Coexistence of Hypertrophic Cardiomyopathy and Hereditary Transthyretin Amyloid Cardiomyopathy.

BACKGROUND: Left ventricular wall thickening may result from disease such as hypertrophic cardiomyopathy (HCM) or infiltrative cardiomyopathies such as transthyretin amyloidosis (ATTR). When features of both conditions coexist, distinguishing the dominant pathology can be challenging and may influence management. CASE SUMMARY: A 72-year-old man presented with progressive exertional dyspnea and syncope. He was found to have severe left ventricular outflow tract obstruction with systolic anterior motion of the mitral valve. He experienced marked symptomatic improvement after initiation of mavacamten for presumed HCM. Genetic testing later revealed a pathogenic TTR p.Val50Met variant, and technetium-99m pyrophosphate scintigraphy demonstrated grade 3 myocardial uptake consistent with hereditary ATTR cardiomyopathy. Persistent symptoms led to septal myectomy, which demonstrated marked myocyte hypertrophy and moderate myocardial amyloid deposition but insufficient infiltration to explain the hypertrophy. DISCUSSION: This case highlights the diagnostic complexity of coexisting HCM and hereditary ATTR cardiomyopathy and underscores the importance of multimodality imaging, genetic testing, and pathologic correlation. TAKE-HOME MESSAGES: Dynamic left ventricular outflow tract obstruction does not exclude cardiac amyloidosis. Dual cardiomyopathies should be considered when clinical, imaging, and genetic findings appear discordant.