Noninvasive etiologic diagnosis of cardiac amyloidosis using (99m)tc-3,3-diphosphono-1,2-propanodicarboxylic Acid scintigraphy

We investigated the diagnostic accuracy of (99m)Tc-3,3- diphosphono-1,2-propanodicarboxylic acid ((99m)Tc-DPD) scintigraphy for differentiation of monoclonal immunoglobulin light-chain (AL) and transthyretin (TTR)-related cardiac amyloidosis. BACKGROUND: Differential diagnosis between TTR-related and AL amyloidosis is often complex and time-consuming. METHODS: Patients under routine observation with TTR-related/AL systemic amyloidosis and echocardiographic evidence of cardiac involvement were studied with (99m)Tc-DPD scintigraphy. RESULTS: Patients with cardiac involvement of TTR-related (group A; n = 15) and AL (group B; n = 10) etiology were comparable for left ventricular mass and renal function. Heart and heart/whole-body tracer retention were significantly higher (p < 0.05) in group A as compared with group B and with 10 unaffected controls. At visual scoring, cardiac (99m)Tc-DPD uptake was present in all group A patients and absent in all group B patients; thus, using genotyping/immunohistochemistry as the reference technique, the accuracy of (99m)Tc-DPD scintigraphy for distinction of TTR-related and AL etiology was 100%. Cardiac (99m)Tc-DPD uptake was also absent among unaffected controls. Using echocardiography as the reference standard for recognition of cardiac involvement, sensitivity and specificity of scintigraphy were both 100% for group A patients; in group B, sensitivity was 0% and specificity was 100% (accu racy, 50%). Eleven patients with myocardial (99m)Tc-DPD uptake underwent (99m)Tc-methylene diphosphonate ((99m)Tc-MDP) scintigraphy; all patients showed a (99m)Tc-MDP myocardial visual score of 0. CONCLUSIONS: Etiology is a third major cause-in addition to type of organ-involved (soft-tissue/heart) and tracer type-of scintigraphic variability in cardiac amyloidosis. This is a highly relevant consideration for future studies. We conclude that (99m)Tc-DPD scintigraphy is a useful step in the workup of the differential diagnosis of TTR versus AL etiology in patients with documented cardiac amyloidosis.