Congenital Hypothyroidism (CH)

Congenital hypothyroidism occurs in babies who are born without the ability to produce adequate amounts of thyroid hormone. Thyroid hormone is important for normal function of all of the body's organs and is essential for normal brain development. If detected early a child will develop normally. Treatment is thyroid medication daily. Congenital Hypothyroidism affects about one in every 3,500 babies.

Clinical features:

Deficiency of thyroid hormone may result in mental and growth retardation. If congenital hypothyroidism is not diagnosed and treated early in life, most infants will still appear clinically normal before 3 months of age, by which time some brain damage has usually occurred. Symptoms or signs, when present, may include prolonged neonatal jaundice, constipation, lethargy and poor muscle tone, poor feeding, a large tongue, coarse facies, wide fontanelle, distended abdomen and umbilical hernia.

Causes of congenital hypothyroidism:

The most common cause of primary congenital hypothyroidism is dysgenesis (various abnormalities in the formation of the thyroid gland). There may be either athyrosis (no gland), ectopic thyroid (small displaced gland) or rarely a hemithyroid (only one half present). Less commonly, hypothyroidism is due to dyshormonogenesis, a hereditary inability to manufacture thyroid hormones due to various rare enzyme defects.

Laboratory tests:

The initial screening test is the TSH (Thyroid Stimulating Hormone) assay. When TSH is slightly increased an urgent repeat sample is requested by letter. When screening results are significantly abnormal the infant's physician is notified by telephone. A blood sample should be collected to perform thyroid function tests (T3, T4, TSH). As well, further diagnostic studies, a thyroid scan, possibly by ultrasound, and bone age x-ray (knee), are used to determine the type, age of onset and severity of hypothyroidism.

Treatment:

Treatment of congenital hypothyroidism with thyroxine is simple and effective. If treatment is started early, the development remains normal. Infants should be seen approximately every 3 months for an examination and blood test to check blood thyroid hormone levels to ensure that the dose of medication is adequate. As infants increase in size, the dose of thyroid hormones is increased.

Screening considerations:

There is a TSH surge in the first 24 to 36 hours of life. Screening before 48 hours produces a high rate of false positive results due to this surge. The results can also be affected by maternal thyroid antibodies, medication for maternal thyroid disease, maternal iodine deficiency, excessive dietary iodine and external application of iodine to mother or baby.