IgG4-Related Retroperitoneal Fibrosis Presenting as Obstructive Acute Kidney Injury: A Case Report.

Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder with retroperitoneal fibrosis (RPF) representing a recognized manifestation. Ureteric encasement by fibroinflammatory tissue may result in obstructive uropathy and acute kidney injury (AKI). We report the case of a 46-year-old male who presented with bilateral flank pain and severe AKI. Cross-sectional imaging demonstrated a retroperitoneal soft-tissue mass causing bilateral hydroureteronephrosis. Initial management with bilateral ureteric stent insertion resulted in marked improvement in renal function. Subsequent CT-guided biopsy revealed a fibroinflammatory spindle cell lesion consistent with IgG4-related RPF. The patient later re-presented with recurrent anuria and deterioration in renal function, raising concern for disease relapse. Rheumatology assessment confirmed IgG4-RD; however, initiation of definitive immunosuppressive therapy was deferred due to a concurrent urinary tract infection. Following resolution of infection, immunosuppressive treatment was commenced. This case underscores the diagnostic and therapeutic challenges of IgG4-related RPF and highlights the importance of multidisciplinary management, particularly in differentiating disease activity from superimposed infection.