IgG4-Related Systemic Disease Can Be Easily Mistaken as a Uroepithelial Tumor.

Immunoglobulin G4-related disease (IgG4-RD) is a newly recognized systemic syndrome characterized by elevated serum IgG4 concentrations and tumefaction or tissue infiltration by IgG4-positive plasma cells. We experienced a case of IgG4-RD involving multiple organs in a 64-year-old female who was referred for a suspected uroepithelial tumor. A mass biopsy confirmed dense lymphoplasmacytic infiltration with an increased number of IgG4-positive plasma cells. We discuss this case and review the literature to bring IgG4-RD to the attention to clinicians because it responds dramatically well to steroid therapy and should be kept in mind as a differential diagnosis to avoid unnecessary surgery.