BONE-DENSITY AND MINERAL METABOLISM IN THYROIDECTOMIZED PATIENTS TREATED WITH LONG-TERM L-THYROXINE

1. A decreased bone mass has been reported in patients with endogenous hyperthyroidism, but the effect on bone density and mineral metabolis m of thyroxine administration in thyroidectomized patients is still co ntroversial. To further contribute to this debate, we studied 25 women thyroidectomized for thyroid cancer on long-term treatment with thyro id-stimulating hormone-suppressive doses of L-thyroxine. Twenty-one se x- and age-matched normal subjects were also studied as a control grou p. 2. The bone density of the spine and serum calcitonin, calcitriol a nd parathyroid hormone concentrations were not different when the whol e patient group was compared with the control subjects, nor when the p atients and central subjects were compared according to their menopaus al status. However, postmenopausal thyroidectomized patients showed si gnificantly lower bone mass (P < 0.001) than premenopausal patients. 3 . L-Thyroxine-treated patients showed significantly higher levels of b one alkaline phosphatase and urine hydroxyproline excretion than contr ol subjects (P < 0.003 and P < 0.001, respectively). These differences were still present when patients and control subjects were analysed a ccording to their menopausal status. However, bone alkaline phosphatas e was significantly higher in postmenopausal than in premenopausal wom en only in L-thyroxine-treated patients (P < 0.05). In postmenopausal L-thyroxine-treated patients a negative correlation between time since menopause and bone mass (P < 0.05) and a positive correlation between bone alkaline phosphatase and hydroxyproline excretion (P < 0.03) wer e also found. 4. We conclude that long-term thyroid-stimulating hormon e-suppressive treatment with L-thyroxine in thyroidectomized women is not associated with a decrease in spinal bone mass nor with calcitonin deficiency, and that L-thyroxine treatment may increase skeletal sens itivity to menopause-related bone loss.