Objective Novel subcutaneous electroencephalography (sqEEG) systems enable prolonged, near-continuous cerebral monitoring in real-world conditions. Nevertheless, the feasibility, acceptability and overall clinical utility of these systems remains unclear. We report on the longest observational study using ultra long-term sqEEG to date. Methods We conducted a 15-month prospective, observational study including ten adult people with treatment-resistant epilepsy. After device implantation, patients were asked to record sqEEG, to use an electronic seizure diary and to complete acceptability and usability questionnaires. sqEEG seizures were annotated visually, aided by automated detection. Seizure clustering was assessed via Fano Factor analysis and seizure periodicity at multiple timescales was investigated through circular statistics. Results Over a median duration of 438 days, ten patients recorded a median 18.8 hours/day, totalling 71,984 hours of real-world sqEEG data. Adherence and acceptability remained high throughout the study. While 754 sqEEG seizures were recorded across patients, over half (52%) of these were not reported in the patient diary. Of the 140 (27%) diary reports not associated with an identifiable sqEEG seizure, the majority (68%) were reported as seizures with preserved awareness. The sqEEG to diary F1 agreement score was highly variable, ranging from 0.06 to 0.97. Patient-specific patterns of seizure clustering and seizure periodicity were observed at multiple (circadian and multidien) timescales. Interpretation We demonstrate feasibility and high acceptability of ultra long-term (months-years) sqEEG monitoring. These systems help provide real-world, more objective seizure counting compared to patient diaries. It is possible to monitor individual temporal fluctuations of seizure occurrence, including seizure cycles. Summary for Social Media if Published [I do not have a X/Twitter handle] People with epilepsy may suffer from severe injuries or sudden death due to uncontrolled seizures. Many seizures remain unnoticed by people and unreported to doctors, despite these potentially catastrophic consequences. There is an urgent need to detect seizures more objectively. Our study used a novel device placed under the skin to monitor brainwave activity continuously, at home, for many months, in people with treatment-resistant epilepsy. By monitoring epilepsy from home, we detected many seizures unreported by patients, and we also found predictable patterns (cycles) of seizure occurrence over time. In the future, this type of monitoring could revolutionize epilepsy care, by improving safety, treatment management and reducing uncertainty in patients’ daily lives.