Preclinical mobility disability predicts incident mobility disability in older women

Physical disability and dependency are serious, and frequent, adverse health outcomes associated with aging and resulting from chronic disease. Reasoning has suggested that there might be a preclinical, intermediate phase of disablement which might develop in parallel with progression of underlying disease and precede and predict disability. Definition of this stage could provide a basis for screening and early intervention to prevent disability. The objective of this study was to determine preclinical functional predictors of incident mobility difficulty and provide evidence for a preclinical stage of disability.

A prospective, population-based cohort study was carried out in Baltimore, Maryland, with two evaluations 18 months apart. The participants were 436 community-dwelling women, 70-80 years of age at baseline, not cognitively impaired, and reporting difficulty in no areas, or only one area, of physical function (primarily mobility), who were participating in the Women's Health and Aging Study II. Participants were recruited from a population-based, age-stratified random sample. Incident mobility disability was studied in the subset without such disability at baseline. The main outcome measure was self-reported incident difficulty walking 1/2 mile or climbing up 10 steps.

At baseline, 69.3% of the cohort reported no difficulty with mobility. After 18 months, 16.0 and 11.7% of this group reported incident difficulty walking 1/2 mile or climbing up 10 steps, respectively. Those reporting baseline task modification due to underlying health problems, our measure of preclinical disability, were at three- to fourfold higher odds of progressing to difficulty than were those without such modification. In multivariate logistic regression analyses, this self-report measure, task modification without difficulty, and objective measures of performance were independently and jointly predictive of incident mobility difficulty. Specifically, for incident difficulty walking 1/2 mile, self-reported task modification odds ratio (OR) = 3.67, walking speed (.5 m/s difference) OR = 2.16; for incident difficulty climbing up 10 stairs, OR for task modification = 3.84, for stair climb speed (1/3 step/s difference) = 2.08 (95% CI did not include 1 for any). Covariates, age, living alone, number of chronic diseases, depression score, knee strength, and balance by functional reach, were not significant predictors in either model.

Two indicators of functional changes in older women without mobility difficulty, self-report of modification of method of doing a task in the absence of difficulty and performance measures, are independent and strong predictors of risk of incident mobility disability. The self-report measure provides substantial strength in predicting risk of incident disability across the full range of performance, and may identify a vulnerable point at which other risk factors act to cause transitions to disability. Together, the preclinical indicators identify a subset of high-functioning older women who are at high risk of mobility disability, and provide a potential basis for screening for disability risk and targeting interventions to prevent mobility disability.