Alpha-synuclein (αSyn) protein misfolds and aggregates forming Lewy bodies in Parkinson disease. The distinct pathological difference between Lewy body dementia (DLB) and Parkinson disease with dementia (PDD) is primarily based on:

• A The presence or absence of amyloid plaques and tau tangles
• B The distribution of Lewy bodies — restricted brainstem in PD vs cortical in DLB
• C The temporal relationship between onset of parkinsonism and dementia (1-year rule) ✓
• D Genetic mutations — LRRK2 in PD vs GBA in DLB

Explanation

DLB and PDD share identical neuropathology (cortical and subcortical Lewy bodies + Lewy neurites). The distinction is clinical, based on the 1-year rule: if dementia precedes or occurs within 1 year of parkinsonism onset → DLB; if dementia develops >1 year after established Parkinson disease → PDD. Both show αSyn Lewy body pathology in limbic and neocortical regions. DLB is associated with fluctuating cognition, visual hallucinations, REM sleep behavior disorder, and sensitivity to antipsychotics. GBA mutations are the most common genetic risk factor for BOTH PD and DLB.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.