Microstructural changes in patients with Parkinson disease and REM sleep behavior disorder: depressive symptoms versus non-depressed.

Search for Parkinson's disease (PD) progression biomarkers has led to the identification of both motor and non-motor symptoms relevant of prodromal PD that could be eye-opening to the spreading underlying Lewy body pathogenesis. One most robust predictor of PD is the REM sleep behavior disorder (RBD), and one most common early non-motor symptom of PD is depression. With RBD, frequently coexisting with clinical depression and both predicting dopamine transmission dysfunction, we aimed to survey structural associates of depressive symptoms in early PD patients with comorbid RBD. Through diffusion MRI connectometry, we tracked fiber differences comparing DWI images obtained from 14 patients with depressive symptoms and 18 without depression from a group with comorbid RBD and PD. DWI images and patients were recruited from the Parkinson's Progression Markers Initiative database. PD-RBD patients with depressive symptoms showed pathways with significantly reduced connectivity in the right cingulum, left and right fornix, left inferior longitudinal fasciculus, right corticospinal tract, left middle cerebellar peduncle and genu of corpus callosum (FDR = 0.0228). Diffusivity alteration of the mentioned fibers in depressed, early PD patients with RBD might reflect underlying PD pathology and serve as common structural DWI signatures for early PD diagnosis.