Background: The standard treatment strategy for differentiated thyroid cancer (DTC) includes surgery followed by radioactive iodine ablation and long-term thyrotropin (TSH) suppression therapy. It has been suggested that the long-term TSH suppression may be associated with undesired adverse effects of thyroxine on bone metabolism. However, there is no consensus about the effects of subclinical hyperthyroidism on BMD induced by TSH suppression therapy of DTC in premenopausal women. In this study, we evaluated the impact on BMD and bone turnover markers of long-term suppressive levothyroxine therapy for DTC in premenopausal women.
Methods: The study enrolled 83 premenopausal women (mean age, 42.2 ± 8.3 years) receiving levothyroxine after total/near-total thyroidectomy and radioactive iodine therapy for DTC (mean follow-up period, 7.3 ± 5.6 years). The subjects were divided into three groups by TSH level [group 1 with TSH level ≤0.10 μIU/mL (n=28), group 2 with TSH level between 0.10 and 0.50 μIU/mL (n=32), group 3 with TSH level >0.50 μIU/mL (n=23)]. levothyroxine dosage, BMD (examined by dual-energy x-ray absorptiometry), and bone turnover markers were evaluated. Biochemical marker of bone resorption was measured by urine deoxypyridinoline and bone formation by serum osteocalcin.
Results: Mean duration of levothyroxine treatment was 7.8 ± 6.1 years, and mean levothyroxine dose was 135.3 ± 41.7 μg/day (range, 75–225 μg/day). Mean BMD contents and T-scores for each group divided by TSH level did not differ significantly among groups. Also, bone turnover markers and prevalence of osteoporosis and osteopenia were not different among groups. The odds ratios for risk of osteoporosis and osteopenia in groups 2 and 3 were not significant when compared to the reference group (group 1).
Conclusion: This cross-sectional study suggests that Long-term levothyroxine suppressive therapy of DTC in premenopausal women did not affect BMD and bone turnover markers or increase the prevalence of osteoporosis.