Abstract
Background and Objective
It has been reported recently in a cross sectional study that patients with amiodarone induced thyrotoxicosis (AIT) showed a ‘white’ thyroid on unenhanced computed tomography, due to intrathyroid iodine accumulation. However, the link between increase in thyroid radiologic density and amiodarone induced thyrotoxicosis remains unknown. We sought to analyze this link.
Methods
We present the case of a 34-year-old patient with severe sarcoidosis-related hypertrophic cardiomyopathy who was followed with successive unenhanced CT scans integrated with FDG PET scans. After the first CT scans the patient, who initially had a normal thyroid function, was exposed to amiodarone during 23 months and developed AIT, very likely by thyroiditis (AIT type 2). There were no thyroid antibodies, no evidence of thyroid sarcoidosis on FDG PET scan, while thyroid sonogram showed a homogenous 22 ml moderate goiter with normal echogenicity and no nodules.
Results
Analysis of the successive enhanced CT scans revealed that after initiation of amiodarone treatment, thyroid radiologic density steadily increased before detection of AIT, peaked after cessation of amiodarone and initiation of thyrotoxicosis treatment, before returning to normal as thyrotoxicosis receded. Thyroid volume also showed a moderate increase, peaking at the detection of thyrotoxicosis, before returning to normal.
Conclusion
This case suggests that AIT is preceded by a very high intrathyroid iodine accumulation before the ‘burst’ of thyroiditis occurs and that measurements of thyroid gland radiological density might predict the development and remission of AIT.
We present here the case of a 34-year-old patient with severe sarcoidosis-related cardiomyopathy who developed amiodarone-induced thyrotoxicosis (AIT). Evolution of sarcoidosis was closely monitored by fluorodeoxyglucose-positron 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).
The originality in our observation is that we could go back to the unenhanced CT scans performed before exposure to amiodarone and we could follow the evolution of thyroid radiologic density on the subsequent CT scans, until remission of thyrotoxicosis. This provided the first analysis of the evolution of intrathyroid iodine accumulation throughout the time course of AIT, showing a close association between thyroid radiologic density, size and function, with radiologic density and also volume, both rising before detection of thyrotoxicosis and then decreasing as a normal thyroid function was restored (Fig. 1).
The clinical story of the patient is in favor of AIT type 2 (thyroiditis) rather than AIT type 1 (increase in thyroid hormone synthesis), as the time between the first introduction of amiodarone and detection of thyrotoxicosis was 23 months (a first 3-month treatment was stopped for 3 months and then resumed for 17 months) and as the patient had no thyroid abnormality prior to amiodarone treatment (2). However, as thyrotoxicosis did not respond quickly to 0.5 mg/kg/day prednisone, an antithyroid treatment was added, as proposed by the European Thyroid Association (ETA) guidelines (2).
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. According to this hypothesis, AIT type 2 could be viewed as a disease linked to an extremely high intrathyroid iodine accumulation, with intrafollicular accumulation of iodinated thyroglobulin, T4 and T3, which are finally released in the circulation when the 'burst' of thyroiditis occurs.
In conclusion, we show that the evolution of unenhanced radiological thyroid gland density is closely related to the evolution of thyroid function throughout the whole time course of AIT. This suggests that measurement of thyroid gland radiological density might predict the development and remission of AIT.
Declaration of interest
The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of this case report.
Funding
This work did not receive any specific grant from any funding agency in the public, commercial or not-for-profit sector.
Consent
Written consent has been obtained from the patient for publication of the results of procedures which had been used for his care.
Ethical appwroval
Study ethics approval was obtained on August 18, 2021 (CECIC Rhône-Alpes-Auvergne, Clermont-Ferrand, IRB 5891).
References
- 1↑
Van den Bruel A, Delanote J, Braeckman A, De Vroe C, Pyfferoen L, Ghekiere J, Duytschaever M, Tavernier R. ‘White thyroid’ on unenhanced computed tomography in amiodarone-induced thyrotoxicosis type 2. Thyroid 2018 28 769–772. (https://doi.org/10.1089/thy.2017.0651)
- 2↑
Bartalena L, Bogazzi F, Chiovato L, Hubalewska-Dydejczyk A, Links TP, Vanderpump M. 2018 European Thyroid Association (ETA) guidelines for the management of amiodarone-associated thyroid dysfunction. European Thyroid Journal 2018 7 55–66. (https://doi.org/10.1159/000486957)