Reticulation is a Risk Factor of Progressive Subpleural non-Fibrotic Interstitial Lung Abnormalities

Rationale: Interstitial lung abnormalities (ILAs) are being increasingly identified in clinical practice. In particular for subpleural non-fibrotic ILAs, the risk of progression over time and the risk factors for progressive behavior are still largely unknown. Objectives: To determine the age band prevalence of ILAs and the risk of radiological progression of subpleural non-fibrotic ILAs over time in a large health check-up population, and to identify how reticulation contributes to the risk of radiological progression. Methods: Based on ILAs definition by the Fleischner Society, low-dose chest CT images from community-dwelling population undergone health check-up were evaluated for ILAs. Multivariable logistic regression was used to assess the risk of radiological progression. Measurements and Main Results: Among 155,539 individuals, 3,300 (2.1%) were confirmed to have ILAs: the vast majority (81.7%) were defined as subpleural non-fibrotic ILAs. The prevalence of ILAs increased linearly with age (P for trend<0.0001). Of 454 individuals with subpleural non-fibrotic ILAs, 198 (43.6%) had radiological progression over 4 years. The presence of reticulation on initial imaging was an independent predictor of radiological progression (OR 1.9; 95%CI 1.2-3.0, P=0.0040). No difference in radiological progression was identified between subpleural non-fibrotic ILAs with extensive reticulation and subpleural fibrotic ILAs (73.0% vs. 68.8%, P=0.7626). Conclusions: The prevalence of ILAs increases linearly with age. Nearly half of subpleural non-fibrotic ILAs progress radiologically over 4 years. The presence of reticulation is a risk factor for radiological progression. Subpleural non-fibrotic ILAs with extensive reticulation are likely to be a feature of subpleural fibrotic ILAs.