The relationship between disease activity, joint destruction, and functional capacity over the course of rheumatoid arthritis

Objective. To investigate the relationship between functional capacity, dis ease activity, and joint destruction over the course of rheumatoid arthriti s (RA). Methods. The followup data on 378 patients with early RA (duration <1 year) , included in an open, prospective study since 1985 at the Department of Rh eumatology of the University Medical Center Nijmegen, were used. Functional capacity, disease activity, and joint destruction were assessed using the Health Assessment Questionnaire disability index (HAQ DI), the Disease Acti vity Score (DAS), and a modification of the sharp radiographic damage score , respectively. Multiple linear regression was used to model the data colle cted at 0, 3, 6, and 9 years after study start, to investigate which variab les influenced functional capacity during the disease course. A general lin ear mixed model for longitudinal data, which included the variables identif ied as significant in the multiple linear regression models and several int eraction terms between the variables, was run. Results. On average, the functional capacity of the patients, as measured b y the HAQ DI, worsened over the course of the disease after an initial impr ovement. After an initial reduction in the extent of disease activity, the mean DAS remained more or less stable over the course of the disease. The m ean modified sharp joint damage score worsened over the course of the disea se, with a slower progression rate later in the disease. In the multiple li near regression at 0, 3, and 6 years after study start, disease activity wa s found to be an important factor influencing functional capacity, and at 6 and 9 years, joint damage had an important effect on functional capacity. Furthermore, at 6 and 9 years, there was an interaction effect of joint des truction with disease activity. In the general linear mixed model, disease activity, joint damage, and an interaction effect of disease activity and j oint damage were the main factors explaining functional capacity. Conclusion. The effect of disease activity and joint destruction on functio nal capacity changes over the course of the disease. In early RA, functiona l capacity is most associated with disease activity, and in late disease, w ith joint damage.