Hashimoto's thyroiditis is a chronic autoimmune disease in which the thyroid gland is gradually destroyed. Early on there may be no symptoms. Over time the thyroid may enlarge, forming a painless goiter. Some people eventually develop hypothyroidism with accompanying weight gain, feeling tired, constipation, depression, and general pains. Thyroid enlargement is very noticeable. After many years the thyroid typically shrinks in size. Diagnosis is confirmed with blood tests for TSH, T4, and anti-thyroid autoantibodies. Hashimoto's thyroiditis is typically treated with levothyroxine long-term.