Hyperthyroidism

What is Overactive Thyroid?

Hyperthyroidism (also known an overactive thyroid or thyrotoxicosis) occurs when the thyroid gland produces excessive thyroid hormones - thyroxine (T4) and triiodothyronine (T3). This causes many of the body's functions to speed up. About 2 in 100 women, and 2 in 1000 men, develop hyperthyroidism at some stage of their life.

Although terms "hyperthyroidism" and "thyrotoxicosis" are often used interchangeably, the thyrotoxicosis means a toxic condition that is caused by an excess of thyroid hormones from any cause.

Signs and symptoms of hyperthyroidism

Most symptoms of overactive thyroid are related to an increase in the metabolic rate:

• Nervousness
• Excessive sweating, moist skin
• Fine hair
• Heat intolerance
• Rapid heart rate, palpitations
• Increased frequency of bowel movements
• Trembling hands
• Weight loss in spite of an increased appetite
• Fatigue, muscle weakness
• Decreased concentration
• Light, irregular menstrual periods
• Enlarged thyroid gland

Treatment of Overactive Thyroid

Hyperthyroidism is treatable and usually not a life threatening condition. There are three main forms of the treatment for hyperthyroidism: antithyroid drugs, radioactive iodine therapy, and thyroidectomy. Each of them has its own advantages and limitations and physicians prefer one to another due to reasons of simplicity, cost and availability and also on the severity of hyperthyroidism, existing illnesses and the age of patient.

The goal of any therapy is to correct the hypermetabolic state with the fewest side effects and the lowest incidence of hypothyroidism.

Antithyroid Drugs (ATD)

For people with sustained forms of hyperthyroidism, such as Graves' disease or toxic nodular goiter, ATD are often used. This is the easiest way to treat hyperthyroidism. The goal is to prevent the thyroid from producing hormones.

ATD interfere with the ability of the thyroid gland to synthesize its hormones. They gradually reduce the thyroid hormone levels over 2-8 weeks or longer, and are usually given in high doses until the thyroid gland functions normally (becomes euthyroid). The treatment with ATD usually continues at least a year and often longer.

Methimazole (Tapazole, Thiamazole) inhibits thyroid hormone by blocking oxidation of iodine in thyroid gland. Often, people prefer methimazole taken once or twice daily than propylthiouracil that should be used 3 or 4 times daily.

Propylthiouracil (PTU) is a derivative of thiourea that inhibits organification of iodine by the thyroid gland. It is often used in severe thyrotoxicosis because of the additional inhibition of thyroxine (T4) to triiodothyronine (T3) conversion. The reduction in T3 may help to reduce the symptoms more quickly than does methimazole. Carbimazole, which is used in Europe, is converted into methimazole in the body.

The dose and duration of ATD is based on the age and severity of the hyperactivity and cause of hyperthyroidism.

Indications and Benefits:

• Availability and simplicity.
• They do not cause permanent damage to the thyroid gland.
• ATD work well to control the overactive thyroid.
• May be used for long-term treatment of Graves' disease. In about 20% to 30% of patients with Graves' disease, treatment with ATD for a period of 12 to 18 months will result in prolonged remission of the disease.
• Propylthiouracil is preferred choice in pregnant women with overactive thyroid.
• Preferred treatment by many endocrinologists for children and for adults who refuse radioactive iodine.
• Pretreatment of older and cardiac patients before radioactive iodine or surgery.
• Methimazole and PTU are considered safe for use while breastfeeding.

Limitations:

• High relapse rate (relapse is more likely in smokers, patients with large goiters, and patients with positive thyroid-stimulating antibody levels at the end of therapy). When treatment is stopped, blood tests are performed to see if the hyperthyroid condition returns, which will occur in about half of all patients.
• Methimazole and Propylthiouracil can cause serious liver damage. PTU can cause elevated liver enzymes (30%), and immunoallergic hepatitis (0.1-0.2%). Methimazole can cause rare cholestasis.
• The most common side effects are allergic reactions, such as rash, fever, and arthralgia.
• Rare side effect is called "agranulocytosis". This is a condition in which the white blood cells, which fight infection, disappear from the body. This could be a serious problem if an infection was developed while those white blood cells were low. Fortunately, there is usually a warning when you get agranulocytosis - a fever and a sore throat. Patients who develop a fever and a sore throat should stop the ATD and call right away to get a blood test. If the blood test shows agranulocytosis, patients must remain off the ATD. The white blood cells usually return to normal within one to two weeks.

