18F-Florbetapir Binds Specifically to Myocardial Light Chain and Transthyretin Amyloid Deposits: Autoradiography Study.

BACKGROUND (18)F-florbetapir is a promising imaging biomarker for cardiac light chain amyloidosis (AL) and transthyretin amyloidosis (ATTR). Our aim, using human autopsy myocardial specimens, was to test the hypothesis that (18)F-florbetapir binds specifically to myocardial AL and ATTR amyloid deposits. METHODS AND RESULTS We studied myocardial sections from 30 subjects with autopsy-documented AL (n=10), ATTR (n=10), and nonamyloid controls (n=10) using (18)F-florbetapir and cold florbetapir compound and digital autoradiography. Total and nonspecific binding of (18)F-florbetapir was determined using the maximum signal intensity values. Specific binding of (18)F-florbetapir was calculated by subtracting nonspecific from total binding measurements (in decays per minute/mm(2), DPM mm(2)) and was compared with cardiac structure and function on echocardiography and the histological extent of amyloid deposits. Diffuse or focally increased (18)F-florbetapir uptake was noted in all AL and ATTR samples and in none of the control samples. Compared with control samples, mean (18)F-florbetapir-specific uptake was significantly higher in the amyloid samples (0.94±0.43 versus 2.00±0.58 DPM/mm(2); P<0.001), and in the AL compared with the ATTR samples (2.48±0.40 versus 1.52±0.22 DPM/mm(2); P<0.001). The samples from subjects with atypical echocardiographic features of amyloidosis showed quantitatively more intense (18)F-florbetapir-specific uptake compared with control samples (1.50±0.17 versus 0.94±0.43 DPM/mm(2); P=0.004), despite smaller amyloid extent than in subjects with typical echocardiograms. CONCLUSIONS (18)F-florbetapir specifically binds to myocardial AL and ATTR deposits in humans and offers the potential to screen for the 2 most common types of myocardial amyloid.