Is previous hyperthyroidism still a risk factor for osteoporosis in post-menopausal women?

Hyperthyroidism is a risk factor for osteoporosis, but the relative contributions of the episode of hyperthyroidism and thyroxine replacement for subsequent hyperthyroidism remain uncertain. In this study we have measured bone mineral density (BMD) in post-menopausal women with a previous history of hyperthyroidism, comparing those requiring thyroxine therapy with those remaining euthyroid and with an historical local control population.

Cross-sectional study.

One hundred and six post-menopausal women with a previous history of hyperthyroidism. These were divided into four groups: treated with radioiodine, remaining euthyroid (group RU, n = 15); treated with radioiodine, receiving thyroxine for at least 5 years (group RT, n = 46); treated with surgery, remaining euthyroid (group SU, n = 21); treated with surgery, receiving thyroxine for at least 5 years (group ST, n = 24). There were 102 control subjects.

Forearm bone mineral density at distal and ultradistal sites as measured by single-photon absorptiometry.

Results were expressed as 'Z-scores' i.e. number of standard deviations from the mean of a 5-year age-band from the local control population. Mean Z-scores at distal and ultradistal sites were as follows: -0.61 and -0.81 in group RU; -0.58 and -0.56 in group RT; -0.27 and -0.30 in group SU; -0.81 and -0.57 in group ST. Patients in groups RU, RT and ST but not SU had significantly lower BMD than controls.

Post-menopausal women with previous hyperthyroidism treated with radioiodine have reduced BMD, whether or not receiving thyroxine. They should be targeted for densitometry and protective therapy with oestrogen should be considered. Those treated with surgery appear to be at less risk; this may be because most are diagnosed and treated whilst premenopausal. Thyroxine may have a deleterious effect in this group; longitudinal studies would provide further clarification.