Congenital hypothyroidism

Definition

Congenital hypothyroidism is decreased thyroid hormone production in a newborn. In very rare cases, no thyroid hormone is produced.

Alternative Names

Causes

Hypothyroidism in the newborn may be caused by:

• A missing or abnormally developed thyroid gland
• Pituitary gland's failure to stimulate the thyroid
• Defective or abnormal formation of thyroid hormones

Incomplete development of the thyroid is the most common defect and occurs in about 1 out of every 3,000 births. Girls are affected twice as often than boys.

Symptoms

Most affected infants have few or no symptoms, because they only have a mild decrease in thyroid hormone production. However, infants with severe hypothyroidism often have a distinctive appearance. Symptoms may include:

• Puffy-appearing face
• Dull look
• Thick, protruding tongue

This appearance usually develops as the disease gets worse. The child may also have:

• Dry, brittle hair
• Low hairline
• Jaundice
• Poor feeding
• Choking episodes
• Lack of muscle tone (floppy infant)
• Constipation
• Sleepiness
• Sluggishness
• Short stature

Exams and Tests

A physical exam may reveal:

• Widely separated skull bones
• Abnormally large fontanelles (soft spots of the skull)
• Growth failure
• Short arms and legs
• Broad hands with short fingers
• Myxedema
• Hypotonia
• Hoarse-sounding cry or voice

Tests include:

• X-ray of the long bones
• Free T4 (thyroxine) levels
• Serum TSH level
• Serum TBG level
• Thyroid scan

Treatment

Early diagnosis is very important. Most of the effects of hypothyroidism are easily reversible.

Replacement therapy with thyroxine is the standard treatment of hypothyroidism. Once medication starts, the blood levels of TSH and free T4 are monitored to keep the values within a normal range.

Outlook (Prognosis)

Very early diagnosis generally results in a good outcome for the infant, in terms of growth and mental capability. Newborns diagnosed and treated in the first month or so generally develop normal intelligence.

Untreated, even mild hypothyroidism can lead to severe mental retardation and growth retardation. Critical development of the nervous system takes place in the first few months after birth. Thyroid hormone deficiency may result in irreversible damage to the nervous system.

Possible Complications

• Mental retardation
• Growth retardation
• Heart problems

When to Contact a Medical Professional

Call your health care provider if you feel your child shows signs or symptoms of hypothyroidism, if you are pregnant and are exposed to antithyroid drugs or procedures, or have signs and symptoms of hypothyroidism.

Prevention

Destruction of the thyroid in the fetus may occur if the mother is treated with radioactive iodine for thyroid cancer while she is pregnant. Infants of mothers taking antithyroid medications should be observed carefully after birth for evidence of drug-induced transient (brief) hypothyroidism.

Most states mandate a routine screening test on all newborns to detect hypothyroidism.

Harris KB, Pass KA. Increase in congenital hypothyroidism in New York State and in the United States. Mol Genet Metab. 2007; 91(3):268-277.

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