ESPE Abstracts

Background: Management of subclinical hypothyroidism (SH) in infancy is still controversial. According to the European Guidelines for Congenital Hypothyroidism (CH), in case of TSH levels between 6 and 20 µUI/ml, both levothyroxine (L-T4) therapy and a wait-and-see approach can be considered.

Aim: to describe the evolution of SH diagnosed in newborns recalled by neonatal screening (TSH values ≥7µUI/ml).

Methods: we conducted a single-center retrospective cohort study. We enrolled 55 children with SH (TSH 6-20 µUI/ml and FT4 in the normal range) referred to a single Pediatric Endocrinology Unit between 2013 and 2023. Family history of thyroid diseases, perinatal history, auxological characteristics, thyroid function, antithyroid antibodies levels and thyroid ultrasound scan were collected.

Results: 26 (47.3%) did not start treatment with levothyroxine (group 1), whilst 29 children (52.7%) started L-T4 therapy (group 2) for persistence of TSH >10µUI/ml. No significant differences between groups in family history of thyroid diseases and auxological parameters both at the birth and at the first visit were reported. TSH was significantly increased in group 2 (13.69±7.60 µUI/ml vs 8.78±2.82 of group 1, P = 0.003). Group 1 patients showed a progressive decrease of TSH values; 26.9% children have been referred back to primary care pediatrician (mean age 0.84±1.06years), 46.2% continued follow-up due to persistent SH and 26.9% were lost at follow-up. In group 2 patients started L-T4 therapy at the age of 42.1±21.0 days with a mean TSH of 14.35±7.39µIU/ml. FT4 was in the normal range (14.94±3.14pmol/L). Starting L-T4 dose was 6.54±3.31µg/kg/day. Nineteen patients of group 2 stopped L-T4 therapy at an age of 3.25±0.69 years, whilst 10 patients were still <3 years of age. Nine children (47.3%) restarted L-T4 treatment after 2.20±2.38 months due to increased TSH values >10 µUI/ml (15.75±13.36µUI/ml), while in the other 10 children (52.7%) L-T4 therapy was definitively stopped. Only one child showed a transient positivity of antithyroid antibodies. All children underwent a thyroid ultrasound scan that documented hypoplasia only in 4 case (7.2%). All children showed regular growth over time, without differences between groups.

Conclusion: although 52.7% of children with SH started L-T4 treatment, the majority did not need to continue therapy during follow-up, suggesting a transient form. A follow-up for infants with SH is needed to assess regular growth and development. Genetic testing for candidate genes of CH could be performed in infants with SH to identify mild forms of permanent CH.