Extracardiac soft tissue uptake, evidenced on early 99mTc-HMDP SPECT/CT, helps typing cardiac amyloidosis and demonstrates high prognostic value

Increased cardiac uptake (CU) on early-phase 99mTc-HMDP scintigraphy has demonstrated diagnostic and prognostic values in amyloid transthyretin (ATTR) cardiac amyloidosis (CA). Extracardiac uptake (ECU) has been poorly studied. We assessed the clinical value of ECU, in combination with CU, on 99mTc-HMDP scintigraphy using a novel Methodological Amyloidosis Diagnostic Index (MADI). We reviewed all patients referred for suspicion of CA, who underwent 99mTc-HMDP scintigraphy over an 8-year period. ECU, CU, and MADI were determined: MADI0 = neither ECU or CU, MADI1 = ECU alone, MADI2 = CU alone, and MADI3 = ECU + CU. Of 308 eligible patients, 247 had CA, including 75 ATTRv, 107 ATTRwt, and 65 light-chain (AL), while 61 had another cardiopathy (controls). ECU was observed in 29% of CA and 3% of controls. Most frequent sites of ECU were pleuropulmonary (16% of CA, 3% of controls) followed by the digestive tract and subcutaneous tissues. The liver and spleen ECU was only observed in AL-CA (n = 8). CU was only observed in CA patients (n = 187), of whom 182 had ATTR-CA vs. 5 AL-CA, P 0 vs. MADI0 in AL and MADI3 vs. MADI2 in ATTR were associated with a worse prognosis (P = 0.03 and P = 0.002, respectively). ECU combined with CU demonstrates high diagnostic and prognostic values in CA patients. MADI seems an easy and reliable score in clinical practice.