The early effects of radioiodine therapy for hyperthyroidism on biochemical indices of bone turnover.

OBJECTIVE

We investigated the early changes following radioiodine therapy for hyperthyroidism, in biochemical indices of bone synthesis and degradation, and their relationship to circulating thyroid hormone concentrations.

DESIGN

Prospective follow-up over the first 12 weeks after radioiodine therapy.

PATIENTS

Six women with clinical and biochemical evidence of hyperthyroidism.

MEASUREMENTS

Serum concentrations of T4, free T3 and osteocalcin, and urinary excretion of the pyridinium cross-links, pyridinaline and deoxypyridinaline, measured before and weekly for 12 weeks after administration of radioiodine therapy.

RESULTS

Biochemical indices of bone metabolism were elevated prior to treatment. There was a brisk reduction in circulating thyroid hormones levels paralleled by a similar fall in pyridinium cross-link excretion, which had returned to normal in five patients by the end of the study. There was a positive correlation between pyridinium cross-link excretion and thyroid hormone concentrations. There was no significant change in serum osteocalcin.

CONCLUSIONS

Treatment of hyperthyroidism results in prompt correction of the associated increased rate of bone collagen degradation suggesting that effective early correction of hyperthyroidism is desirable to limit its detrimental effect on skeletal mass.