Idiopathic rapid eye movement sleep behavior disorder is a harbinger of dementia with Lewy bodies.

Idiopathic rapid eye movement (REM) sleep behavior disorder (RBD) is a parasomnia clinically linked with the alpha-synucleinopathies multiple systems atrophy (MSA), Parkinson's disease (PD), and dementia with Lewy bodies (DLB). Available autopsy information is limited but suggests that the pathologic basis of idiopathic RBD may be neuronal loss and Lewy bodies in pigmented monoaminergic nuclei, including the locus coeruleus and substantia nigra, which project to pontine nuclei mediating atonia during REM sleep. Thus, idiopathic RBD may be an alpha-synucleinopathy per se and a harbinger of impending PD, DLB, or MSA. Inclusion of historical or concurrent idiopathic RBD in the diagnostic criteria for DLB may improve their sensitivity, specificity, and clinical utility.