Hyperthyroidism

Introduction

Have you been losing weight with no explanation, such as a new diet or exercise? Do you find yourself hot in a room where everyone else is cold or feels comfortable? Do you feel that your heart has been racing or beating harder than normal? If so, you may have a malfunctioning thyroid or pituitary gland - specifically, a condition known as hyperthyroidism or high thyroid hormone levels. Hyperthyroidism is a syndrome that affects approximately 2 to 3 out of every 100 women and 2 out of every thousand men. The incidence increases as age increases. While these percentages may seem small, hyperthyroidism is actually the third most common disease of a hormone-producing gland, trailing only diabetes and hypothyroidism. Read on to learn more about this condition.

What is it?

Hyperthyroidism is a medical condition caused by the effects of too much thyroid hormone on tissues of the body. Although there are several different causes of hyperthyroidism, most of the symptoms that patients experience are the same regardless of the cause (see the list of symptoms below). Because the body's metabolism is increased, patients often feel hotter than those around them and can slowly lose weight even though they may be eating more. Sometimes patients actually gain weight because of an increase in their appetite. Patients with hyperthyroidism usually experience fatigue at the end of the day, but have trouble sleeping. Trembling of the hands and a hard or irregular heartbeat (called palpitations) may develop. These individuals may become irritable and easily upset. When hyperthyroidism is severe, patients can suffer shortness of breath, chest pain, and muscle weakness. Symptoms can continue for weeks or months before patients fully realize that they are sick.

So what is the thyroid gland and why is thyroid hormone important? The thyroid gland is a small, butterfly-shaped gland located in the neck just under the Adam's apple. The thyroid gland produces thyroid hormone, which acts on many different parts of the body including the muscles, brain, heart, intestines, and skin and helps regulate many bodily functions such as water balance, fat and sugar metabolism, and body temperature. The thyroid gland and its release of thyroid hormone are actually controlled by other glands in the body, the pituitary and hypothalamus. The hypothalamus senses the level of thyroid hormone in the blood and releases a hormone called thyrotropin releasing hormone (TRH). TRH stimulates the pituitary to release thyroid stimulating hormone (TSH) which then acts on the thyroid to secrete thyroid hormones.

Hypothalamus: thyrotropin releasing hormone (TRH)
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Anterior Pituitary: thyroid stimulating hormone (TSH)
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Thyroid: thyroid hormones (T3 and T4)

What causes it?

Numerous factors have been identified for causing hyperthyroidism.

  1. Graves' Disease

    Graves' disease occurs when the immune or protective mechanisms of the body mistakenly activate the thyroid gland to release thyroid hormone. This is the primary cause of hyperthyroidism and usually causes protrusion of the eyes, redness on the front of the legs, and other signs and symptoms associated with hyperthyroidism as listed below.

  2. Pituitary adenoma

    A pituitary adenoma is a tumor that secretes a hormone that activates the thyroid gland above and beyond normal stimulation. This causes the release of thyroid hormone in excess and the signs and symptoms of hyperthyroidism.

  3. Pituitary resistance

    Normally, circulating thyroid hormone prevents the hypothalamus and pituitary from calling for unnecessary thyroid hormone, similar to the way a warm room prevents a thermostat from releasing more heat into the room. Sometimes the pituitary does not respond to the stimulation it receives from thyroid hormones and continues to release more TSH to the thyroid gland. More thyroid hormone is released which causes the signs and symptoms associated with hyperthyroidism.

  4. Toxic adenoma

    This is a type of tumor that is an abnormal extension of the thyroid gland which releases excess thyroid hormone. This tumor does not need releaser hormone from the pituitary so it continuously releases thyroid hormone on its own.

  5. Multinodular goiters

    Multinodular goiter disease, the second most common cause of hyperthyroidism, is characterized by soft nodules that grow slowly within the thyroid. They can produce thyroid hormone on their own to cause signs and symptoms of hyperthyroidism. Multinodular goiters are often asymptomatic, however, they can grow large and compress the windpipe to cause difficulty breathing or swallowing.

  6. Inflammatory thyroid disease

    Sometimes the thyroid can become inflamed, usually from a virus or occasionally after childbirth. Inflammation from a virus usually is painful and lasts from two to six months. The cause following pregnancy is poorly understood and can reoccur with subsequent pregnancies.

  7. Ectopic thyroid tissue

    Other tissues and organs of the body can abnormally produce another source of thyroid hormone. Examples are tumors in the ovaries and follicular cancer.

  8. Medication

    Hypothyroid patients that are overtreated with thyroid medication can actually become hyperthyroid and display signs and symptoms of excess thyroid hormone. About 2% of patients on amiodarone will become hyperthyroid due to the drug's high concentration of iodine (37% by weight) in its molecular structure. This, through a number of steps, can ultimately cause an increased release of thyroid hormone into the blood stream.

Who has it?

Hyperthyroidism affects 4 to 5 million people in the United States. The condition occurs eight to ten times more commonly in women (approximately 2-3% of women) than in men. As many as 50% of people in the community have microscopic nodules and 15% have goiters that are big enough to be palpated (felt by pushing on the area). Over 30 million Americans have an abnormal thyroid-stimulating hormone (TSH) level, indicating the possibility of thyroid disease without symptoms.

What are the risk factors?

  • Pregnancy - five to eight percent of women develop postpartum inflammation of the thyroid
  • Age 20 to 50 years
  • Women are more likely than men to develop hyperthyroidism
  • Family history of Graves' disease or other forms of hyperthyroidism increases your risk
  • Japanese ancestry appear to be at greater risk of hyperthyroidism

What are the symptoms?

