Hereditary Transthyretin Cardiac Amyloidosis With Severe Left Ventricular Outflow Tract Obstruction Mimicking Hypertrophic Obstructive Cardiomyopathy.

BACKGROUND: Cardiac amyloidosis may mimic hypertrophic cardiomyopathy; however, severe left ventricular outflow tract (LVOT) obstruction is rarely described in transthyretin (TTR) cardiac amyloidosis. CASE SUMMARY: A 49-year-old man presented with exertional dyspnea and presyncope. Echocardiography demonstrated septal hypertrophy with severe LVOT obstruction, leading to an initial diagnosis of hypertrophic obstructive cardiomyopathy. Persistent symptoms prompted further evaluation. Cardiac magnetic resonance imaging revealed diffuse subendocardial late gadolinium enhancement, whereas bone scintigraphy demonstrated low-grade myocardial uptake. Genetic testing identified a pathogenic TTR variant, and endomyocardial biopsy confirmed TTR amyloidosis (ATTR). Tafamidis therapy was initiated, with clinical improvement during follow-up. DISCUSSION: Certain hereditary ATTR variants may present with low-grade tracer uptake, emphasizing the importance of tissue confirmation when suspicion persists. TAKE-HOME MESSAGES: Transthyretin-cardiac amyloidosis may mimic hypertrophic obstructive cardiomyopathy with severe LVOT obstruction. Certain hereditary ATTR variants may demonstrate low-grade tracer uptake on bone scintigraphy. Multimodality imaging, genetic testing, and tissue confirmation are essential when clinical suspicion persists.