Prevalence and Significance of Incidental Findings on Pyp Imaging in The Scan-mp Study: The First 123 Cases

Introduction Imaging with technetium labeled bone-avid tracers is highly sensitive and specific for the non-invasive identification of transthyretin cardiac amyloidosis (ATTR-CA), when used in the proper clinical context. The mechanism of myocardial radiotracer uptake is unclear, possibly related to calcium incorporated into amyloid deposits. Extracardiac uptake of Tc99m-PYP (pyrophosphate) has not been extensively investigated, and if present, the clinical significance is unknown. Aims We aimed to assess (1) extracardiac uptake of PYP in patients undergoing nuclear scintigraphy (2) comorbid illnesses in those with extracardiac uptake (3) the extent of clinically actionable extracardiac uptake. Methods The Screening for Cardiac Amyloidosis with Nuclear Imaging in Minority Populations study (SCAN-MP), utilizes Tc99m-PYP imaging to screen for ATTR-CA in Black or Caribbean Hispanic patients with heart failure over 60 yrs. PYP imaging is limited to the thorax. Baseline demographics, comorbidities, lab and echo data were examined according to the presence or absence of extracardiac uptake. We further assessed additional diagnostics performed for subjects with extracardiac uptake and their outcomes. Results Of 123 subjects, 73 (59%) were male with a mean age of 73 y and 35% with NYHA class III/IV symptoms. The most common comorbidities were hypertension (95%), hyperlipidemia (72%) and diabetes (57%). Extra-cardiac PYP uptake was found in 24 subjects (19.5%), including 1 with breast uptake, 5 with increased bone uptake, and 20 with uptake in one or both kidneys. 2 subjects had both renal and bone uptake. There were no significant differences in age, race/ethnicity, chronic kidney disease or left ventricular function when comparing those with and without renal uptake (Table). Overall, 3 patients had clinically actionable findings. One subject with renal uptake had a renal ultrasound. One subject with bone uptake is scheduled for shoulder arthroplasty. The subject with breast uptake is awaiting mammogram for further evaluation. Conclusions Incidental PYP uptake was noted in almost 1 in 5 participants recruited for SCAN-MP. The high rate of renal uptake is consistent with the known renal excretion of PYP. Only 2.4% (n = 3) had clinically actionable extracardiac uptake and no adverse events occurred from incidental finding reporting.