Thyroid for Dummies (40 page)

If the biopsy does not definitely show cancer, it is safe to wait until after the delivery, when a radioactive iodine scan is done (refer to Chapter 4). Keep in mind that after a radioactive iodine scan, the mother cannot breastfeed her baby. If the scan shows that the iodine uptake is high, the nodule probably 25_031727 ch18.qxp 9/6/06 10:44 PM Page 232

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isn’t cancer. If the scan shows that the nodule remains cold, and the diagnosis remains uncertain, then surgery is needed to obtain a final diagnosis and determine the appropriate treatment. As radioactive iodine can remain in the body for several weeks, breastfeeding should be discontinued in nursing mothers.

If a scan is essential, an alternative is to use radioactive technetium. As technetium is cleared from the body within 30 hours, it is usually safe to continue breastfeeding after this time (discarding milk expressed in the 30 hours after receiving the radioactive injection), but seek advice from your physician.

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Chapter 19

Developing Thyroid Conditions

in Childhood

In This Chapter

ᮣ Understanding thyroid function in newborns and infants

ᮣ Screening for thyroid disease in babies

ᮣ Dealing with hypo- and hyperthyroidism in kids

ᮣ Concentrating on goitres

ᮣ Treating thyroid nodules in the young

Newborns and children with thyroid abnormalities present special problems because their brain and body are developing at the same time, and thyroid hormones are critical for their development. Thyroid hormones are needed in the right amount at the right time for a child to have normal mental function and normal growth.

Children can experience all the kinds of thyroid diseases that are seen in adults. This chapter discusses normal thyroid development and the impact of thyroid diseases on a developing human being. As a parent, you can do little to treat these conditions, but your early recognition of a problem, your understanding of the consequences if the problem is not treated, and your continued support of your child through treatment and recovery can help your child handle this challenge.

Understanding the Onset

of Thyroid Function

First, a quick review. Thyroid hormones (T3 and T4) are produced when thyroid-stimulating hormone (TSH) stimulates the thyroid to make them.

TSH is released from the pituitary gland when the hypothalamus produces thyrotrophin-releasing hormone (TRH). All these structures and their 26_031727 ch19.qxp 9/6/06 10:46 PM Page 234

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hormones are in place when a baby is born. Much recent research has established how this process comes about. (Refer to Chapter 3 for more on thyroid hormones and TSH.)

After just 15 weeks of development, the foetus shows function in its pituitary gland, and TRH can be detected. TSH and the other pituitary hormones start to appear between weeks 10 and 17. The thyroid is functioning by the 10th week, and its production of thyroid hormone becomes significant around the 20th week. The ability of thyroid hormone to shut off TSH production matures towards the end of the pregnancy and in the first two months after delivery.

The placenta acts as a barrier, preventing the mother’s TSH from reaching the circulation of the foetus throughout the pregnancy. The placenta also contains an enzyme that breaks down the mother’s thyroid hormones before they can reach the foetus. In breaking down the hormones, the enzyme releases iodine from the mother’s hormones so the foetus can use the iodine to make thyroid hormone for itself. At the same time, the placenta is producing human chorionic gonadotrophin, a hormone that stimulates the thyroid (refer to Chapter 18).

As the pregnancy progresses, the enzyme in the placenta that breaks down the mother’s thyroid hormones stops working as much, and other enzymes take over to convert T4 into the active hormone, T3. By not working so much, the placental enzyme no longer prevents the mother’s T4 from getting to the foetus.

This is very important, because the foetus needs the T4 for normal development, especially of its brain, at a time when it cannot make much T4 for itself.

One enzyme, which converts T4 to T3, works in the liver, the kidneys, and the thyroid. Another enzyme works mainly in the pituitary gland. If the foetus is not getting enough T4, the enzyme in the pituitary increases, and the other one decreases so the foetal brain gets enough T3.

