Hyperthyroidism occurs when the body has too much thyroid hormone which can be caused by an overactive thyroid that makes too much thyroid hormone or by release of thyroid hormone as the gland is destroyed.
An overactive thyroid is the most common cause of hyperthyroidism and can be caused by Graves' disease (also known as diffuse toxic goiter or when the whole thyroid is hyperactive), toxic multinodular goiter (when more than one nodule is hyperactive), or a toxic nodule (when just one nodule is hyperactive). Approximately 1 million patients in the United States have Graves' disease, the most common cause of hyperthyroidism. Other rare causes of hyperthyroidism include certain medications such as amiodarone (used for certain irregular heart rhythms), eating too much iodine, and rare diseases of the ovary or testicles that can cause the thyroid to be over-stimulated.
Signs and Symptoms
Symptoms associated with hyperthyroidism include:
- Nervousness and irritability
- Increased resting heart rate
- Heat intolerance and increased sweating
- Weight loss or alterations in appetite
- Frequent bowel movements
- Sudden paralysis
- Thyroid enlargement (lump in the neck)
- Thick redness on the front of legs (pretibial myxedema), which occurs with Graves' Disease
- Thin, delicate skin and irregular fingernail and hair growth
- Menstrual disturbance (decreased flow)
- Impaired fertility
- Mental disturbances
- Sleep disturbances (including insomnia)
It is very important to keep in mind that the symptoms of hyperthyroidism are non-specific and can be found with a number of other diseases. While these symptoms MAY be found in patients with hyperthyroidism, the symptoms do not make the diagnosis. The diagnosis of hyperthyroidism is made with blood tests and careful evaluation by an experienced physician.
A patient's history and physical exam are important factors in making the diagnosis of hyperthyroidism. Some patients may have tachycardia (i.e. a rapid heart rate), arrhythmias (i.e. an irregular heart rate such as atrial fibrillation), tremors, thyroid bruit (i.e. a rushing sound in the thyroid when listened to with a stethoscope), a larger than normal thyroid, and eye abnormalities (dryness, bulging eyes, double vision). Blood tests are critical to confirming the diagnosis. Patients with hyperthyroidism will usually have a low TSH and a higher than normal T4 and/or T3 level. In fact, some patients may have no symptoms at all, but blood tests that make the diagnosis of hyperthyroidism.
Once the diagnosis is made, patients will have a RAI scan (i.e. radioactive iodine scan). In this test, patients are given a small dose of radioactive iodine that homes into the thyroid and reveals which areas of the thyroid are hyperactive or "hot." The RAI scan will determine if the hyperthyroidism is caused by an overactive thyroid (i.e. the thyroid will be hotter than normal) or destruction from thyroiditis (i.e. the thyroid will be colder than normal). If the thyroid is overactive, the RAI scan will determine if the whole gland is hyperactive as in Graves' disease or just certain areas as in toxic multinodular goiter, or if just one area is hyperactive as in a toxic nodule.
Hyperthyroidism may be treated with
- medications (anti-thyroid medications),
- radioactive iodine ablation (RAI ablation),
- removal of the thyroid gland (hemithyroidectomy or total thyroidectomy).
Ultimately, the choice of treatment depends on the cause of hyperthyroidism as well as a number of patient-related factors. Thyroiditis often does not require specific treatment because this type of hyperthyroidism usually gets better on its own within a few months. Patients with a toxic adenoma will either receive RAI ablation or removal of the half of the thyroid with the hyperactive thyroid. For patients with Graves' disease or toxic multinodular goiters, treatment usually starts with anti-thyroid medications such as Methimazole or Propylthiouracil (PTU). These medications are designed to stop the production and release of thyroid hormone. In some cases, patients may receive a medication that is designed to block the effect of thyroid hormone on the body such as a beta-blocker. However, only 30% of patients have long-term control of hyperthyroidism with medical therapy. Most patients go on to have a more definitive therapy such as RAI ablation or surgery. See RAI Ablation » | See Thyroid Surgery ».
