SPINAL BONE MASS AFTER LONG-TERM TREATMENT WITH L-THYROXINE IN POSTMENOPAUSAL WOMEN WITH THYROID-CANCER AND CHRONIC LYMPHOCYTIC THYROIDITIS

This study investigated the effect of long-term treatment upon bone de nsity with L-Thyroxine in postmenopausal women compared with untreated postmenopausal women with climacteric symptoms. We measured spinal bo ne density in three groups (n = 84) of postmenopausal women: (A) those treated with TSH-suppressive dosis of L-Thyroxine for a medium of 5 y ears after removal of thyroid cancer; (B) those on L-Thyroxine treatme nt for a median of 9 years after being diagnosed with chronic lynfocit ic thyroiditis (CLT); and (C) those with no thyroid disease or other k nown pathology and without any treatment. There were no differences in dietary calcium intake and daily activity between untreated and L-Thy roxine-treated women. Measurements of bone mineral density were perfor med at spine level L1-L4 using a dual X-ray densitometer and serum thy roid-stimulating hormone (TSH), thyroid hormones, and bone markers (se rum osteocalcin, procollagen I, urinary calcium), and PTH levels were assayed and found to be within normal ranges. Women receiving L-Thyrox ine after thyroid cancer had slightly higher FT4 levels compared with women who had CLT and lower TSH levels, with serum T4 and T3 levels no rmal and similar in both groups. No significant differences were found in spinal bone density after L-Thyroxine treatment between Groups A a nd B and compared with Group C. Bone loss according to 2 SD below refe rence standards (age and sex matched) was found in the 12.9% of L-Thyr oxine-treated patients versus 22.6% of untreated women. No correlation was found between bone loss and thyroid hormone levels and duration o f treatment. Our data suggest that long-term L-Thyroxine therapy in po stmenopausal women maintaining near physiological levels of thyroid ho rmones is not associated with significant axial bone loss, therefore o ther factors should be considered when this occurs.