Anti-CD74 IgA is not associated with modic changes in the Northern Finland Birth Cohort

Chronic low back pain is a common symptom in axial spondyloarthritis (axSpA) and in patients with degenerative spinal disease associated with Modic changes (MC) on MRI. A clear distinction between axSpA and MC might be difficult in early disease, particularly in the absence of axSpA sacroiliac changes. Therefore, a diagnostic serum biomarker for ambiguous cases would be useful. To evaluate if the potential diagnostic biomarker anti-CD74 for axSpA is elevated in patients with MC as well, we measured this antibody in patients with MC and healthy controls. We presumed that a negative anti-CD74 antibody in MC would be helpful to distinguish it from axSpA.

Participants from the NFBC1966 with MC and matched participants without MC were included in this study. Anti-CD74 immunoglobulin A (IgA) was measured with a commercially available kit. An association between continuous log-transformed anti-CD74 IgA was evaluated with a linear regression model adjusted for body mass index (BMI), sex, C-reactive protein (CRP), and presence of low back pain.

The study involved 307 participants, 148 with MC and 159 without MC. There was no association between MC and continuous anti-CD74 IgA after adjustment for potential confounders (Exp(B) = 1.3, 95% CI 0.8 to 2.1). None of the participants with MC had elevated anti-CD74 IgA above the cut-off of 15 U/ml.

Anti-CD74 IgA is not elevated in patients with MC. Further studies comparing directly patients with axSpA and MC are required to evaluate if it is a diagnostic tool to differentiate axSpA and MC in unclear cases. Key Points • Anti-CD74 IgA are not elevated in patients with Modic changes on MRI.