Clinical use of differential nuclear medicine modalities in patients with ATTR amyloidosis

Histological proof remains the gold standard for the diagnosis of amyloidosis. Nuclear medicine imaging techniques are able to determine the amyloid load in the body. Currently, the best imaging modality is (123)I-SAP scintigraphy. This modality has high sensitivity for detecting amyloid deposits in all amyloid subtypes. Involvement of liver and spleen can be visualized before clinical signs are present. The addition of single photon emission computed tomography improves the differentiation of overlying organs. However, (123)I-SAP is not FDA approved. Its availability is limited to two centres in Europe. Furthermore, it is not suitable for imaging cardiac involvement of amyloidosis, due to movement, blood-pool content and lack of fenestrated endothelial in the myocardium. Phosphate derivates labelled with (99m)Tc, are able to detect calcium compounds in cardiac amyloidosis. Finally, (123)I-MIBG, an analogue of norepinephrine, can detect cardiac sympathetic innervation abnormalities as a consequence of amyloid deposits. Both these last techniques seem to be able to detect cardiac involvement before echocardiographic parameters are present. We illustrate the clinical use of these modalities with two patients with ATTR type amyloidosis.