False-Positive 99mTechnetium-Pyrophosphate Scintigraphy in Two Patients With Hypertrophic Cardiomyopathy

Pitfalls for the non-invasive diagnosis of wild-type transthyretin amyloid cardiomyopathy in a young adult: a case report

Background

Using technetium (Tc)-labelled pyrophosphate (PYP) cardiac scintigraphy, a non-invasive diagnosis of transthyretin amyloid (ATTR) cardiomyopathy can be made without histopathological confirmation. In patients suspected of ATTR cardiomyopathy, however, atypical presentations may necessitate further investigation.

Case summary

A 30-year-old man with hypertension and end-stage renal disease on peritoneal dialysis presented with progressive exertional dyspnoea. Left ventricular hypertrophy (LVH) with a maximal end-diastolic wall thickness up to 16 mm was detected on echocardiography. Speckle-tracking analysis revealed a reduced longitudinal strain of left ventricle with a relative apical sparing pattern. Although the absence of monoclonal gammopathy, a grade 3 myocardial uptake in ^99mTc-PYP cardiac scintigraphy, and negative TTR gene mutation inferred the diagnosis of wild-type ATTR, the relative youth of the patient still raised concerns regarding the diagnosis. Under clinical doubt, he underwent further testing. In non-contrast cardiac magnetic resonance (CMR) with native T1 mapping, the native T1 myocardial value was within the normal range. In endomyocardial biopsy (EMB), there was no evidence of amyloid deposition, negative Congo red staining, and no immunohistochemical evidence of transthyretin expression. These results excluded the diagnosis of ATTR cardiomyopathy and prevented subsequent unnecessary treatments.

Discussion

When patients with unexplained LVH meet the non-invasive diagnostic criteria for ATTR cardiomyopathy, an EMB should be considered in selected cases. Patients presenting at an atypical age for wild-type ATTR cardiomyopathy, absence of extracardiac symptoms/signs or classic electrocardiogram features for cardiac amyloidosis should be suspected of another diagnosis and require further CMR or EMB to confirm.

Multimodality assessments of wild‐type transthyretin cardiac amyloidosis with no ventricular hypertrophy

While patients with transthyretin cardiac amyloidosis (ATTR-CA) typically present with concentric or asymmetric hypertrophy, a small percentage of ATTR-CA is known to present with 'atypical' cardiac morphologies such as eccentric hypertrophy or even no hypertrophy. However, detailed report of multimodality assessments of ATTR-CA with no ventricular hypertrophy is lacking. Herein, we report detailed multimodality assessments of an 81-year-old Japanese woman with heart failure and history of carpal tunnel syndrome and lumbar canal stenosis, presenting no ventricular hypertrophy and negative ^99m technetium-pyrophosphate scintigraphy, who was eventually diagnosed as having wild-type ATTR-CA. Our case highlights the role of multimodality assessments for early diagnosis of ATTR-CA in patients with atypical cardiac morphologies and also emphasizes the limitations of bone scintigraphy and the importance of considering ATTR-CA in patients with non-cardiac manifestations of ATTR amyloidosis.

Genotype-Phenotype Correlation of a Rare Transthyretin Variant Causing Amyloidosis

Left ventricular hypertrophy is a common entity with a broad differential diagnosis. We present a case of a middle-aged woman with left ventricular hypertrophy and neuropathy caused by a rare transthyretin variant in the absence of a family history or regional reports of hereditary transthyretin amyloidosis. This report outlines the diagnosis and management of patients with a mixed phenotype of hereditary transthyretin amyloidosis and enriches clinical data supporting the pathogenicity of a rare variant of transthyretin.

Clinical recommendations to diagnose and monitor patients with transthyretin amyloid cardiomyopathy in Asia

Transthyretin amyloid cardiomyopathy (ATTR‐CM) is a debilitating and life‐threatening condition with a heterogeneous clinical presentation. Recent guidelines from the United States and Europe have been published to guide clinical practice and to facilitate management conformity by covering current diagnostic and treatment strategies for patients with ATTR‐CM. These guidelines highlight the importance of an early diagnosis to optimize therapeutic outcomes, specifying the use of tests and imaging techniques to allow accurate, noninvasive diagnosis of ATTR‐CM. However, as regional practice variations across Asia may limit access to healthcare, availability of specific tests, and expertise in assessing diagnostic images, there is an ongoing need to provide an Asian perspective on these clinical guidelines. This review article provides practical recommendations for the diagnosis and monitoring of patients with ATTR‐CM in Asia, highlighting the need for additional guidelines to support a broad and diverse population, consider differing healthcare systems and diagnostic testing availability, and provide a flexible yet robust algorithm.

99m Technetium-pyrophosphate scintigraphy: a practical guide for early diagnosis of transthyretin amyloid cardiomyopathy

Transthyretin amyloid cardiomyopathy (ATTR‐CM) is caused by the cardiac deposition of insoluble amyloid fibrils formed by misfolded transthyretin proteins and is associated with various cardiac symptoms, such as progressive heart failure, conduction disturbance, and arrhythmia. The implementation of ^99mtechnetium (^99mTc)‐labelled bone radiotracer scintigraphy for diagnosing ATTR‐CM has enabled accurate diagnosis of the disease with high sensitivity and specificity and positioned this diagnostic modality as an integral part of disease diagnostic algorithms. In 2020, ^99mTc‐pyrophosphate scintigraphy received exceptional approval for Japanese national health insurance reimbursement as a diagnostic method of ATTR‐CM. Nevertheless, the utility of ^99mTc‐labelled bone radiotracer scintigraphy and the importance of an early diagnosis of suspected ATTR‐CM using this technique have yet to be internalized as common practice by general cardiologists, and guidance on daily clinical scenarios to consider this technique for a diagnosis of suspected ATTR‐CM is warranted. In this review, we discuss the utility of ^99mTc‐labelled bone radiotracer scintigraphy for the early diagnosis of ATTR‐CM based on published literature and the outcomes of an advisory board meeting. This review also discusses clinical scenarios that could support early diagnosis of suspected ATTR‐CM as well as common pitfalls, correct implementation, and future perspectives of ^99mTc‐labelled bone radiotracer scintigraphy in daily clinical practice. The clinical scenarios to consider ^99mTc‐labelled bone radiotracer scintigraphy in daily practice may include, but are not limited to, patients with a family history of the hereditary type of disease; elderly patients (aged ≥60 years) with unexplained cardiac findings (e.g. cardiac hypertrophy associated with abnormalities on an electrocardiogram, heart failure with preserved ejection fraction associated with unexplained left ventricular hypertrophy, and heart failure with reduced ejection fraction associated with atrial fibrillation and left ventricular hypertrophy); and patients with cardiac hypertrophy associated with diastolic dysfunction, right ventricular/interatrial septum/valve thickness, left ventricular sparkling, or apical sparing. Cardiac hypertrophy and persistent elevation in cardiac troponin in elderly patients are also suggestive of ATTR‐CM. ^99mTc‐labelled bone radiotracer scintigraphy is also recommended in patients with characteristic cardiac magnetic resonance findings (e.g. diffuse subendocardial late gadolinium enhancement patterns, native T1 increase, and increase in extracellular volume) or patients with cardiac hypertrophy and bilateral carpal tunnel syndrome.