Hyperthyroidism (overactive thyroid) is a condition in which your thyroid gland produces too much of the hormone thyroxine. Hyperthyroidism can accelerate your body’s metabolism significantly, 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 involves surgery to remove all or part of your thyroid gland. Although hyperthyroidism can be serious if you ignore it, most people respond well once hyperthyroidism is diagnosed and treated.
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 the amount and type of food you eat remain the same or even increase
⦁Rapid heartbeat (tachycardia) — commonly more than 100 beats a minute — irregular heartbeat (arrhythmia) or pounding of your heart (palpitations)
⦁Nervousness, anxiety and irritability
⦁Tremor — usually a fine trembling in your hands and fingers
⦁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
⦁Fine, brittle hair
Older adults are more likely to have either no signs or 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 signs of hyperthyroidism.
Sometimes an uncommon problem called Graves’ ophthalmopathy may affect your eyes, especially if you smoke. In this disorder, your eyeballs protrude beyond their normal protective orbits when the tissues and muscles behind your eyes swell. This pushes the eyeballs forward so far that they actually bulge out of their orbits. This can cause the front surface of your eyeballs to become very dry. Eye problems often improve without treatment.
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
When to see a doctor
If you experience unexplained weight loss, a rapid heartbeat, unusual sweating, swelling at the base of your neck or other 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 as advised so that he or she can monitor your condition.
A number of conditions, including Graves’ disease, toxic adenoma, Plummer’s disease (toxic multinodular goiter) and thyroiditis, can cause hyperthyroidism.
Your thyroid is a butterfly-shaped gland situated 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 is regulated by thyroid hormones.
Your thyroid gland produces two main hormones, thyroxine (T-4) and triiodothyronine (T-3), 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 also produces calcitonin, a hormone that helps regulate the amount of calcium in your blood.
How it all works
The rate at which T-4 and T-3 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 T-4 and T-3 are in your blood. If you don’t have enough T-4 and T-3 in your blood, your TSH will rise; if you have too much, your TSH level will fall. Finally, your thyroid gland regulates its production of hormones based on the amount of TSH it receives. If the thyroid gland is diseased and is releasing too much thyroid hormone on its own, the TSH blood level will remain below normal; if the diseased thyroid gland cannot make enough thyroid hormone, the TSH blood level will remain high.
Reasons for too much thyroxine (T-4)
Normally, your thyroid releases the right amount of hormones, but sometimes it produces too much T-4. This may occur for a number of reasons, including:
⦁Graves’ disease. Graves’ disease, an autoimmune disorder in which antibodies produced by your immune system stimulate your thyroid to produce too much T-4, is the most common cause of hyperthyroidism. 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 and occasionally attack the tissue behind your eyes (Graves’ ophthalmopathy) and the skin, often in your lower legs over the shins (Graves’ dermopathy). 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 T-4. 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 T-4, 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).
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 generally are 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. Untreated, severe eye problems can lead to vision loss.
⦁Red, swollen skin. In rare cases, people with Graves’ disease develop Graves’ dermopathy, which 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.
Tests and diagnosis
Hyperthyroidism is diagnosed using:
⦁Medical history and physical exam. 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.
⦁Blood tests. A 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 — and 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 and your radioiodine uptake is low, you may have thyroiditis.
Be sure to tell your doctor if you have had a recent X-ray or a computerized tomography scan in which you had contrast material was injected. The results of your radioiodine test may be influenced by these procedures.
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.