23rd May 2025

Congenital hypothyroidism

• Congenital hypothyroidism refers to the deficiency of thyroid hormone from birth. It is the commonest neonatal endocrine disorder. It occurs in about 1 in 4000 live births in the UK, with predominance in females. Most of the cases are familial and inherited as autosomal recessive conditions. Errors in the formation or migration of the thyroid tissue can result in thyroid aplasia, dysplasia, or ectopy (primary hypothyroidism). It occurs due to an error in thyroid metabolism, enzyme, or iodine deficiency. If TSH deficiency is present, this can cause secondary or central hypothyroidism. Both of these types cause permanent hypothyroidism. 
• Transient congenital hypothyroidism can be due to maternal ingestion of antithyroid drugs or maternal TPOAbs or iodine deficiency. 

Clinical picture

Clinical features are subtle, so making the diagnosis at birth may be challenging. Later infants show the following symptoms:

• coarse facies, macroglossia, and hoarse cry
• the posterior fontanelle remains open, and closure of the anterior fontanelle is delayed
• umbilical hernia
• cold or mottled skin
• hypotonia and hypothermia
• anaemia or prolonged jaundice may be present
• poor feeding  and constipation
• presence of a palpable goitre

If not detected early and treated, profound intellectual disabilities may develop. If delayed treatment is delivered, neurological problems such as spasticity, gait abnormalities, dysarthria or behavioural issues can result.

Investigations

Due to severe complications resulting from delayed treatment of congenital hypothyroidism, in the UK filter paper blood spot TSH measurement is used for screening. The test is done at least 48 hours after birth (within 2-8 days) to avoid false positive results.

• High TSH is diagnostic for primary hypothyroidism. 
  • Confirmatory examinations within 2 weeks should be done. Serum TSH and free T4 are measured. Again, high TSH and low T4 indicates the diagnosis of primary hypothyroidism.
• Low or normal TSH occurs in secondary hypothyroidism.
• Caution with preterm infants and acutely ill infants should be considered as there is delayed TSH rise. This requires a routine second screening test.

Management

The mainstay of treatment is with thyroxine replacement, which should start as soon as possible within the first 18 days of life. The aim is to increase serum free T4 levels to normal as rapidly as possible. This is because a delay in the restoration of normal T4 levels within a week may result in long-term cognitive function impairment . . Regular monitoring of TSH and T4 levels as well as growth measurement and bone age assessment are required until growth is completed.