Multimodal MRI changes associated with non-motor symptoms of rapid eye movement sleep behaviour disorder in Parkinson's disease patients.

Background and objective: Parkinson's disease (PD), a prevalent neurodegenerative disorder, assumes a more adverse prognosis when accompanied by rapid eye movement sleep disorder (RBD). Non-motor symptoms, particularly sleep and emotional disturbances, significantly impair patients' quality of life. This study aimed to investigate the neuroimaging underpinnings of PD-RBD using structural and functional magnetic resonance imaging (MRI) and to explore the associations between these imaging biomarkers and non-motor symptoms.

Method: Brain scans were acquired from 33 PD patients without and 21 with probable RBD (PD-pRBD). Comparative analyses were performed to evaluate structural and functional alterations between the two groups. Additionally, the correlations between neuroimaging metrics and clinical assessment scales were assessed.

Results: PD-pRBD patients demonstrated more pronounced grey matter atrophy, particularly in the putamen and insula. Functional MRI revealed decreased amplitude of low-frequency fluctuations (ALFF) in the bilateral posterior cingulate cortex and left precuneus of PD-pRBD patients. Furthermore, reduced functional connectivity (FC) was observed in specific regions of the whole brain and within the default mode network (DMN) in PD-pRBD. Notably, a negative correlation was found between mean ALFF values in the left posterior cingulate cortex of PD-pRBD patients and Hamilton Depression Rating Scale scores.

Conclusion: PD-pRBD is characterized by more severe grey matter loss and functional MRI abnormalities compared to PD alone. Dysfunction of the posterior cingulate cortex is implicated in more pronounced affective impairments, providing novel insights into the complex pathophysiology of PD-RBD.