Both treatments have equal success rates and complication rates. In the United States, many patients will have RAI ablation, however clear reasons to have a total thyroidectomy include: a large goiter, nodules that present a risk of thyroid cancer, pregnant patients, a desire to become pregnant within a year of treatment, ocular Graves' disease (i.e. the patient has eye symptoms caused by Graves' disease), a need to control the hyperthyroidism quickly (RAI ablation usually takes 3 to 6 months to work), iodine allergy, children younger than 15, and patient preference. The decision between which therapy is right for the patient should be made with an experienced thyroid specialist who can take into account all the different factors. Regardless of whether the patient has RAI ablation or surgery, the goal of both treatments is to make the patient hypothyroid (i.e. not make enough thyroid hormone). Low dose RAI ablation and partial thyroidectomy is no longer recommended because the chance of hyperthyroidism coming back (i.e. recurring) is high. Patients will require thyroid hormone replacement after appropriate definitive therapy. See RAI Scan ».
Grave's-related Eye Disease
Hyperthyroidism can cause swelling of the tissue in the eye socket (orbit). Symptoms of this condition, called Graves' orbitopathy or ocular Graves' disease, include:
- The eye being pushed forward, creating a wide-eyed or bulging stare. This is known as exophthalmos.
- Pain in the eyes when looking up or down
- Dryness and itching in the eyes
- Double vision
- Temporary or permanent loss of vision in severe cases
Eye symptoms usually occur at the same time as hyperthyroidism, but they may start before or after the symptoms of hyperthyroidism begin. Most patients with thyroid abnormalities will not be affected by eye disease and some patients only mildly so. Vision loss due to pressure on the optic nerve is the most severe form of the disease. Fortunately, this condition is rare, affecting less than 5% of patients with Graves' orbitopathy. Treatment with prednisone, radiotherapy, and/or surgery may be required to restore vision. Although the chance of having ocular Graves' disease is higher and more severe in smokers, there is no way to predict which thyroid patients will be affected. In addition, successful treatment of hyperthyroidism does not guarantee that the eye disease will improve although surgery seems to have better results than RAI ablation in improving eye disease. Once inflamed, the eye disease may remain active from several months to as long as three years. While rare, recurrence of the eye disease can happen and may be asociated with poor control of thyroid hormone levels.
Overall, it is important to keep in mind that eye disease associated with Graves' disease will only improve gradually. The management of ocular Graves' disease includes both medical and surgical therapy and our ophthalmology experts in the Thyroid Center can help plan the appropriate treatment.
Medical Treatment of Thyroid Eye Disease
Early eye symptoms, such as dryness, redness, itching, swelling of the lids and inability to wear contact lenses, are usually mild. Some patients find these symptoms to be particularly irritating at night and during exposure to air conditioning, hot air heating, and wind. A few patients will develop double vision (diplopia), which is the result of asymmetric inflammation of the muscles that control eye movement. Many patients develop mild symptoms that are often misdiagnosed as an "ocular allergy." Therefore, Graves' disease patients should be followed by an ophthalmologist familiar with the condition and available treatments. Patients with mild symptoms can often be successfully treated with frequent use of lubricating eye drops and wearing eye covers at night. Humidification of room air can prevent drying of the eyes, and wrap-around polarizing sunglasses can also help relieve glare. Diplopia can be improved by wearing special prism lenses while awaiting either spontaneous improvement or surgical correction. Temporary plastic prisms may be put on a regular set of eyeglasses and changed as needed. Prednisone, a steroid medication, may be taken in pill form to provide temporary relief from pain, swelling and redness, although side effects of the medication may limit its use.
Surgical Management of Thyroid Eye Disease
If ocular Graves' disease does not improve or if it gets worse despite treatment, surgery may be required. Retracted and puffy eyelids can change a person's appearance and increase the risk of the cornea drying. Corrective eyelid surgery can improve this problem through loosening of the eyelid muscles, as well as removal of scar tissue, excess fatty tissue and skin to place the eyelids into a more normal position. Surgery may also be necessary to correct diplopia when this problem has not improved either spontaneously or with prism lenses. Surgery to correct diploplia involves disconnecting and repositioning the muscles that control eye movement to improve ocular alignment and minimize double-vision.
The enlargement of tissue behind the eye may sometimes cause significant bulging of the eye (exophthalmos), which produces the characteristic wide-eyed stare seen in ocular Graves' disease. Swelling in the orbit may also contribute to vision loss as pressure increases on the optic nerve. Surgical procedures to reduce pressure on the optic nerve can improve vision and allow the eye to settle back to a more normal position. Orbital decompression is indicated in patients with significant exophthalmos, visual loss, or severe exposure of the corneas. Orbital decompression involves surgical removal of fat from behind the eyeball and may also involve removing some of the bone surrounding the eye socket.
For most patients, surgery is performed under general anesthesia and usually requires an overnight hospital stay.