The clinical implications of long-term suppressive thyroxine (TSH) therapy on the skeletal system are critical, largely because of the favorable prognosis of differentiated thyroid carcinomas (DTC). However, the potentialdeleterious effects of TSH suppressive therapy on the bone metabolism remain controversial. The aim of this prospective study was to assess the effects of chronic L-thyroxine (LT4) treatment with supraphysiologic doses of TSH on the bone mineral density (BMD) and biochemical bone remodeling markers.

This cross-sectional study was designed to compare patients with DTC and who were treated with LT4 for more than 2 years after thyroidectomy with an age-matched and gender-matched healthy control group. A total of 100 female outpatients (mean age: 47.5±13.8; 38 pre and 62 post-menopausal) who were on LT4 for between 2 and 10 yearswere enrolled. One hundred and three age-matched healthy volunteers were recruited as a control group. Laboratory tests were performed to exclude other possible factors for secondary osteoporosis. We measured the BMD by dual energy X-ray absorptiometry (DEXA), and bone turnover was assessed by several biochemical parameters.

Our data showed no significant difference between the bone markers for the study group and the control group that had a premenopausal status. However, for the patients with a postmenopausal status, the serum levels of bone alkaline phosphatase were significant higher in the study group than that in the control group (P=0.038). We also found no significant difference between the study patients and the age- and weight-matched controls for the BMD at any site of measurement.

This preliminary report suggests that bone turnover and accelerated bone loss might be related to the long-standing TSH suppression in postmenopausal women. Future prospective studies with an increased number of studied patients and a prolonged time of observation will be necessary in order to better assess the relative risk of osteoporosis in patients who are undergoing TSH suppressive treatment.