A case report of mesalazine-induced lung injury: A reversible drug side effect

Mesalazine is widely used in the treatment of the acute and maintenance phase of ulcerative colitis (UC). The possibility of interstitial lung disease being induced by mesalazine in the form of eosinophilic pneumonia, organizing pneumonia, and nonspecific interstitial pneumonia has been acknowledged for decades. However, mesalazine-related hypersensitivity pneumonitis (HP) constitutes an infrequent entity.

A 55-year-old Caucasian man, with a six-month medical history of UC under long-term maintenance treatment with oral mesalazine, presented with a week-long low-grade fever, dry cough and a diffuse bilateral centrilobular ill-defined micronodular pattern in chest imaging. On examination, he had dyspnea with hypoxemic respiratory failure. After extensive workup, potential differential diagnoses such as pulmonary infections were ruled out. Bronchoalveolar lavage (BAL) cellular analysis demonstrated a predominance of lymphocytes and an eosinophilia. The transbronchial biopsy findings confirmed lymphocytic alveolitis. The diagnosis of subacute HP was made with confidence because of the compatible clinical, radiographic, physiologic, BAL and histopathologic findings. Mesalazine withdrawal was decided. Substantial clinical improvement was promptly noticed. The fever abated within 24 hours alongside with a significant improvement of arterial oxygen saturation and lung function parameters. A radiological recovery was also gradually noticed.

Mesalazine-induced HP has been scarcely described in the literature. This Case indicates that HP is a rare but real entity in UC patients on continuous oral mesalazine treatment; its possibility should also be considered when unexplained respiratory symptoms develop during therapy. Amelioration of symptoms, imaging, and lung function improvement seem to occur only upon the abrupt drug discontinuation.