Expanded detection of early fibrotic phenotypes using lobar traction bronchiolectasis in lung cancer screening

Abstract Rationale Lung cancer screening regularly identifies participants with interstitial lung abnormalities (ILA). Existing classification methods may underestimate the prevalence of clinically relevant ILA phenotypes. Objectives Can a classification system for ILAs developed in a lung cancer screening setting identify clinically relevant phenotypes? Methods Classification criteria based on the presence and lobar extent of traction bronchiolectasis (TBe) were developed internally by expert consensus. Categories included: no ILA, non-fibrotic ILA (NF-ILA), fibrotic ILA (F-ILA), and undiagnosed fibrotic ILD (U-ILD). Interobserver agreement was calculated between two readers. Clinical characteristics, respiratory hospitalisations, and survival were compared between participants of different ILA grades. Measurements and Main Results 8,169 participants were included in the final analysis. TBe showed improved interobserver agreement compared to the American Thoracic Society (ATS) classification, identifying 344 participants (4%) with U-ILD, 86% more than the ATS classification. An additional 405 had F-ILA (5%) and 667 had NF-ILA (8%). Compared to participants without ILA, participants with U-ILD had a higher rate of respiratory hospitalisation (IRR = 4.4, 95% CI 2.7–7.5, P .001) and increased risk of death (aHR = 2.4, 95% CI 1.9–3.0, P .001). Increasing ILA grade was associated with higher modified Medical Research Council dyspnoea scores (OR = 1.1, 95% CI 1.0–1.1, P = .02). Conclusions In a lung cancer screening setting, an ILA scoring system focused on lobar traction bronchiolectasis identifies more high-risk participants and demonstrates improved interobserver concordance than the ATS classification. TBe identifies participants with a respiratory phenotype who may warrant further investigation and follow up.