Epileptiform discharges are associated with increased theta activity over time in patients with Lewy body dementia

Electroencephalography (EEG) slowing and reduced functional connectivity are markers of Alzheimer's disease (AD) and Lewy body dementia (DLB), but the significance of epileptiform discharges to these changes remains unknown. We investigated whether epileptiform discharges are associated with EEG slowing or decreased functional connectivity over time. In this longitudinal observational exploratory study, 15 healthy controls, 25 patients with AD, and 10 patients with DLB were included. Patients underwent conventional resting-state EEG up to three times over 6 months, while baseline ear-EEG recording was used to quantify the number of epileptiform discharges per 24 hours. Compared with healthy controls, both patient groups showed a pattern of slowing and decreased alpha coherence. Epileptiform discharges were not associated with slowing or coherence at baseline. In longitudinal analyses, patients with DLB and epileptiform discharges demonstrated an increase in relative theta power over six months compared with patients with DLB without epileptiform discharges. No significant longitudinal theta-power changes were observed in patients with AD. These findings suggest that while EEG slowing is a characteristic feature of neurodegenerative diseases, epileptiform discharges are not directly associated with baseline EEG theta activity but may be linked to a distinct longitudinal trajectory of theta activity in DLB. Given the small group sizes and unbalanced subgroups analysis, these observations should be considered exploratory and require confirmation in larger longitudinal studies.