Located in the front of the neck, the thyroid gland produces the hormones thyroxine (T4) and triiodothyronine (T3) that regulate thebody's metabolic rate by helping to form protein ribonucleic acid (RNA) andincreasing oxygen absorption in every cell. In turn, the production of thesehormones are controlled by thyroid-stimulating hormone (TSH) that is producedby the pituitary gland. When production of the thyroid hormones increases despite the level of TSH being produced, hyperthyroidism occurs. The excessiveamount of thyroid hormones in the blood increases the body's metabolism, creating both mental and physical symptoms.
Curiously, the thyroid gland is often enlarged whether it is making too muchhormone, too little, or sometimes even when it is functioning normally. TSH increases the amount of thyroxin secreted by the thyroid and also causes the thyroid gland to grow.
- Hyperthyroid goiter--If the amount of stimulating hormone is excessive, the thyroid will both enlarge and secrete too much thyroxin. The result--hyperthyroidism with a goiter. Graves' disease is the most common form of this disorder.
- Euthyroid goiter--The thyroid is theonly organ in the body to use iodine. If dietary iodine is slightly inadequate, too little thyroxin will be secreted, and the pituitary will sense the deficiency and produce more TSH. The thyroid gland will enlarge enough to make sufficient thyroxin.
- Hypothyroid goiter--If dietary iodine is severelyreduced, even an enlarged gland will not be able to make enough thyroxin. The gland will keep growing under the influence of TSH, but it may never be able to make enough thyroxin.
The term hyperthyroidism covers any disease which results in overabundance ofthyroid hormone. Other names for hyperthyroidism, or specific diseases within the category, include Graves' disease, diffuse toxic goiter, Basedow's disease, Parry's disease, and thyrotoxicosis. The disease is 10 times more commonin women than in men, and the annual incidence of hyperthyroidism in the United States is about one per 1,000 women. Although it occurs at all ages, hyperthyroidism is most likely to occur after the age of 15. There is a form of hyperthyroidism called Neonatal Grave's disease, which occurs in infants bornof mothers with Graves' disease. Occult hyperthyroidism may occur in patientsover 65 and is characterized by a distinct lack of typical symptoms. Diffusetoxic goiter occurs in as many as 80% of patients with hyperthyroidism.
Hyperthyroidism is often associated with the body's production of autoantibodies in the blood which cause the thyroid to grow and secrete excess thyroid hormone. This condition, as well as other forms of hyperthyroidism, may be inherited. Regardless of the cause, hyperthyroidism produces the same symptoms,including weight loss with increased appetite, shortness of breath and fatigue, intolerance to heat, heart palpitations, increased frequency of bowel movements, weak muscles, tremors, anxiety, and difficulty sleeping. Women may also notice decreased menstrual flow and irregular menstrual cycles.
Patients with Graves' disease often have a goiter (visible enlargement of thethyroid gland), although as many as 10% do not. These patients may also havebulging eyes. Thyroid storm, a serious form of hyperthyroidism, may show upas sudden and acute symptoms, some of which mimic typical hyperthyroidism, aswell as the addition of fever, substantial weakness, extreme restlessness, confusion, emotional swings or psychosis, and perhaps even coma.
Excess TSH (or similar hormones), cysts, and tumors will enlarge the thyroidgland. Of these, TSH enlarges the entire gland while cysts and tumors enlargeonly a part of it.
The only symptom from a goiter is the large swelling just above the breast bone. Rarely, it may constrict the trachea (windpipe) or esophagus and cause difficulty breathing or swallowing. The rest of the symptoms come from thyroxinor the lack of it.
Physicians will look for physical signs and symptoms indicated by patient history. On inspection, the physician may note symptoms such as a goiter or eyebulging. Other symptoms or family history may be clues to a diagnosis of hyperthyroidism. An elevated body temperature (basal body temperature) above 98.6°F (37°C) may be an indication of a heightened metabolic rate (basalmetabolic rate) and hyperthyroidism. A simple blood test can be performed todetermine the amount of thyroid hormone in the patient's blood. The diagnosisis usually straightforward with this combination of clinical history, physical examination, and routine blood hormone tests. Radioimmunoassay, or a testto show concentrations of thyroid hormones with the use of a radioisotope mixed with fluid samples, helps confirm the diagnosis. A thyroid scan is a nuclear medicine procedure involving injection of a radioisotope dye which will tag the thyroid and help produce a clear image of inflammation or involvement of the entire thyroid. Other tests can determine thyroid function and thyroid-stimulating hormone levels. Ultrasonography, computed tomography scans (CT scan), and magnetic resonance imaging (MRI) may provide visual confirmation ofa diagnosis or help to determine the extent of involvement.
The size, shape, and texture of the thyroid gland help the physician determine the cause of goiter. A battery of blood tests are required to verify the specific thyroid disease. Functional imaging studies using radioactive iodine determine how active the gland is and what it looks like.
Treatment will depend on the specific disease and individual circumstances such as age, severity of disease, and other conditions affecting a patient's health.
Antithyroid drugs are often administered to help the patient's body cease overproduction of thyroid hormones. This medication may work for young adults, pregnant women, and others. Women who are pregnant should be treated with thelowest dose required to maintain thyroid function in order to minimize the risk of hypothyroidism in the infant.
Radioactive iodine is often prescribed to damage cells that make thyroid hormone. The cells need iodine to make the hormone, so they will absorb any iodine found in the body. The patient may take an iodine capsule daily for severalweeks, resulting in the eventual shrinkage of the thyroid in size, reduced hormone production and a return to normal blood levels. Some patients may receive a single larger oral dose of radioactive iodine to treat the disease morequickly. This should only be done for patients who are not of reproductive age or are not planning to have children, since a large amount can concentratein the reproductive organs (gonads).
Some patients may undergo surgery to treat hyperthyroidism. Most commonly, patients treated with thyroidectomy, in the form of partial or total removal ofthe thyroid, suffer from large goiter and have suffered relapses, even afterrepeated attempts to address the disease through drug therapy. Some patientsmay be candidates for surgery because they were not good candidates for iodine therapy, or refused iodine administration. Patients receiving thyroidectomy or iodine therapy must be carefully monitored for years to watch for signsof hypothyroidism, or insufficient production of thyroid hormones, which canoccur as a complication of thyroid production suppression.
Goiters of all types will regress with treatment of the underlying condition.Dietary iodine may be all that is needed. However, if an iodine deficient thyroid that has grown in size to accommodate its deficiency is suddenly supplied an adequate amount of iodine, it could suddenly make large amounts of thyroxin and cause a thyroid storm, the equivalent of racing your car motor at top speed.
Hyperthyroidism can be treated with medications, therapeutic doses of radioactive iodine, or surgical reduction. Surgery is much less common now than it used to be because of progress in drugs and radiotherapy.
Hyperthyroidism is generally treatable and carries a good prognosis. Most patients lead normal lives with proper treatment. Thyroid storm, however, can belife-threatening and can lead to heart, liver, or kidney failure.
Although goiters diminish in size, the thyroid may not return to normal. Sometimes thyroid function does not return after treatment, but thyroxin is easyto take as a pill.
There are no known prevention methods for hyperthyroidism, since its causes are either inherited or not completely understood. The best prevention tacticis knowledge of family history and close attention to symptoms and signs of the disease. Careful attention to prescribed therapy can prevent complicationsof the disease.
Euthyroid goiter and hypothyroid goiter are common around the world because many regions have inadequate dietary iodine, including some places in the United States. International relief groups are providing iodized salt to many ofthese populations. Because mental retardation is a common result of hypothyroidism in children, this is an extremely important project.