Physicians note unusual reaction to radioactive iodine after thyroidectomy

Healthcare experts say that radioactive iodine can be safely administered after a thyroidectomy because only leftover thyroid cells will absorb the isotope. However, a group of physicians recently witnessed an exception to this principle.

A report published in the Journal of Clinical Endocrinology and Metabolism (JCEM) records a case of papillary thyroid cancer in which a patient, whose thyroid had been removed, absorbed an estimated 40 percent of the radioactive iodine given to her post-operatively.

The complete removal of the thyroid gland is a common treatment for cancers of the thyroid. Afterward, physicians may prescribe a course of iodine-131 treatment, which involves taking a dose of radioactive iodine in order to destroy, or "ablate," any remaining cancerous thyroid tissue.

Endocrinologists agree that the thyroid cells are the only tissue that should be affected by radioactive iodine therapy, which is why Cedars-Sinai Medical Center reports that the treatment entails few negative side effects.

However, the JCEM describes a rare exception. In the case study, researchers at Massachusetts General Hospital report admitting a 22-year-old woman for symptoms such as involuntary shaking, elevated heart rate and a lump in her neck.

The group subsequently diagnosed the patient with papillary thyroid cancer, a form of the disease that accounts for 78 percent of all cases of thyroid carcinoma, according to Cedars-Sinai.

Surgeons removed the woman's entire thyroid gland, dissected the left portion of her neck to search for growths and, two months after the operation, prescribed a dose of iodine-131 to ablate any remaining cancerous thyroid cells.

Contrary to typical outcomes for radioactive iodine treatment, the woman's body absorbed almost half of the iodine isotopes. Using an injection of technetium-99, another radioactive isotope, the team discovered where the iodine-131 had gone - the woman's thyroid bed, lungs and the lymph nodes in the center of her chest.

The team said that her cancer had metastasized in these areas. They noted that her body was able to absorb so much radioactive iodine, even without the presence of thyroid cells or thyroid-stimulating hormone due to the fact that she had high levels of thyroid-stimulating immunoglobulin, an antibody that encourages specialized cells called thyrocytes to take up iodine.