Atypical dementia: when it is not Alzheimer's disease.

Dementia represents the most common neurodegenerative disorders affecting approximately 5% of the elderly population over age 65 years. At present, different forms of dementia are distinguished, including Alzheimer's disease (AD), dementia with Lewy bodies, frontotemporal dementia, and dementia secondary to diseases, such as AIDS dementia. Unlike AD, these atypical dementias are often associated with neurological symptoms, reflecting the localization of the degenerative process rather than the nature of the underlying histopathology. The present article provides an overview of the clinical evaluation of patients with atypical dementia and reviews distinguishing features of atypical dementias that may be confused with AD. The laboratory and imaging evaluation of various types of dementias are described. Current practice guidelines and practice parameters are reviewed as relevant for primary care practitioner.