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Ankylosing Spondylitis & Related Diseases Information
Ankylosing Spondylitis (AS): Quick Links
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A rheumatologist is commonly the type of physician that will diagnose ankylosing spondylitis, since they are doctors who are specially trained in diagnosing and treating disorders that affect the joints, muscles, tendons, ligaments, connective tissue, and bones. A thorough physical exam including x-rays, individual medical history, and a family history of AS, as well as blood work including a test for HLA-B27 are factors in making a diagnosis.

Physical Exam
The overall points taken into account when making an AS diagnosis are:

  • Onset is usually under 45 years of age.

  • Pain persists for more than 3 months (i.e. it is chronic).

  • The back pain and stiffness worsen with immobility, especially at night and early morning.

  • The back pain and stiffness tend to ease with physical activity and exercise.

  • Positive response to NSAIDs (nonsteroidal anti-inflammatory drugs).

A physical examine will entail looking for sites of inflammation. Thus, your doctor will likely check for pain and tenderness along the back, pelvic bones, sacroiliac joints, chest and heels. During the exam, you doctor may also check for the limitation of spinal mobility in all directions and for any restriction of chest expansion.

Other symptoms and indicators are also taken into account including a history of iritis or uveitis (inflammation of the eye), a history of gastrointestinal infections (for example, the presence of Crohn's Disease or ulcerative colitis), a family history of AS, as well as fatigue due to the presence of inflammation.

The Hallmark of AS & X-rays vs. MRI
The hallmark of AS is involvement of the sacroiliac (SI) joint (see figure to the upper right). The x-rays are supposed to show erosion typical of sacroiliitis. Sacroiliitis is the inflammation of the sacroiliac joints. Using conventional x-rays to detect this involvement can be problematic because it can take 7 to 10 years of disease progression for the changes in the SI joints to be serious enough to show up in conventional x-rays.

Another option is to use MRI to check for SI involvement, but currently there is no validated method for interpreting the results in regards to an AS diagnosis. Also, MRI can be cost prohibitive.

Blood Work & the HLA-B27 Test
First, HLA-B27 is a perfectly normal gene found in 8% of the Caucasian population. Generally speaking, no more than 2% of people born with this gene will eventually get spondylitis.

Secondly, it is important to note that the HLA-B27 test is not a diagnostic test for AS. Also, the association between AS and HLA-B27 varies in different ethnic and racial groups. It can be a very strong indicator in that over 95% of people in the Caucasion population who have AS test HLA-B27 positive. However, only 50% of African American patients with AS possess HLA-B27, and it is close to 80% among AS patients from Mediterranean countries.

Since there is no single blood test for AS, laboratory work may not be of much help. A simple ESR (erythrocyte sedimentation rate), also known as sed rate, is commonly an indicator of inflammation. However, less than 70% of people with AS have a raised ESR level.

Finally, there is no association with ankylosing spondylitis and rheumatoid factor (associated with rheumatoid arthritis) and antinuclear antibodies (associated with lupus).

VIDEO: Dr. Michael Weisman discusses diagnosis of spondylitis

More video in the member area! SAA Members have access to Dr. Michael Weisman's entire Spondylitis Educational Seminar presentation in the Member Area. We also have recordings of webinars from prominent rheumatologists as well as podcasts - audio interviews with experts.

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