Effects of radioactive iodine therapy on female sex hormones and menstrual cycle in patients with differentiated thyroid carcinoma

Differentiated thyroid carcinoma (DTC) is the most common endocrine malignancy. Total thyroidectomy with subsequent radioactive iodine therapy (RIT) followed by levothyroxine consumption is a routine approach to deal with DTC. Widespread use of RIT in patients with DTC has raised concerns about its potential adverse effects on female reproductive organs. We aimed to check the effects of postoperative RIT on menstrual symptoms and sex hormones in patients with DTC.

Women in reproductive age with DTC admitted in Nuclear Medicine department from 2020 to 2021 were studied. The demographic and menstrual information was recorded at first presentation and follow-up visits. Blood samples were taken for measurement of follicle stimulating hormone (FSH), luteinizing hormone (LH), anti-Müllerian hormone (AMH), and estradiol at baseline, 6 and 12 months after RIT. Data analysis was performed using SPSS software (V20), Chi-square and Fisher exact tests and Friedman non-parametric test.

77 women with DTC and mean age of 35 years were studied. Roughly half (50.4%) received high-dose RIT (i.e. ≥100 mCi administered radioiodine). No patient had distant metastasis. Dysmenorrhea was reported in 23 (29.9%) of the patients and flushing was seen in 6 (7.8%). The number of pads used during menstrual periods, the length of menstrual periods and its frequency decreased significantly 2 months after RIT and returned to baseline values 1 year after RIT. The LH, FSH, and estradiol levels has increased continuously 6 and 12 months after RIT. In contrast, the mean serum level of AMH was not changed compared to that of the pre-treatment level. The changes in sex hormones and menstrual cycles were not different between the low (30 mCi) and high-dose (. ≥100 mCi) RIT groups (p values = 0.13–0.89).

The serum levels of LH, FSH, and estradiol hormones increased after RIT for up to 12 months after RIT while the AMH levels were stable. The menstruations were adversely affected 2 months after radioactive iodine therapy regardless of the dose of radio-iodine and improved by 6 months.