Introduction
Thyroid dysfunction is the most common of endocrine abnormalities in children with Down syndrome. The thyroid is a butterfly-shaped gland located in the neck, just below the voice box (larynx). It produces thyroid hormones called T3 and T4 (also Free T4 and Free T3) and these are responsible for how the body uses and stores energy, and maintaining normal physical and neurological growth and development. Thyroid hormone production is controlled by another hormone called TSH (thyroid-stimulating hormone) which is made in the pituitary gland located in the brain. Thyroid dysfunction may present as hypothyroidism (underproduction of thyroid hormones) either at birth (congenital hypothyroidism) or later on in childhood (acquired hypothyroidism). It can also rarely present as hyperthyroidism (overproduction of thyroid hormone).
Why does my child have thyroid dysfunction?
It is not always clear why children with Down syndrome have higher prevalence of thyroid dysfunction. Some reasons for congenital hypothyroidism include: thyroid glands in DS are often smaller in size (called thyroid hypoplasia) and this commonly leads to congenital hypothyroidism; TSH is released inappropriately or the thyroid gland does not respond as well to TSH; and a delayed maturation in the way the thyroid gland and pituitary gland interact causing elevated TSH values with normal Free T4 values. For acquired hypothyroidism, children with DS have a higher prevalence of autoimmune disorders compared to the general population and have higher rates of thyroid antibodies present.
Congenital hypothyroidism
Every infant in the US undergoes newborn screening which is a small heel prick that looks for over a dozen diseases including congenital hypothyroidism. It is important to know that babies with Down syndrome take longer to normalize their thyroid levels when born, compared to other children. This means that a thyroid level that is abnormal at 2 days of life, may normalize in additional 1-2 days. If the thyroid levels do not normalize and the baby continues to show elevated TSH with low-normal or low Free T4, this confirms the diagnosis of congenital hypothyroidism and the baby will be started on thyroid replacement hormone (Levothyroxine). Your infant will then need frequent monitoring of his/her thyroid levels, usually every 1-2 months for the next 12 months to ensure thyroid hormone remains in a normal range. After the first year, blood draws can be spaced to every 2-3 months and then after 3 years old, to every 6 months. You should never suddenly stop the thyroid medication without talking to your endocrinologist first and we will continue treatment until your child is at least 3 years old as birth to 3 years is the most important time for neurological development and behavior in all children. At the age of three, if appropriate, your endocrinologist will discuss trialing off levothyroxine temporarily and seeing if your child’s thyroid hormone levels remain normal.
Acquired hypothyroidism
A child with acquired hypothyroidism may have the following signs or symptoms: tiredness, feeling cold, dry skin, hair loss, constipation and poor growth. Weight gain, if present, is usually not a significant amount. He/she may also have an enlarged thyroid gland in the neck called a goiter. Your child’s blood test results would show elevated levels of TSH and may also have low levels of Free T4. The degree of hypothyroidism would determine whether your child needs to be treated or not. Your doctor will also check for thyroid antibody levels as antibodies attacking the thyroid is the most common cause of acquired hypothyroidism.
Screening
The American Academy of Pediatrics recommends screening children with Down syndrome for thyroid dysfunction at birth, 6 months old, 12 months old, and then annually. As a result, your child’s medical care will include regular screenings of their thyroid function. When your child’s endocrinologist or pediatrician orders bloodwork for your child, it will commonly include TSH and Free T4 to appropriately assess thyroid function.
Treatment of hypothyroidism
Congenital Hypothyroidism and Acquired Hypothyroidism are both related to under production of thyroid hormones. There is no cure for either but thyroid hormone replacement is safe and effective. It is known by the generic name Levothyroxine or you may also be familiar with brand names Synthroid or Tirosint. Your endocrinologist will most likely advise you to give your child this medication once a day, preferably in the morning 20 -30 minutes before breakfast and close to the same time each day. This medication should be given in tablet form because this gives a more consistent dose than the liquid form. If your child is an infant or too young to swallow pills, you can crush the tablet with a pill crusher and mix with 5ml of water, breastmilk or formula and administer via a syringe, tablespoon or dropper. The same can be done if your child uses a NG tube or Gtube to feed. With proper treatment, children with Down syndrome and thyroid dysfunction can continue to live healthy lives with optimal neurological function and development.
Hope-Elizabeth Clennon, D.O.
Pediatric Endocrinology Fellow PGY 6
Maimonides Children’s Hospital