Testicular function after radioiodine therapy for thyroid carcinoma

Radiotherapy can cause infertility in both men and women. However, few data are available concerning the effects of radioiodine therapy for thyroid ca rcinoma on testicular function. We investigated 25 men (age 23-73 years) wi th differentiated thyroid carcinoma in a longitudinal prospective trial. Fo llicle-stimulating hormone (FSH), inhibin B, luteinising hormone (LH) and t estosterone were measured before (n=25) and 3 months (n=11), 6 months (n=18 ), 12 months (n=22), and 18 months (n=18) after radioiodine therapy [radioi odine dose (mean +/- SEM): 9.8 +/- 0.89 GBq], Before therapy, FSH was 5.4 /- 0.77 IU/I; it increased significantly (P<0.001) to 21.3 +/- 2.4 IU/I aft er 6 months and fell to 7.4 +/- 1.3 IU/I after 18 months (normal range: 1.8 -9.2 IU/I), Inhibin B was significantly decreased (P<0.001) from 178 +/- 25 .3 pg/ml before therapy to 22.2 +/- 5.5 pg/ml after 3 and 29.4 +/- 5.7 pg/m l after 6 months and rose to 154 +/- 23.3 pg/ml after 18 months (normal ran ge 75-350 pg/ml). LII and testosterone were within the normal range during the whole study (1.6-9.2 IU/I and 10.4-34.7 nmol/l, respectively). LH was s ignificantly increased (P<0.001) from 2.8 +/- 0.33 IU/l before therapy to 5 .9 +/- 0.69 IU/I 6 months after therapy and then fell slowly to 4.0 +/- 0.4 5 IU/l after 18 months. Total testosterone was significantly increased (P<0 .01) from 12.8 +/- 0.99 nmol/l at baseline to 19.8 +/- 1.7 nmol/l after 12 months and 19.6 +/- 1.7 nmol/l after 18 months. The testosterone/LH ratio ( normal range: 3.3-17.9 nmol/IU) fell from 5.8 +/- 0.66 nmol/IU to 3.0 +/- 0 .36 nmol/IU after 3 months (P<0.01); it remained close to the latter value after 6 months (3.4 +/- 0.39 nmol/IU) and then rose to 5.5 +/- 0.6 nmol/IU after 18 months. In conclusion, 3 and 6 months alter radioiodine therapy al l patients showed elevated FSH and decreased inhibin B levels, reflecting s everely impaired spermatogenesis. At the same time a compensated insufficie ncy of the Leydig cell function was observed. Eighteen months after the las t radioiodine therapy, mean values of gonadal function had completely recov ered.