Waldenström macroglobulinemia-associated renal AL amyloidosis: a case report and literature review.

Waldenström macroglobulinemia (WM) is a rare indolent B-cell lymphoma, characterized by lymphoplasmacytic infiltration of bone marrow and the existence of monoclonal IgM in circulation. Renal AL amyloidosis is an uncommon complication of WM, and its treatment is an enormous challenge to clinicians. This report describes a 71-year-old woman who presented with a 10-month history of recurrent bilateral lower extremity edema and a progressive fatigue. Physical and laboratory examinations revealed serum monoclonal IgMλ, nephrotic syndrome, moderate anemia and mild enlargement of bilateral inguinal superficial lymph nodes. Bone marrow aspiration demonstrated clonal lymphoplasmacytic infiltration, lymph node biopsy was consistent with lymphoplasmacytic lymphoma, and peripheral blood testing confirmed the presence of the MYD88 L265P mutation. Renal biopsy confirmed the diagnosis of renal AL amyloidosis, evidenced by Congo red-positive amorphous deposits with λ light chain restriction in glomeruli, interstitium, and small arterial walls. Following multidisciplinary consultation, the patient was treated with the bendamustine plus rituximab (BR) regimen. After three cycles, the patient achieved partial hematologic response (serum IgM levels decreased from 23.7 g/L to 7.1 g/L) with slight improvement of proteinuria (urine protein excretion decreased from 18.2 g/d to 15.0 g/d). However, during the subsequent treatment, the patient developed a severe pulmonary infection that led to death. This case underscores two critical points: First, patients with WM should be routinely tested for serum and urine monoclonal free light chains, as they can exist in WM at a high proportion and can independently induce monoclonal gammopathy-associated renal diseases, including renal amyloidosis. Second, for WM patients with renal AL amyloidosis, choosing BR regimen as the first-line treatment is reasonable. However, during the treatment process, it is essential to closely monitor and actively prevent the adverse effects of this regimen, particularly severe infections which may have fatal consequences.