Back pain, broadly speaking, is a common condition in the United States. So when people bring this symptom up at a doctor’s appointment, it’s important for healthcare professionals to ask the right questions to try to figure out what’s causing it — and then follow up with diagnostic tests, if appropriate.
This process often fails to produce an accurate and timely diagnosis in people with nonradiographic axial spondyloarthritis (nr-axSpA). This form of arthritis is characterized by inflammatory back pain, which is sometimes described as a dull ache accompanied by stiffness that tends to get worse with rest or inactivity, and better with movement. Unlike its better-known “sister” disease, ankylosing spondylitis (AS), nr-axSpA doesn’t cause inflammation that’s visible enough on X-ray images to make a definitive diagnosis.
But the lack of clear X-ray findings doesn’t mean that nr-axSpA isn’t serious, or that it can safely be ignored. Updated treatment guidelines released in 2019 recommend more aggressive treatment of nr-axSpA early on to help control pain and other symptoms, and to prevent long-term damage caused by chronic inflammation — both in your spine and in the rest of your body.
Here’s an overview of how and why getting a diagnosis of nr-axSpA can be a challenge, along with tips for getting the attention and tests you need.
Recognizing Symptoms of nr-axSpA
Back pain is most commonly due to mechanical causes, or changes to how one or more structures in your back interact with other structures. Because inflammatory back pain — caused by an immune system response in or near your spine — is less common, some doctors will assume you’re experiencing mechanical pain, and won’t ask the right questions to identify inflammatory pain.
“I think people tend to ascribe symptoms to mechanical issues,” says John Miller, MD, an instructor of medicine in the division of rheumatology at Johns Hopkins Medicine in Baltimore. “It’s not until someone starts talking about stiffness and improvement with activity and NSAIDs” — nonsteroidal anti-inflammatory drugs, like ibuprofen (Advil) and naproxen (Aleve) — “that people start thinking about axial spondyloarthritis.”
Axial spondyloarthritis is an umbrella term that includes both nr-axSpA and AS, and is defined by inflammation in your sacroiliac (SI) joints — where your spine connects to your hips — and in your spine. But in both conditions, inflammation can also affect other areas of your body, such as joints or connective tissues outside your spine, your eyes, or your digestive tract.
If your doctor makes a wrong assumption that you’re experiencing mechanical pain, he or she may not order the right kind of X-rays, or other imaging tests, to detect nr-axSpA or AS. If your doctor looks only at the lumbar region of your spine — where it curves inward toward your abdomen — but not the SI joints further down, “someone might say, ‘I’ve done this thorough evaluation for low back pain, and I don’t see anything,’” Dr. Miller notes. This is a common reason, he says, that “we see a delay between onset of symptoms and seeing a rheumatologist for the first time.”
But even if your doctor recognizes that your pain probably doesn’t have a mechanical cause, “inflammatory back pain doesn’t always mean that you have spondyloarthritis,” notes Jean Liew, MD, a senior fellow and spondyloarthritis researcher in the division of rheumatology at the University of Washington in Seattle. “You have to look for other features that increase your suspicion,” such as symptoms affecting your eyes, skin, or other joints or connective tissues, or a family history of related diseases — something that not all doctors do.
Imaging Tests for nr-axSpA
The first imaging test your doctor will likely order to investigate lower back pain is an X-ray. Assuming your doctor suspects nr-axSpA or AS based on your symptoms, this imaging test will look at your lower spine as well as your SI joints.
AS is distinguished from nr-axSpA by “wear and tear and sclerosis [fusing] of the SI joints” that’s visible on an X-ray image, Miller notes. That means, he says, that even nonspecialists will often have a strong suspicion of AS, and will quickly refer a patient to a rheumatologist, after reviewing the imaging results. A quick referral often means a faster diagnosis.
But “fast” is a relative term when it comes to diagnosing nr-axSpA and AS. “Even when people have true AS, the delay in diagnosis can be very long, sometimes 6 to 10 years or more” after the onset of symptoms, says Dr. Liew. “When you get an X-ray and you don’t see anything, it can be very difficult” for many doctors to know how to proceed, she notes.
The trick is to find a doctor who knows the next step in imaging tests: magnetic resonance imaging (MRI). This technology “has made it easier to detect inflammation along the spine,” says Miller, and is one of the main reasons why the diagnosis of nr-axSpA even exists. But it’s still essential for your doctor to order an MRI test of your SI joints — not just your lumbar spine — to detect inflammation there and correctly diagnose nr-axSpA.
With inflammation caused by nr-axSpA, “even when it’s nonradiographic on X-ray, you’re supposed to be able to see something on MRI,” Liew emphasizes. But that doesn’t mean a diagnosis will be quick or easy.
“Even with MRI, which is a very sensitive imaging modality, it’s hard to know exactly what it means when we see the things that we see,” Liew says. “Experts are still trying to figure out what patterns constitute this disease, and which are nonspecific, meaning they could be caused by other things that are not spondyloarthritis.”
So your MRI results may lead to a quick diagnosis of nr-axSpA — or you may be left looking for answers yet again. If these results are nonspecific, Liew says, you may benefit from seeing a rheumatologist with advanced training in diagnosing and treating nr-axSpA and AS.
Putting the Puzzle Together to Diagnose nr-axSpA
For people with MRI results that don’t clearly indicate nr-axSpA, but whose symptoms suggest this condition, making a diagnosis is a bit like putting a puzzle together — but the puzzle pieces are still never going to fit perfectly, says Liew. These are cases “that are really difficult, where maybe you have lots of confounding issues.” And in these cases, your rheumatologist might do something unorthodox: prescribe a treatment to see how it works, as part of the diagnostic process.
“Something people do is a three-month trial of a biologic, like a TNF inhibitor,” to look for signs of improvement, says Liew. If your symptoms do improve, “I still wouldn’t say it’s diagnostic. Everything just shifts your suspicion higher or lower,” she says.
But even if your doctor can’t say with certainty that you have nr-axSpA, being on a treatment and seeing an improvement in your symptoms should count as progress. And it’s possible that future imaging tests will yield clearer results, giving your doctor the go-ahead to rule definitively that you have nr-axSpA.
In the meantime, it may be helpful to remember that nr-axSpA is a newer diagnosis — the term was officially defined only in 2009 — that is, in some ways, inherently challenging. “When you get an X-ray and you don’t see anything,” Liew emphasizes, “it can be very difficult.”