Apolipoprotein A-IV Cardiac Amyloidosis Presenting as Massive Ventricular Wall Thickening Mimicking Hypertrophic Cardiomyopathy.

BACKGROUND: Apolipoprotein A-IV amyloidosis (AApoAIV) is a rare systemic amyloidosis that can involve the heart and mimic hypertrophic cardiomyopathy. CASE SUMMARY: A 64-year-old woman with presumed hypertrophic cardiomyopathy presented with dyspnea. Imaging showed severe left ventricular wall thickening, outflow tract obstruction, and systolic anterior motion of the mitral valve. Multimodality evaluation suggested infiltrative cardiomyopathy including diffuse late gadolinium enhancement, abnormal nulling, elevated T1 on cardiac magnetic resonance, and an apical-sparing strain pattern on echocardiography. Technetium-99m pyrophosphate scintigraphy demonstrated no myocardial uptake. Endomyocardial biopsy confirmed AApoAIV deposition. DISCUSSION: AApoAIV cardiac amyloidosis may present with massive left ventricular wall thickening. Discordant noninvasive testing may occur, and endomyocardial biopsy remains essential for diagnosis. TAKE-HOME MESSAGES: AApoAIV cardiac amyloidosis is a rare infiltrative cardiomyopathy that may mimic hypertrophic cardiomyopathy and follow an indolent course, allowing myocardial infiltration over years. Negative technetium-99m pyrophosphate scintigraphy does not exclude amyloidosis, particularly in non-transthyretin amyloid subtypes like AApoAIV, and tissue diagnosis is required.