Musculoskeletal manifestations of Reactive Arthritis
Arthritis: In ReA, the joints tend to be moderately inflamed and characterized by prolonged stiffness. Joint involvement is typically asymmetric, oligoarticular (less than five joints), and confined to the knees, ankles, and/or feet. Large joint effusions, especially in the knees, are not unusual. Hip involvement is rare. Upper limb arthritis (e.g., wrist and digits) may also occur (50%) but is never more prominent than the lower extremity arthritis. Uncommonly it can be a polyarthritis. The arthritis always lasts over 1 month, though usually longer. Joint erosions may result from chronic disease.
Enthesitis: An inflammation of the ligament, tendon, joint capsule, or fascia insertion site into bone (enthesis). In ReA, enthesitis commonly causes heel pain (Achilles tendon and plantar fascia), metatarsalgia (plantar fascia), and iliac spine/crest pain. Enthesitis are common in ReA, and may help distinguish it from other differential diagnosis.
Dactylitis: “Sausage” digits of fingers and toes are due to a combination of arthritis, enthesitis, and tendinitis.
Sacroiliitis/spondylitis: Up to 40% of patients with ReA may have axial skeleton symptoms, and 25% develop radiographic changes. The risk of developing sacroiliitis and/or spondylitis is related to disease chronicity and HLA-B27.
