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).
Symptoms of hypothyroidism
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).