ESPE Abstracts (2014) 82 P-D-2-2-604

Levothyroxine Requirement in Congenital Hypothyroidism: 12-year Longitudinal Study

Maria Cristina Vigonea, Rosa Lapollab, Maurizio Delvecchioc, Mariacarolina Salernod, Malgorzata Wasniewskae, Pietro Pio Popolob, Alessandro Mussaf, Giulia Maria Tronconia, Raffaella Di Mased, Ida D’Acunzod, Rosa Maria Falconeg, Andrea Corriasf, Filippo De Lucae, Giovanna Webera, Luciano Cavallog & Maria Felicia Faienzag

aDepartment of Pediatrics Endocrinology, IRCCS Vita-Salute San Raffaele University, Milan, Italy; bDepartment of Pediatrics, University of Foggia, Foggia, Italy; cPaediatrics Unit IRCCS Casa Sollievo della Sofferenza, San Giovanni Rotondo, Foggia, Italy; dDepartment of Pediatrics, University of Naples Federico II,
Naples, Italy; eDepartment of Pediatrics, University of Messina, Messina, Italy; fDivision of Pediatric Endocrinology,
Department of Pediatrics, University of Turin, Turin, Italy;
gSection of Pediatrics, Department of Biomedical Sciences
and Human Oncology, University of Bari Aldo Moro,
Bari, Italy

Background: The replacement therapy with levo-thyroxine (LT4) in congenital hypothyroidism (CH) aims to ensure normal growth and neuropsychological development. Few data are available about the appropriate dose during childhood and early adolescence.

Objective and hypotheses: i) To evaluate LT4/kg per day requirement from diagnosis until 12 years of age; ii) to assess any differences in relation to the different etiology of CH as concerns the LT4/kg per day requirement.

Method: Multicentric observational study; 216 patients (142 females) with permanent CH classified as athyreosis, ectopia, in situ gland, on the basis of the thyroid imaging; LT4 dose was recorded from 6 months to 12 years of age and the LT4/kg per day calculated.

Results: The LT4/kg per day requirement statistically decreased year by year, irrespective of etiology. It was about 3–4 μg/kg per day from 1 to 5 and about 2–3 μg/kg per day from 6 to 12 years of age. It was significantly lower in patients with in situ gland than with athyreosis and with ectopic gland from the age of 1 year. Only at 1, 2, and 10 years the LT4/kg per day requirement was higher in athyreotic than in ectopic patients. The LT4/kg per day requirement at 6 months of age was correlated with the requirement at each later time point. The LT4/kg per day dose was modified less frequently in patients with in situ thyroid (40.5%) than in patients with ectopic gland (47.4%) or with athyreosis (48.9%).

Conclusion: Euthyroidism may be achieved by 3–4 and 2–3 μg/kg per day of LT4 in preschool and in school CH patients. The LT4/kg per day dose is affected by the etiology: patients with in situ gland require a lower dose than the other ones. The patients with ectopia or athyreosis require more frequently a change in the daily dose, and thus such patients have to be followed up more frequently. Since the age of 6 months, some patients require higher doses than other ones, irrespective of etiology.