Comparison of the quantitative measurement of 18F-FDG PET/CT and histopathological findings in IgG4-related disease

Abstract Background Although there is increasing use of 18F-FDG PET/CT in the diagnostic procedure for IgG4-related disease (IgG4-RD), little is known about the quantification of 18F-FDG PET/CT. We aimed to evaluate the utility of the quantification of 18F-FDG PET/CT in the diagnosis of IgG4-RD by analyzing the relation between 18F-FDG PET/CT findings and histopathologic findings. Methods Twenty-one patients with IgG4-RD, in whom 18F-FDG PET/CT was performed at the time of diagnosis between November 2011 and July 2018, were enrolled. Tissue biopsy was performed at 24 sites in 21 patients. To perform quantitative analysis of 18F-FDG PET/CT imaging, the highest standardized uptake value (SUV) of the pixels (SUVmax) and the average SUV (SUVmean) within the biopsied lesion were measured. The SUVmean of the liver was also measured as a reference. Results The mean age at diagnosis was 64.6 ± 11.9 years, and the median serum IgG4 level was 650 mg/dl. Histological findings were consistent with IgG4-RD (histopathology-positive) at 19 out of 24 sites. Although there was no significant difference in the values of SUVmax between histopathology-positive and histopathology-negative tissues, the values of SUVmean were significantly higher in the histopathology-positive tissue than those in the histopathology-negative tissue (4.98 and 3.54, respectively P < 0.05). The value of SUVmean/liver were also higher in the histopathology-positive tissue (2.17 and 1.52, respectively P < 0.05). To establish a cut-off value of SUVmean to determine which of multiple lesions should be biopsied, a receiver operating characteristic (ROC) curve was constructed. ROC curve analysis indicated SUVmean=4.07 or SUVmean/liver = 1.66 as a cut-off value that could discriminate IgG4-RD-related lesions. Conclusions Our present study suggested that quantitative analysis of 18FDG-PET/CT imaging might be useful for selecting the biopsy site in IgG4-RD. The calculation of SUVmean, not of SUVmax, is important for evaluating IgG4-RD-related lesions in 18F-FDG PET/CT imaging.