DOI: https://doi.org/10.36347/sasjm.2026.v12i10.012

Pages: 1084-1090

Background: Cardiac amyloidosis associated with Waldenström macroglobulinemia is rare and diagnostically challenging. In patients with a monoclonal gammopathy, low-grade uptake on bone-avid tracer scintigraphy is insufficient to confirm transthyretin amyloidosis; therefore, tissue confirmation through amyloid typing remains essential. Case presentation: An 84-year-old man presented with progressive heart failure and marked deterioration of his general condition. Cardiac assessment suggested a high probability of amyloid cardiomyopathy. Subsequent hematologic evaluation identified an IgM kappa monoclonal gammopathy, indicative of an underlying lymphoplasmacytic neoplasm. Bone marrow analysis confirmed Waldenström macroglobulinemia, while tissue biopsy demonstrated amyloid deposition. These combined findings established a diagnosis of systemic amyloidosis, with clinicopathologic evidence strongly supporting IgM-related kappa AL amyloidosis. Conclusion: This case demonstrates that cardiac amyloidosis can reveal an underlying IgM-secreting lymphoplasmacytic neoplasm. It emphasizes the importance of early multidisciplinary evaluation, careful interpretation of scintigraphy in the context of monoclonal gammopathy, and timely initiation of clone-directed therapy. Despite these interventions, the prognosis of cardiac involvement in frail elderly patients remains poor.