Hyperthyroidism

Hyperthyroidism, or an overactive thyroid gland, is an increase in the production of thyroid hormones, which speeds up vital body functions.

Hyperthyroidism affects about the same percentage of older people as younger people—fewer than 2%. However, hyperthyroidism is often more serious among older people because they tend to have other disorders as well.

Causes

Hyperthyroidism in older people often results from Graves' disease. In Graves' disease, the body makes antibodies that stimulate the thyroid gland, causing it to produce excessive amounts of thyroid hormones.

Almost as often, hyperthyroidism is caused by the gradual growth of many small lumps (nodules) in the thyroid gland. In this condition, called toxic multinodular goiter, the nodules secrete excessive amounts of thyroid hormones. Sometimes a single nodule is the cause of hyperthyroidism.

Some drugs can cause hyperthyroidism as well. The most common is amiodarone, a drug used to treat heart disease but which may stimulate or damage the thyroid gland. The potential for amiodarone to cause hypothyroidism in some people and hyperthyroidism in others is a reminder of the unpredictability of the effects of amiodarone on the thyroid gland.

Symptoms

Hyperthyroidism can produce many vague symptoms that can be attributed to other conditions. Typically, the symptoms of hyperthyroidism differ between older and younger people. In younger people, the most common symptoms are an increased heart rate, sensitivity to heat, trembling of the hands, and bulging of the eyes (exophthalmos). In contrast, among older people, the most common symptoms are weight loss and fatigue. The heart rate may or may not be increased, and the eyes usually do not bulge. Older people are also more likely to have abnormal heart rhythms (such as atrial fibrillation), other heart problems (such as angina and heart failure), and constipation. Older people occasionally develop diarrhea, sweat profusely, become nervous and anxious, and experience trembling of the hands.

The thyroid gland is of normal size in almost half of the older people with hyperthyroidism. However, the thyroid gland often enlarges in people with Graves' disease. The gland is enlarged only in the areas in which nodules have formed if people have toxic multinodular goiter.

In very rare instances, the thyroid gland becomes extremely overactive. This life-threatening condition is called thyroid storm. Thyroid storm is usually triggered by a stressful event, such as an infection or surgery. It usually occurs in a person with an overactive thyroid gland who has not been under a doctor's care. Occasionally, thyroid storm is unexpectedly triggered by radioactive iodine given to treat hyperthyroidism. In thyroid storm, fever develops and the heart rate increases greatly. A person may feel nauseated or may vomit. Heart failure may develop. The person may become confused and less alert and may lose consciousness.

Diagnosis

To diagnose hyperthyroidism, doctors usually begin by measuring the level of thyroid-stimulating hormone. If the thyroid gland is overactive, the pituitary gland produces less thyroid-stimulating hormone. The level of thyroid-stimulating hormone in the blood is low, sometimes so low that it cannot be detected. The levels of T₃ and, to a lesser extent, T₄ are increased.

Once hyperthyroidism is diagnosed, other tests may be used to determine the cause. A thyroid scan may be performed. A thyroid scan involves the administration of a small amount of a radioactive material, either iodine by mouth or technetium by injection, into the bloodstream. The radioactive material collects in the thyroid gland, where it gives off small amounts of radiation that can be detected with a special camera to produce images of the thyroid gland.

Treatment and Outlook

Often, doctors can quickly begin treating hyperthyroidism using drugs called beta blockers to slow the heart rate and reduce trembling of the hands. Additional treatment is almost always necessary and depends on the cause.

Drugs that reduce the production of thyroid hormones (propylthiouracil and methimazole) are often used to treat hyperthyroidism due to Graves' disease. Usually, the drug is taken for 1 to 2 years. Unfortunately, hyperthyroidism often returns after the drug is discontinued. If this happens, other treatments, such as radioactive iodine, are used.

Radioactive iodine, which is taken by mouth in one dose, is usually successful in treating people who have Graves' disease. Very little radioactive iodine spreads around the body, because iodine is collected, concentrated, and stored only in the thyroid gland. Unfortunately, radioactive iodine treatment almost always results in an underactive thyroid gland (hypothyroidism). When this occurs, people must then take thyroid hormone for the rest of their lives to replace the hormones that the thyroid gland no longer produces. Radioactive iodine is also used very successfully to treat toxic multinodular goiter. Surgery may be needed to remove most or all of the thyroid gland in some situations, especially when the thyroid is greatly enlarged.

Treatment of hyperthyroidism requires time and patience. In almost all cases, however, the condition can be cured and the symptoms eliminated.