The most common cause of hypothyroidism is Hashimoto's thyroiditis (or autoimmune hypothyroidism), a form of thyroid inflammation caused by your own immune system.
But this isn't the sole cause of hypothyroidism there may be a variety of other reasons why you have developed the disorder. This article gives an explanation of each of the possible causes of hypothyroidism.
- Hashimoto’s disease (also called Hashimoto’s thyroiditis or chronic lymphocytic thyroiditis), or inflammation of the thyroid gland. This condition is a disorder of the immune system, which usually protects you from infection. In this case, it destroys thyroid tissue and/or inhibits the action of thyroid hormones. The thyroid gland is initially enlarged (goitre) and cannot produce the required thyroid hormones. Later the gland becomes small and hard.
- Radiation treatment for an overactive thyroid gland (hyperthyroidism) or cancers of the head and neck – this may shrink or destroy the gland.
- Surgical removal of the thyroid gland as treatment for thyroid cancer, hyperthyroidism, goitre or cancerous thyroid nodules.
- Inflammation of the thyroid gland (thyroiditis) after a viral illness – this may lead to temporary hypothyroidism.
- Failure of the pituitary gland to release sufficient TSH to stimulate production of the thyroid hormones (rare).
- Congenital hypothyroidism, a rare condition in infants who are born without thyroid glands or with glands that cannot produce thyroid hormones.
- Pregnancy – may cause a mild hypothyroidism in some women.
- Iodine deficiency in the diet, or an excessive amount of iodine from foods such as seaweed.
- Medications such as propylthiouracil (PTU) or methimazole (used for treating an overactive thyroid); lithium carbonate (used in the treatment of psychiatric illness); or amiodarone (used for controlling abnormal heart rhythms).
Reviewed by Dr Wayne May, Endocrinologist Kingsbury Hospital, Cape Town February 2015.
Previously reviewed by Dr P.H.S. van Zijl, MB.Ch B. MMed (Int).