A case of reactive arthritis caused by a perianal abscess.

Reactive arthritis is an immune-mediated aseptic arthritis resulting from either genitourinary or intestinal tract in a genetically susceptible host. Reactive arthritis is not uncommon, and the most common infectious agents are Chlamydia trachomatis, Salmonella, Yersinia, and Shigella, some new infectious agents include Staphylococcus lugdunensis, Rothia mucilaginosa, and umbilical cord-derived Wharton's jelly, as well as the SARS-CoV-2 virus, which has been more studied in recent years. We found that reactive arthritis caused by infection of perianal abscesses is very rare and few cases have been described in the medical literature. We report a 21-year-old man with polyarticular swelling and pain, and subcutaneous hematoma at his right ankle joint; he was considered reactive arthritis. After treating with non-steroidal anti-inflammatory drugs, sulfasalazine, surgery, and antibiotics, the patient's arthralgia gradually improved and the symptoms largely disappeared at the 1-month follow-up.