The thyroid is a small gland located below the skin and muscles at the front of the neck, just 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's light like a butterfly, too, and usually weighs less than an ounce.

As small as it is, though, the thyroid has an enormously important job to do, especially for teens. It manufactures the hormones that help control metabolism and growth. To do its job, the thyroid needs a chemical element called iodine that the body absorbs from the foods you eat and the water you drink. The entire body contains about 50 milligrams of iodine. About 1/5 to 1/3 of that supply (10 to 15 milligrams) is stored in your thyroid. The thyroid combines the iodine with tyrosine (an essential amino acid) to make important hormones.

Thyroid hormones are released from the gland and travel through the bloodstream to your body's cells. They help control the growth and the structure of bones, sexual development (puberty), and many other body functions. By helping your cells convert oxygen and calories into the energy they need to work properly, these hormones are important in determining if your body will mature as it should.

Thyroid hormones also directly affect how most of your organs function. So if your thyroid isn't operating properly, you can have problems in lots of other parts of your body.

What Is Thyroid Disease?

Thyroid disease occurs when the thyroid gland doesn't supply the proper amount of hormones needed by the body. If the thyroid is overactive, it releases too much thyroid hormone into the bloodstream, resulting in hyperthyroidism. ("Hyper" is from the Greek, meaning "over" or "above.") Hyperthyroidism causes the body to use up energy more quickly than it should, and chemical activity (like metabolism) in the cells speeds up.

An underactive thyroid produces too little thyroid hormone, resulting in hypothyroidism. ("Hypo" means "under" or "below.") When the amount of hormone released into the bloodstream is below normal, the body uses up energy more slowly, and chemical activity (metabolism) in the cells slows down.

Although they are two different conditions, in both hypothyroidism and hyperthyroidism the thyroid can become larger than normal. An enlarged thyroid gland is a lump that can be felt under the skin at the front of the neck. When it is large enough to see easily, it's called a goiter.

People who don't get enough iodine in their diets also can get an enlarged thyroid, but this is rare in the United States because foods here usually supply enough iodine.

Hyperthyroidism

Hyperthyroidism can cause nervousness, irritability, increased perspiration, intolerance to heat, fatigue, difficulty sleeping, a fast heartbeat, irregular menstrual periods in girls, and muscle weakness.

People with this problem might lose weight even though they're eating more than usual. The eyes may feel irritated or look like they're staring. Sometimes the tissues around the eyes become inflamed and swollen, and the eyes appear to bulge out, but this is less common in teens than in adults with hyperthyroidism.

Graves disease, an autoimmune disease, is the most common cause of hyperthyroidism. The condition makes a person's immune system produce abnormal types of antibodies (normally antibodies help the body fight infection). These abnormal antibodies make the thyroid gland produce more thyroid hormones.

Eventually, the thyroid gland enlarges, which can result in a goiter. For reasons that doctors don't yet understand, autoimmune thyroid diseases like Graves disease are much more common in women and are most likely to occur in teens and young and middle-aged adults.

Doctors usually diagnose Graves disease based on a person's symptoms, a physical examination, and blood tests that show high levels of thyroid hormone in the blood.

Once the diagnosis is made, a teen with Graves disease will usually start taking an anti-thyroid medication, which blocks the thyroid's production of thyroid hormones. Medication usually brings the hormone levels down to the normal range in 1 to 2 months.

However, in most cases, the disease doesn't go away. Some people continue taking medication for months or years to keep Graves disease under control, but it can be a hassle to take medication 1 to 3 times a day for a long period. So many doctors recommend a permanent treatment.

Radioactive iodine (RAI) is the most commonly recommended permanent treatment for teens with Graves disease today. It is usually given at a hospital, but doesn't require a hospital stay. RAI is considered safe for teens when given in the standard amount. It is taken in capsules or mixed with a glass of water. The thyroid gland quickly absorbs the RAI from the bloodstream and, within a few months, the gland shrinks and symptoms gradually disappear. RAI has been used to treat Graves disease successfully for more than 50 years.

The other permanent treatment for Graves disease is surgery to remove most of the thyroid gland (thyroidectomy). The operation is performed in a hospital under general anesthesia, meaning the person is asleep and feels nothing during the surgery. A small incision (cut) in the lower central part of the neck usually leaves a thin scar.

After surgery, there typically is swelling in the area of the incision. People sometimes have a sore throat and some trouble swallowing following surgery, although they should be able to eat and drink normally. These symptoms usually disappear within a few days.

After treatment for hyperthyroidism, hormone production often slows down to hypothyroid (underactive) levels, so the person needs to take a thyroid hormone replacement tablet each day. This treatment is a lot easier to manage than taking pills to control the hyperthyroidism — fewer blood tests, doctor visits, and medication adjustments are necessary.

