Associations Between Sleep and Non-Motor Symptoms in RBD-Screened Suspected Prodromal Parkinson's Disease with...

Background and Objectives: Parkinson's disease (PD) includes a prodromal phase characterized by non-motor symptoms (NMS). We investigated whether sleep disturbances co-aggregate with other NMS in suspected prodromal PD (p-PD) to refine early phenotyping and risk stratification. Materials and Methods: A population-based survey was conducted in Kaunas, Lithuania. Participants from the Kaunas City preventive health screening cohort (2024-2025) were screened using the Innsbruck REM Sleep Behaviour Disorder Inventory (RBD-I). Sixty-two individuals were included: 31 with suspected p-PD and 31 controls. Demographic characteristics, clinical features, sleep symptoms, olfactory function, autonomic symptoms, cognition, and mood were assessed. Between-group comparisons and within-group correlation analyses were performed. Results: Groups did not differ in age, sex, education, lifestyle exposures, or family history (all p > 0.05). Compared with controls, individuals with suspected p-PD had a higher prevalence of insomnia (71.0% vs. 12.9%, p < 0.001), pathological daytime sleepiness (22.6% vs. 0%, p = 0.005), cognitive impairment (54.8% vs. 16.1%, p = 0.001), and constipation (32.3% vs. 0%, p = 0.002). As expected from the predefined enrichment strategy, hyposmia and orthostatic hypotension (OH) were observed only among suspected p-PD participants. Within the suspected p-PD group, the Non-Motor Symptoms Questionnaire (NMSQ) scores correlated with depressive/anxiety symptoms (r = 0.578, p = 0.001). Olfactory dysfunction correlated with cognitive impairment (r = 0.410, p = 0.001) and depressive/anxiety symptoms (r = 0.396, p = 0.001). Conclusions: Sleep disturbances, particularly insomnia and excessive daytime sleepiness, co-occurred with cognitive, affective, and gastrointestinal non-motor manifestations in individuals with suspected p-PD, supporting the concept of a broader prodromal phenotype. Comprehensive screening in individuals with RBD symptoms may improve early PD risk stratification beyond single-marker approaches.