Wild-type transthyretin cardiac amyloidosis mimicking hypertrophic obstructive cardiomyopathy : A case report

Wild-type transthyretin cardiac amyloidosis (ATTRwt CA) is increasingly recognized as an important cause of heart failure and arrhythmias in older people. There are several clinical, echocardiographic, electrocardiographic (ECG) and laboratory features that increase the suspicion for ATTRwt CA. Presentation and phenotype can, however, be associated with atypical findings making it difficult to make a correct diagnosis. A 65-year-old man was admitted for an acute coronary syndrome. Echocardiography revealed diffuse concentric left ventricular (LV) thickening. Because of a history of bilateral carpal tunnel syndrome and polyneuropathy, the patient underwent dedicated laboratory testing and diphosphonate scintigraphy the results of which were suggestive of transthyretin cardiac amyloidosis. Also, a dynamic LV outflow tract obstruction due to the systolic anterior motion of the anterior mitral valve was noted on echocardiography during the initial investigations. Genetic testing for hypertrophic cardiomyopathy was negative. Seeking a conclusive diagnosis, endomyocardial biopsy was performed. This confirmed the diagnosis of ATTRwt CA.

The presence of dynamic LV outflow tract obstruction is typically seen in patients with sarcomeric hypertrophic cardiomyopathy. It can be rarely seen also in individuals with cardiac amyloidosis, including ATTR-wt CA. The presence of so-called red flags in patients' history, physical examination, laboratory test, ECG and imaging should raise suspicion for other etiologies of LV wall thickening than hypertrophic cardiomyopathy. Although noninvasive diagnosis of ATTRwt CA is possible in most patients, endomyocardial biopsy remains necessary in cases with diagnostic ambiguity.