Long-Term Follow-Up of Interstitial Lung Abnormality: Implication in Follow-Up Strategy and Risk Thresholds

This study aimed to determine optimal follow-up strategies and extent thresholds for interstitial lung abnormality (ILA) outcomes using CT scans. It included self-referred participants aged 50 and older, including nonsmokers. Consecutive CT scans identified the initial and progressive stages of ILA, quantified using deep learning (AVIEW version 1.1.38.6). Out of 305 participants with a median follow-up of 11.3 years, 78.4% showed ILA on at least one CT scan. ILA progression occurred in 80.5% of participants with serial CT studies, and 17.3% progressed to usual interstitial pneumonia (UIP), with median progression times of 3.2 years and 11.8 years, respectively. Fibrotic ILA extent on CT was an independent risk factor for both ILA progression and UIP progression. Risk groups based on honeycombing and extent of fibrosis (1% in the whole lung or 5% per lung zone) showed significant differences in 10-year overall survival. The study suggests follow-up CT at 3-year intervals, with shorter intervals for those at higher risk based on fibrosis extent and honeycombing.