Complement C3d is not associated with axial spondyloarthritis and magnetic resonance imaging changes at the sacroiliac joint

Abstract

Objectives:To investigate the associations between complement C3d and inflammatory and structural changes by MRI at the sacroiliac joints in a group of patients suggestive of axial spondyloarthritis according to the Assessment of Spondyloarthritis International Society (ASAS) criteria. Methods:A cross-sectional study of patients referred to the Spine Centre of Southern Denmark due to unspecified low back pain (Spines of Southern Denmark cohort). The patients were divided into three groups: Group 1: Patients fulfilling the Assessment of SpondyloArthritis International Society (ASAS) criteria for axial spondyloarthritis (axSpA, n=96); Group 2: Patients with either a positive MRI of the SIJ and no spondyloarthritis features, or a negative MRI of the SIJ but positive HLA-B27 and one spondyloarthritis feature (non-axSpA, n=38); Group 3: Patients with unspecified low back pain >3 months (control group n=82). Complement C3d was measured with the double-decker rocket immunoelectrophoresis and evaluated in relation to the group division and baseline findings by SIJ MRI.Results: One hundred and eighty-four C3d analyses were performed. The mean level of C3d was 33.8 AU/ml with a standard deviation of 8.1. There were no differences between the C3d levels in the three patient groups, the mean values being: axSpA=34.3 AU/ml (SD=7.9), non-axSpA=33.5 AU/ml (SD=6.9), and control group=33.4 AU/ml (SD=9.2).The level of C3d was not related to MRI findings. Conclusions:Complement C3d was not associated with active or structural SIJ changes on MRI in patients suggestive of axial spondyloarthritis.

Exploring complement biomarkers in suspected axial spondyloarthritis

“…Previous studies have shown complement activation to be elevated in r-axSpA patients, 25 whereas others have not. 44 Previous studies (including the latter) are, however, troubled by the expanding understanding of MRI findings, for example, the presence of changes on MRI according to ASAS 2009 criteria 45 in athletes, 46 and postpartum women, 11 which has only been acknowledged in the recent years. This might have resulted in misclassification of patients in clinical cohorts encompassing both r-axSpA and nonradiographic axSpA (nr-axSpA).…”