Objective To determine which neuropsychological test measures and which symptoms at presentation might best differentiate dementia with Lewy bodies (DLB) from Alzheimer's disease (AD).

Methods Cases were from the Columbia University Alzheimer's Disease Research Center, and included cases with pathological diagnosis of pure DLB (n=12), mixed DLB and AD (DLB+AD n=23) and pure AD (n=89) who had Clinical Dementia Rating 0, 0.5 or 1 at their first visit. Clinical symptoms and neuropsychological test measures were compared for pure DLB, DLB+AD and pure AD using univariate analysis of covariance and separate logistic regression analyses.

Results Visual hallucinations, illusions and extrapyramidal tract signs were more frequent as clinical features of the early stage of pure DLB compared with AD. The pure DLB patients showed more impaired visuospatial function than pure AD or DLB+AD patients whereas memory function was more severely impaired in pure AD or DLB+AD than in pure DLB. Analysis of memory subscores suggested that failure of retrieval was the major contributor to the memory deficit of DLB. Multiple logistic regression analysis showed that visuospatial function and delayed memory recognition were independent predictors of pure DLB from pure AD and from DLB+AD. But test measures did not discriminate between DLB+AD and pure AD.

Conclusions Visuospatial function was more affected in pure DLB than in AD while memory retrieval deficit was more affected in AD than in pure DLB, in the early stages of dementia. However, DLB+AD did not show significant neuropsychological difference from pure AD.