Background: The effects on bone metabolism of long-term treatment with thyroid hormone given at suppressive doses have been debated.
Objective: To determine whether long-term thyroxine therapy in the premenopausal period is a risk factor for the development of secondary osteoporosis and whether women receiving this therapy have increased bone loss during the premenopausal period.
Patients and methods: The study enrolled a select group of 19 premenopausal women of mean ages 39 +/- 8 years suffering from differentiated thyroid gland carcinoma. All subjects had undergone total thyroidectomy and subsequently initiated thyroxine suppressive therapy. At the beginning of our study, the women had been on suppressive therapy for 9.4 +/- 6.4 years. Laboratory results were performed to exclud other possible factors for secondary osteoporosis. This prospective study of bone mineral density (BMD) was conducted over a 4-year period on all subjects using the method of dual photon x-ray absorptiometry (DXA) of the spine and the femoral neck and also by the method of single-photon absorptiometry (SPA) of the distal radius.
Results: At the beginning of this study, 2 subjects had osteopenia in the spine and 2 had osteopenia in the femoral neck; they had been on suppressive thyroxine therapy for 10 years. Osteopenia in the distal radius was found in 4 subjects. Overall, 8 of the 19 women had osteopenia at the beginning of the study. One year later, after the second BMD measurement, no statistically significant loss of bone mass occurred in any region of the skeleton in any of the patients. However, a review of the individual scores revealed osteopenia in 6 patients at the distal radius; bone loss also occurred at the spine and the femoral neck in several women, but not to the extent that would establish osteopenia. After the 4 years, BMD measurements indicated significant bone loss.
Conclusion: Our results suggest that women who begin long-term ( ~ 10 years) thyroxine therapy in the premenopausal period can develop osteopenia by the beginning of menopause.