Current Findings on Progressive Fibrosis in Interstitial Lung Disease
Leading pulmonologists around the world recently published the first of a series of three review articles on interstitial lung disease in The Lancet Respiratory Medicine journal. This article focuses on histopathology and the relationship of this disease with lung fibrosis. It also addresses the question of whether progressive lung tissue fibrosis pertains only to usual interstitial pneumonia.
Heterogeneous Group of Diseases
Interstitial pneumonia represents a heterogeneous group of diseases usually defined based on cause (idiopathic or non-idiopathic) and histopathological appearance, sometimes replaced by high-resolution computed tomography (HRCT) images. Recently, due to the failure of conventional therapies and the use of antifibrotic treatments, attention has been drawn to the progressive fibrotic phenotype of interstitial lung disease. The archetype of lung fibrosis is so-called usual interstitial pneumonia.
Findings on Progressive Fibrosis and Their Implications for Practice
Histopathological findings in interstitial lung disease and the technologies used, such as immunohistochemistry methods or single-cell RNA sequencing, provide new insights into the mechanisms that trigger and characterize progressive lung fibrosis. However, progressive fibrosis does not only appear in usual interstitial pneumonia (a histological unit defined by hematoxylin-eosin staining), but we also find it in a subset of idiopathic and non-idiopathic interstitial pneumonias.
In a significant portion of cases of interstitial lung disease with non-idiopathic fibrosis, fibrosis is primarily induced by inflammation and excessive immune system activity. Yet in some of these cases, fibrosis progresses despite immunosuppressive treatment. To find an effective disease-modifying therapy, it will be necessary to identify the pathophysiological mechanisms mediated and not mediated by the immune system and their contribution to fibrosis progression in the individual patient. Identifying the characteristics of the various types of interstitial lung disease that protect against fibrosis progression will be equally important.
Conclusion
The cornerstone in the fight against interstitial lung disease is histopathology using sophisticated diagnostic tools such as immunohistochemical methods and molecular biology.
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Source: Renzoni E. A., Poletti V., Mackintosh J. A. Disease pathology in fibrotic interstitial lung disease: is it all about usual interstitial pneumonia? Lancet 2021 Oct 16; 398 (10309): 1437−1449, doi: 10.1016/S0140-6736(21)01961-9.
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