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Ankylosing spondylitis (AS) is a condition which is very difficult to diagnose before irreversible damage to the sacroiliac joint is visible on x-ray. Diagnosis is often delayed because the early symptoms can be confused with many other conditions and there are no radiologic tests to guide the physician towards a diagnosis of ankylosing spondylitis in the early stages. In addition, many general practitioners may not be familiar with early signs of ankylosing spondylitis and may not be sensitive to the presence of emerging symptoms.

Presently, there are no guidelines for the diagnosis of patients who exhibit clinical signs of ankylosing spondylitis but whose x-rays are negative, such as early stage AS or juvenile patients. This results in a wide gap between the onset of ankylosing spondylitis, definitive diagnosis, and the initiation of treatment. Early diagnosis of ankylosing spondylitis, however, is important so that treatment can be initiated before permanent limitations of spinal mobility and deformity have set in.

The diagnosis of ankylosing spondylitis is made based on patient history, physical exam, laboratory findings and radiological imaging. According to the New York Criteria established in 1984, the diagnosis of ankylosing spondylitis is based on the presence of both of the following factors:

• Radiological evidence of bilateral Grade II changes (erosion and sclerosis) of the sacroiliac joint OR unilateral Grade III changes of the joint (erosion, sclerosis, and early ankylosis)
• Clinical signs of restricted spinal mobility OR inflammatory back pain

The diagnosis of inflammatory back pain is considered in the presence of 4 out of 5 of the following criteria:

• Age at onset of pain is younger than 40 years
• Back pain persists longer than 3 months
• Insidious onset of back pain (vague, gradual onset)
• Morning stiffness
• Relief of stiffness with exercise