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Hypothyroidism in neonates is characterised by decreased thyroid hormone production, in rare cases no thyroid hormones are produced.
Transient disorders of thyroid function are more common than true congenital hypothyroidism, especially in preterm infants.
When thyroid-stimulating hormone (TSH) levels are elevated treatment with thyroxine (either long or short term) is usually indicated.
Congenital hypothyroidism
In Australia the incidence of congenital hypothyroidism is 1:3000-3600 with some geographic variation.
Causes and incidence of hypothyroidism:
- 75 per cent due to dysgenesis (gland development)
- agenesis
- ectopia
- 10 per cent due to dyshormonogenesis (thyroid hormone biosynthesis)
- often autosomal recessive
- Pendred's syndrome = peroxidase deficiency associated with sensorineural deafness
- 5 per cent due to hypothalamic-pituitary (H-P) deficiency
- secondary hypothyroidism
- tertiary hypothyroidism
- 10 per cent due to intrauterine causes
- iodine exposure
- maternal antithyroid antibodies.
Presentation
Issues to note regarding the presentation of hypothyroidism:
- The usual mode of presentation is by the finding of an elevated TSH detected on the newborn screening test (NST) taken at 48-72 hours (except in secondary or tertiary disease).
- Neonates are often subclinically affected and only detected on routine newborn screening.
- Clinical features may include:
- dry skin
- hoarse cry
- constipation
- puffy face
- prominent tongue
- listless
- umbilical hernia
- hypothermia
- bradycardia
- failure to thrive.
- Neonates may also present with jaundice due to an unconjugated hyperbilirubinaemia (glucronyl transferase deficiency).
- Gene mutations have been implicated in all forms of congenital hypothyroidism and in some cases result in an expanded phenotype including respiratory distress, choanal atresia, renal malformation and mental delay (independent of degree of hypothyroidism).
History and examination
When hypothyroidism is suspected or confirmed check for:
- mother - diet, medication history, autoimmune disease
- baby - signs and symptoms of congenital hypothyroidism, jaundice, goitre, growth parameters or other congenital problems.
Investigation for hypothyroidism
Confirmatory investigations include:
- T4 and TSH levels
- serum bilirubin (SBR) if clinically indicated
- thyroid scan (showing absent, lingual or increased uptake of radioisotope).
Management of hypothyroidism
Management guidelines for hypothyroidismin:
- Refer patients to the endocrine team.
- Thyroxine replacement therapy should be commenced as soon congenital hypothyroidism confirmed at a dose of 8-10 ug/kg/day in a single daily dose.
- Tablets should be ground up between two teaspoons and mixed with a few drops of milk. This solution should be transferred to a small, plastic feeding spoon and deposited on the back of the tongue immediately prior to feeds.
- Prepared suspensions of thyroxine are not stable.
- Dosage is adjusted according to TFT’s aiming to keep T4 at the upper end of normal and TSH in the normal range.
Prognosis
The prognosis for infants with hypothyroidism:
- The prognosis is usually one of normal intellectual and physical development if treatment is commenced promptly and monitored closely.
- Over treatment may result in craniosynostosis and has been implicated in causing attention deficit hyperactivity disorder.
Follow-up
Follow-up guidelines for infants with hypothyroidism:
- Follow-up should occur at two weeks, six weeks, three months then every two-three months for first year.
- TFTs repeated at each visit and dosage of thyroxine adjusted as required.
- Growth and development must be closely monitored.
- Hearing tests should be done at four to eight weeks then three-monthly for first year if dyshormonogenesis.
- Developmental assessment performed as clinically indicated.
Transient neonatal hypothyroidism
Transient neonatal hypothyroidism is a group of conditions that can be subdivided into four main categories. Cause and biochemical profiles are listed in the table below. The four categories are:
- Transient hypothyroxinaemia:
- low serum T4 levels seen in approx. 50 per cent of infants delivered before 30 weeks' gestation
- normal or low TSH levels
- corrects spontaneously over four to eight weeks
- no treatment required
- Transient primary hypothyroidism
- low serum T4 levels and high TSH levels
- seen in approx. 20 per cent of premature infants (incidence increases as gestation decreases)
- usually develops within one to two weeks after birth and often superimposed upon transient hypothyroxinaemia
- Repeated screening cards should be sent on all infants < 1500 g. It is recommended test be repeated two weeks after birth in babies 1000-1500 g and at four weeks in those < 1000 g.
- hypothyroidism may persist for two to three months
- treatment recommended
- Transient hyperthyrotropinaemia
- rare (one in 16-19,000 births)
- elevated TSH for three to nine months before reducing spontaneously
- no treatment required but need careful follow-up to exclude partial dyshormonogenesis or ectopia
- Low T3/T4 syndrome ('sick euthyroid')
- non-thyroidal illness
- no treatment required.
| T3 | T4 | TSH | |
|
Low T3 syndrome |
↓ |
N |
N |
|
Low T4 syndrome |
↓ |
↓ |
N |
Causes and biochemical profiles of transient neonatal hypothyroidism
|
|
SERUM LEVELS OF |
CAUSES |
|
|
|
T4 |
TSH |
|
|
Transient hypothyroxinaemia |
↓ |
N |
Immaturity of H-P axis (<30 weeks gestation) |
|
Transient primary |
↓ |
↑ |
Maternal anti-hypothyroidism thyroid therapy, |
|
Transient hyperthyrotropinaemia |
N |
↑ |
Erroneous assay, iodine deficiency or excess, idiopathic |
|
Low T3/T4 syndrome |
Nor↓ |
N |
Prematurity (in preterm infants), surgical stress, |
More information
Clinical
Orphanet Journal of Rare Diseases (2010) Congenital hypothyroidism
Further reading
- Pediatric Endocrinology Sperling MA, WB Saunders 1996, Philadelphia
- Australasian Paediatric Endocrine Group; Guidelines for Management of Congenital Hypothyroidism
- Smith Liz Updated AAP guidelines on Newborn screening and therapy for Congenital Hypothyroidism. Am Fam Physician, 2007 Aug 1;76(3); 439-444
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Version history
First published: April 2016
Review by: April 2019