Predicting Low Disease State and Remission in Early Rheumatoid Arthritis in the First Six Months, Comparing the Simplified Disease Activity Index and European League Against Rheumatism Response Measures: Results From an Early Arthritis Cohort

OBJECTIVE: To compare the European League Against Rheumatism (EULAR) and Simplified Disease Activity Index 50% (SDAI50) response measures (RMs) and their impact on future response to treatment in patients with early rheumatoid arthritis (ERA). METHODS: Biologic agent-naive ERA patients from the Canadian Early Arthritis Cohort study with complete data at baseline, 3, and 6 months were evaluated. Kappa statistics were used to evaluate the agreement between the EULAR (moderate or good response) and SDAI50 RMs. The RMs at 3 months were also compared for their ability to predict low disease activity state (LDAS) or remission (REM) at 6 months. RESULTS: A total of 1,124 patients were evaluated. Of those, 215 patients (30%) and 294 patients (45%) failed to achieve a EULAR and SDAI50 response, respectively. There was a good agreement between EULAR and SDAI50 RMs with a kappa of 0.59 (95% confidence interval 0.53-0.66). Throughout the range of disease activity, the SDAI50 response was shown to be more stringent than the EULAR response. Multivariable linear regression analysis demonstrated that both RMs at 3 months were associated with LDAS or REM at 6 months, and SDAI50 had a more significant impact on this outcome compared to the EULAR response. CONCLUSION: There is a good agreement between the EULAR and SDAI50 RMs. Although a minority of patients have discordant RMs at each end of the disease activity spectrum at baseline, the SDAI50 response at 3 months appears to be a more significant predictor of outcomes at 6 months than EULAR response.