A 58-year-old man presented with dyspnea on exertion and diffuse ground-glass opacities with mosaicism on chest computed tomography in April 201X. A transbronchial lung biopsy revealed organizing pneumonia and lymphocytic infiltration, and steroids were administered. During steroid tapering, the shortness of breath and ground-glass opacities recurred, and a transbronchial lung re-biopsy revealed organizing pneumonia without a granuloma again. Based on the clinical history, imaging features, and amount of humidifier usage, hypersensitivity pneumonitis caused by a humidifier was suspected. The inhalation challenge test was considered positive, and the diagnosis was confirmed. There have been some reports of unidentified granuloma in patients with humidifier lungs. Therefore, this case suggests that humidifier lung should be considered as a possibility even if pathological examination does not reveal granulomas and inflammatory changes such as organizing pneumonia are the only findings.
Keywords: endotoxin; granuloma; humidifier lung.