What Is the Thyroid?

The thyroid is a small gland below the skin and muscles at the front of the neck, at the spot where a bow tie would rest.

It's brownish red, with left and right halves (called lobes) that look like a butterfly's wings. It weighs less than an ounce, but helps the body do many things, such as get energy from food, grow, and go through sexual development. In younger children, it is also important for brain development.

What Is Hypothyroidism?

Hypothyroidism (or underactive thyroid) is when the thyroid gland doesn't make enough of some important hormones. This makes the body use up energy more slowly, and chemical activity (metabolism) in the cells slows down.

Hypothyroidism is a common condition, especially in adult women. But kids can have it too. Some children are born with it — this is called congenital hypothyroidism. Others develop it later, usually late in childhood or as teens. The most common cause of hypothyroidism in kids and teens is the autoimmune disease Hashimoto's thyroiditis.

What Are the Signs & Symptoms of Hypothyroidism?

A person with mild hypothyroidism may feel just fine. In fact, it might cause no symptoms at all.

But if thyroid hormone levels get too low, symptoms can become more obvious. These include:

• sluggishness
• depression
• dry skin or hair loss
• feeling cold
• muscle weakness
• poor memory or trouble concentrating
• constipation
• facial puffiness 
• weight gain (even when not eating more or exercising less)
• slowed growth
• slow sexual development
• irregular menstrual periods in girls

What Is Hashimoto's Thyroiditis?

Hashimoto's thyroiditis (hah-she-MOE-toes thy-roy-DYE-tiss) is an autoimmune disease. It causes most cases of hypothyroidism in kids and teens. Hashimoto's thyroiditis is also called chronic lymphocytic thyroiditis.

What Happens in Hashimoto's Thyroiditis?

Hashimoto's thyroiditis is an ongoing condition in which the immune system attacks the thyroid. Some people have normal thyroid function for a while. But over time, the thyroid stops making enough thyroid hormone, causing hypothyroidism. The body responds by sending a message to the thyroid to work harder to make enough hormone.

This, and the swelling the immune system causes as it attacks the gland, can make the thyroid get bigger, leading to a goiter. The thyroid can keep changing size over months or years.

How Are Hypothyroidism and Hashimoto's Thyroiditis Diagnosed?

To diagnose hypothyroidism and Hashimoto's thyroiditis, doctors ask about a person's symptoms, do an exam, and order blood tests. The tests measure:

• Thyroid hormone levels, particularly  thyroxine (T4) and thyroid-stimulating hormone (TSH). T4 is the thyroid hormone made in the thyroid that works throughout the body. TSH is a hormone made in the pituitary gland 
  (a pea-sized gland just beneath the brain). More TSH is released into the blood when the brain and pituitary sense that the levels of thyroid hormone in the blood are too low. TSH stimulates the thyroid to work harder to make more thyroid hormone.
• Some antibodies (proteins made by the immune system). High levels of these antibodies in the blood are a sign that the gland is being attack by the immune system in Hashimoto's. The two antibodies commonly measured are thyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPO).

How Are Hypothyroidism and Hashimoto's Thyroiditis Treated?

Doctors treat an underactive thyroid with daily thyroid hormone replacement pills. The medicine is the same T4 that the body is no longer making. These will bring the body's levels of thyroid hormone back to normal.

This treatment is fairly simple, but a person will have doctor visits several times a year for an exam, blood tests, and medicine changes as needed.