Abstract
Cardiac amyloidosis (CA) is a life-threatening disease caused by extracellular deposition of amyloidogenic proteins in the heart tissue; it could be associated with a poor prognosis and remains underdiagnosed and underestimated. During the last years, bone scintigraphy has been widely used to facilitate the diagnosis of CA, avoid endomyocardial biopsy, and differentiate amyloid light-chain amyloidosis from transthyretin amyloidosis. Technetium-99m pyrophosphate (99mTc-PYP) is the most used tracer in the United States, but a standardized and shared acquisition protocol is still lacking; technetium-99m 3,3-diphosphono-1,2-propanodicarboxylic acid (99mTc-DPD) is widely used in Europe and can count on a more grounded data than 99mTc-PYP. Both tracers suffer from some diagnostic limitations (due to their biochemical characteristics) and pitfalls that can lead to a misdiagnosis of CA. We aim to briefly describe the main differences between 99mTc-PYP and 99mTc-DPD, analyzing the data available in the literature and highlighting the most frequent causes of misdiagnosis and pitfalls. Both 99mTc-DPD and 99mTc-PYP show good accuracy for the diagnosis of CA with high specificity and sensibility. Nevertheless, to achieve this accuracy, the correct acquisition protocols must be followed for each tracer, as suggested in the latest recommendation. Proper diagnosis of CA has a crucial role in patient management; therefore, it is important for nuclear physicians to have the most specific approaches in acquiring and interpreting bone scintigraphy for transthyretin cardiac amyloidosis.
Highlights
Amyloidosis is a systemic disease with different clinical presentation depending on the tissues and organs involved
The AA form can be evaluated with labeled-SAP scintigraphy, while bone tracer scintigraphy is useless in this type of amyloidosis
The role of single-photon emission computerized tomography (SPECT)/CT images is even more relevant in the population with a low prevalence of Cardiac amyloidosis (CA) to avoid false-positive results at planar scan. Both 99mTc-DPD and 99mTc-PYP showed good accuracy for the diagnosis of CA with high specificity and sensibility, but, to achieve this accuracy, the correct acquisition protocols for each tracer suggested in the latest recommendation must be followed
Summary
Amyloidosis is a systemic disease with different clinical presentation depending on the tissues and organs involved. While the AL form is most frequently associated with hematologic disease (myeloma and monoclonal gammopathies), the TTR forms can be due to a mutated form of TTR (TTRv) or a wild-type form (TTRwt), the latter responsible for senile amyloidosis[2]. Another systemic form of amyloidosis is the AA type, which is related to the deposition of the Serum Amyloid A protein in the organs involved[3]; the most frequent clinical presentation is a chronic inflammatory condition associated with renal insufficiency. The AA form can be evaluated with labeled-SAP scintigraphy, while bone tracer scintigraphy is useless in this type of amyloidosis
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