Testicular function after radioiodine therapy in patients with thyroid cancer

Our aim was to assess testicular function in patients treated with high-dose radioiodine. Luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone levels were determined in 52 men with thyroid carcinoma before and 6, 12, and 18 months after radioiodine therapy (3.7-5.5 GBq I-131; mean, 4.25 GBq I-131) (group 1) and were also determined before and 18 months after the last radioiodine therapy in 22 patients who received high cumulative activities (13-27.7 GBq; mean, 20.3 GBq I-131) (group 2). FSH levels were increased 6 months after therapy in all patients of group 1, while a decline was observed after 12 months, with 37 of 52 (71%) subjects presenting normal values. FSH values returned to normal after 18 months in all patients. In group 2, 12 of 22 (54.5%) patients presented elevated FSH and 8 (66%) of these individuals had oligospermia. Six months after radioiodine, increased LH levels were observed in only 5 of 52 (9.6%) patients of group 1, which returned to normal after 12 months, and in 5 of 22 (22%) of group 2. All patients showed normal testosterone levels. We conclude that I-131 therapy may cause impairment of testicular function. A generally transient increase in FSH is highly common but is usually reversed within 18 months. Oligospermia was common (one third) after high cumulative I-131 activities. Becausee we did not perform a spermiogram before therapy, we cannot state that high cumulative I-131 activities cause permanent infertility. We recommend the routine use of sperm banks in the cases of men who still wish to have children and who will undergo therapy with I-131 activities of 14 GBq or more or in the case of patients with pelvic metastases.