Objective: To detect changes in the different subregions of the substantia nigra pars compacta (SNc) in patients with Parkinson’s disease (PD) and to correlate the results with clinical data.

Background: Reduced midbrain Neuromelanin (NM) in PD is attributed to loss of pigmented dopaminergic neurons localized especially to the SNc. Non-invasive Magnetic Resonance Imaging (MRI) markers of NM can quantify NM, and detect alterations to SNc-NM morphology, thus offering unique opportunities to link pathophysiologic and clinical progression.

Methods: We performed 3T NM-MRI measurements on 38 PD patients; 18 with less than 5 years from disease onset (age at examination 45-76 y; H&Y stage: 1-3), 20 with longer disease duration ranging from from 9-23 y (age at examination 48-78 y; H&Y stage: 1-4), and 20 age-matched healthy controls (aged 50-75 y). All subjects completed a neurological examination assessing motor and cognitive function (Montreal Cognitive Assessment (MoCA)). Circular ROIs were defined in the lateral, central and medial parts of the SN in three consecutive slices (caudal, intermediate, rostral). The contrast-to-noise ratio (CNR) between the each ROI and the cerebral crus was computed, where a lower CNR represents greater loss of NM. The Steel-Dwass test was used to compare the results between groups and the Spearman correlation coefficient was used to examine the correlations between imaging results and clinical data.

Results: Across all ROIs, the CNR values were found to be reduced in PD patients as compared with controls, and were lower in PD patients with longer disease duration. For all subjects, the CNR was higher in the caudal-medial subregion, and in PD patients, greater reductions in CNR were towards the rostral and lateral axes of the SN. A significant correlation between the CNR in the central SNc subregion and cognitive performances (MoCA scores), but not with motor performances, was detected.

Conclusions: Study results support that NM-MRI detected changes in PD patients. While this tool may provide useful diagnostic information to detect degeneration of dopaminergic neurons in SNc, these data suggest that NM changes appear early in the disease course. Clinical relationships between different subregions of SNc emphasize a positive association between the degeneration of its central portion and cognitive function in PD. This relationship needs to be examined prospectively.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/neuromelanin-mri-of-substantia-nigra-subregions-in-parkinsons-disease/