Parathyroid gland function after radioiodine ((131)I) therapy for toxic and non-toxic goitre

The therapeutic effect of radioactive iodine ((131)I) on benign goitre consists of the emission of tissue-destructive beta-radiation. Since the range of beta (131)I 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 (131)I therapy.

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 (131)I. The therapeutic activity of (131)I for each patient was calculated using Marinelli's formula. The serum levels of fT3, fT4, TSH, iPTH and Ca(2+), Ca and phosphates were determined one week before (131)I administration, as well as every two months up to a year following the therapy, and then after three and five years post-treatment.

After two months following the administration of (131)I, 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, Ca(2+), Ca, phosphates concentration remained within normal range throughout the course of the study. The concentrations of fT3 and fT4 quickly returned to normal after (131)I administration, and remained within normal range until the completion of the study.

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