Congenital Hypothyroidism: Long-Term Growth and Intellectual Outcomes With a Lower Initial Levothyroxine Dose.

Abstract

Objectives: This study aims to review the long-term outcome of congenital hypothyroidism (CH) and whether patient- or treatment-related factors impact the outcomes, especially focusing on the initial Levothyroxine dose.

Methods: This is a retrospective, cross-sectional study of the children diagnosed with CH who received Levothyroxine at Ajou University Hospital between 2003 and 2024. Comparative analysis was performed between the low (<10 mcg/kg) and high (≥10 mcg/kg) initial dose groups. Repeated-measures analysis of covariance was employed to evaluate longitudinal changes in growth outcomes, and multivariate linear regression was utilised to evaluate the effects of clinical factors on the intelligence quotient (IQ).

Results: Among the study population, 84 of 144 children were prescribed an initial low dose of Levothyroxine. Most children in both initial dose groups showed appropriate growth within the normal range in the biennial growth evaluation from ages four to eight and in the Wechsler IQ exam. The initial dose seemed to not significantly affect the growth outcomes over time, as no significant differences between the low- and high-dose groups were observed (p values: 0.545, 0.609, 0.532, and 0.501 for bone age-chronological age, height z-score, weight z-score, and BMI z-score, respectively). The effect of the initial dose group on the full-scale IQ was also not statistically significant (p = 0.362).

Conclusion: We demonstrated the favourable long-term outcomes in linear growth and neurodevelopment among children with CH, even in lower initial Levothyroxine doses.