Variant cardiac transthyretin amyloidosis presenting as hypertrophic cardiomyopathy with left ventricular outflow tract obstruction: a case report

Background Left ventricular outflow tract obstruction (LVOTO) is common in hypertrophic cardiomyopathy (HCM) but has not been reported in hereditary transthyretin amyloidosis (ATTRv).Case summary Here, we describe a 67-year-old male patient with a hypertrophic phenotype who was initially diagnosed with LVOTO attributed to HCM. Echocardiographic features included a hyperdynamic left ventricular ejection fraction, severe septal hypertrophy, and elongated residual mitral leaflets permitting their systolic anterior motion. The patient was childless, and family history was negative for any cardiovascular disease. Significant coronary artery disease was diagnosed. In cardiac magnetic resonance imaging, the concurrent presence of different late enhancement patterns initially prevented an unequivocal diagnosis. Due to progressive neuropathy, genetic testing for ATTRv was performed and identified a pathogenic variant in the TTR gene. Cardiac involvement was confirmed by amyloid scintigraphy with a Perugini score of 3, and treatment with ribonucleic acid silencing therapy was commenced.Discussion The present case illustrates that LVOTO can occur in patients with ATTRv. While cardiac imaging pointed towards sarcomeric HCM, the coexisting red flags initiated re-evaluation of the diagnosis suggesting cardiac amyloidosis as a potential cause. The presence of non-cardiac red flags of transthyretin amyloidosis (ATTR) should initiate specific diagnostic work-up even if ATTR is unlikely based on cardiac imaging.