There are many different types of thyroid disorders. The main categories are:

• Hypothyroidism (also known as an underactive thyroid). Reduced production of thyroid hormones. Hypothyroidism involves a problem with the proper functioning of the thyroid gland. When there are too few thyroid hormones in the body, metabolism slows down and the body uses energy slower than it should.
  
  
• Hyperthyroidism (overactive thyroid). Increased production of thyroid hormones. Like hypothyroidism, hyperthyroidism involves dysfunction of the thyroid gland. In this case, too much thyroid hormone increases a person's metabolism, making the body use energy more quickly than it should.
  
  
• Thyroiditis. Inflammation of the thyroid gland. This inflammation can destroy glandular tissue and cause hypothyroidism. There are many types of thyroiditis. Hashimoto's thyroiditis is an autoimmune disorder in which the body's immune system attacks the thyroid gland, and is one of the causes of hypothyroidism and goiter. Hashimoto's thyroiditis may also be associated with an increased risk of heart disease.
  
  
• Goiter. An enlarged thyroid gland. The gland may enlarge in an attempt to overcome mild deficiencies of thyroid hormones. It may also occur with normal thyroid hormone levels. Goiter may appear as a swelling at the base of the neck, or it may feel like a growth or a lump that can be small or large. It is a benign (noncancerous) condition, although it can lead to hypothyroidism or hyperthyroidism in some cases.
  
  
• Thyroid nodules. A condition in which collections of abnormal cells form lumps in the thyroid gland. Most thyroid nodules are benign, although they may sometimes be malignant (cancerous). Patients may have just one thyroid nodule or a collection of several nodules. In some cases, thyroid nodules can produce thyroid hormones and lead to hyperthyroidism. Large nodules may cause breathing or swallowing difficulties.
  
  
• Thyroid cancer. Malignant tumors of the thyroid gland. Nearly 15,000 women and 5,000 men are diagnosed with thyroid cancer every year in the United States, according to the National Cancer Institute.