Real-world validation of the minimal disease activity index in psoriatic arthritis: an analysis from a prospective, observational, biological treatment registry

OBJECTIVE To describe the minimal disease activity (MDA) rate over time in patients with psoriatic arthritis (PsA) receiving antitumour necrosis factor agents, evaluate prognostic factors of MDA achievement and identify the most common unmet criteria among MDA achievers. DESIGN Biologic Treatment Registry Across Canada (BioTRAC): ongoing, prospective registry of patients initiating treatment for rheumatoid arthritis, ankylosing spondylitis or PsA with infliximab (IFX), golimumab (GLM) or ustekinumab. SETTING 46 primary-care Canadian rheumatology practices. PARTICIPANTS 223 patients with PsA receiving IFX (enrolled since 2005) and GLM (enrolled since 2010) with available MDA information at baseline, 6 months and/or 12 months. PRIMARY AND SECONDARY OUTCOME MEASURES MDA was defined as ≥5 of the following criteria: 28-item tender joint count (TJC28) ≤1, 28-item swollen joint count (SJC28) ≤1, Psoriasis Area and Severity Index (PASI) ≤1 or body surface area≤3, Pain Visual Analogue Scale (VAS) ≤15 mm, patient's global assessment (PtGA) (VAS) ≤20 mm, Health Assessment Questionnaire (HAQ) ≤0.5, tender entheseal points ≤1. Independent prognostic factors of MDA achievement were assessed with multivariate logistic regression. RESULTS MDA was achieved by 11.7% of patients at baseline, 43.5% at 6 months, 44.8% at 12 months and 48.8% at either 6 or 12 months. Among MDA achievers at 6 months, 75.7% had sustained MDA at 12 months. Lower baseline HAQ (OR=0.210; 95% CI: 0.099 to 0.447) and lower TJC28 (OR=0.880; 95% CI: 0.804 to 0.964), were significant prognostic factors of MDA achievement over 12 months of treatment. The most commonly unmet MDA criteria among MDA achievers was patient reported pain (25%), PtGA (15%) and PASI (12%). CONCLUSIONS Almost 50% of patients treated with IFX or GLM in routine clinical care achieved MDA within the first year of treatment. Lower baseline HAQ and lower TJC28, were identified as significant prognostic factors of MDA achievement. The most commonly unmet criteria in patients who achieved MDA were pain, PtGA and PASI. TRIAL REGISTRATION NUMBER BioTRAC (NCT00741793).