Acute eosinophilic pneumonia leading to acute respiratory failure in a current systemic corticosteroid user

A 69-year-old female patient visited the emergency room with fever (38.3℃) and dyspnea. She had been taking prednisolone (5 mg once per day) and methotrexate (2.5 mg once per week) for rheumatoid arthritis for 2 years. Chest computed tomography (CT) showed bilateral, multifocal ground glass opacity with interlobular septal thickening. Peripheral blood leukocyte count was 6,520/mm(3) (neutrophils, 77.4%; eosinophils, 12.1%). During the night, mechanical ventilation was initiated due to the development of severe hypoxemia. Bronchoalveolar lavage fluid showed a high proportion of eosinophils (49%). Her symptoms improved dramatically after commencement of intravenous methylprednisolone therapy. This is the first report of idiopathic acute eosinophilic pneumonia developing in a current user of systemic corticosteroids.