Understanding Non-Radiographic Axial Spondyloarthritis - Episode 11
Transcript: Sergio Schwartzman, MD: Atul, take us through the work-up of the patient you see. What work-up do you do?
Atul Deodhar, MD, MRCP: One of the most important things is having clinical suspicion. For everything in rheumatology, we hardly have any diagnostic test for anything that we do. It’s the clinical presentation and the pattern recognition. For example, there may be somebody who presents with disease who is a young person, and they have backache for no apparent reason starting before the age of 45. Philip has touched upon this a little. Classic symptoms of inflammatory back pain are that it gets better with activity, worse with rest, wakes the patient wake up in the middle of the night, the second half of the night to get out of bed and walk around to get some relief.
Inflammatory back pain is 1 of the interesting parts of this disease. As you said, not everybody with inflammatory back pain has axial spondyloarthritis, and not all patients who have axial spondyloarthritis have inflammatory back pain either. I would say chronic back pain starting before the age of 45 for no apparent reason is the first tip-off. Then you get into the other information, in terms of the patient’s history. Do you have any arthritis in the peripheral joints? Do you have any symptoms that, to a doctor, suggest true enthesitis? Have you had red, painful eye? Do you have psoriasis? Do you have a skin rash? Does anyone in the family have any of these conditions? Do you have inflammatory bowel disease?
And then do an examination. One has to build up a case, and this is the pattern recognition. The most important thing I would say—even before you jump on to do investigation—is history, physical examination, and making up your mind on what are my pretest probabilities that this person has axial spondyloarthritis?
Have I ruled out common things that occur commonly first? Once that is done and if your suspicion is high, then I would do a plain x-ray of the sacroiliac joint first to see whether they have obvious sacroiliitis. At the same time, I will send the patient to the lab to look for HLA-B27 and C-reactive protein. Apart from the x-ray of the sacroiliac joint, if it shows definitive sacroiliitis or at least some changes that you are even more suspicious that there is sacroiliac, the C-reactive protein and HLA-B27 are neither diagnosed. They are neither sensitive nor specific.
HLA-B27 is found, according to that NHANES [National Health and Nutritional Examination Survey] study that I mentioned earlier, in white Caucasian population in the United States in about 7.5% of the population. In Mexican Americans, it’s about 4.5%. We believe that 4.5% of the African American population also has HLA-B27. It varies depending on the racial mixture. Some of the Native American groups have it in the 20% range, whereas the Japanese American population has less than 1%.
That’s HLA-B27. The C-reactive protein, as already have been mentioned, is a marker of inflammation. If it is high in somebody with backaches, that would make me think, “Why is this C-reactive protein high?” It’s not very sensitive and found in only 30%, 40% of the patients with axial spondyloarthritis, who despite having that inflammatory disease of the spine, their C-reactive protein can be normal in about 60% of the cases.
Those are the tests that I would do and then revisit the diagnosis. If I am still suspicious and my suspicion is high, and the plain x-ray of the sacroiliac joint is normal or iffy, I will then order an MRI [magnetic resonance imaging] scan. The MRI scan is to be ordered without contrast. The 2 important things you tell the radiologist is, “Please do, the T1-weighted image and the STIR [short tau inversion recovery] image, which is a fat-suppressed T2-weighted image.
It’s important to look at those images side by side for each slice. It’s important to go and discuss with the musculoskeletal radiologist. It’s important to challenge them, “Do you really think this is sacroiliitis? What is your certainty about this?” Because if nothing is there, then you’re wasting the whole diagnosis based on their MRI scan. You really have to be sure the changes you’re seeing are because of inflammation.
I generally discuss every one of those MRI scans with my musculoskeletal radiologist and ask if there are any structural changes along with the inflammatory changes. One of the things I mentioned earlier, even for people who are degenerative spinal involvement, they can have evidence of inflammation on the sacroiliac joint. But then they never have erosions in the sacroiliac joint. If somebody has structural damage along with inflammation, and if the history fits, we are putting these pieces of this jigsaw puzzle together and then making the diagnosis. That would be, in short, by investigation or diagnosis process.
Transcript Edited for Clarity