Predicting the onset of dementia with longitudinal performance-based measures of physical function.

Older adults with dementia have reduced physical function; however, the extent to which declines in physical function are accelerated prior to dementia remains unclear. This study compared changes in three objective physical function measures in 518 older adults who did or did not develop dementia over the course of the study: Time to complete a three-meter out-and-back walk (gait), grip dynamometry (grip strength), and time to complete a functional fine motor test (functional fine motor). Data from three longitudinal Swedish datasets of older adults (OCTO-Twin, GENDER, SATSA) were analyzed. During the studies, 259 participants were diagnosed with dementia; only data prior to dementia onset were included for these participants. Propensity matching identified 259 participants who did not develop dementia and whose age at last observation matched the age of diagnosis in the dementia-onset group. Linear latent growth curve models captured longitudinal changes in each measure prior to the onset of dementia; thus, intercepts reflect an estimate of physical function at dementia onset or the last timepoint in the study. After controlling for sex, the functional fine motor test declined faster in the dementia-onset group, while gait and grip strength showed no group differences in the rate of change between groups. Functional fine motor decline also occurred at a significantly faster rate than cognitive decline (measured with the Mini-Mental Status Exam). These findings suggest that functional fine motor tasks may identify elevated risk for developing dementia, particularly in cases where memory tests may not be reliable.