Hypothyroidism in children

Hypothyroidism in children is usually caused by autoimmune thyroiditis; it can also be late-diagnosed congenital hypothyroidism. The symptoms and signs can be subtle and easily missed. Typical features include lethargy, constipation, cold intolerance, mood changes, slowing of growth, reduced school performance and myxoedema (puffy facial features). Pseudopuberty is an unusual presentation that is more common in girls than boys.

If an elevated serum thyroid stimulating hormone (TSH) concentration is found, repeat the test after 4 to 8 weeks and consider testing for thyroid peroxidase antibody and thyroglobulin antibody. Refer the child to a specialist if the TSH is persistently significantly elevated (eg higher than 10 milliunits/L), or if the child is symptomatic. Referral could also be considered for a child with persistent but mild TSH elevation if thyroid peroxidase antibody or thyroglobulin antibody is positive, as this increases the risk of progression.

The decision to start treatment should be made under specialist guidance. Thyroxine replacement in children is usually started at a low dose and titrated up slowly (unlike in adults, in whom initial full-replacement can often be used). A reasonable starting dose is:

levothyroxine 25 micrograms orally, daily. Adjust the dose every 4 to 8 weeks as required. hypothyroidism (child) levothyroxine

For a child with primary hypothyroidism, titrate the dose according to serum 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.

For a child with hypothyroidism secondary to hypopituitarism, titrate the dose according to clinical response and serum T4 concentration (not serum TSH concentration), targeting a serum T4 concentration in the upper half of the normal range. A low serum TSH concentration is to be expected in hypopituitarism and is not a basis to reduce the dose.

Subtle dose adjustments can be achieved by prescribing different strength tablets on different days of the week.

Temporary neonatal hypothyroidism is uncommon; it can be caused by transplacental passage of maternal antibodies. The neonate may require early thyroxine replacement—seek advice from a paediatric endocrinologist.