Thyroiditis is an inflammation of the thyroid gland. There are many types of thyroiditis that cause various symptoms and health problems. Some types are chronic and progress slowly, whereas others are acute. Most types of thyroiditis are more common in women than men and tend to affect people over the age of 40.

An autoimmune disorder causes most cases of thyroiditis. Other causes include infections and certain medical treatments.

Types of thyroiditis include:

• Hashimoto's thyroiditis. The most common thyroid disorder in the United States and the leading cause of hypothyroidism. This autoimmune condition often comes on slowly, unfolding over months or even years.
  
  
• Painless (silent) thyroiditis. Initially, often causes a temporary increase in levels of thyroid hormones in the bloodstream (transient thyrotoxicosis) before hormone levels fall below normal (transient hypothyroidism). In most cases thyroid levels eventually return to normal. When thyrotoxicosis occurs, it can cause symptoms of hyperthyroidism.
  
  
• Postpartum thyroiditis. Similar to painless thyroiditis, except that it may occur only after a woman gives birth.
  
  
• Subacute thyroiditis. Similar to painless thyroiditis, except that it causes throat pain and typically is triggered by a viral infection.
  
  
• Infectious thyroiditis. Caused by a bacterial or viral illness.
  
  
• Drug-related thyroiditis. Caused by certain medications. It can lead to hypothyroidism and thyrotoxicosis.
  
  
• Radiation-induced thyroiditis. May occur as a result of using radioactive iodine to treat hyperthyroidism or radiation therapy to treat certain cancers. As with drug-induced thyroiditis, this type of thyroiditis can cause hypothyroidism and thyrotoxicosis.
  
  
• Riedel's thyroiditis. A rare but potentially serious disorder involving the formation of fibrous tissue in the neck.

Symptoms of thyroiditis may differ, depending on the type of thyroiditis involved and the condition it has caused in a patient’s body. Slow, chronic damage to cells of the thyroid gland causes symptoms of hypothyroidism such as fatigue, constipation and unexplained weight gain. Acute damage may cause symptoms that mimic hyperthyroidism, such as a rapid heartbeat, insomnia and unexplained weight loss.

Most physicians diagnose thyroiditis by using thyroid blood tests and radioactive iodine nuclear scans. Treatment options vary depending on the type of thyroiditis. Thyroid hormone replacement medications may be given to patients who experience hypothyroidism. Beta blockers, a type of antihypertensive, may be given to patients experiencing symptoms that mimic hyperthyroidism. There is no known method to prevent most cases of thyroiditis.