Objective: To compare bone mineral density (BMD) of lumbar spines (LS) and femoral neck (FN) by Dual energy X-ray absorptiometry (DEXA) in premenopausal well-differentiated thyroid carcinoma women S/P total or near total thyroidectomy with a control group and the effect of Levothyroxine (LT4) to BMD between short term and long term treatment.
Material and Method: DEXA were performed at LS (L1-L4) and FN in 22 premenopausal thyroid carcinoma women S/P total or near total thyroidectomy followed by I-131 ablation and long term suppressive dose LT4 and 22 healthy premenopausal women.
Results: Mean BMD of LS and FN were not significantly different between thyroid cancer group and control (LS 1.023 +/- 0.088 VS 0.980 +/- 0.075 g/cm2,p > 0.05, FN 0.800 +/- 0.068 VS 0.770 +/- 0.061 g/cm2, p > 0.05). Period of time taking suppressive doses LT4 was divided into 3 groups (2-5 yrs, 6-10 yrs and 11-14 yrs). Mean LS BMD +/- S.D of 2-5 yrs, 6-10 yrs and 11-14 yrs therapy are 1.042 +/- 0.135, 1.004 +/- 0.044 and 1.042 +/- 0.055 respectively (p > 0.05). Mean FN BMD +/- S.D of 2-5 yrs, 6-10 yrs and 11-14 yrs therapy are 0.808 +/- 0.084, 0.781 +/- 0.067 and 0.816 +/- 0.013 respectively (p > 0.05).
Conclusion: The suppressive doses LT4 was not the risk factor of osteoporosis. Although, there was no statistically significant difference of BMD between short and long-term suppressive doses LT4 groups, the present sample size was not enough to conclude that long-term suppressive doses LT4 did not decrease BMD.

Keywords: Bone mineral density, Levothyroxine suppressive doses, Thyroid cancer