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Hypothyroidism - What Happens

Untreated hypothyroidism may get better or worse over time, depending on its cause and your age.

Hypothyroidism in infants and children

Although rare, hypothyroidism can occur in infants and children. If hypothyroidism is treated within the first month of life, a child will grow and develop normally. Untreated hypothyroidism in infants can cause brain damage, leading to intellectual disability and developmental delays. In the United States, all children are tested for hypothyroidism at birth.

Intellectual disability usually does not occur if hypothyroidism develops after age 3. But untreated childhood hypothyroidism typically delays physical growth and sexual development, including the onset of puberty. Children may gain weight yet have a slowed growth rate.

Hypothyroidism in adults

Hypothyroidism caused by Hashimoto's thyroiditis sometimes will disappear on its own. More often, the disorder causes a gradual loss of thyroid function. Your symptoms may develop slowly and be so mild that you do not notice them for years. But symptoms usually grow worse. And health problems may develop as the disease continues.

If untreated, hypothyroidism may lead to:

  • Myxedema, a condition that causes swelling of tissues, increased fluid around the heart and lungs, slowed muscle reflexes, and a slowed ability to think.
  • Myxedema coma, a rare, life-threatening condition. This can occur if you have had hypothyroidism for many years that becomes markedly worse. It usually occurs when older adults who have severe hypothyroidism become ill with another condition, suffer from cold exposure, or take painkillers or sleeping pills. Symptoms include mental deterioration, such as apathy, confusion, and psychosis. You may lose consciousness (coma) and may have an extremely low body temperature (hypothermia), slow heartbeat (fewer than 60 beats per minute), heart failure, and trouble breathing.
  • Complications, such as:

People with mild (subclinical) hypothyroidism have only slightly abnormal thyroid blood test results and often do not have obvious symptoms or health problems. Some people who have mild hypothyroidism regain normal thyroid function. But about 1 out of 10 people who have mild hypothyroidism will go on to have hypothyroidism within 3 years.1

If your thyroid gland has been removed during surgery, hypothyroidism will occur within a few weeks. If you have been treated with radioactive iodine therapy, hypothyroidism may develop within a year. In these cases, thyroid function typically does not return, and you will need to take thyroid hormone medicine from now on.

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