Biomarkers in axial spondyloarthritis

Purpose of review To assess the literature for biomarker validation studies that address key unmet needs related to the evaluation and management of patients with axial spondyloarthritis (SpA). This review focused on biomarkers facilitating early diagnosis and reflecting disease activity, structural damage on radiography, and clinical response to major therapies. Recent findings Early diagnosis may be facilitated by measurement of antibodies to the human leukocyte antigen class II-associated invariant chain peptide (anti-CD74) but sensitivity declines with increasing duration of disease. No disease activity biomarkers have demonstrated consistent superiority over standard C-reactive protein (CRP), and future validation should employ multivariate analysis aimed at demonstrating the added value of any associated biomarkers beyond available clinical parameters of disease activity and the use of magnetic resonance imaging inflammation as the primary endpoint. Several biomarkers reflecting inflammation (CRP and calprotectin), angiogenesis (vasoactive endothelial growth factor), and connective tissue turnover (C2 M, C3M, and citrullinated metalloproteinase degraded fragment of vimentin) have recently been shown to reflect radiographic progression in multivariate studies adjusted for baseline severity. Future studies should be prospective and demonstrate that predictive capacity adds to the information provided by known predictors such as CRP and baseline modified Stoke AS Spine Score. Calprotectin is a promising predictor of response to major therapies for axial SpA. Summary Several promising biomarkers addressing major unmet clinical needs require further validation in prospective studies.