OBJECTIVES: Differentiating immunoglobulin light-chain (AL) from transthyretin-related cardiac amyloidoses (ATTR) is imperative given implications for prognosis, therapy, and genetic counseling. We validated the discriminatory ability of (99m)Tc-pyrophosphate scintigraphy ((99m)Tc-PYP) in AL vs. TTR-related cardiac amyloidoses.
METHODS: 45 subjects (12 AL, 16 ATTR wild-type, and 17 ATTR mutants) underwent (99m)Tc-PYP planar and single-photon positive emission computed tomography (SPECT) cardiac imaging. Scans were performed by experienced nuclear cardiologists blinded to the subjects’ cohort assignment. Cardiac retention was assessed with both a semi-quantitative visual score (range 0, no uptake to 3, diffuse uptake) and by quantitative analysis by drawing a region of interest (ROI) over the heart corrected for contralateral counts and calculating a heart-to-contralateral ratio (H/CL).
RESULTS: Subjects with ATTR cardiac amyloid had a significantly higher semi-quantitative cardiac visual score than the AL cohort (2.9Â±0.06 vs. 0.8Â±0.27, p<0.0001) as well as a higher quantitative score (1.80Â±0.04 vs.1.21Â±0.04, p<0.0001). Using a H/CL ratio â‰¥1.5 consistent with intensely diffuse myocardial tracer retention had a 97% sensitivity and 100% specificity with area under the curve 0.992, p<0.0001 for identifying ATTR cardiac amyloidosis.
CONCLUSIONS: (99m)Tc-PYP cardiac imaging distinguishes AL from ATTR cardiac amyloidosis and may be a simple, widely available method for identifying subjects with ATTR cardiac amyloidosis which should be studied in a larger prospective manner.