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Imaging in Ankylosing Spondylitis

Medically reviewed by Ariel D. Teitel, M.D., M.B.A.
Written by BJ Mac
Posted on July 23, 2021

Imaging tests help doctors see inside the body, which can help diagnose and monitor people with spondyloarthritis (SpA). Spondylitis, as it’s also called, is a group of inflammatory arthritides that attack the entheses (tissues between ligaments or tendons and bone) and joints, primarily in the spine. Spondylitis includes axial spondyloarthritis (axSpA) and ankylosing spondylitis.

If a person under the age of 45 is experiencing chronic back pain lasting more than three months, a doctor might suspect spondylitis. A rheumatologist can confirm or rule out a diagnosis of spondylitis by evaluating a person’s medical history, performing physical exams such as a musculoskeletal exam, and ordering a battery of tests. Some tests used to support a spondylitis diagnosis are imaging tests.

Following are some of the imaging tests used to confirm a diagnosis of spondylitis. These tests can also be used to track the progression of the disease and monitor how effectively a current treatment is working.

Radiographic Imaging

The various types of spondylitis fall into two categories or disease stages: radiographic (X-rays) or nonradiographic. Nonradiographic axial spondylitis refers to an early stage of the disease before bone changes can be seen by X-ray. Radiographic axSpA — also called ankylosing spondylitis — refers to spondylitis that has progressed and caused visible bone changes on X-rays.

Radiographs (X-rays or conventional radiography) may be the first imaging tests a doctor performs when they suspect spondylitis. A notable disadvantage to X-rays is that they do not detect early disease activity, however. X-rays pick up bone changes caused by inflammation rather than early disease activity present in soft tissues. It can sometimes take five years or more from disease onset for changes caused by spondylitis to be detected by an X-ray.

Why imaging is vital for early detection of axial spondyloarthritis

Radiographic images can be used to help diagnose radiographic spondylitis, or ankylosing spondylitis, by detecting bone changes. Spondylitis inflammation usually attacks the sacroiliac joints first, causing sacroiliitis.

Some of the bone changes typical of spondylitis that may be detected by X-ray include:

  • Joint damage and erosion from inflammation (evidence of sacroiliitis)
  • Syndesmophytes, osteophytes, spondylophytes, and enthesophytes (types of bone spurs or growths)
  • Ossification (new bone formation between the vertebrae)
  • Ankylosis (fusion) of the spine
  • Disc calcifications
  • Subchondral sclerosis (thickening of bone in joints)

X-rays emit less radiation than computerized tomography (CT) scans, another imaging test option. They are also more accessible than magnetic resonance imaging (MRI) because they are quicker, less expensive, and have shorter wait times.

Following Up With X-Rays

It can take two years or more between X-rays for radiologists to detect disease progression. Still, X-rays play an important role in tracking spondylitis progression because they are easily accessible, yield quick results, and remain the standard for capturing bone changes.

Magnetic Resonance Imaging

MRI is the imaging test ordered when changes are not detected by X-ray in a person suspected to have spondylitis.

MRI can help the diagnostic accuracy of early spondylitis because it can detect inflammation before it causes damage that’s visible on an X-ray. Using an MRI, a doctor can diagnose nonradiographic spondylitis before it becomes radiographic. Early diagnosis allows for early intervention, which may help prevent long-term damage caused by spondylitis. MRI is also safer than X-ray because it does not emit radiation.

MRI is a sensitive test that uses magnetic energy to detect active inflammatory changes in early spondylitis. It can detect:

  • The same bone changes seen on X-rays, as well as early cartilage abnormalities and erosions
  • Active sacroiliitis not yet visible on X-rays
  • Bone marrow edema (inflammation of bone marrow)
  • Osteitis (bone inflammation)
  • Synovitis (inflammation of synovium)
  • Bursitis (inflammation of soft tissues)
  • Enthesitis (inflammation of entheses, where tendons attach to bone)
  • Enthesopathy (inflammation of ligaments or tendons)
  • Slipped discs
  • Spinal inflammation of facet joints (the joints that link the vertebrae together at the back of the spine)
  • Costovertebral inflammation (inflammation of the joints that connect ribs to the spine)

There are some limitations to MRI for diagnosing spondylitis. It can be difficult to distinguish spondylitis-related changes from those related to other possible diagnoses. Additionally, MRI can sometimes incorrectly detect normal structures, such as blood vessels, as active inflammation (known as the coil effect), resulting in a false-positive test result for spondylitis.

A few other disadvantages of using MRI to diagnose spondylitis include the high cost, the wait times for an appointment, and the risk of a flare-up due to the length of the actual test. MRI may not be possible for people with claustrophobia or metal implants and pacemakers.

Tracking Spondylitis by MRI

MRIs are ideal for follow-ups because they are safe for children, young adults, or anyone who has been overexposed to radiation. MRIs are also sensitive enough to track spondylitis progression, predict some changes to come, and even track the efficacy of treatment such as the biologic infliximab (Remicade), a tumor necrosis factor (TNF) inhibitor.

Uveitis (eye inflammation) or certain heart conditions may lead to the diagnosis of spondylitis in patients with chronic low back pain after confirmatory X-rays or spine MRI.

