Introduction: The therapeutic effect of radioactive iodine (131I) on benign goitre consists of the emission of tissue-destructive beta-radiation. Since the range of beta 131I radiation in tissue can reach 2.4 mm, it can affect the adjacent parathyroid glands. The purpose of this paper
is to assess parathyroid function in patients with toxic and non-toxic goitres, up to five years following 131I therapy.

Material and methods: The study sample consisted of 325 patients with benign goitres (220 with toxic nodular goitre (TNG), 25 with
non-toxic nodular goitre (NTNG), and 80 with Graves’ disease (GD) treated with 131I. The therapeutic activity of 131I for each patient was
calculated using Marinelli’s formula. The serum levels of fT3, fT4, TSH, iPTH and Ca2+, Ca and phosphates were determined one week before
131I administration, as well as every two months up to a year following the therapy, and then after three and five years post-treatment.

Results: After two months following the administration of 131I, all the treated patients showed a statistically significant above normal increase in iPTH concentrations (amounting to a value almost twice the norm in patients with TNG), which remained stable up to ten months after treatment, to return to normal level in the following months. In all the patients, Ca2+, Ca, phosphates concentration remained within normal range throughout the course of the study. The concentrations of fT3 and fT4 quickly returned to normal after 131I administration, and remained within normal range until the completion of the study.

Conclusion: Radioiodine treatment of benign thyroid disorders results in transient (up to ten months after 131I administration) hyperparathyroidism.
The condition does not influence the level of calcium and phosphates concentration in any significant way.

(Endokrynol Pol 2013; 64 (5): 340–345)