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Elevated Serum IgG4 Complicated by Pericardial Involvement with a Patchy (18)F-FDG Uptake in PET/CT: Atypical Presentation of IgG4-related Disease.

IgG4-related pericardial involvement has rarely been reported and its clinical features remain unknown. We herein report a case of a 50-year-old woman with pericarditis who presented with a fever, elevated C-reactive protein levels, elevated serum IgG4 concentrations, and thickened pericardium with a patchy (18)F-fluorodeoxyglucose (FDG) uptake. A biopsy specimen of (18)F-FDG accumulated in the mediastinal lymph nodes revealed an abundant infiltration of IgG4-bearing plasma cells without fibrosis. Moderate-dose glucocorticoids promptly resolved the physical, serological, and imaging abnormalities, thus indicating a relatively acute and reversible nature of IgG4-related pericardial involvement.