BACKGROUND
Thyroid cancer is common, and, fortunately, has an excellent prognosis. This is because we have excellent treatments for thyroid cancer. Most patients initially get surgery to remove the thyroid. In patients at risk for the cancer recurring, or if all the cancer was not able to be removed, radioactive iodine therapy is the next step. Radioactive iodine therapy takes advantage of the fact that the thyroid is the only gland in the body that takes up, concentrates and retains iodine, which is used in making thyroid hormone. When patients are treated with radioactive iodine therapy, the remaining thyroid cells, both normal and cancer cells, take up the radioactive iodine and are destroyed.

Salivary glands also take up and concentrate iodine but do not store it. Because of this, the side effects of radioactive iodine therapy can include problems of the salivary gland. While these effects can be seen in all salivary glands, the parotid gland appears to be more susceptible to radioactive iodine. The complications can be immediate or long term and range from inflammation of the salivary gland and reduction in saliva production to gum and dental issues such as dental cavities.

This study reviews the potential impact of radioactive iodine therapy on salivary gland function and oral health in a patient population with thyroid cancer.

THE FULL ARTICLE TITLE
Terrazas JR, et al. Influence of radioiodine therapy on oral health and salivary production in patients with differentiated thyroid carcinoma. Endocr Pract. Epub 2025 Jan 10:S1530-891X(25)00019-9; doi: 10.1016/j. eprac.2025.01.001. PMID: 39800100.

SUMMARY OF THE STUDY
The study uses data from patients with a history of thyroid cancer who received radioactive iodine therapy. The amount of saliva produced was assessed using a standardized questionnaire answered by the patients and through an objective measurement of salivary flow. In addition to this, an assessment of oral health was done by a dental specialist.

A total of 67 patients were included in the study and a majority (81%) were female. The average age at the time of diagnosis of thyroid cancer was 43 years. The study data was collected on average of 69 months (5.8 years) after radioactive iodine therapy was administered and ranged from 1 month to 25 years.

Frequent decreased salivation was reported by 15%, dry mouth by 13% and difficulty eating by 12% of patients. The greater the number of radioactive iodine therapies and total dose, the more likely patients were to have a low salivary flow measurement. When evaluated by a specialist, 61% had good or very good and 17% of the study subjects had below average oral health. When assessing for plaque or bacterial biofilm visible on the teeth, 53% patients had slight film adherence and 15% had moderate to significant film adherence. Finally, 46% of patients had inflammation of the gums.

There are several factors that may influence the data seen in this study. In this particular study population, 24% of patients received neck external radiotherapy during their childhood which may have had an impact on salivary gland function. Given that the data was collected from a single hospital, the radioactive iodine therapy protocol and measures used to protect the salivary gland may influence outcomes and these may differ from other hospitals. Finally, comparison with a patient population that did not receive radioactive iodine would be helpful to understand the data better.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
Similar to other studies, this study raises the concern about risk for changes in salivary gland function and oral health following radioactive iodine therapy given for the treatment of thyroid cancer. The use of radioactive iodine therapy has changed over the years, from the practice where radioactive iodine therapy was part of the standard therapy recommended to all patients with thyroid cancer, to current recommendations to consider radioactive iodine for patients when there is a higher risk for recurrence or to treat thyroid cancer tissue present in the body. A discussion on the effect of radioactive iodine on the salivary gland and oral health should be part of the counseling provided to patients. It is also important for patients to have regular on-going visits with their dentist following radioactive iodine therapy to ensure any concerns can be addressed appropriately.

— Poorani Goundan, MD

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