Functional neuroimaging and clinical features of drug naive patients with de novo Parkinson's disease and probable RBD

Introduction: The association between Parkinson Disease (PD) and REM sleep behavior disorder (RBD) has been related to a specific, malignant clinical phenotype. Definite RBD diagnosis requires video-polysomnography that is often unfeasible. A malignant clinical PD-RBD phenotype could be expected also in PD patients with probable RBD. Aim of this cross-sectional study was to evaluate whether a more severe neuropsychological and functional neuroimaging phenotype can be identified in PD patients with probable RBD. Methods: Thirty-eight de novo, drug naïve PD patients underwent a first-line clinical assessment and a second-line multimodal assessment, including neuropsychological evaluation, 123I-FP-CIT-SPECT and 18F-FDG-PET, which were compared between PD patients with (PD + RBD+) and without (PD + RBD-) probable RBD. Results: On first-line assessment, PD + RBD + patients had significantly more constipation (p = 0.02) and showed worse olfaction (p = 0.01) compared with PD + RBD-while the two groups were similar as for age, presence of orthostatic hypotension, UPDRS-III and MMSE scores. On second-line assessment, PD + RBD + patients showed a worse neuropsychological test profile, more severe nigro-striatal dopaminergic impairment, mainly at caudate level in the less affected hemisphere (p = 0.004) and impaired brain glucose metabolism, with relative hypometabolism in posterior cortical regions and relative hypermetabolism mainly in anterior regions of the more affected hemisphere (p = 0.015). Conclusions: PD patients with probable RBD are likely to have a more severe neuropsychological and functional brain-imaging phenotype already at the time of diagnosis.