Thyroid for Dummies (41 page)

If no tissue is seen on the thyroid scan, a thyroid ultrasound shows whether tissue exists and whether it’s unable to take up iodine, possibly due to a genetic abnormality. This information is helpful in counselling the parents about the chance of hypothyroidism in future children.

Treatment

Babies with congenital hypothyroidism usually receive a relatively high dose of thyroxine (T4) hormone replacement for the first week to restore their thyroid hormone levels. The daily dose given afterwards depends on their individual needs.

The baby’s thyroid function is usually checked at 7, 14, and 28 days. In view of all the changes taking place in thyroid function soon after birth, the stabilisation of thyroid function may take time. Once the tests are normal and stable, they are typically measured every three months until two years of age and then every year.

26_031727 ch19.qxp 9/6/06 10:46 PM Page 239

Chapter 19: Developing Thyroid Conditions in Childhood
239

Proper dosing of thyroid hormone is determined by thyroid-function tests and by ensuring that the baby is growing properly. The height and weight of the baby are checked regularly to verify the hormone dosage.

If thyroid hormone treatment is delayed more than four to eight weeks after birth, a child with congenital hypothyroidism will almost certainly have some decrease in intellectual function.

Acquired hypothyroidism

Children may acquire hypothyroidism at any time after birth. When hypothyroidism occurs in a child over the age of two, it does not damage brain function, but it does greatly affect growth and development.

Causes

Children may develop hypothyroidism for all the same reasons as adults.

Iodine deficiency is, by far, the most common cause throughout the world.

Where iodine is sufficient, autoimmune thyroiditis (check out Chapter 5) is the leading cause. Less common reasons for acquired hypothyroidism include: ߜ Drugs like iodine or lithium

ߜ Irradiation – externally (for a tumour, for example) or internally, in treatment of hyperthyroidism with radioactive iodine

ߜ Removal of the thyroid for any reason

ߜ Abnormal production of thyroid hormone

ߜ Resistance to thyroid hormone

ߜ Central or secondary hypothyroidism due to a tumour in the pituitary or hypothalamus or a lack of production of TSH or TRH

Signs and symptoms

Again, the findings in these conditions are similar to the signs and symptoms found in adults, except that a growing, developing child experiences the consequences of poor growth. Constipation and dry skin are a feature of any hypothyroid person. In addition, children do not keep pace with normal height and weight charts.

A child who becomes hypothyroid after he or she starts school has trouble with schoolwork and keeping up with their friends’ level of physical activity due to lack of energy.

Interestingly, some of these kids appear unusually muscular, despite their weakness, as they develop swelling of muscle fibres – a condition called
muscle pseudohypertrophy
.

26_031727 ch19.qxp 9/6/06 10:46 PM Page 240

240
Part IV: Special Considerations in Thyroid Health
The growth of the skeleton and the teeth is delayed, and other signs include: ߜ Enlarged thyroid (goitre), unless it is previously removed ߜ Dry, cool skin that is puffy, pale, and yellowish

ߜ Brittle nails and dry, brittle hair that tends to fall out excessively ߜ Swelling that does not retain an indentation, especially of the legs ߜ Hoarseness and slow speech with a thickened tongue

ߜ An expressionless face

ߜ A slow pulse

Some of these children occasionally show early sexual development. This development is thought to result from their high levels of TSH, which has a similar structure to follicle-stimulating hormone (FSH). As a result, TSH activates cells that normally respond to FSH, so girls may have early vaginal bleeding, and boys may have large testicles for their age. Boys do not have a lot of male hormone (testosterone) however, as its production results from the action of another hormone, luteinizing hormone (LH). TSH does not share features with LH. The girls, however, do have increased oestrogen for their age since their ovaries can respond to the FSH-like properties of TSH; LH-like stimulation is not needed for this.

Adolescents who develop hypothyroidism have signs and symptoms similar to those found in an adult, with a few differences. If the child has begun puberty, further sexual development may stop unless the child is given thyroid hormone treatment. The growth of permanent teeth is often delayed, and the child doesn’t gain height as quickly as expected.

