Elevations in anti-CD74 immunoglobulin G (IgG) and IgA antibodies are of limited value in the diagnosis of early axial spondyloarthritis (axSpA) in patients age <45 who present with early, chronic back pain, according to the results of the spondyloarthritis caught early (SPACE) prospective cohort study published in Arthritis Research & Therapy.
Researchers from the University of Amsterdam in The Netherlands and the Medical University of Hannover in Germany assessed anti-CD74 IgG and IgA antibodies were in an exploratory cohort of 138 individuals with ankylosing spondyloarthritis (AS) and 57 healthy controls. Anti-CD74 IgG and IgA antibodies were then measured in 274 patients with early axSpA and in 286 patients with non-SpA chronic back pain from the SPACE cohort. All participants were age <45 and had early back pain for ≥3 months, but for ≤2 years.
In participants in the exploratory cohort, anti-CD74 IgG antibodies were detected in a significantly greater percentage of patients with AS compared with healthy controls (79.7% vs 43.9%, respectively; P <.001). Moreover, anti-CD74 IgA antibodies were detected in a significantly higher percentage of patients with AS compared with controls (28.5% vs 5.3%, respectively; P <.001).
In the SPACE cohort, anti-CD74 IgG antibodies were detected in 46.4% of participants with axSpA and 47.9% of participants with chronic back pain (P =.71). In contrast, anti-CD74 IgA antibodies were detected in a significantly greater percentage of patients with axSpA than with chronic back pain (54.7% vs 37.0%, respectively; P <.001). These latter findings were associated with a positive predictive value of 58.8% and a negative predictive value of 59.1%.
In a multivariate logistic regression model, total serum IgA was associated with a diagnosis of axSpA (odds ratio [OR], 1.19; P <.001), whereas anti-CD4 IgA was not (OR, 1.01; P =.33). In addition, anti-CD4 IgA was significantly associated with sacroiliitis on magnetic resonance imaging (OR, 2.50; P =.005) and heel enthesitis (OR, 2.56; P =.002).
The investigators concluded that although anti-CD74 IgA levels are elevated in individuals with early axSpA, the elevation is not sufficiently specific to be of significant diagnostic value in patients age <45 who present with early back pain. Further study is warranted to examine whether the presence of anti-CD74 IgA antibodies might be predictive of axSpA characteristics, including radiographic damage, extra-articular manifestations, and peripheral joint disease.
de Winter JJ, van de Sande MG, Baerlecken N, et al. Anti-CD74 antibodies have no diagnostic value in early axial spondyloarthritis: data from the spondyloarthritis caught early (SPACE) cohort. Arthritis Res Ther. 2018;20(1):38.