Recombinant Human TSH Modulates In Vivo C-Telopeptides of Type-1 Collagen and Bone Alkaline Phosphatase, but Not Osteoprotegerin Production in Postmenopausal Women Monitored for Differentiated Thyroid Carcinoma

At study entry, all patients had subclinical thyrotoxicosis as effect of L-thyroxine (L-T4) treatment. The patients had higher serum CrossLaps and OPG levels and lower BMD than healthy subjects. Postmenopausal patients showed comparable serum FT4 and FT3 concentrations with those found in premenopausal patients. However, postmenopausal patients showed higher serum CrossLaps (p < 0.001), OPG (p = 0.03), and BALP (p < 0.001) levels and lower BMD (p < 0.001) than those measured in premenopausal patients. Two days after the first administration of rhTSH, all patients had serum TSH values >100 mUI/liter. At this time, serum CrossLaps levels decreased significantly (p < 0.001) and BALP values increased (p = 0.001) with respect to the baseline values in postmenopausal but not in premenopausal patients. rhTSH did not induce any significant change in serum OPG values either in premenopausal or in postmenopausal patients. One week after the first rhTSH administration, serum CrossLaps values decreased again to values comparable with those measured at baseline, whereas serum BALP values remained high. This study shows that subclinical thyrotoxicosis is accompanied by high bone turnover rate with an increase in serum OPG levels compared with euthyroid healthy subjects. Acute increase in serum TSH levels is accompanied by a reversible inhibition of bone resorption. This effect is characterized by a decrease in serum CrossLaps and an increase in BALP levels without any evident effect on OPG production. The activity of TSH occurs specifically in postmenopausal women in whom the negative effects of L-T4 suppressive therapy on bone mass and metabolism are more marked compared with premenopausal women.