Atypical MGRS-associated renal injury in Waldenström macroglobulinemia: occult intraluminal monoclonal κ light chain deposition, a case report

Abstract Background Waldenström macroglobulinemia (WM) is a rare, indolent lymphoplasmacytic lymphoma. Renal involvement in WM can be attributed to three mechanisms: monoclonal protein deposition, direct tumor cell infiltration, and indirect injury unrelated to deposition or infiltration, with AL amyloidosis being the most common clinical presentation. We report a case of atypical monoclonal gammopathy of renal significance (MGRS) renal injury associated with WM. Case presentation A 58-year-old man with a 5-year history of asymptomatic WM was admitted with foamy urine, nocturia, dizziness, and blurred vision. Physical examination revealed pallor, a diffuse purplish-red non-blanching rash over the entire body, and no bilateral lower extremity edema. Laboratory tests showed elevated total protein, globulin, IgG, and IgM; increased serum creatinine; and mildly reduced hemoglobin. Serum protein electrophoresis combined with serum and urine immunofixation electrophoresis identified a monoclonal IgM-κ band. Bone marrow examinations were consistent with the WM disease spectrum, and imaging revealed multiple enlarged extramedullary lymph nodes. Renal biopsy demonstrated occult monoclonal κ light-chain deposition within vascular lumens accompanied by focal glomerular ischemia, confirming the diagnosis of atypical MGRS renal injury associated with WM. Conclusions Renal injury secondary to WM exhibits substantial pathological heterogeneity, and renal biopsy remains the cornerstone for subtyping and definitive diagnosis. This case may provide a reference for the clinical recognition of this disorder.