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Hypersensitivity Pneumonitis: A Comprehensive Review


Spagnolo P1, Rossi G2, Cavazza A3, Bonifazi M4, Paladini I5, Bonella F6, Sverzellati N5, Costabel U6

1Medical University Clinic, Canton Hospital Baselland, and University of Basel, Liestal, Switzerland
2Section of Pathology, University Hospital of Modena, Modena, Italy
3Operative Unit of Pathology, Arcispedale S. Maria Nuova/I.R.C.C.S., Reggio Emilia, Italy
4Operative Unit of Pulmonology, Azienda Ospedaliero-Universitaria Ospedali Riuniti, Ancona, Italy
5Section of Diagnostic Imaging, Department of Surgery, University of Parma, Parma, Italy
6Interstitial and Rare Lung Disease Unit, Ruhrlandklinik, University Hospital, University of Duisburg-Essen, Germany

J Investig Allergol Clin Immunol 2015; Vol. 25(4): 237-250



Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is a complex pulmonary syndrome mediated by the immune system and caused by inhalation of a wide variety of antigens to which the individual has been previously sensitized. The pathobiology of the disease is not fully understood, but in addition to the triggers that initiate the disease, host/genetic factors are likely to be important, as only a minority of exposed individuals develop HP. Due to the lack of a diagnostic gold standard, the diagnosis of HP is not straightforward and relies on the integration of a number of factors, including history of exposure, precipitating antibodies to the offending antigen, clinical features, bronchoalveolar lavage, and radiological and pathologic features. However, in the appropriate setting, a high index of suspicion is critically important and may obviate the need for more invasive tests.
Clinical presentation and natural history vary widely. Acute forms generally resolve without sequelae, while chronic forms, which are caused by persistent low-grade exposures, are associated with poor prognosis. Corticosteroids may be useful in acute episodes for symptomatic relief or in chronic and progressive disease, but their long-term efficacy has never been validated in prospective clinical trials. Ideally, patients with HP should be referred to centers with expertise, as the overlap with other forms of interstitial lung disease may be substantial. Making the correct diagnosis has critical therapeutic and prognostic implications.

Key words: Hypersensitivity pneumonitis. Extrinsic allergic alveolitis. Idiopathic pulmonary fibrosis. Interstitial lung disease. Pathogenesis. Differential diagnosis. Management.