Hyperthyroidism

Definition
Hyperthyroidism, also known as overactive thyroid, is a condition that occurs when the thyroid gland produces too much of the hormones triiodothyronine (T3) and thyroxine (T4).

Anatomy
The thyroid gland is located in the neck, just below the voice box and on top of the windpipe. This butterfly-shaped gland produces T3 and T4, which help regulate several body systems, including metabolism and the conversion of calories to energy. The thyroid hormones also help control body temperature, growth and skeletal development, heart rate and function, muscle tone and function, nervous system development, mental function and body weight. When the gland produces too much of the thyroid hormones, your metabolism speeds up.

Causes/associated factors
Hyperthyroidism is a common condition. It often develops around ages 30 to 40 or older, and it's especially prevalent in women. Hyperthyroidism may develop for many reasons, including:
inappropriate and excessive use of medications prescribed for a known thyroid condition
exposure to large doses of iodine or medications containing iodine
a viral infection that inflames the thyroid gland, resulting in temporary overactivity
postpregnancy thyroiditis (inflammation of the thyroid gland)
one or more benign tumors that enlarge the thyroid gland, or, rarely, cancer
Graves' disease (autoimmune thyroid disease), the most common type of hyperthyroidism
pituitary tumor
rarely, an ovarian tumor
Sometimes, infants born to mothers with thyroid disorders develop transient hyperthyroidism. In other cases, the cause of hyperthyroidism is unknown.

Risk factors for hyperthyroidism may include a genetic predisposition or history of autoimmune disorders (when the body produces antibodies, compounds that help neutralize or destroy foreign substances in the blood, to fight against its own tissues), thyroid nodules, excessive iodine exposure or intake of thyroid hormones.


Signs/symptoms
Age often affects the symptoms associated with hyperthyroidism. For example, infants may be born prematurely, appear irritable, and be overly alert with their eyes wide open. They may also have rapid breathing or a rapid heartbeat, run a fever, and develop jaundice (yellowing of the skin and whites of the eyes). People age 70 and older, on the other hand, may appear apathetic or inactive and complain of fatigue, an irregular heartbeat or appetite loss.
Without diagnosis and treatment, symptoms will increase in severity. Because the thyroid hormone affects so many bodily functions, possible symptoms may include:

goiter (enlarged thyroid gland)
rapid pulse rate and heart palpitations
hair loss
thinning of skin
nervousness
heat intolerance and excessive sweating
weight loss despite an increased appetite
frequent and/or loose bowel movements
red or inflamed eyes
exophthalmos (protruding or bulging eyeballs)
a grainy feeling in the eyes
blurred or double vision
excess tearing
decreased eye movement
visual sensitivity to light
mood swings
muscle weakness
red, thickened and lumpy skin over the shins or tops of the feet
swollen skin around the base of the fingernails
for men, enlarged breasts

Diagnosis
The doctor will review your medical history and do a physical exam. You'll probably need blood tests to measure your thyroxine (T4) levels. Other thyroid hormone studies may measure T3 resin uptake, T3, free T3, free T4 and TSH. Depending on the circumstances, you may also need a thyroid scan. With this test, you drink (or take in pill form) a radioactive iodine substance and a picture of your thyroid gland is taken. This test indicates the overall level of thyroid functioning by measuring the amount of iodine the thyroid gland takes from the body. (Because this test may not be done if you're pregnant, doctors often give pregnancy tests to women before doing a radioactive iodine uptake test.) To evaluate the size and position of the gland, a thyroid scintiscan (a test that makes a map of emissions from radioactive substances) may be done. Antithyroid antibodies (antibodies that attack the thyroid gland) may also be measured.

