About 20 million Americans have some form of thyroid disease. These are the most common:

Graves’ Disease – This is the most common cause of hyperthyroidism. It is a chronic disorder in which the affected person’s immune system produces antibodies that attack the thyroid, causing inflammation, damage, and the production of excessive amounts of thyroid hormone.

Hashimoto’s Thyroiditis – This is the most common cause of hypothyroidism in the United States. Like Graves’ disease, it is a chronic autoimmune condition related to the production of antibodies that target the thyroid and cause inflammation and damage. With Hashimoto’s thyroiditis, however, the body makes decreased amounts of thyroid hormone.

Thyroid Cancer—Thyroid cancer is fairly uncommon, with only about 1500 deaths and 33,550 new cases diagnosed in 2007 in the U.S. There are four main types of thyroid cancers: papillary, follicular, anaplastic, and medullary cancer. About 60-70% of thyroid cancer cases are papillary. This type affects more women than men and is more common in younger people. About 15% of thyroid cancers are follicular, a more aggressive type of cancer that tends to occur in older women. Anaplastic cancer, also found in older women, accounts for about 5% of thyroid cancers and tends to be both aggressive and difficult to treat. Medullary thyroid cancer (MTC) produces calcitonin and may be found alone or linked with other endocrine cancers in a syndrome called multiple endocrine neoplasia syndrome. MTC can also be difficult to treat if it spreads beyond the thyroid.

Thyroid Nodules—A thyroid nodule is a small lump on the thyroid gland that may be solid or a fluid-filled cyst. As many as 4% of women and 1% of men will have one or more thyroid nodules; however, the overwhelming majority of these nodules are harmless. Occasionally, thyroid nodules can be cancerous and need to be treated.

Thyroiditis—Thyroiditis is an inflammation of the thyroid gland. It may be associated with either hypo- or hyperthyroidism. It may be painful, feeling like a sore throat, or painless. Thyroiditis may be due to autoimmune activity, an infection, exposure to a chemical that is toxic to the thyroid, or an unkown cause. Depending on the cause, it can be acute but transient or chronic.

Goiters—A thyroid goiter is a visible enlargement of the thyroid gland. In the past, this condition was relatively common and was due to a lack of iodine in the diet. Iodine is a necessary component of thyroid hormone production. In the United States, where iodine is now routinely added to table salt (iodized) and used to clean milking cows’ udders, the incidence of dietary-related goiters has declined significantly. In other parts of the world, however, iodine-related goiters are still common and represent the most common cause of hypothyroidism in some countries. Any of the diseases listed above can also cause goiters. Goiters may compress vital structures of the neck, including the trachea and esophagus. This compression can make it difficult to breathe and swallow.