To determine whether mildly impaired physical function (based on performance-based assessment) is associated with the development of dementia of the Alzheimer type (DAT) in cognitively normal older adults.
Longitudinal, observational study with yearly assessments of physical and cognitive function. Mean follow-up was 5 years.
Knight Alzheimer’s Disease Research Center at Washington University, St. Louis, Missouri.
Four hundred thirty-five cognitively normal adults, age 60 years or older participating in longitudinal studies of aging.
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 the PPT total scores and time to cognitive impairment and DAT; as well as the association of time to these events while adjusting for, and simultaneously testing the effects of age, gender, education, and presence of at least one apolipoprotein (APOE) ε4 allele.
During the follow-up period, 81 participants developed DAT. Compared to those who remained cognitively normal, participants diagnosed with DAT were older (81 vs 74.2 years; p=.001) and had worse performance on the PPT (25.5 vs 28.1; p=.009). Time to DAT diagnosis was associated with total scores on the PPT (hazard ratio [HR] =.89, 95% CI=.86–.93, p<.001) such that time to a DAT diagnosis was slower for participants with higher physical performance scores. In the adjusted analysis, the PPT scores significantly predicted time to a DAT diagnosis (HR =.94, 95% CI=.89–.99, p<.022).
The presence of 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 with performance-based assessments, its presence may predate clinically detectable cognitive decline.