(P157) EQUIVOCAL VERSUS POSITIVE TC-99M-PYROPHOSPHATE SCINTIGRAPHY FOR TRANSTHYRETIN AMYLOID CARDIOMYOPATHY: COMPARISON OF PATIENT DEMOGRAPHICS AND CARDIAC IMAGING FINDINGS

Background: Transthyretin cardiac amyloidosis (ATTR-CM) is an underdiagnosed infiltrative cardiomyopathy leading to heart failure, arrhythmias, and valvular disease. The diagnosis of ATTR-CM is largely based on Technetium-99m-pyrophosphate bone scintigraphy (Tc-99m-PYP) scans. Semi-quantitative grading (Perugini) has been utilized with Perugini 2 and 3 regarded as positive for ATTR-CM. However, the interpretation and clinical significance of Perugini 1 (referred to as equivocal scans by the American Society of Nuclear Cardiology) are unclear. Our study aims to describe the prevalence of and differences in clinical and imaging characteristics among those with equivocal compared to positive Tc-99m-PYP and to describe outcomes of further investigations in these patients.

METHODS AND RESULTS: This was a retrospective study of all patients who underwent Tc-99m-PYP scans at two local institutions between January 2017 and November 2022. Baseline demographics, laboratory, and imaging data were collected. A total of 508 Tc-99m-PYP scans performed with SPECT/CT 3-hours post-tracer injection were analyzed: 353 (69%) were negative, 46 (9%) were equivocal, and 109 (21%) were positive. The median age was 78 (IQR 72-84) years and 38 (25%) were female. Average follow-up was 19.7 +/- 14.6 months. None of the patients with Perugini 1 scans were diagnosed with ATTR-CM (Figure 1). Two patients had a monoclonal gammopathy, one of whom was diagnosed with AL-amyloidosis. Only 12 (26%) of patients in our cohort underwent further imaging including cardiac MRI, repeat Tc-99m-PYP scan, or biopsy. The majority of patients with Perugini 1 scans were presumed negative after cardiologist review. Compared to patients with positive scans, patients with Perugini 1 scans tended to be younger (74 years (IQR 66-79) vs. 80 years (IQR 74-86)) and had echocardiographic characteristics less consistent with ATTR-CM, including lower wall thicknesses (intraventricular septum thickness 11mm (IQR 10-11) vs. 15mm (IQR 12-17)), larger left ventricular end diastolic dimension 50mm (44-56) vs. 43mm (40-50), more negative global longitudinal strain (-18.3 (IQR -21.8-15.5) vs. -13.8 (IQR -17.9-10.9)), and less apical sparing (n=7, 18% vs. n=42, 70%). Our findings emphasize that many patients should not have undergone Tc-99m-PYP scans given the lack of evidence on echocardiogram to suggest ATTR-CM. In contrast, patients with an ATTR-CM phenotype and Perugini 1 scans should undergo further workup including biopsies or imaging (eg. echocardiogram, cardiac MRI) because this may represent earlier stage disease.

Conclusion: In our study, patients with equivocal scans did not yield a diagnosis of ATTR-CM. Further research is needed to determine the clinical significance of equivocal studies.