Hypothyroidism (redirected from Hypothyreosis)

Hypothyroidism 

Definition

Hypothyroidism, or underactive thyroid, develops when the thyroid gland fails to produce or secrete as much thyroxine (T₄) as the body needs. Because T₄ regulates such essential functions as heart rate, digestion, physical growth, and mental development, an insufficient supply of this hormone can slow life-sustaining processes, damage organs and tissues in every part of the body, and lead to life-threatening complications.

Description

Hypothyroidism is one of the most common chronic diseases in the United States. Symptoms may not appear until years after the thyroid has stopped functioning and they are often mistaken for signs of other illnesses, menopause, or aging. Although this condition is believed to affect as many as 11 million adults and children, as many as two of every three people with hypothyroidism may not know they have the disease.

Nicknamed "Gland Central" because it influences almost every organ, tissue, and cell in the body, the thyroid is shaped like a butterfly and located just below the Adam's apple. The thyroid stores iodine the body gets from food and uses this mineral to create T₄. Low T₄ levels can alter weight, appetite, sleep patterns, body temperature, sex drive, and a variety of other physical, mental, and emotional characteristics.

There are three types of hypothyroidism. The most common is primary hypothyroidism, in which the thyroid doesn't produce an adequate amount of T₄. Secondary hypothyroidism develops when the pituitary gland does not release enough of the thyroid-stimulating hormone (TSH) that prompts the thyroid to manufacture T₄. Tertiary hypothyroidism results from a malfunction of the hypothalamus, the part of the brain that controls the endocrine system. Drug-induced hypothyroidism, an adverse reaction to medication, occurs in two of every 10,000 people, but rarely causes severe hypothyroidism.

Hypothyroidism is at least twice as common in women as it is in men. Although hypothyroidism is most common in women who are middle-aged or older, the disease can occur at any age. Newborn infants are tested for congenital thyroid deficiency (cretinism) using a test that measures the levels of thyroxine in the infant's blood. Treatment within the first few months of life can prevent mental retardation and physical abnormalities. Older children who develop hypothyroidism suddenly stop growing.

Factors that increase a person's risk of developing hypothyroidism include age, weight, and medical history. Women are more likely to develop the disease after age 50; men, after age 60. Obesity also increases risk. A family history of thyroid problems or a personal history of high cholesterol levels or such autoimmune diseases as lupus, rheumatoid arthritis, or diabetes can make an individual more susceptible to hypothyroidism.

Causes and symptoms

Hypothyroidism is most often the result of Hashimoto's disease, also known as chronic thyroiditis (inflammation of the thyroid gland). In this disease, the immune system fails to recognize that the thyroid gland is part of the body's own tissue and attacks it as if it were a foreign body. The attack by the immune system impairs thyroid function and sometimes destroys the gland. Other causes of hypothyroidism include:

Hypothyroidism is sometimes referred to as a "silent" disease because early symptoms may be so mild that no one realizes anything is wrong. Untreated symptoms become more noticeable and severe, and can lead to confusion and mental disorders, breathing difficulties, heart problems, fluctuations in body temperature, and death.

Someone who has hypothyroidism will probably have more than one of the following symptoms:

Hypothyroidism usually develops gradually. When the disease results from surgery or other treatment for hyperthyroidism, symptoms may appear suddenly and include severe muscle cramps in the arms, legs, neck, shoulders, and back.

It's important to see a doctor if any of these symptoms appear unexpectedly. People whose hypothyroidism remains undiagnosed and untreated may eventually develop myxedema. Symptoms of this rare but potentially deadly complication include enlarged tongue, swollen facial features, hoarseness, and physical and mental sluggishness.

Myxedema coma can cause unresponsiveness; irregular, shallow breathing; and a drop in blood pressure and body temperature. The onset of this medical emergency can be sudden in people who are elderly or have been ill, injured, or exposed to very cold temperatures; who have recently had surgery; or who use sedatives or anti-depressants. Without immediate medical attention, myxedema coma can be fatal.

Diagnosis

Diagnosis of hypothyroidism is based on the patient's observations, medical history, physical examination, and thyroid function tests. Doctors who specialize in treating thyroid disorders (endocrinologists) are most apt to recognize subtle symptoms and physical indications of hypothyroidism. A blood test known as a thyroid-stimulating hormone (TSH) assay, thyroid nuclear medicine scan, and thyroid ultrasound are used to confirm the diagnosis. A woman being tested for hypothyroidism should let her doctor know if she is pregnant or breastfeeding and all patients should be sure their doctors are aware of any recent procedures involving radioactive materials or contrast media.

The TSH assay is extremely accurate, but some doctors doubt the test's ability to detect mild hypothyroidism. They advise patients to monitor their basal (resting) body temperature for below-normal readings that could indicate the presence of hypothyroidism.

Treatment

Natural or synthetic thyroid hormones are used to restore normal (euthyroid) thyroid hormone levels. Synthetic hormones are more effective than natural substances, but it may take several months to determine the correct dosage. Patients start to feel better within 48 hours, but symptoms will return if they stop taking the medication.

