Understanding Hyperthyroidism
By Mayo Clinic Staff
Hyperthyroidism, or overactive thyroid, is a condition in which the thyroid gland produces too much of the hormone thyroxine.
The condition can accelerate the body’s metabolism significantly, causing sudden weight loss, a rapid or irregular heartbeat, sweating, and nervousness or irritability.
Several treatment options for hyperthyroidism are available. Doctors use anti-thyroid medications and radioactive iodine to slow the production of thyroid hormones. Sometimes, treatment involves surgery to remove all or part of the thyroid gland.
Hyperthyroidism can become serious if ignored, but most people respond well once their hyperthyroidism is diagnosed and treated.
The thyroid is a butterfly-shaped gland at the base of the neck, just below the Adam’s apple. Although it weighs less than an ounce, the thyroid gland has an enormous impact on the person’s health. Every aspect of one’s metabolism is regulated by thyroid hormones.
The thyroid gland produces two main hormones, thyroxine (T-4) and triiodothyronine (T-3), which influence every cell in the body. These hormones maintain the rate at which the body uses fats and carbohydrates, help control body temperature, influence heart rate, and help regulate the production of protein. The thyroid also produces calcitonin, a hormone that helps regulate the amount of calcium in your blood.
The rate at which T-4 and T-3 are released is controlled by the pituitary gland and the hypothalamus – an area at the base of the brain that acts as a thermostat for one’s whole system. Here’s how the process works:
The hypothalamus signals the pituitary gland to make a hormone called thyroid-stimulating hormone (TSH). The pituitary gland then releases TSH, the amount of which depends on how much T-4 and T-3 are in the blood. If there’s not enough T-4 and T-3 in the blood, the TSH will rise; if there’s too much, the TSH level will fall. The 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.
Normally, the 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, an autoimmune disorder in which antibodies produced by the immune system stimulate the thyroid to produce too much T-4, and the antibodies mistakenly attack the thyroid and occasionally attack the tissue behind the eyes and the skin, often in the lower legs over the shins. It is the most common cause of hyperthyroidism. Scientists aren’t sure exactly what causes Graves’disease, although several factors – including a genetic predisposition – are likely involved.
Plummer’s Disease, a form of hyperthyroidism that occurs when one or more adenomas of the 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 the thyroid gland can become inflamed for unknown reasons. The inflammation can cause excess thyroid hormone stored in the gland to leak into the bloodstream. One rare type of thyroiditis, known as subacute granulomatous thyroiditis, causes pain in the thyroid gland. Other types are painless and may sometimes occur after pregnancy (postpartum thyroiditis).
RISK FACTORS
Hyperthyroidism, particularly Graves’ disease, tends to run in families and is more common in women than in men. If a member of the family has a thyroid condition, a doctor must be sought as to what it may mean for the health of other family members.
COMPLICATIONS
Hyperthyroidism can lead to a number of complications: Heart problems. Some of the most serious complications of hyperthyroidism involve the heart, including a rapid heart rate, a heart rhythm disorder called atrial fibrillation and congestive heart failure – a condition in which the heart can’t circulate enough blood to meet the 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 the bones depends, in part, on the amount of calcium and other minerals they contain. Too much thyroid hormone interferes with the body’s ability to incorporate calcium into the bones.
Eye problems. People with Graves’ op ht hal mo pa thy develop eye problems, including bulging, red or swollen eyes, sensitivity to light, and blurring or double vision. If 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 entails risk of thyrotoxic crisis – a sudden intensification of symptoms, leading to a fever, a rapid pulse and even delirium. If this occurs, medical attention must be sought immediately. (www.