Age-specific incidence rates of Alzheimer's disease - The Baltimore Longitudinal Study of Aging

Objective: To estimate age-specific incidence rates of AD in the Baltimore Longitudinal Study of Aging (BLSA). Background: The BLSA is a volunteer coh ort of normal subjects followed longitudinally with biennial evaluations at the Gerontology Research Center of the National Institute on Aging. Method s: Subjects are 1236 participants (802 men, 434 women) in the BLSA with lon gitudinal follow-up between January 1985 and May 1998. The average length o f follow-up was 7.5 years, with participants evaluated every 2 years by phy sical, neurologic, and neuropsychological examinations. Using Diagnostic an d Statistical Manual of Mental Disorders, 3rd ed,, revised and National Ins titute of Neurological and Communicative Disorders and Stroke-Alzheimer's D isease and Related Disorders Association criteria, the authors diagnosed de mentia and AD. Results: The authors diagnosed 155 cases of dementia, of whi ch 114 (74%) were AD. Incidence rates of AD increased with age from an esti mated 0.08% per year (95% CI 0.00 to 0.43) in the 60 to 65 age group to an estimated 6.48% per year (95% CI 5.01 to 8.38) in the 85+ age group for men and women combined. The doubling time of incidence rates was estimated to be approximately 4.4 years and the median time of conversion from mild cogn itive impairment to diagnosis of AD was estimated to be 4.4 years. There wa s a trend for women to have higher incidence rates than men and for fewer y ears of education to be associated with higher incidence rates; however, th ese effects mere not significant. Conclusion: Incidence rates for AD in the BLSA are consistent with published rates in other studies. The longitudina lly followed subjects of the BLSA offer a unique opportunity to prospective ly investigate the antecedents of AD.