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Cardiac amyloidosis — ABIM Board MCQ

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HardCardiovascularCardiac amyloidosisABIM Board

A 74-year-old man with no history of hypertension has progressive exertional dyspnea and orthostatic presyncope. He underwent bilateral carpal tunnel release 6 years ago. ECG shows low-voltage QRS complexes. Echocardiography shows preserved left ventricular ejection fraction, concentric left ventricular wall thickening, biatrial enlargement, restrictive filling, and relative apical sparing of longitudinal strain. Serum and urine immunofixation detect no monoclonal protein, and the serum free light-chain ratio is normal. Technetium-99m pyrophosphate scintigraphy shows grade 3 uptake; SPECT confirms that the tracer uptake is myocardial rather than within the blood pool. Which of the following is the most likely diagnosis?

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Correct answer: B — Transthyretin cardiac amyloidosis

The diagnosis is transthyretin cardiac amyloidosis (ATTR-CM). Advanced age, bilateral carpal tunnel syndrome, autonomic symptoms, low ECG voltage despite increased ventricular wall thickness, restrictive physiology, biatrial enlargement, and apical-sparing strain are characteristic red flags. Grade 3 myocardial pyrophosphate uptake with a negative complete monoclonal protein evaluation establishes ATTR-CM noninvasively; SPECT excludes blood-pool artifact. AL cardiac amyloidosis is unlikely because serum and urine immunofixation and the serum free light-chain ratio are normal. Hypertensive heart disease is inconsistent with the absent hypertension and extracardiac amyloid features. Hypertrophic obstructive cardiomyopathy typically causes asymmetric hypertrophy and dynamic outflow obstruction. Constrictive pericarditis may cause restrictive hemodynamics but does not cause myocardial thickening, apical sparing, or myocardial pyrophosphate uptake.

Reference: Kittleson MM, et al. Transthyretin Cardiac Amyloidosis Evaluation and Management: 2025 ACC Concise Clinical Guidance, diagnostic evaluation algorithm. American College of Cardiology, 2025. https://www.acc.org/latest-in-cardiology/journal-scans/2025/10/30/20/22/new-concise-clinical-guidance