Impact of parathyroid status and Ca and vitamin-D supplementation on bone mass and muscle-bone relationships in 208 Belarussian children after thyroidectomy because of thyroid carcinoma.

This observational study analyzes Ca-P metabolism and its impact on bone mass accrual and density and the muscle-bone mass/mass relationships in male and female children and adolescents who were parathyroidectomized because of thyroid carcinoma. Two hundred and eight children and adolescents (119 girls and 89 boys) from Gomel city (Belarus) and its rural surroundings were referred to our institution after having undergone total thyroidectomy for the treatment of advanced papillary thyroid cancer. A subgroup of children with demonstrated primary hypoparathyroidism received dihydrotachysterol (AT-10) and/or Ca supplementation. Among routine procedures over a maximum follow-up period of 5 years (average 3.7 years, maximum 8 visits), whole-body scans were taken using dual energy X-ray absorptiometry (DXA) at each visit in order to determine whole-body bone mineral content (TBMC), projected "areal" bone mineral density (TBMD), total lean mass (TLM) and total fat mass (TFM). The average serum Ca, P and AP concentrations over the whole observation period were significantly different between the groups; however, TBMC z-scores for all studied children were statistically similar in all visits. In girls, no between-group differences in height- and weight-controlled TBMC and TBMD or the TBMC/TLM ratio were observed (ANCOVA) and supplementation exerted no effect on these data, suggesting that the total bone mass accrual was not impaired by PTH deficiency in the studied conditions. However, non-supplemented boys showed lower values of the TBMC/TLM ratio than girls, and supplementation normalized these values in direct correlation with the induced improvement in serum P availability to bone. Results indicate that the primary impairment in parathyroid function and bone metabolism indicators in the thyroidectomized children was unrelated to any measurable change in crude bone mass values. However, in boys this condition impaired the TBMC/TLM ratio in such a way that the administered supplementation could normalize it as a function of improved P availability. Girls' skeleton seemed to have been naturally protected against the negative metabolic effect of the studied condition. An estrogen-induced enhancement of the biomechanical impact of muscle contractions on bone mass and structure could not be excluded in this group.