Iodine is essential for normal thyroid function, as the thyroid hormones contain iodine. World-wide, iodine deficiency is an important cause of hypothyroidism. However, exposure to an excessive amount of iodine can actually cause hyperthyroidism. This type of iodine-induced hyperthyroidism is called the Jod– Basedow effect and it typically presents a few weeks after exposure to a large amount of iodine. Those with preexisting thyroid nodules are felt to be particularly at risk. Iodinated contrast media (ICM) that is administered before specific radiologic tests, such as CT scans, contains a considerable amount of iodine. Given that over 80 million doses of ICM were provided to people in 2005 worldwide, iodine-induced hyperthyroidism may be more common that we think. As a result, some physicians choose to monitor thyroid hormone levels after ICM exposure. Some may even consider proactively treating patients at high risk of iodine-induced hyperthyroidism with antithyroid medications before radiological procedures. However, the overall risk of iodine-induced hyperthyroidism after ICM is unclear.
The authors of the current study performed a systematic review of the literature to better understand iodineinduced hyperthyroidism due to ICM.
THE FULL ARTICLE TITLE
Bervini S et al 2020. Incidence of iodine-induced hyperthyroidism after administration of iodinated contrast during radiographic procedures: A systematic review and meta-analysis of the literature. Thyroid. Epub 16 Dec 2020.
SUMMARY OF THE STUDY
The authors searched the literature and identified 30 studies that were suitable to estimate the incidence of iodine-induced hyperthyroidism. Studies involving children or pregnant women were excluded. The overall incidence of overt hyperthyroidism after iodated contrast medial was 0.1% based on all the pooled data. Regarding the timing of hyperthyroidism after exposure to contrast, there were no cases of iodine-induced hyperthyroidism one week after exposure in the 6 studies that examined that time point. At 30 days following ICM exposure, the incidence of iodine-induced hyperthyroidism was 0.4%. Baseline thyroid status (i.e. whether people were hyperthyroid, euthyroid or hypothyroid at the time of contrast administration) was not a risk factor for developing iodine-induced hyperthyroidism.
WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Despite the widespread use of ICM, this review suggests that the incidence of hyperthyroidism following ICM exposure is extremely low. Based on these results, there is no evidence to use antithyroid medications before ICM exposure or even to monitor thyroid hormone levels afterwards on a routine basis.
— Philip Segal, MD
ABBREVIATIONS & DEFINITIONS
Hyperthyroidism: a condition where the thyroid gland is overactive and produces too much thyroid hormone. Hyperthyroidism may be treated with antithyroid meds (Methimazole, Propylthiouracil), radioactive iodine or surgery.
Iodine: an element found naturally in various foods that is important for making thyroid hormones and for normal thyroid function. Common foods high in iodine include iodized salt, dairy products, seafood and some breads.
Hypothyroidism: a condition where the thyroid gland is underactive and doesn’t produce enough thyroid hormone. Treatment requires taking thyroid hormone pills.