Pyrophosphate imaging aids in diagnosing cardiac amyloidosis - Healio
September 28, 2020
3 min read
Ruberg FL. Amyloid-Best Practices. Presented at: Scientific Session and Exhibition of the American Society of Nuclear Cardiology; Sept. 25-26, 2020 (virtual meeting).
Disclosures: Ruberg reports he received research support from Akcea Therapeutics, Eidos Therapeutics, NIH/NHLBI and Pfizer.
Utilization of pyrophosphate imaging to identify patients with cardiac amyloidosis has increased, although questions remain regarding its use for screening and to assess responses to therapy, according to a presentation.
Although pyrophosphate imaging has been used and researched for decades, data on its use in differentiating light-chain (AL) amyloidosis from transthyretin (ATTR) amyloidosis started around 2013, Frederick L. Ruberg, MD, associate professor of radiology and program director of the Pilot Translational and Clinical Studies Program at Boston University School of Medicine, said during the presentation at the Scientific Session and Exhibition of the American Society of Nuclear Cardiology.
“That really accelerated the pathway of [pyrophosphate] adaptation in the United States,” Ruberg added.
The American Society of Nuclear Cardiology has published several practice points on the use of pyrophosphate imaging in cardiac amyloidosis, the first of which was released in 2016. The organization also published expert consensus recommendations in 2019 on multimodality imaging in cardiac amyloidosis.
“This really served the purpose to standardize how the imaging is done, and that really has led to a significant uptick in community adaptation,” Ruberg said in the presentation. “Now, people who are practicing around the world, particularly in the United States for [pyrophosphate] imaging, have a document they can look to that can tell them exactly how to do this and exactly how to report it. That really wasn’t present from the literature that was first reported of its efficacy.”
In 2020, the American Heart Association published a scientific statement on the diagnosis and management of patients with cardiac amyloidosis. This document describes how pyrophosphate imaging is essential to diagnose amyloidosis, particularly ATTR amyloidosis.
“ATTR amyloidosis, by far ... is the more important disease in terms of frequency in population,” Ruberg said in the presentation. “AL is critical and cannot be missed ... but [pyrophosphate] imaging is the means to diagnose ATTR in the right context, and that’s why it figures so centrally in the guidelines.”
The diagnosis of ATTR amyloidosis has increased over the past few years due to the increase utilization of pyrophosphate imaging, according to the presentation. Despite this increased use, there have been several unfavorable trends related to common avoidable errors in pyrophosphate imaging. This includes the failure to perform or properly interpret light-chain testing, using pyrophosphate imaging in inappropriate clinical scenarios and failure to obtain single-photon emission CT to differentiate blood pool from cardiac uptake.
Pyrophosphate imaging cannot be interpreted without light-chain assessment, which is done through serum-free light chains, serum and urine immunofixation electrophoresis.
“When one looks at these results, one can then appropriately determine whether or not [pyrophosphate] imaging can be diagnostic for TTR amyloidosis,” Ruberg said during the presentation. “Cardiologists are not comfortable nor should they be necessarily with these assay ranges. ... Basically, the concept here is that when the free light-chain ratio is abnormal or when the serum immunofixation is abnormal, you must refer to hematology for further evaluation.”
It is important to obtain scans in the right clinical scenario especially because AL amyloidosis is life-threatening, according to the presentation. In addition, incorrectly diagnosing AL amyloidosis may lead to treating inappropriate patients with tafamidis (Vyndamax and Vyndaqel, FoldRx/Pfizer). Although the drug is an effective treatment for AL amyloidosis, it is expensive. After financial assistance, patients prescribed this drug may have copays of $1,700 per month, according to the presentation.
“If patients are basically being asked to shoulder the burden of a very expensive drug, you really want to make sure they actually have the disease for which they’re being treated,” Ruberg said in the presentation.
Future trends in the use of pyrophosphate imaging may be shaped by several unanswered questions regarding the use of bone scintigraphy as a screening test, cost-effectiveness of screening, follow-up in asymptomatic allele carriers of TTR mutations and the role of imaging for prognostication or following disease response.
“We’ve reached a perfect storm for ATTR amyloidosis,” Ruberg said during the presentation. “We have an understanding that the epidemiology is much greater than we thought before and, in large part, shaped by the access to [pyrophosphate] imaging, an easy diagnosis in scenarios where we didn’t think about it before.”
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