Objective: To assess the loss of dorsolateral nigral hypersensitivity (DNH), which seems to correspond to nigrosome-1, using susceptibility-weighted imaging (SWI) at 3.0 Tesla (T) in subjects with idiopathic REM sleep behaviour disorder (IRBD).

Background: RBD is a parasomnia characterized by lack of muscular atonia during REM sleep associated with dream-enacting behaviour and unpleasant dreams. Prospective cohort studies of subjects with IRBD have shown that a majority go on to develop an alpha-synuclein-related neurodegenerative disease. These findings suggest that a proportion of subjects with IRBD could represent patients in a pre-motor stage of Parkinson’s disease (PD). Recently, several groups have reported a novel MRI marker for PD based on the loss of DNH using iron-sensitive MRI including SWI at 3.0 and 7.0 Tesla.

Methods: 15 IRBD patients were studied with 3T MRI. In order to compare DNH status (present or absent) between subjects with IRBD, healthy controls (HC) and PD we used imaging data of our recently published cohort of 104 PD subjects and 42 HC. 19 randomly selected subjects from our previous study (10 HC and 9 PD patients) were added to the analysis set of MR images of IRBD subjects and DNH raters were kept blind to diagnostic categories. Unilateral absence of DNH was classified as abnormal. The main per-protocol analysis to assess differences of DNH loss between groups was performed excluding scans of insufficient quality for reliable assessment.

Results: Ten out of 13 (77%) IRBD patients showed loss of DNH, which was distinct from HC (corrected p<0.001) but similar to patients with PD (corrected p=0.27). Overall, one of 35 controls (3%) and 83 of 90 (92%) patients with PD patients showed loss of DNH.

Conclusions: In this study we found that 77% of IRBD patients showed loss of DNH, which is distinct from HC but similar to patients with PD. In PD this imaging finding has been linked to loss of dopaminergic cells in the Nigrosome 1 area of the substantia nigra (SN), corresponding to a calbindin-negative subregion in the healthy SN pars compacta. This finding not only further supports the role of IRBD as a biomarker for prodromal PD but also raises the possibility that absent DNH on MR SWI might be a diagnostic tool to identify those IRBD subjects in whom there is ongoing synuclein pathology in the SN.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dorsolateral-nigral-hyperintensity-on-3-0-tesla-susceptibility-weighted-imaging-in-idiopathic-rapid-eye-movement-sleep-behaviour-disorder/