18F-FDG PET/CT and HRCT: a combined tool for risk stratification in idiopathic inflammatory myopathy-associated interstitial lung disease

Objectives Rapidly progressive interstitial lung disease (RP-ILD) is a life-threatening form of idiopathic inflammatory myopathy (IIM)-associated interstitial lung disease (ILD). We aimed to assess the combination of 18 F-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) and high-resolution computed tomography (HRCT) for the quantification of IIM-ILD activity and risk stratification for RP-ILD. Method Patients with IIM and undergoing 18 F-FDG PET/CT were included in this retrospective study. Pulmonary FDG uptake was assessed using the maximum standardized uptake value (SUV lung ) and visual score (PET score). HRCT was evaluated using visual analysis (HRCT score). Multivariable logistic regression was used to identify risk factors for RP-ILD. Results Seventy-three patients with IIM (17 with RP-ILD, 38 with non-RP-ILD, and 18 without ILD) were included. SUV lung , PET score, and HRCT score were significantly higher in RP-ILD than in non-RP-ILD. Strong positive correlations were observed between SUV lung , PET score, and the HRCT parameters. The area under the curve (AUC) of the PET score to differentiate between RP-ILD and non-RP-ILD (AUC = 0.860) was higher than that of the SUV lung (AUC = 0.802) and HRCT scores (AUC = 0.806). We developed a risk score based on the number of positive risk factors (PET score > 18, HRCT score > 140, and positive anti-melanoma differentiation-associated gene 5 (MDA5) antibody) to differentiate between RP-ILD and non-RP-ILD (AUC = 0.955). Patients with higher risk scores had significantly worse prognoses. Conclusions 18 F-FDG PET/CT is useful for assessing disease activity in patients with IIM-ILD. The combination of PET score, HRCT score, and anti-MDA5 antibody can be used to identify patients at increased risk of RP-ILD and with poor prognoses. Key Points • 18 F-FDG PET/CT helps to assess the inflammatory burden in patients with IIM-ILD. • Whole-lung FDG uptake assessment (PET score) showed superior performance in discriminating RP-ILD and non-RP-ILD compared with SUV lung and HRCT visual analysis. • The combination of PET score, HRCT score, and anti-MDA5 antibody can identify patients at increased risk of RP-ILD and with poor prognoses.