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Cardiac amyloid scintigraphy and MUGA
Bone-seeking tracers (Tc-99m PYP, DPD or HMDP) bind transthyretin (ATTR) amyloid in the heart; grade 2–3 cardiac uptake without a monoclonal protein in blood and urine diagnoses ATTR without biopsy.
Why it matters in the exam
The exam presents an older adult with heart failure with preserved ejection fraction, thick walls, bilateral carpal tunnel syndrome or spinal canal stenosis, and a whole-body scan showing cardiac uptake. The grading (Perugini): 0 — no cardiac uptake; 1 — less than the ribs; 2 — equal to the ribs; 3 — more than the ribs with attenuated rib uptake. With PYP the heart-to-contralateral ratio (H/CL) is also calculated — 1.5 or more at one hour supports ATTR. SPECT is mandatory to confirm that uptake is in the myocardium and not in the blood pool.
The critical condition: exclude light-chain (AL) amyloidosis with serum and urine immunofixation and serum free light chains. AL may give low-grade and even grade 2 uptake, so a positive scan with a monoclonal protein requires biopsy. After an ATTR diagnosis genetic testing separates the hereditary form from the wild-type form, which matters for treatment and for family members.
MUGA (radionuclide ventriculography) labels red blood cells with Tc-99m and images gated to the ECG; it measures left ventricular ejection fraction accurately and reproducibly, so it was used to monitor cardiotoxicity of anthracyclines and trastuzumab. Under ESC 2022 a fall of 10 percentage points or more to an ejection fraction of 40%–49% is moderate toxicity. Poor labelling leaves free pertechnetate, which is taken up by the thyroid, stomach and salivary glands. An arrhythmia such as atrial fibrillation degrades gating and accuracy. Today echocardiography with strain and MRI replace MUGA in most cases.
Key points
- PYP, DPD or HMDP bind ATTR.
- Grade 2–3 without a monoclonal protein — ATTR without biopsy.
- SPECT is mandatory to separate from blood pool.
- After diagnosis — genetic testing.
- MUGA — accurate ejection fraction; free pertechnetate with poor labelling.
Summary table
| Study | Principle | Decisive finding | Pitfall |
|---|---|---|---|
| PYP, DPD or HMDP | Binding to ATTR amyloid | Grade 2–3 uptake without a monoclonal protein | AL may give uptake |
| Cardiac SPECT | Separates myocardium from blood pool | Myocardial uptake | Blood pool looks positive on planar |
| Immunofixation and light chains | Excluding AL | Negative | Mandatory in every positive scan |
| MUGA | Labelled red cells | Accurate ejection fraction | Free pertechnetate, arrhythmia |
Free exam questions
מה נכון בבדיקתMultigated Radionuclide Angiography (MUGA) ? 99m (the question as examined, in Hebrew)
- א. Tc נקשר לשרשרת α של ההמוגלובין בכדוריות הדם האדומות
- ב. הבדיקה מתבצעת במבט פלנארי קדמי של בית החזה 99m
- ג. הבדיקה מתבצעת עם כדוריות דם אדומות מסומנות ב- Tc
- ד. בחולים המטופלים בתרופות קרדיוטוקסיות ירידה של לפחות20% בהתכווצות החדר השמאלי( LVEF ) מצריכה שינוי הטיפול התרופתי
לפניך מיפוי כל גופי בגבר בן70 עם אי ספיקת לב . איזה מבין המשפטים הבאים נכון? 99m (the question as examined, in Hebrew)
- א. זהו מיפוי עצם כל גופי עם Tc-MDP
- ב. הקליטה בלב תיתכן על רקע ארטיפקט או הכנה לקויה של החומר
- ג. הממצאים אופייניים למעורבות של שריר הלב ב- Light chain amyloidosis 99m
- ד. עוצמת הקליטה של Tc-DPD הינה בקורלציה שלילית עם תפקוד החדר השמאלי
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Sources
- ASNC/AHA/ASE/EANM/HFSA/ISA/SCMR/SNMMI Expert Consensus Recommendations for Multimodality Imaging in Cardiac Amyloidosis, 2021 — Bone-avid tracer scintigraphy and grading
- ESC Position Statement on Diagnosis and Treatment of Cardiac Amyloidosis, 2021 — Non-invasive diagnostic algorithm
- ESC Guidelines on Cardio-Oncology, 2022 — Definitions of cancer therapy-related cardiac dysfunction
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.