Endocrine Abstracts

Background: Radioiodine (RAI) therapy has been used for a long time in benign and malign diseases of the thyroid gland. During the application of radioiodine treatment, parathyroid glands may also be exposed to radiation due to its close proximity to the thyroid gland. There is interest in the effects of RAI treatment on parathyroid functions in clinical studies. The aim of this study is to evaluate whether the dose of RAI treatment for benign or malignant thyroid diseases has an effect on parathyroid functions in long-term follow-up or not.

Methods: The study sample consisted of 197 patients with or without receiving RAI treatment followed up for benign or malignant thyroid disease. The clinical features, preoperative and postoperative biochemical parameters and postoperative histopathological results of the patients with DTC were examined. Serum calcium, phosphorus, parathormone and 25 OH Vit d3 levels were recorded at the 3rd month, 1st year, 3rd year and 5th year after RAI treatment in all patients with or without receiving RAI treatment.

Results: A total of 197 patients, 189 of whom were diagnosed with DTC, were included in the study. 159 (80.7%) of the patients were female and 38 (19.3%) were male. The mean age at diagnosis was 43±13.4 years. Total thyroidectomy was performed in 179 patients with the diagnosis of DTC and in 6 patients with Graves’ disease. While the PTH levels measured in the preoperative period were higher (P=0.002) in 92 patients who received RAI treatment at doses of 100 mci and above, the calciıum and PTH levels measured after the 1st year of RAI treatment were found to be lower (P=0,020, P=0.031). When the patients at 5-years of follow-up after RAI treatment were evaluated, no statistically significant differences were found in terms of serum calcium, phosphorus, parathormone and 25ohvitd3 levels. However, it was found that normocalcemic hyperparathyroidism developed at ten years of follow-up in 2 patients who were treated with RAI.

Conclusions: Although the effect of RAI treatment for thyroid diseases on parathyroid functions seem to be safe in long term follow-up, normocalcemic primary hyperparathyroidism was detected in 2 patients. For this reason, before RAI treatment, patients should be informed about the potential risk of developing abnormal parathyroid function in the future. In addition, patients should be followed-up periodically to control parathyroid function after RAI treatment. Patients should be followed up for low PTH and calcium in the early period and for hyperparathyroidism in the long term.