Nuclear imaging of cardiac amyloidosis

Excerpt

Amyloidosis is a multi-system disorder affecting various organs and histologically defined by deposition of abnormal proteins (amyloid fibrils) with characteristic staining pattern. Cardiac involvement may be seen with AL amyloidosis, characterized by deposition of light chains, and TTR amyloidosis, characterized by deposition of transthyretin, either genetically abnormal (mutant transthyretin, familial form of cardiac amyloidosis) or normal (wild-type transthyretin-wt, senile systemic amyloidosis). Cardiac amyloidosis (CA) is an underdiagnosed clinical entity affecting 50% of the patients with AL amyloidosis, in almost all patients with wt-TTR amyloidosis and with variable frequency of cardiac involvement in mutant-TTR amyloidosis depending on the underlying mutation.1,2 Under-diagnosis is partly due to the inherent difficulty in making a definitive diagnosis of CA, for which endomyocardial biopsy remains the gold standard. Tissue-based diagnosis, however, is an invasive approach and it is not uncommon for patients either to be considered too high of a risk to undergo biopsy, or refuse biopsy. In these cases, diagnosis of CA relies on (a) obtaining tissue from a different site (abdominal fat pad, salivary glands etc.) and (b) identifying signs indicative of CA on cardiac magnetic resonance imaging. Another reason why diagnosis of CA is challenging is because its cardinal echocardiographic features (increased ventricular wall thickness, impaired diastolic function) are also frequently seen with other common disorders, most notably hypertensive heart disease and other restrictive cardiomyopathies. …