IS PREVIOUS HYPERTHYROIDISM STILL A RISK FACTOR FOR OSTEOPOROSIS IN POSTMENOPAUSAL WOMEN

OBJECTIVE Hyperthyroidism is a risk factor for osteoporosis, but the r elative contributions of the episode of hyperthroidism and thyroxine r eplacement for subsequent hypothroidism remain uncertain. In this stud y we have measured bone mineral density (BMD) in postmenopausal women with a previous history of hyperthyroidism, comparing those requiring thyroxine therapy with those remaining euthyroid and with an historica l local control population. DESIGN Cross-sectional study. PATIENTS One hundred and six post-menopausal women with a previous history of hype rthyroidism. These were divided into four groups: treated with radioio dine, 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 su rgery, receiving thyroxine for at least 5 years (group ST, n = 24). Th ere were 102 control subjects. MEASUREMENT Forearm bone mineral densit y at distal and ultradistal sites as measured by single-photon absorpt iometry. RESULTS Results were expressed as 'Z-scores' i.e. number of s tandard deviations from the mean of a 5-year age-band from the local c ontrol 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, Ri and ST but not SU had significantly lower BMD than contr ols. CONCLUSION Post-menopausal women with previous hyperthyroidism tr eated with radioiodine have reduced BMD, whether or not receiving thyr oxine. They should be targeted for densitometry and protective therapy with oestrogen should be considered. Those treated with surgery appea r to be at less risk; this may be because most are diagnosed and treat ed whilst premenopausal. Thyroxine may have a deleterious effect in th is group; longitudinal studies would provide further clarification.