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

Area of Science:

• Pediatric Endocrinology
• Developmental Pediatrics
• Metabolic Disorders

Background:

• Congenital hypothyroidism (CH) requires lifelong Levothyroxine replacement therapy.
• Optimizing initial Levothyroxine dosage is crucial for long-term outcomes in CH patients.
• Understanding the impact of initial dosage on growth and neurodevelopment is essential for clinical practice.

Purpose of the Study:

• To evaluate the long-term outcomes of congenital hypothyroidism (CH) in children.
• To determine if patient- or treatment-related factors, particularly initial Levothyroxine dose, influence these outcomes.
• To assess the impact of low versus high initial Levothyroxine doses on growth and neurodevelopment.

Main Methods:

• Retrospective, cross-sectional study of 144 children with CH treated between 2003 and 2024.
• Comparative analysis between low (<10 mcg/kg) and high (≥10 mcg/kg) initial Levothyroxine dose groups.
• Longitudinal growth assessment and multivariate regression analysis for intelligence quotient (IQ) were performed.

Main Results:

• Most children exhibited normal growth and cognitive function regardless of initial Levothyroxine dose.
• No significant differences in growth parameters (bone age-chronological age, height, weight, BMI z-scores) were observed between low- and high-dose groups.
• The initial dose group did not significantly affect full-scale IQ scores.

Conclusions:

• Children with CH demonstrate favorable long-term linear growth and neurodevelopmental outcomes.
• Lower initial Levothyroxine doses appear as effective as higher doses in achieving positive long-term results.
• These findings support the potential for individualized initial Levothyroxine dosing strategies in CH management.