CT Contrast Causes Thyroid Damage Says Study. Implications?

We order a lot of CT scans in this country.   Why?  Because we can.  We likely have more access to immediate CT technology than any country in the world.  Go to any ER in this country and complain of a headache, abdominal pain or chest pain and chances are pretty good that someone, at some point, is going to order a CT scan on you.  In fact, the  annual percentage rise in advanced radiology imaging continues.  

We already know about the potential long term dangers of CT scan radiation exposure.  Go to this link and have your eyes opened to the dangers of frequent CT scan exposure.  Some studies suggest one CT scan of the abdomen is the equivalent of 2000 xrays of radiation, or 30 years of background radiation.  What does this have to do with your risk of developing cancer?  Go read all about it.

Now comes reports out of the Archives of Internal Medicine  that CT contrast exposure may cause thyroid damage and lead  to higher rates of incident hyperthyroid and overt hypothyroid states.  CT contrast (and any contrast used on angiographic studies such as heart catheterizations and other invasive arterial and venous studies) is a form of iodinated contrast media.  In other words, they contain iodine. Contrast is used to enhance CT and angiographic imaging and is required to make certain diagnostic determinations.

Thyroid homeostasis is dependent on complicated iodine metabolism.  I couldn't even begin to remember the complex physiology behind the association.  Suffice to say, while cause and effect hasn't been definitively proven, this study raises the possibility the thyroid of some folks are incapable of handling the large iodine load associated with CT contrast and other angiographic studies. 

This appears to be the first study suggesting the possibility of long term thyroid dysfunction with the use of iodinated contrast media.  What does this mean from an informed consent stand point?   Should all patients receiving CT or angiographic contrast media be required to sign documents detailing  the growing list of complications and potential complications from these medical tests?  

Should all patients who have received iodinated contrast media receive thyroid screening tests before and after, like we do with creatinine levels?  If so, when should those test be performed?  One week out?  One month out?  Should they be repeated in series?  And who should pay for them?   Does the risk of long term (and even short term) thyroid disease outweigh the potential benefits of  the CT scan?  Should greater weight be given to the pre-test probability of finding an abnormality on CT? Should ordering a  "just to make sure" CT scan to avoid being sued for failure to diagnose give doctors second thoughts about the potential dangers present on the other side of the equation.

Untreated thyroid dysfunction can lead to a whole host of other medical problems too including weight gain,  heart disease lipid metabolism dysfunction, depression and anxiety.  Lots to think about.  I don't know what the right answer is.   But I'm sure, eventually, the lawyers will tell us.

By the way, some folks may ask, "Does MRI contrast have iodine in it?".  The answer is no.  Most commonly, gadolinium is the contrast of choice for MRI.  It is not an iodine based medium.  MRI is rarely used in the evaluation and treatment of diseases screened or followed by CT.  The two technologies are simply not interchangeable in most circumstances.

Source article: Connie M. Rhee, MD; Ishir Bhan, MD, MPH; Erik K. Alexander, MD; Steven M. Brunelli, MD, MSCE; Arch Intern Med. 2012;172(2):153-159. doi:10.1001/archinternmed.2011.677

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