Progressive versus catastrophic loss of the ability to walk: Implications for the prevention of mobility loss

OBJECTIVES: Loss of mobility is an important functional outcome that can have devastating effects on quality of life and the ability of older persons to remain independent in the community. Although a large amount of research has been done on risk factors for disability onset, little work has focused on the pace of disability progression. This study characterizes the development of severe walking disability over time and evaluates risk factors and subsequent mortality as they relate to mobility disability with progressive or catastrophic onset. DESIGN: Population-based prospective cohort study with annual follow-up assessments for up to 7 years SETTING: Three communities of the Established Populations for Epidemiologic Studies of the Elderly. PARTICIPANTS: There were 5,355 persons not disabled at baseline and the first follow-up who had adequate data available to classify mobility disability during subsequent follow-ups. MEASUREMENTS: Severe mobility disability was defined as the need for help from a person to walk across a room or inability to walk across a room. Those developing severe mobility disability were classified as having progressive mobility disability if they had been unable to walk half a mile in either of the prior 2 years. They were classified as having catastrophic mobility disability if they reported having been able to walk half a mile in two previous annual interviews. RESULTS: The overall incidence of severe mobility disability was 11.6 cases/1,000 person years. Those age 85 and older or having three or more chronic conditions at baseline were significantly more likely to develop progressive disability than catastrophic disability. Stroke, hip fracture, and cancer occurring during follow-up were associated with very high risk of severe mobility disability. For stroke and hip fracture, the risk was twice as high for catastrophic disability as for progressive disability, but this difference did not reach statistical significance. Risk for catastrophic disability from cancer was significantly greater than for progressive disability. Half of catastrophic disability subjects had stroke, hip fracture, or cancer in the year immediately preceding this disability. Incident heart attack did not predict severe mobility disability. Among those who developed severe mobility disability, type of disability did not influence subsequent survival for the first 3 years, but beyond 3 years those with catastrophic disability had a relative risk of death of 0.4 (95% confidence interval 0.2-0.9) compared with those with progressive disability. CONCLUSION: The observation that risk factors and mortality outcomes were both different for progressive and catastrophic mobility disability supports the value of ascertaining the pace of disability development as a useful characterization of disability. Further progress in developing prevention and treatment strategies may be made by taking the pace of disability development into account.