Plasma calprotectin as a biomarker of ultrasound synovitis in rheumatoid arthritis patients receiving IL-6 antagonists or JAK inhibitors

Abstract

Objectives:To analyse the accuracy of plasma calprotectin in patients with rheumatoid arthritis (RA) receiving monoclonal antibodies against IL-6 receptors (anti-rIL-6) or JAK inhibitors (JAKis) in detecting ultrasound (US) synovitis and compare it with acute phase reactants [high-sensitivity C-reactive protein (hs-CRP) and ESR].Methods:An observational cross-sectional study of RA patients receiving anti-rIL-6 (tocilizumab or sarilumab) or JAKi, (baricitinib or tofacitinib) was made. Plasma calprotectin for the diagnosis of US synovitis [synovial hypertrophy grade (SH) ⩾ 2 plus power Doppler signal (PD) ⩾ 1] was analysed using receiver operating characteristic curves (ROCs). The performance of ESR and hs-CRP was also studied. The three ROC curves were compared to determine which had the highest discriminatory power. Associations between plasma calprotectin and US scores were made using correlation analysis.Results:Sixty-three RA patients were included. Mean plasma calprotectin levels were significantly higher in patients with US synovitis than in those without (0.89 ± 0.85 vs 0.30 ± 0.12 μg/ml; p = 0.0003). A moderate correlation between calprotectin and all US scores (HS score Rho = 0.479; PD score Rho = 0.492; and global score Rho = 0.495) was found. The discriminatory capacity of plasma calprotectin showed an AUC of 0.795 (95% CI: 0.687–0.904). The AUC of hs-CRP and ESR was 0.721 and 0.564, respectively. hs-CRP serum levels showed a low positive correlation with the three US scores (Rho < 0.40). After analysis according to the drugs administered, the correlation disappeared in patients receiving anti-rIL-6.Conclusion:Plasma calprotectin may be a sensitive biomarker of synovial inflammation in RA patients treated with anti-rIL-6 or JAKi.