DIFFERENCES IN LEVOTHYROXINE DOSAGES FOR REPLACEMENT IN CHILDREN WITH DISTINCT CAUSES OF PERMANENT HYPOTHYROIDISM

Objectives: L-tiroxine (L-T4) is considered the treatment of choice in hypothyroidism, either congenital (CoH), autoimmune (AH) or central (CH). The study objective was to find the mean L-T4 doses for CoH, AH and CH in pediatric age to maintain optimal hormone replacement. Methods: In this one center, cross-sectional and retrospective study, 67 of 267 evaluated patients, aged <18.0 yrs, with overt and permanent hypothyroidism, followed at the Outpatient Pediatric Endocrinology Clinic of University of Messina, were enrolled on the basis of the following inclusion criteria: a) age <14.0 years at hypothyroidism diagnosis; b) follow-up at least 3 yrs under L-T4 therapy; c) normal value of fT4 and/or TSH for at least six months under unchanged L-T4 therapy. Our study population consisted of: 22 children affected by CoH (14 by thyroid dysgenesis- CoH1, 8 by dyshormonogenesis- CoH2), 23 by AH and 22 by CH (13 by idiopathic hypopituitarism- CH1, 9 secondary to pituitary tumors- CH2). Serum fT4 and TSH levels were measured by commercial kits at mean age of 14.9 ± 2.3 yrs. Results: In AH children, mean L-T4 maintenance euthyroid doses were significantly lower than in the CoH and CH groups (p = 0.02 and p = 0.008 respectively), while no differences were found between CoH and CH groups (p = 0.1) (Table1). Mean L-T4 doses to maintain euthyroidism were similar in patients with athyreosis vs dyshormonogenesis (p = 0.1) and in those with idiopathic and secondary CH (p = 0.4). Moreover, there was no statistically significant 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 CH children need (weight-based daily) L-T4 dosages similar to CoH ones, while significantly lower doses are sufficient to maintain clinical and biochemical euthyroid status in those with AH. These findings are agreeing with the hypothesis that LT-4 replacement dose is inversely correlated with the functionally of thyroid tissue.