Thyroid Disease in Childhood
Most thyroid disease seen in adults also occur in children. Although there are some differences in management, the principles remain the same. This pamphlet is to be used together with the other Health Guides on Thyroid Disease, to outline the causes and treatment of similar conditions in adults.
It is very important to explain to the child, depending on their level of understanding, where the thyroid is and what it does. A good way to describe the shape of the thyroid is to compare it to a butterfly sitting in the centre of the front of the neck over the windpipe and just above the collar bone. The outline can be seen on a child’s neck by raising the chin and tilting the head slightly back, especially if the thyroid is larger than normal. Its function, or job, can be compared to that of a furnace. If the thyroid is overactive (hyperthyroid), it can be considered as turned up too high; if underactive (hypothyroid), as turned down too low; or if the thyroid, no matter what its size, is making the right amount of thyroid hormone, then the thermostat is set just right.
The thyroid is a different type of structure from the small round lymph nodes which are easily felt on the sides of every child’s neck. The lymph nodes are there to protect against infection. The thyroid gland is there to make thyroid hormone, a body chemical needed by all cells so that they will work properly and at the right speed. The hypothalamus and pituitary gland (see Health Guide 1), are small downward extensions of the brain. They are about the size of the end of a fingertip and are located just behind the bridge of the nose and between the eyes. The hypothalamus produces a hormone called TRH which travels down to command certain cells in the pituitary to make another hormone called TSH (Thyroid Stimulating Hormone). TSH in turn directs the thyroid to make thyroid hormone (thyroxine) also called T4. If the thyroid makes too much T4, then the hypothalamus and pituitary, will cut down the production of TRH and TSH. If the thyroid makes too little T4, then the level of TSH rises to drive the thyroid to get bigger and to make more thyroid hormone (T4).
What Tests are Usually Done to Make a Diagnosis in Your Child?
A simple blood test for TSH and T4 measurement can be taken to see if the thyroid gland is functioning normally. This also checks to ensure the medication dosage is the correct amount.
In children with hypothyroidism, an x-ray of the hand and wrist (knee in infants) may be taken to determine the degree of delayed bone growth. It is usually unnecessary to perform ultrasounds of the thyroid unless the enlargement is uneven, a lump or a nodule is suspected. If there is a nodule, an ultrasound will help to tell if it is fluid-filled or solid. A thyroid scan uses a very safe weak radioactive material to see if the thyroid behaves in a normal way by taking up the radioactivity evenly. A spot with no uptake of radioactivity may be described as “cold” and could be a tumour. In some cases a thyroid biopsy, using a small needle may be done. The needle is placed in the thyroid to remove some cells for examination under a microscope. Older children tolerate this procedure well without sedation. If they are scared, a hand held by a parent and some anaesthetic cream helps.
Congenital hypothyroidism affects a ratio of 1 in 4000 newborn babies and used to be a major cause of mental disabilities. Development of the brain, as well as normal growth of the child, is dependent upon normal levels of thyroid hormone.
Screening for congenital hypothyroidism is routine in Canada. A thyroid blood test (TSH or T4) is routinely done on a small heel-prick blood sample obtained between day 2 and day 5 after birth. If the TSH is high (or the T4 is low), the parents are informed and the findings are confirmed by repeating the blood test.
The thyroid gland begins as a few cells at the back of the tongue in early fetal life. These cells increase in number and travel down to the normal position in the front of the neck during the first weeks after conception. The developing fetus depends mainly upon its own thyroid gland to make thyroid hormone, but thyroid hormone from the mother can also cross the placenta. In infants with congenital hypothyroidism, the thyroid gland, for reasons unknown, may either fail to develop or be much smaller than normal. The position of this poorly developed thyroid gland may be anywhere from the back of the tongue to its normal place in the front of the neck. About 10% of infants with congenital hypothyroidism will have an inherited inability to make thyroid hormone although the thyroid gland is present (congenital goitre). Although rare, the thyroid may be temporarily unable to make thyroid hormone. Antibodies present in the blood of a mother with thyroid disease, may cross the placenta and temporarily block the baby’s own thyroid from working. Except for these few babies, the hypothyroidism is permanent.