  • Nervousness and irritability
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  • Thinning of hair
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  • Increased resting heart rate
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  • Separation of the nail from the nail bed
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  • Palpitations
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  • Moist skin
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  • High blood pressure
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  • Decreased menstrual flow
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  • Heat intolerance and increased sweating
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  • Impaired fertility
  • Tremor
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  • Mental disturbances
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  • Weight loss, unexplained
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  • Sleep disturbances (including insomnia)
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  • Frequent bowel movements
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  • Thyroid enlargement
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  • Sudden paralysis
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  • Thick redness on the front of legs (with Graves' disease)
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  • Significant protrusion of the eyes due to swelling of the tissue behind them (with Graves' disease)
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    Hyperthyroidism can be missed by many practitioners because of its wide range of symptoms. If you have any of the above symptoms, you should have a thyroid function lab panel done to rule out or confirm the diagnosis.

    How is it treated?

    The goals of treatment for hyperthyroidism include the elimination of excess thyroid hormone production, the relief of symptoms, and the prevention of becoming hypothyroid after treatment.

    In cases where the thyroid is producing too much thyroid hormone, drugs can be given that block the hormone's formation or its conversion to a more active form. This drug class is called thionamides and includes two drugs, methimazole and propylthiouracil. They are indicated in Graves' disease to induce remission and usually cause a decrease in hormone levels and symptoms within 4-8 weeks. Dose changes are likely necessary over this beginning period but should be able to be tapered down as thyroid function normalizes. Therapy usually lasts for 1-2 years with an average remission rate of almost 50%. If relapse occurs, radioactive iodine is an alternate therapy.

    Iodides are used in combination with surgery as a means to rapidly acquire a euthyroid state (normal thyroid function or normal levels of TSH,) or with radioactive iodine (see below) to prevent thyroid hormone release. Iodides block thyroid hormone release, inhibit the hormone's formation, and decrease the size of the thyroid gland.

    Beta blockers are often given to help control symptoms such as palpitations, increased heart rate, sweating, and anxiety. They do not affect the level of thyroid hormone in the blood but act on the heart within hours to provide relief. They may cause fatigue, nausea, or light headedness, but are usually well-tolerated if started at a lower dose and slowly increased. In most cases, unless the physician and patient carefully monitors, beta blockers should not be used by those with asthma, heart failure, COPD, or a resting heart rate below 60. An alternative to control the heart rate and these symptoms is diltiazem.

    Radioactive Iodine is the agent of choice to treat Graves' disease, toxic adenoma, and multinodular goiters. It is a liquid that concentrates in the thyroid gland and causes ablation (destruction of the cells.) This therapy commonly causes hypothyroidism which results in the need for thyroid hormone supplementation.

    Thyroid removal is uncommonly performed in the United States. If surgery is elected for a patient with a toxic nodule, the surgeon removes the part of the thyroid which is dysfunctional and the thyroid remnant usually resumes normal function. However, if the entire thyroid is over productive, as in Graves' disease, the surgeon must remove most or the entire gland. In such cases, the patient must then take thyroid hormone replacement pills for the rest of his or her life. Candidates for surgery may include pregnant hyperthyroid patients intolerant of antithyroid drugs, patients desiring definitive therapy without the use of radioactive iodine, children, and patients with very large or nodular goiters.

    Thyroid storm, also called thyrotoxic crisis, is a life threatening medical emergency where a hyperthyroid patient enters a high metabolic state. It is a rare condition, more likely in adolescents and females, but extremely fatal (mortality rate > 50%) if untreated. Presentation is that of an extreme level of thyroid hormones and includes fever, fast heart rate, delirium, nausea, vomiting, diarrhea, high blood pressure. Untreated thyroid storm progresses to heart failure, low blood pressure with shock, arrhythmias, seizures, and coma.

    Factors that can cause thyroid storm are infection, surgery, trauma, treatment with radioactive iodine, pregnancy, and an overdose of thyroid hormone. Treatment is aimed at suppressing thyroid function, usually with high doses of propylthiouracil. Steroids, beta blockers and supportive therapy to correct fluids and prevent arrhythmias are often given.

    What is on the horizon?

    There is a procedure, termed arterial embolization that is being used and is less invasive than the standard thyroid surgical procedure. It works by cutting off the blood flow in the arteries that feed the thyroid gland. This procedure enables the function of the thyroid gland to return to normal.

    References

    1. Harrison's Principles of Internal Medicine, 14th ed. McGraw Hill; 2001.
    2. Wang C, Crapo LM. The epidemiology of thyroid disease and implications for screening. Endocrinol Metab Clin North Am. 1997 Mar;26(1):189-218.
    3. Woeber, KA. Update on the management of hyperthyroidism and hypothyroidism. Archives of Family Medicine. 2000; 9: 743-747.
    4. Abhay Singhal, MD. Thyroid Storm. Available at www.emedicine.com. Accessed December 6, 2005
    5. Talbert RL. Thyroid disorders. In: Dipiro JT, Talbert RL, Yee GC et al, eds. Pharmacotherapy: a pathophysiologic approach. 6th Ed. New York: McGraw-Hill, 2005: 1369-1381.
    6. The American Thyroid Association. Available at: http://www.thyroid.org/ Accessed August 23, 2007.
    7. The Thyroid Foundation of America. Available at: http://www.tsh.org/ Accessed August 23, 2007.

    Hyperthyroidism Health Condition Last Updated: August 2007

    Note: The above information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist, or other healthcare professional. It is not intended to diagnose a health condition, but it can be used as a guide to help you decide if you should seek professional treatment or to help you learn more about your condition once it has been diagnosed.

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