Renal presentation of diffuse large B-cell lymphoma emerging after pre-existing IgG4-related disease and monoclonal gammopathy of undetermined significance.

A woman in her late 70s with a congenital solitary kidney, end-stage renal disease on haemodialysis, prior biopsy-proven IgG4-related disease (IgG4-RD) involving the liver and porta hepatis and monoclonal gammopathy of undetermined significance presented after a fall. Trauma-related CT imaging revealed a 20 cm infiltrative renal mass with bulky retroperitoneal lymphadenopathy. The laboratory data showed persistently elevated serum IgG4 levels with stable kappa-to-lambda free light chain ratios. Biopsy of the renal mass confirmed aggressive diffuse large B-cell lymphoma with a high proliferative index and cytogenetic abnormalities. This case raises the possibility that chronic immune dysregulation in IgG4-RD may be associated with lymphomagenesis.