A Nondiagnostic 99mTc-PYP Scan with Absent Skeletal Uptake.

Area of Science:

• Nuclear Medicine
• Cardiology
• Radiopharmacy

Background:

• 99mTc-PYP scintigraphy is a key noninvasive tool for diagnosing transthyretin cardiac amyloidosis.
• Accurate interpretation requires assessing both myocardial uptake and systemic radiotracer biodistribution.
• Abnormal biodistribution can mimic or obscure true findings.

Purpose of the Study:

• To report a case of 99mTc-PYP scintigraphy with abnormal biodistribution mimicking free pertechnetate.
• To highlight the importance of recognizing incorrect biodistribution for accurate diagnosis.
• To emphasize that such scans should be considered nondiagnostic, not negative.

Main Methods:

• A case study of a 75-year-old woman with suspected cardiac amyloidosis.
• Initial 99mTc-PYP scintigraphy showed unexpected gastric and thyroid uptake with absent skeletal activity.
• SPECT/CT was used for detailed imaging. A repeat scan was performed 1.5 months later.

Main Results:

• The initial scan demonstrated a biodistribution pattern consistent with free 99mTc-pertechnetate, not 99mTc-PYP.
• No definite myocardial uptake was observed in either scan.
• The repeat scan showed expected skeletal uptake, confirming the initial scan's error.

Conclusions:

• Abnormal 99mTc-PYP biodistribution (gastric/thyroid uptake, absent skeletal activity) indicates a preparation or administration error.
• Such findings render the scan nondiagnostic for cardiac amyloidosis.
• Clinicians should be aware of this potential pitfall and consider repeat imaging if necessary.