Neuromelanin-MRI identifies locus coeruleus and substantia nigra degeneration as key differentiators in isolated rapid eye movement sleep behavior disorder

To explore the neuromelanin depigmentation of locus coeruleus (LC) and substantia nigra pars compacta (SNc) in the isolated rapid eye movement sleep behavior disorder (iRBD) using neuromelanin-sensitive MRI (NM-MRI), and to evaluate its utility for iRBD diagnosis. A total of 25 iRBD patients and 25 healthy controls were recruited and underwent NM-MRI. The contrast-to-noise ratio (CNR) of SNc and LC, and the volume of SNc were compared between groups and evaluated visually. The power of NM measures in discriminating iRBD patients from healthy controls were performed with receiver operating characteristic (ROC) curves and the area under curve (AUC) was calculated. The CNR of SNc and LC, the volume of SNc, the SNc/midbrain volume ratio as well as the visual scores of SNc and LC in iRBD patients were significantly decreased than those in controls (all P < 0.05). For quantitative analysis, the LC CNR acquired the highest accuracy in predicting iRBD (AUC 0.95, sensitivity 80%, specificity 100%), followed by SNc volume (AUC 0.93, sensitivity 88%, specificity 96%) and SNc CNR (AUC 0.74, sensitivity 92%, specificity 44%). For visual analysis, the accuracy of the visual score for SNc and LC were 78% (sensitivity 68%, specificity 88%) and 86% (sensitivity 88%, specificity 84%), respectively. The NM in the SNc and LC regions were significantly reduced in iRBD patients. NM measures showed good capability in discriminating iRBD from controls, suggesting that NM-MRI may be a valuable screening tool for iRBD.