The typical and atypical spectrum of subclinical rhythmic EEG discharges in adults and its electrical origin

Subclinical rhythmic EEG discharges in adults (SREDA) is a very rare benign EEG pattern. We aimed to localize the electrical origin of SREDA using electrical source imaging (ESI), identify the mechanism responsible for SREDA and describe its characteristics.

An electronic term search for SREDA was performed on all video EEG reports between January 2020-June 2024. Both typical and atypical SREDA patterns were included. The clinical details, EEG, and neuroimaging findings were noted. ESI was performed using classical LORETA analysis recursively (CLARA).

On reviewing 10,574 EEG recordings, 13 subjects (0.1 %) with SREDA were identified. Six patients had typical patterns and seven had atypical patterns. The posterior cingulate and/or the lingual gyrus were found to be the most common electrical origin for typical SREDA. Additionally, ESI source localized to the hippocampus/anterior cingulate in atypical SREDA. One patient with obstructive sleep apnea (OSA) had SREDA correlating with the period of apnea/hypopnea during polysomnography.

The posterior cingulate/lingual gyrus were found to be the most common electrical sources using ESI. The possible association between hypoxia and SREDA may warrant further study.

Our paper electrically source localises SREDA, a field in which there is a paucity of literature. The occurrence of SREDA with apnea/hypopnea in a patient with OSA is a novel finding.