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.
