Are parathyroid functions affected in patients with differentiated thyroid cancer who have received radioactive iodine therapy: two-year follow-up results

Background/aim: Administration of external ionizing radiation to the neck may causes hyperparathyroidism (HPT) over the years. Radioactive iodine (RAI) therapy which applied in differentiated thyroid cancers (DTC) exposes parathyroid glands to radiation. This may cause hyperparathyroidism, parathyroid adenoma and hyperplasia. The aim of this study is to determine whether RAI treatment changes the parathyroid gland functions in patients with DTCs. Methods: The 2-years parathormon (PTH), calcium (Ca) and phosphorus (P) levels of 145 patients who had previously undergone RAI ablation in our hospital were reviewed retrospectively. Pretreatment PTH, Ca, and phosphorus levels were compared to the at 1st, 6th, 12th, and 24th month results after treatment. Results: During the 2-years follow-up, there were not any significant differences between baseline and follow-up PTH, Ca and phosphorus levels (p> 0.05). In patients with receiving low dose RAI therapy, 12th month phosphorus level was significantly lower than baseline (p = 0.015; p <0.05). In patients with receiving high-dose RAI therapy, 6th month PTH levels were significantly lower than baseline (p = 0.014; p <0.05). Conclusion: Transient decrease in PTH levels may be observed in patients receiving RAI treatment for DTC at 6 months. However, RAI treatment does not affect PTH functions in two years of follow-up.