CASE 10: Ankylosing spondylitis

- The SI joints have completely fused, leaving no trace of the joint surfaces. There is some sclerosis where the joints used to be. There are syndesmophytes connecting the margins of the vertebral bodies on both the AP and the lateral views. On the AP view these are symmetric. In later stages, the anterior borders of the vertebral bodies lose their concavity.

. There also has been fusion of the facet joints in the posterior elements. The fusion of the facet joints is best noticed on the lateral view of the cervical spine. Occasionally there are fractures of the posterior elements due to the stress of the immobility. This creates a pseudoarthrosis with destruction of the disc at the same level.

The differential diagnosis includes psoriatic arthritis, Reiter's Disease, and the arthritis of inflammatory bowel disease. The symmetry of the findings as well as the marginal syndesmophytes suggest AS or inflammatory bowel disease rather than psoriatic arthritis, as in the latter the SI joint findings may be asymmetric and the syndesmophytes may be larger and nonmarginal.