There are many types of thyroiditis, with varying symptoms and causes. These include:

• Hashimoto's thyroiditis. This is the most common thyroid disease in the United States, according to the U.S. Department of Health and Human Services, and is the nation's leading cause of hypothyroidism. It is an autoimmune disease, meaning the body's immune system is hyperactive and mistakenly attacks the thyroid gland. It typically comes on slowly, often unfolding over a period of months or even years. In most cases, patients with Hashimoto's thyroiditis have hypothyroidism for the rest of their lives for which they must take medication. Some patients develop inflammatory thyroid nodules, small noncancerous growths in the gland.
  
  Patients with Hashimoto's thyroiditis have a modestly increased risk of developing one or more of the following disorders, according to the American Association of Clinical Endocrinologists (AACE): type 1 diabetes, Graves' disease (the leading cause of hyperthyroidism), Addison's disease (adrenal insufficiency), rheumatoid arthritis, lupus, pernicious anemia, vitiligo (a skin disease), thrombocytopenic purpura (a bleeding disorder) or premature ovarian failure (early menopause).
  
  About 14 million Americans, most of them women, have Hashimoto's thyroiditis, according to the AACE. It is named after the Japanese physician who described it in the early 20th century. Alternative terms include chronic lymphocytic thyroiditis and chronic thyroiditis.
  
  
• Painless (silent) thyroiditis. Usually, this condition initially causes a temporary rise in levels of thyroid hormones in the blood (transient thyrotoxicosis) before hormone levels temporarily fall below normal (transient hypothyroidism). This may cause mild symptoms that mimic hyperthyroidism for up to three months, followed by mild symptoms of hypothyroidism for up to 12 months. In about one-third of all cases, patients experience just one of these phases, according to the American Thyroid Association (ATA). Patients with painless (silent) thyroiditis usually experience a return to normal thyroid functioning within 18 months. However, about 20 percent of cases result in permanent hypothyroidism.
  
  
• Postpartum thyroiditis. This condition is virtually identical to painless (silent) thyroiditis, but it may occur only after a woman gives birth. In most cases, signs of inflammation first appear four to six months after delivery. The progression of this disease and its prognosis are similar to those of painless (silent) thyroiditis. Both conditions are thought to be autoimmune disorders, according to the American Association of Clinical Endocrinologists (AACE). Between 5 and 10 percent of pregnant women will experience postpartum thyroiditis, according to the National Institutes of Health. Up to 25 percent of pregnant women with type 1 diabetes will develop it, according to the AACE.
  
  Women at increased risk for this condition include those with a personal history of thyroiditis or immune system disorders, who test positive for antithyroid antibodies and who have a family history of thyroid problems. Postpartum thyroiditis is different from another disorder called Sheehan's syndrome, which can cause hypothyroidism following childbirth. This rare syndrome usually occurs in women who experience severe blood loss during childbirth that causes damage to the pituitary gland.
  
  
• Subacute thyroiditis. Also known as painful thyroiditis or DeQuervain's disease, it is similar to painless or postpartum thyroiditis in disease progression and prognosis. However, subacute thyroiditis is also a major source of pain in the thyroid gland. This pain usually persists throughout the transient thyrotoxicosis phase, which may appear as symptoms that mimic hyperthyroidism. Fever may also be present. Viral illnesses often cause subacute thyroiditis, particularly upper respiratory infections (e.g., the flu) and mumps. Permanent hypothyroidism occurs in 5 percent of cases, according to the ATA.
  
  
• Infectious thyroiditis. Also known as acute suppurative thyroiditis, it involves infection with a viral or bacterial illness, primarily the latter. Symptoms include thyroid gland pain, enlargement of the thyroid gland (goiter), as well as symptoms of hypothyroidism or other systemic illness.
  
  
• Drug-related thyroiditis. Taking certain medications can cause thyrotoxicosis (which symptoms mimic hyperthyroidism) and hypothyroidism. In many cases, the thyrotoxicosis lasts for only a short period before resolving. Hypothyroidism associated with medication use is likely to resolve once a patient stops using the drug causing the condition. Medications that may cause this condition include amiodarone (antiarrhythmic heart drug), lithium (treatment for bipolar disorder), and interferons and other cytokines (anti-inflammatory proteins).
  
  
• Radiation-induced thyroiditis. This type of thyroiditis may occur as a result of using radioactive iodine to treat hyperthyroidism or external-beam radiation therapy to treat certain cancers. As with medication-induced thyroiditis, this type of thyroiditis can cause thyrotoxicosis (mimicking symptoms of hyperthyroidism) and hypothyroidism. However, hypothyroidism associated with radiation typically is permanent.
  
  
• Riedel's thyroiditis. This rare but potentially serious disorder, also known as fibrous thyroiditis, involves the abnormal formation of fibrous tissue in the thyroid gland and nearby structures in the neck. It may be an autoimmune disorder or a fibrotic condition. Symptoms may include hoarseness, cough, difficulty swallowing (dysphagia), difficulty breathing (dyspnea) and underproduction of parathyroid hormone (hypoparathyroidism). It typically requires thyroid surgery.