DIFFERENCES IN LEVOTHYROXINE DOSAGES FOR REPLACEMENT OF CHILDREN WITH PRIMARY AND CENTRAL PERMANENT HYPOTHYROIDISM

Objectives: Replacement of Congenital (CH), Autoimmune (AH) and Central (PH) hypothyroidism is based on Levothyroxine (L-T4) administration. However, the initial L-T4 doses used for the optimal treatment in CH, AH or PH patients are widely different. Several studies evaluated L-T4 maintenance euthyroid doses administered for the appropriate replacement in children with CH and AH, while data concerning PH are scanty. Objective and hypotheses: To compare mean L-T4 doses administered in CH, AH or PH children to maintain optimal hormone replacement. Methods: This is cross-sectional and retrospective study. We enrolled 67 children (Female 37), with overt and permanent hypothyroidism, who were appropriately replaced (on the basis of serum fT4 and TSH levels for CH and AH and fT4 for PH) for almost 3 yrs (mean 8.2 ± 5.2 yr). Our study population consisted of : 22 children affected by CH (14 by thyroid dysgenesis, 8 by dyshormonogenesis), 23 by AH and 22 by PH (13 by idiopathic hypopituitarism, 9 secondary to pituitary tumors). Serum fT4 and TSH levels were measured at mean age of 14.6±2.6 yrs. Serum fT4 and TSH levels were measured by commercial kits, Statistical analysis was performed by ANOVA. Results: In AH children, mean L-T4 maintenance euthyroid doses were significantly lower than in the CH and PH groups (1.4±0.4 vs 1.7±0.4, p= 0.01 and 1.4±0.4 vs 1.9±0.5, p = 0.008 respectively), while no differences were found between CH and PH groups (1.9±0.5 vs 1.7±0.4, p=0.2). Mean L-T4 doses to maintain euthyroidism were similar in patients with athyreosis vsdyshormonogenesis (1.6±0,3 vs 1.7±0.6, p=0.1) and in those with idiopathic and secondary PH (1.8±0.8 vs 1.9±0.5, p=0.3). There is no correlation between LT4 dosage and serum FT4 levels or chronological age in all forms of permanent hypothyroidism in our study population. In all groups mean fT4 levels were not different, and in AH and CH mean TSH values were similar. Conclusions: In our experience PH children need (weightbased daily) L-T4 dosages similar to CH ones, while significantly lower doses are sufficient to maintain clinical and biochemical euthyroid status in those with AH.