Based on the elevated serum IgG4 level, postoperative pathology, and the features of F-fluoro-2-deoxy-D-glucose (F-FDG) positron emission tomography/computed tomography (PET/CT), which revealed diffuse increased FDG uptake in many structures, he was diagnosed with IgG4-related disease involving the bilateral orbits, salivary glands, submandibular glands, lymph nodes, and prostate.
A follow-up FDG PET/CT after glucocorticoid therapy revealed resolution of FDG avidity in the prostate with fall in serum IgG4 levels, hence confirming a diagnosis of atypical immunoglobulin G4-related disease involving isolated prostate gland.
As such, joint F-FDG PET and MRI assessment during therapy may have a potential interest for treatment response evaluation in pituitary IgG4-related disease.
The characteristic tracer uptake pattern described on FDG PET/CT may not be always present in IgG4-RD, especially in the setting of postabdominal surgery.