Association of Concurrent Olfactory Dysfunction and Probable Rapid Eye Movement Sleep Behavior Disorder with Early Parkinson's Disease Progression.

Background: Parkinson's disease (PD), with either rapid eye movement sleep behavior disorder (RBD) or olfactory dysfunction (OD), has been associated with disease progression. However, there is currently heterogeneity in predicting prognosis. Objectives: To identify whether the concurrent presence of OD and probable RBD (pRBD) in PD (Dual hit in PD, PD-DH) is associated with disease progression. Methods: We included 420 patients with de novo PD from the Parkinson's Progression Markers Initiative: 180 PD only (PD), 82 PD with OD (PD-OD), 94 PD with pRBD (PD-pRBD), and 64 PD with both OD and pRBD (PD-DH). Participants underwent motor and nonmotor evaluations, dopamine transporter imaging, and cerebrospinal fluid (CSF) assessment. Data were analyzed with generalized estimating equations and Cox proportional hazards analysis. Results: The PD-DH subtype was associated with higher scores and faster progression rates in Movement Disorder Society-Unified PD Rating Scale (MDS-UPDRS) Parts II and III. Also, patients in PD-DH group had faster deterioration in nonmotor symptoms, including MDS-UPDRS Part I score, Montreal Cognitive Assessment, Hopkins Verbal Learning Test-Revised, Wechsler Memory Scale-Third edition (WMS-III) Letter Number Sequencing score, Symbol Digit Modalities Test, and Scales for Outcomes in PD-Autonomic scores, with all Conclusion: Coexisting pRBD and OD in patients with PD may be associated with faster progressions in motor measurements and in cognitive and autonomic symptoms, indicating PD-DH as a more aggressive subtype for PD.