Dementia with Lewy bodies (DLB) and Parkinson's Disease with dementia may overlap clinically and pathologically. Some would say that trying to distinguish the two conditions is futile, since they represent different presentations of the same pathologic process.


Features that may be shared:

(1) presence of Lewy bodies

(2) presence parkinsonian (extrapyramidal) motor features


Differences between the two:

(1) distribution of Lewy bodies

(2) not all patients with DLB develop parkinsonian features


A patient is classified as having Parkinson's disease with dementia:

(1) presence of established Parkinson's disease for several years with preserved cognition

(2) gradual cognitive decline affecting multiple domains (memory, executive function, etc)

(3) exclusion of other causes of cognitive decline (vascular dementia, depressive pseudodementia, etc)


A patient is classified as having dementia with Lewy bodies:

(1) presence of progressive dementia

(2) presence of other supportive features (visual hallucinations, fluctuating cognition, etc)

(3) absence of parkinsonian features or onset after the dementia or as a result of neuroleptic therapy


The problem in classification occurs when both dementia and parkinsonian motor features occur at the same time. Some include these with dementia with Lewy bodies. Others require a "1 year rule" between onset of dementia and parkinsonian motor changes before calling it DLB.


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