Lewy body dementia is distinguished from Parkinson's disease dementia primarily by:

• A Presence of Lewy bodies in the brainstem only
• B Response to levodopa therapy (PDD responds, DLB does not)
• C The 1-year rule: dementia developing within 1 year of onset of parkinsonism suggests DLB; dementia >1 year after established parkinsonism suggests PDD ✓
• D DLB exclusively shows neocortical Lewy bodies while PDD shows only brainstem Lewy bodies

Explanation

DLB and PDD are part of the Lewy body spectrum and share similar neuropathology (alpha-synuclein Lewy bodies). The clinical distinction is primarily temporal: DLB is diagnosed when dementia and parkinsonism onset are concurrent or within 1 year of each other (dementia precedes or appears within 1 year of motor symptoms). PDD is diagnosed when well-established Parkinson's disease (motor symptoms >1 year) is later complicated by dementia. Both can respond to levodopa, and both show cortical and brainstem Lewy bodies — the 1-year rule is the accepted clinical discriminator.

Reference: Kaplan & Sadock's Synopsis of Psychiatry, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.