Endocrine Abstracts

Treatment for congenital hypothyroidism (CH), based on thyroid extracts, was introduced more than 100 years ago and resulted in a compelling improvement of impaired growth, obesity, depression and severe delay of motor development. However, severe mental retardation remained despite treatment. It was only after the implementation of neonatal screening for CH in 1970s that intellectual outcomes improved to an average normal IQ. However, whether complete normalization of cognitive outcome is possible remains controversial, since some studies have found significant gaps compared to control populations including healthy siblings. Furthermore, there is some evidence that quality of life (QoL) scores are lower compared to the general population. To further improve the outcome, higher starting doses of more than 10 μg/kg and commencement of treatment within the first two weeks of life were recommended. The most recent outcome study from New Zealand, reporting patients treated according to a regimen consistent with these recommendations, documented IQ at age 10 years that was no longer different from sibling control subjects. Nevertheless treatment with higher starting doses has raised concerns regarding adverse effects of supraphysiological T4 levels, with studies in rodents and patients with neonatal hyperthyroidism suggesting abnormal CNS development. In addition, it has been repeatedly shown that the recommended high LT4 dose of >10 μg/kg results in fT4 levels in newborns and infants with CH that exceed the reference ranges in this age group. However, after decades of neonatal screening and recent confusion about an “unfavourable” outcome with a high dose LT4 treatment, we now provide strong evidence –based on a recent IQoutcome study- that the present recommendations of a high initial dose above 10 μg/kg is necessary, efficient and safe to achieve optimal cognitive development in all CH patients including those who are severely affected.