Presentation, diagnosis and clinical course of the spectrum of progressive-fibrosing interstitial lung diseases.

Although these conditions are rare, a proportion of patients with interstitial lung diseases (ILDs) may develop a progressive-fibrosing phenotype. Progressive fibrosis is associated with worsening respiratory symptoms, lung function decline, limited response to immunomodulatory therapies, decreased quality of life and, potentially, early death. Idiopathic pulmonary fibrosis may be regarded as a model for other progressive-fibrosing ILDs. Here we focus on other ILDs that may present a progressive-fibrosing phenotype, namely idiopathic nonspecific interstitial pneumonia, unclassifiable idiopathic interstitial pneumonia, connective tissue disease-associated ILDs (e.g. rheumatoid arthritis-related ILD), fibrotic chronic hypersensitivity pneumonitis, fibrotic chronic sarcoidosis and ILDs related to other occupational exposures. Differential diagnosis of these ILDs can be challenging, and requires detailed consideration of clinical, radiological and histopathological features. Accurate and early diagnosis is crucial to ensure that patients are treated optimally.