Bone tracers for transthyretin amyloid cardiomyopathy: are [99mTc]Tc-DPD and [99mTc]Tc-HMDP truly equivalent?

Background The management of transthyretin amyloid cardiomyopathy (ATTR-CM) has revolved around the scintigraphic diagnosis since the introduction of a specific treatment; however, the equivalency of the bone radiotracers remains unclear. This retrospective monocentric observational study compared [ 99m Tc]Tc-3,3-diphosphono-1,2-propanodicarboxylic acid ([ 99m Tc]Tc-DPD) and [ 99m Tc]Tc-hydroxy-methylene diphosphonate ([ 99m Tc]Tc-HMDP) for ATTR-CM diagnosis. Methods One hundred and twenty-nine patients who underwent single photon emission computed tomography (SPECT/CT) after intravenous injection of [ 99m Tc]Tc-DPD or [ 99m Tc]Tc-HMDP for ATTR-CM were included. The patients’ current visual Perugini grades were retrieved. Regions of interest (ROI) were measured on the heart (H) and on contralateral mediastinum (CM), and H/CM ratios were calculated. Results Although the distribution of quantitative assessments of heart to contralateral mediastinum ratios is wider with [ 99m Tc]Tc-DPD, suggesting a trend towards improved diagnosis, no difference in Perugini grades was found between [ 99m Tc]Tc-DPD or [ 99m Tc]Tc-HMDP for the diagnosis of ATTR-CM in evocative/non-evocative conditions. There was no difference in ATTR-CM diagnosis between the 2 tracers with a threshold of 1.5 (p-value = 3.316*10 −10 for [ 99m Tc]Tc-HMDP and p-value = 2.59*10 −15 for [ 99m Tc]Tc-DPD). Conclusions We show in our local cohort that [ 99m Tc]Tc-DPD and [ 99m Tc]Tc-HMDP for amyloidosis diagnostic are equivalent for ATTR-CM diagnosis based on the Perugini grading scale. With [ 99m Tc]Tc-DPD, a wider range of the H/CM ratio was noted, which may be considered as a better discrimination of the disease by this bone tracer. Additional research with a final diagnosis of the disease is necessary to evaluate the utility of this quantitative evaluation.