IgG4-related kidney disease presenting as severe renal failure: Diagnostic challenges of a multimodality imaging approach.

IgG4-related disease (IgG4-RD) is a systemic immune-mediated fibroinflammatory condition that can involve virtually any organ. Renal involvement, referred to as IgG4-related kidney disease (IgG4-RKD), represents an uncommon manifestation and may pose significant diagnostic challenges, particularly when renal dysfunction is the only presenting feature. We report the case of an 80-year-old man who presented with severe renal insufficiency, manifested by markedly elevated serum creatinine levels, in the absence of prior renal disease or significant comorbidities. Imaging evaluation revealed no abnormalities in abdominal organs other than the kidneys. A comprehensive non-contrast multimodality imaging assessment-including ultrasound, computed tomography, and magnetic resonance imaging-was performed due to impaired renal function. Imaging demonstrated multiple bilateral renal parenchymal lesions with features suggestive of an inflammatory process. Histopathological examination of the renal biopsy specimens revealed dense lymphoplasmacytic infiltrates with storiform fibrosis, and immunohistochemical analysis confirmed the presence of abundant IgG4-positive plasma cells, establishing the diagnosis of IgG4-related kidney disease (IgG4-RKD). Corticosteroid therapy resulted in progressive improvement and stabilization of renal function. This case highlights the importance of considering IgG4-related kidney disease (IgG4-RKD) in the differential diagnosis of unexplained renal failure, particularly in elderly patients with bilateral renal lesions. Integration of imaging findings with histopathological confirmation is essential for early diagnosis and timely treatment, which may prevent irreversible renal damage.