Age and postmenopausal state related risk of axial bone demineralization in goitrous women treated with L-thyroxine. A longitudinal study

The demineralizing effect of L-thyroxine (L-T4) treatment at lumbar spine level was prospectively evaluated in 27 nontoxic goiter women (14 premenopausal, 13 postmenopausal; age 34-65 years) before and after one year of therapy. All the patients admitted had normal densitometric parameters for age and sex. The L-T4 dose was adjusted to reduce circulating TSH without suppressing it below the limit of sensitivity of the method, and to maintain FT3 and FT4 within normal range throughout treatment. At the control after therapy, mean densitometric parameters were decreased; in particular, the mean bone mineral density (BMD) percentage change was -1.85 [2.6]%, a decrease not significantly different from the expected change due to the physiological rate of bone loss at lumbar spine. However, a relevant individual variability was observed, with an annualized BMD decrease > 3.0%, suggestive of increased risk of osteoporosis, in 5 out of 27 women. By logistic regression analysis, the elevated BMD decrease (> 3.0% year) was positively correlated with age and postmenopausal state, but not with other parameters examined (body mass index, TSH levels during treatment, bone Gla-protein, L-T4 daily dose pro kg, L-T4 cumulative dose). Our longitudinal study indicates that thyroid hormone treatment, even when complete suppression of circulating TSH is avoided, can significantly increase the risk of spinal demineralization in aged and/or postmenopausal subjects. Conversely, the treatment with not completely suppressive doses of L-T4 was effective in reducing goiter size in a proportion of patients (48%) comparable to previous reports obtained with higher doses of L-T4.