Factors Associated with Insidious and Noninsidious Disability

Background: Although disability is often precipitated by an illness/injury, it may arise insidiously. Our objectives were to identify the factors associated with the development of insidious and noninsidious disability and to determine whether these risk factors differ between the two types of disability. Methods: We prospectively evaluated 754 community-living persons, 70+ years, from 1998 to 2016. The unit of analysis was an 18-month person-interval, with risk factors assessed at the start of each interval. Disability in four activities of daily living and exposure to intervening events, defined as illnesses/injuries leading to hospitalization, emergency department visits, or restricted activity, were assessed each month. Insidious and noninsidious disability were defined based on the absence and presence of an intervening event. Results: The rate of noninsidious disability (21.7%) was twice that of insidious disability (10.8%). In multivariable recurrent-event Cox analyses, six factors were associated with both disability outcomes: non-Hispanic white race, lower extremity muscle weakness, poor manual dexterity, and (most strongly) frailty, cognitive impairment, and low functional self-efficacy. Three factors were associated with only noninsidious disability (older age, number of chronic conditions, and depressive symptoms), whereas four were associated with only insidious disability (female sex, lives with others, low SPPB score, and upper extremity weakness). The modest differences in risk factors identified for the two outcomes in multivariable analyses were less apparent in the bivariate analyses. Conclusions: Although arising from different mechanisms, insidious and noninsidious disability share a similar set of risk factors. Interventions to prevent disability should prioritize this shared set of risk factors.