X-rays only show something if the bone is destroyed or if increased new bone formation takes place as a reaction to the bone destruction. Accordingly, you only see something relatively late. This is where magnetic resonance imaging (MRI) comes into play. Scintigraphy used to be deployed, but it is relatively unspecific and therefore less significant in diagnosing. MRI, on the other hand, offers the enormous advantage that you can see the inflammation in the bones.
So you don’t have to wait until the bone is destroyed. This makes early diagnosis possible. That’s why we now say axial spondyloarthritis. This includes the entire disease group, regardless of whether there are X-ray changes or not. This can be broken down further into:
- Non-radiographic axial spondyloarthritis (nr-axSpA) with no radiographic changes visible
- Radiographic axial spondyloarthritis with evidence of radiographic changes in the sacroiliac joints
In addition, the term ankylosing spondylitis exists.
ER: This means that the change in terminology has a lot to do with how the disease has been diagnosed in the past and today. After all, how common is the diagnosis of axSpA today — and how is it made?
JS: There is an older study from a general practice in England. We always refer to that. It’s still a bit vague, but we estimate that about 5 % of people with chronic back pain who go to the doctor because of it have axSpA. That’s relatively little. And because of this, any test that is positive on its own results in a relatively low post-test probability.
This is a term that is discussed again and again in connection with the coronavirus: What is the probability that I have the disease if I have antibodies? But that’s generally true in medicine, and because we have a relatively low pre-test probability, you cannot diagnose with a simple test. You have to make various tests and take the overall picture into account.
With this in mind, we have been saying for a number of years that there are two strategies. For once, what do you offer the doctor who first sees this patient with chronic back pain? We actually don’t think they are able to diagnose well just like that — because it’s complex, and one needs experience. And that’s why we have developed other so-called screening parameters, i.e. “red flags”, that show the doctors when they should also think about axSpA when a patient with symptoms is sitting in front of them.
ER: Back pain is actually a widespread disease, but axSpA is rare. So how do you get a grip on axial spondyloarthritis in the first place? Initially, I would present a problem that isn’t very specific at the doctor’s office. I would probably complain of lower back pain. But that can be caused by many things, for example by stress.
JS: But if, for example, this patient says, “Oh, the back pain comes on in the morning when I wake up and if I walk around a bit, it gets better. But when I sit down, it doesn’t get any better.” Then that’s an indication that axial spondyloarthritis may be an issue there.
But also when other parameters are positive, for example psoriasis is present or a laboratory test was carried out and this gene, HLA-B27, was positive, this should lead one to investigate further.
Especially in young patients, if only one of these parameters is positive, we have recommended referral to a rheumatologist. In some countries, specialists in physical medicine also take care of these patients. In Germany, this is most likely an assignment in the field of rheumatology, and the rheumatologist then has to do all the examinations.
ER: What questions would one ask in the anamnesis, for example? I am also thinking of secondary diseases such as psoriasis, which often occur together with axSpA. So how would you go about doing that?
JS: When taking the medical history, one must ask when the pain occurs (rather in the morning or more in the evening). How does it feel when active or moving? In addition, they are asked about psoriasis, Crohn’s disease and other diseases — including whether they may have run in the family. Then the HLA-B27 gene and inflammation parameters such as blood sedimentation and C-reactive protein must be determined. And then imaging comes into play.