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Serum thyroxine and thyroid stimulating hormone concentrations after treatment of congenital hypothyroidism
S S Abusrewil1, L Tyfield, D C Savage
1Bristol Royal Hospital for Sick Children.
Insights
Infants treated for congenital hypothyroidism often show elevated thyroid stimulating hormone (TSH) levels, requiring dose adjustments of L-thyroxine. Regular monitoring and dose reviews are crucial during rapid growth periods in early childhood.
Area of Science:
- Pediatric Endocrinology
- Neonatal Care
- Thyroid Disorders
Background:
- Congenital hypothyroidism requires lifelong L-thyroxine replacement therapy.
- Infants experience rapid growth and weight changes, particularly in the first two years of life.
- Thyroid hormone dosage needs careful management to ensure appropriate levels and prevent complications.
Purpose of the Study:
- To monitor serum thyroid stimulating hormone (TSH) and thyroxine concentrations in infants treated for congenital hypothyroidism.
- To investigate the relationship between L-thyroxine dosage, body weight, and TSH levels in this population.
- To evaluate the long-term stability of the hypothalamic-pituitary-thyroid axis in treated infants.
Main Methods:
- Prospective monitoring of serum TSH and thyroxine levels in 42 infants with congenital hypothyroidism.
- Correlation analysis of TSH levels with age, L-thyroxine dosage (mg/kg/body weight), and infant weight gain.
- Assessment of hypothalamic-pituitary-thyroid axis maturation based on TSH suppression after L-thyroxine dose adjustments.
Main Results:
- Elevated TSH concentrations were observed in a significant proportion of infants across different age groups (52% at 2-4 months, 38% at 5-11 months, 33% at 12-18 months, 19% at 2-4 years).
- Infants with elevated TSH had significantly lower serum thyroxine and lower L-thyroxine doses per kilogram of body weight.
- TSH levels were effectively suppressed with increased L-thyroxine dosage, with only one case of delayed axis maturation.
Conclusions:
- Rapid infant weight gain necessitates adjustments in L-thyroxine dosage (mg/kg/body weight) to maintain euthyroidism.
- Treatment for congenital hypothyroidism in infants requires frequent monitoring and dose adjustments every two to three months, especially during the first two years of life.
- The hypothalamic-pituitary-thyroid axis generally demonstrates appropriate response to L-thyroxine therapy, with minimal long-term immaturity observed.
Abstract:
Serum thyroid stimulating hormone and thyroxine concentrations were monitored in 42 infants who had been treated for congenital hypothyroidism. Serum thyroid stimulating hormone concentrations were raised in 22 of the infants (52%) at 2 to 4 months, in 16 (38%) at 5 to 11 months, in 14 (33%) at 12 to 18 months, and in eight (19%) at 2 to 4 years. Serum thyroxine and the dose of L-thyroxine/kg/body weight were significantly lower in those infants with raised thyroid stimulating hormone concentrations. Thyroid stimulating hormone was appropriately suppressed when the dose of L-thyroxine was increased, and only one child had delayed maturation of the hypothalamic/pituitary/thyroid axis. We believe it is the infant's rapid gain in weight in the first two years of life that necessitates this decrease in the dose of L-thyroxine/kg body weight and recommend that the treatment of this age group is reviewed every two to three months.