Pulmonary ¹⁸F-FDG uptake helps refine current risk stratification in idiopathic pulmonary fibrosis (IPF)

There is a lack of prognostic biomarkers in idiopathic pulmonary fibrosis (IPF) patients. The objective of this study is to investigate the potential of ¹⁸F-FDG-PET/ CT to predict mortality in IPF.

A total of 113 IPF patients (93 males, 20 females, mean age ± SD: 70 ± 9 years) were prospectively recruited for ¹⁸F-FDG-PET/CT. The overall maximum pulmonary uptake of ¹⁸F-FDG (SUV_max), the minimum pulmonary uptake or background lung activity (SUV_min), and target-to-background (SUV_max/ SUV_min) ratio (TBR) were quantified using routine region-of-interest analysis. Kaplan-Meier analysis was used to identify associations of PET measurements with mortality. We also compared PET associations with IPF mortality with the established GAP (gender age and physiology) scoring system. Cox analysis assessed the independence of the significant PET measurement(s) from GAP score. We investigated synergisms between pulmonary ¹⁸F-FDG-PET measurements and GAP score for risk stratification in IPF patients.

During a mean follow-up of 29 months, there were 54 deaths. The mean TBR ± SD was 5.6 ± 2.7. Mortality was associated with high pulmonary TBR (p = 0.009), low forced vital capacity (FVC; p = 0.001), low transfer factor (TLCO; p < 0.001), high GAP index (p = 0.003), and high GAP stage (p = 0.003). Stepwise forward-Wald-Cox analysis revealed that the pulmonary TBR was independent of GAP classification (p = 0.010). The median survival in IPF patients with a TBR < 4.9 was 71 months, whilst in those with TBR > 4.9 was 24 months. Combining PET data with GAP data ("PET modified GAP score") refined the ability to predict mortality.

A high pulmonary TBR is independently associated with increased risk of mortality in IPF patients.