Radionuclide imaging of amyloid infiltration in systemic AA and AL amyloidosis

Regarding the prognostic value of the pattern of organ function loss a non-invasive test would be helpful in evaluating the extent of organ involvement in amyloidosis. We performed whole-body scintigraphy with sup(99m)Tc-labeled methylene diphosphonate (Tc-MDP) and pyrophosphate (Tc-PYP) in 6 patients with systemic amyloidosis associated with inflammatory conditions (AA amyloid) and 6 patients with systemic amyloidosis associated with plasma cell dyscrasia (AL amyloid), as well as in 2 patients with localized amyloidosis. The purpose of this study was firstly to establish the efficacy of 'bone-scanning' in demonstrating amyloid deposits and secondly to determine the relative efficacy of Tc-MDP versus Tc-PYP. The results of scintigraphy were compared with the results of clinical studies. Scanning with sup(99m)Tc-labeled phosphates appeared to be a sensitive non-invasive test for the extent and the distribution of organ involvement in both the systemic (AA and AL) and the localized types of amyloidosis. There was no difference in the intensity or the extent of soft-tissue uptake between Tc-MDP and Tc-PYP. We prefer, however, Tc-MDP because of the better contrast. The affinity of amyloid for Tc-MDP and Tc-PYP is probably due to the presence in amyloid deposits of calcium bound to the non-fibrillar glycoprotein AP (amyloid P-component), which is a common constituent of all forms of amyloid. (Author)