Objective: To investigate early non-motor symptoms between the RBD-positive and RBD-negative PD patients from the Early Parkinson’s Disease Longitudinal Singapore study (PALS) cohort.

Background: REM sleep behaviour disorder (RBD) occurs in about 19-70% of patients with Parkinson’s disease (PD). RBD is strongly associated with the body-first subtype during the prodromal phase, usually characterized by early autonomic dysfunction before dopaminergic degeneration and more prominent non-motor symptoms. In contrast, RBD-negative PD is often linked to the brain-first subtype, marked by earlier dopaminergic degeneration and fewer or milder non-motor symptoms at diagnosis. Previous studies also found that the RBD onset tends to happen before PD diagnosis in the body-first subtype but occurs later after diagnosis in the brain-first subtype.

Method: PD patients were categorized as RBD-positive or RBD-negative based on the RBD Single-Question Screen at baseline. Non-motor symptoms within the first year were assessed using the Non-Motor Symptom Scale (NMSS), which evaluates nine domains. Mann-Whitney U tests were used to compare NMSS scores between the RBD-positive and RBD-negative groups, and between patients with RBD onset before versus after PD diagnosis.

Results: A total of 214 PD patients were included, of whom 54 were RBD-positive and 160 were RBD-negative. Among the RBD-positive patients, 37 reported RBD onset before PD diagnosis and 17 reported after diagnosis. RBD-positive patients had a significantly higher NMSS total score than RBD-negative patients (27.41 vs 18.31, p < 0.001). They also showed significantly higher scores in NMSS domain 6 (Gastrointestinal) (3.09 vs 2.05, p = 0.0129), NMSS domain 7 (Urinary) (8.63 vs 4.71, p < 0.001) and NMSS domain 8 (Sexual) (1.59 vs 0.98, p = 0.00406). No significant differences were found in the remaining NMSS domains between the two groups. There were also no significant differences across all NMSS domains between patients with RBD onset before versus after PD diagnosis.

Conclusion: RBD-positive patients exhibited significantly more early non-motor symptoms than RBD-negative patients, particularly in the gastrointestinal, urinary and sexual function domains. The findings suggest that these domains may potentially help to identify the body-first subtype in early PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/rem-sleep-behaviour-disorder-and-early-non-motor-symptoms-in-parkinsons-disease/