Ten-year incidence of dementia in a rural elderly US community population

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Abstract
Objective: To determine incidence rates by age, sex, and education of overall dementia and probable/possible AD in a largely rural community. Methods: Ten-year prospective study of a randomly selected community sample aged 65+; biennial cognitive screening followed by standardized clinical evaluation. Incidence rates were estimated for overall dementia (Diagnostic and Statistical Manual of Mental Disorders, 3rd ed., revised, criteria and Clinical Dementia Rating [CDR]) and for probable/possible AD (National Institute of Neurological and Communicative Disorders and Stroke–Alzheimer’s Disease and Related Disorders Association criteria). Results: The cohort consisted of 1,298 individuals free of dementia at study entry. Among these, 199 incident (new) cases of overall (all-cause) dementia with CDR stage ≥ 0.5, including 110 with CDR ≥ 1, were detected during follow-up. Among the incident cases, 153 (76.9%) had probable/possible AD. Age-specific incidence rates are reported for all dementia and for probable/possible AD, by sex and CDR stage. Among all-cause dementias with CDR = 0.5, controlling for age and education, men had a higher incidence rate than women. In the same group, those with less than high school education had significantly higher incidence rates than those with more education. Rates did not vary significantly by sex or education for probable/possible AD or for dementia with CDR ≥ 1. Conclusions: Incidence rates of all dementias and of AD increased with age; men and those with lesser education had higher rates of possible/incipient dementia (CDR = 0.5) in this community. Potential explanations for these sex and education effects are discussed.