Objective: To determine whether neuromelanin-MRI signal changes in the substantia nigra and locus coeruleus in patients with REM sleep behaviour disorder (RBD) are predictive of dopaminergic basal ganglia abnormalities and clinical risk of Parkinson’s disease

Background: Patients with RBD present an opportunity to study prodromal Parkinson’s disease, since the majority will go on to develop a Parkinsonian disorder in future. Methods that could stratify these patients according to near-term conversion risk would have important implications for individual prognosis and the design of neuroprotective clinical trials. Neuromelanin-sensitive MRI is a promising new modality that can image PD-related changes in the substantia nigra and locus coeruleus, structures known to be involved in prodromal disease. We sought to investigate the clinical significance of these NM-MRI measures in patients with RBD by comparing them to dopaminergic imaging and clinical risk estimates

Methods: 37 patients with polysomnographically proven RBD and 25 healthy controls were recruited. Dopamine active Transporter (DaT) Single Photon Emission Computed Tomography (SPECT/CT) was performed in all RBD patients. Neuromelanin-sensitive MRI was performed in 32 RBD patients and all controls. An automated segmentation method was used to measure the volume, peak signal intensity and contrast ratio in the substantia nigra and locus coeruleus. Probability estimates for prodromal PD were calculated using the MDS research criteria

Results: Substantia nigra neuromelanin volume was reduced by an average of 12% in RBD patients compared to controls. A greater reduction of 32% was seen in locus coeruleus volume. Abnormal DaT SPECT imaging was observed in 17 RBD patients (46%). These patients had reduced contrast ratio (p=0.001) and peak signal intensity (p=0.002) within the substantia nigra compared to those with normal dopaminergic imaging. Negative correlations between MDS probability estimates and neuromelanin volumes in the substantia nigra (r =-0.44, p=0.03) and locus coeruleus (r =-0.60, p=0.001), respectively, indicated that volume reductions were associated with increased risk of prodromal Parkinson’s

Conclusions: Neuromelanin MRI provides quantifiable measures of prodromal neurodegeneration in the locus coeruleus and substantia nigra, which predict dopaminergic deficits and clinical Parkinsonian risk in patients with RBD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/neuromelanin-mri-in-rem-sleep-behaviour-disorder-predicts-dopaminergic-dysfunction-and-clinical-risk-of-parkinsons-disease/