Reactive arthritis: an unusual presentation of acute colitis.

A 20-year-old Caucasian man with a history of psoriasis presented to the emergency department due to a 2-week history of severe polyarthralgia and a 3-week history of non-bloody diarrhoea. The initial workup 2 days prior in an urgent care clinic returned negative for all enteric pathogens including nucleic acid amplification test. Investigations revealed colitis on CT and pseudomembranous colitis on colonoscopy. The aspirate returned positive for toxin. Tissue biopsies of the ascending, transverse, sigmoid colon and rectum were negative for chronicity to suggest inflammatory bowel disease with extraintestinal manifestation as the aetiology of polyarthralgia, which had been the most likely differential diagnosis until that point. The biopsy confirmed the diagnosis of reactive arthritis in the setting of colitis. The patient improved on treatment with naproxen and was referred to rheumatology where he was found to be HLA-B27 positive.