Presentation
Abnormal transthoracic echo.
Patient Data
Imaging of the chest/heart obtained 3 hours after the injection of 21 mCi of 99mTc-PYP IV.
Anterior planar view demonstrates moderately increased radiotracer uptake associated with the heart. Incidental intense uptake is present at the right sternoclavicular joint due to osteoarthritis. Phyiologic uptake is present in the ribs and sternum. A small amount of radiotracer activity is present in the upper abdomen, representing excreted radiotracer in the renal pelves.
Left lateral planar view again demonstrates moderately increased radiotracer uptake associated with the heart.
SPECT MIP and axial images show the uptake to be in the myocardium and similar in intensity to the ribs. This is grade 2 based upon the Perugini grading scale and is positive for ATTR.
Case Discussion
Amyloidosis is a disorder characterized by the deposition of insoluble protein fibrils in the extracellular space. Many organs can be affected, but the heart is one of the most common sites of disease and results in restrictive cardiomyopathy. It is typically seen with two subtypes of amyloidosis, amyloid transthyretin (ATTR), and amyloid immunoglobulin light chain (AL).
Cardiac scintigraphy with 99mTc-pyrophosphate (Tc-99m PYP), and other Tc-99m bone-seeking radiotracers such as DPD, HDP, and HMDP, are useful as a non-invasive means to confirm the diagnosis of ATTR cardiac amyloidosis.
When originally adopted, scintigraphy used planar imaging and measurement of the heart-to-contralateral lung (H/CL) ratio on the anterior view. Unfortunately, this led to a small but significant percentage of incorrect interpretations. More recently, it has been recommended to use SPECT or SPECT/CT for diagnosis, as it allows direct visualization of radiotracer uptake in the myocardium and avoids pitfalls related to superimposed osseous uptake, retained activity in the blood pool, and other issues.
Cardiac uptake of 99mTc-DPD and HMDP is evaluated using a semi-quantitative visual scoring method (Perugini grading scale) with relation to bone (rib) uptake:
grade 0: no myocardial uptake and normal bone uptake
grade 1: myocardial uptake less than rib uptake
grade 2: myocardial uptake equal to rib uptake
grade 3: myocardial uptake greater than rib uptake
Visual scores of 2 or 3 are positive for ATTR, and scores of 0 or 1 are negative.
Myocardial tracer uptake can be seen in some cases of AL cardiac amyloidosis, so it is encouraged that the report includes a recommendation to exclude an underlying plasma cell dyscrasia.
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