Hypothyroidism is most commonly caused by autoimmune thyroid disease. The most common form is Hashimoto’s thyroiditis. It is named after the Japanese doctor who first described the condition in 1912. It occurs when your child’s autoimmune system attacks their thyroid gland and can cause inflammation and swelling of the thyroid gland – also called a goitre. Goitres do not always appear or can go unnoticed. As a result of autoimmune thyroid disease your child becomes hypothyroid, which means that their thyroid gland does not produce enough thyroid hormone. Young people with Hashimoto’s thyroiditis very occasionally develop signs of an over-active thyroid gland (this is sometimes called Hashitoxicosis) because the swollen gland makes too much thyroid hormone. This period of ‘over-activity’ is usually brief and the main problem in the long term is likely to be a thyroid gland that is under-active.

There is often a family history of thyroid disease or other autoimmune disorders in children who have Hashimoto’s thyroiditis.

How common is Hashimoto’s thyroiditis?

Autoimmune thyroid disorders, including Hashimoto’s thyroiditis, occur in approximately one in 3,500 children.