Dementia with Lewy bodies (DLB) is the second leading cause of
cognitive impairment among the elderly. While it is usually accompanied by the neocortical
neuritic plaques (NP) and entorhinal neurofibrillary tangles (NFT) characteristic of
Alzheimer disease (AD), and so can be construed as a Lewy body variant of AD (LBV), it also occurs in pure form as
diffuse Lewy body disease (DLBD). We assessed cognitive status in 17 DLB patients (12 with LBV and 5 with DLBD) and compared the results with 12 AD subjects and 5 controls. We then sought to determine which neuropathologic abnormalities correlated with
cognitive impairment. Among DLB cases, neocortical Lewy body (LB) counts, modified Braak stages of NFT burden in the entorhinal cortex, neocortical NP counts, and loss of
choline acetyltransferase (ChAT) activity all correlated with
dementia severity. Unlike AD, neocortical NFT and
anti-synaptophysin reactivity were uncorrelated with DLB
dementia. Despite comparable LB counts and ChAT losses, the DLBD were significantly less demented than the LBV patients. We conclude that neocortical LB and ChAT depletion contribute to
cognitive impairment in DLB and that concomitant AD pathology in LBV, represented by higher Braak stages and NP, promotes increased
dementia severity compared with that encountered in DLBD.