Abstract
A man in his 60s exhibited persistent dry cough and dyspnoea, which persisted even after smoking cessation. Chest high-resolution CT showed diffuse ground-glass opacities in the subpleural areas of both lungs. He underwent bronchoscopy, but no definitive diagnosis could be made. Histopathological analysis of the specimen obtained by surgical lung biopsy showed a desquamative interstitial pneumonia (DIP) pattern, with lymphocyte and plasma cell infiltrates in the alveolar septa; the ratio of IgG and IgG4-positive cells was more than 90%. He quit smoking, but the radiological findings worsened. Based on the pathological findings, we diagnosed the patient with DIP due to IgG4-related lung disease. Prednisolone was initiated, and the symptoms and radiological findings improved.