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Mattana et al. Vessel Plus 2022;6:13 https://dx.doi.org/10.20517/2574-1209.2021.87 Page 9 of 11

Figure 8. Technetium-99m pyrophosphate bone scan: (A) mild tracer uptake that overlaps the cardiac area on planar images; and (B)
single photon emission computed tomography/computed tomography images show no uptake on heart walls.

the non-infarcted segments. In this scenario, the degree of uptake and the ratio on planar imaging may be
below the threshold reported for definite diagnosis; however, SPECT imaging can help detect amyloid
cardiac involvement .
[35]

We must remember that myocardial infiltration could be minimal, especially in the early stage of disease,
resulting in false-negative scan even in patients with proved ATTR-CA. Patients with certain pathogenic
TTR mutations, including Phe64Leu, Glu81Ala, and Val30Met, resulting positive for cardiac involvement
on echocardiography could have negative cardiac bone scan [36,37] , while patients with hereditary
apolipoprotein A1 could present a positive bone scan . The role of SPECT/CT images is even more relevant
[5]
in the population with a low prevalence of CA to avoid false-positive results at planar scan.

CONCLUSION
99m
Both Tc-DPD and Tc-PYP showed good accuracy for the diagnosis of CA with high specificity and
99m
sensibility, but, to achieve this accuracy, the correct acquisition protocols for each tracer suggested in the
latest recommendation must be followed. The advantage of radionuclide images is that it allows a non-
invasive diagnosis of CA and to differentiate the two main forms, AL and TTR-CA. This issue has a
paramount clinical role because the two forms have different prognosis and treatment. The presence of new
specific disease-modifying therapies underlines the importance of an early detection of CA even before the
clinical presentation or when the echocardiography diagnostic criteria are not satisfied. The lack of head-to-
99m
99m
head studies of Tc-DPD vs. Tc-PYP and the differences in the acquisition protocol does not allow
comparing the performance of the two tracers. The ECU is better described with Tc-DPD, but its
99m
diagnostic role and prognostic value need to be better investigated with multicenter studies.
It seems reasonable to assume that this increased utilization of bone tracer scintigraphy for the detection of
CA will continue to expand in the future into even lower-risk populations that include screening of
asymptomatic “at risk” patients. It will therefore be crucial for nuclear physicians to have the most specific
approaches in acquiring and interpreting bone scintigraphy for ATTR-CA.

DECLARATIONS
Authors’ contributions
Conception and design of the study: Mattana F, Muraglia L, Girardi F, Cerio I, Porcari A, Dore F,
Bonfiglioli R, Fanti S