TY - JOUR
T1 - Misdiagnosis of paraganglioma by 123I-mIBG without stable iodine blockade of thyroidal radioiodine uptake
AU - Chen Cardenas, Stanley M.
AU - Duan, Daisy
AU - Rooper, Lisa M.
AU - Santhanam, Prasanna
AU - Cooper, David S.
AU - Ladenson, Paul W.
N1 - Publisher Copyright:
© Endocrine Society 2020.
PY - 2020/9/1
Y1 - 2020/9/1
N2 - Iodine-123/iodine-131 (123I/131I)-metaiodobenzylguanidine (mIBG) scan is an established tool for the localization and treatment of neuroendocrine tumors such as paragangliomas (PGL). To minimize thyroid irradiation by the radioactive iodine in the mIBG preparation, blockade of thyroidal iodine uptake with high doses of stable iodine used to be given routinely as part of all mIBG protocols. As 123I is now more frequently utilized than 131I, concern about thyroid radiation has lessened and thyroid blockade is often considered unnecessary. However, in certain situations, the lack of thyroid blockade can significantly impact treatment decisions. This report describes 2 patients who had mediastinal masses incidentally discovered on CT scans, and on further evaluation were found to have symptoms suggesting catecholamine excess with mildly elevated plasma normetanephrine levels. 123I-mIBG scans were performed without thyroid blockade, which demonstrated accumulation of tracer in the masses that were therefore deemed positive for PGL. Both patients underwent surgical resection of the masses with their surgical pathology revealing ectopic thyroid tissue (ETT). These cases illustrate that if appropriate thyroid blockade is not performed, ETT concentrating radioiodine from mIBG can lead to falsely positive mIBG scans and unnecessary surgical procedures. We conclude that in the setting of a mass suspicious for PGL in a location potentially representing ETT, such as the mediastinum, thyroid blockade should be employed for mIBG protocols to avoid false positive scans caused by ETT.
AB - Iodine-123/iodine-131 (123I/131I)-metaiodobenzylguanidine (mIBG) scan is an established tool for the localization and treatment of neuroendocrine tumors such as paragangliomas (PGL). To minimize thyroid irradiation by the radioactive iodine in the mIBG preparation, blockade of thyroidal iodine uptake with high doses of stable iodine used to be given routinely as part of all mIBG protocols. As 123I is now more frequently utilized than 131I, concern about thyroid radiation has lessened and thyroid blockade is often considered unnecessary. However, in certain situations, the lack of thyroid blockade can significantly impact treatment decisions. This report describes 2 patients who had mediastinal masses incidentally discovered on CT scans, and on further evaluation were found to have symptoms suggesting catecholamine excess with mildly elevated plasma normetanephrine levels. 123I-mIBG scans were performed without thyroid blockade, which demonstrated accumulation of tracer in the masses that were therefore deemed positive for PGL. Both patients underwent surgical resection of the masses with their surgical pathology revealing ectopic thyroid tissue (ETT). These cases illustrate that if appropriate thyroid blockade is not performed, ETT concentrating radioiodine from mIBG can lead to falsely positive mIBG scans and unnecessary surgical procedures. We conclude that in the setting of a mass suspicious for PGL in a location potentially representing ETT, such as the mediastinum, thyroid blockade should be employed for mIBG protocols to avoid false positive scans caused by ETT.
KW - Ectopic thyroid tissue
KW - I/I-metaiodobenzylguanidine
KW - Normetanephrine
KW - Paraganglioma metanephrine
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U2 - 10.1210/jendso/bvaa099
DO - 10.1210/jendso/bvaa099
M3 - Article
C2 - 32793847
AN - SCOPUS:85096489330
SN - 2472-1972
VL - 4
JO - Journal of the Endocrine Society
JF - Journal of the Endocrine Society
IS - 9
ER -