By Dr Vera Oh, Paediatrician, SBCC Baby & Child Clinic, Growth and Endocrinology Centre
What is the Thyroid Gland and what does it do?
The thyroid gland is a butterfly-shaped gland that lies in front of the neck. It produces thyroid hormones which control growth, metabolism and energy levels. Low thyroid hormones cause “hypothyroidism” while excess thyroid hormones lead to the condition known as “hyperthyroidism”.
Symptoms of low thyroid hormone (hypothyroidism)
Children with low thyroid hormones may experience tiredness or poor growth. They may have low activity levels or be noted to be placid babies. Neonates may also experience prolonged jaundice. In more severe cases, infants and very young children may have delayed milestones and intellectual development. Forgetfulness and learning difficulties may be a sign of hypothyroidism. Some patients may have a swollen thyroid gland, appear puffy or have dry skin and hair. Older patients may complain of cold intolerance, irregular menstrual cycles and infertility.
What causes hypothyroidism?
Hypothyroidism can be congenital (from birth) or may be acquired later in life. Congenital hypothyroidism is usually diagnosed during the neonatal period. All babies born in Singapore have a TSH level checked at birth. In congenital hypothyroidism, there is often an abnormally raised TSH. Congenital hypothyroidism may be due to developmental abnormalities of the thyroid gland. The gland may be in the wrong position, malformed, absent or simply have poor function.
Transient neonatal hypothyroidism in the neonatal period may also be due to exposure to maternal anti-thyroid medication while still in the womb or antibodies that cross the placenta. The mother may have a history of thyroid disease but sometimes she may be completely asymptomatic, and not even be aware of her condition. Hypothyroidism in the baby in this case, is usually transient. As the antibodies are cleared from the baby’s system, the child’s thyroid gland recovers and functions normally in about 3 months.
Other causes of low thyroid hormone may be due to Iodine deficiency or excess. Certain medications like lithium and amiodarone also interfere with thyroid function. More commonly, an overactive immune system destroys the thyroid gland, causing autoimmune thyroid disease (Hashimoto’s disease). As a result, the gland is unable to function normally. This condition may run in families. Autoimmune thyroid disease can also cause high thyroid hormone levels. (See section on Hyperthyroidism below.)
How is hypothyroidism treated?
The deficient hormone can be easily replaced with oral thyroxin once a day. The dose may need to be adjusted depending on the response and as a growing child increases in size. Thyroxin should not be taken with soy milk formulas or iron supplements as these interfere with its absorption.
What are the symptoms of excess thyroid hormone (hyperthyroidism)?
Hyperthyroidism may manifest with weight loss, increased sweatiness, shakiness and tremors. High thyroid hormones can cause a rapid or irregular heart beat. Some patients have difficulty sleeping or just feel tired. They can also experience heat intolerance, irritability or anxiousness. The thyroid gland itself may be enlarged.
What causes hyperthyroidism?
Graves disease, an autoimmune condition, is the most common cause of hyperthyroidism. The immune system produces abnormal antibodies that stimulate excessive thyroid hormone production. There may be a family history of similar thyroid problems. Aside from symptoms of the high hormone levels, there may be associated puffy eyelids, prominent, protuberant eyes, dry eyes or double vision because of limitation in eye movements.
Other causes of hyperthyroidism include toxic multinodular goitre where there are multiple areas of excessive function, or toxic nodular goitre where there is a focal area responsible for the over-production of thyroid hormones.
Very rarely, neonatal thyrotoxicosis can occur when maternal antibodies cross the placenta and stimulate the baby’s thyroid gland. Soon after birth, these babies have very high heart rates, appear irritable, feed poorly, have diarrhoea, vomiting or even have fever because of their high metabolic state. This is a transient condition but because of the serious side effects, these babies have to be closely monitored and treated until the antibodies are cleared from their bodies in about 3 months.
How is hyperthyroidism treated?
Depending on the underlying cause of hyperthyroidism, anti-thyroid medication (like carbimazole), surgery or radio-iodine may be considered. Meanwhile, iodine or beta-blockers may be required to minimize the symptoms of the high thyroid hormones.
The benefits, side-effects and drawbacks of each treatment modality should be discussed and considered before a final decision is made.