¹⁸F-florbetapir binds specifically to myocardial light chain and transthyretin amyloid deposits: Autoradiography study

Background - ¹⁸F-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 ¹⁸F-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 ¹⁸F-florbetapir and cold florbetapir compound and digital autoradiography. Total and nonspecific binding of ¹⁸F-florbetapir was determined using the maximum signal intensity values. Specific binding of ¹⁸F-florbetapir was calculated by subtracting nonspecific from total binding measurements (in decays per minute/mm², DPM mm²) and was compared with cardiac structure and function on echocardiography and the histological extent of amyloid deposits. Diffuse or focally increased ¹⁸F-florbetapir uptake was noted in all AL and ATTR samples and in none of the control samples. Compared with control samples, mean ¹⁸F-florbetapir-specific uptake was significantly higher in the amyloid samples (0.94±0.43 versus 2.00±0.58 DPM/mm²; P<0.001), and in the AL compared with the ATTR samples (2.48±0.40 versus 1.52±0.22 DPM/mm²; P<0.001). The samples from subjects with atypical echocardiographic features of amyloidosis showed quantitatively more intense ¹⁸F-florbetapir-specific uptake compared with control samples (1.50±0.17 versus 0.94±0.43 DPM/mm²; P=0.004), despite smaller amyloid extent than in subjects with typical echocardiograms. Conclusions - ¹⁸F-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.