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

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.

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.

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.

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.