Proteinase 3 anti-neutrophil cytoplasmic antibody (PR3-ANCA) positive IgG4-related retroperitoneal fibrosis: utility of PET-CT with 18F-fluorodeoxy glucose (FDG).

A 55-year-old man showed a serum creatinine level of 1.51 mg/dL, CRP of 0.79 mg/dL, and proteinase 3 anti-neutrophil cytoplasmic antibody (PR3-ANCA) of 43.9 EU (normal range: below 10). The serum levels and ratios of IgG1, IgG2, IgG3, and IgG4 to total IgG were 1,570 mg/dL (49%), 1,190 mg/dL (37%), 82 mg/dL (3%), and 351 mg/dL (11%), respectively. Positron emission tomography and CT with (18)F-fluorodeoxyglucose (PET-CT) demonstrated retroperitoneal fibrosis. After a diagnosis of IgG4-related retroperitoneal fibrosis with PR3-ANCA was made, oral prednisolone improved serum creatinine and the titer of PR3-ANCA to normal levels, with no abnormal findings on PET-CT.