Findings: Image #1 demonstrates ankylosis of the sacroiliac joints

. Image #2 demonstrates axial joint space narrowing of the left hip with extensive erosions and a few osteophytes. There is bony proliferation seen on the ischial spines. This is a manifestation of enthesopathy which is a frequent finding in the seronegative spondylar arthropathies.

Image # 3 demonstrates syndesmophytes of the lower lumbar spine. The syndesmophytes bridge the intervertebral disc spaces.

Diagnosis: Ankylosing spondylitis.

Discussion: Ankylosing spondylitis is a chronic inflammatory disease which primarily affects the axial skeleton, although the appendicular skeleton may on occasion be involved. The onset of ankylosing spondylitis is most often between the ages of 15 and 35. It most commonly occurs in men. The earliest clinical manifestations include low back pain, although chest pain or fever and weight loss are occasionally identified. Although low back pain is the most common presenting symptom, there may be tenderness over the sacroiliac joints as well. The hips and shoulders may also be involved with pain and swelling which can actually simulate rheumatoid arthritis. Associated manifestations of ankylosing spondylitis include pericarditis, pulmonary involvement such as fibrosis and inflammatory bowel disease. Most commonly, changes are identified in the sacroiliac joint prior to the development of thoracolumbar and lumbosacral abnormalities. The differential diagnosis for isolated SI joint abnormalities would include inflammatory bowel disease is symmetric and Reiters or psoriasis if asymmetric. The disease begins in the lower lumbar region and ascends. The radiographic abnormalities include syndesmophytes which extend from one vertebral body to another in a thin flowing pattern. The synovial joint abnormalities may be similar to the findings seen in rheumatoid arthritis including osteoporosis, joint space narrowing, and osseous erosion. Another differentiating point between rheumatoid arthritis and ankylosing spondylitis is that in ankylosing spondylitis, the ankylosis occurs in the large joints including the sacroiliac joints and hips. In rheumatoid arthritis, the ankylosis is more characteristic in the carpal and tarsal regions. Sacroilitis is a hallmark of ankylosing spondylitis which often occurs early in the course of the disease. The changes most commonly are bilateral and symmetric including periarticular osteoporosis and loss of definition as well as superficial erosion and focal sclerosis of the subchondral bone. As this progresses, complete ankylosis develops.

Reference:
Resnick D. Bone and Joint Imaging. W. B. Saunders, Co.,
Philadelphia; 1996:246-249.

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