Hypersensitivity pneumonitis

Abstract

Hypersensitivity pneumonitis (HP), previously called extrinsic allergic alveolitis, is a form of diffuse interstitial lung disease resulting from sensitization to an inhaled antigen, involving complex hypersensitivity reactions types III and IV. The disease can be caused by multiple agents that are present at work places and at home, such as microbes, animal and plant proteins, organic and inorganic chemicals. HP is classified as acute/subacute or chronic, depending on the intensity and frequency of exposure to causative antigens. Diagnostic criteria have been proposed, based on exposure, clinical presentation, lung function tests, imaging findings, bronchoalveolar lavage, and biopsies. Being an immune reaction in the lung, the most obvious treatment of HP is avoidance of the contact with the offending antigen, although the complete removal is not always possible. Systemic corticosteroids represent the only reliable pharmacologic treatment of the disease, but they do not alter the long-term outcome, and prognosis is poor, leading to irreversible lung damage in the form of fibrosis or emphysema, respiratory insufficiency and even death.