Idiopathic pulmonary fibrosis: significance of the usual interstitial pneumonia (UIP) CT-scan patterns defined in new international guidelines

Abstract Introduction. The new 2018 international guidelines for diagnosing usual interstitial pneumonia (UIP)/idiopathic pulmonary fibrosis (IPF) by CT scan split the old pattern possible UIP (2011 IPF guidelines) into two new patterns: probable UIP and indeterminate for UIP. However, the proportions and prognoses of these new CT-scan patterns are not clear. Methods. We used a monocentric retrospective cohort of 322 patients suspected of having IPF (University Hospital of Rennes; Competence Center for Rare Lung Diseases; 1 January 2012-31 December 2017). All patients initially diagnosed by CT scan as possible UIP were included. The chest CT-scans were then reclassified according to the new 2018 international guidelines by 3 observers. These data were then subjected to survival analysis with multivariate Cox regression using a composite endpoint of death, lung transplantation, a decline of ≥ 10% in forced vital capacity (FVC), or hospitalization. Results. Of the 89 possible UIP patients included, 74 (83%) were reclassified as probable UIP and 15 (17%) as indeterminate for UIP. Probable UIP patients were more likely to meet the composite endpoint (56/74 [75.7%] vs. 5/15 [33%] patients; HR [IC 95%] = 3.12 [1.24 ; 7.83], p=0.015). Multivariate analysis indicated that the probable UIP pattern was associated with significantly increased risk of reaching the composite endpoint (HR [95% CI] = 2.85[1.00; 8.10], p=0.049). Conclusion. The majority of possible UIP diagnoses corresponded to probable UIP, which was associated with a significantly worse prognosis than indeterminate for UIP. This distinction between these two CT patterns emphasizes the relevance of the new international guidelines for the diagnosis of IPF.