Organizing pneumonia in Crohn's disease: a case report and literature review.

Organizing pneumonia (OP) is a rare pulmonary manifestation in patients with inflammatory bowel disease (IBD). Distinguishing between a primary extra-intestinal manifestation of Crohn's disease (CD) and mesalazine-induced lung injury remains a major clinical challenge, as both conditions are steroid-responsive. We report the case of a 31-year-old woman with CD who developed progressive dyspnea and migratory pulmonary infiltrates one month after initiating mesalazine. Laboratory findings revealed marked peripheral eosinophilia (1276/mm3) and a mixed eosinophilic bronchoalveolar lavage profile (30.8%). Histopathology confirmed OP with Masson bodies. Due to the diagnostic overlap, mesalazine was replaced by azathioprine, and systemic corticosteroid therapy (0.75 mg/kg) was initiated. Complete radiological resolution was achieved at 8 months. This case illustrates the diagnostic complexity of eosinophilic-rich OP in CD and emphasizes that while pathology confirms the pattern, the etiology often remains a dual hypothesis between systemic disease and drug toxicity.