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Thyroid , Overactive / Hyperthyroidism (Overactive Thyroid Gland)

Definition:
Your thyroid is a butterfly-shaped gland located at the base of your neck, just below your Adam's apple. Although it weighs less than an ounce, the thyroid gland has an enormous impact on your health. Every aspect of your metabolism, from your heart rate to how quickly you burn calories, is regulated by thyroid hormones. You cannot live without your thyroid gland or the thyroid hormone, thyroxine.

As long as your thyroid produces the right amount of these hormones, your metabolism functions normally. But sometimes your thyroid gland produces too much of the hormone thyroxine — a condition known as hyperthyroidism (overactive thyroid disease). Hyperthyroidism can significantly accelerate your body's metabolism, causing sudden weight loss, a rapid or irregular heartbeat, sweating, and nervousness or irritability.

Several treatment options are available if you have hyperthyroidism. Doctors use anti-thyroid medications and radioactive iodine to slow the production of thyroid hormones. Sometimes, treatment of hyperthyroidism means surgical removal of part of the thyroid gland. Although hyperthyroidism can be fatal if it's ignored, most people respond well once hyperthyroidism is diagnosed and treated.

Causes:
Your thyroid gland produces two main hormones, thyroxine and triiodothyronine, that influence every cell in your body. They maintain the rate at which your body uses fats and carbohydrates, help control your body temperature, influence your heart rate and help regulate the production of protein. Your thyroid gland also produces calcitonin, a hormone that helps regulate the amount of calcium in your blood.

The rate at which thyroxine and triiodothyronine are released is controlled by your pituitary gland and your hypothalamus — an area at the base of your brain that acts as a thermostat for your whole system. Here's how the process works:

The hypothalamus signals your pituitary gland to make a hormone called thyroid-stimulating hormone (TSH). Your pituitary gland then releases TSH — the amount depends on how much thyroxine and triiodothyronine are in your blood. If you don't have enough thyroxine or triiodothyronine in your blood, your TSH blood level will be above normal; if you have too much, your TSH level will fall below normal. Finally, your thyroid gland regulates its production of hormones based on the amount of TSH it receives.

Reasons for too much thyroxine
Normally, your thyroid releases the right amount of hormones, but sometimes it produces too much thyroxine. This may occur for a number of reasons, including:
  • Graves' disease. The cause of most hyperthyroidism is Graves' disease, an autoimmune disorder in which antibodies produced by your immune system stimulate your thyroid to produce too much thyroxine. Normally, your immune system uses antibodies to help protect against viruses, bacteria and other foreign substances that invade your body. In Graves' disease, antibodies mistakenly attack your thyroid gland and occasionally the tissue behind your eyes and the skin of your lower legs over the shins. Scientists aren't sure exactly what causes Graves' disease, although several factors — including a genetic predisposition — are likely involved.
  • Hyperfunctioning thyroid nodules (toxic adenoma, toxic multinodular goiter, Plummer's disease). This form of hyperthyroidism occurs when one or more adenomas of your thyroid produce too much thyroxine. An adenoma is a part of the gland that has walled itself off from the rest of the gland, forming noncancerous (benign) lumps that may cause an enlargement of the thyroid. Not all adenomas produce excess thyroxine, and doctors aren't sure what causes some to begin producing too much hormone.
  • Thyroiditis. Sometimes your thyroid gland can become inflamed for unknown reasons. The inflammation can cause excess thyroid hormone stored in the gland to leak into your bloodstream. One rare type of thyroiditis, known as subacute thyroiditis, causes pain in the thyroid gland. Other types are painless and may sometimes occur after pregnancy (postpartum thyroiditis).
When to seek medical advice:
If you experience unexplained weight loss, a rapid heartbeat, unusual sweating, swelling at the base of your neck, or other signs and symptoms associated with hyperthyroidism, see your doctor. It's important to completely describe the changes you've observed, because many signs and symptoms of hyperthyroidism may be associated with a number of other conditions.

