Myocardial infiltration is the worst prognostic factor for patients affected by amyloidosis. The most frequent forms of systemic amyloidosis associated with cardiac dysfunction are transthyretin-related (ATTR) and light chains amyloidosis (AL), leading to different pathological features so had to be considered different diseases with different treatments and prognosis. We aimed to verify the usefulness of 99mTc-DPD in the detection and etiologic differentiation of ATTR from AL, mandatory for the appropriate clinical management of amyloidotic cardiomyopathy (CA).
Of 51 patients suspected to have CA that received 99mTc-DPD (740 MBq intravenously), 47 with cardiac involvement and 4 without echocardiographic signs, 49 were included in the analysis. 32 affected by ATTR-wt, 9 AL and 8 non-CA diagnosed by physicians of Amyloidosis Research and Treatment Center of Pavia. Whole body scan were obtained at 5 min and at 3 h. Myocardial uptake was visually scored from 0 to 3 according to Rapezzi (0: absent cardiac and normal bone uptake; 1: mild cardiac uptake < bone; 2: moderate cardiac uptake associated to attenuated bone uptake; 3: strong cardiac uptake with mild/absent bone uptake). Heart retention (HR%), whole-body retention (WB) and their ratio (H/WB) evaluated from region-of-interest (ROI) were semiquantitatively assessed. G-SPET was performed in score 2 and 3. Echocardiography (US), serum assay of NTproBNP and troponin-I were performed within 15 days before/after the scan.
All the patients without US signs of CA showed no myocardial tracer uptake. All ATTR subjects (32) had score 3 (30) or 2 (2). Among AL: one score 2, three score 1 and five score 0. The diagnostic accuracy, sensibility and specificity of visual scoring were 98%, 100% and 94.1% for the diagnosis of TTR related AC and 81.6%, 88.9% and 89% for the AL one. Therefore score 3 was observed in ATTR only, score 2 in ATTR (2) or AL (1), score 1 in AL (1) while score 0 to AL (5) or non-CA (8). The visual scoring PPVs for ATTR and AL were 0.97 and 0.53 respectively, the NPVs were 1.00 and 0.98. HR and H/WB were significantly higher among TTR-related CA (p < 0.05), but not statistically different between AL or non-CA. On the other side only the organ dysfunction markers were significantly different (p < 0.05) among the three patients groups: mean NTproBNP 683, 4431 and 11401 ng/L, mean troponin-I 0.04, 0.13 e 0.24 ng/mL respectively in the negative, ATTR and AL group.
In our experience DPD scan was useful to further confirm TTR CA at the end of the non-invasive work-up, likely reducing the number of endomyocardial biopsies, while its role in the differential diagnosis between the two other subject groups remains to be ascertained. In addition the high prevalence of disease is explained by the fact that patients under study were previously selected by an amyloidosis reference centre, therefore with high suspicious of cardiac involvement and heart failure. Instead the recruitment of a different population, elderly with non-specific cardiac and/or humoral signs of CA, would be useful for the validation of scoring prognostic value in an earlier stage of disease.