Extranodal Marginal Zone Lymphoma Presenting as Acute Kidney Injury due to Cast Nephropathy: A Case Report.

Acute kidney injury (AKI) in non-Hodgkin lymphoma has diverse etiologies. We report a case in which AKI due to light chain cast nephropathy was the initial manifestation of extranodal marginal zone lymphoma, occurring without systemic symptoms. A 64-year-old male presented with severe AKI without other symptoms. His physical examination and renal ultrasound were unremarkable. Renal biopsy revealed light chain cast nephropathy, and a subsequent bone marrow biopsy confirmed marginal zone lymphoma. The patient received R-CHOP chemotherapy (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone) for a total of six cycles. The patient had a partial response to lymphoma. However, his renal function did not improve, and ultimately he progressed to end-stage kidney disease, requiring maintenance hemodialysis. This case highlights extranodal marginal zone lymphoma presenting as AKI, emphasizing its unique renal-limited manifestation in the absence of systemic symptoms and the critical role of renal biopsy in diagnosing unexplained AKI.