If you've been treated for hyperthyroidism or currently are being treated, see your doctor regularly so he or she can monitor your condition.

Symptoms:
Hyperthyroidism can mimic other health problems, which may make it difficult for your doctor to diagnose. It can also cause a wide variety of signs and symptoms, including:
  • Sudden weight loss, even when your appetite and food intake remain normal or increase
  • Rapid heartbeat (tachycardia) — commonly more than 100 beats a minute — irregular heartbeat (arrhythmia) or pounding of your heart (palpitations)
  • Nervousness, anxiety or anxiety attacks, irritability
  • Tremor — usually a fine trembling in your hands and fingers
  • Sweating
  • Changes in menstrual patterns
  • Increased sensitivity to heat
  • Changes in bowel patterns, especially more frequent bowel movements
  • An enlarged thyroid gland (goiter), which may appear as a swelling at the base of your neck
  • Fatigue, muscle weakness
  • Difficulty sleeping
Older adults are more likely to have either no symptoms or subtle ones, such as an increased heart rate, heat intolerance and a tendency to become tired during ordinary activities. Medications called beta blockers, which are used to treat high blood pressure and other conditions, can mask many of the symptoms of hyperthyroidism.

Graves' ophthalmopathy
Sometimes an uncommon problem called Graves' ophthalmopathy may affect your eyes. In this disorder, your eyeballs protrude beyond their normal protective orbit when tissues and muscles behind your eyes swell, pushing the eyeballs forward so far that they actually bulge out of your orbits. This can cause the front surface of your eyeballs to become very dry. Other signs and symptoms of Graves' ophthalmopathy include:
  • Red or swollen eyes
  • Excessive tearing or discomfort in one or both eyes
  • Light sensitivity, blurry or double vision, inflammation, or reduced eye movement

Dignosis:
Hyperthyroidism is diagnosed using your medical history, a physical exam and blood tests. During the exam your doctor may try to detect a slight tremor in your fingers when they're extended, overactive reflexes, eye changes and warm, moist skin. Your doctor will also examine your thyroid gland as you swallow.

The diagnosis can be confirmed with blood tests that measure the levels of thyroxine and TSH in your blood. High levels of thyroxine and low or nonexistent amounts of TSH indicate an overactive thyroid. The amount of TSH is important because it's the hormone that signals your thyroid gland to produce more thyroxine. These tests are particularly necessary for older adults, who may not have classic symptoms of hyperthyroidism.

If blood tests indicate hyperthyroidism, your doctor may recommend one of the following tests to help determine why your thyroid is overactive:
  • Radioactive iodine uptake test. For this test, you take a small, oral dose of radioactive iodine (radioiodine). Over time, the iodine collects in your thyroid gland because your thyroid uses iodine to manufacture hormones. You'll be checked after two, six or 24 hours — or sometimes after all three time periods — to determine how much iodine your thyroid gland has absorbed.

    A high uptake of radioiodine indicates your thyroid gland is producing too much thyroxine. The most likely cause is either Graves' disease or hyperfunctioning nodules. If you have hyperthyroidism but your radioiodine uptake is low, you may have thyroiditis.

    Knowing what's causing your hyperthyroidism can help your doctor plan the appropriate treatment. A radioactive iodine uptake test isn't uncomfortable, but it does expose you to a small amount of radiation.

  • Thyroid scan. During this test, you'll have a radioactive isotope injected into the vein on the inside of your elbow or sometimes into a vein in your hand. You then lie on a table with your head stretched backward while a special camera produces an image of your thyroid on a computer screen.

    The time needed for the procedure may vary, depending on how long it takes the isotope to reach your thyroid gland. You may have some neck discomfort with this test, and you'll be exposed to a small amount of radiation.

    Sometimes you may have a thyroid scan as part of a radioactive iodine uptake test. In that case, orally administered radioactive iodine is used to image your thyroid gland.

