Azathioprine hypersensitivity reaction in a patient with ulcerative colitis

To describe a case of azathioprine hypersensitivity in a patient with ulcerative colitis.

A 40-year-old white man with ulcerative colitis, treated with chronic mesalamine and occasional steroids, was admitted to the hospital with a 3-day history of fever, nausea, vomiting, and a rash. Fourteen days prior to admission, the patient had been started on azathioprine for ulcerative colitis. Upon admission, azathioprine therapy was temporarily withheld, resulting in resolution of his signs and symptoms. Symptoms returned when azathioprine was restarted. It was decided that these signs and symptoms were most likely caused by azathioprine hypersensitivity, and the agent was discontinued.

To our knowledge, this is the first reported case of azathioprine hypersensitivity in a patient with ulcerative colitis. The time course and presenting signs and symptoms support the diagnosis of azathioprine hypersensitivity, as does the patient's response to rechallenge. The mechanism of this hypersensitivity reaction is unclear, but may involve the nitroimidazole portion of the azathioprine molecule.

Azathioprine hypersensitivity often presents with signs and symptoms resembling a systemic infection such as fever, leukocytosis, and evidence of end organ dysfunction. The diagnosis of azathioprine hypersensitivity should be considered in patients who have recently either initiated or increased their dosage of azathioprine.