Epidemiology of Axial Spondyloarthritis

Atul A. Deodhar, MD: The prevalence of axial spondyloarthritis was recently studied in the United States. In the NHANES study, which is the National Health and Nutritional Examination Survey study done between 2009 and 2010, it was found that about 1% of the population in the United States has axial spondyloarthritis. This was a population-based study. This is the gold standard. This is not the case-based study based on which patients come to your clinic. This is what happens in real life, in the general population in the United States.

We also found out, interestingly, that 19.4% of patients in the United States have chronic low-back pain. Five percent to 6% of patients with chronic back pain will ultimately receive a diagnosis of axial spondyloarthritis. So if you do the math, of the total population, about 1% of the general population in the United States has axial spondyloarthritis. Within that group, half of the patients will have ankylosing spondylitis and half will have nonradiographic axial spondyloarthritis. If you look at the burden of the disease, it’s very similar between nonradiographic axial spondyloarthritis and ankylosing spondylitis.

As I said earlier, patients with ankylosing spondylitis have definitive radiographic changes of sacroiliitis. They may also have some radiographic changes in their spine. So their disability, difficulty to work, and signs and symptoms are because of inflammation plus radiographic changes—structural damage. In nonradiographic disease, there is no structural damage, but they have a high level of inflammatory burden. So from the patient’s point of view, the signs and symptoms, the pain and the stiffness, and the difficulty to work or inability to work, etc, are very similar. There are several studies that look at this health-related quality of life, the disability, the problems with work, etc, in both of these conditions. [They are] very comparable.

The NHANES study also found that the disease generally starts at a younger age. It occurs in the second decade or third decade of life. It is axial spondyloarthritis.

Ankylosing spondylitis is seen as a ratio of 3:2 or 3:1 in men to women. So ankylosing spondylitis is more common in men. The prevalence of nonradiographic axial spondyloarthritis is equal, 1:1. As I said earlier, some patients with nonradiographic disease will progress to ankylosing spondylitis. This tells us that male sex is a risk factor for progression of nonradiographic to radiographic disease. That’s why there are more patients who are men who have ankylosing spondylitis. When it comes to nonradiographic disease, it is equal. Another thing that was found is that the disease generally starts in patients during their teens or in their 20s, or maybe in their 30s. Almost always, the disease starts before age 40. It’s very rare for axial spondyloarthritis to start after age 45.