A Zebra Hiding in Plain Sight?
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Although amyloid cardiomyopathy can be thought of as a zebra hiding in plain sight, that it truly is a zebra is perhaps a misconception. AL or light-chain cardiac amyloidosis is indeed a rare disease, with annual incidence estimated at 1 in 100 000 or ≈3000 to 4000 new cases identified each year in the United States,1 but transthyretin amyloidosis (ATTR), owing to misfolding and deposition of TTR (transthyretin protein), is likely much more common. Autopsy studies demonstrate that ≈25% of all adults >85 years of age have histologically demonstrable wild-type TTR cardiac amyloid deposits,2 with a smaller percentage, perhaps ≈5% to 10%, manifesting the clinical phenotype of ATTR wild-type cardiac amyloidosis.3 The disease has been implicated as an unrecognized cause of congestive heart failure in older patients with preserved ejection fraction4 and also in patients with severe aortic stenosis.5 Further, the most common TTR genetic mutation that causes the inherited form of cardiac amyloidosis, Val122Ile, has been reproducibly demonstrated in 3.4% of people of African origin6 and is a disease that manifests an age-dependent clinical penetrance causing heart failure in as many as 8% of Afro-Caribbeans.7 In short, cardiac amyloidosis is likely much more common than presently appreciated, but remains concealed and unrecognized, camouflaged by the background of more common wall thickening processes, such as hypertrophic cardiomyopathy, aortic stenosis, and hypertensive remodeling.8
See Article by Pagourelias et al
Diagnosis of cardiac amyloidosis in 2017 still requires integration of different clinical inputs, including history, physical findings, and imaging, such as echocardiography, cardiac magnetic resonance (CMR), and most recently, the highly ATTR-specific bone avid nuclear tracers 99mTc-PYP (pyrophosphate) and 99mTc-DPD (3,3-diphosphono-1,2-propanodicarboxylic acid).9 Other than cardiac biopsy, there is no one test that alone confirms the diagnosis. A high degree of clinical suspicion …