A 50-year-old woman presents with a 4-week history of fever, shoness of breath and dry cough. She repos that her chest feels "tight." The patient is a pigeon fancier. Blood tests show leukocytosis and neutrophilia, an elevated erythrocyte sedimentation rate and increased levels of immunoglobulins and C-reactive protein. A lung biopsy reveals poorly formed granulomas composed of epithelioid macrophages and multinucleated giant cells. Which of the following is the appropriate diagnosis?

Hypersensitivity pneumonitis (extrinsic allergic alveolitis) is a response to inhaled antigens. The inhalation of a variety of antigens leads to acute or chronic interstitial inflammation in the lung. Hypersensitivity pneumonitis may develop in response to repeated exposure to a variety of organic materials (e.g., bird droppings, feathers, mushrooms and tree bark). Histologically, the lung contains poorly formed granulomas, which differ from the compact (solid) noncaseating granulomas of sarcoidosis and the caseating granulomas of tuberculosis or histoplasmosis.