Two types of bacteria cause reactive arthritis in the majority of cases:

• Bacteria that cause bowel infection such as Salmonella, Shigella, Yersinia, Campylobacter, Clostridium difficile, and Chlamydia pneumoniae

• Bacteria that cause genital infection, such as Chlamydia

Reactive arthritis typically occurs in men between 20 and 40 years old. It can appear in women also, usually with milder signs and symptoms. The genetic factor may play a role in the likelihood of developing reactive arthritis; however, HLA-B27 is found in less than 50% of cases. Thus, HLA-B27 testing is reserved for patients with a high to intermediate likelihood of having reactive arthritis and has little diagnostic value in isolation.

Clinical Manifestations. The symptoms of reactive arthritis generally appear 1 to 4 weeks after the triggering infection, with asymmetric oligoarthritis of the extremities as the most common pattern. Other musculoskeletal features include enthesitis, sausage digits (dactylitis), and low back pain.

Genital and urinary symptoms may include genital lesions, pain or burning during urination, rash, redness or inflammation, increased frequency of urination, and urethral discharge. Eye involvement in reactive arthritis can manifest with conjunctivitis and uveitis. Cutaneous signs of the disease include oral and genital ulcers and characteristic keratosis on the palms and soles.

Imaging. The diagnosis of reactive arthritis cannot be established with bone radiographs alone, but they can be used to exclude other types of arthritis with similar presentations. Because enthesitis is common, additional imaging such as ultrasonography, MRI, or bone scanning can be used to document changes suggestive of enthesitis.

Treatment/Prognosis. In general, the prognosis is good. The disease may be self-limiting, lasting only a few weeks or months, although attacks may last as long as a year. A small group of patients may develop persistent joint symptoms for years that may be associated with HLA-B27.

Therapy for the arthritic component includes the following:

• NSAIDs to relieve the pain and inflammation are the mainstay of treatment.

• Intra-articular corticosteroid injection may be used if the joint is persistently inflamed.

• DMARDs (sulfasalazine) or anti–TNF-α agents may be used if the symptoms do not improve after therapy with NSAIDs or corticosteroids.

• Physical therapy can help to improve joint function.

Antibiotics to eliminate the documented infection may be prescribed; however, long-term chronic antibiotic therapy is not recommended in reactive arthritis.