Continuation of 99mTc-PYP shortage prompts need for alternative cardiac amyloidosis imaging
After three years of intermittent shortages of nuclear imaging tracer technetium-99m pyrophosphate (PYP), there are no signs of the shortage abating, according to an update from the American Society of Nuclear Cardiology (ASNC). ASNC is urging members to consider switching to alternative imaging methods.
The bone scintigraphy radiopharmaceutical was adopted for cardiac imaging a few years ago because it is very good at imaging amyloid transthyretin (ATTR) cardiac amyloidosis to confirm diagnosis and enable initiation of treatment. The emergence of drug therapies have significantly improved outcomes in ATTR patients and has increased demand for this nuclear test. However, since December 2023 the radiotracer's shortage has forced providers to seek alternatives. Prior to the use of PYP SPECT imaging to confirm the disease, endomyocardial biopsy was needed for confirm the presence of ATTR amyloid.
"Bone scintigraphy has really revolutionized ATTR amyloidosis diagnostics," explained ASNC President Panithaya Chareonthaitawee, MD, FACC, FAHA, director of the nuclear cardiology laboratory and a professor of medicine at Mayo Clinic in Rochester, Minnesota.
She has seen an increasing demand for ATTR imaging the past few years, and feels the pinch of the shortage from time to time when they cannot get access to the PYP injection kits they use to mix with the Tc-99m radiotracer. She said the shortage is due to a lack of the active ingredient used to make the PYP kit injections used in the hot lab.
The agent remains on the U.S. Food and Drug Administration (FDA) drug shortage list, impacting two vendors, Curium U.S. LLC and Sun Pharmaceutical Industries Inc. According to the FDA website, Sun expects the shortage to linger until at least the second quarter of 2025, although ASNC said neither vendor is sure when they will again have stable PYP supplies.
Alternative to PYP imaging is HMDP
Tc99m pyrophosphate has become a standard of care for ATTR imaging. Chareonthaitawee said this is because there is already a lot of clinical data on PYP. But, she said there are other ways to image ATTR, that these methods just do not have as much robust data. However, she expects that to change with the shortage causing many nuclear labs to make the switch to Tc-99m hydroxymethyl diphosphonate (HMDP or HDP) imaging as substitute, or even as a replacement.
Tc-99m methylene diphosphonate (MDP) can also be used, but she said it is discouraged because it has lower sensitivity.
"HMDP is a great alternative. Some centers have decided to only use HMDP to avoid the stops and starts with the supply of PYP. In some ways, it might be easier to change to HMDP," Chareonthaitawee explained.
She added that there are some differences in imaging protocols, but overall the image quality is very similar. Chareonthaitawee said the biggest protocol difference is HMDP uses a one hour uptake time before imaging, compared to a two to three hour uptake time using PYP.
"We wanted to stick with PYP, but we may not be able to because of the continuing shortage," she explained, adding that Mayo is collecting its own research data with its use of HMDP.
In October 2022, ASNC released the information statement Radiopharmaceutical Supply Disruptions and the Use of 99mTc-Hydroxymethylene Diphosphonate as an Alternative to 99mTc-Pyrophosphate for the Diagnosis of Transthyretin Cardiac Amyloidosis. This provides guidance for making this switch to HMDP, which the society reissued links too this week.
ASNC is also hosting an upcoming webinar Optimizing the Diagnosis of ATTR-CM, which will explore how to use 99mTc-HMDP as an alternative to 99mTc-PYP with the latest guidance on acquisition, interpretation and reporting techniques. The webinar is March 18 from 6-7 pm (eastern time).
Dave Fornell has covered healthcare for more than 17 years, with a focus in cardiology and radiology. Fornell is a 5-time winner of a Jesse H. Neal Award, the most prestigious editorial honors in the field of specialized journalism. The wins included best technical content, best use of social media and best COVID-19 coverage. Fornell was also a three-time Neal finalist for best range of work by a single author. He produces more than 100 editorial videos each year, most of them interviews with key opinion leaders in medicine. He also writes technical articles, covers key trends, conducts video hospital site visits, and is very involved with social media. E-mail: dfornell@innovatehealthcare.com