A Predictive Model for Simplified Disease Activity Index (Sdai) Remission in Rheumatoid Arthritis

Abstract

Objectives. To identify predictors for Simplified Disease Activity Index (SDAI) remission in patients with established rheumatoid arthritis (RA) under 12 months of anti-TNF therapy combined with synthetic disease modyfing antirheumatic drugs (sDMARD). Methods. We performed a prospective observational study in 90 RA patients with a high active disease refractory to sDMARDs, starting anti-TNFs. Patients were assessed every 3 months based on a well-defined protocol, including individual parameters (clinical, inflammatory) and composite tools (simplified disease activity index SDAI, functional index HAQ-DI); total and IgA-isotype rheumatoid factor (RF) as well as anti-citrullinated peptide antibodies (ACPAs) were measured at baseline, 6 and 12 months. Therapeutic response was evaluated according to EULAR criteria. The primary endpoint was SDAI remission (≤ 3.3) at 12 months of treatment. Univariate and multivariate logistic regression analysis (Forward LR method) were used to assess the manner and intensity in which several parameters (demographics, disease-related, labs and medication) power SDAI remission. Results. SDAI remission was reported in 39.7% cases. We identified nine relevant predictors for SDAI remission at 12 months of therapy by univariate analysis, including: age ≤ 50 years, disease onset ≤ 5 years, RA stages I and II, functional capacity stages I and II, HAQ-DI ≤ 2, concomitent sDMARD, baseline CRP ≤ 20 mg/l, IgA-RF ≤ 20 IU/ml and ACPAs ≤ 40 IU/ml. A mathematical model was further generated, based only on six out of nine parameters: age, disease stage, functional capacity, concomitent sDMARDs, CRP and ACPA. This model expresses a solid approximation for the analysed casess (the Hosmer-Lemeshow test λ² = 0.931, p = 0.920 ≥ 0.05, Cox and Snell R2 0.399). Finally, three significant factors were recognized (age under 50, disease stages I and II, ACPA levels ≤ 40 IU/ml), predicting SDAI remission with an overall constant precision of 83.3%. However, no significant impact on SDAI remission prediction was reported when adding other parameters to the above mentioned model. Conclusion. SDAI remission can be predicted in established RA patients using three major predictors, including age ≤ 50 years, disease stages I and II and baseline ACPA levels ≤ 40 IU/ml.