Beta-blockers

Beta-blockers (e.g., Inderal, Tenormin, Lopressor) are used to immediately relieve the symptoms caused by excessive thyroid hormones. They usually make you feel better within hours. Beta-blockers help to reduce rapid heart rate, palpitations, sweating, nervousness, and agitation.

They won't reduce the thyroid hormone levels in the blood. However, they greatly improve hyperthyroidism symptoms until thyroid hormones levels are reduced by other therapies.

Indications and Benefits:

• Very helpful for all types of hyperthyroidism.
• Prompt relief of the cardiac and nervous system symptoms of hyperthyroidism such as tremor, palpitations, heat intolerance, and nervousness.
• Appropriate for people with temporary forms of hyperthyroidism such as thyroiditis (inflammation of the thyroid gland).
• First line therapy before surgery, radioactive iodine, and ATD.
• Short term therapy in pregnancy.

Limitations:

• Must be used with caution in older people and those with pre-existing heart disease, chronic obstructive pulmonary disease, or asthma.
• Do not cure the hyperthyroidism.

Radioactive Iodine (RAI)

Radioactive iodine therapy is the most widely used permanent treatment of hyperthyroidism in the United States.

The thyroid cells are the only cells in the body that are able to absorb iodine. No other tissue or organ in the body is able to absorb the radioactive iodine. Thyroid cells need iodine to make thyroid hormone, and they take up any form of iodine in the blood stream, whether it is radioactive or not.

By giving radioactive iodine, cells in the thyroid are damaged or destroyed and are unable to produce further thyroid hormone. Radioiodine therapy involves taking a drink, or swallowing a capsule, which contains radioactive iodine. The dose of radioactivity to the rest of the body is very low and is not dangerous. There has been a misconception in the minds of general public and most of the physicians that radioiodine therapy is very harmful. However, since the dose administered is very small and no significant side effects are documented many feel that this cheapest and simplest and probably once for all treatment of hyperthyroidism is underutilized.

Indications and Benefits:

• Inexpensive, highly effective, simple, and safe. Hospitalization is not required.
• High cure rates (80%).
• Treatment of choice for Graves' disease in the United States, multinodular goiter, toxic nodules in patients older than 40 years.
• Because of concern that the radioactive iodine might somehow damage other body cells and have other long-term negative effects, the physicians who first used radioactive iodine therapy were very cautious and observed patients for the rest of their lives. According to the long-term follow-up data no complications from radioiodine have become apparent over many decades of treatment.

Limitations:

• Majority of people who receives radioactive iodine eventually develop post-treatment hypothyroidism (an underactive thyroid), regardless of the received dosage. However, doctors believe this to be an acceptable consequence, since hypothyroidism has fewer long-term complications and can be easily controlled with levothyroxine (Synthroid).
• Delayed control of symptoms.
• Contraindicated in pregnant, breastfeeding, or planning to become pregnant women.
• Can cause transient neck soreness, flushing, and decreased taste.
• Radiation thyroiditis in 1% of patients.
• Radioactive iodine may cause the worsening of thyroid eye disease, so it is not appropriate for people with severe ophthalmopathy.
• May require pretreatment with antithyroid drugs in older or cardiac patients.
• Not recommended for children and adolescents. Treatment of hyperthyroidism in children remains controversial.
• Reluctance to use in women of childbearing years.

Surgery (thyroidectomy)

Thyroid gland surgery is the least used treatment for hyperthyroidism.

In a situation where radioiodine is not available and the patient is not responding to ATD, patients are subjected to a surgery. Surgery (thyroidectomy) involves removing part of the thyroid gland. If too much of the thyroid is removed it is not usually a problem as you can take synthetic form of thyroxine to keep its level normal. It is usually a safe operation, although as with all operations there is a small risk. Thyroidectomy requires 5-10 days of hospitalization.

Indications and Benefits:

• Treatment of choice for people:
  • with very large goitre (thyroid swelling)
  • who cannot tolerate or fail ATD
  • who refuse radioactive iodine
  • who have opthalmopathy (staring/bulging eyes)
  • young women and contemplating pregnancy
  • with severe disease who could not tolerate recurrence
• May be performed for cosmetic reasons.

Limitations:

• Higher risk of complications than with radioactive iodine.
• Risk of hypothyroidism (25%) or hyperthyroid relapse (8%).
• Temporary or permanent hypoparathyroidism or laryngeal paralysis (less than 1%).
• Requires patient to be euthyroid preoperatively with ATD or iodides to avoid thyrotoxic crisis.

Last updated: May, 2011