Diagnosis of multiple endocrine neoplasia type 2A in patients with positive thyroid imaging by iodine-131 metaiodobenzylguanidine scintigraphy.

We retrospectively analyzed iodine-131 metaiodobenzylguanidine (I-131 MIBG) scintigraphy in 320 patients (male, 108 cases; female, 211 cases; average age, 45±15 years). All patients received thyroid block before examination between 2007 and 2010 in our department. Various degrees of radioactivity were found in the thyroid glands or thyroid region after bilateral thyroid surgery, in addition to bilateral or unilateral abnormal radioactivity in the adrenal glands in 3 patients. These cases were confirmed for medullary thyroid carcinoma and adrenal pheochromocytoma by pathology after surgical removal of the glands, and the diagnosis of multiple endocrine neoplasia type 2A was established from the patients' history and genetic examination. The possibility of medullary thyroid carcinoma should be considered on the finding of abnormal radioactivity in the thyroid or thyroid region by I-131 MIBG scintigraphy after excluding normal radioactivity in the thyroid. When significant abnormal radioactivity is seen in the adrenal gland on I-131 MIBG scintigraphy, the possibility of adrenal pheochromocytoma should be considered. Adrenal pheochromocytoma cannot be excluded when adrenal uptake is increased. The possibility of multiple endocrine neoplasia type 2A should be considered taking into account the history of these patients.