“White Thyroid” on Unenhanced Computed Tomography in Amiodarone-Induced Thyrotoxicosis Type 2

Abstract

Amiodarone-induced thyrotoxicosis is a common complication of long-term amiodarone treatment. In a patient with amiodarone-induced lung toxicity and amiodarone-induced thyrotoxicosis type 2 (AIT2), a "white thyroid" was incidentally observed on an unenhanced chest computed tomography (CT) scan. This "white thyroid" resembled a thyroid image on a contrast-enhanced CT scan. Therefore, the thyroid density was prospectively evaluated on unenhanced CT scans in cases of AIT2, in euthyroid patients on amiodarone (AEuth), and in unexposed controls. The aim was to test the hypothesis of a higher thyroid density in AIT2 compared to AEuth. The thyroid density, as measured in Hounsfield Units on unenhanced CT scans, is higher in AIT2 compared to AEuth and much higher than in controls. The causality of this association and its potential diagnostic use require further study.

Rise and fall of thyroid radiologic density during the time course of amiodarone-induced thyrotoxicosis

“…Evolution of sarcoidosis was closely monitored by fluorodeoxyglucosepositron emission tomography (FDG-PET) with integrated unenhanced CT scan. Although there was no thyroid signal on FDG PET, we noticed that in the unenhanced CT scan the thyroid had become 'white', suggesting that intrathyroid accumulation of iodine brought by amiodarone acted like an endogenous contrast medium, a phenomenon recently reported (1).…”

“…Van den Bruel et al proposed that the high thyroid radiologic density in AIT might be due to lysosome trapping of amiodarone ( 1 ). One could also propose that it might rather be related to uptake by the thyroid of the large excess of iodine released by amiodarone in the circulation.…”

Short review: novel concepts in the approach to patients with amiodarone-induced thyrotoxicosis

“…The evidence of increased thyroid density at unenhanced CT scan of AIT2 patients was originally reported in 2018 [ 26 ]. In details, the authors reported the incidental finding in an AIT2 patient of a “white thyroid” resembling a thyroid image on an enhanced CT scan; a subsequent comparison between thyroid densities (measured in Hounsfield units) of AIT2 patients compared to either patients with no thyroid dysfunction under amiodarone treatment or to healthy controls revealed a significant decrease when moving from the former to the latter [ 26 ].…”

“…The evidence of increased thyroid density at unenhanced CT scan of AIT2 patients was originally reported in 2018 [ 26 ]. In details, the authors reported the incidental finding in an AIT2 patient of a “white thyroid” resembling a thyroid image on an enhanced CT scan; a subsequent comparison between thyroid densities (measured in Hounsfield units) of AIT2 patients compared to either patients with no thyroid dysfunction under amiodarone treatment or to healthy controls revealed a significant decrease when moving from the former to the latter [ 26 ]. This study was further supported by a report of a single patient who underwent several CT scans before and along the course of AIT2: as a matter of fact, thyroid density increased after amiodarone administration and before detection of AIT, peaked after initiation of treatment for thyrotoxicosis, and returned to normal when thyrotoxicosis remitted [ 27 ].…”

Relationship between Thyroid CT Density, Volume, and Future TSH Elevation: A 5-Year Follow-Up Study

“…Accordingly, iodine-rich intake may result in increased thyroid CT densities prior to the onset of the aforementioned conditions. Although comprehensive studies on the relationship between dietary iodine exposure and thyroid CT densities are lacking, it is known that excessive iodine exposure through medications like amiodarone can lead to an increase in thyroid densities [16,17]. Additionally, there are scarce longitudinal data regarding thyroid volume.…”