Am Fam Physician. 2011;83(8):943-944
See related article on subclinical hyperthyroidism.
What is subclinical hyperthyroidism?
Hyperthyroidism is a condition in which there is too much thyroid hormone in the body. The thyroid gland is located in the front of your neck. It produces hormones that regulate the way your body uses energy. If there is too much thyroid hormone, your body functions speed up. Subclinical hyperthyroidism is a mild form of hyperthyroidism. “Subclinical” means that you do not have any symptoms, or that your symptoms are mild.
What causes it?
Several things can cause your body to have too much thyroid hormone. Your thyroid gland may be producing too much. A virus can cause inflammation of the thyroid, which leads to a temporary increase in thyroid hormone levels. Taking too much thyroid medicine or getting too much iodine in your diet also can cause subclinical hyperthyroidism. Some people have benign (noncancerous) growths on their thyroid that can produce too much hormone. This condition is called a toxic nodular or multinodular goiter.
Who gets it?
Only about three to five people out of 100 have subclinical hyperthyroidism. It is more common in older adults and in people who live in areas where there is not enough iodine in the food.
What are the symptoms?
People with subclinical hyperthyroidism usually do not have any symptoms. If you do have symptoms, they may include one or more of the following:
Frequent bowel movements
Fatigue or feeling tired
Unable to tolerate heat
Racing or rapidly beating heart
Losing weight without trying
Hair loss or balding
Lack of menstrual periods in women
The more symptoms you have, or the worse they are, the more likely you are to have hyperthyroidism.
What problems can it cause?
People older than about 65 years who have subclinical hyperthyroidism have an increased risk of developing a type of irregular heartbeat called atrial fibrillation. Women who have gone through menopause and who have subclinical hyperthyroidism may have more bone loss than other women.
Should I be tested for it?
Most doctors do not test patients for subclinical hyperthyroidism unless they have symptoms. There is no evidence that treating subclinical hyperthyroidism will improve health outcomes.
Where can I get more information?
AAFP's Patient Education Resource
American Thyroid Association
American Association of Clinical Endocrinologists