Rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia during REM sleep in which abnormal behaviors occur, along with a loss of normal muscle atonia during REM sleep. It is characterized by episodes of vigorous and often violent motor activity, calling out, and/or vivid dreams during REM sleep. Self-injury or injury to others may occur.

The prevalence of RBD is about 1%-2% in the general population and about 50% in those with Parkinson disease. Although RBD affects men and women equally, men typically have more violent behaviors and more frequently recall dreams with aggressive content. Men are more often diagnosed than women due to this increased violent activity and greater likelihood of observant bed partners. RBD typically occurs in the fifth or sixth decade of life.

RBD is a strong predictor of alpha-synucleinopathies, such as Parkinson disease, and usually precedes the development of a neurodegenerative disease by about 10 years. At least 90% of patients with RBD will be diagnosed with a neurodegenerative disease by 15 years after RBD onset.

It is suggested that the etiology of RBD is neurodegeneration of glutamatergic neurons in the sublaterodorsal tegmental nucleus in the pons or their projection target, glycinergic neurons in the ventral medulla. Normally, these neurons project to spinal motor neurons and result in hyperpolarization during REM sleep, causing muscle atonia. Therefore, degeneration causes lack of atonia.