Introduction. IgG4-associated diseases are a systemic immune-dependent pathology characterized by diffuse or focal infiltration of affected tissues by lymphocytes and plasma cells expressing IgG4, followed by the development of phlebitis and fibrosclerosis in the affected tissues. In extremely rare cases, an IgG4-associated disease affects the ureter that mimics its malignant tumor, which presents a diagnostic challenge. We present a rare case of IgG4-associated iwhich was misdiagnosed as ureter tumor.

Clinical observation. Patient P. Sixty four years old patient admitted for left lower back pain and weight loss by (4 kg for the last 2 months). There were a stenosing tumor at the border of middle and lower parts of left ureter, left-side hydronephrosis and retroperitoneal lymphadonopathy on computed tomography. Uretelial cancer was suspected and nephroureterectomy with lymphadenectomy was done. Pathomorphological study revealed fibrosis, periflebitis with narrowing of veins and venules, diffuse inflammatory infiltration by lymphocytes, plasma cells and epsinophils in the ureter wall. There were no tumor growth there. Immunohistochemical staining revealed the presence of IgG4- positive plasma cells in the altered ureter wall. There was also an encreased IgG4 level up to 1,49 g/L in the patient’s serum.

Conclusion. An IgG4-associated disease of the ureter was diagnosed at the pathological study of removed kidney and ureter. It is necessary to take into account the possibility of IgG4-associated disease in patients with ureteral neoplasms. It makes possible to do a proper diagnose and avoid unjustified surgery