BONE-MINERAL DENSITY IN THYROXINE TREATED FEMALES WITH OR WITHOUT A PREVIOUS HISTORY OF THYROTOXICOSIS

OBJECTIVE The results of studies examining the influence of T4 therapy upon bone mineral density (BMD) are conflicting. This conflict may, i n part, reflect inclusion of patients with varying thyroid disorders. We have therefore examined the influence of preceding thyroid history and T4 therapy on BMD. DESIGN Case-control studies of patients on long -term T4 therapy who have or have not previously received radioiodine treatment for thyrotoxicosis, as well as previously thyrotoxic patient s who have not required T4 replacement. PATIENTS Twenty-seven premenop ausal and 60 postmenopausal females with a past history of thyrotoxico sis and subsequent T4 treated hypothyroidism (group 1), 39 post-menopa usal females with a past history of radioiodine treated thyrotoxicosis not receiving T4 (group 2) and 22 post-menopausal females with primar y hypothyroidism on T4 (group 3). Female controls individually matched to patients by age and menopausal status. MEASUREMENTS BMD measured b y dual-energy X-ray absorptiometry. Serum biochemistry and tests of th yroid function. RESULTS No significant differences were found in femor al or lumbar spine BMD measurements between premenopausal patients and controls in group 1 or between group 2 patients and controls. Measure ments of BMD at all sites were lower in post-menopausal patients in gr oups 1 and 2 than in controls; when allowance was made for differences in BMD due to body mass index by analysis of variance, significant re ductions in femoral trochanter BMD (3.9%, P < 0.05) and lumbar spine ( 5.6-8.5%, P < 0.01) BMD results were found in post-menopausal females in group 1 and reductions in femoral trochanter (3.9%, P < 0.01), Ward 's triangle (5.6%, P < 0.05) and lumbar spine (8.5%, P < 0.01) BMD res ults in group 2. Separate analysis of BMD results of those with normal or reduced serum TSH did not affect outcome. BMD measurements were no t significantly correlated with duration of T4 therapy, T4 dose, or se rum free T4 or TSH in any patient group. CONCLUSIONS Thyroxine therapy alone does not represent a significant risk factor for loss of bone m ineral density but there is a risk of bone loss in post-menopausal (bu t not premenopausal) females with a previous history of thyrotoxicosis treated with radioiodine.