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- What is ankylosing spondylitis?
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- How is ankylosing spondylitis diagnosed?
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How is ankylosing spondylitis diagnosed?
The diagnosis of ankylosing spondylitis is based on evaluating the patient's symptoms, a physical examination, X-ray findings (radiographs), and blood tests. Stiffness, pain, and decreased range of motion of the spine are characteristic of the inflammatory back pain of ankylosing spondylitis. Symptoms include pain and morning stiffness of the spine and sacral areas with or without accompanying inflammation in other joints, tendons, and organs. Early symptoms of ankylosing spondylitis can be very deceptive, as stiffness and pain in the low back can be seen in many other conditions. It can be particularly subtle in women, who tend to (though not always) have more mild spine involvement. Years of disease can pass before the diagnosis of ankylosing spondylitis is even considered.
The examination can demonstrate signs of inflammation and decreased range of motion of joints. This can be particularly apparent in the spine. Flexibility of the low back and/or neck can be decreased. There may be tenderness of the sacroiliac joints of the upper buttocks. The expansion of the chest with full breathing can be limited because of rigidity of the chest wall. Severely affected people can have a stooped posture. Inflammation of the eyes can be evaluated by the doctor with an ophthalmoscope.
Further clues to the diagnosis are suggested by X-ray abnormalities of the spine and the presence of the genetic marker HLA-B27 identified by a blood test. Other blood tests may provide evidence of inflammation in the body. For example, a blood test called the sedimentation rate is a nonspecific marker for inflammation throughout the body and is often elevated in inflammatory conditions such as ankylosing spondylitis. X-ray tests of the sacroiliac joints can demonstrate signs of inflammation and erosion of bone. X-rays of the spine can progressively demonstrate straightening, "squaring" of the vertebrae, and end-stage fusion of one vertebra to the next (ankylosis). Fusion up and down the spine can lead to a "bamboo spine" appearance on X-ray tests with complete loss of mobility.
Urinalysis is often done to look for accompanying abnormalities of the kidney as well as to exclude kidney conditions that may produce back pain that mimics ankylosing spondylitis. Patients are also simultaneously evaluated for symptoms and signs of other related spondyloarthropathies, such as psoriasis, venereal disease, dysentery (reactive arthritis or Reiter's disease), and inflammatory bowel disease (ulcerative colitis or Crohn's disease).