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

Objectives: To investigate the utility of 18F-FDG PET/CT in the diagnostic procedure of IgG4-related disease (IgG4-RD), we analysed the association between quantitative method of 18F-FDG PET/CT and histological findings.
Methods: Twenty-one patients with IgG4-RD in whom 18F-FDG PET/CT was performed at the time of diagnosis were enrolled. Tissue biopsy was performed at 24 sites in 21 patients. To perform quantitative analysis of 18F-FDG PET/CT imaging, the highest standardised 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 (4.98 and 3.54, respectively p<0.05). The values 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 ROC curve was constructed. ROC curve analysis indicated SUVmean=4.07 or SUVmean/liver=1.66 as a cut-off value.
Conclusions: Our present study suggested that quantitative analysis of 18F-FDG-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.