Mild cognitive impairment (MCI): a historical perspective

Descriptions of dementia can be traced to antiquity. Prichard (1837) described four dementia stages and Kral (1962) described a "benign senescent forgetfulness" condition. The American Psychiatric Association's DSM-III (1980) identified an early dementia stage. In 1982, the Clinical Dementia Rating (CDR) and the Global Deterioration Scale (GDS) were published, which identified dementia antecedents. The CDR 0.5 "questionable dementia" stage encompasses both mild dementia and earlier antecedents. GDS stage 3 described a predementia condition termed "mild cognitive decline" or, alternatively, beginning in 1988, "mild cognitive impairment" (MCI). This GDS stage 3 MCI condition is differentiated from both a preceding GDS stage 2, "subjective cognitive impairment" (SCI) stage and a subsequent GDS 4 stage of mild dementia. GDS stage 3 MCI has been well characterized. For example, specific clinical concomitants, mental status and psychological assessment score ranges, behavioral and emotional changes, neuroimaging concomitants, neurological reflex changes, electrophysiological changes, motor and coordination changes, and changes in activities, accompanying GDS stage 3 MCI have been described. Petersen and associates proposed a definition of MCI in 2001 which has been widely used (hereafter referred to as "Petersen's MCI"). Important differences between GDS stage 3 MCI and Petersen's MCI are that, because of denial, GDS stage 3 MCI does not require memory complaints. Also, GDS stage 3 MCI recognizes the occurrence of executive level functional deficits, which Petersen's MCI did not. Nevertheless, longitudinal and other studies indicate essential compatibility between GDS stage 3 MCI and Petersen's MCI duration and outcomes.