Presentation
Heart failure with myocardial thickening on transthoracic echocardiogram.
Patient Data
Tc-99m PYP scan
Increased activity within the myocardium of the left ventricle on the 1-hour delayed planar image. This persists on the 3-hour delayed image.
Perugini score = 3
Heart to contralateral lung ratio (HCL ratio) = 1.76
Focal uptake in the left 6th and 10th rib from rib fractures of indeterminate age was localized on SPECT-CT (not shown).
Moderate uptake in the right innominate bone is suggestive of Paget's disease.
Case Discussion
Tc-99m pyrophosphate (PYP) scan is used to diagnose transthyretin cardiac amyloidosis (ATTR) cardiac amyloidosis. The bone agent relies on calcium in amyloid deposits to bind to phosphate.
The Perugini score is a qualitative measure comparing myocardial to rib uptake. A grade greater than 2 is considered a positive finding for ATTR cardiac amyloidosis.
The heart to contralateral lung (HCL) ratio is a quantitative measure comparing the counts of the myocardium with the contralateral lung. It is vital to not include the sternum, liver or fractures in the region of interest of the contralateral lung as it would confound the ratio. A ratio less than 1 is considered negative. A ratio greater than 1.5 is strongly suggestive. A ratio between 1 and 1.5 is equivocal.
The main differential diagnosis for this appearance includes myocardial infarction although it is usually more focal.