The key finding was that while mean Spondyloarthritis Research Consortium of Canada sacroiliac joint MRI scores for inflammation, fatty deposition, and erosions were higher in the SpA group, many of the same changes were present to a lesser degree in the others.
“The takeaway is this is a clinical diagnosis and you can’t make the diagnosis just based on the imaging, regardless of what the radiologist is reporting. You have to put it in context,” the rheumatologist said.
“This adds to a growing body of evidence that says MRI is not the gold standard for diagnosing axial spondyloarthritis,” Dr. Kavanaugh added. “In other studies, you see those kinds of changes in active military, snowboarders, hockey players. So like with every diagnostic test, we have to wrestle with the fact that the more sensitive it is, the less specific it is, and vice versa.”
What about color Doppler ultrasound?
Argentinian rheumatologists used color Doppler ultrasound to look for sacroiliitis in 198 joints evaluated in 99 consecutive patients with inflammatory back pain and suspected SpA without a definitive diagnosis. All participants also had an MRI scan and clinical evaluation as well. At the joint level, ultrasound had a sensitivity of 60% and specificity of 93% for diagnosis of sacroiliitis. For diagnosis of SpA, the positive predictive value was 79% and the negative predictive value was 59% (J Rheumatol. 2018 Dec 15. doi: 10.3899/jrheum.180550).
“I don’t think this suggests that ultrasound replaces MRI, but MRI is a more expensive test and harder to get, and if you could get some information with an ultrasound done properly in the office it might be an interesting way to identify those patients who truly have axial spondyloarthritis and inflammatory sacroiliitis. That specificity of 93% is pretty good,” Dr. Ruderman noted.
“What about doing this: If it’s positive then you don’t need the MRI and maybe you do an injection at that time, but if it’s negative you do the MRI?” Dr. Kavanaugh asked.
Orrin M. Troum, MD, a pioneer in the use of extremity MRI in the United States for evaluation of patients with inflammatory peripheral arthritis, had reservations.
“Availability and cost are important, but one of the distinctions between MRI and ultrasound is that you can’t see bone marrow edema. I think that’s one of the classic features of MRI that’s important here,” according to Dr. Troum, a rheumatologist at the University of Southern California, Los Angeles.
Dr. Kavanaugh asked Paul Emery, MD, a renowned authority on the use of ultrasound in rheumatology, for his thoughts.
“We don’t use ultrasound for sacroiliitis. It’s too unreliable,” said Dr. Emery, professor of rheumatology and director of the University of Leeds (England) Musculoskeletal Biomedical Research Center. “It’s such a big decision to start a biologic for an ankylosing spondyloarthritis patient that none of our people who use ultrasound rely on it.”
Dr. Ruderman and Dr. Kavanaugh reported receiving research funding from and serving as consultants to numerous pharmaceutical companies.