Disease pathology in fibrotic interstitial lung disease: is it all about usual interstitial pneumonia?

The interstitial pneumonias comprise a diverse group of diseases that are typically defined by their cause (either idiopathic or non-idiopathic) and their distinct histopathological features, for which radiology, in the form of high-resolution CT, is often used as a surrogate. One trend, fuelled by the failure of conventional therapies in a subset of patients and the broad-spectrum use of antifibrotic therapies, has been the focus on the progressive fibrosing phenotype of interstitial lung disease. The histological pattern, known as usual interstitial pneumonia, is the archetype of progressive fibrosis. However, it is clear that progressive fibrosis is not exclusive to this histological entity. Techniques including immunohistochemistry and single-cell RNA sequencing are providing pathogenetic insights and, if integrated with traditional histopathology, are likely to have an effect on the pathological classification of interstitial lung disease. This review, which focuses on the histopathology of interstitial lung disease and its relationship with progressive fibrosis, asks the question: is it all about usual interstitial pneumonia?

Automated summary

Interstitial pneumonias encompass a diverse group of diseases with distinct histopathological features, often defined by their cause. There is a growing focus on the progressive fibrosing phenotype of interstitial lung disease, particularly due to the failure of conventional therapies in some patients and the widespread use of antifibrotic therapies. Apart from the typical usual interstitial pneumonia, other histological entities are also associated with progressive fibrosis, and techniques like immunohistochemistry and single-cell RNA sequencing are providing pathogenetic insights that could impact the pathological classification.