RBD: a red flag for cognitive impairment in Parkinson's disease?

Increasing evidence indicates a strong association between rapid eye movement sleep behavior disorder (RBD) and Parkinson's disease - cognitive impairment (PD-CI). Numerous longitudinal and cross-sectional studies have shown that RBD may be an important risk factor and predictor of Parkinson's disease - mild cognitive impairment (PD-MCI) and Parkinson's disease dementia (PDD); which may be explained by the association of mechanisms between RBD and PD-CI, including neurotransmitter alterations, genetic mutation, neuroinflammation, alpha-synuclein inclusion, abnormal cerebral metabolism and cortical activity slowing. Understanding the role of RBD in cognition of PD, we may predict and prevent the presence of PD-CI. The purpose of our comprehensive narrative review was to investigate the role of RBD in cognition of PD patients and its possible mechanism with lights from clinical epidemiological evidence, neuroimaging and electrophysiology studies.