REM Sleep Behaviour Disorder (RBD) is characterized by loss of normal muscle atonia during REM sleep, resulting in dream enactment behavior. Its strong association with which neurodegenerative condition makes it a prodromal biomarker?
- A Alzheimer's disease
- B Alpha-synuclein disorders (Parkinson's disease, DLB, MSA) ✓
- C Huntington's disease
- D Amyotrophic lateral sclerosis (ALS)
Correct answer: B. Alpha-synuclein disorders (Parkinson's disease, DLB, MSA)
Explanation
Idiopathic RBD has a >80% risk of converting to an alpha-synucleinopathy (Parkinson's disease, Dementia with Lewy bodies, or Multiple System Atrophy) over 10-15 years of follow-up, making it a prodromal biomarker. The mechanism involves loss of brainstem circuits (pedunculopontine nucleus, sublaterodorsal nucleus) that normally generate REM atonia. Clonazepam 0.5-1 mg at bedtime is the treatment of choice for RBD symptoms.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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