Hypothyroidism

(Thyroid Problems, Low Thyroid, Underactive Thyroid)

In this factsheet:
• The Facts on Hypothyroidism
• Causes of Hypothyroidism
• Symptoms and Complications of Hypothyroidism
• Diagnosing Hypothyroidism
• Treating and Preventing Hypothyroidism

The Facts on Hypothyroidism

The thyroid is a gland located in the neck below the Adam's apple. It helps control the body's metabolic rate by producing the hormones thyroxine (T4) and triiodothyroxine (T3).

Hypothyroidism is the most common of the thyroid disorders. It occurs when the thyroid gland becomes underactive and does not produce enough thyroid hormones. The metabolic rate falls and normal bodily functions slow down. Up to 10% of women over the age of 65 show some signs of hypothyroidism. Although less common, hypothyroidism does occur among the young. Neonatal hypothyroidism, called cretinism, is associated with mental retardation, jaundice (yellowing of skin), poor feeding, breathing difficulties, and growth problems. Childhood (juvenile) hypothyroidism is characterized by delayed growth and problems with mental development; however, with prompt treatment, problems can be minimized.

Causes of Hypothyroidism

The most common cause of adult hypothyroidism is Hashimoto's thyroiditis. It's caused by an autoimmune reaction: the body produces antibodies that attack and gradually destroy the thyroid gland. Women are eight times more likely than men to develop Hashimoto's thyroiditis, especially as they age. It can also run in families, or be associated with syndromes of genetic abnormalities, such as Turner's syndrome, Klinefelter's syndrome, and Down syndrome.

Hypothyroidism can also be caused by treatments for hyperthyroidism. To treat hyperthyroidism, the thyroid gland may be rendered inactive with medications or radioactive iodine treatment or may be surgically removed. The result may be a lack of thyroid hormones, causing hypothyroidism.

The thyroid gland requires iodine to function properly. A chronic lack of iodine means that less thyroid hormone can be produced and this causes the thyroid to enlarge. Since salt manufacturers now add iodine to salt, this form of hypothyroidism is extremely rare in North America. However, it is still the major cause of hypothyroidism in underdeveloped countries, where iodine is often lacking in the diet.

Some rare inherited disorders cause enzyme abnormalities in the thyroid gland that don't allow it to make the hormones. Secondary hypothyroidism may occur if the pituitary gland in the brain isn't working properly, and not producing a hormone, called thyroid-stimulating hormone (TSH), needed to stimulate the thyroid gland. These disorders are quite rare and not a major cause of hypothyroidism.

Symptoms and Complications of Hypothyroidism

Because the hormones T4 and T3 are lacking, the body's metabolic rate and organ functions slow down. Symptoms aren't always obvious, and hypothyroidism may sometimes be mistaken for other diseases. People with hypothyroidism often experience:

• fatigue/feeling sluggish
• weakness
• cold intolerance
• weight gain
• constipation
• depression
• irritability
• dry, scaly skin
• coarse and dry hair
• hair loss
• muscle cramps
• increased menstrual flow (women)
• slower heart rate
• confusion or forgetfulness (often mistaken for dementia in seniors)

If hypothyroidism isn't treated, the symptoms will progress and, rarely, a severe form of hypothyroidism called myxedema will develop. With myxedema, the body temperature drops, anemia occurs, and there is a risk of congestive heart failure. Myxedema coma occurs in some people with severe hypothyroidism who are exposed to some kind of stress, such as infection, severe cold, trauma, or the use of sedatives. Symptoms include loss of consciousness, seizures, slowed breathing, and lack of blood flowing to the brain.

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