[REM sleep behavior disorders and their characteristics in Parkinson's disease]

REM sleep behavior disorders (RBD) are vigorous, complex movements corresponding to enacted dreams. They may disturb sleep, and injure the patients or their bed partner. RBD are frequently associated with neurodegenerative diseases, especially synucleopathies. They can precede parkinsonism or dementia by five to 10 years. These presymptomatic RBDs are frequently associated with EEG slowing, reduced olfaction, mild visuospatial cognitive impairment, and decreased dopamine transport in functional brain imaging. In Parkinson's disease, 15 to 60% patients speak, laugh, shout, kick, punch or fight invisible enemies during REM sleep. In contrast to sleepwalkers, patients with RBD rarely stand up or walk, but can fall out of bed. Sleep monitoring indicates an imperfect abolition of muscle tone during REM sleep in these patients. RBD are probably caused by nondopaminergic pontine lesions in the REM sleep atonia system. This condition may also expose patients with Parkinson's disease to a higher risk of daytime and nighttime hallucinations, and to more frequent cognitive impairment. Interestingly, several spouses reported that they observed a sharp contrast between the slow, limited movements, and poorly intelligible, low voice of their affected spouse when awake, and the fast, vigorous movements with loud voice that the very same patient exhibited during enacted dreams. We recently demonstrated that parkinsonism indeed disappears during RBD, in a large study combining the interview of 100 couples and the sleep and video monitoring of 50 patients. The mechanism of this improvement is now being explored.