Spinal bone mineral content in myxoedema and thyrotoxicosis. Effects of thyroid hormone(s) and antithyroid treatment

The effects of thyroid hormones and antithyroid treatment upon lumbar spine bone mineral content (lumbar BMC) were studied in a consecutive series of patients with myxoedema and thyrotoxicosis, respectively. All patients were investigated in the untreated state and 3-monthly during appropriate treatment for 1 year by using dual-photon [153Gd] absorptiometry. Patients with myxoedema (n = 8) did not differ from normal individuals as regards initial lumbar BMC, but levothyroxine-treatment caused significant reduction in this variable. The median decrease in lumbar BMC after 1 year was 8.9% (95% confidence limits 1.5-15.4%, P less than 0.05). This loss of bone might be attributed to an inappropriate increase in bone turnover in the euthyroid state. It is as yet uncertain whether it predisposes to spinal osteopenia. Median lumbar BMC in patients with thyrotoxicosis (n = 25) was 12.6% (2.0-16.6%, P less than 0.05) lower than that of normal individuals before the beginning of treatment. Lumbar BMC increased during antithyroid therapy. The median gain in bone mineral after 1 year was 3.7% (1.6-9.6%, P less than 0.01). These findings suggest that excess of thyroid hormones leads to negative spinal bone mineral balance. The revealed bone loss was clinically insignificant, however, and it appeared to be at least partially reversible after antithyroid treatment.