Here, we characterized for the first time the baseline features of the synovial tissue of a homogeneous group of 37 inadequate responders to csDMARDs by applying a histologic algorithm previously validated in a different and independent large cohort of early RA patients and evaluated whether synovial histological characteristics prior-to-treatment correlated with clinical response to the TNFα inhibitor certolizumab-pegol. Here, TNF is linked to rheumatoid arthritis.