Hyperthyroidism

Definition

Hyperthyroidism is the overproduction of thyroid hormones by an overactive thyroid.

Description

The term hyperthyroidism covers any disease which results in overabundance of thyroid 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.

Located in the front of the neck, the thyroid gland produces the hormones thyroxin (T4) and triiodothyronine (T3), which regulate the body's metabolic rate by helping to form protein ribonucleic acid (RNA) and increasing oxygen absorption in every cell. In turn, the production of these hormones is controlled by thyroid-stimulating hormone (TSH) that is produced by the pituitary gland. When production of the thyroid hormones increases despite the level of TSH being produced, hyperthyroidism occurs. The excessive amount of thyroid hormones in the blood increases the body's metabolism, creating both mental and physical symptoms.

Demographics

Only about 5 percent of all individuals with hyperthyroidism are younger than 15 years of age. About five times as many girls as boys develop hyperthyroidism. Almost all cases of pediatric hyperthyroidism are the form called Graves' disease. There is a form of hyperthyroidism called neonatal Graves' disease, which occurs in infants born of mothers with Graves' disease. Children with other conditions, such as trisomy 21, Addison's disease, diabetes, systemic lupus erythematosus, rheumatoid arthritis, myasthenia gravis, vitiligo, pernicious anemia, and immune thrombocytopenic purpura are more likely to develop Graves' disease.

Causes and symptoms

Hyperthyroidism is often associated with the body's production of autoantibodies in the blood which causes 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. Adolescent girls may also notice decreased menstrual flow and irregular menstrual cycles.

Patients with Graves' disease often have a goiter (visible enlargement of the thyroid gland), although as many as 10 percent do not. These patients may also have bulging eyes. Thyroid storm, a serious form of hyperthyroidism, may show up as sudden and acute symptoms, some of which mimic typical hyperthyroidism, as well as the addition of fever , substantial weakness, extreme restlessness, confusion, emotional swings or psychosis, or coma. Fortunately, such a fulminant course of Graves' disease is rare in children and adolescents.

Babies with neonatal Graves' disease may suffer from prematurity , airway obstruction, and heart failure. Death occurs in as many as 16 percent of these babies, and other complications from which survivors may suffer include craniosynostosis (early closure of the sutures of the skull, which can result in compression of the growing brain), and developmental delay .

When to call the doctor

Parents should contact a child's pediatrician if the child shows the following symptoms: rapid weight loss, shortness of breath, intolerance to heat, heart palpitations, increased frequency of bowel movements, weak muscles, tremors, anxiety, and difficulty sleeping. An enlarged thyroid gland, seen as a bulge in the neck, should be examined by a doctor.

Diagnosis

Physicians will look for physical signs and symptoms indicated by patient history. On inspection, the physician may note symptoms such as a goiter or eye bulging. 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 (basal metabolic rate) and hyperthyroidism. A simple blood test can be performed to determine the amount of thyroid hormone in the patient's blood. The diagnosis is usually straightforward with this combination of clinical history, physical examination, and routine blood hormone tests. Radioimmunoassay (a test to 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 tags the thyroid and helps 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 of a diagnosis or help to determine the extent of involvement.

Treatment

Treatment depends on the specific disease and individual circumstances such as age, severity of disease, and other conditions affecting a patient's health.

Antithyroid drugs

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 the lowest dose required to maintain thyroid function in order to minimize the risk of hypothyroidism in the infant.

Radioactive iodine

Radioactive iodine is often prescribed to damage cells that make thyroid hormone. The cells need iodine to make the hormone, so they absorb any iodine found in the body. The patient may take an iodine capsule daily for several weeks, resulting in the eventual shrinkage of the thyroid, 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 more quickly. 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 concentrate in the reproductive organs (gonads).

Surgery

Some patients may undergo surgery to treat hyperthyroidism. Most commonly, patients treated with thyroidectomy, in the form of partial or total removal of the thyroid, suffer from large goiter and have suffered relapses, even after repeated attempts to address the disease through drug therapy. Some patients may 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 signs of hypothyroidism (insufficient production of thyroid hormones), which can occur as a complication of thyroid production suppression.

Prognosis

Hyperthyroidism is generally treatable and carries a good prognosis. Most patients lead normal lives with proper treatment. Thyroid storm, however, can be life-threatening and can lead to heart, liver, or kidney failure. Luckily, this form of fulminant hyperthyroidism is rare in children and adolescents.

Prevention

As of 2004 there are no known prevention methods for hyperthyroidism; its causes are either inherited or not completely understood. The best prevention tactic is knowledge of family history and close attention to symptoms and signs of the disease. Careful attention to prescribed therapy can prevent complications of the disease.

Parental concerns

Parents should be aware that hyperthyroidism is very rare in young children. However, once diagnosed, the condition needs short- and long-term treatment, with regular follow-up visits to the doctor.

Resources

BOOKS

"Hyperthyroidism." In Nelson Textbook of Pediatrics. Edited by Richard E. Behrman et al. Philadelphia: Saunders, 2004.

PERIODICALS

Hanna, C. E. "Adolescent Thyroid Disorders." Adolescent Medicine 13 (February 2002): 13–35.

ORGANIZATIONS

Thyroid Foundation of America. 350 Ruth Sleeper Hall, RSL 350, Parkman St., Boston, MA 02114. Web site: http://www.clark.net/pub/tfa.

Teresa Norris, RN Rosalyn Carson-DeWitt, MD