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Cardiac Amyloidosis Masked as Hypertrophic Cardiomyopathy: A Case Report

It is well known that cardiac amyloidosis and hypertrophic cardiomyopathy (HCM) have different physiologies and pathologies. However, it might be difficult to differentiate cardiac amyloidosis from HCM in certain clinical situations.


Introduction
Both hypertrophic cardiomyopathy (HCM) and amyloidosis present with increased myocardial thickness and mass. The delayed enhancement patterns on cardiac magnetic resonance imaging (CMR) are thought to distinguish these two diseases. However, we report a case where the patient had patchy delayed enhancement and was thought to have HCM but then found to have amyloid pattern 5 months later. The lesson to be learned here is that in early stages of cardiac amyloid, a patient could present with less apparent delayed enhancement patterns and the imaging findings have to be correlated with the patient's clinical presentation in order to make a correct diagnosis.

Case Report
A 64-year-old female presented with recurrent chest pain and progressive shortness of breath in April 2015. She had a history of asthma and panic attacks. The worsened symptoms triggered a cardiac workup which included cardiac catheterization which showed no obstructive lesions. The findings on echocardiography and CMR in 2015 suggested the diagnosis of HCM (Table 1). The patient did not have a family history of HCM, but her father died suddenly at age 48. Her paternal grandfather and two paternal uncles all died suddenly before the age of 40. Genetic testing was negative for pathogenic variants. A serum protein electrophoresis and urine protein electrophoresis were unrevealing. Her breathlessness had improved with a diuretic regimen of low dose furosemide and aldactone with stable volume status. As part of the follow-up, she was reexamined in February 2016, at which time ECG showed low voltage and echocardiography demonstrated restrictive filling pattern. Repeated CMR provided the most important diagnostic information, which is the pattern of abnormal subendocardial late gadolinium enhancement (LGE) suggesting cardiac amyloidosis (Fig. 1). Based on CMR findings, a fat pad biopsy was completed, but negative. A subsequent endomyocardial biopsy was positive for amyloidosis.

Discussion
To the authors' knowledge, such a dramatic change in CMR LGE pattern from faint patchy mid-myocardial enhancement to global subendocardial enhancement in 6-month follow-up has not been reported. This case raises an important question: could early stage of amyloidosis begin with cardiac hypertrophy without significant amyloid deposition elsewhere and thus could be confused with HCM?
Amyloidosis is a rare protein deposition disease caused by misfolding followed by tissue deposition of highly ordered aggregate proteins forming amyloid fibrils leading to progressive organ failure [1]. The definitive diagnosis should be made by endomyocardial biopsy.
The QRS amplitude on ECG is a useful discriminator in infiltrative versus HCM, since voltages are usually increased in muscular hypertrophy and diminished in the infiltrative myopathies. For our case, the voltage showed a decreasing course between the two examinations. Of note, the QRS voltage was normal on the baseline ECG, not increased, which is atypical for HCM, but certainly does not exclude HCM.
CMR is becoming the standard imaging modality for the diagnosis of cardiac amyloidosis. The goals of a comprehensive CMR evaluation of cardiac amyloidosis should include evaluation of cardiac function and myocardial characteriza- tion. The classic CMR findings demonstrate an endocardialepicardial signal intensity gradient typical for heart amyloidosis, with the early gadolinium clearance from the blood pool [2]. LGE patterns could be divided into no LGE, global subendocardial involvement, and transmural LGE. Transmural LGE was significantly associated with mortality (hazard ratio, 4.1; 95% confidence interval, 1.3 -13.1; P < 0.05) [3].
Our case showed global subendocardial enhancement on the repeat CMR, which is different from patchy mid-myocardial delayed enhancement in first CMR. Amyloid deposition essentially restructures the heart and restricts it from stretching and properly filling with blood. Our case showed the global hypokinesis and further decreased left ventricular ejection fraction in the repeat CMR, which may have reflected the progression of disease.
The findings on this case suggest that at the early stage, cardiac amyloid may demonstrate hypertrophy as the only imaging feature without significant abnormalities on LGE. It is only after the accumulation of the infiltrative substances for a period of time that the characteristics of cardiac amyloidosis on CMR begin to appear and could be detected. We have the chance to observe the progressive course in this case and place it on the continuum of amyloid accumulation as determined by LGE pattern progressing from normal to transmural [4].

Funding Sources
None.