Extract
We read with great interest the article published in the European Respiratory Journal by Hambly et al. on the prevalence and characteristics of progressive fibrosing interstitial lung disease (ILD) in patients diagnosed with fibrotic ILD [1]. The study showed that half (50.1%) of 2,746 patients with fibrotic ILD develop progressive fibrosing ILD within 24 months and that the prevalence of progressive fibrosing ILD is 59% in idiopathic pulmonary fibrosis, 58% in hypersensitivity pneumonitis, 51% in unclassifiable ILD and 45% in connective tissue disease-associated ILD [1]. Interestingly, the study showed that the time to progression was similar between patients with idiopathic pulmonary fibrosis and hypersensitivity pneumonitis (HP) [1]. Our question is, what factor(s) associated with the development of disease progression in fibrotic HP? From previous studies, we learned that the inability to identify the inciting agent, increased age, smoking history, low lung function, and the presence of lung fibrosis are independent factors of poor prognosis in chronic HP patients [2, 3]. However, risk factors for disease progression in patients with fibrotic HP have not been described. A subgroup analysis in the fibrotic HP cohort assessed by Hambly et al. in this report could address this question [1]. Unfortunately, the authors did not show the results of the subgroup analysis. They only showed the independent risk factors of time to progression, including aging, male sex, decreased lung function, and gastroesophageal reflux disease in all patients with fibrotic ILD (table 5 of the reported article) [1]. Are these risk factors the same in fibrotic HP? A recent study has shown that the decline of forced vital capacity, which is one of the criteria used for the diagnosis of progressive fibrosing ILD, is very heterogenous and “strongly influenced by ILD subtype” [4]. Therefore, it would not be appropriate to generalize that the risk factors determined for all progressive fibrosing ILD patients may also apply to fibrotic HP or other subtypes of fibrotic ILD. Under the statistical analysis section, the authors stated that “subgroup analyses were performed to identify variables associated with time to progression for individual ILD subtypes” [1]. The results of this subgroup analysis would be particularly informative in HP, where avoidance of environmental factors (inciting antigen, active or passive smoking) or change of environment is the mainstay of the therapeutic approach [5, 6].
Footnotes
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Conflict of interest: All authors declared no conflict of interest regarding this correspondence.
- Received September 27, 2021.
- Accepted September 15, 2022.
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