Radiation: cancer. Iodinated contrast: renal injury. Now, iodinated contrast: thyroid dysfunction.
This is a retrospective, matched, case-control study performed in Boston to evaluate any association between CT administration of IV contrast and hyper- and hypothyroidism. They gathered 178 new-onset hyperthyroid and 213 new-onset hypothyroid cases and statistically matched them in their patient database to euthyroid “controls”. There were no significant differences between the groups at baseline – although, they don’t match between terribly many clinical variables.
In the end, they find the patients who developed thyroid dysfunction had higher rates of iodinated contrast exposure – primarily from cardiac catheterization, but also from CT scans. For hyperthyroidism, 6.1% of controls had contrast exposure, whereas 10.7% of their hyperthyroid patients had received contrast. For hypothyroidism, the numbers are 8.5% controls vs. 12.2% hypothyroid.
It’s a bit of a backwards way to approach it – ideally they’d compare a group receiving iodinated contrast against a group that did not, and observe the incidence of thyroid dysfunction – but it seems that’s not the format of data to which they have access. In any event, the physiologic basis is reasonable for the association – more data needed to confirm these findings.
Just in case you needed another reason to not order a contrasted CT.
“Association Between Iodinated Contrast Media Exposure and Incident Hyperthyroidism and Hypothyroidism”
http://www.ncbi.nlm.nih.gov/pubmed/22271121