When a lack of TRH or TSH is the cause, the signs and symptoms of hypothyroidism are usually milder. The main symptoms are due to the underlying cause, such as a brain tumour, for example, in which the child complains of headaches or trouble with vision.

Laboratory confirmation

A TSH and free T4 test can confirm the diagnosis of hypothyroidism. In order to make a diagnosis of chronic (autoimmune) thyroiditis, the child is tested for the presence of thyroid autoantibodies. The child’s bone age is determined with X-rays to evaluate any growth abnormalities.

If central hypothyroidism is responsible, the free T4 and the TSH are low, as are other hormones made in the pituitary gland. An X-ray or scan of the pituitary is then needed to look for a tumour.

26_031727 ch19.qxp 9/6/06 10:46 PM Page 241

Chapter 19: Developing Thyroid Conditions in Childhood
241

Treatment

The current treatment for hypothyroidism is thyroxine (T4) hormone replacement. However, some studies in adults have been given both T3 and T4

replacement, in the same proportions that are made in the normal thyroid and this approach may gain future support (see Chapter 5).

In most cases, the dose of replacement hormone is adjusted until the TSH is normal. However, if the cause is central hypothyroidism, TSH is not used as a guide because the pituitary is not making any TSH.

In some cases, starting the child at a low dose and gradually increasing to the full therapeutic dose is necessary. Some children show more symptoms when they suddenly go from no thyroid hormone to full replacement. They experience trouble sleeping, restlessness, and deterioration in their school performance. Rarely, headaches may develop due to increased pressure in the brain.

Lowering the dose and gradually building it back up helps this situation.

If the child’s growth is delayed, he or she usually catches up when thyroid hormone is given.

Giving too much thyroid hormone may cause early closure of bone growth resulting in stunted growth and a decrease in bone mineral content.

Dealing with Hyperthyroidism

in Children

Hyperthyroidism is rarely seen in babies and is less common in children and adolescents than it is in adults. Almost always, kids with hyperthyroidism have Graves’ disease (refer to Chapter 6). When a newborn is hyperthyroid, usually the mother is also hyperthyroid (check out Chapter 18), and the mother’s thyroid-stimulating antibodies have passed to the foetus. When these antibodies naturally clear from the foetus after it’s born, the hyperthyroidism subsides about 3 to 12 weeks after birth.

Signs and symptoms

When a mother with hyperthyroidism passes a large amount of thyroid-stimulating antibodies to her baby through the placenta, the foetus develops hyperthyroidism. The signs of the hyperthyroidism in the foetus include: 26_031727 ch19.qxp 9/6/06 10:46 PM Page 242

242
Part IV: Special Considerations in Thyroid Health
ߜ Rapid heart rate

ߜ Increased foetal movements

ߜ Poor foetal body growth

ߜ Abnormally rapid bone growth

After the baby is born, the baby shows a number of signs and symptoms of hyperthyroidism. They are the result of excessive metabolism and include: ߜ Low birth weight and failure to gain weight

ߜ Increased appetite

ߜ Irritability

ߜ Rapid heart rate

ߜ Enlarged thyroid

ߜ Prominent eyes

Hyperthyroidism is rare in children under the age of five and is usually due to Graves’ disease. Once in a while, the cause is a functioning
thyroid adenoma
–

a new growth of tissue on or within the thyroid that makes excessive amounts of thyroid hormone. Girls develop thyroid adenomas more often than boys. A family history of other autoimmune diseases (for example, Type 1 diabetes) is often present when the cause is Graves’ disease.

In children under the age of five, the signs and symptoms of hyperthyroidism are like those seen in adults (refer to Chapter 6) plus problems resulting from the needs of a growing child who has now reached school age. Unique signs at this age include:

ߜ Poor school performance

ߜ Trouble sleeping

ߜ Poor athletic performance related to muscle weakness ߜ Tiredness

ߜ More rapid growth in height but early closure of bone growth ߜ Stunted final height

ߜ Irritability

These children are hungry all the time but don’t gain weight despite eating.

They generally have mild eye disease. They have a goitre and also have bowel movements more frequently than normal.

