Congenital Hypothyroidism/Cretinism

What is Congenital Hypothyroidism (CHT)?

Congenital hypothyroidism (CHT) or cretinism refers to a partial or complete loss of function of the thyroid gland that is present at birth (congenital).

The thyroid is a small butterfly-shaped endocrine gland in the lower neck. It synthesizes iodine-containing hormones, namely T3 (triiodothyronine) and T4 (thyroxine). These hormones are essential for regulating growth, metabolism and brain development.

Babies born with congenital hypothyroidism have lower-than-normal levels of these important hormones and is the commonest disorder in babies. It occurs in one in every 3,000 - 4,000 births and in almost 90% of these cases, it persists throughout life and will require regular replacement with thyroid tablets.

There are usually two types of CHT - one that is permanent and another that is temporary.

Majority of CHT are permanent type (85%). In this, either the thyroid gland is missing or poorly developed. In some cases the thyroid hormone production itself maybe impaired due to genetic issues and in some others the central controlling gland called the pituitary gland or hypothalamus itself may not be functioning adequately.

Temporary Hypothyroidism in infants occurs in about 20% of overall cases and the cause remains unknown. Generally pregnant women who have an underactive thyroid are at increased risk for not only delivering babies with CHT but also premature and low birth weight babies.

What are the Causes of Congenital Hypothyroidism?

• Treatment of maternal hyperthyroidism during pregnancy with anti-thyroid drugs can cause temporary hypothyroidism in the baby.

• Iodine Deficiency - Commonest cause of congenital hypothyroidism around the world. In some regions of the world such as the Himalayas, there is widespread iodine deficiency due to leaching by glaciers, floods or high rainfall.
• Absent (aplasia) or reduced size (hypoplastic) thyroid gland.
• Normal gland but deficient thyroid hormone production. This is caused by impairment in one of the several steps of thyroid hormone synthesis. These cases are referred to as thyroid dyshormonogenesis.
• Improper stimulation of thyroid gland by the pituitary gland, which is the master gland. These cases are referred to as 'central' or 'pituitary' hypothyroidism.
• Presence of maternal antibodies against thyroid tissue that block the baby''s thyroid function. It is an uncommon cause of congenital hypothyroidism.

What are the Symptoms and Signs of Congenital Hypothyroidism?

• Decreased activity and sleeping more
• Difficulty in feeding
• Weak cry

• Constipation
• Puffy face
• Poor muscle strength
• Prolonged jaundice (yellowish discoloration of skin) after birth
• Large and protruding tongue
• Distended abdomen
• Larger than normal fontanelles (soft regions) on the head

How do you Diagnose Congenital Hypothyroidism?

1. T3, T4 and TSH Levels Measurement

• Diagnosis of primary hypothyroidism is confirmed by demonstrating decreased levels of serum thyroid hormone (total or free T4) and elevated levels of thyroid-stimulating hormone (TSH).
• In most Western countries, a sample of the baby's blood is taken from the heel (heel-prick test) before discharge and tested for levels of T3, T4 and TSH.

• If the T3 and T4 levels are low and TSH is high, the infant''s doctor and parents are informed and referred to a pediatric endocrinologist to confirm the diagnosis and begin treatment.

2. Thyroid Scanning

• Thyroid scanning is not required to make the diagnosis of congenital hypothyroidism, but can provide information about the cause.
• Usually a technetium (Tc-99m pertechnetate) thyroid scan is performed to detect a structurally abnormal gland.
• A radioactive iodine (RAIU) scan will help differentiate congenital absence of gland or a defect in organification (a process necessary to make thyroid hormone).

3. Ultrasound Study

Can be done instead of radioactive scanning. However ultrasound will not reveal ectopic thyroid tissue, that will be shown by radioactive scans.

4. Radiograph (x-ray) Study

A lateral radiograph of the knee may be taken to look for the distal femoral epiphysis. This ossification center appears at about 36 weeks'' gestation. Its absence in a term or post-term infant indicates prenatal effects of hypothyroidism.

Before the introduction of hormone measurements, radiograph was used as a diagnostic test for congenital hypothyroidism.

How do you Treat Congenital Hypothyroidism?

Early diagnosis is a must so that treatment can start as soon as possible. A screening test for a newborn should include tests related to the thyroid gland. If you are on thyroid replacement treatment you must inform your doctor prior to the delivery of the baby.

Optimal care includes diagnosis before age 2 weeks and bring the levels of thyroid hormone levels in blood to normal before 3 weeks of age. If this is not done there are likely to be normal development issues with the baby.

• Congenital hypothyroidism is treated by giving thyroid hormone in the form of an oral pill called levothyroxine. Most babies will require treatment for life.

• The tablet is crushed and administered once daily, mixed with a small amount of water, formula, or breast milk using a syringe or dropper.
• It is essential that the tablet is administered without fail every day. It is even more important to have regular check-ups with a pediatric endocrinologist. This will help ensure that the baby will have normal growth and brain development.
• The thyroid hormone (T3 and T4) and TSH levels have to be monitored regularly and the dosage adjusted accordingly.

How can Congenital Hypothyroidism be Prevented?

• The importance of early diagnosis and institution of therapy for congenital hypothyroidism cannot be over emphasized. It is one of the important treatable causes of mental retardation.
• Neonatal screening of T3, T4, and TSH levels should be done in all infants between 2 - 4 days of birth. If this is not possible, then testing should be done within 7 days of birth before the baby is discharged.
• Dietary iodine supplementation in iodine-deficient endemic areas helps prevent endemic cretinism. It is noteworthy that dietary iodine deficiency is the most common preventable cause of brain damage worldwide.
• Babies of mothers who have been treated with anti-thyroid drugs for hyperthyroidism during pregnancy are at high risk for development of congenital hypothyroidism.

Similarly, babies of mothers who have undergone radioactive iodine treatment for thyroid cancer during pregnancy are also at risk for development of congenital hypothyroidism.

Such babies have to be carefully monitored and followed up regularly for the slightest signs of hypothyroidism.

Health Tips

• Intake of iodine supplemented salt is recommended to prevent hypothyroidism caused by iodine deficiency.
• Do not neglect symptoms such as failure to feed properly, constipation, weak cry, or decreased activity in your newborn. Consult your pediatrician immediately. It may need further investigation.

References:

1. Congenital hypothyroidism - (https://en.wikipedia.org/wiki/Congenital_hypothyroidism)
2. What is congenital Hypothyroidism? - (http://www.btf-thyroid.org/information/leaflets/42-congenital-hypothyroidism-guide)
3. Information About Congenital Hypothyroidism - (https://ghr.nlm.nih.gov/condition/congenital-hypothyroidism)
4. Updated AAP Guidelines on Newborn Screening and Therapy for Congenital Hypothyroidism - (http://www.aafp.org/afp/2007/0801/p439.html)

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