Diagnosis of Ankylosing Spondylitis

A rheumatologist is commonly the type of physician who will diagnose ankylosing spondylitis (AS), 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.

Note that AS can present differently at onset in some people. This tends to be the case in women more than men. Quoting Dr. Elaine Adams, "Women often present in a little more atypical fashion so it's even harder to make the diagnosis in women." For example, we have heard anecdotally from some women with AS that their symptoms started in the neck rather than in the lower back.

Varying levels of fatigue may also result from the inflammation caused by AS. The body must expend energy to deal with the inflammation, thus causing fatigue. Also, mild to moderate anemia, which may also result from the inflammation, can contribute to an overall feeling of tiredness.

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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 three months (i.e., it is chronic).
  • Back pain and stiffness worsen with immobility, especially at night and early morning.
  • Back pain and stiffness tend to ease with physical activity and exercise.

A physical examination entails 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, your doctor may also check for limitations in 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), and a family history of AS, as well as fatigue due to the presence of inflammation.

Blood Work and the HLA-B27 Test

First, HLA-B27 is a perfectly normal gene found in 8 percent of the Caucasian population. Generally speaking, no more than 2 percent of people born with this gene will eventually develop spondylitis.

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

Since there is no single blood test for AS, laboratory work may, or may not, be of help. Elevated erythrocyte sedimentation rate (ESR), also known as SED rate, and C-reactive protein (CRP) are common indicators of inflammation. Elevated levels of these markers, however, are not present in all AS patients and, when they are, it can be from other causes such as anemia, infection, or cancer. For example, it is estimated that less than 70 percent of people with AS have a raised ESR level.

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

The Hallmark of Ankylosing Spondylitis

The hallmark of AS is involvement of the sacroiliac (SI) joints. Some physicians still rely on X-ray to show erosion typical of sacroiliitis, which is inflammation of the sacroiliac joints. Using conventional X-rays to detect this involvement can be problematic because it can take seven to 10 years of disease progression for the changes in the SI joints to be serious enough to show up on conventional X-rays.

Another option is to use MRI to check for SI involvement, but MRI can be cost prohibitive in some cases.

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