Case Study: Wild-Type Transthyretin Cardiac Amyloidosis in the Setting of Familial Hypertrophic Obstructive Cardiomyopathy

A case study highlights the importance of avoiding anchoring bias in the diagnosis of cardiac amyloidosis. The findings were presented at AHA 2024.

The case describes a 62-year-old man with hypertrophic obstructive cardiomyopathy (HOCM) with incidental wild-type transthyretin cardiac amyloidosis (ATTRwt-CA) discovered after septal myectomy.

The patient had history of bilateral carpal tunnel syndrome as well as a family history (father’s side) of sudden cardiac death consistent with HOCM on autopsy. He presented to the clinic with symptoms of exertional shortness of breath, hypotension, and pre-syncope. The findings of an external monitor revealed one episode of non-sustained supraventricular tachycardia.

The patient suffered worsening symptoms for which emergency department evaluation revealed anterior lead T-wave inversions on EKG. A cardiac catheterization showed non-obstructive coronary artery disease. Subsequently, a cardiac MRI was significant for probable HOCM based on septal hypertrophy, late gadolinium enhancement (LGE) with mid-wall fibrosis in the basal/mid inferolateral segments, and systolic anterior motion (SAM) of the mitral valve. Also, the patient was administered a pre-stress echocardiogram which revealed a sigmoid septum with septal wall thickness of 1.6 cm and no left ventricular outflow tract (LVOT) gradient.

While genetic testing was negative, the pathology of the myocardium ultimately showed histological features suggestive of HOCM in addition to confirmed ATTRwt-CA for which tafamidis was initiated.

The researchers noted that reporting HOCM and ATTRwt-CA within the same patient is rare. “Both conditions cause increased myocardial thickness which can present phenotypically similar, making diagnosis difficult. Utilization of modern imaging modalities such as cardiac MRI and echocardiography should provide valuable information for differentiation, but as in our case, direct tissue visualization can be required for diagnosis,” they concluded.

Reference

Santer M, Bianco C. Serendipitously Discovered Wild-Type Transthyretin Cardiac Amyloidosis in the Setting of Familial Hypertrophic Obstructive Cardiomyopathy. Abstract #Sa2140. Presented at the American Heart Association Scientific Sessions 2024; November 16-18, Chicago, Illinois.