Evaluating Use of 99mTc-PYP Scan in Diagnosis of ATTR- A Tertiary Care Center Experience

Abstract

Purpose The 99mTc-pyrophosphate (PYP) scan for the diagnosis of Transthyretin Related Cardiac Amyloidosis (ATTR) may be used in an inappropriate context or with incorrect interpretation, leading to misdiagnosis and futile financial burden. Here we report the use of PYP scans at our institution. Methods We retrospectively reviewed 99 consecutive patients’ data who underwent PYP between May 2018 and June 2020. ATTR diagnostic criteria were defined as any of: 1) cardiac biopsy-proven ATTR; 2) non cardiac biopsy-proven ATTR with evidence of echocardiographic features (unexplained left ventricular hypertrophy or apical sparing); 3) ATTR mutation with echocardiographic features and no evidence of plasma cell dyscrasia; 4) MRI suggestive of cardiac amyloidosis and no evidence of plasma cell dyscrasia. Comparisons between ATTR and non-ATTR were made using Chi-square, Fisher's Exact or Wilcoxon rank-sum tests. Sensitivity and specificity of PYP scan were estimated with Clopper-Pearson confidence intervals (CI). Results 48 (48%) patients had adequate data to evaluate diagnostic ATTR criteria. These patients were male (73%), African American (44%), with median age of 68 yrs, NYHA class ≥ 3 (50%), NICM (62%), neuropathy (44%) and orthopedic manifestations (31%). PYP scan (100%), cardiac MRI (44%), cardiac biopsy (31%), genetic testing (58%) and other organ biopsy (21%) were used to diagnose ATTR. The sensitivity of PYP scan for cardiac ATTR was 100% (95% CI: 78-100) and the specificity was 58% (95% CI: 41-74). All indeterminate PYP scans (17%) were negative for ATTR. On TTE, median septal wall thickness was 1.7 mm in those with cardiac ATTR compared to 1.2 mm in those without (p=0.002); median posterior wall thickness was 1.6 mm and 1.1 mm, respectively (p=0.007). 88% of patients who did not have adequate data to evaluate for ATTR had normal or indeterminate PYP scans. Conclusion In our center representing real world data, PYP scan had similar sensitivity but reduced specificity compared to previously reported data. Our data shows the need for more selective use of PYP scan and reiterates need for ruling out plasma cell dyscrasia if only imaging is used to diagnose ATTR.