Census of Cardiac Uptake on Routine Bone Scintigraphy, a Methodology to Assess the Prevalence of the TTR Amyloidosis

Objective: Transthyretin cardiac amyloidosis is a rapidly progressive disease, remains underdiagnosed, and has long been considered a rare disease. Diagnosis decision making cannot be based on echography and MRI findings alone because they lack accuracy. However, it requires invasive test of myocardial or fat pad biopsies. Thus, the diagnosis is challenging, and the non-invasive scintigraphic technique using bone-seeking radiopharmaceuticals has become a cornerstone in the workup revealing a myocardial uptake. Our work consists of a single institution retrospective study aiming to estimate the bone scintigraphies, and the prevalence of the transthyretin cardiac amyloidosis in our population. Methods: We have carried out a census of the incidental cardiac uptake on routine bone scintigraphy in 2211 consecutive patients enrolled between 2009 and 2020, mostly performed for oncologic purposes. The visual analysis of the scintigraphic images classifies the cardiac uptake into 3 levels of gradation and evokes the diagnosis of the TTR cardiac amyloidosis in grades 2 and 3. Results: Different grades of myocardial uptake were observed in 1.37 % of all patients. Prevalence of uptake was 0.37% in the 50th, increased dramatically at the 60th (2.49%), and reached 4% above the age of 80. The diagnostic grades 2 and 3 cardiac uptakes were identified in 5 patients (0.23% of overall patients) ranging between 56- and 91-y-old. Our results concord with the trend of disease increases with age. Conclusion: The careful analysis of the bone scintigraphy of all incoming adult patients should allow to make the diagnosis of the TTR cardiac amyloidosis at a preclinical stage and establish new effective treatments. Our results provide an estimate of the number of patients that could be diagnosed and improve the awareness of the corresponding prevalence in our population. In this way, multicentric studies should be implemented by enrolling large cohorts of bone scintigraphy cases.