Congenital hypothyroidism
Congenital hypothyroidism occurs in 1 in 2500 to 3500 neonates, and is usually identified through neonatal screening programs. Most cases are caused by thyroid dysgenesis, including athyreosis (an absence of the thyroid gland) and thyroid ectopia (thyroid tissue is outside the usual location). The next most common cause is thyroid dyshormonogenesis (dysfunctional synthesis of thyroid hormone). A technetium thyroid scan, performed as an urgent procedure before starting thyroxine replacement, helps to differentiate between the causes. Thyroid ultrasound can also be useful.
Congenital hypothyroidism should be managed in consultation with a paediatric endocrinologist. Start replacement therapy as soon as the diagnosis is made (within 24 to 48 hours), and ideally before 2 weeks of age, to prevent intellectual disability.
The levothyroxine dose required in infants is relatively higher than in adults. A reasonable starting dose is:
levothyroxine 10 to 15 micrograms/kg orally, daily1. hypothyroidism, congenital levothyroxine
The dose should be titrated according to serum thyroid stimulating hormone (TSH) and free thyroxine (T4) response. The aim of treatment is to keep:
- serum TSH concentration in the lower half of the normal range
- serum T4 concentration in the upper half of the normal range.
Assess thyroid function weekly for the first month. If the serum TSH concentration is normalised, the frequency of assessment can be gradually reduced. Assess intellectual and physical development, along with thyroid function tests, every 2 to 3 months for the first 5 years of life, then every 3 to 6 months until the patient is fully grown. The dose can usually be reduced progressively with age towards the dose used for acquired hypothyroidism (see Thyroxine replacement in adults). Treatment is usually required lifelong but some cases can be transient.