Predictor of the Simplified Disease Activity Index 50 (SDAI 50) at Month 3 of bDMARD Treatment in Patients with Long-Established Rheumatoid Arthritis

The Simplified Disease Activity Index (SDAI) 50 has good agreement with European League Against Rheumatism (EULAR) response measures for early Rheumatoid Arthritis (RA). There have been reports on early RA, but not on long-established RA. In this study, we analysed the relationships between various baseline factors and SDAI 50 after three months of treatment with biological disease-modifying antirheumatic drugs (bDMARDs) to determine the prognostic factors for long-established RA.

Subjects were 260 RA patients who had been treated with bDMARDs for 3 months. The following characteristics were investigated: Patient backgrounds, the erythrocyte sedimentation rate (ESR), C-reactive protein and serum matrix metalloproteinase-3 levels, SDAI scores, and health assessment questionnaire disability index and short form-36 scores. As a primary outcome index, the SDAI response was defined as a 50% reduction in the SDAI score between baseline and 3 months (SDAI 50).

Baseline values of disease duration (odds ratio: 0.942, 95% CI: 0.902-0.984), smoking history (odds ratio: 2.272, 1.064-4.850), 28-tender joint count (odds ratio: 0.899, 0.827-0.977), evaluator's global assessment (odds ratio: 1.029, 1.012-1.047) and ESR (odds ratio: 1.015, 1.001-1.030) were determined to be significant factors based on logistic regression analysis.

Our study demonstrated that RA patients with shorter disease duration, no smoking, and higher RA disease activity are more likely to achieve SDAI 50 through bDMARD treatment.