Congenital hypothyroidism

Definition

Congenital hypothyroidism describes a newborn with decreased (or, very rarely, absent) thyroid hormone production.

Causes, incidence, and risk factors

Hypothyroidism in the newborn may result from absence or abnormal development of the thyroid gland, destruction of the thyroid gland, failure of stimulation of the thyroid by the pituitary gland, or defective or abnormal formation of thyroid hormones.

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

Most affected infants have few or no symptoms, because they only have a mild deficiency of thyroid hormone. However, infants that are profoundly hypothyroid often have a distinctive appearance. The affected infant may have puffy-appearing face, a dull look, and a large tongue that protrudes from the mouth, which is usually kept open.

This appearance usually develops as the disease progresses. The child may have dry, brittle hair, low hairline, and jaundice (yellow eyes and skin). Feeding is poor and the infant may choke frequently. Constipation is common. Affected children do not cry much, sleep a lot, are sluggish and inactive. Muscle tone is usually decreased.

If untreated, even mild hypothyroidism can lead to severe mental retardation and growth retardation. Development is delayed early on, often indicated by failure to meet normal milestones.

The appearance of teeth may be delayed. These problems become more severe as the child ages. Growth failure in terms of body length is noted very early.

Symptoms

• Floppy infant
• Thick, protruding tongue
• Poor feeding
• Choking episodes
• Constipation
• Prolonged jaundice
• Short stature

Signs and tests

• Widely separated skull bones
• Abnormally large fontanelles (soft spots of the skull)
• Dull-appearing facial features
• Dry, brittle hair and low hairline
• Short, thick neck
• 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 (unbound) T4 (thyroxine) levels
• Serum TSH level
• Serum TBG level (if total thyroxine values are measured)
• Thyroid scan (technetium)

Treatment

Early diagnosis is very important. Most of the effects of hypothyroidism are easily reversible. However, 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 with marked mental retardation.

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.

Expectations (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 to month-and-a-half generally develop normal intelligence. Absence of thyroid hormone during early life gives a poor outlook in terms of mental development.

Complications

• Mental retardation
• Growth retardation

Calling your health care provider

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

Absence of the thyroid and defective thyroxine production are not preventable. 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.

Illustrations

Thyroid gland

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