Evolution of the ‘Indeterminate UIP’ HRCT pattern; a cohort snapshot

Background: The prognosis of IPF remains poor and identifying patients early may allow intervention which could limit progression. Objective: To evaluate the progression of patients with ‘Indeterminate UIP’ (iUIP) CT pattern to IPF. Method: We performed a retrospective analysis of an IPF cohort (n=240) seen in the Oxford ILD Service between 2013-2017, and analysed all HRCTs performed up to August 2019. HRCT images were re-categorised to meet 2018 IPF guidelines. Cases with iUIP were categorised as non-progressor or progressors. CT features, smoking history and co-morbidities were examined to explore potential contribution to progression. Results: 48 (19.6%) patients had an initial HRCT showing iUIP; mean age 75.6 yrs ±8.2 (SD); male 73%. 16 had only one CT; 13 discharged after 2.1 years. Of the remaining, 9 (28%) showed no change in CT over 2.1 ±0.9 yrs. 6 (19%) showed worsening of iUIP but no change in pattern over 3.1 ±0.8 yrs. 11 (34%) progressed to probable UIP over 3.8 ±1.6 years and 6 (19%) to definite UIP over 4.1 ±2.4 yrs. All those with definite or probable UIP were later diagnosed with IPF. Conclusion: In our cohort, 43% of evaluable iUIP patients progressed to IPF over 3.9 ±1.8 yrs. There was a trend towards greater first year lung function decline, presence of GGO on CT and previous smoking history in those progressing to IPF.