Concomitant Transthyretin Amyloid Cardiomyopathy in Patients With Multiple Myeloma

Background: Cardiac amyloidosis is a restrictive cardiomyopathy caused by myocardial deposition of insoluble amyloid fibrils. The 2 most frequent types are transthyretin amyloid cardiomyopathy (ATTR-CM) and light-chain amyloid cardiomyopathy (AL-CM). AL-CM is a type of plasma cell dyscrasia characterized by overproduction of light chains by a plasma cell clone. Some plasma cell dyscrasias, such as monoclonal gammopathy of undetermined significance, are common in patients with ATTR-CM; however, the coexistence of multiple myeloma and ATTR is rarely described in the literature. Case Summary: We describe 2 patients with confirmed plasma cell disorders: one with smoldering multiple myeloma and another with multiple myeloma receiving chemotherapy. Both exhibited cardiac imaging findings of infiltrative cardiomyopathy and were initially suspected to have AL-CM due to concomitant multiple myeloma. However, after bone marrow biopsy and fat pad aspiration did not show evidence of amyloidosis, an endomyocardial biopsy was performed that led to the diagnosis of ATTR-CM. Discussion: These cases underscore the necessity of tissue confirmation when evaluating cardiac amyloidosis in the context of plasma cell dyscrasias. Adhering to guideline-directed diagnostic pathways is essential to distinguish ATTR-CM from AL-CM, as misclassification may result in delayed or inappropriate therapy. Take-Home Messages: ATTR-CM can occur in patients with multiple myeloma. Endomyocardial biopsy is essential to accurately distinguish ATTR-CM from AL-CM in the presence of plasma cell dyscrasia and to ensure appropriate and timely treatment.