Differences in the progression among mild, moderate and severe pulmonary fibrosis on HRCT scan in Usual Interstitial Pneumonia (UIP) cohort in the United Arab Emirates (UAE)

<bold>Background:</bold> UIP is a progressive fibrotic lung disease defined in 2022 ATS/ERS Clinical Practice Guideline into definite, probable and indeterminate based on high resolution CT scan (HRCT) with different potential risk of progression. <bold>Aim:</bold> To determine statistical difference in number of patients who had progression of fibrosis on their last follow up HRCT among predefined subgroups of mild, moderate and severe fibrosis on baseline HRCT. <bold>Methods:</bold> This is a retrospective study of 98 consecutive patients of UIP diagnosed between January 2015 and June 2023 at a tertiary center. The diagnosis of UIP was based on multidisciplinary team decision constituted of two pulmonologists experts in IPF and a radiologist. 76 patients of definite or probable UIP were analyzed. The degree of fibrosis at baseline (˂10% 10-30% and ˃30%) and progression were based on the first and last HRCT respectively over the follow-up period using predefined visual scoring. <bold>Results:</bold> <fig><object-id>erj;64/suppl_68/PA4753/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> There was no difference in progression between probable and definite UIP group (41% vs. 59%, respectively, P=0.95). <bold>Conclusion:</bold> To our knowledge, this is the first study comparing definite/probable UIP patients in terms of fibrosis progression based on predefined severity of fibrosis on HRCT. The significant increase in mortality in the severe group could have confounded the results.