E2308. Diagnostic Criteria Thresholds for Transthyretin Cardiac Amyloidosis on TC99m PYP Scintigraphy
TC99m PYP cardiac scintigraphy is being used for diagnosing cardiac amyloid and differentiating Transthyretin (TTR) related amyloidosis from primary amyloidosis, the two most common causes of cardiac amyloidosis. Currently there are two diagnostic criteria for the planar images. Quantitative analysis: Heart to contra lateral chest (H/CL) counts ratio, currently values > 1.5 are considered diagnostic. Semi-quantitative analysis: visual grading of the heart uptake compared to the ribs, with uptake equal or greater than ribs considered diagnostic. Currently the sensitivity of PYP is reported as 97%.
Materials and Methods:
This is a retrospective analysis. Patients with TC99m-PYP scintigraphy who had myocardial biopsy and or TTR genetic testing were identified through the medical record. Patients were injected with 25(+/- 10%) mCi Tc99m-PYP, with image acquisition 2.5hr post injection. Planar images of these patients were reviewed for quality, visual grading and validity of ROIs for heart/contralateral chest.
Total of 30 patients were included in the study. 21 patients had endomyocardial biopsy, 8 positives and 13 negatives for amyloidosis. All 9 patients that did not undergo a biopsy had genetic testing positive for TTR gene mutation.
All patients with negative biopsy were also negative on quantitative analysis average with H/Cl ranging from 0.9 to 1.2. Of patients with no biopsy but TTR gene mutation, 1 had H/CL>1.5, 8 cases with H/CL ranging from 0.93 to 1.47 (average: 1.15). 7 of the patients which would be considered negative based on H/CL, showed grade 2 and grade 3 uptakes.
4 of the patients with positive biopsy, had H/CL >1.5. The other 4 had H/CL of 0.98, 1.44, 1.45, and 1.45 but all were positive on visual grading scale, one was positive for TTR mutation. Other 3 cases had labs non-consistent with primary AL.
TC99m-PYP scintigraphy can be very useful and sensitive test for diagnosing and differentiating cardiac amyloidosis. The findings of this study suggest that the sensitivity of PYP scan can be improved by lowering the quantitative threshold to 1.4.
TC99m-PYP cardiac scintigraphy is being increasingly used as the noninvasive diagnostic tool for amyloidosis with great sensitivity and specificity. Our findings suggest that the current quantitative threshold reported in the literature should be lowered to 1.4 which would increase the sensitivity of this study.