If your thyroid gland works too slowly, then too little thyroid hormone will be produced and too little hormone will end up in your bloodstream. Your body will then have a thyroid hormone deficiency. This condition is called hypothyroidism. Hypothyroidism can have several causes. Hypothyroidism may be present at birth (congenital hypothyroidism) or it can develop later on during childhood or adolescence.

Congenital hypothyroidism (CH)

In the case of congenital hypothyroidism, your blood levels of thyroid hormone are too low at the time of your birth. The problem usually lies with the thyroid gland itself. Perhaps it did not form at all or did not form properly, or perhaps it did not migrate to the normal location or does not synthesize any hormone (dyshormonogenesis). We call this condition congenital hypothyroidism of thyroidal origin or CH-T.

You can also have a thyroid hormone deficiency because your hypothalamus or pituitary does not function properly, and the thyroid gland is not properly controlled. We call this congenital hypothyroidism of central origin or CH-C. This is the case in approximately 10% of newborns with congenital hypothyroidism.

Sometimes a newborn has too little thyroid hormone because substances in the mother's uterus were passed on to the child. For example, if the mother uses thyroid-suppressant medicines, has thyroid disease or has an excess or a deficiency of iodine. This type of CH is called transient CH.

How common is CH?

In the Netherlands, approximately 1 in every 2500 children has CH. That means that approximately 75 children are born with CH each year. The disorder occurs twice as frequently in girls as it does in boys.

What symptoms do newborns with CH have?

Most newborns (80%) with CH have very few or no symptoms at all. However, the following symptoms and complaints may occur:

• Behavior: sleepy and groggy, does not react adequately to stimuli, a hoarse, low cry or a soundless cry.
• Skin: jaundice (yellowish in color), often chronically dry, cold skin.
• Head-throat: enlarged fontanelles, wide and low nose bridge, swelling around the eyes, large tongue, palpable swelling in the throat.
• Abdomen: large, rounded belly, clearly visible blood vessels, naval hernia.
• Stomach-intestinal tract: feeding problems (poor drinking, frequent vomiting), constipation.
• Muscle tone: reduced muscle tone, feels limp.
• Bodily functions: slow heart rate, low temperature.

In addition to these, newborns with CH due to hypothalamus or pituitary problems may also have the following symptoms or features:

• Blood sugar level too low (hypoglycemia).
• In boys: penis too small and undescended testicles.

How is CH diagnosed?

Since 1981, CH has been included in the neonatal heel prick (Guthrie Test), which means that this disorder can be detected in newborns. In the blood that is taken with the heel prick, the amount of T4 and, if necessary, the amounts of TSH and TBG are determined. The possible results of the heel prick are normal, abnormal or borderline abnormal. The results of the heel prick test are sent to the primary care physician who refers the patient to a pediatrician for additional examination if CH is suspected. Approximately one quarter of the referred children actually have CH, the rest do not. In the case of a borderline abnormal heel prick result, it is not clear whether the values were really abnormal or not. A borderline abnormal heel prick will therefore be repeated. Then, additional examination is performed only if the second heel prick is either abnormal or again borderline abnormal.

Additional examination
In the first consultation, the pediatrician will ask about any symptoms, illnesses in the family, and about the course of the pregnancy and the delivery. After that, the baby is physically examined. A blood sample is taken and sometimes a urine sample. The blood is tested for thyroid hormone (free T4, T4 and T3), TSH, thyroxine-binding globulin (TBG), thyroglobulin (Tg) and sometimes for antibodies against the TSH receptor. The amount of iodine in the urine may also be tested. An ultrasound of the throat is also performed to see if the thyroid gland is situated in its normal location and to see how large it is. Another examination is performed in which the active thyroid gland tissue is made visible (radioactive iodine uptake test). If there are indications that CH is present due to an alteration in a gene (gene mutation) or if organs besides the thyroid gland are also physically abnormal, genetic testing may be prescribed. If there is a chance that the problem lies with the hypothalamus or the pituitary, further supplemental examinations (e.g. a TRH test, blood testing for other hormones, and MRI imaging) will follow.
These tests can clarify whether or not the newborn has CH and, if so, they can usually show the cause of the CH: an alteration in the structure of the thyroid gland, an error in the production of thyroid hormone, an insensitivity to stimulation by TSH, or because the hypothalamus and the pituitary are not properly controlling the thyroid gland.

How can CH be treated?

If you do not have enough thyroid hormone, you must take a daily dose of the hormone in the form of levothyroxine (Thyrax®, Euthyrox® or Eltroxin®). With levothyroxine, you may choose tablets or a drink; the lowest single-tablet dose is 25 micrograms. However, the tablets are easy to split into two or four pieces. The official advice is to take levothyroxine approximately one half hour before eating and not to mix it with food containing locust bean gum or soy. These substances bind with the thyroid hormone in the levothyroxine. Levothyroxine can be taken in the morning or in the evening. Contrary to the official advice, you may also take this medicine shortly before eating. In this case, however, you should take it in the same way every day so that it becomes a habit. If you take other medicines (such as gastric acid blockers or medicines containing iron), this may have an influence on the uptake of the thyroid hormone. Your doctor and pharmacist can tell you more about this. To verify that the prescribed dosage is correct, blood will be taken regularly and tested for TSH and FT4 levels.
If a diagnosis of CH is made, then it is important to start taking this medicine as quickly as possible to avoid problems.