Most doctors prescribe levothyroxine sodium tablets, and most people with hypothyroidism will take the medication for the rest of their lives. Aging, other medications, and changes in weight and general health can affect how much replacement hormone a patient needs, and regular TSH tests are used to monitor hormone levels. Patients should not switch from one brand of thyroid hormone to another without a doctor's permission.

Regular exercise and a high-fiber diet can help maintain thyroid function and prevent constipation.

Alternative treatment

Alternative treatments are primarily aimed at strengthening the thyroid and will not eliminate the need for thyroid hormone medications. Herbal remedies to improve thyroid function and relieve symptoms of hypothyroidism include bladder wrack (Fucus vesiculosus), which can be taken in capsule form or as a tea. Some foods, including cabbage, peaches, radishes, soybeans, peanuts, and spinach, can interfere with the production of thyroid hormones. Anyone with hypothyroidism may want to avoid these foods. The Shoulder Stand yoga position (at least once daily for 20 minutes) is believed to improve thyroid function.

Prognosis

Thyroid hormone replacement therapy generally maintains normal thyroid hormone levels unless treatment is interrupted or discontinued.

Prevention

Primary hypothyroidism can't be prevented, but routine screening of adults could detect the disease in its early stages and prevent complications.

Key terms

Cretinism — Severe hypothyroidism that is present at birth.

Endocrine system — The network of glands that produce hormones and release them into the bloodstream. The thyroid gland is part of the endocrine system.

Hypothalamus — The part of the brain that controls the endocrine system.

Myxedema — A condition that can result from a thyroid gland that produces too little of its hormone. In addition to a decreased metabolic rate, symptoms may include anemia, slow speech, an enlarged tongue, puffiness of the face and hands, loss of hair, coarse and thickened skin, and sensitivity to cold.

Pituitary gland — Small, oval endocrine gland attached to the hypothalamus. The pituitary gland releases TSH, the hormone that activates the thyroid gland.

Thyroid-stimulating hormone (TSH) — A hormone secreted by the pituitary gland that controls the release of T₄ by the thyroid gland.

Thyroxine (T₄) — Thyroid hormone that regulates many essential body processes.

Resources

Organizations

American Thyroid Association. Montefiore Medical Center, 111 E. 210th St., Bronx, NY 10467.

Endocrine Society. 4350 East West Highway, Suite 500, Bethesda, MD 20814-4410. (301) 941-0200.

Thyroid Foundation of America, Inc. Ruth Sleeper Hall, RSL 350, Boston, MA 02114-2968. (800) 832-8321 or (617) 726-8500.

Thyroid Society for Education and Research. 7515 S. Main St., Suite 545, Houston, TX 77030. (800) THYROID or (713) 799-9909.

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hypothyroidism /hy·po·thy·roid·ism/ (-thi´roid-izm) deficiency of thyroid activity, a cause of cretinism in children and myxedema in adults, with decreased metabolic rate, tiredness, and lethargy.hypothy´roid

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hy·po·thy·roid·ism (hp-throi-dzm)

n.

1. Insufficient production of thyroid hormones.

2. A pathological condition resulting from thyroid insufficiency, which may lead to cretinism or myxedema.

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hypo·thyroid adj.

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hypothyroidism,

n underactivity of hormones. Symptoms include in-creased sensitivity to cold, depres-sion, recurring infections, weight loss difficulties, problems with menstruation, dry skin, and fatigue are common symptoms. The condition can be caused by a defect in the synthesis of hormones, a decrease in the pituitary gland's rate of stimulation or limited cellular conversion.

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hypothyroidism (hī´pōthī´roid-izm),

n a diminished activity of the thyroid gland with decreased secretion of thyroxin, resulting in lowered basal metabolic rate, lethargy, sleepiness, dysmenorrhea in females, and a tendency toward obesity. Occasionally there is accompanying gingival hyperplasia. The condition is called cretinism in children and myxedema in adults.

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hypothyroidism

deficiency of thyroid gland activity, with underproduction of thyroxine, or the condition resulting from it. Common in adult dogs, particularly certain breeds, as a result of an idiopathic atrophy of the thyroid or a lymphocytic thyroiditis. Alopecia, weight gain, mental dullness, fatigue, cold intolerance, infertility and neurological deficits are seen. In food animals the syndrome is classical neonatal colloid goiter. See also goiter.

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autoimmune hypothyroidism

see lymphocytic thyroiditis.

congenital hypothyroidism

results from congenital thyroid dysgenesis, defective hormone synthesis or severe iodine deficiency. There is dwarfism, macroglossia and mental dullness.

iatrogenic hypothyroidism

may follow treatment for hyperparathyroidism in cats.

juvenile hypothyroidism

congenital hypothyroidism (above).

primary hypothyroidism

that resulting from disease of the thyroid glands.

secondary hypothyroidism

caused by a deficiency of thyroid-stimulating hormone, usually as a result of a lesion in the pituitary gland.

tertiary hypothyroidism

caused by a lack of synthesis or release of thyrotropin releasing hormone.