[Cross-sectional imaging of peripheral involvement in ankylosing spondylitis]

Ankylosing spondylitis is the most common spondyloarthropathy. It is characterized by enthesopathy (inflammation at the insertion of ligaments, tendons or fascia to bone). The os calcis is most frequently involved. Additional peripheral manifestations include synovitis and dactylitis. Unlike radiographs that demonstrate late manifestations of the disease, ultrasound and MRI demonstrate early inflammatory changes of bones and soft tissues. Multiple sites of involvement may also be detected on a single examination. Both imaging modalities facilitate early diagnosis, a crucial element for patient management. Both modalities may also monitor lesion regression during treatment.