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 and Hypothyroidism in the Newborn.)
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
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 1,700 to 3,500 live 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.
Congenital hypothyroidism can occur if the mother did not have enough iodine in her diet while pregnant (iodine deficiency), because a woman's body needs more iodine when she is pregnant. Iodine deficiency is rare in areas of the world where iodine is added to table salt but is more common in areas where people do not get enough iodine in their diet. 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
Acquired hypothyroidism occurs after birth.
In the United States, acquired hypothyroidism is most commonly caused by Hashimoto thyroiditis (autoimmune 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. About 50% of affected children have a family history of autoimmune thyroid disease. Autoimmune thyroiditis occurs most commonly during adolescence, but it can also occur in younger children, typically after the first few years of life. Children who have Down syndrome are at increased risk of autoimmune thyroiditis.
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.
Symptoms
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.
Diagnosis
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.
Once congenital hypothyroidism is diagnosed, doctors may do imaging tests such as radionuclide scanning or ultrasonography to determine the size and location of the thyroid gland.
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.
Prognosis
Most children who are treated during infancy have normal movement control and intellectual development.
Most children with hypothyroidism who properly take their drugs achieve normal growth and development.
Treatment
Replacement of thyroid hormone
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.
