Assessment of the effects of levothyroxin (l-t4) treatment on bone turnover parameters in children with subclinical hypothyroidism.

ASSESSMENT OF THE EFFECTS OF LEVOTHYROXIN (L-T4) TREATMENT ON BONE TURNOVER PARAMETERS IN CHILDREN WITH SUBCLINICAL HYPOTHYROIDISM. Objective: The aim of this study is to assess the effect of 6-month-long L-T4 treatment on children with subclinical hypothyroidism, which there has been no consensus whether treating them are warranted, on the metabolic bone markers. Cases and method: In the study group, which consists of 28 prepubertal cases (10 girls) at an average chronological age (CA) of 6.19 year, at the beginning auxologic data (Height, weight, bone age (BA)) and biochemical criteria of the bone (sT3, sT4, TSH, serum Cr, Ca, P, BALP, Mg, PTH, 25-OH vitamin D3, urine Cr, Ca, P), bone cycle indicators (OC, PINP, NTx, DPyr) and bone mineral density were evaluated and compared with the data obtained after treatment. Findings: There was a significant improvement in the BA-CA difference in male cases after the treatment. TSH and sT3 levels were reduced significantly, whereas there was a significant increase in sT4 levels all within normal limits. Serum phosphorus and Mg levels and urine P excretion were reduced significantly. PINP levels increased significantly while NTx/Cr levels were found to be significantly reduced. No differences in lomber and femoral BMD Z-scores have been observed at the end of the therapy. Discussion: After the six-month-long L-T4 treatment, the fact that average BA/CA ratio stayed as <1 demonstrated that physiologic L-T4 treatment does not create any negative effect on BA and moreover, has an improving effect on the somatic development as seen in male children. A decrease in sT3 levels is the sign of euthyroid metabolism as a consequence of L-T4 treatment. Also all thyroid hormone values measured throughout the treatment were within physiologic limits, demonstrating that the L-T4 treatment applied was accurate and suitable. Serum and urine phosphorus changes suggested that phosphorus might be used in bone formation and thyroid hormones have a direct effect on the phosphorus balance. A decrease in serum Mg levels pointed to the improvement in Mg retention after euthyroid metabolism was established through L-T4 treatment. An increase in PINP levels reflects stimulated osteoblastic activity while a decrease in NTx/Cr ratio indicates decreased osteoclastic activity. No change in BMD Z-score values proves that the physiologic dose of L-T4 treatment in subclinical hypothyroid prepubertal children does not have any negative impact on bone mineral density. Key words : subclinical hypothyroidism, bone, bone turnover markers, bone mineral density (BMD)