Calprotectin is not independent from baseline erosion in predicting radiological progression in early rheumatoid arthritis. Comment on ‘Calprotectin as a marker of inflammation in patients with early rheumatoid arthritis’ by Jonssonet al

We have read with great interest the article by Jonsson et al that was recently published online in ARD ,1 which suggested that calprotectin, also known as S100A8/S100A9 heterodimer, was associated with radiographic progression in early rheumatoid arthritis (RA). Calprotectin correlates significantly with inflammatory markers and disease activity score.2 Besides correlations between baseline calprotectin levels, Clinical Disease Activity Index and ultrasonography power Doppler, the authors showed that baseline calprotectin levels correlated with van der Heijde modified Sharp score (SHS) progression (defined as an increase ≥1 unit/year from 0 to 24 months), independently of age, gender, Clinical Disease Activity Index, erythrocyte sedimentation rate (ESR), C reactive protein (CRP) levels and rheumatoid factor positivity.1 We analysed the initial serum calprotectin among patients with early RA fulfilling American College of Rheumatology/European League Against Rheumatism 2010 of the French observational cohort Etude et Suivi des POlyarthrites Indifferenciees Recentes (ESPOIR). Calprotectin serum concentrations were assessed according to manufacturer method (Hycult, Frontstraat, Netherlands; …