Mild physical impairment predicts future diagnosis of dementia of the Alzheimer's type

Abstract

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) ε4 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.

Keywords: dementia of Alzheimer's type; frailty; physical performance; predictors.

Conflict of interest statement

Conflict of Interest:

Dr. Wilkins has grants from the National Institutes of Health and the Barnes-Jewish Hospital Foundation.

Dr. Morris has participated or is currently participating in clinical trials of anti dementia drugs sponsored by the following companies: Janssen Immunotherapy, Eli Lilly and Company, and Pfizer.

Dr. Morris has served as a consultant or has received speaking honoraria for the following companies: Eisai, Janssen Alzheimer Immunotherapy Program/Elan, Glaxo-Smith-Kline, Novartis, Otsuka Pharmaceuticals, and Pfizer/Wyeth.

Dr. Galvin has grants from the National Institutes of Health, Michael J Fox Foundation, Morris and Alma Schapiro Fund and the State of New York. He holds the copyright for the AD8 dementia screening test and received licensing fees from Novartis, Pfizer and Eisai.

© 2013, Copyright the Authors Journal compilation © 2013, The American Geriatrics Society.

Figures

Figure 1

Kaplan-Meier Curves Showing the Association between Functional Status on the Physical Performance Test at Baseline and Time to Diagnosis of Dementia of the Alzheimer Type (DAT).