Analogies and disparities among scintigraphic bone tracers in the diagnosis of cardiac and non-cardiac ATTR amyloidosis

In this issue of JNC, BW Spery and Coll report a retrospective analysis of 57 patients with transthyretin-related amyloidosis (ATTR) in an advanced phase of the disease who underwent 99mTechnetium-pyrophosphate (99mTcPYP) scintigraphy. Although relatively small and "negative," the study is relevant since it broadens our knowledge on the uptake of "bone tracers" in ATTR and contributes to understand the limitations of the clinical use of scintigraphy in this disease. The paper raises, directly or indirectly, at least three questions: To what extent are the different bone tracers interchangeable for the diagnosis of ATTR cardiac amyloidosis? Are bone tracers able to image non-cardiac ATTR amyloidosis? What is the explanation for the variable performance of the different bone tracers in the diagnosis of cardiac and extracardiac ATTR amyloidosis?