A patient with REM sleep behavior disorder who subsequently developed proba
ble Lewy body dementia is now reported to have a definite pathologic diagno
sis of Lewy body dementia. Examination of brain revealed Lewy bodies as wel
l as marked neuronal loss in brainstem monoaminergic nuclei-particularly lo
cus coeruleus and substantia nigra-that inhibit cholinergic neurons in the
pedunculopontine nucleus mediating atonia during REM sleep.