Combined Immunoglobulin Heavy- and Light-Chain Amyloidosis Associated With Waldenström Macroglobulinaemia: A Case Report With Diagnostic Challenges and a Favourable Treatment Outcome.

Waldenström macroglobulinaemia (WM) is a rare lymphoplasmacytic lymphoma that produces monoclonal IgM, and renal amyloidosis is an uncommon complication. Light-chain amyloidosis occurs more frequently than heavy-chain or combined heavy- and light-chain (AHL) amyloidosis. This report describes a woman with proteinuria in the nephrotic range, elevated IgM, and IgM kappa monoclonal protein in serum and urine. Kidney biopsy revealed AHL amyloidosis with IgM and kappa deposition. Laser microdissection-liquid chromatography-tandem mass spectrometry (LMD-LC-MS/MS) confirmed the presence of peptides from heavy and light chains. WM with renal amyloidosis was diagnosed, and the patient was started on bendamustine and rituximab. She had a significant hematologic response, achieving a very good partial response according to the international criteria. A renal response characterized by a reduction in proteinuria and stabilization of renal function was also observed. The patient remains asymptomatic after 43 months of follow-up. This case of WM with renal AHL amyloidosis highlights the importance of keeping renal amyloidosis in mind in patients with proteinuria. The favourable hematologic and renal response to treatment with bendamustine and rituximab in this case adds valuable data for the management of WM complicated by renal amyloidosis.