Usefulness of Positron Emission Tomography in the Evaluation of Distribution and Activity of Systemic Lesions Associated with Autoimmune Pancreatitis

Background/Aims: Autoimmune pancreatitis (AIP) is an lgG4-related systemic disease often accompanied with a variety of lesions outside of the pancreas and is treated with steroid therapy. The aim of this study is to analyze the usefulness of positron emission tomography with 18F-fluorodeoxyglucose (FDG-PET) in the evaluation of distribution and activity of systemic lesions of AIP during steroid therapy. Methods: Eleven cases of AIP had their FDG-PET images evaluated before and 3 months after steroid therapy and another 2 cases only before therapy. AIP activity was determined by the level of serum markers, IgG and lgG4, and compared with findings of PET. Results: In all 13 cases of AIP, a moderate to intense level of FDG accumulation was recognized in the pancreatic lesion before steroid therapy. Of 13 patients, 11 (84.6%) showed FDG accumulation in the multiple organs, such as mediastinal and other lymph nodes, salivary gland, biliary tract, prostate, and aortic wall. In 11 patients who underwent PET before and after steroid therapy, FDG accumulation was diminished in almost all systemic lesions, with a mean of maximum standardized uptake value (SUVmax) in the pancreatic lesion from 5.12 to 2.69. Similar to the SUV level, serum IgG and lgG4 were decreased in most of the cases after steroid therapy. Conclusions: FDG-PET is an effective modality to evaluate the response of steroid therapy and the distribution and activity of various systemic lesions of AIP.