Tc-99m-PYP imaging for cardiac amyloidosis: Defining the best protocol before the flood gates burst
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Division of Cardiology, New York Presbyterian Hospital, New York, NY Division of Cardiology, Cleveland Clinic, Cleveland, OH
Received Jun 26, 2020; accepted Jun 26, 2020 doi:10.1007/s12350-020-02273-3
See related articles, https://doi.org/10.1 007/s12350-020-02205-1 and https://do i.org/10.1007/s12350-020-02139-8.
WHAT IS CARDIAC AMYLOIDOSIS AND WHY IS IT IMPORTANT TO MAKE A DIAGNOSIS? Cardiac amyloidosis can be caused by deposition of immunoglobulin light chains produced by a clonal plasma cell disorder (AL) or liver produced transthyretin protein (ATTR). The most prevalent form of ATTR is the wild-type caused by age-related transthyretin misfolding (ATTRwt) with the autosomal dominant gene mutation variant being less common (ATTRv). Since there are now effective treatments for ATTR-CA, early accurate diagnosis is key as treatment is more effective if started early in the natural history of the disease. Left untreated after diagnosis, survival for AL is \ 6 months and 3-5 years for ATTR. To date, the diagnosis of cardiac amyloidosis continues to be made in patients with advanced disease. More needs to be done to improve awareness of its clinical manifestations and the potential of therapeutic intervention to improve prognosis.1
Reprint requests: Sabahat Bokhari, MD, FASNC, FACC, Division of Cardiology, New York Presbyterian Hospital, 622W 168th Street, New York, NY 10032; [email protected] J Nucl Cardiol 1071-3581/$34.00 Copyright Ó 2020 American Society of Nuclear Cardiology.
HOW IS A DIAGNOSIS OF CARDIAC AMYLOIDOSIS MADE? Once ATTR-CA is suspected, a definitive diagnosis can usually be achieved on endomyocardial biopsy or non-invasively on bone scintigraphy with either Technetium-99m pyrophosphate (Tc-99m- PYP), Tc-99mdiphosphono-1,2-propanodicarboxylic acid (Tc-99mDPD) or Tc-99m-hydroxymethylene diphosphonate (Tc-99m-HMDP) in the absence of abnormal light chains on serum free light chain assay and immunofixation of the serum and urine.2 The exact molecular mechanism underlying myocardial transthyretin amyloid uptake of 99mTc-labeled bone agents is not known but it has been hypothesized to be due to binding of calcium in transthyretin amyloid fibrils to the phosphate domains in these radiotracers. Although echocardiography and cardiac magnetic resonance imaging maybe suggestive of CA, endomyocardial biopsy or Tc-99m bone scintigraphy are required to make a diagnosis. HOW ACCURATE IS TC-99M IMAGING FOR CA? In 2002, Puille et al showed that whole body 99mTcDPD scintigraphy was a valuable diagnostic aid to evaluate the severity of ATTR-CA and the risk of associated complications3. In 2005, Perugini et al showed that whole body 99mTc-DPD scintigraphy was 100% sensitive and 100% specific for diagnosing ATTR-CA4. 99mTc-DPD is not approved in the USA; however, 99mTc-PYP is readily available. 99mTc-PYP is currently approved for blood pool imaging (GI bleed and gated cardiac blood pool studies), cardiac imaging (detection of acute MI), and bone scintigraphy. In the late 70’s and early 80’s, 99mTc-PYP was employ
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