Abstracts

Rationale: Based on patient diary or intracranial recordings, recent publications have shown that seizures have a high circadian and infradian rhythmicity for most patients (Karoly et al., Lancet Neurol, 2018 (17), 11, P977-985). We investigate whether the same observations can be made based on ultra long-term EEG from a minimally-invasive subcutaneous device. Methods: A beta-version of the UNEEG 24/7 EEG™ SubQ was used to monitor the EEG of nine patients continuously for a period of up to three months (Weisdorf et al., J Neurophysiol, 2018 (130), 3, Pages 1451-1460). The implant consists of a wire with three electrodes and a coil embedded in a ceramic housing smaller than a quarter for external communication. It is implanted in the sub-scalp layer and can stay in the same location for weeks, months or more. An external device is needed for powering of the implant as well as storage of data. A small disc is attached on the scalp aligned with the housing of the implant. The two parts of the device are communicating through an inductive link. A small wire goes from the disc on the scalp to a small box worn underneath the clothes of the patient. The external device needs to be charged every second day and can hold up to 60 days of continuous data. Results: A total of 259 EEG recorded seizures were identified and analyzed in terms of time of day as well as infradian rhythmicity. Five of the nine patients had at least five seizures for analysis of rhythmicity. Three out of these five had clear circadian as well as infradian rhythmicity of EEG recorded seizures. One patient seemed to have infradian rhythms without circadian rhythms and the last patients had circadian rhythms without infradian rhythms. More data for all patient would be needed to have statistical power to investigate rhythmicity extending over periods of months or seasons. Conclusions: Ultra long-term subcutaneous EEG is very suitable for analysis of seizure rhythmicity. Previous findings of circadian and infradian rhythmicity based on seizure diary or intracranial recordings were confirmed with this minimally-invasive method which accommodates the possibility of objective, unobtrusive recordings in the every-day life of epilepsy patients. Funding: National Danish Science Foundation, UNEEG medical A/S, Zealand Regional Research Council.