Potential pitfall in parathyroid sestamibi imaging resulting from a cardiac pacemaker

A 47-year-old woman with a history of end-stage renal disease and hyperparathyroidism after total parathyroidectomy had Tc-99m sestamibi imaging to identify possible ectopic parathyroid tissue. This study was prompted by increasing calcium and parathyroid hormone levels after several years of taking calcium supplements necessitated by a surgically induced hypoparathyroid state and end-stage renal disease. The scan showed persistent linear activity in the upper right mediastinum in delayed images, after washout of the thyroid had occurred. Because of the unusual configuration of this finding, investigation of the patient's clinical history and other imaging studies was undertaken. The authors concluded that the unusual mediastinal uptake was not hyperactive parathyroid tissue, but rather was attributed to the presence of central venous pacemaker wires. Thus, this case illustrates a potential pitfall in parathyroid sestamibi imaging, the uptake of which may increase in the presence of a cardiac pacemaker, and it emphasizes the importance of correlative imaging.