Early identification of cognitive deficits: preclinical Alzheimer's disease and mild cognitive impairment.

With the projected dramatic increase in the number of people who will be diagnosed with Alzheimer's disease (AD) in the coming years, interest is growing in identifying and treating adults at high risk for developing the disorder. Recent research suggests that individuals who will go on to receive a diagnosis of AD exhibit deficits in cognitive performance years beforehand. Those with mild cognitive impairment (MCI), for example, have characteristic cognitive deficits, such as memory loss, and convert to a diagnosis of AD at a faster rate than cognitively healthy controls. MCI has thus become a focus of research because it may help identify high-risk individuals for whom prophylactic treatments designed to slow the progress toward AD can be prescribed. After describing the diagnostic criteria and dementia outcomes associated with MCI, this article discusses several challenges to the study of cognitive impairment before the diagnosis of AD.