It can be quite a challenge to diagnose ankylosing spondylitis. That is because a patient can feel the symptoms of the disease years before changes in the spine anatomy, such as the growth of bones and the fusing of joints, can be seen on x-rays. Early diagnosis is important, however, as patients can better maintain flexibility and movement if treatment is started before the disease and associated joint pain progress too far.

Patients can expect doctors to use a three-part protocol to confirm a diagnosis of ankylosing spondylitis. This typically involves reviewing a patient’s medical history, performing a physical exam, and reviewing the results of diagnostic tests, including x-rays, CAT scans (CT scans), and magnetic resonance images, as well as blood tests.

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Ankylosing Spondylitis Medical History

Patients will be asked to describe when and how their joint pain or other symptoms first occurred, if they have changed in severity or location, and if any treatment has provided pain relief. The presence or history of related conditions including uveitis (inflammation of the eye), gastrointestinal infections (Crohn’s disease, ulcerative colitis), and frequent fatigue are also important factors in an accurate diagnosis.

In addition, because this form of arthritis does have a genetic component, information about any family members who suffer from the disease or symptoms similar to the patient’s are also considered.

Ankylosing Spondylitis
Ankylosing Spondylitis. Enlarge

Ankylosing Spondylitis Physical Exam

A patient’s physician, typically a general practitioner, will first look at the patient’s posture to see if the lumbar spine (lower back) is losing its normal curve and beginning to flatten out. An examination of the whole spine can identify whether the inflammation has moved up from the lumbar region.

Because symptoms can be different between patients (and notably so for women and children), it is important that other joints, particularly the hips and ankles, be also examined. The physician may also assess flexibility and the range of motion of specific joints to quantify the impact of the patient’s symptoms.

If classic symptoms of ankylosing spondylitis are present, most general physicians will refer patients to a rheumatologist. A rheumatologist is trained to recognize the symptoms of ankylosing spondylitis and will most likely conduct more extensive testing.

Ankylosing Spondylitis Diagnostic Tests

There are two categories of diagnostic tests used to identify ankylosing spondylitis: imaging scans (e.g., x-rays, magnetic resonance images) that capture a picture of the spine and affected joints, and blood tests that identify certain markers of ankylosing spondylitis.

Imaging Scans
In the early disease process, plain x-rays may be read as normal. To diagnose ankylosing spondylitis, the sacroiliac joints (SI joints) at the back of the pelvis must be affected. X-ray evidence of sacroiliitis is one of the most telling signs of this condition. More accurate and earlier diagnosis can be done using magnetic resonance imaging (MRI scans) and or CAT scans (CT scans).

Blood Tests
An elevated C-Reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR) can be found in any inflammatory state, including ankylosing spondylitis. As mentioned previously in this article, 90% of people with ankylosing spondylitis test positive for the HLA-B27 gene. Having this gene, however, does not necessarily mean that ankylosing spondylitis is present or that it will develop. 8% of healthy Caucasians and 2% of health African-Americans carry this gene. In fact, a healthy person who carries this gene and has no relatives with ankylosing spondylitis has only a 2% chance of getting this form of arthritis.

Some doctors may also run blood tests to rule out possible causes of similar symptoms, including fibromyalgia, spinal or bone tumors, infection, pelvic inflammatory disease, metabolic bone disease, diffuse idiopathic skeletal hyperostosis (DISH), and prolapsed intervertebral disc.

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Written by Judith Frank, MD
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