Clinical and morphological characteristics of hypersensitivity pneumonitis

Hypersensitivity pneumonitis (HP) is an immune-mediated disease that manifests in susceptible individu-als after exposure to a provoking inhalation factor. The literature review describes etiological factors of the disease, its epidemiology and pathogenesis, as well as clinical features of various disease courses. A new clinical and morphological classification of HP is also presented. We analyzed changes in functional tests (external respiration function), CT images, cellular components of bronchoalveolar lavages, and modern approaches to the disease treatment. The review includes detailed morphological criteria according to the new classification, which will facilitate the diagnosis by pathologists. Since the diagnosis of the condition presents significant challenges, there are histological criteria for differential diagnosis of the fibrotic HP and usual interstitial pneumonia (idiopathic pulmonary fibrosis), sarcoidosis, lymphoid interstitial pneumonia, and pulmonary manifestations of connective tissue diseases. Keywords: hypersensitivity pneumonitis, interstitial lung diseases