An elderly patient with Parkinson's disease develops vivid, formed visual hallucinations of children playing in his garden (non-threatening), fluctuating cognitive impairment, and daytime sleepiness. His family notes he 'acts out his dreams.' He subsequently develops mild resting tremor. What sequence of events described here most specifically suggests Dementia with Lewy Bodies over Parkinson's disease dementia?
- A Presence of parkinsonism features
- B Visual hallucinations in the setting of cognitive decline
- C REM sleep behaviour disorder preceding cognitive and motor features (DLB 1-year rule) ✓
- D Fluctuating cognition
Explanation
The '1-year rule' distinguishes DLB from Parkinson's disease dementia (PDD): in DLB, dementia occurs within 1 year of (or before) parkinsonism onset, whereas in PDD, established parkinsonism precedes dementia by >1 year. In this case, the cognitive and perceptual symptoms preceded or co-occurred with motor features, and REM sleep behaviour disorder (acting out dreams) is a core biomarker feature of DLB. Visual hallucinations and fluctuating cognition are core DLB features but are also seen in advanced PD; the temporal relationship is the differentiating criterion. DLB patients are exquisitely sensitive to antipsychotics, which are contraindicated.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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Written and medically reviewed by the StethoPrep medical team.