An unusual complication of immunosuppressive therapy in inflammatory bowel disease.

A 68-yr-old man with steroid refractory distal ulcerative colitis was treated with low-dose 6-mercaptopurine, and corticosteroids were successfully discontinued. He later presented with dyspnea and fever, was diagnosed with Pneumocystis carinii pneumonia by bronchoalveolar lavage, and died despite aggressive therapy. Serological tests for HIV were negative, and his white blood cell count was normal. This is the first report of P. carinii pneumonia complicating therapy of inflammatory bowel disease with 6-mercaptopurine. Although the mechanism is not entirely clear, 6-mercaptopurine appears to decrease cell-mediated immunity. Opportunistic infections such as P. carinii pneumonia should be added to the list of potential bronchopulmonary complications of antimetabolite immunosuppressive therapy of inflammatory bowel disease.