Survey weighs notion of 'stunning' caused by treatment for thyroid cancer

In a new review of medical literature, a pair of nuclear medicine specialists from Stanford University has reviewed the long-held endocrinological notion of "thyroid stunning" caused by radioactive iodine treatment for thyroid cancer.

The group, whose material appears in the journal Seminars in Nuclear Medicine, determined that the phenomenon - whose existence has been hotly contested for years - may actually exist, though not necessarily in the proportions some doctors cite.

For many forms of thyroid cancer, healthcare specialists can prescribe a course of radioactive iodine therapy to destroy malignant growth. Thyroid cells absorb iodine, and those that grow out of control are destroyed by iodine-131, a radioactive isotope of the element.

The concept of thyroid stunning is relatively straightforward. It is said to occur when a treatment of radioactive iodine is absorbed by thyroid cells, and then a second course of iodine-131 is poorly absorbed, or in some cases, not taken up at all.

This phenomenon was first described in 1951 in the Journal of Clinical Endocrinology. Since that time, clinicians have debated what causes stunning, and whether it is a distinct condition or merely a symptom of some undetected physical change.

The authors of the new study said that the danger of stunning, if there is one, might be that poor uptake of iodine-131 would prevent effective treatment of thyroid cancers through targeted chemotherapy.

After reviewing previous studies of thyroid stunning, the researchers concluded that stunning is likely a real phenomenon, though they declined to estimate how common it is.

They noted that there are several possible causes of thyroid stunning. One may be that an initially diagnostic scan, which uses iodine, may reduce cell uptake of the element. Another possibility is that radioactive iodine therapy simply results in thyroid cell death, which reduces the amount of tissue able to take up subsequent doses of iodine-131.

Radioactive iodine is used for many forms of thyroid cancer, which is a disease that is diagnosed in nearly 45,000 Americans every year, according to the National Cancer Institute.