Mild cognitive impairment: risk of Alzheimer disease and rate of cognitive decline.

OBJECTIVE: To examine the extent to which persons with mild cognitive impairment (MCI) have an increased risk of Alzheimer disease (AD) and a more rapid rate of decline in cognitive function compared to similar persons without cognitive impairment.

METHOD: Participants were 786 community-based persons (221 with MCI and 565 without cognitive impairment) from the Rush Memory and Aging Project, an ongoing longitudinal clinical-pathologic study of common chronic conditions of old age. All participants underwent detailed annual clinical and neuropsychological evaluations. The authors examined the risk of incident AD and rate of change in global cognitive function among persons with MCI and those without cognitive impairment; all statistical models controlled for age, sex, and education.

RESULTS: Over an average of 2.5 years of follow-up, 57 persons with MCI (25.8%) developed AD, a rate 6.7 times higher than those without cognitive impairment. In addition, persons with MCI declined considerably more rapidly each year on a measure of global cognitive function than those without cognitive impairment.

CONCLUSIONS: Mild cognitive impairment is associated with a greatly increased risk of incident Alzheimer disease and a more rapid rate of decline in cognitive function.