The long term effect of levothyroxine on bone mineral density in patients with well differentiated thyroid carcinoma after treatment.

To date a few studies have focused on the possible effects of subclinical hyperthyroidism on bone metabolism, showing conflicting results. This study was designed to evaluate this possibility. Sixty-six patients, 22 pre-menopausal women, 33 post-menopausal women and 11 men, who had received iodine-131 ((131)I) ablation postoperatively for well differentiated thyroid carcinoma (WDTC) and were treated for a long term with levothyroxine (T(4)), entered the study and were compared with sixty-six healthy controls individually matched to the patients for age, gender and menopausal status. The bone mineral density (BMD) of lumbar and hip regions of the patients was measured, while on the T(4) suppressive treatment, with average duration of 14.93+/-2.17 months after initiation of the T(4) suppressive treatment and was compared with the BMD of healthy controls. All patients were in the subclinical hyperthyroid state, while all controls were serologically and clinically euthyroid. Our results show that there was no significant difference in BMD measured at the lumbar spine of patients and controls in any subgroup (P>0.05). Analysis of the data of BMD from the hips in men, premenopausal women and controls, also revealed no difference. It was noted that the mean BMD of the femur in the postmenopausal women were at the statistical limit of significance as compared to the control group (P=0.05). In conclusion, our findings indicate that the replacement dose of T(4) in WDTC patients after (131)I ablation, does not have a significant effect on BMD in men, in pre and post-menopausal women and hence on the risk of osteoporosis. In post-menopausal women, the mean femoral BMD was at the limit of statistical significance.