When the baby is born, leaving the warmth of the uterus for the colder temperatures of the outside world, the baby’s pituitary releases a large amount of TSH. This action stimulates the thyroid to release a large amount of T3 and T4, causing the temperature of the baby’s body to rise. This process is known as the TSH surge. The TSH surge peaks after only 30 minutes but continues to stimulate extra thyroid hormone for the next 24 hours.

A premature baby has similar hormone changes to a normal-term baby, but to a lesser extent. It does not have as much of a TSH surge and does not produce as much thyroid hormone. The T3 does not increase as much either, because the converting enzymes are not yet as active. This baby cannot defend its body temperature in the way that a normal-term baby can.

As the baby grows, it stores more thyroid hormones in its thyroid along with thyroglobulin (refer to Chapter 4), and it produces more thyroid hormone.

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The thyroid gland grows so the lobes are normally about the same size as the part of the baby’s thumbs after the last joint (the terminal phalanx).

A lack of thyroid hormone during foetal growth has important consequences (refer to Chapter 12). Thyroid hormone is particularly important in the development of hearing, but many other body organs also need it for proper development. Some of the damage that results from lack of thyroid hormone includes the following:

ߜ Immature bones

ߜ Immature liver

ߜ Reduced mental function

ߜ Increased sleepiness

The brain is dependent on thyroid hormone for development for the first two to three years after birth. For every month that thyroid hormone is not given to a hypothyroid newborn, he or she suffers a loss of five IQ (intelligence quotient) points.

During the first 20 years of life, the free T3 and free T4 slowly decline, as does the total T3 and total T4 (check out Chapter 3 for an explanation of the difference between free and total). As oestrogen levels begin to rise during puberty in the female, her body makes more thyroid-binding globulin, and more total T3 and total T4. The decrease in the free T3 and free T4 is probably because of a gradual decline in TSH.

Screening the Newborn

Noah is the newborn son of Barry and Sally. Sally finds that Noah feeds poorly and is cold to the touch, but otherwise he appears fine.

As part of the UNITED KINGDOM neonatal screening programme, Noah is checked for hypothyroidism a few days after birth. The TSH level comes back high. The paediatrician notifies Barry and Sally and asks them to bring Noah in for testing. A blood test confirms that his TSH is elevated, and the free T4

is low. The paediatrician diagnoses congenital hypothyroidism.

Noah has a thyroid scan which shows little active thyroid tissue. Noah is given thyroid hormone, and his feeding and his body temperature rapidly improve.

Sally notices that Noah looks less puffy as well. The doctor measures thyroid functions frequently until Noah stabilises. Noah grows and feeds normally. He does not appear to have any problems reaching his developmental milestones.

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congenital hypothyroidism as early as possible. Congenital hypothyroidism means hypothyroidism that is present when the baby is born (see the next section, ‘Coping with Hypothyroidism in Children’).

In a study of 800 children with congenital hypothyroidism before the era of screening, the average IQ was 80, which is low. However, those babies with obvious signs of hypothyroidism who had received testing and appropriate treatment had a normal IQ. Because the consequence of not treating hypothyroidism in newborns is so great and the response to early treatment is so successful, screening for thyroid disease is considered essential.

Screening is a simple process. A spot of the baby’s blood, from a heel prick, is placed on filter paper. Then the filter paper is tested for TSH. If the TSH is very high, the baby has a regular blood test for TSH and free T4, and the doctor begins treating the baby with thyroid hormone while waiting for the result. If the TSH is moderately raised, blood tests are taken, but no treatment is begun until the diagnosis is confirmed. The reason is that up to 75

per cent of babies with a TSH that is moderately raised during the screening test will have normal thyroid function according to the regular blood test.

This is because a TSH surge occurs immediately after birth, and screening on the first day may result in a false diagnosis due to this surge.

