Hypothyroidism is decreased production of thyroid hormone.
- Hypothyroidism in children usually occurs when there is a structural problem with the thyroid gland or the thyroid gland is inflamed.
- Symptoms depend on the child's age but include delayed growth and development.
- The diagnosis is based on newborn screening tests, blood tests, and imaging tests.
- Treatment includes giving thyroid hormone replacement.
(See also Hypothyroidism in adults.)
The thyroid gland is an endocrine gland located in the neck. Endocrine glands secrete hormones into the bloodstream. Hormones are chemical messengers that affect the activity of another part of the body.
Locating the Thyroid Gland
The thyroid gland secretes thyroid hormone. Thyroid hormone controls the speed of the body's metabolism, including how fast the heart beats and how the body regulates temperature. If the thyroid gland does not produce enough thyroid hormone, these functions slow down.
There are two types of hypothyroidism in infants and children:
- Congenital hypothyroidism: Present at birth
- Acquired hypothyroidism: Develops after birth
Congenital hypothyroidism occurs when the thyroid gland does not develop or function normally before birth (see Hypothyroidism in the Newborn). This type of hypothyroidism occurs in about 1 in 2,000 to 3,000 births. Most cases occur spontaneously, but about 10 to 20% are inherited.
About half of cases of congenital hypothyroidism occur because the thyroid gland is missing, underdeveloped, or developed in the wrong place. Less often, the gland has developed normally but does not produce thyroid hormone correctly.
Rarely, congenital hypothyroidism occurs if the mother did not have enough iodine in her diet while pregnant (iodine deficiency) because her body needs more iodine when she is pregnant. Iodine deficiency is rare in the United States but is more common in certain developing countries. Another rare cause is central hypothyroidism. Central hypothyroidism is caused by structural problems that occur in the pituitary gland while it is developing (see Overview of the Pituitary Gland).
Rarely, drugs that are used to treat thyroid disorders or substances in foods cross the placenta and temporarily cause congenital hypothyroidism.
Acquired hypothyroidism occurs after birth. It occurs during later childhood and adolescence.
In the United States, acquired hypothyroidism is most commonly caused by Hashimoto thyroiditis. In Hashimoto thyroiditis, the body's immune system attacks the cells of the thyroid gland, causing chronic inflammation and decreased production of thyroid hormones.
Worldwide, the most common cause of hypothyroidism is iodine deficiency, but this cause is rare in the United States. However, pregnant women in the United States can develop mild iodine deficiency because their bodies need more iodine when they are pregnant. Children who have multiple food allergies or who are following restrictive diets may not eat enough of the proper foods and thus develop iodine deficiency.
Other less common causes of acquired hypothyroidism include radiation therapy to the head and neck for certain cancers and the use of certain drugs (for example, lithium or amiodarone). Hypothyroidism also occurs as a result of treatment for hyperthyroidism or for thyroid cancer.
Symptoms of hypothyroidism differ depending on the age of the child.
Infants and young children
If iodine deficiency occurs very early during pregnancy, infants may have severe growth failure, abnormal facial features, intellectual disability, and stiff muscles that are difficult to move and control (called spasticity).
Most other infants who have hypothyroidism initially have few if any symptoms because some thyroid hormone from the mother crosses the placenta. Once infants no longer receive thyroid hormone from the mother, symptoms develop slowly and the disease is detected only when they are screened as newborns.
However, if hypothyroidism remains untreated, brain development slows and infants may have low muscle tone, hearing loss, a large tongue, poor feeding, and hoarse crying. Delayed diagnosis and treatment of severe hypothyroidism can lead to intellectual disability and short stature.
Older children and adolescents
Some symptoms in older children and adolescents are similar to symptoms of hypothyroidism in adults (such as weight gain; fatigue; constipation; coarse, dry hair; and coarse, dry, and thick skin). Symptoms that appear only in children include slowed growth, a delay in the development of the skeleton, and delayed puberty.
- Newborn screening test
- Blood tests
- Sometimes imaging tests
Because infants with hypothyroidism at birth often do not have any abnormal findings, doctors do routine screening tests of all newborns. If the screening is positive, tests to determine levels of thyroid hormones in the blood (thyroid function tests) are done to confirm the diagnosis of hypothyroidism. If confirmed, newborns must be treated quickly to prevent developmental delays.
Thyroid function tests are also done in older children and adolescents who doctors think may have hypothyroidism. Ultrasonography may also be done if a goiter is present.
Doctors do magnetic resonance imaging (MRI) of the brain and pituitary gland in children who have central hypothyroidism to rule out problems in the brain.
Most infants who are treated have normal movement control and intellectual development.
Most children with hypothyroidism who properly take their drugs achieve normal growth and development.
- Replacement of thyroid hormone
Children who have congenital or acquired hypothyroidism are usually given the synthetic thyroid hormone levothyroxine. Thyroid hormone replacement is given to children in tablet form, which can be crushed and made into paste for infants. It should not be given simultaneously with soy formula, or iron or calcium supplements because these substances can decrease the amount of replacement thyroid hormone that is absorbed. Most children who have congenital or acquired hypothyroidism need to take thyroid hormone replacement for life. However, some children who have congenital hypothyroidism, usually those who have not required a dose increase after infancy, may be able to stop treatment after they are about 3 years of age.
Doctors continue to monitor children by doing blood tests at regular intervals depending on their age. Children are monitored more frequently during the first few years of life.
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