[Bone tissue mineral density in patients with thyroid gland cancer on levothyroxine natrium therapy]

The subjects of the study were 319 patients (55 men and 264 women) aged 17 to 55 (mean age 40.8 +/- 1.9 years), who had been on suppressive therapy with levothyroxine natrium in a dose of 100 to 300 mkg/day, or 247 +/- 0.32 mkg/kg/day, for 4.9 0.3 years following special treatment of diferentiated thyroid gland cancer (TGC). The control group included 55 subjects (11 men and 44 women) aged 18 to 55 (mean age 38.9 +/- 1.4 years) without thyroid gland dysfunction. In the patients of the main group bone mineral density (BMD) was determined by means of dual-energy x-ray absorptiometry using Sophos L-XRA device (France). Serum levels of free fractions of thyroid hormones and thyrotropin were measured by radioimmunoassay (RIA) using Medipan diagnostic (Germany) and Immunotech (Czechia) kits. Blood levels of testosterone, estradiol, lutropin, and follicle-stimulating hormone were determined by RIA using IOPIBOKH (Belarus) kit in order to exclude the role of sex hormone deficit in BMD disorder. Peripheral blood level of parathormone was determined by RIA using CIS Biointernational (France). General calcium levels were determined by arsenazo III method, inorganic phosphorus level--by kinetic phosphomolybdic method using Technicon RA-XT analyzer (USA), ionized calcium serum level--by ionoselective method using OP-270 analyzer (Radelkis, Hungary) and DiaSys kits (Russia). The study revealed no increase of osteoporosis frequency in patients under 55 years old on suppressive therapy with levothyroxine natrium following a surgery for differentiated TGC. The study found a significant increase in frequency of lumbar osteopenia (22.9% vs. 9.1% in the control group, chi squared = 3.9, p = 0.049) due to decrease of skeleton mineralization in women (21.96% vs. 681% in the control group, chi squared = 4.02, p = 0.045), which was associated with peripheral blood level of triiodothyronine (T3) free fraction (r = -0.45, p = 0.03.) Subjects with a level of T3 free fraction higher than 5.8 mmol/l displayed a significant increase of calcium excretion: 4.6 +/- 0.2 mmol/day vs. 3.7 +/- 0.2 mmol/day in the control group, T = 3.06, p = 0.049); a weak correlation between T3 free fraction level higher than 5.8 mmol/l and calcium excretion (r = 0.28, p = 0.002) was found The study revealed age peaks of osteopenia in the women of the main group--25 years old and older than 40. The results show that postoperative parathyroid insufficiency does not lead to decrease of skeleton mineralization.