What Is Axial Spondyloarthritis?

Axial spondyloarthritis (AxSpA) is a general term that can refer to ankylosing spondylitis (also called radiographic axial spondyloarthritis) or non-radiographic axial spondyloarthritis. The chief symptom is back pain.1,2 AxSpA, just like AS, is chronic, inflammatory disease that impacts the axial skeleton or sacroiliac joints and spine. The end of the spine, the sacrum, connects to the ilium, or hip, with ligaments, so this area is called the sacroiliac joint.

In AxSpA, the sacroiliac area may show signs of irritation but is not yet fully deformed or fused by the long-term, severe inflammation of full-blown AS. AxSpA may cause mild pain and stiffness for years and never progress into the more severe form of ankylosing spondylitis, also called radiographic axial sponyloarthritis.

Birth of a new name

The term axial spondyloarthritis (AxSpA) is a relatively new term, having been proposed by doctors in 2012 at the Assessment of Spondyloarthritis International Society (ASAS).

In the past, doctors did not diagnose a patient with ankylosing spondylitis unless an X-ray or MRI showed sacroiliitis, or severe inflammation of the bones at the bottom of the spine. The problem was that many patients exhibit all the other symptoms of AS for as long as 10 years before progressing to a more advanced stage of the disease. Some people have AS symptoms but no evidence on imaging tests for their entire life. This is called non-radiographic axial spondyloarthritis.1

Epidemiology

AxSpA is equally common in men and women, compared to AS, which is more common in men. It is most often diagnosed in people in their 30s.3 Studies estimate that as many as 1 percent of adults in the U.S. may have AxSpA, which equates to 2.7 million people.1,5 Like ankylosing spondylitis, more than 90 percent of those diagnosed with AxSpA inherited the disease due to the gene HLA-B27, but as many as 30 genes may be associated with the condition.4

Types of axial spondyloarthritis

There are two types of AxSpA:

  • Radiographic AxSpA, in which X-ray or MRI reveals the characteristic inflammatory changes of the sacroiliac joints (those joints linking the lowest part of the spine to the pelvis).
  • Nonradiographic AxSpA, where the sacroiliac joints show little or no damage due to inflammation.

Diagnosis of axial spondyloarthritis

Your doctor will use the same techniques to diagnose AxSpA that are used for AS. This includes:

    • Medical history and physical exam
    • X-ray and/or MRI of the base of the spine and hips (sacroiliac joints)
    • A blood test for the HLA-B27 gene

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Written by: Jessica Johns Pool | Last reviewed: March 2019