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What is the thyroid gland or thyroid?

The thyroid gland is a small gland in the neck, in front of the windpipe. It produces and secretes thyroid hormones, which regulate growth and metabolism.

Thyroid hormones are the mediators that circulate throughout the body and affect the function of organs.

The main hormone secreted by the thyroid gland is thyroxine (T4). It controls the energy that our body consumes for breathing, blood circulation and digestion. It affects the development of the child both physically and mentally. Excess thyroxine makes the body work too fast, while on the contrary, a lack of thyroxine slows it down.

Hypothyroidism occurs when we have low levels of thyroid hormones. It is the most common thyroid gland disorder.

Children can have either congenital hypothyroidism (present from birth) or acquired hypothyroidism (developing later). There are important differences between the two conditions.

Congenital Hypothyroidism

When a newborn baby does not produce enough thyroid hormones, they have congenital hypothyroidism. They are born with an underactive or absent thyroid gland.

The most common causes of congenital hypothyroidism are:

• Hypoplasia of the gland (it did not develop properly during intrauterine life
• Thyroid gland in the wrong place, usually smaller (hypoplastic)
  e.g. hypoglossal
• Thyroid agenesis (the gland was not formed at all)

These cases are not hereditary.

Other causes include:

• Thyroxine synthesis disorders or dyshormonogenesis (may be hereditary)
• Central hypothyroidism (disorder of the pituitary gland that produces TSH, a hormone that tells the thyroid gland to function)
• More rarely, congenital hypothyroidism may be due to the mother’s thyroid dysfunction or to medications she took during pregnancy

The infant may not show any symptoms or may show one or more of the following:

• Jaundice
• Laziness
• Difficulty feeding
• Harsh crying
• Drowsiness
• Constipation
• Hypotonia
• Large tongue
• Swollen face
• Umbilical hernia

Unfortunately, all of these symptoms are common in babies, even when they do not have a congenital hypothyroidism. For this reason, we perform a preventive examination on all newborns in the first week of life (in the maternity hospital, with a small amount of blood from the heel) where we measure TSH. The examination, in most cases, informs us of the possibility of congenital hypothyroidism, which is followed by further testing. It is very important to start treatment early in order to avoid the consequences of hypothyroidism on the child (on his physical and mental development).

When a baby presents with a pathological test in the maternity hospital (screening) or symptoms as mentioned above, a venous blood sample will confirm or not the diagnosis. We measure the levels of thyroxine (T4) and TSH. Low levels of T4 and high levels of TSH indicate congenital hypothyroidism.

Once the diagnosis is confirmed, treatment must be started, which in most cases will continue for life. We give a thyroxine replacement pill daily. Levothyroxine is the treatment of choice, it is a synthetic form of T4, identical to that naturally produced by the thyroid gland.

Thyroid function (substitution) is checked very regularly, especially in the first months, when the infant grows rapidly and the dose must be adjusted frequently. If the treatment is too high, then the baby may experience restlessness, weight loss, mild diarrhea. Clinical monitoring of physical and psychomotor development is also very important.

Acquired hypothyroidism:

Acquired hypothyroidism occurs when the thyroid becomes underactive later in childhood.

It is often the result of an autoimmune disease, Hashimoto’s thyroiditis. Here, the immune system that protects our body and fights infections, it produces antibodies that attack its own body, specifically, the thyroid gland. This weakens the thyroid, it produces fewer hormones and as a result hypothyroidism.

The diagnosis of acquired hypothyroidism is made by blood testing of the levels of the hormones T4 and TSH.
We have hypothyroidism when TSH is high (the pituitary gland tries to push the thyroid to produce more thyroxine) and T4 is low. However, at the beginning of the disease we can find high TSH with normal T4. In cases of autoimmune disease (Hashimoto’s thyroiditis), we also measure positive (i.e. high) antibodies against the thyroid.

An ultrasound of the thyroid gland is a very useful examination. It gives us information about the anatomy of the gland, which may have been altered due to, for example, Hashimoto’s thyroiditis.

Fortunately, in most cases, acquired hypothyroidism has no symptoms. Children with severe hypothyroidism show symptoms.

Symptoms may include:

• Slow growth rate
• Delayed puberty or, more rarely, early puberty
• Weight gain, facial swelling
• Fatigue, decreased physical activity
• Constipation
• Intolerance to cold
• Decreased school performance
• Goiter (large, abnormal thyroid)
• Bradycardia

The treatment of acquired hypothyroidism is the same as that of congenital hypothyroidism. We give daily levothyroxine to supplement the thyroid’s inability to produce enough thyroxine. The dose is adjusted as the child develops, and the child must have regular clinical check-ups regarding his/her growth, puberty, and thyroid anatomy.

Daily treatment is important, which is why we must help adolescents to be consistent by explaining to them the importance of treatment.

Which children are at increased risk of developing hypothyroidism?

Thyroid diseases are often hereditary. Approximately 40% of children with acquired hypothyroidism have a family member with some thyroid pathology.
The risk of developing autoimmune thyroid disease is 16 times greater for children with a parent with autoimmune thyroiditis. Girls are more prone to developing the disease (3 girls per 1 boy).

Children with:

• Family history of Hashimoto’s thyroiditis
• Turner syndrome
• Klinefelter syndrome
• Other autoimmune disease such as: celiac disease, type 1 diabetes, alopecia, vitiligo

It is a good idea for children in these categories to be tested.