Iodine Usage In Scans Affects Thyroid Function

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Academic Journal
Main Category: Radiology / Nuclear Medicine
Also Included In: MRI / PET / Ultrasound
Article Date: 25 Jan 2012 - 13:00 PST

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Using iodinated contrast media in imaging scans has been linked to alterations in thyroid function, which in turn raises the risk of developing hyperthyroidism, researchers from Brigham and Women's Hospital and Massachusetts General Hospital, Harvard Medical School, Boston, reported in Archives of Internal Medicine. The authors explained that iodinated contrast media are utilized in imaging procedures and scans, such as CT scans and cardiac catheterization.

The authors wrote, as background information:

"Iodinated contrast media (ICM) are commonly administered pharmaceutical agents. Although certain complications of ICM (e.g., contrast-induced nephropathy) have been extensively studied, there has been little examination of the effect of ICM on thyroid function."

Connie M. Rhee, M.D., and team set out to determine whether patients exposed to ICM, who had no history of hyperthyroidism or hypothyroidism, subsequently experienced changes in thyroid function. They gathered data from patients who had been treated between 1990 and 2010. They were matched with a control group with normal thyroid function (euthryoid). Exposure to ICM was assessed using claims data.

They compared 178 individuals with incident hyperthyroidism and 213 with incident hypothyroidism against 655 and 799 euthryoid individuals.

They found that:

• Exposure to ICM raised the risk of subsequent incident hyperthyroidism
• Exposure to ICM did not appear to raise the risk of incident hypothyroidism

A secondary analysis revealed a link between ICM exposure and incident overt (clinical) hypothyroidism and incident overt hyperthryroidism.

The scientists concluded:

"In summary, these data support association between ICM exposure and incident hyperthyroidism, incident overt hyperthyroidism and incident overt hypothyroidism. Given the pervasive use of ICM in contemporary practice and the known sequelae of thyroid functional derangements, further studies are needed to confirm and evaluate generalizability of these findings, to establish causality and to explore mechanisms."

Invited Commentary in the same journal - Iodine-Induced Thyroid Dysfunction

The Commentary, written by Elizabeth N. Pearce, M.D., M.Sc., of Boston University School of Medicine, explains that the authors..:

". . . . describe significant associations between contrast exposure and the development of hyperthyroidism. While no overall association exists between contrast exposure and all forms of hypothyroidism, an association was noted when cases were restricted to those with overt hypothyroidism.

These data represent an important contribution to our knowledge about a clinically relevant and understudied area. 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."

Written by Christian Nordqvist
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