A final diagnosis of cardiac amyloidosis is rare in patients with equivocal Tc-99m PYP: A single-center experience.

Introduction: We sought to determine the frequency of a final diagnosis of cardiac amyloidosis in patients with an equivocal Tc-99m pyrophosphate (PYP) scan.

Methods: Data were obtained by IRB-approved retrospective review of patients who underwent a PYP scan at the UPMC Cardiac Amyloidosis Center from Jan 1, 2016, through August 1, 2021. Planar and SPECT imaging were performed at 1 hour and 3 hours after injection of 15 mCi of Tc-99m PYP. Positive and negative scans were defined by the presence or absence, respectively, of myocardial PYP uptake on the SPECT scan. A scan was deemed equivocal if tracer was present in the field of view but could not be definitively localized to the myocardium. Planar imaging was used as supportive data. Serum studies for AL amyloidosis were performed in all patients. A tissue biopsy was performed when indicated clinically. Chart review was performed to determine the subsequent evaluation and final diagnostic determination of patients with equivocal PYP.

Results: Among 586 PYP scans performed, 394, 160 and 23 were read as negative, positive and equivocal, respectively. The following data pertain to patients with equivocal scans. 74% were men and 78% Caucasian, with a median age of 77 (51-89 years). At 1 hour, 15 (65%) patients had a heart-to-contralateral lung (H/CL) ≥ 1.5. At 3 hours, this ratio was ≥ 1.3 in 13 (57%) patients. The listed indications for PYP scan were left ventricular hypertrophy (n=17), aortic stenosis (n=3), heart failure (n=2) and family history of V142 mutation (n =1). All patients had a clinical diagnosis of heart failure, 3 (13%) had bilateral carpal tunnel syndrome, 3 (13%) had peripheral neuropathy, 3 (13%) had spinal stenosis and 5 (22%) had low voltage EKG. 19 (83%) patients had an intraventricular septal thickness (IVS) ≥ 1.2 cm, 16 (70%) had elevated BNP and 3 (13%) had mildly elevated baseline troponin. Cardiac magnetic resonance (cMR) was performed in 16 (70%) patients and was not suggestive of cardiac amyloidosis in any. No patient had a final diagnosis of cardiac amyloidosis. The final diagnosis was hypertensive heart disease (14), hypertrophic cardiomyopathy (5), coronary artery disease (3) and chronic pericarditis (1).

Conclusions: In an expert single-center experience, patients with equivocal PYP rarely have a final diagnosis of cardiac amyloidosis.