Hyperphosphatemia-Related False-Positive 99m Tc-Pyrophosphate Myocardial Scan: A Case Report With Endomyocardial Biopsy Result.

With documented high specificity, 99m Tc-pyrophosphate (PYP) scan enables the diagnosis of transthyretin cardiomyopathy to be made reliably without endomyocardial biopsy in patients who do not have monoclonal gammopathy. We report a case with extensive myocardial uptake of Perugini 3 score in the 3-hour 99m Tc-PYP myocardial SPECT that suggested transthyretin cardiac amyloidosis. However, a followed endomyocardial biopsy revealed no amyloid deposition. In this case, hyperphosphatemia was the most likely and presumptive cause of the false-positive 99m Tc-PYP scan. With this case, our experiences of the potential causes of false-positive results of 99m Tc-PYP are further expanded.