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Hypothyroidism is relatively common in childhood. If treated on time, it usually doesn't lead to serious consequences to a child's health, but if a child misses treatment for some reason, it can lead to serious neurological and physical damage.

Underactive thyroid is not that uncommon in infancy and childhood. If the thyroid fails to make the necessary amount of thyroid hormone that the body needs to function well, the condition is called hypothyroidism. Having thyroid gland that works well is a crucial thing in infancy because the baby brain needs the thyroid hormone to develop and function properly. If hypothyroidism in infants is left untreated, it may cause various disabilities and problems during growth.

Infants can get two types of underactive thyroid – congenital and acquired hypothyroidism. Congenital type is present as soon as the baby is born, and acquired is – as the name says – developed sometimes during infancy or childhood.

Congenital type of underactive thyroid

If a mother suffers from underactive thyroid during pregnancy, a child is often born with a condition known as congenital hypothyroidism. This means that the baby's thyroid gland can't produce enough thyroid hormone to meet the body's needs. This affects one in 4,000 newborns, making it a relatively common disorder in infancy.

Unfortunately, this type of hypothyroidism could be prevented with proper treatment during pregnancy, and it's still one of the top common preventable disorders that cause intellectual and developmental problems.

Thyroid gland that failed to develop properly whether it's too small or nonexistent, or at the wrong side is the most common cause of congenital hypothyroidism in children. Sometimes everything seems fine, but the gland still can't produce the hormone as it should. This can be caused by mother not consuming enough iodine during pregnancy, and rarely because of the medications used to treat hyperthyroidism or overactive thyroid gland.

Congenital underactive thyroid is rarely inherited, meaning that if one of your children is affected, it doesn't have to mean the other children will have it as well. Regarding the prevalence, studies have shown that congenital hypothyroidism is the most common in Hispanic newborns and Asian babies. According to studies, African-American newborns have the least prevalence among all races.

Is hard to detect the symptoms of congenital underactive thyroid as soon as the baby is born, so they're mostly discovered during some routine checkups within the first week of a baby's life. Here are some symptoms to look for:

  • Newborn refuses to feed
  • Lack of sleep
  • Constipation
  • Puffiness of the face
  • Jaundice
  • Weak muscles
  • The tongue that seems swollen
  • Distended abdomen
  • Fontanelle that seems too large
Heel prick test that is conducted about 24 hours after the baby is born can detect congenital hypothyroidism and other congenital disorders. It works by detecting low levels of the thyroxine hormone, as well as abnormalities in thyroid-stimulating hormone levels. If hypothyroidism is detected by this test, a child should receive therapy as soon as possible.

Therapy for infants with congenital hypothyroidism

If it's discovered that the baby has congenital hypothyroidism, it's important to start hormone replacement therapy immediately after the necessary tests are conducted. Postponing treatment for any reason beyond six weeks of age increases risk of neurological impairment. Congenital hypothyroidism is mostly treated with levothyroxine – a man-made replacement hormone in a pill.

It can be hard to give levothyroxine to infants, but it's possible by crushing the pill and mixing it with breast milk or formula. You shouldn't put a crushed pill in the bottle though because the baby might not eat it all and you'll have to throw away the medicine. It's easiest to use a spoon or a syringe.

Parents shouldn't combine hormone replacement therapy with soy formula, or iron-fortified products because iron affects the absorption of levothyroxine. The recommended amount of the thyroid hormone is between 10 and 15 μg/kg/day. Children with increased levels of thyroid-stimulating hormone should receive hormone replacement therapy until they are two years old to make sure that there won't be any permanent damage to the brain.

Most children born with hypothyroidism will probably need therapy for the rest of their lives, but up to 30 percent of infants need hormone replacement therapy for the first few years.

It's important to visit your child's endocrinologist often and control their condition, especially for the first couple of years. If left untreated, hypothyroidism can cause permanent damage to your child's brain, but with therapy and regular checkups, the majority of children with congenital hypothyroidism will lead a healthy life as same as their peers.

Acquired type of hypothyroidism

The acquired form of hypothyroidism is quite common, with 1 in 1,250 children developing the disease sometime in childhood, or even adolescence. An autoimmune condition known as Hashimoto's disease – where a person's own immune system attacks the thyroid gland, making it inflamed and unable to provide enough hormone to meet body's needs – is the most common reason that some children develop hypothyroidism. This disorder is also a number one cause for hypothyroidism in adult people in the United States.

Besides Hashimoto's disease, hypothyroidism can originate from the thyroid or pituitary glands, if they can't produce thyroid-stimulating hormone (TSH). There are various reasons thyroid and pituitary gland may decrease in function – surgery, exposure to radiation, autoimmunity (attack of a person's own antibodies), severe head injury, certain substances in medications such as lithium, but also lack of iodine in the diet.

Certain children have an increased risk of developing hypothyroidism:

  • Children with other types of congenital diseases like Turner or Down syndrome
  • Children suffering from certain autoimmune disorders such as type 1 diabetes
  • Children who underwent radiation due to cancer.

Children who have underactive thyroid can experience symptoms same as adults including:

  • Tiredness
  • Increase in body weight
  • Constipation
  • Being cold often
  • Dry and scaly skin
  • Dry and thinning hair

Certain symptoms of hypothyroidism rarely or never occur in adults, only in children:

  • A thyroid gland that is bigger than usual (occurs in almost half children with the disease)
  • Delayed growth and puberty
  • Slow tooth development
  • Doing badly in school
  • Decreased energy
  • Lethargy

Acquired type of underactive thyroid is usually diagnosed with several tests. In children with hypothyroidism, thyroid-stimulating hormone levels are high, and thyroxine levels are low. Normal levels of certain hormones differ in adults and children, so its important to consult your child's doctor to discuss the illness in detail.

How to treat acquired hypothyroidism?

Apparently, there's no cure for hypothyroidism. Hormone replacement therapy works but only temporary. The pill of levothyroxine, a synthetic hormone should be taken once a day, preferably in the morning. When it comes to the acquired type of hypothyroidism, the dose is determined by age and weight. For a child between the ages one and three, the recommended dose is 4.0 to 6.0 mcg/kg once a day. For ages three to ten, it's 3.0 to 5.0 mcg/kg. If a child is between 10 and 16, the dose of levothyroxine should be anywhere between 2.0 to 4.0 mcg/kg. If a child is actually an adolescent older than 17, the recommended daily dose is 1.6 mcg/kg per day, preferably in the morning.

It's important that the child goes through all the necessary screening and testing before the amount of levothyroxine is determined. It's necessary to give the body a few weeks to adapt to new hormone levels, so screening shouldn't be conducted too soon after the initial treatment. If hormone replacement therapy is successful, these tests will show normal levels of thyroxine and thyroid-stimulating hormone.

Children with thyroid-stimulating hormone over 10 mU/L and normal thyroxine levels are considered to have a subclinical form of an underactive thyroid. These children rarely need therapy: only if their TSH increases, or if they show symptoms of goiter or underactive thyroid.

Levothyroxine rarely has side-effects, and even when they happen, it's something minor caused by higher dose than recommended. These side-effects can include:

  • Bad sleep
  • Restlessness
  • Headaches
  • Lack of concentration

If your child experiences these, it would be good to visit his doctor to adjust the therapy. If the condition is often and closely monitored by a pediatric endocrinologist, children with hypothyroidism can lead a normal and thriving life. It's important to teach a child that pill of levothyroxine a day keeps their endocrinologist away.

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