Unilateral methotrexate-induced pneumonitis

To date, all reported cases of methotrexateinduced pneumonitis had bilateral pulmonary parenchymal involvement. The authors describe the development and probable pathogenesis of unilateral methotrexate-induced pneumonitis in a patient with carcinoma of the tonsil that was metastatic to the lung and produced unilateral pulmonary artery obstruction.