Bronchiolitis obliterans in a patient with ulcerative colitis receiving mesalamine

An 18-year-old woman with ulcerative colitis (UC) developed diffuse pulmonary infiltrates and hypoxemia three months after reinstitution of oral mesalamine. Lung biopsy revealed bronchiolitis obliterans with interstitial pneumonitis. Clinical and radiographic abnormalities improved upon discontinuation of mesalamine and treatment with corticosteroids. This patient presented the problem of differential diagnosis of pulmonary disease associated with inflammatory bowel disease (IBD), including lesions believed to result from lung involvement secondary to IBD, as well as adverse reactions to medications. We present and analyze evidence associating mesalamine with pulmonary toxicity in this patient, but emphasize that the distinction between adverse drug reaction and extraintestinal manifestations of IBD is difficult.