Brain Neuroimaging of Rapid Eye Movement Sleep Behavior Disorder in Parkinson’s Disease: A Systematic Review

REM-sleep behaviour disorder (RBD) is a parasomnia and a common comorbidity in Parkinson's disease (PD). There is evidence that the presence of RBD is associated with more severe PD. The differences in the clinical manifestations and the natural history are likely to imply underlying differences in the pathophysiology among PD patients with and without RBD. The increasing number of neuroimaging studies support this notion.Our primary objective was to review the current evidence regarding the brain neuroimaging findings in PD patients with RBD (PDRBD).A systematic review of articles, published in PubMed between January 1, 2000 and September 23, 2020 was performed. We evaluate previous studies that assessed PD patients with RBD using various brain structural and functional magnetic resonance imaging (MRI) techniques and brain nuclear medicine imaging.Twenty-nine studies, involving a total of 3,347 PD subjects among which 912 subjects with PDRBD, met the selection criteria and were included. The presence of RBD in PD patients is associated with structural and functional alterations in several brain regions, mainly in brainstem, limbic structures, frontotemporal cortex, and basal ganglia, raising the hypothesis of a PDRBD neuroimaging phenotype.The current review provides up-to-date knowledge in this field and summarizes the neurobiological/neuroimaging substrate of RBD in PD.