Rare but characteristic MRI Shoulder findings of chlamydia trachomatis-associated reactive arthritis

Spondyloarthritis is an inflammatory disease characterised by tendon adhesions and sacroiliitis. Herein, we present a case of reactive arthritis (ReA) after Chlamydia infection. The condition was characterised by rotator cuff enthesitis accompanied by inflammation of the rotator cuff muscles and presence of contrast-enhanced lesions at several tendon attachments without pelvic sacroiliitis. Some studies have reported about shoulder joint involvement observed on magnetic resonance imaging (MRI) in ankylosing spondylitis and psoriatic arthritis. However, there are no reports on shoulder lesions detected on MRI in C. trachomatis infection-associated ReA. The patient presented with hip, lower back and right shoulder pain. MRI of the pelvis revealed inflammation of the tendon attachments such as the spinous process, sciatic tuberosity and greater and lesser trochanter. However, sacroiliitis was not observed. These imaging findings indicated enthesitis. The patient tested positive for C. trachomatis immunoglobulin but negative for HLA-B27 antigen. Hence, he was diagnosed with Chlamydia-related ReA. Antibiotic treatment combined with sulfasalazine was initiated. This resulted in an evident clinical improvement without remission. To the best of our knowledge, this is the first case report showing the presence of shoulder lesions on MRI in C. trachomatis infection-associated ReA. Further, this study showed that shoulder lesions in spondyloarthritis, including ReA, are characterised by not only adhesive inflammation but also bone marrow oedema in the tendon attachments and rotator cuff inflammation.