How Is Axial Spondyloarthritis Diagnosed?

Posted on October 01, 2020

Article written by
Annie Keller

Axial spondyloarthritis is usually diagnosed by a combination of symptoms, imaging scans, and blood test results.
Negative results on imaging tests, such as X-rays, do not rule out an axial spondyloarthritis diagnosis.
Early diagnosis can allow prompt treatment that helps minimize symptoms and maintain function.

Most people have to deal with back pain at one time or another. For people living with axial spondyloarthritis, back pain is more complex than a pulled muscle or an injury. Since chronic low back pain is such a common symptom, it’s not always easy to diagnose the correct cause. It’s estimated that 6 percent of people with chronic back pain have axial spondyloarthritis, but delays in diagnosis as long as 10 years are common. This is unfortunate because a prompt diagnosis can lead to better management of symptoms, help retain function, and lower the risk for permanent damage. Here are the basics on how axial spondyloarthritis is recognized and diagnosed.

Common Symptoms of Axial Spondyloarthritis

While most people won’t have all the symptoms of axial spondyloarthritis, common symptoms include:

Inflammatory back pain
Pain in joints in the limbs (peripheral arthritis)
Uveitis (inflammation of the eyes)
Enthesitis (inflammation where the tendons and bones meet, especially at the heel)
Dactylitis (swelling in the fingers and toes)
Inflammatory bowel disease (IBD)

Any of these symptoms, especially when they have gone on for three months or more, should be regarded as a potential symptom of axial spondyloarthritis.

Mechanical or Inflammatory Back Pain?

Common back pain is mechanical in nature; you overwork yourself and strain your muscles. Mechanical pain is temporary and will improve with rest and other methods to ease the muscles.

Inflammatory back pain, one of the primary symptoms of axial spondyloarthritis is the opposite — it may get better with physical activity. Inflammatory back pain tends to be chronic, and doesn’t ease over time. Back pain from an inflammatory cause is usually worse at night and upon awakening, and is often accompanied by morning stiffness. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as Ibuprofen or Aleve (Naproxen), may help ease the pain. Axial spondyloarthritis is not the only cause of inflammatory back pain, but this type of pain is a hallmark of the condition.

Is There a Test for Axial Spondyloarthritis?

There is no one test that can definitively diagnose axial spondyloarthritis. Anyone who has had back pain for more than three months with no clear cause should see a rheumatologist, a doctor who specializes in inflammation of the bones, joints, and muscles. The back pain may be the result of inflammation and not a mechanical injury, and this is one of the keys to an axial spondyloarthritis diagnosis.

The first steps in determining whether someone has axial spondyloarthritis are a medical history and physical examination. Your doctor will ask you to bend your joints in different directions to see if your range of motion has been affected. They will also move your legs in different directions and press on areas of the pelvis (the sacroiliac joints) to see if pain results. Your doctor will ask you when and how often you experience symptoms. A family history will also be taken; if a family member has axial spondyloarthritis or another autoimmune condition, like psoriasis or inflammatory bowel disease, this is considered a risk factor.

Axial spondyloarthritis cannot be diagnosed with a simple test. There are several tests that may indicate the presence of axial spondyloarthritis. The Assessment of SpondyloArthritis International Society has produced a handbook for diagnosing spondyloarthritis that recommends the following tests.

Imaging Tests

Axial spondyloarthritis may be radiographic (showing symptoms in X-rays) or nonradiographic (symptoms are invisible on X-rays). Radiographic axial spondyloarthritis is also known as ankylosing spondylitis, which may be considered a more severe or advanced form of the condition. Unlike ankylosing spondylitis, nonradiographic axial spondyloarthritis may not show any signs in X-rays or other imaging scans.

It’s important to note that imaging scans that show inflammation can help confirm a diagnosis, but negative imaging scans do not rule out a diagnosis of nonradiographic axial spondyloarthritis. Read Intense Pain, Invisible Damage: What X-Rays and MRI Can’t Reveal.

X-Rays

X-ray imaging can be used to check for inflammatory changes to the sacroiliac joint, where the spine meets the hips. These changes are called sacroiliitis. If no changes are visible, the X-ray can be saved to compare to later scans to see if damage has developed from further disease activity.

Magnetic Resonance Imaging

MRI scans are better at distinguishing early changes in bones and soft tissues than X-rays, but they are more expensive. MRI may reveal sacroiliitis in earlier stages, before an X-ray shows any damage.

Computed Tomography

CT scans are often less expensive than MRI scans and can distinguish fusing of bones better than either MRI or X-ray. Radiation exposure can be a concern with CT scans.

