[Case of bird-related hypersensitivity pneumonitis in a farmer]

A 48-year-old female farmer presented to our hospital with shortness of breath and cough. Her partial pressure of arterial oxygen (PaO2) level on room air was 58.4Torr, and chest computed tomography (CT) showed centrilobular ground-glass micronodules. She was admitted for further evaluation. After admission, symptoms, PaO2, and radiological findings improved without any treatment; however, her symptoms recurred when she returned to work. Exposure to her house did not elicit any symptomatic response. We initially suspected farmer's lung, but inhalation provocation tests with hay showed no significant change in symptoms, laboratory data or radiological findings. Antibody tests for Thermoactinomyces vulgaris or Saccharopolyspora rectivirgula were negative. Because many pigeons were found roosting on her farm, we suspected bird-related hypersensitivity pneumonitis. Precipitating antibodies testing against pigeon serum and IgG and IgA antibodies testing against pigeon dropping extracts were all positive, and bird-related hypersensitivity pneumonitis was diagnosed. Because typically, many birds roost on farms, not only farmer's lung, but also bird-related hypersensitivity pneumonitis, should be included in a differential diagnosis when a farmer clinically suspected to have hypersensitivity pneumonitis is encountered.