Parkinson's disease dementia: a diminished role for the Lewy body.

The literature currently views Lewy bodies as central in the pathogenesis of Parkinson's disease dementia (PDD) when Alzheimer's disease (AD) or vascular pathology is not present. Because the neuropathology of PDD is not well understood, the pathological features of PDD were characterized in eighteen PD brain specimens using published criteria for AD, Diffuse Lewy Body Disease (DLBD), and Vascular Disease as a framework. Among the PD dementia (n=16) subjects, 3 (19%) did not have LBs outside of the brain stem, nor AD or vascular pathology. In two additional cases, one did have rare LBs in the neocortex and cingulate gyrus. However, these two cases did not meet the diagnostic criteria for DLBD. Beyond these 5 cases, the remaining PD dementia subjects fitted a classical pathological profile consistent with AD (38%), vascular disease (12.5%), DLBD (6%), or a combination of these pathologies (12.5%). The findings from this study do not support the hypothesis that LBs are the main substrate for dementia in PD. More research with a larger sample size is needed to determine whether the LB may be a secondary phenomenon and/or an "innocent-bystander". The entire role of the LB in PD dementia is again brought into question.