The screening test is not perfect. Children with secondary hypothyroidism, which results from the body’s failure to secrete TSH, are missed. And screening does not identify children with a normal TSH and a low T4 whose TSH

becomes abnormal a week later. Premature babies, especially, may show this pattern. Babies who fail to secrete TSH often have failure of other hormones as well, which leads to many signs and symptoms that point to ill-health.

Infants with low birth weight are sometimes misdiagnosed because they tend to have low levels of hormones at birth, which soon rise to normal.

Congenital hypothyroidism affects about 1 in 3,750 babies. Screening of newborns for hypothyroidism is now carried out by law in most westernised countries, and a major campaign is underway to promote neonatal screening for thyroid disease throughout the world.

Coping with Hypothyroidism in Children

A number of conditions can cause hypothyroidism in newborn and older children. Specialists disagree as to whether pregnant mothers should have routine testing for hypothyroidism to protect their babies from a hypothyroid environment. A study in the
New England Journal of Medicine
shows that babies experience a slight loss of IQ if their mothers are hypothyroid and untreated during pregnancy.

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Transient congenital hypothyroidism

Some babies are diagnosed with hypothyroidism at birth because their TSH

levels are high, but these levels fall to normal shortly after birth. This condition is called transient congenital hypothyroidism because it doesn’t last.

One common cause of this condition is iodine deficiency in the mother (refer to Chapter 12).

This condition is especially prevalent in very low-birth-weight infants, who are normally screened for thyroid disease not only at birth, but also at two weeks and six weeks of age.

Because this condition is so common in premature infants, the question is whether these babies need thyroid supplementation for a short time at birth. A study in the
Texas Medical Journal
in 2000, suggests that babies who have gestated for more than 27 weeks at the time of birth don’t need supplemental thyroid hormone and may actually do worse with such treatment, whereas babies who spend less than 27 weeks in the womb may benefit from supplementation.

Sometimes, determining whether hypothyroidism is transient or permanent isn’t possible. In this case, the baby is treated with thyroid hormone until the age of 4 years, and then treatment is stopped for a short time to see if the child can make his or her own thyroid hormone. This treatment does not affect the child’s brain development.

Congenital hypothyroidism

Babies who are born with hypothyroidism that doesn’t correct itself shortly after birth have congenital hypothyroidism. Thanks to neonatal thyroid screening, this condition is no longer a significant cause of mental retardation.

Causes

There are many causes of congenital hypothyroidism, but 80 per cent of cases result from
thyroid dysgenesis
– a failure of the thyroid gland to grow or to end up in its proper place in the neck. Thyroid dysgenesis can result in: ߜ No thyroid at all (a condition called
thyroid agenesis
) ߜ A small gland that makes little thyroid hormone (
thyroid hypoplasia
) ߜ A thyroid gland that grows in the wrong place, often at the base of the tongue (
ectopic thyroid
)

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Some other, less frequent causes of congenital hypothyroidism include: ߜ An inability of a baby’s thyroid to respond to TSH.

ߜ Exposure of the mother to radioactive iodine that destroys the baby’s thyroid.

ߜ Failure of the baby’s hypothalamus to release TRH (thyrotrophin-releasing hormone) – a condition called
hypothalamic hypothyroidism
.

ߜ An abnormality of some step in the synthesis of thyroid hormone.

With the exception of maternal exposure to radioactive iodine, these conditions are all relatively rare genetic diseases (see Chapter 17).

Signs and symptoms

Many babies with congenital hypothyroidism have few signs or symptoms of hypothyroidism at birth. This condition is discovered by screening (refer to the section ‘Screening the Newborn’ earlier in the chapter). If the condition is severe, the baby shows some or all of the following signs: ߜ Low body temperature

ߜ Slow heart rate

ߜ Poor feeding

ߜ Umbilical hernia (an outward protrusion of the umbilicus – the belly button – that may contain intestines)

Once the condition is recognised and confirmed, treatment is started immediately. A thyroid scan just before treating the baby may help detect any functioning thyroid tissue, a lack of which indicates the need for lifelong treatment.