Longitudinal Quantitative MRI Study on Abnormal Brain Iron Progression in Rapid Eye Movement Sleep Behavior Disorder and Parkinson’s Disease

Motivation: Although Parkinson’s disease (PD) and isolated REM sleep behavior disorder (iRBD) demonstrate elevated substantia nigra (SN) iron concentration, topography of change is still debated. Goal(s): To quantify abnormal brain iron progression over time using quantitative susceptibility mapping (QSM). Approach: Subjects were assessed three times 2 years apart. Mean QSM template was developed to quantify SN and its subdivisions, and subthalamic nucleus. Then caudate nucleus, putamen, globus pallidus and thalamus were also quantified. Results: At baseline, PD without RBD demonstrated +17.8% posteroventral SN iron overload and during the follow-up, 26.2% overload versus controls. None of the other tested regions showed significant differences between groups. Impact: Abnormal iron concentration was only found in the posteroventral SN and not in any other basal ganglia region over time. Further, PD without RBD showed highest iron concentration. Iron-sensitive quantitative MRI could be a potential longitudinal biomarker of the future.