IgG4-related kidney disease mimicking renal cell carcinoma: a case report and literature review

IgG4-related kidney disease (IgG4-RKD) presenting as renal masses is a very rare clinical entity. It represents the renal manifestation of IgG4-related disease (IgG4-RD) and is primarily characterized by tubulointerstitial nephritis caused by the infiltration of IgG4-positive plasma cells. Typical imaging findings include renal enlargement and cortical low-density lesions. However, a very small proportion of IgG4-RKD cases may present as space-occupying renal lesions, which are easily misdiagnosed as renal malignancies. In the reported case, a patient hospitalized for a respiratory disease had an abdominal computed tomography (CT) scan revealing a space-occupying lesion in the right kidney. Clinicians initially suspected a malignant renal tumor and proceeded with radical nephrectomy of the right kidney. Postoperative histopathology and immunohistochemistry confirmed the diagnosis of IgG4-RKD.