Hypothyroidism and Hyperthyroidism in Your Newborn

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Hypothyroidism — an underactive thyroid — and hyperthyroidism — an overactive thyroid — are both seen in newborns. Let's take a look at the risks, signs, symptoms, and treatment of thyroid problems in newborns.

Neonatal hypothyroidism/permanent congenital hypothyroidism/transient hypothyroidism

A lack of thyroid hormone in a newborn is a serious problem that can have permanent health implications. Insufficient thyroid hormone can impair the growth and development of an infant, eventually resulting in cognitive problems or even mental retardation. Severe hypothyroidism that is undetected and untreated is actually the leading preventable cause of mental retardation around the world.

This is why it is so important to detect hypothyroidism and begin treatment as early as possible in newborns. This can be a challenge because most infants with neonatal hypothyroidism appear normal at birth and do not have obvious signs of hypothyroidism. Some nations, including the United States, have mandatory newborn “heel-stick” thyroid screening, which detects most cases of neonatal hypothyroidism.

There are several types of neonatal hypothyroidism: congenital permanent hypothyroidism, and transient neonatal hypothyroidism.

Signs and symptoms of neonatal hypothyroidism

Most newborns who are hypothyroid do not show any signs or symptoms of an underactive thyroid. When symptomatic, however, the following symptoms are seen in newborns and infants.

  • Higher-than-normal birth weight
  • Higher-than-normal head circumference
  • Sleepy when awake, sleeps more than usual
  • Slower-than-normal movements
  • A hoarse cry
  • Difficulty breastfeeding
  • Constipation
  • A bloated stomach
  • An enlarged tongue that may stick out
  • Episodes of choking
  • Dry skin
  • Dry, brittle hair
  • Lower-than-normal body temperature
  • Prolonged jaundice (yellowing of the skin)
  • An enlarged thyroid, known as a goiter
  • Lower-than-normal muscle tone, floppy limbs
  • Puffiness in the face
  • Cold hands and feet
  • A low hairline, with hair growing low on the forehead
  • A large fontanel (soft spot)
  • A herniated bellybutton
  • Slow growth
  • Arms or legs may be shorter than normal
  • Hands can be wide with short fingers
  • Skull bones may be widely separated

Permanent congenital hypothyroidism

Permanent congenital hypothyroidism refers to a child who is born without a thyroid, or whose thyroid is permanently incapable of producing sufficient thyroid hormone. In some cases, the thyroid dysfunction is caused by a malfunctioning pituitary gland in the newborn. A mother’s exposure to radioactive iodine during pregnancy can also cause permanent damage to the baby’s thyroid function.

Congenital permanent hypothyroidism requires lifelong treatment with thyroid hormone replacement medication. In the United States, congenital hypothyroidism is not common, occurring in one in 3,000 to 4,000 infants. Girls are about twice as likely to have congenital hypothyroidism as boys.

Transient neonatal hypothyroidism

An estimated 10 to 20 percent of newborns with hypothyroidism have transient neonatal hypothyroidism. These newborns can be hypothyroid due to a mother who took antithyroid medication during pregnancy, a deficiency or excess of iodine in the mother before birth, exposure to iodine, maternal use of antithyroid medication during pregnancy, exposure to topical iodine, premature birth before 30 weeks gestation, and a mother’s history of Graves’ disease and antibodies that block thyroid hormone production.

Transient neonatal hypothyroidism requires treatment with thyroid hormone replacement medication until the underlying cause has been resolved. At that point, most infants or children are able to stop taking thyroid medication and have normal thyroid function.

Detection and diagnosis of hypothyroidism in newborns

Permanent and transient hypothyroidism in newborns is usually detected in the United States with the heel-stick newborn screening done after birth. Typically, testing thyroid stimulating hormone (TSH) and thyroxine (T4) can detect hypothyroidism in newborns and infants.

Treatment of hypothyroidism in newborns

Treatment of newborns and infants with any type of hypothyroidism is the thyroid drug levothyroxine (Synthroid, Levoxyl, Tirosint). Tirosint-SOL, a liquid form of levothyroxine, is frequently recommended for treating hypothyroidism in infants. Some doctors recommend crushing the tablets into a powder and mixing with a small amount of milk to administer to an infant.

Prognosis

The prognosis for a child born with either permanent and transient hypothyroidism is excellent, as long as the condition is detected quickly and treatment starts right away. Most studies show that these children grow and develop normally, physically and in terms of their cognitive development.

Congenital hyperthyroidism/neonatal hyperthyroidism

The most common reason for hyperthyroidism in a newborn is the transfer of antibodies — known as thyroid stimulating immunoglobulins (TSI) — from a mother with a history of Graves’ disease to her baby. These antibodies cross the placenta and cause overactive thyroid in the baby.

The mother may have active Graves' disease during pregnancy or may have already been treated, but antibodies are still present.

Signs and symptoms of neonatal hyperthyroidism

The signs and symptoms of hyperthyroidism in a newborn include the following:

  • A low birthweight
  • Premature birth
  • A smaller-than-normal head circumference
  • A prominent forehead
  • A dangerous accumulation of fluid in the belly, lungs, and skin, known as fetal hydrops
  • Enlarged liver and/or spleen
  • Warm, moist skin
  • Elevated blood pressure
  • A higher-than-normal heart rate
  • Heart rhythm abnormalities such as palpitations
  • Behavioral changes, such as irritability, nervousness, hyperactivity, restlessness, difficulty sleeping
  • An enlarged thyroid known as a goiter
  • Choking episodes, difficulty breathing
  • An unusually big appetite
  • Inability to gain weight, or weight loss despite eating
  • Bulging eyes
  • Vomiting
  • Diarrhea
  • Abnormal, uncontrolled muscle movements
  • Jaundice
  • Craniosynostosis — a condition in which the skull prematurely fuses together

Hyperthyroidism symptoms can be present at birth or may take several weeks to develop. Delayed appearance of symptoms is more likely in a woman taking antithyroid drugs during pregnancy.

Treatment of neonatal hyperthyroidism

Hyperthyroidism in newborns and infants is typically treated with the antithyroid drug methimazole and less commonly, propylthiouracil (PTU).

Other drugs may also be used:

  • If there is an elevated heart rate or muscle spasms, a beta-blocking drug such as propranolol is also prescribed.

  • Some doctors also recommend administering iodine — usually an iodine/iodide combination like Lugol’s solution — to help block the production and release of thyroid hormones.

  • For severe hyperthyroidism in a newborn, steroid drugs are sometimes given to reduce inflammation of the thyroid gland, and slow the production and release of thyroid hormones.

  • If the infant is experiencing congestive heart failure, the drug digoxin is often prescribed.

With treatment, most infants have a remission between 12 and 20 weeks after birth, and almost always within 48 weeks.

If an infant fails to respond to these drug treatments, thyroidectomy may be performed, but it is rare.

An infant with hyperthyroidism is monitored frequently, usually by a pediatric endocrinologist. As the infant improves, treatment is typically slowly decreased, and eventually discontinued.

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