Prognostic Factors in Patients with Idiopathic Pulmonary Fibrosis; Evaluation using Quantitative CT Analysis of Fibrosis and Emphysema

Background: A considerable portion of patients with idiopathic pulmonary fibrosis (IPF) has smoking history and emphysematous lesions. However, the prognostic factors of combined pulmonary fibrosis and emphysema in IPF are controversial. Recently, it is reported that there is no prognostic impact of visualized emphysema in IPF. However, no reports used non-visualized quantitative computed tomography (CT) analysis of both emphysema and fibrosis. The aim of this study was to assess the extent of fibrosis and/or emphysema quantitatively and to predict the mortality in IPF. Methods: Chest CTs of 300 IPF patients were retrospectively evaluated. We quantified CT Honeycombing Area (HA), which is low density area surrounded by thick wall, as fibrosis, and subtracted Low Attenuation Area (sLAA), which is low density area surrounded by thin wall, as emphysema. The percentage of HA and sLAA to total lung area were also calculated (%HA and %sLAA, respectively). Results: The median %HA and %sLAA were 3.2% and 7.5%, respectively. On survival analysis adjusted by age, gender, BMI, and pack-years, continuous %HA was a predictor of mortality (HR: 1.165, p<0.0001), whereas continuous %sLAA was not (HR: 0.986, p=0.229). When binarized with each median value, both %HA≥3.2% and %sLAA≥7.5% were predictors of mortality (HR: 2.708, p<0.0001 and HR: 0.596, p=0011, respectively). However, on the multivariate analysis, only %HA≥3.2% was a predictor (HR: 2.562, p<0.0001). Conclusions: The extent of fibrosis assessed by quantitative CT is a prognostic factor of IPF. On the other hand, the extent of emphysema has no prognostic impact when corrected by the extent of fibrosis.