Complication:
Hyperthyroidism can lead to a number of complications:
  • Heart problems. Some of the most serious complications of hyperthyroidism involve the heart. These include a rapid heart rate, a heart rhythm disorder called atrial fibrillation and congestive heart failure — a condition in which your heart can't circulate enough blood to meet your body's needs. These complications are generally reversible with appropriate treatment.
  • Brittle bones. Untreated hyperthyroidism can also lead to weak, brittle bones (osteoporosis). The strength of your bones depends, in part, on the amount of calcium and other minerals they contain. Too much thyroid hormone interferes with your body's ability to incorporate calcium into your bones.
  • Eye problems. People with Graves' ophthalmopathy develop eye problems, including bulging, red or swollen eyes, sensitivity to light, and blurring or double vision.
  • Red, swollen skin. In rare cases, Graves' disease also affects the skin, causing redness and swelling, often on the shins and feet.
  • Thyrotoxic crisis. Hyperthyroidism also places you at risk of thyrotoxic crisis — a sudden intensification of your symptoms, leading to a fever, a rapid pulse and even delirium. If this occurs, seek immediate medical care.
Treatment:
Several treatments for hyperthyroidism exist. The best approach for you depends on your age, physical condition and the severity of your disorder:
  • Radioactive iodine. Taken by mouth, radioactive iodine is absorbed by your thyroid gland, where it causes the gland to shrink and symptoms to subside, usually within three to six months. Because this treatment causes thyroid activity to slow considerably, you may eventually need to take a medication every day to replace thyroxine.
  • Anti-thyroid medications. These medications gradually reduce symptoms of hyperthyroidism by preventing your thyroid gland from producing excess amounts of hormones. They include propylthiouracil and methimazole (Tapazole). Symptoms usually begin to improve in six to 12 weeks, but treatment with anti-thyroid medications typically continues at least a year and probably longer. For some people, this clears up the problem permanently, but other people may experience a relapse.
  • Beta blockers. These drugs are commonly used to treat high blood pressure. They won't reduce your thyroid levels, but they can reduce a rapid heart rate and help prevent palpitations. For that reason, your doctor may prescribe them until your thyroid levels are closer to normal.
  • Surgery (thyroidectomy). If you can't tolerate anti-thyroid drugs and don't want to have radioactive iodine therapy, you may be a candidate for thyroid surgery, although this is an option in only a few cases.

    In a thyroidectomy, your doctor removes most of your thyroid gland. Risks of this surgery include damage to your vocal cords and parathyroid glands — four tiny glands located on the back of your thyroid gland that help control the level of calcium in your blood. In addition, you'll need lifelong treatment with levothyroxine to supply your body with normal amounts of thyroid hormone. If your parathyroid glands also are removed, you'll need medication to keep your blood-calcium levels normal.

Graves' ophthalmopathy
If Graves' disease affects your eyes, you can manage mild symptoms by avoiding wind and bright lights and using artificial tears and lubricating gels. If your symptoms are more severe, your doctor may recommend treatment with corticosteroids, such as prednisone, to reduce swelling behind your eyeballs. In some cases, a surgical procedure may be an option:
  • Orbital decompression surgery. In this surgery, your doctor removes the bone between your eye socket and your sinuses — the air spaces next to the eye socket. When the procedure is successful, it improves vision and provides room for your eyes to return to their normal position. But there is a risk of complications, including double vision that persists or appears after surgery.
  • Eye muscle surgery. Sometimes scar tissue from Graves' ophthalmopathy can cause one or more eye muscles to be too short. This pulls your eyes out of alignment, leading to double vision. Eye muscle surgery may help correct double vision by cutting the affected muscle from the eyeball and reattaching it farther back. The goal is to achieve single vision when you read and look straight ahead. In some cases, you may need more than one operation to attain these results.
Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.
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