Self report scores of physical disability and the use of devices or assistance in performing activities are sometimes integrated in one index of physical function, although they are aimed at measuring different dimensions of physical disability. The properties of both parameters were evaluated in two groups of patients with rheumatoid arthritis (RA).
A group of patients with RA of recent onset was compared with a group with established disease on four parameters of disability: use of devices, use of personal assistance, and scores on a validated Dutch version of the Health Assessment Questionnaire Disability Index, with and without integrating the use of devices or assistance. Correlation coefficients among disability parameters were calculated. In multiple regression analysis the influence of disease duration on the disability parameters was determined after disease activity, psychological wellbeing, and demographical characteristics had been controlled.
Functional disability scores were mainly related to inflammatory activity and psychological wellbeing, whereas the uses of devices had a strong relation with disease duration, independent of current disease activity. Integrating these parameters of disability yielded a parameter that was still mainly associated with disease activity.
Self report scores of functional disability and the use of devices represent distinct dimensions of physical function in RA. Integrating both parameters into one measure of physical disability does not provide an index adequately reflecting both dimensions. The use of both parameters to measure outcome in long term clinical studies is recommended.