REM sleep behavior disorder, hallucinations, and cognitive impairment in Parkinson's disease

The objective of this study was to evaluate the relationship between REM sleep behavior disorder (RBD), hallucinations, and cognitive impairment in Parkinson's disease (PD). One hundred and ten PD patients, divided into three groups (without RBD or hallucinations; with RBD but no hallucinations; with RBD and hallucinations), were submitted to neuropsychological evaluation. The group without RBD and hallucinations showed normal neuropsychological tests when compared to normal controls. The group with hallucinations was characterized by a more severe cognitive impairment affecting both short- and long-term memory, logical abilities, and frontal functions, while the RBD-only group presented frontal impairment. The hypothesis that RBD in PD can be considered a risk factor not only of the hallucinations but also of more severe and diffuse cognitive abnormalities needs to be strengthened through a longitudinal evaluation.