Brain pathway differences between Parkinson's disease patients with and without REM sleep behavior disorder

REM (rapid eye movement) sleep behavior disorder (RBD) is characterized by increased muscle tone and violent limb movements and is a usual symptom of the early stages of Parkinson's disease (PD). PD patients with RBD represent faster motor and cognitive dysfunction progression. However, there are limited studies on possible structural brain changes underpinning this disorder. Diffusion magnetic resonance imaging (DMRI) was used to assess whether microstructural abnormalities in the brain of 23 RBD positive PD are detectable compared to 31 RBD negative PD. DMRI scans were analyzed without a prior hypothesis. Diffusion MRI connectometry was used to carry out group analysis between age and gender matched PD patients with and without RBD. Diffusion MRI connectometry is based on spin distribution function (SDF) which quantifies the density of diffusing water and is more sensitive to psychological differences between groups. Patients with RBD positive showed microstructural white matter changes in the left and right cingulum, inferior front occipital fasciculus (IFOF), bilateral corticospinal tracts (CST), and middle cerebellar peduncles (MCPs), compared to patients without RBD. White matter alterations in the cingulum, IFOF regions, and corpus callosum might explain faster cognitive deterioration in PD patients with RBD, in terms of visual recognition and visuospatial dysfunction and executive function. Disturbed brain structural tissue markers in CST in PD + RBD patients, could be justified in the light of faster motor progression in these patients.