Longitudinal Evolution and Plasma Biomarkers for Excessive Daytime Sleepiness in Parkinson’s Disease

Excessive daytime sleepiness (EDS) is one of the most frequent nonmotor symptoms in Parkinson's disease (PD); however, the pathogenesis of EDS is unclear, and there is a lack of information on plasma biomarkers for EDS in PD. We aimed to investigate the plasma biomarkers of EDS in a large PD cohort. A total of 159 PD patients were included in the prospective cohort study and followed up annually for 3 years. Plasma biomarkers including glial fibrillary acidic protein, amyloid-beta, p-tau181, and neurofilament light chain (NfL), were measured using an ultrasensitive single-molecule array (Simoa) technology at each visit. EDS was evaluated using the Epworth Sleepiness Scale (ESS). The frequency of EDS in PD increased from 15.1% at baseline to 25.0% after 3 years. The mean ESS scores increased from 5.1 (standard deviation [SD]: 4.8) at baseline to 6.1 (SD: 5.5) at the third year of follow-up. At baseline, compared with patients with PD without EDS, those with EDS were more likely to be male, had poorer cognitive performance, and more severe motor and nonmotor symptoms. The adjusted generalized estimating equations models showed that higher plasma NfL levels (OR: 1.047 [1.002-1.094], p = .042) were associated with EDS during follow-ups. The adjusted linear mixed-effects model showed that higher plasma NfL levels (β 0.097 [0.012-0.183], p = .026) were associated with ESS scores during follow-ups. Higher plasma NfL levels were associated with EDS in PD, indicating an association between neuro-axonal degeneration and EDS in PD.