Paediatrics: Congenital hypothyroidism

Congenital hypothyroidism

Hypothyroidism may be due to a number of conditions that result in in-sufficient secretion of thyroid hormones. Congenital hypothyroidism is a relatively common condition, occurring in approximately 1/4000 births. It is twice as common in girls than in boys.

Aetiology

The causes of congenital hypothyroidism include the following:

·  Thyroid dysgenesis (85%): usually sporadic; resulting in thyroid aplasia/ hypoplasia, ectopic thyroid (lingual/sublingual).

·  Thyroid hormone biosynthetic defect (15%): hereditary, e.g. Pendred’s syndrome.

·  Iodine deficiency (rare UK; but common worldwide).

·  Congenital TSH deficiency (rare): associated with other pituitary hormone deficiencies.

Clinical features

Usually non-specific; they are difficult to detect in first month of life. They include:

·  umbilical hernia;

·  prolonged jaundice;

·  constipation;

·  hypotonia;

·  hoarse cry;

·  poor feeding;

·  excessive sleepiness;

·  dry skin;

·  coarse faecies;

• delayed neurodevelopment.

Diagnosis

In most developed countries there are national neonatal biochemical screening programmes.

·  Test in 1st week of life.

·  Blood spot—filter paper collection (e.g. ‘Guthrie card’).

·  TSH (high) and/or fT4 (low) estimation.

Thyroid imaging is also recommended to determine whether the cause is due to thyroid dysgenesis or due to hormone biosynthetic disorder.

·  Thyroid US.

Radionucleotide scanning (⁹⁹Tc or ¹³¹I).

Treatment

Without early hormone replacement therapy a number of adverse seque-lae may occur.

·Neurodevelopmental delay and mental retardation.

·Poor motor coordination.

·Hypotonia.

·Ataxia.

·Poor growth and short stature.

The earlier the treatment with oral thyroid hormone replacement therapy is initiated the better the prognosis: levothyroxine (initial dose 10–15micrograms/kg/day).

Monitoring therapy

Monitor serum TSH and T4 levels:

·Every 1–2mths 1st year; every 2–3mths age 1–2yrs; every 4–6mths age >2yrs.

·Maintain T4 level in upper half of normal range; TSH in lower end of normal range.

Transient hyperthyrotropinaemia

This is uncommon and is usually detected at the time of neonatal thy-roid screening. It is characterized by slightly elevated serum TSH level in presence of otherwise normal serum T4 levels. It is probably due the transplacental transmission of maternal thyroid antibodies to the child in utero. Presumed cases do not need treatment, but must be monitored. TSH levels that remain persistently elevated after a few months or low T4 levels should be treated with oral levothyroxine.