BACKGROUND
Papillary and follicular cancers make up roughly 90% of thyroid cancer cases. The primary treatment is surgery. In cases of more advanced disease, radioactive iodine therapy is given after surgery. This works because thyroid cells, including cancerous ones, possess a unique ability to take up, concentrate and utilize iodine to make the thyroid hormones. During radioactive iodine therapy, the radioactive iodine selectively targets and destroys any thyroid cancer cells that may remain after surgery. Tear duct and salivary glands can also take up radioactive iodine but not concentrate it. However, this exposure to radioactive iodine can cause inflammation, blockages, and a range of symptoms, including pain, dry mouth, dry eyes, mouth infections, taste disturbances, and digestion issues. While these side effects are well described, few studies in the medical literature examine the truel rate of tear duct and salivary complications after radioactive iodine therapy.

In this study, the authors of the current study set out to investigate whether a) radioactive iodine truly causes tear duct and salivary gland problems, b) the relationship between the dose of radiation and symptoms, and c) the patient factors that may predict the likelihood of developing problems six months after radioactive iodine therapy.

THE FULL ARTICLE TITLE
Baudin C et al 2023 . Dysfunction of the salivary and lacrimal glands after radioiodine therapy for thyroid cancer: Results of the START study after 6-months of follow-up. Thyroid. Epub 2023 Jun 23.

SUMMARY OF THE STUDY
The researchers studied 136 patients with thyroid cancer awaiting radioactive iodine therapy in 2020 at the St Pitié-Salpêtrière Hospital in France. Patients were grouped according to the dose of radioactive iodine that they received as low dose (44 patients) vs. high dose (92 patients). Subjects were then followed for 6 months after their radioactive iodine therapy. Researchers used validated questionaires asking patients about symptoms such as dry eyes and dry mouth to assess for tear duct and salivary gland problems.

They also analyszed saliva and tear samples from patients. Finally they used a technique called dosimetry to estimate the actual dose of radiation that the tear duct and salivary gland cells absorbed in each patient. The average age of patients was 47.1 years. The group was 71.3% women, 85% with papillary cancer, 47% with a remaining portion of their thyroid after receiving radioactive iodine therapy, 40% with a history of other medical problems and only 7% had a history of salivary problems prior to therapy.

Overall, there were no significant differences in salivary gland pain or saliva volume between the baseline and 6-month follow-up. However, more patients (22%) reported experiencing dry mouth, and a significant portion (17%) reported dry eye sensation after the therapy. The decrease in saliva flow and the sensation of dry mouth were positively correlated with the radiation dose absorbed by the salivary glands. Similarly, an increased sensation of dry eyes was associated with the dose of radioactive iodine absorbed by the lacrimal glands, but only in the group that received 1.1 GBq of radiation. Finally, patient age, menopausal status, symptoms of depression and anxiety, and a history of other systemic diseases were risk factors for experiencing symptoms related to tear duct and salivary gland problems. Interestingly, individuals who had used painkillers in the past three months had a lower risk of problems.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study provides new knowledge on the impact of radioactive iodine exposure on the teat duct and salivary glands. Although the study was small in size and only only 6 months long, the findings suggest that, while radioactive iodine may lead to certain symptoms of tear duct and salivary gland dysfunction, it does not appear to result in severe, long-lasting effects.

— Philip Segal, MD

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