Diagnostic Dilemmas in Cardiac Transthyretin Amyloidosis With Coexistent Low-Grade B-Cell Lymphoma: A Case Report

Cardiac amyloidosis, though a rare clinical entity, is increasingly recognized as an important etiology of heart failure and cardiac arrhythmias. The deposition of misfolded amyloid fibrils in the myocardium leads to restrictive cardiomyopathy and progressive cardiac dysfunction. Two main precursor proteins are implicated in cardiac amyloidosis: transthyretin (TTR), synthesized by the liver, and immunoglobulin light chain (AL), usually associated with plasma cell dyscrasias and lymphomas. Given the substantial differences in treatment and prognosis between TTR and AL amyloidosis, accurate differentiation between these subtypes is critical for delivering optimal patient care. We report the case of a 64-year-old man with progressive dyspnea and atrial flutter who was found to have severe concentric left ventricular hypertrophy and a characteristic "cherry on top" strain pattern on echocardiography. A technetium-99m pyrophosphate (PYP) scan demonstrated grade 3 uptake, but a concurrent abnormal IgM spike on serum electrophoresis prompted further hematologic evaluation. Bone marrow biopsy revealed a low-grade B-cell lymphoma without amyloid deposition, while endomyocardial biopsy with mass spectrometry confirmed wild-type TTR amyloidosis. The patient underwent atrial flutter ablation and was initiated on tafamidis with clinical improvement. To our knowledge, this represents the first reported case of coexisting ATTR cardiac amyloidosis and B-cell lymphoma diagnosed simultaneously. This case highlights the diagnostic challenges when hematologic malignancy and cardiac amyloidosis coexist, underscores the importance of endomyocardial biopsy for definitive typing, and emphasizes the role of a multidisciplinary approach in guiding management and optimizing outcomes.