How much disability in rheumatoid arthritis is explained by rheumatoid arthritis?

Objective. To measure the proportion of disability explained by disease man ifestations compared with nondisease factors in rheumatoid arthritis (RA). Methods. A hypothetical model of the disablement process specific for RA wa s constructed using the demographic, sociocultural, and clinical characteri stics of a consecutive cohort of RA patients. Disability was measured with the modified Health Assessment Questionnaire (M-HAQ) and the physical funct ion scale of the Medical Outcomes Study Short Form 36 (SF-36) questionnaire . Independent variables, grouped according to their position in the RA disa blement process model, were sequentially entered in a series of hierarchica l regression models. The proportion of variance in disability explained by each group of variables was measured by the group's incremental R-2. Results. The overall proportion of disability explained by the full model w as 59%, Factors in the main disease-disability pathway explained 33%, of wh ich 3% was explained by disease duration, 5% by the Westergren erythrocyte sedimentation rate, 14% by articular signs and symptoms, and 11% by perform ance-based functional limitations. External modifiers and contextual variab les explained 26% of the variance in disability, of which age and sex accou nted for 2%, formal education 4%, psychological status 17%, and symptoms of depression 3%. Conclusion. Both the main disease-disability pathway and factors external t o this pathway contribute significantly to disability in RA. These findings provide evidence of the relative influence of psychosocial factors, compar ed with disease manifestations, on the disability of patients with RA.