"Clinically, this finding helps differential diagnosis and reduces the risk of misdiagnosis between two conditions with very different therapeutic options," said Claudio Rapezzi, M.D. from the University of Bologna and S. Orsola-Malpighi Hospital in Bologna, Italy.
Clinicians have a difficult time distinguishing between transthyretin amyloidosis, which is often hereditary, and acquired monoclonal immunoglobulin light-chain amyloidosis, which is often a consequence of multiple myeloma. Although the two forms of abnormal protein deposition look similar and both stiffen the heart muscle, ultimately leading to heart failure; they require different treatments. Treatment of transthyretin amyloidosis can include liver transplantation, while bone marrow transplantation may be indicated for acquired monoclonal immunoglobulin light-chain amyloidosis.
This small trial is the first assessment of scintigraphy in patients with cardiac amyloidosis. Intravenous solutions containing a radioactive isotope (99mTc-DPD) were given to 15 patients with transthyretin amyloidosis and 10 patients with acquired monoclonal immunoglobulin light-chain amyloidosis. Genotyping and immunohistochemistry were used as the reference standards for this study.
Detectors showed that the radioactive tracer was taken up by the heart muscle tissue of the transthyretin amyloidosis patients, but not by the hearts of the patients with acquired monoclonal immunoglobulin light-chain amyloidosis.
"From a research perspective, the study also indicates that etiology, the cause of a disease, is a third major cause, in addition to type of organ involved and tracer type, of scintigraphic variability in cardiac amyloidosis: this is a highly relevant consideration for future studies," Dr. Rapezzi said.
Dr. Rapezzi said this finding needs to be confirmed in larger groups of patients.
Myron C. Gerson, M.D., F.A.C.C., at the University of Cincinnati in Cincinnati, Ohio, who was not connected with this study, noted that correct classification of the disorder is essential to effective treatment.
"There has been no simple, widely available test for distinguishing hereditary from immunoglobulin light-chain amyloid," Dr. Gerson said. "Although this is a small study requiring independent confirmation, the findings suggest that 99mTc-DPD imaging may provide a useful step in the workup of the differential diagnosis of transthyretin versus immunoglobulin light-chain (AL) etiology in patients with documented cardiac amyloidosis."
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