Biochemical assessment of bone loss in patients on long-term thyroid hormone treatment

To test conditions under which thyroid hormone might be deleterious to bone, we studied a group of 58 patients who had undergone thyroidectomy because of thyroid cancer 1 to 21 years previously and were treated with steady doses of exogenous thyroid hormone. Vertebral bone density (BMD Z-score) was significantly reduced and biochemical indices of bone resorption (urinary hydroxyproline and plasma tartrate-resistant acid phosphatase activity) and of osteoblastic activity (plasma osteocalcin and bone isoenzyme of serum alkaline phosphatase) as well as the calculated prevalence of bone resorption relative to osteoblastic activity (HBP) were significantly increased in thyroid hormone-treated post-menopausal women but not in men and premenopausal women. The HBP as well as the biochemical indices of bone remodeling were significantly negatively correlated with serum TSH levels. In treated patients, BMD Z-score was significantly dependent on the HBP, menopausal state, duration of treatment and serum TSH levels. In conclusion, the further increase in bone resorption by thyroid hormone is predisposed by menopausal changes in bone turnover. The simultaneous evaluation of biochemical indices of bone resorption and formation improves the assessment of bone loss in patients treated with thyroid hormone in a suppressive dose.