Likelihood of Usual Interstitial Pneumonia: A Novel Approach to Prognosis for Pulmonary Fibrosis

Background and Objectives: In fibrotic lung disease, radiological features of usual interstitial pneumonia (UIP) are associated with adverse outcomes. The aim of this study was to evaluate the likelihood of definite UIP on HRCT as a determinant of outcome in patients with pulmonary fibrosis. Methods: All available HRCT from the Australian IPF Registry (AIPFR) were retrospectively reviewed by two radiologists. The radiologists were asked to assign a likelihood (%) within each of the four ATS/ERS/JRS/ALAT 2018 UIP categories, summating to 100%, enabling them to not be constrained by a single UIP category (e.g., 5% definite UIP, 95% alternative to UIP). Likelihood of UIP was defined as the percentage likelihood score for the definite UIP category. Semi-quantitative features were also estimated. Cox proportional hazards regression was performed to evaluate the prognostic utility of the likelihood scores. Results: HRCT was available for analysis in 515 patients. Median follow-up of the cohort was 4.1 years (IQR 2.0–6.2 years). Median total ILD extent was 30% (IQR20-45%), with traction bronchiectasis and honeycombing present in 96.3% and 45.4% of cases respectively, and all three variables were associated with worse transplant-free survival. A pattern of definite or probable UIP was favoured in 26.4% and 32.4% of cases respectively. Likelihood of definite UIP was independently associated with both reduced transplant-free survival (HR1.12, 95% CI 1.04–1.20; p = 0.002) and 12-month progression (HR1.19, 95% CI 1.04–1.35; p = 0.009) and was superior to the ATS/ERS/JRS/ALAT 2018 guideline-based categories for these associations. Conclusions: We demonstrate that estimation of the likelihood of definite UIP is strongly associated with transplant-free survival and 12-month disease progression.