Hypothyroidism onset in children or adolescents

If the thyroid gland starts to work slowly during childhood or adolescence, this is referred to as acquired hypothyroidism. This may arise due to a deficiency of iodine, although this no longer occurs in the Netherlands and in most other countries in Europe. This is because iodine is added to our food, which means that you ingest sufficient quantities every day. In other parts of the world, though, iodine deficiency does occur.
Hypothyroidism usually occurs due to an auto-immune reaction that results in an inflamed and damaged thyroid gland. For example, Hashimoto's thyroiditis or chronic auto-immune thyroiditis.
Other, less frequently occurring causes are: thyroid gland damage due to radiation, an operation, cancer, a thyroid gland inhibited by the use of some medicine or food (rare), or problems with the hypothalamus or pituitary (hypothyroidism of central origin).

How frequent does hypothyroidism occur in children and adolescents?

In the Netherlands, approximately one to two in 1000 children has acquired hypothyroidism. It occurs more frequently (five to eight times) in girls than it does in boys. Chronic auto-immune thyroiditis occurs more frequently in children with Down's syndrome, Klinefelter's syndrome, type 1 diabetes mellitus, juvenile idiopathic arthritis, and polyglandular syndrome type 1.

What are the possible symptoms of hypothyroidism?

Every child with hypothyroidism has his or her own individual symptoms, and they are not all equally affected by the symptoms they do have. The longer the child has had hypothyroidism, the more symptoms he or she will have. In young children, the symptoms are sometimes difficult to recognize, because they are not yet able to talk about their symptoms. Symptoms may include:

• Behavior: listlessness, being tired and sleepy, feeling gloomy, reduced responsiveness, slowed speech.
• Skin and hair: dry, pale and cold skin, reduced sweat production, tingling, edema (swelling), hair loss.
• Head-throat: palpable swelling (goiter) in throat, swelling around the eyes.
• Abdomen: large, rounded belly, clearly visible blood vessels, naval hernia.
• Stomach-intestinal tract: constipation.
• Muscles and joints: reduced muscle tone, loss of power, muscle pain, joint pain.
• Bodily functions: slow heart rate, low body temperature.
• Slowed reflexes.
• Late onset of puberty, menstrual disorders, secretion of milk (lactation w/o pregnancy).
• Sensory: hearing loss, visual problems.
• Weight gain.
• Reduced longitudinal growth; small for age.

How is hypothyroidism diagnosed?

Problems with your thyroid gland can be diagnosed using blood tests. Blood is taken from a blood vessel in your arm or hand (vene puncture). Tests are then done to see how much free T4 and TSH are present in your blood. If there is a problem with the thyroid gland itself, the free T4 will be too low and the TSH will be too high. If the problem is not the thyroid gland but instead the hypothalamus or the pituitary, for example, then the free T4 will be too low and the TSH will be too low, normal or just slightly increased. To know why the thyroid gland is working too slowly, more blood tests are needed, for example to check if any antibodies against the thyroid are present. If there is a problem with the hypothalamus or the pituitary, then measuring the levels of other hormones (such as cortisol and IGF-1) and a TRH test (to test the function of the pituitary gland) can provide more clarity.

Hashimoto's thyroiditis

Hashimoto's thyroiditis is an auto-immune disease. This means that there is a disruption in your immune system. Your immune system protects you from intruders, such as bacteria and viruses, so that you do not get sick. It is a very intelligent system that can recognize, attack and deactivate foreign substances that enter your body. When this happens, you will often have fever, swelling, pain and redness: the signs of an infection. Sometimes this response is intense, and sometimes you hardly notice it. If you have an auto-immune disease, your immune system attacks your own tissues, just as if they were foreign substances. In the case of Hashimoto's thyroiditis, the thyroid gland cells are attacked and, as a result, they become damaged. It is not clear why the immune system does this. Children with chromosomal abnormalities (such as Down's, Klinefelter's, and Turner's syndromes) and children with other auto-immune diseases (such as diabetes mellitus type 1) have a greater chance of getting Hashimoto's thyroiditis, also called chronic auto-immune thyroiditis.

What are the symptoms of Hashimoto's thyroiditis?

In most children (70%), the thyroid gland is enlarged and swollen but not painful to the touch. Hyperlink or inclusion of “What are the possible symptoms of hypothyroidism?"

How is Hashimoto's thyroiditis diagnosed?

Blood tests are run to determine if your thyroid gland is working too slowly. Blood is taken from a blood vessel in your arm or hand (vene puncture). Tests are then done to see how much free T4 and TSH are present in your blood. In the case of Hashimoto's thyroiditis, the problem lies in the thyroid gland itself, and the free T4 is too low while the TSH is too high. Your blood is also tested for antibodies against thyroid peroxidase (anti-TPO antibodies). These antibodies are found in the blood of most children (more than 90%), but we also see them in children who do not have thyroid problems or in children suffering from Graves' disease (see Section 5 below).

How is Hashimoto's thyroiditis treated?

When you have Hashimoto's thyroiditis, you have too little thyroid hormone in your body, and, therefore, you must take levothyroxine (Thyrax®, Euthyrox® or Eltroxin®) daily. The amount you take depends on your age and your body weight. With levothyroxine, you may choose tablets or a drink; the lowest single-tablet dose is 25 micrograms. However, the tablets are easy to split into two or four pieces. The official advice is to take levothyroxine approximately one half hour before eating and not to mix it with food containing locust bean gum or soy. These substances bind with the thyroid hormone in the levothyroxine. Levothyroxine can be taken in the morning or in the evening. Contrary to the official advice, you may also take this medicine shortly before eating. In this case, however, you should take it in the same way every day so that it becomes a habit. If you take other medicines (such as gastric acid blockers or medicines containing iron), this may have an influence on the uptake of the thyroid hormone. Your doctor and pharmacist can tell you more about this. To verify that the prescribed dosage is correct, blood will be taken regularly and tested for TSH and FT4 levels.
Levothyroxine may produce side effects. A dose that is too high can cause heart palpitations and make you feel stressed and agitated. It can also cause sleep problems.