Diagnosis of Ankylosing Spondylitis

Diagnosing of ankylosing spondylitis (AS) may be difficult, especially in the initial stages of the disease as joint pain, stiffness and other symptoms occur in several types of arthritis. Apart from this, there is no single test that can confirm the diagnosis of ankylosing spondylitis. Diagnosis is made based on the patient's symptoms, a physical examination, imaging studies and blood tests.

Medical history and physical examination

The doctor will take a detailed medical history and do physical exam to diagnose the cause of back pain and stiffness. History may include questions such as location of the pain, time and pattern of the pain, presence or absence of stiffness and any other associated symptoms. Physical examination will include examination of back for pain, stiffness, range of motion, deformity and other  symptoms.

Examination may show decreased range of motion and flexibility of joints particularly in the spine. Flexibility may be decreased in lower back and/or neck and some people may have tenderness of the sacroiliac joints. In advanced cases, expansion of the chest with full breathing may be limited. This occurs due to involvement of the spine and ribs.

Imaging studies

• X-ray of sacroiliac joint: Characteristic feature of AS is involvement of the sacroiliac (SI) joint. In typical cases, the x-rays show erosion of sacroiliac joint (sacroiliitis). The term sacroilitis means inflammation of the sacroiliac joints. In most cases, however, conventional x-rays fail to detect this involvement as it can take 7 to 10 years of disease progression for the changes in the SI joints to become evident on conventional x-rays.
• MRI scan: This is a painless and non-invasive test, which is more sensitive than other imaging modalities for detection of most pathology in the body. Until a few years ago, X-ray changes were considered as a test to confidently confirm AS. MRI scan of the sacroiliac joints, however, is being used increasingly to confirm the diagnosis at an early stage. A more detailed view of a joint is obtained on MRI scan as compared with conventional X-ray picture and it can show inflammation in the sacroiliac joints much earlier than X-ray.

Blood tests and HLA-B27 Test

There is no single blood test for AS, which can confirm the diagnosis of AS. Hence, laboratory work up may not be of much help. Presence of the genetic marker HLA-B27 identified by a blood test in the presence of X-ray or MRI abnormalities of the spine, may suggest AS. Some people may have an elevated ESR (erythrocyte sedimentation rate, this is a general indicator of inflammation).

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