The evaluation of anti-CD74 IgA antibodies is not specific enough to provide a significant benchmark for the diagnosis of axial spondyloarthritis in patients younger than 45 years who present with early back pain, according to findings published in Arthritis Research and Therapy.
“Current biological disease markers in [axial spondyloarthritis (axSpA)], [such as] human leukocyte antigen (HLA)-B27, C-reactive protein, sacroiliitis shown on radiography or MRI, have insufficient diagnostic properties to rely on for making a diagnosis, impeding early diagnosis and treatment,” Janneke J. de Winter, MD, of the Academic Medical Center/University of Amsterdam, and colleagues wrote. “Although diagnostic delays have decreased over recent years as a result of modern imaging techniques and more awareness of axSpA, the current diagnostic delay ranging from 5 to 10 years prevents treatment in the early disease phase.”
To determine the value of elevated anti-CD74 antibodies in diagnosing axSpA with early back pain, the researchers collected serum from 138 patients with ankylosing spondyloarthritis (AS) and 57 healthy participants, recruited from the Academic Medical Center/University of Amsterdam and the Medical University of Hannover as part of an exploratory cohort. They then measured for anti-CD74 IgG and IgA antibodies.
Figure 1. Information provided by anti-CD74 IgA antibodies is not specific enough to confirm a diagnosis of axial spondyloarthritis in patients younger than 45 years who present with early back pain.
Additionally, the researchers used baseline serum samples from 274 patients with early axSpA, and 319 with non-SpA chronic back pain, who had been included in the SPACE prospective cohort study, which focused on patients younger than 45 years with early back pain.
According to the researchers, anti-CD74 IgG antibodies were present in 79.7% of patients with AS, and in 43.9% of healthy participants, in the exploratory cohort (P <.001). For anti-CD74 IgA antibodies, the totals were 28.5% in patients with AS and 5.3% in those in the control group (P <.001). Meanwhile, in the SPACE cohort, anti-CD74 IgG antibody levels were present in 46.4% of the patients with axSpA, and in 47.9% of the patients with chronic back pain (P = .71). Further, researchers found anti-CD74 IgA antibodies in 54.7% of patients with axSpA, and in 37% of the patients with chronic back pain (P <.001).
Those findings indicated a positive predictive value of 58.8% and a negative predictive value of 59.1%, the researchers wrote. In their regression model, the researchers also found that total serum IgA correlated with axSpA (OR = 1.19; P <.001). However, they did not observe such an association with anti-CD74 IgA (OR = 1.01; P = .33). Further, anti-CD74 IgA correlated with sacroiliitis on MRI (OR = 2.5; P = .005) and heel enthesitis (OR = 2.56; P = .002).
“We conclude that anti-CD74 IgG and IgA antibodies are of limited value in diagnosing axSpA in patients with early, chronic back pain,” de Winter and colleagues wrote. “Long-term follow up of patients in the SPACE cohort will show whether anti-CD74 IgA antibodies contribute to predicting certain axSpA characteristics such as radiographic damage, extra-articular manifestations or peripheral joint disease.” – by Jason Laday
Disclosure: de Winter reports no relevant financial disclosures. See the full study for additional researchers’ disclosures.