RESUMEN
75-year-old man had the right lower lobe resected because of pulmonary adenocarcinoma (stage IIB) and received 4 courses of postoperative chemotherapy 4 years earlier. Thereafter, he continued to complain of cough, sputum, and progressive exertional breathlessness. The preoperative chest CT showed ground glass opacity (GGO) at the bottom of both lung fields, and over time the GGO changed to honeycombing with traction bronchiectasis. He was administered prednisolone, clarithromycin, and pirfenidone but with little improvement. He exhibited hypoxemia (PaO<sub>2</sub> 56 mmHg) and was admitted. An interview revealed that he had worked in the poultry farming business for 45 years having had contact with and breeding 3,000 game fowl at the time of hospitalization. We suspected bird-related hypersensitivity pneumonitis. Results of the reaction to pigeon dropping extracts (PDE) were high, with PDE IgG 0.697 and PDE IgA 0.445. He was diagnosed with chronic bird-related hypersensitivity pneumonitis. Although the chest CT appearance was difficult to distinguish from that of idiopathic interstitial pneumonia, the test for PDE and the interview were useful for reaching a diagnosis.