Cardiac Amyloidosis Diagnosis with 99mTc-PYP Scintigraphy

Diagnostic Utility and Indications

The American Heart Association recommends 99mTc-PYP scintigraphy for confirming ATTR cardiac amyloidosis after ruling out light chain disease, with diagnostic accuracy achieved when Grade 2 or 3 myocardial uptake is present on visual scoring and serum/urine immunofixation plus free light chains are negative 2, 3
The American College of Cardiology suggests screening for ATTR in new symptomatic heart failure with left ventricular wall thickness ≥12-14 mm, particularly when there is voltage-to-mass discordance on ECG, using 99mTc-PYP scintigraphy 1, 4, 3
Asymptomatic TTR gene carriers can undergo early detection of cardiac involvement using 99mTc-PYP scintigraphy 1, 2

A positive PYP scan requires BOTH visual and quantitative criteria, including a heart-to-contralateral lung ratio >1.5 at 1 hour OR >1.3 at 3 hours 8
SPECT imaging should be added to planar imaging to differentiate true myocardial uptake from blood pool activity 8

The presence of monoclonal protein can lead to false positive PYP scan interpretations, and patients with abnormal monoclonal protein evaluation require referral to a specialist amyloid center and consideration of endomyocardial biopsy for definitive tissue typing 1, 2, 8
Over 10% of patients with monoclonal gammopathy can have ATTR deposits, making tissue diagnosis essential when both PYP is positive and monoclonal protein studies are abnormal 8

The diagnostic pathway should begin with echo or MRI to identify infiltrative cardiomyopathy, then proceed to PYP for ATTR confirmation after excluding AL disease 1, 2, 4
If monoclonal protein IS present, PYP scan alone is insufficient, and endomyocardial biopsy with mass spectrometry is required 1, 4, 10

Cardiac MRI and echocardiography are rated "Appropriate" for initial screening, while PYP is specifically diagnostic for ATTR subtyping 1, 2, 4
Bone scintigraphy tracers (PYP in USA, DPD/HMDP outside USA) are mechanistically bone tracers that happen to bind ATTR deposits, providing diagnostic capability with possible early detection 5, 6, 7