Computerized Tomography Scans

CT scans can capture a full view of the sacral and iliac joints from every angle. Compared to MRI and X-ray, CT scans may be superior for detecting chronic bone changes. However, CT scans have difficulty picking up the soft tissue and bony changes found in early spondylitis sacroiliitis.

CT scans also emit more radiation than X-rays, so CT is not recommended for a typical diagnosis of spondylitis. CT scans can still be used in the diagnostic process when a suspected spondylitis case is nonradiographic and an MRI can’t be performed, such as in the case of claustrophobia. CT may also be required with MRI to make distinctions in differential diagnoses.

Following Up With CT Scans

Computerized tomography is used sparingly in tracking disease progression because of the level of radiation. CT can sometimes play a role after some spondylitis complications and comorbidities.


Ultrasound is generally used as a complementary diagnostic tool because it is limited to only a superficial view of the sacroiliac joints. Ultrasound, a noninvasive modality with no radiation, may be better than MRI at detecting and evaluating enthesitis in people living with spondylitis.

Ultrasound also plays an important role in the diagnosis of psoriatic arthritis, a type of spondylitis, because these scans can detect a common feature called dactylitis — inflammation of an entire finger or toe.

Following Up With Ultrasound

Ultrasound plays an important role in spondylitis follow-ups. Ultrasound is used to guide corticosteroid injections to help alleviate pain in affected joints.

Because ultrasound can detect increased synovial fluid in joints quickly and safely, it can be ideal for tracking disease activity and medication efficacy in entheses affected by spondylitis.

A type of cardiac ultrasound, called an echocardiogram, is also used to follow some heart comorbidities.

What To Expect During Imaging Tests for Spondylitis

Talking to your doctor and asking how to prepare can help each imaging test go smoothly. Different tests have different requirements in terms of what you can eat or drink beforehand and what items (such as jewelry) need to be removed. If you’re nervous, your doctor can also alleviate your concerns and answer your questions.

Make sure to arrive early to fill out paperwork, bring your ID and insurance card, and wear comfortable clothes. You’ll probably want to leave your valuables at home and bring a book or some music for the wait.

Some imaging tests take a long time or require you to hold difficult positions. Anticipate that some physical and emotional stress may cause a flare, so any medications and assistive devices should be on hand just in case.

Results from imaging tests are usually completed fairly quickly, and they can give your doctor a wealth of accurate and useful information to help better manage and treat your spondylitis.

Find Your Support

The road to a spondylitis diagnosis and treatment can be difficult, but you’re not alone. By joining MySpondylitisTeam, the social network and online support group for those living with spondylitis, you gain a support group of more than 85,000 members.

What imaging tests have you had done for your spondylitis? Comment below or start your own conversation on MySpondylitisTeam.

  1. Non-Radiographic Axial Spondyloarthritis: What Is It, and How Is It Treated? — CreakyJoints
  2. Diagnosis of Ankylosing Spondylitis — Spondylitis Association of America
  3. Rheum2Learn: Musculoskeletal Exam — American College of Rheumatology
  4. Ankylosing Spondylitis Imaging — Medscape
  5. The Role of Imaging in Diagnosing Axial Spondyloarthritis — Frontiers in Medicine
  6. Diagnostic Imaging of Sacroiliac Joints and the Spine in the Course of Spondyloarthropathies — Polish Journal of Radiology
  7. Ankylosing Spondylitis — Radiopaedia
  8. Spinal Changes in Patients With Spondyloarthritis: Comparison of MR Imaging and Radiographic Appearances — RadioGraphics
  9. MRI in Seronegative Spondyloarthritis: Imaging Features and Differential Diagnosis in the Spine and Sacroiliac Joints — American Journal of Roentgenology
  10. Radiation Risk From Medical Imaging — Harvard Health Publishing
  11. Clinical and Imaging Efficacy of Infliximab in HLA-B27-Positive Patients With Magnetic Resonance Imaging-Determined Early Sacroiliitis — Arthritis & Rheumatology
  12. Radiographic Progression in Patients With Ankylosing Spondylitis After 2 Years of Treatment With the Tumour Necrosis Factor α Antibody Infliximab — Annals of the Rheumatic Diseases
  13. Magnetic Resonance Imaging of Uveitis — Neuroradiology
  14. Non-Radiographic Axial Spondyloarthritis (nr-axSpA): Advances in Classification, Imaging and Therapy — Rheumatology and Therapy
  15. The Importance of Ultrasound in Identifying and Differentiating Patients With Early Inflammatory Arthritis: A Narrative Review — Arthritis Research & Therapy
  16. Ultrasound Imaging in Psoriatic Arthritis: What Have We Learnt in the Last Five Years? — Frontiers in Medicine
  17. Ultrasound-Guided Sacroiliac Joint Injection in Patients With Established Sacroiliitis: Precise IA Injection Verified by MRI Scanning Does Not Predict Clinical Outcome — Rheumatology
  18. How To Prepare for an Imaging Test — Family Private Care Services
  19. Imaging in Ankylosing Spondylitis — The Rheumatologist
Posted on July 23, 2021
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Ariel D. Teitel, M.D., M.B.A. is the clinical associate professor of medicine at the NYU Langone Medical Center in New York. Review provided by VeriMed Healthcare Network. Learn more about him here.
BJ Mac is a freelance writer who was diagnosed with ankylosing spondylitis in 2013 and has experience writing about various chronic health conditions. Learn more about her here.

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