Amyloidosis Prediction Score: A Clinical Model for Diagnosing Transthyretin Cardiac Amyloidosis

Introduction Tc-99m Pyrophosphate (PYP) scintigraphy has a high diagnostic accuracy for transthyretin cardiac amyloidosis (ATTR-CA). Referral for PYP imaging is guided by certain clinical features which are variably present among patients with ATTR-CA. We aimed to derive a clinical score that would allow for prediction of a positive PYP study. Hypothesis We hypothesized that a clinical score, derived from multiple predictive variables, could be used to predict positive PYP. Methods Demographic, clinical, ECG and echocardiographic data for all patients who underwent PYP imaging between 06/2015 to 01/2020 were recorded. Variables that independently predicted a positive PYP study were identified from multivariable logistic regression analysis, and were assigned a numerical value (e.g. -1 for age 80 years). These values were then weighted by the prevalence of these predictors in the study cohort. Amyloidosis Prediction Score (APS) was derived, for each patient, as the sum of the weighted scores of the independent predictors. Receiver operating curve analysis was used to determine the accuracy of APS for predicting a positive PYP study. Results Data of 440 patients (mean age at PYP 75 ± 11, 71% men, 81% Caucasians) was analyzed, of which 126 (28.6%) had a positive PYP study. Age, male gender, bilateral carpal tunnel syndrome, lumbar spinal stenosis, atrial fibrillation, low QRS voltage, pseudo-infarct pattern and left ventricular hypertrophy were significant independent predictors of a positive PYP study (table). APS values ranged from -10 to +13, and predicted a positive PYP study with an accuracy of 0.98 (figure). An APS value of 3.2 conferred a sensitivity and specificity of 96% and 91% for predicting a positive PYP study, respectively, with a positive likelihood ratio of 10. Conclusion The Amyloidosis Prediction Score has a high diagnostic accuracy for a positive PYP study and can be easily determined from clinical history and routinely assessed ECG and echocardiographic features. This score has the ability to increase the diagnostic yield of PYP scintigraphy.