Hypersensitivity pneumonitis: the current state of the problem

Hypersensitive pneumonitis (HP) is an inflammatory interstitial lung disease (ILD) that occurs in predisposed individuals in response to repeated exposure to various aerosol antigens. In 2020 and 2021, specialists made changes to the latest clinical recommendations, to the classification of HP, allowing to distinguish between fibrous and non-fibrous types of HP. The fibrous type is associated with the progression of the disease and an unfavorable prognosis. The diagnosis of HP and its division into types are based on a combination of clinical and anamnestic data, a high-resolution computed tomography (HRCT) picture, the results of cytological examination of bronchoalveolar lavage (BAL) and lung biopsy. Specialists also use lung function tests to determine the progression of the disease. The key diagnostic method is high-resolution computed tomography, which reveals signs of lung tissue pathology ("frosted glass", mosaic density) and signs of damage to the small respiratory tract (centrilobular foci, air traps). In fibrotic HP, experts have identified signs of fibrosis: traction bronchiectasis, reticular changes, decreased lung volume, and the formation of a "cellular lung" is possible. Non-fibrotic HP is characterized by: lymphocytic cytogram type (more than 30% of the total number of cells), while in fibrotic HP lymphocytosis is less common. Experts often use lung biopsies for differential diagnosis with other diseases. In nonfibrotic HP, scientists evaluate the signs of involvement of bronchioles and adjacent alveoli in the inflammatory process, the nature of inflammatory infiltration and the presence of granulomas. Fibrotic HP has bronchiolocentric fibrosis, chronic interstitial pneumonia, peribronchiolar metaplasia and other signs. HP therapy includes the elimination of contact with the antigen, the administration of glucocorticosteroids and/or immunosuppressants, as well as antifibrotic therapy in the presence of a progressive variant of fibrous HP.