In medical terms, the suffix -itis means inflammation; thyroiditis is inflammation of the thyroid gland which may be associated with an underactive thyroid gland or hypothyroidism. In some cases, people have an overactive thyroid gland or hyperthyroidism prior to experiencing hypothyroidism.
There are several different kinds of thyroiditis. Although each different type of thyroiditis may cause different symptoms, many times they can be quite similar.
In the case of thyroiditis, the thyroid gland is damaged by an inflammatory process. When thyroid cells are attacked by inflammation, they stop functioning. Without thyroid cells, the thyroid is no longer able to produce enough thyroid hormone to maintain the body's normal metabolism. Hypothyroidism, or an underactive thyroid gland, results.