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Longitudinal assessment of L-T4 therapy for congenital hypothyroidism: differences between athyreosis vs ectopia and
M García1, R Calzada-León, J Pérez
1Endocrine Service, National Institute of Pediatrics, Mexico City, Mexico.
Insights
Levothyroxine (LT4) treatment for congenital hypothyroidism (CH) in infants normalized thyroid-stimulating hormone (TSH) levels. Despite elevated T4 and FT4, infants remained clinically euthyroid, with some showing bone age acceleration.
Area of Science:
- Pediatrics
- Endocrinology
- Neonatal Screening
Background:
- Congenital hypothyroidism (CH) requires timely thyroid hormone replacement.
- Optimal LT4 dosing in infants with CH is crucial for development.
- Neonatal screening identifies CH, enabling early intervention.
Purpose of the Study:
- To evaluate the effects of a standardized LT4 dose on thyroid hormone serum levels in infants with CH.
- To assess the impact of initial diagnosis parameters (bone age, thyroid anatomy) on treatment response.
- To monitor thyroid hormone profiles, bone age, and clinical status during the first two years of LT4 therapy.
Main Methods:
- Prospective, longitudinal, comparative study of 56 term eutrophic infants with CH.
- Initial LT4 dose of 50 mcg/day (12.9-13.7 mcg/kg/day).
- Bimonthly (year 1) and quarterly (year 2) follow-up with thyroid profile and bone age assessments at 6, 12, and 24 months.
Main Results:
- At diagnosis, hormone levels differed based on thyroid ectopia and bone age (p < 0.001, p < 0.05).
- During treatment, all infants were clinically euthyroid, with supra-normal T4/FT4 but normal T3/FT3 levels (p < 0.001, p > 0.05).
- TSH normalized within 8 weeks; bone age accelerated in 8 children with delayed bone age at birth, with no craniosynostosis.
Conclusions:
- A fixed initial LT4 dose effectively manages CH in infants, normalizing TSH and maintaining clinical euthyroid status.
- Elevated T4/FT4 levels during treatment may be acceptable, as T3/FT3 remained normal and no adverse effects like craniosynostosis were observed.
- Early diagnosis and monitoring are key, with potential for bone age catch-up in infants with delayed bone age at birth.
Abstract:
To study the effects of LT4 dose on thyroid hormone serum levels, a prospective, longitudinal and comparative study was designed, including 56 term eutrophic 1-89 day-old infants with congenital hypothyroidism (CH) detected by neonatal screening. Patients were divided into four groups according to delayed or normal bone age at birth, and athyreosis or ectopic thyroid. All received an initial dose of 50 micrograms/day (12.9-13.7 micrograms/kg/day) LT4 and were followed bimonthly (first year) and quarterly (second year) with thyroid profile and bone age determinations at 6, 12 and 24 months. At diagnosis, hormone levels were higher in cases of ectopia than in athyreosis (p < 0.001), and T4 was lower in children with delayed than in normal bone age at birth (p < 0.05). During treatment, all groups were clinically euthyroid despite T4 and FT4 serum levels higher than the upper normal limit (p < 0.0.001), though T3 and FT3 were within the normal limit (p > 0.05). TSH normalized within 8 weeks. Bone age accelerated at 2 years in eight children of the bone age delayed group. No patient had craniosynostosis.