Real-life prevalence of progressive fibrosing interstitial lung diseases

Abstract

The concept of progressive fibrosing interstitial lung disease (PF-ILD) has recently emerged. However, real-life proportion of PF-ILDs outside IPF is still hard to evaluate. Therefore, we sought to estimate the proportion of PF-ILD in our ILD cohort. We also determined the proportion of ILD subtypes within PF-ILD and investigated factors associated with PF-ILDs. Finally, we quantified interobserver agreement between radiologists for the assessment of fibrosis. We reviewed the files of ILD patients discussed in multidisciplinary discussion between January 1st 2017 and December 31st 2019. Clinical data, pulmonary function tests (PFTs) and high-resolution computed tomography (HRCTs) were centrally reviewed. Fibrosis was defined as the presence of traction bronchiectasis, reticulations with/out honeycombing. Progression was defined as a relative forced vital capacity (FVC) decline of ≥ 10% in ≤ 24 months or 5% < FVC decline < 10% and progression of fibrosis on HRCT in ≤ 24 months. 464 consecutive ILD patients were included. 105 had a diagnosis of IPF (23%). Most frequent non-IPF ILD were connective tissue disease (CTD)-associated ILD (22%), hypersensitivity pneumonitis (13%), unclassifiable ILD (10%) and sarcoidosis (8%). Features of fibrosis were common (82% of CTD-ILD, 81% of HP, 95% of uILD). After review of HRCTs and PFTs, 68 patients (19% of non-IPF ILD) had a PF-ILD according to our criteria. Interobserver agreement for fibrosis between radiologists was excellent (Cohen's kappa 0.86). The main diagnosis among PF-ILD were CTD-ILD (36%), HP (22%) and uILD (20%). PF-ILD patients were significantly older than non-F-ILD (P = 0.0005). PF-ILDs represent about 20% of ILDs outside IPF. This provides an estimation of the proportion of patients who might benefit from antifibrotics. Interobserver agreement between radiologists for the diagnosis of fibrotic ILD is excellent.

Figure 1

Relative proportion of ILD subtypes within all ILD (panel A). Panel (B) shows CTD subgroups within CTD-ILD. Panel (C) shows ILD subclasses (based on fibrosis, inflammation and progression) within the whole population and panel (D) the proportion of ILD within non-IPF PF-ILD.

Figure 2

Proportion of fibrosing ILD (panel A), progressive and fibrosing ILD (panel B) and merge (panel C) within ILD subgroups.

Figure 3

Example of a patient suffering from fibrosing hypersensitivity pneumonitis. 10 month follow-up high-resolution CT scan shows progression of fibrosis with honeycombing (white arrows). Longitudinal pulmonary function tests demonstrate decline of both forced vital capacity and lung diffusion capacity. FVC: forced vital capacity; DLCO: lung diffusion capacity.

Figure 4

Clinical factors associated with ILD. Panel A shows a significant difference in age between IPF, PF-ILD/F-ILD and non-F-ILD (statistics, ANOVA followed by Holm-Sidak’s multiple comparisons test. Panel B shows transplant-free survival of IPF (grey line), PF-ILD (red line) and non-F-ILD (blue line) and Non-F-ILD (green). Statistics: Log-Rank test.