Hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP), also known as extrinsic allergic alveolitis, is an immunologically induced inflammatory disease involving the lung parenchyma and terminal airways secondary to repeated inhalation of an inciting agent in a sensitized host. The inciting agent may be derived from a wide variety of fungal, bacterial, animal, or chemical sources. Three clinical presentations are generally recognized: acute, subacute, and chronic. The clinical course associated with HP is variable. With early diagnosis and avoidance of the offending antigen, the prognosis tends to be favorable and permanent respiratory impairment can be avoided. However, chronic forms of HP may be complicated by development of pulmonary fibrosis and progressive respiratory insufficiency.

Histopathologic evidence of fibrosis on surgical lung biopsy has been associated with reduced survival in patients with HP and allows for identification of patients at higher risk of mortality. However, surgical lung biopsy is not commonly employed in the diagnosis of HP. In contrast, high-resolution CT (HRCT) is routinely obtained in the course of evaluating patients with interstitial lung diseases. HRCT features of HP are well recognized and include a spectrum of abnor-malities. In this study, we sought to correlate HRCT evidence of parenchymal fibrosis with survival in a consecutive series of patients with HP seen at our tertiary care medical center.

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