Ankylosing Spondylitis Diagnosis

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.

Note that AS can present differently at onset in women than in men. Quoting Dr. Elaine Adams, "Women often present in a little more atypical fashion so it's even harder to make the diagnoses in women." For example, anecdotally we have heard from women with AS who have stated 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.

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.

Related Diseases

Ankylosing spondylitis is the hallmark disease in a family of related diseases. If ankylosing spondylitis is not relevant to you, one of these others may be.

Psoriatic Arthritis Reactive Arthritis Enteropathic Arthritis

Blood Work and 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 ankylosing spondylitis. Also, the association between ankylosing spondylitis 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 ankylosing spondylitis test HLA-B27 positive. However, only 50% of African American patients with ankylosing spondylitis possess HLA-B27, and it is close to 80% among ankylosing spondylitis patients from Mediterranean countries.

Since there is no single blood test for ankylosing spondylitis, 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. However, these elevated levels are not present in all AS patients and when they are, it can be from other causes such as anemia, infection and cancer. For example, it is estimated that less than 70% of people with ankylosing spondylitis 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).

The Hallmark of Ankylosing Spondylitis

The hallmark of ankylosing spondylitis is involvement of the sacroiliac (SI) joint. 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 a diagnosis of ankylosing spondylitis, and MRI can be cost prohibitive.