Updates in hypersensitivity pneumonitis

14 Oct 2022 15:00 15:30

Hypersensitivity pneumonitis (HP) is an immune-mediated interstitial lung disease caused by recurrent exposure to inciting antigen in genetically susceptible individuals. It mimics other acute and chronic pulmonary diseases and is quiet often misdiagnosed as idiopathic pulmonary fibrosis or another idiopathic interstitial pneumonia if the history of exposure to the inducer is not elicited. There was a long time unmet need for new guideline on HP since the last one was more than 30 years old and outdated. Recently two new guidelines have consecutively emerged, one ATS guideline published in AJRCCM 2020 and the second one being published 2021 in CHEST. Both guidelines come with concept of fibrotic and non fibrotic HP, which reflects properly the difference of the two main phenotypes of HP with distinct radiologic and histopathologic findings and clinical behaviour. The need for identification of inciting antigen not only for the diagnosis and management but also for assessing prognosis is crucial and is a initial part of diagnostic process in both guidelines. High resulution computed tomography is crucial for HP diagnosis and lymphocytosis in bronchoalveolar lavage (BAL) suppports the diagnosis as well. However, the approach to bronchoscopy with BAL is different. While BAL is obligatory part of diagnostic process in the ATS guidelines, in the CHEST guidelines bronchoscopy is not recommended when clinical picture, exposure and radiologic findings fit the HP diagnosis. Biopsy is applied in both guidelines in case the HP diagnosis is not sure. While the CHEST guideline does not comment on type of biopsy, the ATS guideline for the first time establishes a role of cryobiopsy in the fibrotic form of HP. The two guidelines bring reasonable approach to diagnosis of this phenotypically diverse disease based on complex and multidisciplinary approach with central role of multidisciplinary discussion. Treatment of HP is based on the phenotype of the disease, i.e. in nonfibrotic corticosteroids can be used either alone or in combination with other immunosuppressants, i.e. azathioprne or mycophenolate mophetil. If the disease is fibrotic and fulfills criteria of progressive pulmonary fibrosis, nintedanib is a method of choice. For advanced HP lung transplantation might be a solution for some individuals. Complex palliative and symptomatic care is the best approach for all patients with advanced HP.