Axial Spondyloarthritis Defined

Atul A. Deodhar, MD: Axial spondyloarthritis is an umbrella term that includes nonradiographic axial spondyloarthritis and ankylosing spondylitis. There is a lot of confusion about this term. In medical school and during residency, we always learned about ankylosing spondylitis. This condition has been recognized for a long time mainly because there are x-ray changes of sacroiliitis as well as changes on the spine of the patient that you can see on x-rays in patients with ankylosing spondylitis.

In nonradiographic axial spondyloarthritis, which is the earlier stage of the condition in patients with ankylosing spondylitis, there are no diagnosable x-ray changes. And so for the longest time, we couldn’t recognize these patients until more recently when we had MRI [magnetic resonance imaging] testing become available to us to use for diagnostic purposes. So axial spondyloarthritis is an umbrella term. Nonradiographic axial spondyloarthritis and ankylosing spondylitis are 2 aspects of it. It’s like rheumatoid arthritis. It could be erosive or nonerosive. So earlier stages of the condition are nonerosive. In later stages, the condition can become erosive. These are not 2 different diseases. It is the same disease spectrum. Some patients have nonradiographic axial spondyloarthritis, and some of them will actually develop ankylosing spondylitis over the years. But every ankylosing spondylitis patient, at some stage, was nonradiographic.

The x-ray changes of ankylosing spondylitis are definitive radiographic sacroiliitis on sacroiliac joint x-ray. That takes anywhere from 6 years to 10 years for diagnosis, which has been one of the problems in the diagnosis of axial spondyloarthritis. Unless there are definitive x-ray changes, patients will be missed. So for the first 6 to 10 years, the patient may be completely missed as having a disease that is immunologically mediated and can be treated aggressively. This patient will just be counted as another patient with back pain. Back pain is so common in the general population. This person with back pain caused by axial spondyloarthritis could get lost during follow-up or get inappropriate treatment, which is another reason why there is a delay in the diagnosis of patients with axial spondyloarthritis—the lack of radiographic changes in the early stages of their disease.

When I’m describing axial spondyloarthritis to my general practice friends, I tell them that they should consider axial spondyloarthritis to be like a river. Initially, the river is flowing during a mechanical back pain type of situation. It could be inflammatory back pain, in most patients. Some patients, in fact, might just have mechanical back pain. This is very common. Some of these patients are going to develop axial spondyloarthritis and will generally have inflammatory back pain, which is characterized by pain that is worse with rest and better with activity. This is the opposite of mechanical back pain, where the pain is better with rest and worse with activity. If you ask a typical patient with axial spondyloarthritis what they do if their back hurts and whether they get up and move around or lie in bed, they will tell you that they get up and move around. This is very different from what is seen in patients with common mechanical back pain.

So in this big river of back pain, you need to find the patients who have inflammatory back pain. Some of them, going forward, are going to develop ankylosing spondylitis, but some of them might just remain as nonradiographic axial spondyloarthritis patients. That’s where the crux is. How do you find these patients, with nonradiographic axial spondyloarthritis, in this big river who have just back pain? Back pain is so common in the general population.

And the answer to that—and this is what I teach primary care physicians, family practice doctors, and even rheumatologists—is that it generally comes with other spondyloarthritis features. So they may have inflammation in their eye called iritis or uveitis. They may have skin problems like psoriasis. They may have inflammatory bowel disease. They may have peripheral arthritis or inflammatory arthritis. All of these kinds of things make you think, “Hmm, this back pain is different.” Then you ask them whether their back pain is better with exercise and activity and worse with rest. If they have other features of spondyloarthritis, they may have axial spondyloarthritis, whether or not they have x-ray changes of sacroiliitis. And that should increase your interest and your suspicion in this particular patient.

So there are ways and means of diagnosing these patients early, as long as you keep your antennae up. In this common mechanical back pain river, there may be some patients who are hidden and have inflammatory back pain. They may have axial spondyloarthritis.