Small airway lesions appear with the course of IPF and relate to the severity of pulmonary fibrosis progression.

Aim: Idiopathic Pulmonary Fibrosis (IPF) has long been considered a disease primarily involving the lung interstitium, with relative sparing of the airways. This study aimed to investigate the presence and characteristics of small airway abnormalities in patients with IPF.

Methods: We analyzed 137 patients with IPF and 84 controls from a prospective, multicenter cohort (trial registration: NCT03666234). IPF patients were stratified by fibrosis severity on CT and clinical disease severity scores. Small airway function was assessed using predicted maximal expiratory flow at 25% (MEF25%), 50% (MEF50%), and 25-75% of forced vital capacity (MEF25-75%). Airway segmentation and quantitative analysis of airway number, length, and volume were performed using FACT-Digital Lung™ software. Group differences were analyzed using SPSS (version 26).

Results: The IPF group comprised 114 men and 23 women, with a mean age of 64.5 ± 10.7 years. MEF50%, MEF25%, and MEF25-75% were significantly lower in IPF patients than in controls across all severity stages. Conversely, the total number, length, and volume of segmented bronchi were higher in IPF patients, with the most pronounced differences observed in bronchi at generations 9-14. Small airway abnormalities were evident even in patients with mild fibrosis.

Conclusion: Small airway abnormalities, including increased airway counts and functional impairment, are detectable in early-stage IPF and persist throughout disease progression, suggesting that small airway involvement is a fundamental feature of IPF.