Usefulness of the PET/CT to predict the progression and mortality risk in patients with diffuse interstitial lung disease

Abstract Objective: to assess the capacity of the PET/CT to predict pulmonary function deterioration and increased mortality risk in patients with idiopathic interstitial pneumonia (IIP) and to establish a possible SUVmax cutoff which identifies these patients. Material and methods: retrospective study between January 2007-December 2020. Inclusion criteria: patients > 18 years of age, diagnosed with IIP by PET/CT and pulmonary function test, with less than 6 months’ difference between the two tests. A study was made of the outcome variables associated with the PET/CT, the pulmonary function test measured at 2 stages (initially at the time of the PET/CT and at the end of follow-up), the mortality risk (using the GAP index) and the relationship between them all. Other variables of interest observed were age, sex, department requesting the PET/CT, indication, and the presence of lung cancer (LC). The statistical analysis was performed using the SPSS program. Results: 39 patients were analysed: 34 males (87%), with an age of 75 ± 8 years (mean ± DS). The mean ± SD of the SUVmax was 2.57 ± 1.17, with a statistically insignificant difference (p = 0.670) between patients with and without lung cancer. LC was confirmed in 21 cases (54%). There is a small inverse correlation between the SUVmax and the initial and final predicted FVC% (r= -0.154, r= -0.252), together with a medium correlation for the initial and final predicted DLCO% (r= -0.523, r= -0.514). The mean ± SD of the GAP index was 3.77 ± 1.08. There is a medium correlation between the SUVmax and the mortality risk of stages I and II (r = 0.468). By means of ROC curve analysis, an SUVmax of 2.2 was established to predict the fall of the FVC below 80%, of 1.9 to predict the fall of the DLCO below 60%, and of 2.15 to predict the progression from GAP stage I to II in mortality risk. Conclusions: There is an inverse correlation between the SUVmax and the pulmonary function, together with a direct relationship between the SUVmax and the mortality risk.