Research progress in rapid eye movement sleep behavior disorder.

Rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by abnormal dream acting behavior such as vocalization and twitching related to dream content during REM sleep. The diagnosis requires polysomnography demonstrating a loss of normal skeletal muscle atonia during REM sleep. Both idiopathic RBD and secondary RBD are highly related to synucleinopathy including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Almost all idiopathic RBD patients will develop synucleinopathy after a few years. Therefore, RBD may be an early marker in the progression of synucleinopathy.