Characterizing IgG4-related disease with ¹⁸F-FDG PET/CT: a prospective cohort study

IgG4-related disease (IgG4-RD) is an increasingly recognized clinicopathological disorder with immune-mediated inflammatory lesions mimicking malignancies. A cohort study was prospectively designed to investigate the value of (18)F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in characterizing IgG4-RD.

Thirty-five patients diagnosed with IgG4-RD according to the consensus criteria were enrolled with informed consent. All patients underwent baseline (18)F-FDG PET/CT evaluation. Among them, 29 patients underwent a second (18)F-FDG PET/CT scan after 2 to 4 weeks of steroid-based therapy.

All 35 patients were found with (18)F-FDG-avid hypermetabolic lesion(s); 97.1% (34/35) of these patients showed multi-organ involvement. Among the 35 patients, 71.4% (25/35) patients were found with more organ involvement on (18)F-FDG PET/CT than conventional evaluations including physical examination, ultrasonography, and computed tomography (CT). (18)F-FDG PET/CT demonstrated specific image characteristics and pattern of IgG4-RD, including diffusely elevated (18)F-FDG uptake in the pancreas and salivary glands, patchy lesions in the retroperitoneal region and vascular wall, and multi-organ involvement that cannot be interpreted as metastasis. Comprehensive understanding of all involvement aided the biopsy-site selection in seven patients and the recanalization of ureteral obstruction in five patients. After 2 to 4 weeks of steroid-based therapy at 40 mg to 50 mg prednisone per day, 72.4% (21/29) of the patients showed complete remission, whereas the others exhibited > 81.8% decrease in (18)F-FDG uptake.

F-FDG PET/CT is a useful tool for assessing organ involvement, monitoring therapeutic response, and guiding interventional treatment of IgG4-RD. The image pattern is suggested to be updated into the consensus diagnostic criteria for IgG4-RD.