Delayed Tc-99m Sestamibi Washout in Graves’ Disease

Abstract

Tc-99m sestamibi has overtaken TI-201 as the preferred radiopharmaceutical to localize parathyroid adenomas. The differences in kinetics of sestamibi in the thyroid and parathyroid glands have resulted in the development of a two-phase imaging technique performed after a single injection of the tracer. Unfortunately, false-positive results occur in patients with thyroid nodules, although the addition of Tc-99m pertechnetate imaging to the protocol helps to differentiate between the two. Cases of concomitant primary hyperparathyroidism and Graves' disease are well documented, but there is little information about the handling of sestamibi in the latter condition. A 64-year-old woman with a history of Graves' disease and hyperparathyroidism was referred to the nuclear medicine department for a Tc-99m sestamibi parathyroid scintigram for preoperative localization of an adenoma. Early and delayed images showed diffuse delay in tracer washout in both lobes of the thyroid. A Tc-99m pertechnetate study performed 2 days later showed uniformly increased uptake consistent with Graves' disease. This case shows a hitherto unreported finding of sestamibi retention in Graves' disease. As with thyroid and parathyroid nodules, the mitochondrial content and p-glycoprotein expression may be factors responsible for this finding.