Differential diagnosis of Alzheimer's disease.

AD is by far the leading cause of dementia, accounting for about 75% of cases. Vascular dementia and Parkinson's disease, with or without concomitant AD, are responsible for much of the remainder of pathologically confirmed causes of dementia. The differential diagnosis of AD remains clinically based; even in the absence of a biologic marker for the disease, diagnostic accuracy can be high. Informant interviews can be helpful in detecting early dementia and in distinguishing the various stages and features of AD. Characterization of phenotypic variants of AD and refinement of diagnostic criteria for the non-AD dementias is needed to clarify the inter-relationships of these conditions and facilitate molecular genetic and other basic investigations of the etiopathogenesis of AD.