Accurately Diagnosing Axial Spondyloarthritis

Atul A. Deodhar, MD: Like everything in medicine, the diagnosis of axial spondyloarthritis is based on pattern recognition. If a patient comes in with back pain, the first thing you are going to think is that the case could be mechanical back pain because that’s the most common type of back pain. If you take 100 patients with mechanical back pain or back pain in general, 94% of them would probably have mechanical back pain and 1% would have pathological back pain. This is the serious one that we shouldn’t miss. This would be a fracture, cancer, a malignancy, an infection, osteomyelitis, etc. And 4% to 5% of these patients would have inflammatory back pain or axial spondyloarthritis.

And so the pattern recognition starts by asking the patient with back pain, “Tell me about your back pain. Is the back pain better or worse with exercise? Is the back pain better or worse with rest?” You are looking for inflammatory back pain, which is better with activity or exercise and worse with rest. In the second half of the night, patients may have back pain that wakes them from sleep. Other common symptoms include significant early-morning stiffness, pain starting before the age of 45, and insidious onset with no cause. There is no trauma. All these things should make you say, “Hmm, this is something different.”

And when that happens, the next thing you do is look at a patient’s history. “Do you have any peripheral arthritis? Are there any swollen joints? Have you noticed whether one of your toes is swollen like a sausage?” We call that dactylitis. Or we look for typical features of enthesitis like plantar fasciitis, Achilles tendinitis, etc. “Do you have psoriasis?” “Do you have uveitis?” “Do you have inflammatory back pain?” These are all features of spondyloarthritis. Any of these issues would increase the probability that this person has axial spondyloarthritis. So that’s the pattern recognition.

Once you do that, then you do the examination. Examination of the patient is important because you rule out other reasons for their backache and find out whether the patient really has peripheral arthritis. Does the patient have psoriasis? Does the patient have any evidence of enthesitis, dactylitis, uveitis, etc? Those are the things that you often find during the examination.

And then come the investigations. The typical investigations that I would send for look for evidence of inflammation. For the blood test, I send sedimentation rate or C-reactive protein. A high C-reactive protein tells me that there is inflammation somewhere. It doesn’t tell me where the inflammation is, but in the patient for whom I’m suspecting axial spondyloarthritis, that is yet another piece of the puzzle. Imaging comes after that. A plain x-ray of the sacroiliac joint will show me whether there is sacroiliitis or not. If that is not there and my suspicion is still high, I will send a blood test called HLA-B 27. HLA-B 27 is a genetic marker for axial spondyloarthritis.

Seven and a half percent of Caucasian people in the United States have that marker. So having that marker increases your risk of getting axial spondyloarthritis. However, that alone never declares a diagnosis. So that is yet another piece of the puzzle in somebody who has inflammatory back pain and other features of axial spondyloarthritis.

After HLA-B 27, the last investigation we have is the MRI [magnetic resonance imaging] scan of the sacroiliac joint. I always tell my colleagues that we should not be ordering an MRI scan in the beginning. It is expensive and can also provide false-positive results. One has to know what one is looking at. So the MRI scan can be useful, but it can also show false-positive results. And so that is the journey a doctor would take to diagnose somebody with axial spondyloarthritis. It all starts with pattern recognition and suspicion. We often diagnose this condition in somebody with chronic back pain starting before age 45 with insidious onset, for which we don’t believe the patient has mechanical back pain. This may be inflammatory.