As the body adjusts to the hormone replacement tablets, a doctor may increase or reduce the dosage until the levels of thyroid hormone in a person's blood are normal. Once the doctor finds the proper dosage, people usually feel well and free of symptoms. However, the doctor will continue to check hormone levels to make sure the dosage is right, especially for growing teens whose levels might change over just a few months.

Hypothyroidism

A person with mild hypothyroidism may feel just fine — in fact, the condition might cause no symptoms at all. However, symptoms can become more obvious if hypothyroidism progresses.

People with underactive thyroids might feel depressed and sluggish. They might gain weight, even though they're not eating more or getting less exercise than usual. Teens with hypothyroidism also might have slow growth in height, slow sexual development, irregular menstrual periods in girls, muscle weakness, dry skin, hair loss, poor memory, and difficulty concentrating.

Hashimoto's thyroiditis (pronounced: hah-she-moe-toes thy-roy-dye-tiss) is also an autoimmune disease and is the most common cause of hypothyroidism in teens. In this condition, the body's immune system attacks the cells in the thyroid gland, preventing it from producing enough thyroid hormone. The thyroid responds by working harder to make enough hormones. This can make it become enlarged and may result in a goiter.

Hypothyroidism is usually easily diagnosed with a physical examination and blood tests, and treatment with thyroid hormone replacement pills can restore normal levels of thyroid hormone in the blood. This treatment is pretty simple, but it does require doctor visits once or twice a year for an examination, blood tests, and medication adjustments as needed.

Goiters and Thyroid Nodules

It can take months or years for a goiter to develop. In teens, goiters are usually caused by the autoimmune thyroid conditions discussed above, which might show no obvious symptoms until the goiter is visible as a swelling at the front of the neck. People with this problem might have the sensation that food is stuck in the throat, especially when they lie down or sleep on their backs.

Generally, treatment of the thyroid disease causing the goiter will decrease or control the enlargement. If the thyroid continues to get larger despite treatment and becomes large enough to cause discomfort or a lump in the neck, surgery may be required. However, surgery is not necessary for most people.

A thyroid nodule is a lump or enlarged area in the thyroid gland. Sometimes a nodule can appear in a healthy gland. It may feel like a lump in the throat, or there may be tenderness or pain in the front of the neck. If the nodule is large enough, it may be visible at the front of the neck.

Most thyroid nodules are harmless. A nodule may simply be an overgrowth of normal thyroid tissue, a swelling caused by inflammation (such as in autoimmune thyroid diseases) or a collection of fluid called a cyst.

The doctor usually discovers nodules by touch during a physical examination. If the doctor finds a nodule, blood tests might be needed to find out how the thyroid gland is working. A doctor may also take an ultrasound image of the gland to detect whether the nodule is a cyst or a solid growth or tumor.

In addition to doing a physical examination, the doctor will ask you about any concerns and symptoms you have, your past health, your family's health, any medications you're taking, any allergies you may have, and other issues. This is called the medical history.

Another test called a thyroid scan can tell the doctor what type of nodule a person has. For this test, a person swallows a pill containing a small amount of radioactive iodine or another radioactive substance. The thyroid absorbs the radioactive substance. Next, a special camera measures where the radioactive substance is taken up by the thyroid gland, giving the doctor a better picture of the location, size, and type of thyroid nodule.

In addition, a fine-needle biopsy may be done to help determine whether a nodule is cancerous. During the biopsy, the doctor inserts a thin needle through the skin into the thyroid nodule (the skin is numbed with medication first). Through the needle, the doctor takes a sample of tissue or some fluid from a cyst. The tissue or fluid is then sent to a lab to be examined. In some cases, a person might need to have the nodule surgically removed for more detailed examination in the lab.

Fortunately, cancer is rare in children and teens, and most thyroid cancers can be cured or controlled with treatment.

Thyroid Disease, Growth, and Puberty

Once puberty starts, the body goes through some very noticeable changes. Because thyroid hormones play an important role in this process, thyroid disease may slow down or interfere with a teen's physical development. But it's important to know that not everyone grows or develops at the same age or at the same rate. If your friend seems to grow 4 inches overnight and you haven't had a growth spurt yet, it doesn't mean there's something wrong with you or your thyroid.

A thyroid problem also may cause a girl to have changes in her periods. Girls with thyroid problems may have a decrease or increase in menstrual flow or there may be a shorter or longer time between periods than usual. However, because girls who are just starting to menstruate often have irregular periods for the first year or so, changes in periods are usually nothing to worry about and don't mean a girl has thyroid disease.

People who are concerned that they might have a thyroid problem should visit the doctor. Chances are, the problem is something simpler. And if someone does have thyroid disease, diagnosing and treating it properly — including bringing the blood levels of thyroid hormones back to normal — will usually prevent or correct any problems.

Reviewed by: Steven Dowshen, MD
Date reviewed: February 2012