Other causes of primary hypothyroidism include:

• Thyroiditis: Inflammation of the thyroid gland. This can be caused by a virus, bacteria, or autoimmune reaction.
• Congenital hypothyroidism: A condition in which a baby is born with an underdeveloped thyroid gland or a thyroid gland that doesn't work properly.
• Iodine deficiency: Iodine is a mineral that the thyroid gland needs to produce hormones. Iodine deficiency is rare in developed countries because table salt is iodized.
• Medications: Certain medications can interfere with the thyroid gland's ability to produce hormones.
• Treatment for hyperthyroidism: If you have been treated for hyperthyroidism (an overactive thyroid), you may develop hypothyroidism as a side effect. This can happen if you have radioactive iodine treatment or surgery to remove part of your thyroid gland.

Secondary hypothyroidism is a less common condition that occurs when the pituitary gland, a small gland at the base of the brain, doesn't produce enough thyroid-stimulating hormone (TSH). TSH tells the thyroid gland how much thyroid hormone to make. Causes of secondary hypothyroidism include:

• Pituitary gland tumor
• Pituitary injury
• Inflammation of the pituitary gland

Tertiary hypothyroidism is an even less common condition that occurs when the hypothalamus, a part of the brain located above the pituitary gland, doesn't produce enough thyrotropin-releasing hormone (TRH). TRH tells the pituitary gland to release TSH. Causes of tertiary hypothyroidism include:

• Brain tumor
• Infection
• Injury