Objective: To investigate the prevalence and severity of mild Parkinsonian motor signs in a longitudinal cohort stratified by the Movement Disorder Society (MDS) prodromal risk criteria.

Background: Mild Parkinsonian signs (MPS) represent a spectrum between normal aging and clinical Parkinson’s disease (PD) and are considered potential prodromal markers for future PD development. In this abstract, we present the prevalence and severity of MPS in a longitudinally followed cohort in Singapore.

Method: 330 participants were recruited from the local community and stratified into three groups based on calculated post-test probability: Low-Risk (LR <30%), High-Risk (LR≥30%), and RBD group (identified via the RBDSQ with a cutoff ≥ 5). Motor burden was quantified using the Movement Disorder Society-Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) Part III total motor score. MPS were defined as a total MDS-UPDRS Part III score greater than 6, excluding postural and kinetic tremors. Inter-group differences were analyzed using the Kruskal-Wallis test with post-hoc comparisons. Statistical workflows and data validation were assisted by Google Gemini AI.

Results: Among the 330 participants (male = 173, female = 157), 16 individuals (4.85%) were identified to have mild Parkinsonian signs. The distribution varied markedly across risk groups: the high-risk had the highest prevalence with 9 individuals (81.8% of the group), whilst the low-risk group had 5 individuals (1.6% of the group), and the RBD group had 2 individuals (11.1% of the group). MDS-UPDRS Part III scores differed significantly across risk groups (p < 0.0001). The high-risk group (n=11) showed significantly higher motor scores (8.45 ± 3.05), compared to both the low-risk group (n = 301, motor score: 2.42 ± 1.99, p < 0.001) and the RBD group (n = 18, motor score: 2.67 ± 2.72, p < 0.001). Notably, the RBD group’s motor burden was comparable to the low-risk group (p = 0.875).

Conclusion: Probability-based stratification effectively identified individuals already manifesting objective, though subclinical, motor signs. In contrast, RBD identified an earlier, predominantly pre-motor stage. These findings suggest that whilst both RBD and high post-test probability (high LR) identify at-risk individuals, the latter captures a phenotype already manifesting mild parkinsonian motor signs, whereas RBD identifies a predominantly pre-motor stage in this population.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mild-parkinsonian-signs-in-prodromal-parkinsons-disease/