Lewy body dementia (DLB) is distinguished from Parkinson's disease dementia (PDD) primarily by which temporal criterion?
- A DLB has more severe tremor than PDD
- B In DLB, dementia precedes or occurs within 1 year of parkinsonism; in PDD, dementia follows established parkinsonism by >1 year ✓
- C DLB has higher levodopa responsiveness
- D DLB lacks visual hallucinations, while PDD has prominent hallucinations
Correct answer: B. In DLB, dementia precedes or occurs within 1 year of parkinsonism; in PDD, dementia follows established parkinsonism by >1 year
Explanation
The '1-year rule' distinguishes DLB from PDD: in DLB, cognitive symptoms (dementia) precede or co-occur within 1 year of parkinsonism onset; in PDD, established Parkinson's disease is present for >1 year before dementia develops. Both share alpha-synuclein Lewy body pathology, fluctuating cognition, visual hallucinations, and REM sleep behavior disorder. Both have reduced levodopa responsiveness for the cognitive symptoms.
Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.
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