AIM: Contrast media adversely affects thyroid function

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Exposure to iodinated contrast media (ICM) during imaging procedures is associated with changes in thyroid function and an increased risk of hyperthyroidism, according to a report in the Jan. 23 issue of Archives of Internal Medicine. An accompanying commentary argued that the study is a good example of why patients who may be particularly vulnerable to thyroid dysfunction should be monitored after iodine exposure.

Connie M. Rhee, MD, and colleagues from Brigham and Women’s Hospital and Massachusetts General Hospital, Harvard Medical School in Boston, examined data from patients treated between January 1990 and June 2010 who did not have pre-existing hyperthyroidism or hypothyroidism. Patients were matched with euthyroid (normal thyroid function) controls, and exposure to iodinated contrast media was assessed using claims data. A total of 178 patients with incident hyperthyroidism and 213 patients with incident hypothyroidism were matched to 655 and 779 euthyroid persons, respectively.

The authors found that iodinated contrast media exposure was associated with incident hyperthyroidism, but no statistically significant association was found with incident hypothyroidism. Secondary analysis indicated an association between iodinated contrast media exposure and incident overt hypothyrodism and incident overt hyperthyroidism.

“The observed association between ICM exposure and incident hyperthyroidism is likely explained by the iodine or iodide load conveyed by ICM,” wrote the authors. “Under physiological conditions, the capture and organification of iodide and the subsequent synthesis and release of triiodothyronine and thyroxine are tightly regulated. However, exposure to supraphysiological levels of iodide may overwhelm regulatory capacity and precipitate hyperthyroidism via jodbasedow [a thyrotoxic condition caused by exposure to excessive amounts of iodine].”

Results were not affected by sex, race/ethnicity or renal function, according to Rhee et al.

While further studies are needed to confirm the generalizability of these findings and establish causality, the authors wrote that physicians and patients should be aware of the potential thyroidal complications associated with ICM and take the necessary precautions.

An accompanying commentary, written by Elizabeth N. Pearce, MD, MSc, of the Boston University School of Medicine, agreed and expanded on the authors’ point about caution.

“These data represent an important contribution to our knowledge about a clinically relevant and understudied area,” wrote Pearce. “Rhee et al have demonstrated that a relatively large proportion of individuals who developed iodine-induced thyroid dysfunction were not known to have underlying risk factors. Therefore, patients who may be particularly unable to tolerate thyroid dysfunction, such as those with underlying unstable cardiovascular disease, are also good candidates for monitoring of thyroid function after iodine exposure.”