Case Presentation Corner
18F-FDG/13N-ammonia cardiac PET findings in ATTR cardiac amyloidosis

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Abstract

18F-flurodeoxyglycose (FDG)/13N-ammonia positron emission tomography/computed tomography (PET/CT) is frequently utilized to evaluate cardiac sarcoidosis (CS) but findings can reflect other forms of myocardial inflammation or altered myocardial metabolic activity. Herein, we present five cases where cardiac PET findings suggested CS, but right ventricular endomyocardial biopsy samples revealed ATTR-type cardiac amyloidosis.

Introduction

18F-flurodeoxyglycose (FDG) positron emission tomography/computed tomography (PET/CT) has emerged as a prominent imaging modality for diagnosis and prognosis of cardiac sarcoidosis (CS) or idiopathic granulomatous myocarditis.1,2 The Japanese Cardiovascular Society, the World Association for Sarcoidosis and Other Granulomatous Disorders, and Heart Rhythm Society diagnostic criteria include 18F-FDG PET in the diagnostic criteria of CS.3,4 However, the specificity of 18F-FDG PET for CS is limited by physiologic myocardial 18F-FDG uptake and other disorders that may increase global or regional myocardial glucose utilization.5

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an infiltrative disease that results from the deposition of misfolded transthyretin (TTR) protein in the myocardium.6 ATTR-CM is not typically associated with myocarditis. We report five patients with a clinical presentation suggestive of CS with abnormal 18F-FDG/13N-ammonia cardiac PET findings that were subsequently found to have ATTR-CM (Table 1). All patients had appropriate metabolic preparation for the 18F-FDG/13N-ammonia cardiac inflammatory PET, hereafter referred to as cardiac PET, including a combination of ketogenic meals and prolonged fasting for myocardial suppression.2 All patients underwent endomyocardial biopsy (EMBx), where light microscopic analysis of the myocardial tissue demonstrated extracellular amorphous deposits that were stained with both sulfated Alcian blue and Congo red, the latter of which demonstrating classic green birefringence under cross-polarized light. Amyloid typing was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based proteomics following laser-capture microdissection on paraffin-embedded tissue.7

Section snippets

Case One

The initial case involves a 77-year-old man with history of bilateral carpal tunnel syndrome and spinal stenosis who presented with progressive dyspnea on exertion. Electrocardiogram showed sinus rhythm with first-degree atrioventricular block, multiple premature ventricular contractions (PVC), and q-waves in the inferior leads consistent with prior inferior myocardial infarction (Figure 1). Transthoracic echocardiogram (TTE) demonstrated newly reduced ejection fraction (EF) of 35% with

Discussion

In the setting of clinically suspected CS, cardiac PET/CT is one of the most sensitive imaging modalities for the diagnosis of CS.2, 3, 4, 5 Proper patient preparation is imperative when using 18F-FDG to suppress physiologic myocardial uptake in favor of free fatty acid utilization by the myocardium, in order to unmask 18F-FDG uptake due to myocardial inflammation.1,2,5 Other causes of myocardial 18F-FDG uptake include other forms of myocarditis, hibernating myocardium (assessed via a different

Conclusion

We present five patient cases in which cardiac PET/CT was obtained due to suspicion for CS and demonstrated positive myocardial FDG uptake, which can represent a surrogate for myocardial inflammation. However, histological analysis including LC-MS/MS demonstrated only ATTR-type cardiac amyloidosis, suggesting an inflammatory component of the disease process with regional heterogeneity. In this clinical context, the specificity of cardiac PET/CT for CS may be decreased.

Disclosures

No relevant disclosures for Kathleen A Young, MD, Melissa Lyle, MD, Andrew N Rosenbaum, MD, Ian C Chang, MD, Grace Lin, MD, Melanie C Bois, MD, Omar F Abou Ezzeddine, MD, CM, MS, Hayan Jouni, MD, Panithaya Chareonthaitawee, MD, Suraj Kapa, MD, Martha Grogan, MD, Leslie T Cooper, MD, Lori Blauwet, MD, and John P Bois, MD

Funding

No funding support for this work.

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