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Updated 13 February 2013

Hyperthyroidism

Hyperthyroidism is a condition in which there are too many thyroid hormones circulating through the body.

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Summary

  • Hyperthyroidism is a condition in which there are too many thyroid hormones circulating through the body.
  • The symptoms vary widely and are more pronounced in the later stages of the condition.
  • Reliable testing is available for the diagnosis and treatment of hyperthyroidism.
  • Treatment may consist of medication, surgery and iodine radiation.

Description

Hyperthyroidism is most commonly a condition in which the thyroid gland produces an excessive amount of thyroid hormones, usually because of an overactive thyroid gland. Hyperthyroidism speeds up the body’s chemical processes, causing mental and physical changes. It is also called thyrotoxicosis.

The thyroid is a small gland wrapped around the windpipe below the Adam’s apple. It takes iodine from the food we eat to make iodine-containing hormones called thyroxine (T4) and triiodothyronine (T3). These hormones regulate the rate at which you burn kilojoules for energy. They also regulate growth and the rate of chemical reactions (metabolism) in the body.

Iodine is found in seafood (including seaweed), bread and salt.

Normally the pituitary gland controls the rate of thyroid hormone production. The pituitary gland is located at the base of the brain. When the thyroid does not supply enough thyroid hormones, the pituitary gland releases thyroid-stimulating hormone (TSH) to stimulate the production of thyroid hormones in the thyroid gland. If the thyroid produces an excessive supply of thyroid hormones, the pituitary gland stops production of TSH. This means that high levels of thyroid hormones lower the TSH level, resulting in no further stimulation of the thyroid gland. In hyperthyroidism there are continuously elevated levels of the thyroid hormones.

Cause

The following are causes of hyperthyroidism:

  • Graves’ disease, the most common cause, especially in young individuals
  • Overdosing on replacement thyroid hormones, for example to treat thyroid cancer, or in the case of abuse of these hormones for weight loss
  • Inflammation of the thyroid gland (thyroiditis), usually a temporary cause
  • Nodules or lumps – small non-cancerous growths in the thyroid gland that produce thyroid hormones (this condition, toxic adenoma, is more prevalent in the elderly)
  • Excessive use of iodine-containing drugs, for example cough medicines or amiodarone, which is used for the treatment of heart problems
  • Oversecretion of thyroid hormones after pregnancy (postpartum thyroiditis)
  • A growth on the uterus (trophoblastic tumour) that releases hormones which trigger thyroid hormone production
  • A rare tumour (struma ovarii) on the ovaries that releases thyroid hormones into the body (the tumour contains thyroid tissue)
  • A rare pituitary gland tumour which secretes thyroid-stimulating hormone (TSH)

Symptoms

At first there are no symptoms. Later the symptoms and their severity depend on the severity of the condition, the length of time that hyperthyroidism has been present and the person’s age.

The following symptoms may appear:

  • Restlessness and nervousness
  • Tremors
  • Rapid heart rate or heart flutters (palpitations)
  • Staring eyes and a tendency for eyelids to lag
  • Weight loss despite an increased appetite
  • Sweating and intolerance to heat
  • Frequent bowel movements
  • Fatigue and weakness
  • Insomnia
  • Hair loss
  • Decreased concentration
  • Irregular and decreased menstrual flow
  • Emotional lability

Course

Initially the symptoms of hyperthyroidism are barely noticeable. Older people, for example, often attribute the symptoms to the normal ageing process.

In about 33% of cases, the condition will improve without any treatment, especially if the thyroid gland is only slightly enlarged. The shorter the period of hyperthyroidism, the better the chance of recovery.

Untreated hyperthyroidism could also get worse. Irregular heartbeat, worsening heart failure and chest pain (angina pectoris) could even develop into a life-threatening condition, called thyroid storm or thyroid crisis, although this rarely happens.

Risk factors

  • People with Graves’ disease and those with family members who have Graves’ disease are more likely to develop hyperthyroidism.
  • Women are more likely to develop Graves’ disease, the most common cause of hyperthyroidism.