Treatment
The goal of treatment is to decrease thyroid hormone production to normal levels. Treatment options may include medication, radioactive iodine, or surgical removal of part or all of the thyroid gland. If the condition is caused by a viral illness, the doctor may recommend simple observation.
If you're being treated for hyperthyroidism, keep the following self-care measures in mind:

Do not stop taking your medication or adjust the dosages without consulting your doctor.
Get adequate rest.
Eat a well-balanced diet and drink plenty of fluids.
Keep follow-up appointments with your doctor, even if you're feeling well.
Ask your doctor if you need regular checkups with an ophthalmologist for eye care.
Medications
Antithyroid medications such as propylthiouracil (PTU) or methimazole (brand name Tapazole) decrease the amount of thyroid hormone produced, which, in turn, eases the symptoms of hyperthyroidism. Improvement is usually noticed in about two to four weeks. If treating Graves' disease, you may need to take the medication for one to two years. Rarely, propylthiouracil or methimazole can cause agranulocytosis (decreased white blood cells), which may lower your resistance to infection. If you develop a sore throat, fever or rash while taking propylthiouracil or methimazole, contact your doctor immediately for a white blood cell count.

Your doctor may also prescribe beta-adrenergic blocking drugs, such as atenolol or propranolol, which control symptoms by blocking the action of thyroxine in the body. This can help reduce the racing heart, shakes and nervousness. These drugs may not be prescribed if you have asthma or other lung problems, however.

Radioactive iodine therapy
Radioactive iodine is given orally, usually as a one-time dose. The thyroid gland absorbs it from the bloodstream, and the radiation destroys part or all of the gland. Symptoms often improve because the partially destroyed gland can't produce as much hormone. An expected side effect of radioactive iodine is hypothyroidism or underactive thyroid. Since hypothyroidism from radioactive iodine therapy may take years to develop, you'll need periodic thyroid testing indefinitely.

Surgery
Surgical removal of part or all of the thyroid gland decreases the amount of thyroid hormones produced and released into your bloodstream. Complications of surgery are rare, but may include recurrent hyperthyroidism if not enough thyroid tissue is removed, hypothyroidism if too much thyroid tissue is removed. Injury to nerves in the throat may cause hoarseness. Injury to the parathyroid glands (the glands that secrete the parathyroid hormone, which regulates calcium and phosphorus metabolism) is also possible.


Complications
When properly treated, complications may include continued hyperthyroidism or a new case of hypothyroidism.
If left untreated, hyperthyroidism can lead to osteoporosis (bone loss), atrophy (shrinking) of the muscles, paralysis, infertility, eye problems or disorders, heart problems (such as an irregular heart rhythm or heart failure) and possible stroke.

If there is a severe, sudden overproduction of thyroid hormones, a thyroid crisis or storm may develop. Physically stressful events such as traumatic surgery, a severe blood infection or other serious illness may bring on this life-threatening condition. If the crisis is not treated immediately, overstimulation of the heart and nervous system may lead to a high fever, irregular heartbeat, heart failure, collapse or coma. In some cases, a thyroid crisis may be fatal.


Pregnancy-specific information
Hyperthyroidism may affect your menstrual cycle and cause infertility. If you have hyperthyroidism, make sure your obstetrician and endocrinologist (a doctor who specializes in treating disorders of the endocrine glands, such as the thyroid) work together during your pregnancy to manage your condition. Sometimes, childbirth triggers hyperthyroidism.
During pregnancy, hyperthyroidism may increase your risk of certain pregnancy-related complications, including premature delivery, abruptio placenta (early separation of the placenta from the uterus), preeclampsia (pregnancy-induced high blood pressure) or eclampsia (a life-threatening condition for pregnant women and/or fetuses). You are also at a higher risk for congestive heart failure and thyroid storm. Certain medications, such as PTU, may be safely used during pregnancy to treat hyperthyroidism and reduce the risk of these possible complications.

Surgical removal of part or all of the thyroid gland may be considered during the second and third trimesters of pregnancy for certain causes of hyperthyroidism. Because radioactive iodine treatment may damage the thyroid of a developing baby, it is inappropriate for pregnant women. This treatment hasn't been shown to affect fertility or cause birth defects in future children, but waiting at least several months after completing this treatment before attempting to conceive is recommended.


Senior-specific information
If you have an existing heart condition and then develop hyperthyroidism, the heart condition may become considerably more severe. Atrial fibrillation (an irregular heartbeat) may occur, which can increase your risk of stroke. Ask your doctor about the need to consult a cardiologist (a doctor who specializes in treating disorders of the heart) to manage your heart disease.

Prevention
Although hyperthyroidism is usually not preventable, early diagnosis and treatment are important. If you're at risk, ask your doctor about possible testing to detect thyroid abnormalities.