An unusual but unmissable link between summer-type hypersensitivity pneumonitis and asthma in an old house.

While hypersensitivity pneumonitis (HP) and asthma are usually recognized as different disease entities based on their different allergic mechanisms, they may have some connections. A previously healthy 54-year-old Japanese man with no history of allergic diseases was hospitalized due to fever and breathlessness. He had lived in an old musty wooden house. He was diagnosed with acute summer-type HP induced by Trichosporon asahii based on bilateral ground-glass opacities on chest computed tomography (CT), a high titer of serum anti-T. asahii antibody, an increased number of lymphocytes and a decreased CD4/CD8 ratio in bronchoalveolar lavage fluid (BALF) and lung pathology suggestive of HP. However, untypical increased eosinophils in BALF (25.2%) and infiltrative eosinophils around bronchial walls were observed. After systemic corticosteroid treatment was started, he recovered, and was discharged with oral prednisone. However, two weeks after returning to his former house, he had fever and severe cough, and was re-hospitalized. While chest CT showed no abnormal shadows indicating a worsening of HP, pulmonary function test revealed a typical obstructive defect and eosinophilic inflammation in his sputum. He spontaneously recovered after re-hospitalization without increasing any treatments. During this second hospitalization, he was diagnosed with asthma, although it remains to be determined whether both HP and asthma were caused by T. asahii. Clinicians should not miss the possible overlapping presentations between HP and asthma, caused by environmental antigens.