IgG4-related disease of the ureter mimicking malignant ureter tumor: a case report and experience sharing.

Background: Immunoglobulin G4-related disease (IgG4-RD) is an autoimmune disease that can affect any organ or tissue in the body, and is characterized by intensive infiltration of IgG4-positive plasma cells, and elevated serum IgG4 levels. IgG4-RD causes renal impairment of unknown pathogenesis that may progress to kidney failure. However, few case of IgG4-RD mimicking malignant ureter tumor leading to severe hydronephrosis. Case Description: This report describes a 38-year-old male patient who was hospitalized for sudden waist pain. Enhanced abdominal computed tomography (CT) revealed a mass involving the right ureter. He presented to the urologist with severe right hydronephrosis. Urinalysis revealed occult blood (3+), and atypical cells were observed in urine cytology, raising the possibility of a ureteral malignancy. After that, the patient underwent diagnostic ureteroscopy instead of direct nephroureterectomy and was found not to have any malignancy. The patient received laparoscopic partial ureteral resection and anastomosis. Histologically, there were observations of IgG4-positive plasma cell infiltration exceeding 10 cells per high-power field, as well as a high ratio of IgG4-positive/IgG-positive cells exceeding 40%. And histopathology revealed ureteral IgG4-related disease, with no evidence of urothelial carcinoma. Conclusions: IgG4-RD has previously been reported in lesions involving the ureters, but misdiagnosis and subsequent radical nephroureterectomy can cause lifelong regret for the patient in having lost one side of the urinary tract. To avoid such misdiagnoses, clinicians should consider IgG4-RD as a potential condition.