[Bone metabolism during substitution therapy of primary hypothyroidism]

The relation between thyroid hormones and bone metabolism markers in hyperthyroidism is well known. Earlier studies indicate the possibility of bone metabolism acceleration during the excessive replacement therapy with l-thyroxin in hypothyroid patients especially in one with other risk factors for bone metabolism impairment. This study evaluated the effect of physiological l-thyroxine treatment on bone metabolism in patient with primary hypothyroidism.

In the study group of 30 hypothyroid patients individual thyroxine replacement was performed targeting euthyroid status. Bone and calcium metabolism parameters (osteocalcin-OC, alkaline phosphates-ALP, C-terminal cross-linking telopeptide type l-CL, parathormone-PTH, Ca, ionized Ca, P), thyroid hormone levels (T3, T4, TSH) were measured before treatment and when euthyroid status was achieved.

A significant treatment effect was observed for bone formation and resorption parameters before and during the therapy; OC (p = 0.000024), CL (p = 0.002648). Ionized calcium levels also showed significantly higher values in euthyroid status confirming bone metabolism acceleration during the l-thyroxine therapy (p = 0.020). Thus, calcium metabolism hormone regulators were not significantly different before and after the therapy; PTH (p = 0.27). Thyroid hormone levels showed significant correlation with bone metabolism parameters before the therapy whereas this correlation was not found during therapy because of different individual l-thyroxine doses.

It can be concluded that physiological doses of l-thyroxine therapy accelerate bone metabolism in hypothyroid patients. Thus, the argument against bone loss during physiological substitution is highly specific mutual correlation between bone formation and resorption parameters. These assumptions require further investigations in long-term prospective studies in patients on replacement l-thyroxine therapy.