Regional Neuromelanin Reduction in the Substantia Nigra in Different Subtypes of Parkinson’s Disease

Motivation: The intricate pathophysiological mechanisms differentiating these PD subtypes remain unclear. Goal(s): This study aimed to investigate NM-MRI characteristics in the SNc subregions of PD patients across different clinical subtypes. Approach: Four groups were included: PD-MMP, PD-IM, PD-DM and HCs. CNR were calculated for the sensorimotor, associative, and limbic territories of the SNc and compared between groups using NM-MRI. The correlation analyses were performed to evaluate the relationships between CNR and clinical scores. Results: Neuromelanin values showed a gradual decline, with a descending gradient in PD-MMP, followed by PD-IM and PD-DM and regional neuromelanin loss was associated with motor and cognitive impairments. Impact: These findings suggest underlying pathological mechanisms for PD subtypes and indicate that regional neuromelanin loss is associated with motor and cognitive impairments.