MSFinals-2466

A 15-year-old boy presents with a 4-month history of lower back and left heel pain, making walking painful and difficult. He reports experiencing morning stiffness lasting for about an hour, which improves with exercise throughout the day. He denies any prior history of similar symptoms and reports that they suddenly started about 4 months ago.

During examination, the patient exhibits reduced lateral and forward flexion of the spine, tenderness upon palpation of the sacroiliac joints, and decreased chest expansion. What other conditions may be associated with this likely diagnosis?