Objective: Radiologic progression in rheumatoid arthritis (RA) is considered the consequence of persistent inflammatory activity. To determine whether a change in disease activity is related to a change in radiologic progression in individual patients, we investigated the longitudinal relationship between inflammatory disease activity and subsequent radiologic progression.
Methods: The databases of the University Medical Center Nijmegen (UMCN) cohort and the Maastricht Combination Therapy in RA (COBRA) followup study cohort were analyzed. The UMCN cohort included 185 patients with early RA who were followed up for up to 9 years. Patients were assessed every 3 months for disease activity and every 3 years for radiologic damage. The COBRA cohort included 152 patients with early RA who were followed up for up to 6 years. Patients were assessed at least every year for disease activity and every 12 months for radiologic damage. Disease activity was assessed with the Disease Activity Score (DAS) (original DAS in the UMCN cohort, DAS28 in the COBRA cohort). Radiologic damage was measured by the Sharp/van der Heijde score in both cohorts. Data were analyzed with longitudinal regression analysis (generalized estimating equations [GEE]), using autoregression for longitudinal associations and radiologic damage as the dependent variable. Time, time(2) baseline predictors for radiologic progression and their interactions with time, as well as DAS/DAS28 (actual values or interval means and interval SDs of the means) were subsequently modeled as explanatory variables.
Results: Data analyzed by GEE showed a decrease in radiologic progression over time (regression coefficient for time(2) -1.0 [95% confidence interval -1.4, -0.6] in the UMCN cohort and -0.4 [95% confidence interval -0.8, 0.0] in the COBRA cohort). After adjustment for time effects and baseline predictors of radiologic progression and their interactions with time, a positive longitudinal relationship was indicated by autoregressive GEE between the mean interval DAS and radiologic progression in the UMCN cohort (regression coefficient 5.4 [95% confidence interval 2.1, 8.6]), and between the DAS28 and radiologic progression in the COBRA cohort (regression coefficient 1.4 [95% confidence interval 0.8, 2.0]). In the UMCN cohort, the SD of the mean interval DAS was independently longitudinally related to the radiologic progression over the same periods (regression coefficient 20.2 [95% confidence interval 7.2, 33.3]). In both cohorts, the longitudinal relationships between (fluctuations in) disease activity and radiologic progression were found selectively in rheumatoid factor (RF)-positive patients.
Conclusion: Radiologic progression is not linear in individual patients. Fluctuations in disease activity are directly related to changes in radiologic progression, which supports the hypothesis that disease activity causes radiologic damage. This relationship might only exist in RF-positive patients.