REM behavior disorder, hallucinations and cognitive impairment in Parkinson's disease: a two-year follow up.

In Parkinson's disease (PD) the presence of REM parasonnias as REM Behaviour Disorder (RBD) or vivid dreams/nightmares, is recognized as largely associated with hallucinations, even if the risk of the development of hallucinations seem not to depend on how long the REM parasomnias had been occurring. The aim of this study was to establish if RBDs occurring earlier than hallucinations in PD are predictive of cognitive impairment development. Three groups of PD patients: i) group 1, without RBD and without hallucinations; ii) group 2, with RBD but without hallucinations; iii) group 3, with RBD and hallucinations have been prospectively investigated at baseline and after two years throughout a clinical and neuropsychological evaluation. After two years, the group 1 continued to present normal neuropsychological tests and did not present either RBDs or hallucinations. In the group 2, the frontal impairment evidenced at baseline was confirmed; the onset of newly hallucinations was reported in a subgroup of 12 patients, who proved to be older, with a more severe executive impairment at baseline and with a more severe motor symptoms progression than those RBD patients who had not manifested hallucinations. The group 3, characterized at baseline by a more severe cognitive impairment presented, after two years, a cognitive worsening and a higher mortality rate. The longitudinal but at preliminary step investigation identified a PD subgroup of patients, in whom a common background disease profile, including the presence of RBD, could represent a "red flag" in developing further cognitive impairment.