Mild Physical Impairment Predicts Future Diagnosis of Dementia of the Alzheimer's Type

OBJECTIVES: To determine whether mildly impaired physical function (based on performance-based assessment) is associated with development of dementia of the Alzheimer's type (DAT) in cognitively normal older adults. DESIGN: Longitudinal, observational study with yearly assessments of physical and cognitive function. Mean follow-up was 5 years. SETTING: Knight Alzheimer's Disease Research Center at Washington University, St. Louis, Missouri. PARTICIPANTS: Four hundred thirty-five cognitively normal adults aged 60 and older participating in longitudinal studies of aging. MEASUREMENTS: Survival analyses were used to examine whether scores on the 9-item Physical Performance Test (PPT) predicted time to DAT diagnosis. Cox proportional hazards models were used to examine associations between PPT total scores and time to cognitive impairment and DAT; as well as the association between time and these events, adjusting for and simultaneously testing the effects of age, sex, education, and presence of one or more apolipoprotein (APOE) epsilon 4 alleles. RESULTS: During the follow-up period, 81 participants developed DAT. Participants diagnosed with DAT were older (81.0 vs 74.2, P = .001) and had worse performance on the PPT (25.5 vs 28.1, P = .009) than those who remained cognitively normal. Time to DAT diagnosis was associated with PPT total score (hazard ratio (HR) = 0.89, 95% confidence interval (CI) = 0.86-0.93, P < .001) such that time to DAT diagnosis was longer for participants with higher physical performance scores. In the adjusted analysis, PPT score significantly predicted time to DAT diagnosis (HR = 0.94, 95% CI = 0.89-0.99, P = .02). CONCLUSION: Mild physical impairment in cognitively normal older adults is associated with subsequent development of DAT. Although the physical impairment may be sufficiently mild that it is recognized only using performance-based assessments, its presence may predate clinically detectable cognitive decline.