Irene van der Horst-Bruinsma, MD, PhD, a rheumatologist at the VU University Medical Center in Amsterdam, considers non-radiographic axial spondyloarthritis an important new disease entity, but she admits some clinicians have found the updated criteria confusing. “Part of it is that we don’t yet understand how to predict which subset of non-radiographic axial spondyloarthritis patients will eventually develop radiographic changes. We know that patients who have a positive MRI with inflammation around the sacroiliac joint and raised CRP [C-reactive protein] levels have a higher chance of radiographic progression, but there are also many patients who don’t progress,” she states.
Yet with the advent of potentially effective treatments for both radiographic and non-radiographic axial spondyloarthritis, it is even more important to diagnose axial spondyloarthritis patients as soon as possible. Dr. van der Horst-Bruinsma notes, “I see some rheumatologists who do not see many spondyloarthritis patients who do not feel confident with this concept and how to treat it.” Importantly, even though patients with non-radiographic axial spondyloarthritis show less damage on imaging compared with those with the radiographic subtype, several studies have shown these patients may experience similar levels of disease activity, impairment and pain.7
Prevalence
In the 1940s, the earliest studies of ankylosing spondylitis in men vs. women put its occurrence at around 10 to 1.8 However, studies in the 1970s, 1980s and 1990s performed with later diagnostic criteria put the ratio at about 3 to 1.1,7,9 The prevalence of non-radiographic axial spondyloarthritis is not as well established, partly due to its newness as a diagnostic category, but the occurrence in men vs. women is estimated at roughly 1:1.6,9 But some physicians, especially non-rheumatologists, may not be completely comfortable with it as a disease category.
For clinicians, knowing the exact ratio is not as important as recognizing that both radiographic and non-radiographic axial spondyloarthritis do occur in women. Therefore, it must be considered in any differential diagnosis of back pain, especially back pain with inflammatory features.1
Disease Differences Between Men & Women
It’s not known how sex may mediate downstream effects, but sex hormones are known to have specific effects on the immune system.3 Some data suggest men with axial spondyloarthritis, on average, have higher levels of TNF-α, CRP and interleukin-17 (IL-17) compared with women.7,10,11 It may be that genes activated via sex hormones play a role in either curbing or exacerbating aspects of disease pathophysiology, modifying the influence of a patient’s existing genetic load. Dr. van der Horst-Bruinsma notes it may be helpful to further explore differences in genetic expression between men and women with axial spondyloarthritis, perhaps via mRNA studies, noting men and women display relevant differences in many other diseases. Early work in this area has shown some potentially relevant differences in genetic expression, showing unique expression of certain genes in males diagnosed with ankylosing spondylitis compared with unaffected males and affected females.11
