P251 The utility of FDG PET/CT in the diagnosis and management of IgG4 related disease

Introduction IgG4 related disease (IgG4-RD) is a rare immune mediated fibroinflammatory condition that can affect nearly any organ. Pancreaticobiliary (PB) manifestations include autoimmune pancreatitis (AIP) and cholangiopathy. [18F]-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) is the only technique that allows imaging of metabolic activity by detecting FDG accumulation in cells and correlation with anatomical structures. Increased tracer uptake is typically seen in inflammatory or neoplastic tissue thereby potentially aiding diagnosis, and assessment of disease extent and activity. There is limited data currently available on its utility in IgG4-RD and whether this varies according to presentation. The aim of this study is to determine the utility of FDG PET/CT in diagnosis, monitoring disease activity and identifying multi system involvement. Methods We performed a retrospective study of a prospectively maintained multi-disciplinary IgG4-RD database to identify patients who underwent FDG PET/CT over a 3-year period. Additional organ involvement and change in management consequent on FDG PET/CT was recorded. Fisher’s exact test was used for the comparison of proportions. Results 25 patients with a diagnosis or suspicion of IgG4-RD underwent FDG PET/CT between November 2016 and October 2019. The median age [IQR] at presentation was 59 [48.5–65.5], 18 (72%) were male. 15 (72.5%) suspected or proven PB disease, 6 (24%) head and neck (HN), 1 (4%) each of retroperitoneal, both PB and HN, pulmonary and renal. In 22 (88%) cases (15/15 PB, 7/10 non PB) FDG PET/CT findings had a direct impact on management. The difference in utility between PB (100%) and non-PB (70%) was not quite statistically significant (p=0.059). In 1 patient it enabled exclusion of PB IgG4-RD. In 15 (60%) it led to a decision to escalate therapy this included 3 AIP cases (21.4% of definite PB cases) in which new organ involvement was identified. In 6 cases (5 PB and 1 renal IgG4-RD) with concern of active disease because of persistently elevated or rising IgG4 levels it excluded FDG avid inflammation. Conclusion In this retrospective study FDG PET/CT had a clinically important impact on management of IgG4-RD. Identifying other organ involvement as well as influencing therapeutic decision making particularly in PB disease. Further studies are required to fully delineate its role in IgG4-RD.