Reactive Arthritis

Reactive arthritis, historically called Reiter syndrome, is a sterile inflammatory spondyloarthritis that appears after an infection rather than from bacteria multiplying inside the joint. The usual interval is 1–6 weeks after a gastrointestinal or genitourinary infection. Recognized triggers include Chlamydia trachomatis, Salmonella, Shigella, Yersinia, and Campylobacter; reactive arthritis has also been reported after SARS-CoV-2 infection. The typical joint pattern is abrupt, asymmetric oligoarthritis: a few joints, often in the lower limbs, become painful, warm, and swollen. Enthesitis— inflammation where a tendon or ligament inserts into bone—is particularly useful clinically. Achilles tendon pain or plantar heel pain may be more prominent than the patient’s knee findings. The inflammation can also involve the eyes, genitourinary tract, skin, and mucous membranes. The traditional triad of arthritis, urethritis, and conjunctivitis is incomplete in many patients and is not required for diagnosis. A patient may have arthritis and heel enthesitis after infectious diarrhea without urinary or eye symptoms. Conversely, a patient with eye pain or urinary symptoms may have an extra-articular complication that changes the urgency of care. “Sterile” refers to the joint inflammation, not...