Silent Progression: Cardiac Amyloidosis Unmasking IgG Lambda Myeloma in an Elderly Patient

Background: Cardiac amyloidosis is an underrecognized etiology of heart failure with preserved ejection fraction (HFpEF), particularly in elderly patients. Light-chain (AL) amyloidosis, when associated with multiple myeloma, is highly aggressive and portends a poor prognosis, especially in advanced cardiac stages. Case Presentation: We report the case of a 79-year-old male with type 2 diabetes, hypertension, and a history of pacemaker implantation for complete atrioventricular block in the context of atrial fibrillation. He was admitted with progressive exertional dyspnea and an episode of syncope. Clinical examination revealed fine basal crackles and signs of decompensated heart failure. ECG demonstrated a paced rhythm. Echocardiography and cardiac MRI revealed concentric left ventricular hypertrophy with a sparkling myocardial texture, biatrial dilation, restrictive filling pattern, and diffuse subendocardial late gadolinium enhancement—features highly suggestive of cardiac amyloidosis. Laboratory tests revealed anemia, renal dysfunction, elevated troponin and NT-proBNP, and a monoclonal IgG lambda spike. Bone marrow biopsy confirmed the diagnosis of multiple myeloma with plasma cell infiltration. Based on clinical and laboratory findings, the patient was classified as Mayo stage IIIB AL cardiac amyloidosis and ISS stage I multiple myeloma. He received bortezomib-cyclophosphamide-based chemotherapy and supportive care, but unfortunately died five months after diagnosis. Discussion: This case highlights the importance of early recognition of cardiac amyloidosis in elderly patients with unexplained heart failure and monoclonal gammopathy. Cardiac MRI and serum free light chain analysis are critical tools in the diagnostic pathway. Despite advances in treatment, outcomes remain poor in advanced cardiac involvement. Early intervention may improve prognosis, underscoring the need for heightened clinical awareness. Conclusion: Infiltrative cardiomyopathies like AL amyloidosis should be considered in elderly patients with heart failure and systemic red flags. Timely diagnosis and multidisciplinary management are essential but often insufficient in advanced stages.