Background and aim: Radio-labelled Aprotinin has been shown to bind with amyloid fibrils in vitro as well as in vivo. The aim was to test the usefulness of 99mTc-Aprotinin imaging in systemic amyloidosis.
Methods: Thirty-five cases who had 99mTc-Aprotinin scans for the assessment of systemic amyloidosis were reviewed retrospectively. Eighteen had biopsy-proven amyloidosis and 17 were controls (amyloidosis was excluded by negative biopsies and non-invasive tests). Five of 18 patients with amyloidosis had final diagnosis of cardiac amyloid.
Results: Physiological uptake of 99mTc-Aprotinin was noted in the urinary tract (kidneys and bladder) and in the liver of all patients and controls; and non-specific uptake of 99mTc-Aprotinin was visualised in the spleen and oro-facial structures in the majority of both groups. Myocardial 99mTc-Aprotinin uptake was noted in all five patients with final diagnosis of cardiac amyloidosis and in none of the 30 subjects who did not have cardiac amyloid. The median heart to background uptake ratio was 2.0 in cardiac amyloid patients and 1.1 in subjects without cardiac amyloid (P = 0.0004). Single Photon Emission Tomography (SPECT) studies of the thorax confirmed that the site of uptake lay within the myocardium. In the amyloidosis group, site-specific 99mTc-Aprotinin uptake was also identified in the subcutaneous tissue of the legs and in a breast nodule shown to be positive for amyloidosis on biopsy.
Conclusions: 99mTc-Aprotinin imaging may be a useful non-invasive method for the assessment of the presence and extent of extra-abdominal amyloid, particularly cardiac amyloidosis. It has little role in diagnosis of amyloidosis involving the oro-facial and abdominal structures.