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Do Imaging Tests Harm Thyroid?

Tuesday, 24 January 2012 07:44 AM

Chemicals used to enhance pictures obtained from medical imaging tests may lead to overactive or underactive thyroid glands, a study showed.

Patients injected with contrast material were about twice as likely as those who didn’t get the chemical to develop hyperthyroidism, when the gland produces too much thyroid hormone and can cause rapid or irregular heart rates, according to a study published Monday in the Archives of Internal Medicine. Results also showed an increased risk for hypothyroidism.

The use of the chemicals, called iodinated contrast media, has risen in the past two decades as more people get computed tomography scans and heart catheterizations, which are used to diagnose and treat some heart conditions, the researchers said. Companies that make iodinated contrast material include Fairfield, Connecticut-based General Electric Co., Leverkusen, Germany-based Bayer AG, and Paris-based Guerbet Group.

“There is this association and people should be mindful of it, they shouldn’t panic,” Steven Brunelli, the study’s senior author and director of dialysis services at Brigham and Women’s Hospital in Boston, said Monday in a telephone interview. “They and their healthcare provider should be aware so that this could factor into discretionary testing and to undergo follow-up thyroid testing when appropriate.”

Doctors should discuss whether alternative imaging tests are available and if not, check some patients’ thyroids after the tests are completed, said Brunelli, an assistant professor of medicine at Harvard Medical School.

Iodine’s Role

The thyroid, a gland shaped like a butterfly and located in the neck, uses iodine to make thyroid hormone. In most cases, if a large amount of iodine, like that found in iodinated contrast media, gets into the body, the thyroid would either shut down thyroid hormone production or the body would decrease the amount of iodine it allows to get into the thyroid, said Elizabeth Pearce, an associate professor of medicine at Boston University School of Medicine, who wrote an accompanying editorial in the journal.

In some people, when an influx of iodine occurs, the body’s defense mechanisms may not function, causing patients to develop hyperthyroidism and strain on the heart, she said. They may also develop hypothyroidism, when not enough thyroid hormone is made, she said.

The researchers looked at patients from January 1990 to June 2010 who didn’t have any thyroid disease. They also checked to see if they were exposed to iodinated contrast media.

They found that 178 people developed hyperthyroidism, and, of those, 11 percent received contrast agents.

Long-Term Health Concern

Brunelli said it would appear that once a patient develops hyperthyroidism it becomes a long-term health issue.

The study also showed that 213 developed hypothyroidism and of those, 12 percent received contrast agents. Those who used contrast were 1.5 times more likely than those who didn’t to develop hypothyroidism, a finding the researchers couldn’t rule out was due to chance, Brunelli said.

Monday's paper is the first to study if receiving contrast for imaging tests harms thyroid function, the researchers said. Brunelli said it’s unclear why some people who receive the chemicals are fine and others may develop thyroid problems. Those who have goiters, or nodules on their thyroids, or those with undiagnosed Graves disease, an autoimmune disorder, may be at an increased risk, he said.

“What’s interesting about these findings just seems to be that this is occurring,” Pearce, who wrote the accompanying editorial, said Monday in a telephone interview. “People who have underlying poor health, those are people who may not tolerate even short-term hyperthyroidism. Hyperthyroidism puts a strain on the heart. It’s always reasonable to ask a provider before you have a study why and make sure there’s a reasonable explanation for why you’re doing it.”

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Chemicals used in medical imaging tests are associated with overactive and underactive thyroid glands in some patients, a new study shows.
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Tuesday, 24 January 2012 07:44 AM
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