Implementing diagnostic criteria and estimating frequency of mild cognitive impairment in an urban community

Background: Reported rates of mild cognitive impairment (MCI) range widely depending on methodologic differences, including specific sample characteristics, cognitive measures used, normative samples used for neuropsychological tests, and diagnostic criteria. Objectives: To operationalize diagnostic criteria for MCI and examine the frequency of MCI in ethnically and linguistically diverse elders (individuals older than 65 years). Design: Prospective, community-based longitudinal cohort study. Setting: Northern Manhattan, New York, NY. Participants: A cohort of 1315 nondemented elderly participants. Main Outcome Measure: A diagnosis of MCI was assigned retrospectively on the basis of comprehensive neuropsycho logical, functional, and neurologic assessments. Amnestic MCI, as well as forms of mild impairment with other cognitive characteristics, were classified. Results: The frequency of amnestic MCI was 5.0% (95% confidence interval, 3.8-6.2). Other subtypes of MCI ranged in frequency from 2.1% to 6.2%. Mild cognitive impairment was more common among those older than 75 years compared with those aged 65 to 75 years. Individuals with fewer than 9 years of schooling were more likely to meet MCI criteria. Apolipoprotein (APOE) E4 allele was more frequent among those with amnestic MCI. Conclusions: When proper normative values are used, only age and education, and not race or ethnicity, are associated with higher frequency of MCI. The proportion of nondemented elders with isolated memory deficits is smaller than the proportion with deficits in multiple cognitive domains. The strong association of the APOE E4 allele with only amnestic MCI suggests that there are likely to be multiple causes of cognitive impairment and differential rates of conversion to Alzheimer disease within the cognitive subtypes of MCI.