ESPE Abstracts

Background: Recently congenital hypothyroidism (CH) is increased,particularly mild forms. Current guidelines recommend initial levothyroxine (LT4) dose of 10–15 mcg/kg per day as soon as possible, if diagnosis is confirmed by serum test, even if FT4 concentration is normal and venous TSH concentration is >20 microUI/ml.

Objective and hypotheses: The aim of our study was to evaluate the initial LT4 dose in newborn with congenital hypothyroidism, normal FT4 and thyroid gland in situ.

Method: We conducted a retrospective charts review of all CH patients seen at Bambino Gesù Children’s Hospital from 2013-present. We included all newborn in whom confirmatory serum test demonstrated TSH>20 microUI/ml and normal FT4 levels. Thyroid ultrasonography showed a normal gland in situ. Exclusion criteria: preterm birth, genetic syndrome, chronic diseases.

Results: We identified 24 patients (10 female e 14 male), mean (SD) birth weight was 3.2 (0.4) Kg. Median TSH at diagnosis was 38.65 microUI/ml (IQ 31.1–56),mean (SD) FT4 1 ng/dl (0.72–1.4). Patients started LT4 treatment at a mean (SD) age of 29.2 (7.9) days with a mean (SD) initial dose 5.6 (1.7) mcg/kg/day. Median TSH after 15 days of treatment was 2.1 microUI/ml (IQ 0.8–5.5) and after 1 month was 2.4 microUI/ml (IQ 0.5–3.7). Mean (SD) FT4 after 15 days of treatment was 1.6 ng/dl (0.28) and after 1 month was 1.58 ng/dl (0.28). 11 patients had thyrotoxicosis (FT4 ≥1.7 ng/dl) after 15 days of treatment at mean (SD) starting LT4 dose 6.7 mcg/kg per day (1.5) vs 13 patients with normal FT4 at mean (SD) starting dose 4.6 mcg/kg per day (1.16) (P=0.002).

Conclusion: We obtained euthyroidism at 15 days of treatment at mean dose of 4.6 mcg/kg per day, avoiding thyrotoxicosis. These results indicate that CH mild forms may require lower LT4 dose. Larger prospective studies are needed to validate our findings and to investigate the optimal LT4 dose required in CH mild forms.