• idiopathic pulmonary fibrosis
• imaging/CT MRI etc

The prevalence of interstitial lung disease (ILD) is high and progressively increasing.1 Mortality and morbidity vary according to ILD subtype, but overall median survival is poor, ranging from 5 to 14 years.2 Irrespective of classification and cause of lung fibrosis, several patients present with progressive-fibrosing ILD (PF-ILD), characterised by a rapid decline in lung function.3

A recent landmark study demonstrated a reduction in PF-ILD disease progression using costly antifibrotic drugs.4 However, half of patients with ILD do not benefit from these expensive antifibrotic drugs but could be better treated with anti-inflammatory or combined treatment. Hence, there is an unmet need for a monitoring tool to phenotype patients with ILD by assessing the amount of pulmonary fibrosis and inflammation to guide treatment choices and monitor response.3

Current monitoring, namely, high-resolution CT (HRCT) and pulmonary function test, cannot differentiate between fibrotic lung disease and active inflammation.3 5 Histology can make this distinction, but biopsy is a high-risk procedure not routinely performed in patients with ILD. Conversely, chest MRI can offer a one-stop-shop solution for ILD providing structural and functional information in a single examination, such as ventilation inflammation perfusion and structure (VIPS-MRI).6 Using VIPS-MRI, both lung fibrosis and inflammation can be detected to select the best cost-effective treatment and to monitor its effect.7

In line with this concept, the interesting article published in this issue of Thorax, Weatherley and colleagues proposed a semiquantitative image measure of pulmonary perfusion based on the first pass of gadolinium-based contrast agent using dynamic contrast-enhanced MRI in a cohort of patients with PF-ILD. The study compares the full-width at half-maximum (FWHM_mean) of the dynamic contrast curve averaged over the whole lung as an estimate of global pulmonary perfusion response to IPF and possible change in disease severity between baseline and a 6-month follow-up study. A second semiquantitative measure of the IQR of the distribution of FWHM values over the whole lung (FWHM IQR) is used as a candidate measure of pulmonary perfusion heterogeneity. The study presents promising and clinically relevant first results of pulmonary perfusion quantification as measure of disease progression and response to treatment in PF-ILD. New biomarkers are needed to evaluate progression of PF-ILD at earlier stages of disease.3 Previous studies on CT using quantitative methods, such as CALIPER, have clearly shown the close relationship between vascular pruning and progression of fibrosis.8 Quantification of pulmonary vasculature and perfusion are therefore strong predictors of patient outcome in PF-ILD.9 This strongly supports further development of MRI to assess pulmonary perfusion as a possible biomarker of early progression in PF-ILD.7 Despite the small cohort, the FWHM_mean shows reasonable repeatability, which is crucial for the selection of robust biomarkers, and that could be further improved by protocol refinement.

A few uncertainties remain. The use of a semiquantitative surrogate for pulmonary perfusion might be influenced by cardiac output, which in elderly population of PF-ILD can be quite variable, especially when another cardiac comorbidity is present. The biomarker proposed as measure of perfusion heterogeneity showed marginal repeatability, so FWHM_mean seems a better candidate as image biomarker. Finally, it is unclear if the difference measured using FWHM_mean between the two time points is related to progression of fibrosis rather than a reflection of true underlying vascular injury.

Said that, the study of Watherley and colleagues can generate new momentum to innovate lung diagnostic of PF-ILD. It would be important to coordinate a joint effort for a multicentre study in an adequately selected group of patients with PF-ILD including measures of disease activity (eg, Krebs-von-den-Lungen 6, also known as KL-6), patient-reported outcome (eg, King’s Brief Interstitial Lung Disease) and quantitative HRCT biomarkers. Such validation will be crucial to introduce VIPS-MRI as a clinical tool for PF-ILD.