IgG4-related disease (IgG4-RD) is a rare fibroinflammatory condition that can mimic malignancies, including upper tract urothelial carcinoma (UTUC). Accurate differentiation between IgG4-RD and malignancies is crucial to prevent unnecessary surgical interventions and to initiate appropriate immunosuppressive therapy.

 

Here, we presented a 60-year-old male presented with bilateral hydronephrosis. Imaging studies, including computed tomography (CT) and magnetic resonance imaging (MRI), revealed a 16.6 mm nodular lesion in the right ureter and an ill-defined 4.8 cm soft tissue mass at the left ureteropelvic junction (UPJ) (Figure 1 and 2), initially suggestive of UTUC. Histopathological examination of a CT-guided biopsy from the left kidney demonstrated chronic inflammation with IgG4-positive plasma cells. Serum IgG4 levels were elevated at 254 mg/dL. After corticosteroid therapy with prednisolone, the patient showed significant regression of hydronephrosis, confirming the diagnosis of IgG4-RD.

In the literature review, several case reports have documented IgG4-RD mimicking UTUC, leading to diagnostic uncertainty and, in most cases, unnecessary nephroureterectomy. Our case highlights the importance of a multidisciplinary approach, integrating imaging, histopathology, and serology, to ensure accurate diagnosis and appropriate immunosuppressive therapy while avoiding unwarranted surgical interventions.