The thyroid, a butterfly-shaped gland in the lower front of the neck, regulates the body's energy level, including heart rate, blood pressure and temperature, reports MayoClinic.com. There are many causes for a nonfunctioning thyroid. Because it does not produce hormones needed to regulate metabolism, most people with a nonfunctioning thyroid must take thyroid replacement hormones for their entire life.
Surgical Removal of the Thyroid
Most people with thyroid cancer have a thyroidectomy, removal of their entire thyroid gland, reports MayoClinic.com. In addition, a few people with thyroid nodules or Graves' disease, a disorder in which the immune system attacks the thyroid by mistake, end up having their thyroid surgically removed. As a result, no thyroid hormones are produced and the gland doesn't function.
Radiation Therapy
The thyroid gland is deliberately destroyed by treatment with radioactive iodine in people with certain diseases, including thyroid cancer, Graves' disease, and severely enlarged thyroid, reports the American Thyroid Association. A nonfunctioning thyroid also occurs when patients receive radiotherapy to the neck, such as for head or neck cancer, lymphoma or Hodgkin's disease.
Birth Defect
Some babies are born without a thyroid. Other have a deformed thyroid gland or a thyroid located in the wrong place, reports the American Thyroid Association. This causes the thyroid cells and enzymes to malfunction, if they work at all.
Damaged Pituitary Gland
A damaged pituitary gland prevents the thyroid from functioning because it is unable to produce thyroid-stimulating hormone, TSH, which tells the thyroid to make thyroxine, the main thyroid hormone, reports the American Thyroid Association. Injury to the pituitary gland, which is "the boss" of the thyroid, can be caused by surgery, cancer or exposure to radiation.
Rare Diseases
Because they drop abnormal substances onto the gland, a few rare disorders cause a nonfunctioning thyroid, according to the American Thyroid Association. These include sarcoidosis, which leaves tiny lumps of cells, amyloidosis, which deposits amyloid protein and hemochromatosis, which leaves excess iron on the gland.
Inherited Disorders
Rarely, hereditary problems can cause a nonfunctioning thyroid, reports the Merck Manual. For example, an inherited defect in thyroid enzymes prevents the gland from making thyroid hormones.
