MEDizzy - A 27-year-old man is seen at his primary care physician’s

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Immunology

A 27-year-old man is seen at his primary care physician’s office for evaluation of painful arthritis involving the right knee that is associated with finger welling diffusely. He is otherwise healthy, but does recall a severe bout of diarrheal illness about 3–4 weeks prior that spontaneously resolved. He takes no medications and reports rare marijuana use. On review of systems, he reports painful urination. Examination shows inflammatory arthritis of the right knee, dactylitis, and normal genitourinary examination. He is diagnosed with reactive arthritis. Which of the following is the most likely etiologic agent of his diarrhea?

ExplanationReactive arthritis refers to an acute, nonpurulent arthritis that occurs after an infection elsewhere in the body. Often presenting with lower joint inflammatory arthritis occurring 1–4 weeks after a diarrheal episode, reactive arthritis may also include uveitis or conjunctivitis, dactylitis, urogenital lesions, and characteristic mucocutaneous lesions such as keratoderma blennorrhagica. The most common organism associated with reactive arthritis is Shigella species, although Yersinia, Chlamydia, and, to a much lesser extent, Salmonella and Campylobacter have been described.