Remission of hypersensitivity pneumonitis after allogeneic hematopoietic stem cell transplantation

A 50-year-old man was diagnosed with hypersensitivity pneumonitis caused by the environment of his bar owing to worsening symptoms, laboratory test results, and computed tomography images after an environmental inhalation challenge test. His hypersensitivity pneumonitis exacerbated despite receiving prednisolone 20 mg/day. The patient underwent allogeneic hematopoietic stem cell transplantation (HSCT) from a human leukocyte antigen-matched unrelated donor for myelodysplastic syndrome. No exacerbation of hypersensitivity pneumonitis was observed after HSCT. An environmental inhalation challenge test involving exposure to his bar confirmed the remission of hypersensitivity pneumonitis after HSCT. This case demonstrates that hypersensitivity pneumonitis can be remitted by HSCT.