A Progressive <sup>99m</sup>Tc-MDP Uptake in Transthyretin Cardiac Amyloidosis

A 90-year-old man with a history of prostate cancer presented with dyspnea.He had undergone prostatectomy 20 years previously and was followed with 99m-technetium methylene diphosphate ( 99m Tc-MDP) scintigraphy for metastatic surveillance.Electrocardiography revealed 2:1 atrioventricular block (Picture 1).Echocardiography showed left ventricular hypertrophy (Picture 2).He underwent pacemaker implantation.99m Tc-MDP scans from 16, 9, and 7 years prior revealed progressive myocardial uptake (Picture 3), raising suspicion of cardiac amyloidosis (CA).Subsequent 99 m Tc-pyrophosphate ( 99 m Tc-PYP ) scintigraphy showed Perugini grade 3 uptake (Picture 4).Serum and urine immunofixation and free light chain assays ruled out a monoclonal component.Transthyretin gene sequencing confirmed no pathogenic variants.The diagnosis was consistent with probable wild-type transthyretin CA according to established criteria.In contrast to 99m Tc-PYP, 99m Tc-MDP has low sensitivity for CA and is not recommended (1), although some reports described the uptake of MDP in CA (2).In this case, the progressive uptake of MDP appeared to reflect disease progression.