Thyroid Aplasia - Types, Causes, Symptoms, Diagnosis, and Management

Introduction:

The thyroid gland located in the lower neck produces two important hormones, namely T3 (triiodothyronine) and T4 (thyroxin), that regulate different body functions like metabolism, bone growth, brain development, body temperature, and digestion. The hypothalamus and pituitary gland located at the base of the skull produces the thyroid hormones. The hypothalamus-pituitary complex releases a hormone called thyroid-stimulating hormone (TSH) into the bloodstream that makes the thyroid gland release T3 and T4 when there is an imbalance in hormonal levels in the bloodstream.

Thyroid hormone is essential from the time of birth till two to three years of age, mainly for normal brain and intellectual development. From then on, it is essential for normal growth, metabolism, and functioning of various important organs like the heart, brain, and muscles.

Thyroid aplasia, also called congenital hypothyroidism, is a condition in which there is a partial or complete absence of thyroid gland function since birth (congenital). A defect in the baby’s thyroid gland or a lack of iodine in the mother’s diet during pregnancy can lead to the condition. The thyroid gland needs iodine to make hormones. Therefore, lack of iodine leads to impaired growth, neurological problems, and physical deformities. One in 2000 to 4000 infants are born with the condition, affecting girls twice more commonly than boys.

The introduction of iodized salt in diet in countries like the United States (US) and Canada, and other countries have made congenital hypothyroidism very rare. However, the condition is still prevalent in developing countries. Iodine is not produced in the body but gets into the food we take from the soil. Hence, a lack of iodine in the soil can cause an iodine deficiency.

What Are the Other Names of Thyroid Aplasia?

The other names of the condition include:

• Congenital myxedema.

• Cretinism.

• CHT.

• CH.

What Are the Types of Thyroid Aplasia?

Based on the location and size of the thyroid gland and hormone production, thyroid aplasia is of the following types:

1. Thyroid Dysgenesis: In 80 to 85 percent of the cases, the thyroid gland is completely absent, very small in size, or abnormally located, called thyroid dysgenesis.

2. Thyroid Dyshormonogenesis: A normal or enlarged thyroid gland produces little or no thyroid hormones, called thyroid dyshormonogenesis.

3. Central or Pituitary Hypothyroidism: Disruption of thyroid hormone production is due to impairment of the production process in the brain, called central hypothyroidism.

What Are the Causes of Thyroid Aplasia?

The most common causes of thyroid aplasia or congenital hypothyroidism include the following:

• A missing, underdeveloped, or abnormally small thyroid gland.

• A genetic defect that causes less production of thyroid hormones.

• Very less iodine intake by the mother during pregnancy.

• Antithyroid or radioactive iodine therapy to the mother for cancer treatment during pregnancy.

• Medications like Sulfonamides and Lithium during pregnancy affect thyroid hormone production.

• Pregnant mothers who have Hashimoto’s thyroiditis (inflammation of the thyroid gland) have a thyroid-blocking antibody, which they tend to pass to the baby.

What Are the Symptoms of Thyroid Aplasia?

Many babies do not have any signs and symptoms at birth. They develop symptoms in the initial days to the first few months after birth. Signs and symptoms of thyroid aplasia in babies include:

• Puffed face.

• Enlarged tongue.

• Stunted growth.

• No weight gain.

• Tiredness and lethargy.

• Poor feeding.

• Excess sleep.

• Abnormal growth of bones.

• Thick facial features.

• Mentally retarded babies.

• Less crying.

• Jaundice (yellow coloring of the eyes and skin).

• Hoarseness of voice.

• Floppy and weak muscles.

• Constipation.

• Umbilical hernia (a condition in which abdominal contents protrude through the abdominal wall muscles).

• Cool, dry and pale skin.

• Swelling of the skin.

• Swelling in the neck due to an enlarged thyroid gland (goiter).

What Are the Complications of Thyroid Aplasia?

The following complications can occur in children with thyroid aplasia, which include:

1. A very low IQ (intelligence quotient).

2. Difficulty in walking.

3. Mutism, or unable to speak.

4. Memory and attention problems.

5. Problems with vision and hearing.

6. Autistic behavior (a disorder with impaired social communication and restricted, repetitive behavior).

How Is Thyroid Aplasia Diagnosed?

• Standard newborn screening is done one to two days after birth in the United States (US), Canada, and many other developed countries, for the purpose of screening the baby for several conditions. Thyroid aplasia can be detected in the standard screening.

• A heel-prick blood test is done in which a small quantity of blood collected from the heel-prick is sent to the laboratory to assess the levels of the hormones T4 and TSH. Elevated levels of TSH and low levels of T4 suggest thyroid aplasia, which is further confirmed by a blood test, for which the blood is collected from the veins and sent for testing.

• Doctors may also recommend scans like ultrasound scans or thyroid scans to look out for a specific cause of thyroid aplasia.

How Is Thyroid Aplasia Managed?

Treatment aims to replace missing thyroid hormones to restore the levels to normal. The most commonly used thyroid hormone is a synthetic hormone that is identical to T4 produced by the thyroid gland, called levothyroxine. It is available in tablet form. The tablet is to be crushed and added to a small quantity (about one teaspoon of liquid) of either expressed breast milk or formula and fed to the baby using a teaspoon or a medicine dropper. Care must be taken not to mix levothyroxine with soy protein formula, as the soy protein has a tendency to bind to the thyroid hormones, making the absorption of the hormone difficult. Parents have to cautiously administer the hormone in a timely manner daily, to maintain steady hormonal blood levels.

How Often Do Blood Levels Need to Be Tested?

Doctors may recommend checking the blood hormone levels every one to two months in the initial six months, followed by checking every two to three months above six months of age. Regular monitoring is necessary to assess if the doses of medications are sufficient to keep up with the pace of the growing baby.

Conclusion:

Thyroid aplasia is a condition in which newborn babies have a deficiency of thyroid hormones due to the absence of or small sized thyroid gland. Early screening and immediate start of treatment in the first few days of life are of utmost importance to prevent damage due to retarded brain development. Children may require hormonal treatment for their entire lives. However, in a few cases, doctors may advise an off-treatment period, especially after three years of age, to check for the blood levels of T4 and TSH and assess if they can sustain without treatment or if the treatment has to be started again. With proper treatment, children with thyroid aplasia can lead a normal life like their peers.