Bone mineral density changes and bone turnover in thyroid carcinoma patients treated with supraphysiologic doses of thyroxine.

The aim of this one-year prospective study was to determine whether longterm thyroxine treatment is a risk factor for elevated bone turnover, loss of bone mass and subsequent development of osteoporosis. Premenopausal women (N = 19), and men (N = 9) suffering from differentiated thyroid gland carcinoma in the mean age of 39.0 +/- 8.0 years and 41.8 +/- 10.0 years were investigated. All of them had undergone a total thyroidectomy and subsequent thyroxine therapy. The duration of the TSH-suppressive therapy prior to the the beginning of our study was 9.4 +/- 6.4 years in the female and 8.1 +/- 6.0 years in the male group. The prospective observation was performed by dual X-ray absorptiometry (DXA) at the spine and the femoral neck and by single-photon absorptiometry (SPA) at the distal radius. Laboratory testings included thyroid hormones T3, T4 and TSH, serum calcium, phosphate and PTH, and urinary calcium and phosphate from spontaneous and 24-hour urine samples. Markers of bone formation (osteocalcin, alkaline phosphatase and PICP) and resorption (Ca/Cr and ICTP) were determined. Statistically significant loss of bone mass was observed only on the distal radius in males (p<0.05). At the lumbar spine and femoral neck, only a minor bone loss was registered in a small number of patients. Almost 50 % of the females showed values above the reference range. In more than 30 % of the females, and smaller number of male patients, ICTP values ranged above the reference range, corresponding to elevated bone turnover. These two variables exhibited a slight correlation with bone density at the measured skeletal areas, mostly considering the male group. The results are a proof that accelerated bone turnover and subsequent bone loss occurs during TSH-suppressive thyroxine therapy. In future prospective studies a prolonged time of observation will be necessary, as well as to increase the number of studied patients, in order to better assess the relative risk of osteoporosis in patients undergoing TSH-suppressive treatment more precisely.