REM sleep behavior disorder is a feature of which disease?

• A. Lewy body dementia (LBD)
• B. PSP
• C. Normal pressure hydrocephalus (NPH)
• D. Neurosyphilis

Answer: (A)

REM sleep behavior disorder arises from loss of the normal REM-atonia that keeps you still during dreams. This loss occurs most clearly in Lewy body disease, a synucleinopathy, so dream-enactment behaviors are a notable nonmotor clue to Lewy body–related disorders and can even precede dementia or parkinsonian features. PSP, normal pressure hydrocephalus, and neurosyphilis don’t typically feature this REM-related motor dream enactment, as they involve different pathologies and symptom patterns. So the best fit is Lewy body dementia, where RBD is a commonly observed and clinically meaningful sign.