The preclinical phase of Alzheimer disease - A 22-year prospective study of the Framingham cohort

Objectives: To relate performance on tests of cognitive ability to the subs equent development of probable Alzheimer disease (pAD) and to identify the pattern of earliest changes in cognitive functioning associated with a diag nosis of pAD. Design: From May 1975 to November 1979, a screening neuropsychological batt ery was administered to Framingham Study participants. They were followed u p prospectively for 22 years and examined at least every years for the deve lopment of PAD. Setting: A community-based center for epidemiological research. Participants: Subjects were 1076 participants of the Framingham Study aged 65 to 94 years who were free of dementia and stroke at baseline (initial) n europsychological testing. Main Outcome Measure: Presence or absence of pAD during a 22-year surveilla nce period was related to test performance at initial neuropsychological te sting. Results: Lower scores for measures of new learning, recall, retention, and abstract reasoning obtained during a dementia-free period were associated w ith the development of pAD. Lower scores for measures of abstract reasoning and retention predicted pAD after a dementia-free period of 10 years. Conclusions: The "preclinical phase" of detectable lowering of cognitive fu nctioning precedes the appearance of PAD by many years. Measures of retenti on of information and abstract reasoning are among the strongest predictors of pAD when the interval between initial assessment and the development of pAD is long.