Thyroiditis is the general term used to describe several different disorders in which the thyroid gland becomes inflamed. Most commonly, the inflammation takes the form of a chronic, progressive disease known as chronic lymphocytic thyroiditis or Hashimoto's disease (in honor of the Japanese physician who first described the microscopic changes in the thyroid tissue of patients with the condition in 1912). Patients with this form of thyroiditis sometimes exhibit so few symptoms that the disease may go unnoticed for many years, but eventually it may destroy so much thyroid tissue that hypothyroidism develops.
Lymphocytic thyroiditis may also occur as a self-limited condition which lasts 2-6 months, resolving spontaneously, and leaving most patients with normal thyroid function. When it occurs after pregnancy, it is termed postpartum thyroiditis. Another painless variant of lymphocytic thyroiditis may occur at other times and has been termed silent thyroiditis.
Subacute thyroiditis or DeQuervain's disease is another condition caused by thyroid inflammation, one that is distinct from those mentioned above. The disease often seems to follow the course of a viral infection. The thyroid gland is usually painful and looks quite different on microscopic examination.
Finally, very rarely the thyroid may become suddenly and dramatically inflamed with a bacterial infection. This condition is referred to as acute suppurative thyroiditis.