When to see a doctor

Seek immediate emergency assistance if a diagnosed hyperthyroid person shows signs of shock or delirium. These are the symptoms of thyroid storm or thyroid crisis. If not treated immediately, the person could go into shock and coma, and may die.

See a health professional immediately if a diagnosed hyperthyroid person shows the following symptoms:

  • Extreme irritability or mental disorientation
  • High blood pressure (hypertension)
  • Rapid heartbeat (tachycardia)
  • Vomiting
  • Fever that increases rapidly
  • Jaundice

Make an appointment with a health professional:

  • If you have symptoms of hyperthyroidism
  • If you have swelling on one or both sides of the throat
  • If you have unexplained hoarseness which continues for longer than a week
  • If you have itchy, irritated and puffy eyes that cannot be ascribed to an allergy (possibly indicating Graves’ disease).

Diagnosis

A physical examination, a history of symptoms and laboratory tests are used to diagnose hyperthyroidism. Symptoms, especially in the more advanced stages of the condition, can lead to an initial diagnosis. Blood tests confirm the diagnosis. Hyperthyroidism is determined by testing the levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), the levels of free T4 in the blood, and the levels of the pituitary gland’s thyroid-stimulating hormone, TSH. High levels of thyroid hormones and low levels of TSH indicate an overactive thyroid. In hyperthyroidism caused by diseases (i.e. rarely occurring, secondary hyperthyroidism), the pituitary gland produces too much TSH.

Thyroiditis can be detected by a thyroid scan, which is an X-ray of the thyroid gland after radioactive iodine has been taken by mouth. Other available but expensive tests to rule out other conditions or to determine the specific cause of hyperthyroidism are thyroid ultrasound and radioiode uptake (RAIU) scans.

If a person has severe thyroid eye disease (ophthalmopathy), diagnostic imaging of the eyes may be done to exclude other eye problems, such as tumours.

Treatment

General

It is important to go for thyroid check-ups for the rest of your life once you have been diagnosed with a thyroid problem.

Home

  • Follow the treatment your doctor has prescribed. Do not change the treatment without notifying your doctor.
  • Get enough rest.
  • Raise your head when sleeping.
  • Drink plenty of fluids.
  • Eat regularly and eat a balanced diet.

Medication

It usually takes about eight weeks for antithyroid medication to control hyperthyroidism, but the treatment should continue for a year or longer. Although neither radiation nor surgery is necessary with this drug treatment, the disease frequently recurs.

The antithyroid medication carbinazole may cause skin rashes in about five percent of people.

Where thyroiditis is the cause of hyperthyroidism, beta blockers are prescribed to counteract the effect of the thyroid hormones without altering their levels. The beta blockers will reduce the effect of the hormones on your metabolism and therefore relieve the symptoms. In severe thyroiditis, a corticosteroid may be prescribed to reduce inflammation.

The prescribed treatment will take into account your age, and the type and severity of the condition.

Surgery

Part or all of the thyroid gland or a nodule in the gland may be surgically removed (hemithyroidectomy, subtotal thyroidectomy or total thyroidectomy). In 90% of cases this will cure the disease. However, there are risks associated with surgery, including nerve damage to the vocal cords, accidental removal of the parathyroid glands (located behind the thyroid gland) and low thyroid hormone levels if too much of the thyroid gland is removed. Nowadays this procedure is only done for patients with very large thyroid glands.

Other

The most popular form of treatment is radiation treatment with iodine (I-131) in the form of a capsule or a liquid taken by mouth. The iodine destroys the thyroid tissues by direct radiation. However, repeated treatment usually leads to low levels of thyroid hormones and hypothyroidism, a condition easily treated with medication. Iodine radiation treatment should not be administered during pregnancy.

Prevention

  • Take note of the prevalence of Graves’ disease in your family.
  • Have regular physical examinations.

Reviewed by Dr P.H.S. van Zijl, MB.Ch B. MMed(Int).

 
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