Hypersensitivity pneumonitis: A perspective from members of the pulmonary pathology society

Context.-Hypersensitivity pneumonitis (HP) is a lung disease that develops in susceptible individuals after inhalational exposure to an organic antigen or chemical compound. Pathogenesis is attributed to a combination of type III (immune complex-mediated) and type IV (delayed) hypersensitivity reactions to the inciting agent. Objective.-To provide an overview of the current status of the medical literature regarding hypersensitivity pneumonitis. Data Sources.-A literature search was performed using PubMed and Google search engines. The terms "hypersensitivity pneumonitis" and "extrinsic allergic alveolitis" were used, with the search starting on January 9, 2017, and concluding March 8, 2017. Conclusions.-As a pathologist, it is important to consider hypersensitivity pneumonitis when examining lung specimens because it is often clinically and pathologically overlooked. Recognizing the often subtle findings and correlating them with the patient's history or suggesting a thorough clinical investigation of potential exposures can be of help in identifying the underlying condition so that the patient can be appropriately managed.