Cardiac Amyloidosis: Approach to Diagnosis

Abstract

Amyloid is an amorphous, fibrillar material formed from various abnormally folded proteins that deposits locally or systemically. Over 95% of cases have been attributed to light chain deposition (AL) or transthyretin deposition (ATTR) amyloidosis. The basic investigations in the evaluation of cardiac amyloidosis include the electrocardiogram, echocardiography and cardiac biomarkers. Echocardiography in a patient with cardiac amyloidosis shows biatrial enlargement, biventricular hypertrophy, diastolic dysfunction, interatrial septal thickening, valvular thickening, a glistening appearance of the interventricular septum, and pericardial effusion. Magnetic resonance imaging can help distinguish amyloidosis from other causes of infiltrative/restrictive cardiomyopathy, from example, sarcoidosis, hemochromatosis, and Fabry disease based on characteristic enhancement patterns in these diseases. The latest Expert Consensus recommends that serum/urine immunofixation electrophoresis along with a serum free light chain assay must be done in all the cases of suspected cardiac amyloidosis. If the light chain assays are positive, we proceed with tissue diagnosis for confirmation of AL amyloidosis. If the screening assays are negative for monoclonal gammopathy, the next step is to obtain cardiac scintigraphy. If the nuclear scan is negative, but the index of suspicion remains high, an endomyocardial biopsy can be done. Once amyloid is demonstrated in histopathologic specimens, it must be typed to distinguish between AL and ATTR. The ideal method for this is tandem mass spectrometry, although this may not be widely available. It has a sensitivity of 88% and specificity of 96% higher than other techniques 23. In resource-poor settings, immunohistochemistry or immunoelectron microscopy can allow this distinction, although with lesser sensitivity.