Revealing Cardiac Amyloidosis Disguised as Hypertrophic Obstructive Cardiomyopathy

Cardiac amyloidosis “is an infiltrative cardiomyopathy that usually presents with angina, syncope, and progressive right- and left-sided heart failure. It leads to significant morbidity and mortality which is compounded by the fact that it is a diagnostic challenge even with imaging.”

In this case, a 79-year-old male with a history of hypertension and chronic obstructive pulmonary disease presented to the Lehigh Valley Heart Institute, Allentown, PA, with worsening dyspnea on exertion for 6 months. His examination revealed “a mid-systolic crescendo-decrescendo murmur accentuating with Valsalva. Electrocardiogram showed normal voltage. Echocardiogram showed severe concentric left ventricular hypertrophy and an ejection fraction of 60%.” The patient’s resting peak velocity across outflow tract was 5.78 m/s and peak gradient 133 mm Hg, “which increased to 6.59 m/s and 174 mm Hg, respectively, with Valsalva. Systolic anterior motion of mitral valve was present.”

Because of a high suspicion for hypertrophic obstructive cardiomyopathy, the treating clinicians ordered cardiac magnetic resonance imaging (MRI), which showed “left ventricular hypertrophy with severe septal thickening. However, it also showed global subendocardial late gadolinium enhancement indicative of cardiac amyloidosis.” Nuclear pyrophosphate scan was strongly suggestive of amyloid transthyretin subtype. The patient was started on transthyretin stabilizer therapy. The patient received beta-blockers for symptom management of left ventricular outflow tract obstruction. Septal ablation versus disopyramide was also considered, despite being off label for cardiac amyloidosis.

“Differentiating cardiac amyloidosis and hypertrophic obstructive cardiomyopathy is a dilemma as both can present with asymmetrical septal hypertrophy. Left ventricular outflow tract obstruction and systolic anterior motion can add to this confusion and lead to missed diagnosis of cardiac amyloidosis which could be treated with targeted drug therapy. MRI with supplemental information from nuclear pyrophosphate scan is the diagnostic imaging modality that helps distinguish the two. Some amyloid cases can present without the typical late gadolinium enhancement and are discovered by positive Congo red dye staining of biopsy specimen of treated hypertrophic obstructive cardiomyopathy,” said Bilal Saqi, MD, PGY-5 Cardiovascular Disease Fellow, Lehigh Valley Health Network, Allentown, and colleagues.

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