26_031727 ch19.qxp 9/6/06 10:46 PM Page 243

Chapter 19: Developing Thyroid Conditions in Childhood
243

Laboratory confirmation

Confirmation of the diagnosis of hyperthyroidism is made from a free T4 and a TSH level. If foetal hyperthyroidism is suspected, these levels are determined from umbilical cord blood at birth. If hyperthyroidism is present, the free T4 is high and the TSH low. Rarely, if the hyperthyroidism is due to excessive TSH secretion from the pituitary, the TSH is high. In that case, the baby is screened for a pituitary tumour.

Treatment

If your child has hyperthyroidism, there are many treatment options. The important thing to remember is that continued vigilance is needed, as all forms of treatment are associated with the recurrence of hyperthyroidism or the development of hypothyroidism in some cases.

You need to ensure that your child’s condition is followed up regularly after treatment because the disease process is ongoing. Regularly means every six months or yearly, as recommended by your doctor. All children with neonatal thyrotoxicosis usually have yearly neurological assessments until at least the age of six years.

If a developing foetus is hyperthyroid, antithyroid drugs are given to the mother. The drugs pass through the placenta to affect the foetus’s thyroid hormone production. The goal is to have a foetal heart rate less than 140

beats per minute. Sometimes, the mother takes a beta-blocker (such as propranolol) to control severe symptoms.

Treatment of hyperthyroidism in babies also involves antithyroid drugs. Once treatment is given, the baby rapidly improves. In a few months, the antithyroid drugs are withdrawn as the thyroid-stimulating antibodies passed from mother to baby naturally disappear from the baby’s circulation.

Radioactive iodine

At one time, doctors resisted using radioactive iodine to treat hyperthyroidism in children. However, this treatment is more commonly used today because long-term studies show no negative effects upon the child. Specifically, no increase in cancer or loss of fertility and no negative effect upon the offspring of children treated with radioactive iodine is found.

The problem with radioactive iodine is that most children become hypothyroid after some time. (The same is true of adults; refer to Chapter 6.) In addition, thyroid eye disease may get worse when radioactive iodine is used because of the release of a lot of antigen (material that the immune system may recognise as foreign) from the thyroid.

26_031727 ch19.qxp 9/6/06 10:46 PM Page 244

244
Part IV: Special Considerations in Thyroid Health
Antithyroid drugs

Antithyroid drugs such as propylthiouracil (PTU) and carbimazole are the preferred treatment for hyperthyroidism in children. They take three to six weeks to work, but they control the disease in at least 85 per cent of children.

If the medication doesn’t work, the child usually has a very large goitre or doesn’t take the medication as prescribed. In most cases, treatment is continued for two to four years.

How does the doctor choose which of these two drugs to use? PTU has the advantage of blocking the conversion of T4 to T3, whereas carbimazole lasts longer after taking it. In practise, these differences don’t seem to matter much.

If the disease is going to recur after the pills are stopped, the child usually has measurable amounts of TSH receptor-stimulating antibodies. This test is done at the time treatment is stopped to help predict a future recurrence.

The drugs fail to produce a permanent remission in up to half of children treated, even though 85 per cent are controlled.

Just as in adults, antithyroid medications cause side effects in children. The most important is that the production of white blood cells is halted. The prescribing doctor monitors white blood cells, and if the white cell count falls, the drug is stopped. If PTU was used initially, the child is not switched to carbimazole or vice versa – a totally different treatment is needed. Sometimes, the white cell count falls a little, but it returns to normal after some weeks.

Another important side effect is the development of a rash, which is treated without needing to stop taking the drug.

If your child is taking an antithyroid drug, you need to promptly report symptoms or signs of infection, especially a sore throat.

Surgery of the thyroid

Sometimes, antithyroid drugs cause serious side effects or the child doesn’t take the pills correctly, and radioactive iodine is unsuitable (usually because the parents are concerned about giving radioactivity to their child). In these cases, surgery is a safe and rapid form of treatment in the hands of a competent surgeon who has experience with children. If possible, the child should have normal thyroid function accomplished with antithyroid drugs before having surgery. Iodine is given for two weeks prior to surgery to block the thyroid gland and reduce blood flow into it. The usual operation is a near total thyroidectomy (check out Chapter 13 for more on surgery of the thyroid).