A recent study found that patients with transthyretin amyloid cardiomyopathy (ATTR-CM) who receive tafamidis may experience decreased uptake of [99mTc]Tc-pyrophosphate (PYP), a tracer used to diagnose the disease via noninvasive bone scans. The results were published in the European Journal of Nuclear Medicine and Molecular Imaging.
Bone scintigraphy is a common method of accurately diagnosing individuals with ATTR-CM. Patients are given [99mTc]Tc-PYP intravenously before undergoing nuclear imaging. In the case of ATTR-CM, certain patterns of tracer uptake in the heart can be indicative of cardiac amyloidosis.
What is ATTR-CM?
Transthyretin amyloidosis cardiomyopathy (ATTR-CM) is a rare progressive disease of the heart muscle that leads to congestive heart failure. It occurs when the transthyretin protein produced by the liver is unstable. Symptoms include fatigue; shortness of breath; irregular heart rate or palpitations; swelling of the legs, ankles and stomach; brain fog; wheezing; and dizziness. It often goes underdiagnosed because of a lack of awareness and knowledge of the disease. There is currently no cure for ATTR-CM.
“This study is the first to evaluate the effect of tafamidis treatment in patients with ATTR-CM over an extended follow-up period using multiple [99mTc]Tc-PYP scans,” the investigators said.
Read more about ATTR-CM therapies
The study included individuals with a confirmed diagnosis of A97S hereditary ATTR-CM, meaning the 97th amino acid of the transthyretin protein was mutated from alanine to serine. Of these patients, 19 were treated with 61 mg per day of tafamidis, while nine had not received any disease-modifying therapy.
All participants underwent [99mTc]Tc-PYP single-photon emission computed tomography/computed tomography (SPECT/CT) scan at baseline and received subsequent scans during the follow-up period. The authors calculated planar and volumetric heart-to-lung (H/L) ratios to evaluate uptake in the heart compared to surrounding lung tissues.
From baseline to two years, patients receiving tafamidis experienced a significant reduction in tracer uptake using both planar (P < 0.001) and volumetric measurements (P < 0.001). No significant difference was observed in the control group.
When followed from year to year, however, the investigators observed that the effect of tafamadis on H/L ratio began to level off. While patients who received scans after one year of treatment saw a decrease in planar (P < 0.001) and volumetric (P = 0.004) H/L ratio, no significant changes were observed from one to two years.
A subset of participants receiving tafamidis were followed for three years. The study found that in these patients, there was no significant mean change in [99mTc]Tc-PYP uptake during the third year.
“While tafamidis may continue to lower [99mTc]Tc-PYP uptake, the effect seems to plateau after the first year of treatment,” the authors concluded. “However, due to the limited number of patients included in the current study, further research with larger patient cohorts is needed.”
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