Reviewed by Kathleen C. Moltz, MD, a pediatric endocrinologist at DMC Children's Hospital of Michigan and a member of the American Association of Clinical Endocrinologists, the American Diabetes Association and the Pediatric Endocrine Society.
Hypothyroidism is the most common kind of thyroid disorder in children. It occurs when the thyroid gland is underactive and doesn’t produce enough thyroid hormone to meet the body’s needs. 1, 2, 3
Healthy thyroid function is critical for infants and children, whose developing brains and bodies rely on adequate levels of thyroid hormone. Untreated, hypothyroidism can lead to intellectual disability and growth failure. 1, 4
There are two types of hypothyroidism in infants and children: Congenital hypothyroidism, which is present at birth, and acquired hypothyroidism, which develops after birth, usually during late childhood or adolescence. 5
Congenital hypothyroidism affects 1 in 1,500-3,000 newborns in the U.S. each year. The condition most often occurs for no known reason, but 10-20% of the time it is inherited. 5
The disorder can result from insufficient maternal iodine consumption during pregnancy, but this is rare in the U.S., where dietary iodine is generally adequate (iodine is added to table salt and is present in seafood and milk). Rarely, medications taken during pregnancy--mainly those for treating overactive thyroid—can lead to congenital hypothyroidism, though the condition is usually transient and resolves with no effects. 4, 5, 6 Still, it's important for women to have their own thyroid function checked during pregnancy.
Congenital hypothyroidism is one of the most common and preventable causes of intellectual disability. Because most newborns show no signs of it, the condition is usually detected during routine newborn screening, which is mandatory at U.S. hospitals. 1 The newborn screen, which is collected by gathering blood via heel prick 24 hours after birth, checks for congenital hypothyroidism and a number of other congenital diseases. Parents who choose home birth should be sure to secure the screening for their newborns.
Blood samples may reveal low levels of T4 (thyroxine), a hormone secreted by the thyroid, and/or high levels of TSH (thyroid stimulating hormone), which is released by the pituitary gland. 1
If the diagnosis is confirmed through further thyroid tests, newborns must be treated as quickly as possible, usually with synthetic thyroid hormone, which should be given as a crushed pill mixed with a small amount of breast milk or formula. It should not be given with soy formula or iron or calcium supplements, which can reduce absorption of replacement hormone.4 Thyroid hormone replacement should also not be given in liquid form, which is unstable.
Most babies will need to take replacement hormone for the rest of their lives, although up to 30% may have a transient form and only require treatment for the first three years of life. In all cases, early treatment and regular checkups with a pediatric endocrinologist are essential to help ensure normal growth and brain development. Children with congenital hypothyroidism are monitored more frequently during the first few years of life.4, 5
Some data have shown that the incidence of congenital hypothyroidism is 100% higher in Hispanic newborns than in whites, and 44% higher in Asians. The incidence has also been shown to be 30% lower in black newborns than in whites. Babies with Down syndrome have a 10-fold increased incidence of congenital hypothyroidism. 7
Acquired hypothyroidism develops after birth, typically during late childhood or adolescence. The condition is very common, affecting 1 in 1,250 children. About 4.6% of the U.S. population age 12 and older has hypothyroidism, according to the National Health and Nutrition Examination Survey (NHANES III). 8, 9
Hormones produced by the thyroid perform several essential functions during childhood including maintaining normal growth and bone development and regulating metabolism. 8
The most common cause of acquired hypothyroidism in children and teens is an autoimmune disease known as Hashimoto’s thyroiditis, in which the immune system attacks the thyroid, causing inflammation and interfering with the gland’s ability to produce thyroid hormone. (Hashimoto’s is also the leading cause of hypothyroidism in adults in the U.S.) 8, 2, 10
Less commonly, hypothyroidism can arise from the thyroid itself or from the pituitary, if the gland fails to produce enough thyroid stimulating hormone. Certain medications (like lithium) can decrease thyroid hormone production, and too much or too little iodine in the diet can lead to hypothyroidism, as can radiation exposure and infiltrative disease.
Some children are at greater risk of Hashimoto’s including those with congenital disorders like Down syndrome; those with other autoimmune diseases like type 1 diabetes; and those who have received radiation for cancer treatment. Hashimoto’s is also more common in females than males and often runs in families. 8, 2
While some symptoms of Hashimoto’s in older children and teens are similar to those in adults, others appear only in children. These include slowed rate of growth, delayed puberty and delayed tooth development. Another common sign is an enlarged thyroid gland (goiter). Studies have shown that a noticeable goiter is present in nearly 40% of children with autoimmune thyroiditis. 5, 3
Hypothyroidism symptoms that children and adolescents have in common with adults include: fatigue, constipation, coarse, dry hair and skin, and weight gain, although the vast majority of weight gain experienced by children and adolescents is not due to thyroid disease. 5
Acquired hypothyroidism can be diagnosed with blood tests. Usually TSH levels are high and T4 levels are low. Sometimes both levels are low. Normal ranges for TSH and T4 are different in children than in adults, so it’s important to consult a pediatric endocrinologist. 8
As with congenital hypothyroidism, acquired hypothyroidism is treated with synthetic thyroid hormone, usually in the form of a once-daily pill. Side effects typically result from overtreatment and can include difficulty falling asleep, restless sleep and headache. 8
There is no cure for either form of hypothyroidism but hormone replacement is considered safe and effective. With proper use of medication and close follow-up with a pediatric endocrinologist, children can expect to live a normal, healthy life. Older children may be monitored more frequently if there are concerns about their adhering to the daily pill regimen. 8