Thyroid Research Thyroid Research Archive Thyroid Cancer

Radioiodine therapy can cause abnormal testicular function in men with thyroid cancer

(November 2006)

The background of the study. Men with thyroid cancer who are treated with radioactive iodine (I-131) may have abnormal testicular function, but the extent of the abnormalities and their relationship to the dose of I-131 are not well defined. In this study, testicular function was assessed in men with thyroid cancer who were treated with I-131.

How the study was done. Serum follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone were measured before and 6, 12, and 18 months after a dose of 100 or 150 mCi of I-131 in 52 men with thyroid cancer.

The same measurements were done before and 18 months after the last dose of I-131 in 22 men with thyroid cancer who had lung metastases and who received several doses of I-131. In addition, semen analyses were done in the men who had high serum FSH concentrations at the latter time. Their mean total dose of I-131 was 550 mCi. The interval between the hormonal measurements in these men was 60 months.

The results of the study. Among the 52 men given a single dose of I-131, the average serum FSH concentration was normal (< or = to14 mIU/ml) before treatment, high 6 months after treatment, and normal 12 and 18 months after treatment. Their average serum LH and testosterone concentrations were normal at all times, and no man had a low serum testosterone value at any time.

Among the 22 men given several doses of I-131 and studied 18 months after their last dose, 12 (54 percent) had a high serum FSH concentration and 5 (23 percent) had a high serum LH concentration; none had a low serum testosterone concentration. Among the 12 men with high serum FSH concentrations, 8 (67 percent) had a low sperm count (sperm concentration <20 X 10⁶/ml). The total dose of I-131 was higher in the 8 men who had a low sperm count than the 4 men who did not.

The conclusions of the study. Men with thyroid carcinoma who are treated with single doses of 100 to 150 mCi of I-131 may have transient testicular damage, manifested by high serum FSH or LH concentrations, and those treated with higher doses may have a low sperm count.

The original article. Rosario PW, Barroso AL, Rezende LL, Padrao EL, Borges MA, Guimaraes VC, Purisch S. Testicular function after radioiodine therapy in patients with thyroid cancer. Thyroid 2006;16:667-70.