Imaging of the Autonomic Nervous System in Cardiac Amyloidosis

Abstract

Cardiac amyloidosis is a restrictive cardiomyopathy with potentially fatal consequences due to amyloid deposition in the myocardial tissue, but also to amyloid infiltration in the nerve conduction system. The prognosis is poor because of progressive cardiac disease. Early detection of cardiac involvement has become of major clinical interest, because its occurrence and severity limits the choice of treatment. The use of iodine-123 labelled metaiodobenzylguanidine ([123I]-MIBG), a chemical modified analogue of norepinephrine, is well established in patients with heart failure and plays an important role in cardiac amyloidosis. [123I]-MIBG is stored in vesicles in the sympathetic nerve terminals and is not catabolised like norepinephrine. Decreased heart-to-mediastinum ratios (HMR) on late planar images and increased wash-out rates indicate cardiac sympathetic denervation and are associated with poor prognosis. Single-photon emission computed tomography (SPECT) provides additional information and has advantages for evaluating abnormalities in regional distribution in the myocardium. However, inferior wall defects should be interpreted with caution.