Author Affiliation: Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Criteria for the clinical diagnosis of Alzheimer disease (AD) were established in 1984.1 Over the past 27 years, it has become abundantly clear that the pathology of AD may evolve years before the dementia is recognized. The concept of mild cognitive impairment (MCI) has been a focus of attention since the late 1990s and pertains to the gradual impairment of cognitive function that precedes the point at which significant interference in daily activities occurs, but AD pathology is accumulating.2 In addition, there is increasing evidence that AD pathophysiological processes are present in some individuals who have normal cognition or only minimal impairment (the preclinical phase). Thus, it has become clear that there is a spectrum (from preclinical to MCI to AD dementia) during which the disease is evolving.
McKhann GM. Changing Concepts of Alzheimer Disease. JAMA. 2011;305(23):2458-2459. doi:10.1001/jama.2011.810