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 ha ve 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 focuse d on the pace of disability progression. This study characterizes the devel opment of severe walking disability over time and evaluates risk factors an d subsequent mortality as they relate to mobility disability with progressi ve or catastrophic onset. DESIGN: Population-based prospective cohort study with annual follow-up ass essments 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 fir st follow-up who had adequate data available to classify mobility disabilit y during subsequent follow-ups. MEASUREMENTS: Severe mobility disability was defined as the need for help f rom a person to walk across a room or inability to walk across a room. Thos e developing severe mobility disability were classified as having progressi ve mobility disability if they had been unable to walk half a mile in eithe r of the prior 2 years. They were classified as having catastrophic mobilit y disability if they reported having been able to walk half a mile in two p revious 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 ii-tore chro nic conditions at baseline were significantly more likely to develop progre ssive disability than catastrophic disability. Stroke, hip fracture, and ca ncer occurring during follow-up were associated with very high risk of seve re mobility disability. For stroke and hip fracture, the risk was twice as high for catastrophic disability as for progressive disability, but this di fference did not reach statistical significance. Risk for catastrophic disa bility from cancer was significantly greater than for progressive disabilit y. Half of catastrophic disability subjects had stroke, hip fracture, or ca ncer in the year immediately preceding this disability. Incident heart atta ck did not predict severe mobility disability. Among those who developed se vere mobility disability, type of disability did not influence subsequent s urvival for the first 3 years, but beyond 3 years those with catastrophic d isability 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 b oth different for progressive and catastrophic mobility disability supports the value of ascertaining the pace of disability development as a useful c haracterization of disability. Further progress in developing prevention an d treatment strategies may be made by taking the pace of disability develop ment into account.