Now that a screening test is universally available, this condition can be recognized and treated rapidly. Lifetime treatment with a daily thyroid tablet will prevent mental disabilities and will result in normal growth. The dose is monitored and adjusted throughout infancy and childhood by measurement of the levels of TSH in the blood.
There are several uncommon inherited causes of goitre (thyroid enlargement) in children. Although these children may be hypothyroid, thyroid function is usually normal and the only abnormality is a thyroid enlargement. The treatment is to give thyroid hormone which causes the thyroid to shrink somewhat by “shutting off” TSH production from the pituitary gland. One of these conditions, known as Pendred’s syndrome, is associated with hearing loss, which may also be present in the other family members.
Hashimoto’s Thyroiditis (Autoimmune Thyroiditis)
The most frequent cause of thyroid enlargement in children and adolescents is Hashimoto’s thyroiditis. This is more common in girls and in those with a family history of Hashimoto’s or other thyroid disorders. Apart from the enlarged thyroid, there may be no other changes unless hypothyroidism develops. The management of Hashimoto’s thyroiditis in children and adolescents is exactly the same as in adults. Over time, the thyroid will become smaller but this may take several years. In Hashimoto’s thyroiditis, thyroid hormone secretion may be normal at diagnosis, but monitoring is recommended in case hypothyroidism develops. Treatment with thyroid hormone, once started, is taken for life. There are special groups of children, such as those with Diabetes Mellitus type 1, Down Syndrome, or Turner Syndrome, who should be regularly checked, as they are more likely to develop Hashimoto’s thyroiditis.
Graves’ Disease (Hyperthyroidism)
See also Hyperthyroidism (thyrotoxicoses)
Graves’ Disease, the most common cause of hyperthyroidism in children, increases in frequency as adolescence approaches. Development of eye complications (ophthalmopathy) occurs, but is not nearly as severe as in adults. Children can have the same symptoms as adults, but the child may not actually complain about them. The biggest problem before the diagnosis is known, may be extreme restlessness and short attention span. This may lead to school difficulties and often parental frustration. Treatment is usually started with antithyroid drugs. Some children are best managed by removing the thyroid gland once the hyperthyroidism is under control. In other children long term use of the antithyroid drugs is best. Treatment with radioactive iodine is only occasionally used in early childhood. It may be very helpful in older adolescents, particularly those whose hyperthyroidism is difficult to control.
Other Thyroid Disorders
Single thyroid nodules, multi-nodular goitre, subacute thyroiditis, and other thyroid disorders occur but are uncommon.
Thyroid Disease and Growth
Hypothyroidism in babies is usually detected by neonatal screening, and treatment is started right away. If left untreated, it can be associated with defects in growth and development as described earlier in the section on congenital hypothyroidism.
Children with hypothyroidism can have all the same symptoms as adults but the most striking change may be short stature despite a normal or increased weight. Once treated with thyroid hormone, “catch-up growth” is the rule. Puberty may be delayed or occasionally advanced.
There is no change in intelligence if hypothyroidism develops after two years of age.
For treatment of children and adolescents with hypo or hyperthyroidism, it is essential that the tablets be taken regularly. Supervision of treatment by parents, along with a pill minder box can a helpful way to monitor and train the child.
For those children with long standing hypothyroidism, returning to normal thyroid function may be associated with a significant change in behaviour as their level of activity may increase. This can result in school difficulties. Teachers should be made aware of the child’s condition along with any ongoing medical recommendations. In the case of children with Graves’ Disease, the difficulties mainly occur before treatment is started. However, if the medication is not taken regularly, symptoms of hyperthyroidism will reappear.