The lungs were on fire: a pilot study of 18F-FDG PET/CT in idiopathic-inflammatory-myopathy-related interstitial lung disease

Background: Interstitial lung disease (ILD) and its rapid progression (RP) were main contributors to unfavorable outcome of idiopathic inflammatory myopathy (IIM) patients. This study aimed at identifying the clinical value of PET/CT scan in IIM-ILD patients as well as constructing a predicting model for RP-ILD. Methods: : Adult IIM-ILD patients who were hospitalized at four divisions of the First Affiliated Hospital, Zhejiang University School of Medicine (FAHZJU) from Jannuary 1 st 2017 to December 31 st 2020 were reviewed. PET/CT scan as well as other factors of patients who met the inclusion and exclusion criteria were collected and analyzed. Results: : A total of 61 IIM-ILD patients were finally enrolled into this study. Twenty-one patients (34.4%) developed RP-ILD and 24 patients (39.3%) died in follow-up. After false discovery rate (FDR) correction, percent-predicted diffusing capacity of the lung for carbon monoxide (DLCO%, P=0.014), bilateral lung mean standard uptake value (SUVmean, P=0.014) and abnormal mediastinal lymph node (P=0.045) were significantly different in comparison between RP-ILD and non-RP-ILD groups. A “DLM” model was hereby established by including the above three values to predict RP-ILD with a cutoff value of ≥2 and an area under the curve (AUC) of 0.905. Higher bilateral lung SUVmean (P=0.019) and spleen SUVmean (P=0.011) were observed in IIM-ILD patients who died within three months, and a moderate correlation was recognized between the two values. Conclusions: : Elevated bilateral lung SUVmean and abnormal mediastinal lymph node were associated with RP-ILD in IIM-ILD patients. The “DLM” model was valuable in predicting RP-ILD and demanded further evaluation.