Mid-term Follow-up of Patients with Negative Myocardial 99mTc-pyrophosphate Uptake but Suspected Transthyretin Cardiac Amyloidosis

Background: Technetium-99m pyrophosphate (PYP) imaging is an established non-invasive tool for detecting transthyretin cardiac amyloidosis (ATTR-CA).Although the absence of myocardial uptake on single photon emission computed tomography (SPECT) generally rules out ATTR-CA, early-stage disease may yield falsenegative results, and the value of follow-up imaging for such cases is unclear.Therefore, this study aimed to examine whether follow-up PYP imaging could detect the development of myocardial uptake in cases with initially negative findings.Methods: This single-center retrospective study included 12 of 446 consecutive patients who underwent PYP imaging for suspected ATTR-CA, showed no myocardial uptake on initial SPECT, and underwent repeat PYP imaging.Myocardial PYP uptake was visually assessed using the Perugini classification on planar and SPECT images solely, and quantitatively by the heart-to-contralateral lung uptake (H/CL) ratio.Pretest probability for ATTR-CA was estimated using the Kumamoto criteria.Results: The median interval between the initial and second PYP imaging was 473 days (interquartile range, 312-848 days).All patients had a low pretest probability of ATTR-CA (Kumamoto score 0-1) at baseline, and only one patient showed an increase in the Kumamoto score from 1 to 2 during follow-up.However, no patient developed myocardial PYP uptake on SPECT at the second PYP imaging.The H/CL ratio did not significantly change between the two scans (1.32±0.10 vs. 1.28±0.15,P=0.37).Conclusions: Patients with initially negative PYP SPECT and a low pretest probability of ATTR-CA did not develop myocardial PYP uptake over 1-2 years, suggesting that routine follow-up PYP imaging may be unnecessary unless new clinical indicators of ATTR-CA arise.