Blog | Wednesday, February 1, 2012

QD: News Every Day--Iodinated contrast media associated with thyroid dysfunction

Iodinated contrast media is associated with subsequent incident hyperthyroidism and incident overt hypothyroidism, a study concluded.

Thyroid, Diffuse Hyperplasia by euthman via Flickr and a Creative Commons licenseUse of iodinated contrast media has grown along with imaging in general, as much as an eight-fold increase in such tests in the past 20 years. A typical dose of contrast media contains about 13,500 micrograms of free iodide and 15 to 60 g of bound iodine that may become free iodide in the body. "This represents an acute iodide load of 90 to several hundred thousand times the recommended daily intake of 150 [micrograms]," the authors noted.

Researchers performed a nested case-control study of patients treated between January 1990 and June 2010, who did not have preexisting hyperthyroidism or hypothyroidism. In a parallel analyses, incident hyperthyroid or hypothyroid cases were defined by a change in thyrotropin level from normal to low or high.

Results appeared in the Jan. 23 edition of Archives of Internal Medicine.

The source cohort consisted of 4,096 patient intervals matched to 3,678 patient intervals that served as eligible controls. In total, 178 and 213 incident hyperthyroid and hypothyroid cases were matched to 655 and 779 euthyroid controls. Iodinated contrast media exposure was associated with incident hyperthyroidism (odds ratio [OR], 1.98; 95% confidence interval [CI], 1.08 to 3.60), but not with incident hypothyroidism (OR, 1.58; 95% CI, 0.95 to 2.62).

In the secondary analysis, iodinated contrast media exposure was associated with incident overt hyperthyroidism (follow-up thyrotropin level less than or equal to 0.1 mIU/L; OR, 2.50; 95% CI, 1.06 to 5.93) and with incident overt hypothyroidism (follow-up thyrotropin level greater than 10 mIU/L; OR, 3.05; 95% CI, 1.07 to 8.72).

An editorialist wrote that an association was noted when cases were restricted to those with overt hypothyroidism. There was also an association between iodinated contrast media and incident hypothyroidism when the analysis was restricted to cases that occurred within 180 days of exposure, "likely related to the transitory nature of iodine-induced hypothyroidism."

Scattered reports in the literature report an association between iodinated contrast media and hyperthyroidism, called Jod-Basedow phenomenon. This study suggests the incidence is more widespread than previously believed, the editorialist said.

In terms of practical clinical practice, the editorialist noted, "First, the ALARA ("as low as reasonably achievable") principle should always be exercised in determining the need for radiation exposure, as potential risks of iodinated contrast studies extend beyond the thyroidal risk from iodine exposure. Second, particular care should be taken in patients at high risk to develop thyroid dysfunction after the administration of iodinated contrast medium. Palpation of the neck for the detection of goiter is reasonable before ordering contrast studies, although nodular goiter may occasionally be missed even with a careful physical examination."

The editorial continued, "[P]atients 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."