BACKGROUND
Iodine is essential for normal thyroid function. The thyroid hormones all contain iodine. Not enough iodine in the diet can cause decreased production of the thyroid hormones and hypothyroidism. Indeed, iodine deficiency is the most common cause of hypothyroidism in many parts of the world. Too much iodine, on the other hand, can cause or worsen thyrotoxicosis, particularly in patients with thyroid conditions.

Contrast media commonly used in some radiological studies, such as CT scans, contain very high amounts of iodine. Getting these high levels of iodine during these scans can cause a short-lived thyrotoxicosis in some patients. This is known as contrast-induced thyrotoxicosis. To avoid such complications, treating patients before getting these scans with antithyroid drugs such as methimazole (MMI) has been recommended by some. In fact, some small studies have shown beneficial effects of using antithyroid drugs before exposure to contrast to prevent contrast-induced thyrotoxicosis. The current study was done to evaluate the effectiveness of MMI in preventing contrast induced thyrotoxicosis, particularly in patients with prior history of thyroid conditions.

THE FULL ARTICLE TITLE
Ayalon-Dangur DI, et al. Methimazole for prevention of iodinated contrast media induced exacerbation of thyrotoxicosis in susceptible patients. Endocr Pract. Epub 2024 Nov22:S1530-891X(24)00833-4;

SUMMARY OF THE STUDY
This study was done is Israel. The authors looked at the thyroid levels of 179 hospitalized patients before and after receiving iodinated contrast. All the patients had a history of thyroid conditions and 91% were already taking MMI before receiving contrast. Overall 64% were women, their average age was 72 years and 26% had Graves’ disease. The MMI dose was adjusted according to the physician’s recommendations. Of the patients who had low TSH levels before admission, indicating a mild degree of hyperthyroidism, 19% normalized the thyroid levels after discharge and 62% had lower FT4 levels. These improvements in thyroid levels were due to an increase in their MMI dose. Of the patients who had normal TSH levels, 71% continued to be in the normal range while only 13% developed low TSH levels indicating a mild hyperthyroid state. Of the patients whose TSH levels were elevated before receiving contrast, about half continued to have mild TSH elevations at discharge, indicating a mild hypothyroid state.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Treatment with MMI in patients with hyperthyroidism who receive iodinated contrast helps prevent contrastinduced thyrotoxicosis in most patients. However, this study does not answer the question of what to do for patients without thyroid disease who receive iodinated contrast. For now, MMI treatment before iodinated contrast could be considered only for those patients with pre-existing hyperthyroidism.

— Susana Ebner MD

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