Axial Spondyloarthritis: Does Visibility With X-Rays Make a Difference in Management?

Sara Freeman

August 11, 2023

Knowing whether a patient has radiographic or nonradiographic axial spondyloarthritis will not change management, experts say. What matters is recognizing that the patient has inflammatory back pain (IBP) and clinical features of spondyloarthritis and that the patient is referred to a rheumatologist as soon as possible.

Out With the Old, In With the New

Axial spondyloarthritis is characterized by chronic inflammation of the sacroiliac (SI) joints, and spine. It's a modern term that includes ankylosing spondylitis (AS) and that refers to opposite ends of a disease spectrum.

  • Nonradiographic axial spondyloarthritis (nr-axSpA) is so termed because there are no definitive visible changes on plain x-rays, although inflammatory changes may be seen on MRI.

  • Radiographic axial spondyloarthritis (r-axSpA) is the same as AS to some extent and is associated with clear signs of joint damage (ie, of past inflammation) on x-rays.

"Axial spondyloarthritis is one disease, and whether it is radiographic on non-radiographic makes zero difference in the management of the patient," says Atul Deodhar, MD , professor of medicine and medical director of rheumatology clinics at Oregon Health and Science University (OHSU) in Portland. The distinction came about in 2009 to facilitate scientific and clinical research, he explains, and to enable the use of tumor necrosis factor inhibitors, which were new at the time, for patients who could not be classified as having AS.

"We have known what ankylosing spondylitis is for a long time because we have been doing plain x-rays of the sacroiliac joints, and if we see classical changes of sacroiliitis, we have the diagnosis. However, MRI changed everything," Deodhar says. Now it's possible to see inflammatory changes in the SI joints and early joint damage, which was not possible to see on x-ray until many years later.

Reassuring for Patients?

"Currently, we don't really have different treatments," Deodhar notes. Perhaps the only benefit is that it might be reassuring for patients to know that they have the nonradiographic form. Receiving a diagnosis of axial spondyloarthritis comes as quite a shock. It's a diagnosis that is potentially going to affect them for the rest of their lives, and some patients worry that they'll develop the classic "bamboo" spine of AS, he adds. So, being able to tell patients that they have nr-axSpA and that they are going to be treated early and aggressively may be somewhat comforting.

"It's a continuum of a disease state, but a lot of people will stay at the nonradiographic stage," points out Portland-based internist Beth Smith, DO , associate professor of medicine at OHSU.

"A good portion of individuals who may have an MRI that's positive will either go into remission or just stay at that stage of the disease; they won't necessarily progress to radiographic sacroiliitis," she adds.

Spotting nr-axSpA in Practice

nr-axSpA can be tricky to spot in clinical practice, and its diagnosis in primary care largely relies on patients' clinical presentation and identifying IBP. This is the key symptom. When someone younger than 45 years experiences back pain that is characterized by insidious and chronic onset and that improves with anti-inflammatory agents and activity but that worsens with rest and is worse at night, then imaging of the SI joints may be appropriate.

"You have to have that index of suspicion in order to even think about ordering the appropriate imaging test," Smith says. IBP may be the big clue, but patients may also return on separate occasions with multiple associated complaints, such as plantar fasciitis, tennis elbow, or other conditions, such as psoriasis, she says.

Ordering HLA-B27 and C-reactive protein tests may be useful prior to conducting any imaging, Smith says, "and if imaging is ordered, make sure it is an x-ray of the sacroiliac joint, not the lumbar spine."

Deodhar cautions: "A single anterior-posterior view of the pelvis is enough to look at the sacroiliac joint." There is no need to order separate views of the right and left SI joints; doing so will provide no additional useful information and exposes the patient to unnecessary radiation.

Importantly, consider whether an x-ray of the lumbar spine is needed for a patient with chronic back pain, he says. "You should do an investigation that is going to make a difference to your management. If you take 100 patients with back pain, 95% of the time, it is going to be mechanical back pain. Why do an x-ray of the lumbar spine?" Deodhar asks rhetorically.

It should also be borne in mind that x-rays can be nonspecific, and several conditions may mimic sacroiliitis, such as osteitis condensans ilii in women who have given birth, osteoarthritis of the SI joints, and old infection of the SI joints.

MRIs Need Specialist Interpretation

MRIs of the lumbar spine are overused to diagnose back pain, and while they might be sensitive to early inflammatory changes in SI joints, they require an expert eye for interpretation.

"MRI of the SI joints is to be used wisely in patients when there is enough clinical suspicion," Deodhar advises. Even when an MRI is negative for sacroiliitis, patients could still have axial spondyloarthritis.

MRIs of the SI joints are needed, but not of the lumbar spine, he stresses. Views of the lumbar spine may show only signs of disk degeneration and perhaps osteoarthritis.

Moreover, Deodhar says, "MRI is so sensitive that we used to think that bone marrow edema is good enough for telling us there is sacroiliitis." However, even people without IBP can have bone marrow edema; "exercise can show bone marrow edema," he says.

So, "If there's a suspicion of axial spondyloarthritis, the patient should be referred to a rheumatologist," who will discuss the interpretation with highly specialized musculoskeletal radiologists.

Take-Home Messages

Whether it is nr-axSpA or r-axSpA, "the burden of disease for the patient is the same; treatment is the same," says Deodhar. Patients should be referred to a rheumatologist as soon as possible if axial spondyloarthritis is suspected. A single x-ray of the pelvis should be performed to see the SI joints, but MRIs should be left to secondary care, he suggests.

Smith notes: "Having that index of suspicion of an inflammatory etiology for the back pain is essential." It ensures that "patients can get early and appropriate treatment for a disease that's very different from the mechanical back pain that we mostly see in primary care."

Deodhar has received research grants or has acted as a consultant to multiple pharmaceutical companies, including AbbVie, Bristol-Myers Squibb, Celgene, Janssen, UCB, Novartis, Pfizer, and Eli Lilly. Smith reports no relevant financial relationships.

Sara Freeman is a freelance journalist based in London, United Kingdom.

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