Definition of Chronic thyroiditis (Hashimoto's disease):

Chronic thyroiditis is swelling (inflammation) of the thyroid gland that often results in reduced thyroid function (hypothyroidism).

Causes, incidence, and risk factors:

Chronic thyroiditis or Hashimoto's disease is a common thyroid gland disorder. It can occur at any age, but is most often seen in middle-aged women. It is caused by a reaction of the immune system against the thyroid gland.

The disease begins slowly. It may take months or even years for the condition to be detected. Chronic thyroiditis is most common in women and people with a family history of thyroid disease. It affects between 0.1% and 5% of all adults in Western countries.

Hashimoto's disease may, in rare cases, be associated with other endocrine disorders caused by the immune system. Hashimoto's disease can occur with adrenal insufficiency and type 1 diabetes. In these cases, the condition is called type 2 polyglandular autoimmune syndrome (PGA II).

Less commonly, Hashimoto's disease occurs as part of a condition called type 1 polyglandular autoimmune syndrome (PGA I), along with:

• Adrenal insufficiency
• Fungal infections of the mouth and nails
• Hypoparathyroidism