Objective: To evaluate the associations between striatal and motor asymmetry in Parkinson’s disease with probable RBD compared to without.

Background: Parkinson’s disease is typically characterized by unilateral motor symptom onset that associated with asymmetric nigrostriatal damage. In contrast, PD patients with RBD are reported to more likely have symmetric motor symptom onset, despite reports of asymmetric nigrostriatal dysfunction in the prodromal PD phase such as in isolated REM sleep behaviour disorder. Therefore, this study aimed to characterize whether the presence of RBD affects the association between striatal and motor asymmetry in patients with newly diagnosed PD with and without probable RBD.

Method: 120 de novo Parkinson’s disease participants (<3 years since diagnosis, drug-naïve) from the Parkinson’s Progression Markers Initiative were used for analysis. The REM Sleep Behavior Disorder Questionnaire was used to divide participants into those with and without probable RBD (47 pRBD+, 73 pRBD-). Asymmetry indices were calculated for MDS UPDRS-III rigidity, bradykinesia, and tremor by taking the absolute value of (right side – left side)/(right side + left side). Using [¹²³I]FP-CIT SPECT imaging, asymmetry index scores of striatal binding ratios in the putamen and caudate were similarly calculated. Based on normality, Pearson or Spearman correlations were used to assess the association between motor and striatal asymmetry scores. Fisher’s Z transformation was used to evaluate whether correlations were significantly different between groups.

Results: There were no significant differences in age or disease duration between groups. Striatal and motor asymmetry scores were not significantly different between groups. In the pRBD- group, caudate asymmetry had a significant but weak correlation with bradykinesia asymmetry (r = 0.262, p = .025); however, compared to the pRBD+ group (r = 0.139, p = .356), this association was not significantly different (Z = -0.67, p = .50).  No other significant associations were found.

Conclusion: These results do not support that a body-first subtype would be associated with a more symmetric pathology and motor symptom onset in PD and highlight the potential importance of asymmetry as a prodromal marker as well as the possible contribution of non-dopaminergic neurotransmitter systems to motor asymmetry.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/associations-between-striatal-dopamine-transporter-binding-and-motor-asymmetry-in-de-novo-pd-with-and-without-rbd/