Positron Emission Tomography

One study indicated that PET scans could find areas of inflammation the other scans mentioned above could not. Since this is a recent finding, PET scans may not be part of a typical diagnostic exam.

Blood Tests

Like imaging tests, positive blood test results can provide evidence supporting a diagnosis of axial spondyloarthritis, but negative results do not rule out the condition.

HLA-B27

Human leukocyte antigen B27 is a protein found on white blood cells in 90 percent of people who have axial spondyloarthritis. Whether you have HLA-B27 is determined by genes. Not all people with axial spondyloarthritis will test positive for HLA-B27. Less than 2 percent who do test positive will develop axial spondyloarthritis. Still, the presence of the protein can be a valuable factor that supports a diagnosis.

C-reactive Protein (CRP) Levels

C-reactive protein levels measure the amount of inflammation in the body. Taken by themselves, they are not indicative of much, since inflammation can have many different causes. However, if high CRP levels are accompanied by other signs and symptoms of axial spondyloarthritis, it may make a diagnosis seem more likely. CRP levels are considered raised when they exceed 10 milligrams per liter of blood.

Erythrocyte Sedimentation Rate (ESR)

Also known as “sed rate,” ESR is another indication of inflammation in the body. ESR is measured by putting a sample of blood in a tube and seeing how many red blood cells sink to the bottom of the tube in an hour. Any reading over 20 millimeters per hour is abnormal, but readings over 100 may be a stronger sign of an autoimmune condition. Like CRP levels, the test doesn’t indicate the cause of inflammation, but it can point toward a diagnosis when there are other symptoms of axial spondyloarthritis. Less than 70 percent of people with ankylosing spondylitis show a high ESR level when tested.

Getting To a Diagnosis

Diagnosing axial spondyloarthritis requires a rheumatologist to consider a person’s symptoms and family medical history of inflammatory diseases, as well as the results of imaging scans and blood tests.

Axial spondyloarthritis may be diagnosed in cases where someone has experienced chronic back pain for at least three months, starting before age 45, and either of the following criteria are present:

Imaging shows sacroiliitis, and there is at least one clinical feature of spondyloarthritis.
Regardless of imaging results, HLA-B27 is present, and there are at least two clinical features of axial spondyloarthritis.

Axial spondyloarthritis clinical features include:

Inflammatory back pain
Pain in other joints (arthritis)
Enthesitis
Dactylitis
Uveitis
Psoriasis or psoriatic arthritis
Crohn’s disease or ulcerative colitis
Family history of spondyloarthritis
NSAIDs effective at managing symptoms
Positive for HLA-B27
Elevated CRP levels

Some rheumatologists have concerns about the current diagnostic criteria for axial spondyloarthritis. For instance, some criteria tend to differ between men and women. Women are less likely to show axial spondyloarthritis damage on X-rays and less likely to have elevated CRP levels. Women are also more likely to experience a delay in axial spondyloarthritis diagnosis than men. There is also an ongoing discussion about how to interpret MRI scans, and whether some changes visible on scans may also be present in people without axial spondyloarthritis.

Differential Diagnosis

An axial spondyloarthritis diagnosis may also require ruling out other conditions that can cause inflammatory back pain in a process called differential diagnosis. For instance, rheumatoid arthritis is a similar condition, but there usually are enough differences between the two to distinguish them. Both have similar patterns of bone erosion that can be seen on imaging, but axial spondyloarthritis may also have regrowth of bone in the affected area.

Nonradiographic Axial Spondyloarthritis vs. Ankylosing Spondylitis

If you do receive a diagnosis of axial spondyloarthritis, you are classified as having either nonradiographic axial spondyloarthritis or radiographic axial spondyloarthritis (also referred to as ankylosing spondylitis). The difference between the two is fairly simple. Nonradiographic axial spondyloarthritis is diagnosed when there are enough symptoms, based on the classification criteria, but there are no changes visible on imaging scans. Radiographic axial spondyloarthritis is diagnosed when criteria for axial spondyloarthritis are present along with damage that is visible on scans. Radiographic axial spondyloarthritis is sometimes called ankylosing spondylitis, which refers to a later stage of the condition where bones in the spine fuse to one another.

Radiographic and nonradiographic axial spondyloarthritis are considered to be the same condition in different stages, with the nonradiographic form being an early stage. People with nonradiographic axial spondyloarthritis can sometimes progress to the radiographic type over time. However, even those with nonradiographic axial spondyloarthritis share the same disease burden (including chronic pain and decreased functioning) as those with radiographic symptoms.

Receiving a diagnosis of axial spondyloarthritis is a step in the right direction toward understanding and treating your condition. If you’re experiencing symptoms associated with axial spondyloarthritis, it’s best to share your concerns with your doctor as soon as possible.