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Hypothyroidism

Description

An in-depth report on the causes, diagnosis, treatment, and prevention of hypothyroidism.

Alternative Names

Autoimmune thyroiditis; Hashimoto's thyroiditis

Complications

Hypothyroidism carries serious physical and mental risks for all ages. Studies indicate that subtle adverse health effects occur even with subclinical hypothyroidism, a condition in which the patient has no symptoms but blood tests indicate hypothyroidism. Fortunately, hypothyroidism is now easily diagnosed, and treatment will restore normal thyroid function and relieve symptoms and physical signs of the disease. With treatment, a patient should expect to live a normal life, free of harmful consequences. Iodine deficiency and goiter are still major problems in less developed nations and cause varying degrees of mental retardation in millions of people.

Emergency Conditions

Myxedema Coma. Myxedema coma is a rare, life-threatening complication of untreated hypothyroidism. Symptoms include a severe drop in body temperature (hypothermia), delirium, reduced lung function, slow heart rate, constipation, urine retention, seizures, stupor, fluid build-up, and finally coma. It is uncommon, but may develop in untreated patients subjected to severe stress, such as infection, surgery, or extreme cold. Certain drugs (such as sedatives, painkillers, narcotics, amiodarone, and lithium) may increase the risk. Emergency treatment is required. Mortality rates are high (between 30 - 60%) with the highest risks in older patients and those with persistent hypothermia or heart problems.

Suppurative Thyroiditis. Suppurative thyroiditis is a life-threatening infection of the thyroid gland. It is very rare, since the thyroid is normally immune to infection. People with pre-existing thyroid diseases, such as Hashimoto's thyroiditis, however, may be at higher than average risk for it. It often begins with an upper respiratory infection. Symptoms include fever, neck pain and rash, and trouble swallowing and speaking. Immediate treatment is critical.

Effects of Hypothyroidism and Subclinical Hypothyroidism on the Heart

Thyroid hormones, notably triiodothyronine (T3), affect the heart directly and indirectly. They are closely linked with heart rate and heart output. T3 provides particular benefits by relaxing the smooth muscles of blood vessels. This helps keep the blood vessels open so that blood flows smoothly through them.

Hypothyroidism is associated with:

• Unhealthy cholesterol levels . Hypothyroidism raises levels of total cholesterol, LDL (the so-called bad cholesterol), triglycerides, and other lipids (fat molecules) associated with heart disease. Treating the thyroid condition with thyroid replacement therapy can significantly reduce these levels.
• Mild high blood pressure . Hypothyroidism may slow the heart rate to less than 60 beats per minute, reduce the heart's pumping capacity, and increase the stiffness of blood vessel walls. All of these effects may lead to high blood pressure. Indeed, patients with hypothyroidism have triple the risk of developing hypertension. All patients with chronic hypothyroidism, especially pregnant women, should have their blood pressures checked regularly.
• Heart failure . Hypothyroidism can affect the heart muscle’s contraction and increase the risk of heart failure in people with existing heart disease.

The evidence for subclinical hypothyroidism and heart disease is mixed. Some studies suggest that subclinical hypothyroidism increases the risks for coronary artery disease and heart failure. However, a 2006 study in the Journal of the American Medical Association found that while subclinical hypothyroidism was associated with atrial fibrillation (irregular heart beat), it was not associated with other types of heart disease. Many experts believe that treatment of subclinical hypothyroidism will not help prevent or improve heart problems

Effects of Hypothyroidism and Subclinical Hypothyroidism on the Mind

Depression. Depression is common in hypothyroidism and can be severe. Some psychiatrists suspect that even subclinical hypothyroidism may contribute to depression. The two disorders may have some common physiological basis. Adding thyroid hormones to antidepressants may hasten a depressed patient's recovery, even in some patients who have not been diagnosed with hypothyroidism. Hypothyroidism should be considered as a possible cause of any chronic depression, particularly in older women.

Mental and Behavioral Impairment. Untreated hypothyroidism can, over time, cause mental and behavioral impairment and eventually, even dementia. Whether treatment can completely reverse problems in memory and concentration is uncertain, although many experts believe that only mental impairment in hypothyroidism that occurs at birth is permanent.

Other Health Effects of Hypothyroidism

The following medical conditions have been associated with hypothyroidism. Often the causal relationship is not clear in such cases:

• Iron deficiency anemia
• Respiratory problems
• Kidney function
• Glaucoma. (Some research has associated hypothyroidism with an increased risk for glaucoma.)
• Headache. (Hypothyroidism may worsen headaches in people predisposed to them.)
• Thyroid lymphoma. (Patients with Hashimoto's thyroiditis are at higher risk for this rare form of cancer.)
• Joint stiffness. (Women with hypothyroidism may actually have fewer problems with joint stiffness than women with normal thyroid.)

Effects of Hypothyroidism on Infertility and Pregnancy

Most women with hypothyroidism fail to produce eggs, and many younger women with hypothyroidism are diagnosed with the condition for the first time during a fertility evaluation. A pregnant woman with hypothyroidism has a fourfold risk for miscarriage. In one study, nearly 40% of women with a history of miscarriages and normal thyroid levels had antithyroid antibodies (immune factors that attack thyroid tissue). Those who continue to have hypothyroidism near the time of delivery are in danger of developing high blood pressure and premature delivery. They are also prone to postpartum thyroiditis, which is said to be a contributor to postpartum depression.

Effects of Hypothyroidism on Infants and Children

Children of Untreated Mothers. Children born to untreated pregnant women with hypothyroidism are at risk for impaired mental performance, including attention problems and verbal impairment. Studies on the effects on children of women with subclinical hypothyroidism are less clear, with some reporting lower IQs in such children and others reporting no significant problems.

Effects of Hypothyroidism During Infancy. Transient hypothyroidism is common among premature infants. Although temporary, severe cases can cause difficulties in neurologic and mental development.

Infants born with permanent congenital (inborn) hypothyroidism need to receive treatment as soon as possible after birth to prevent mental retardation, stunted growth, and other aspects of abnormal development (a syndrome referred to as cretinism). It has been estimated that untreated infants can lose up to three to five IQ points per month during the first year. An early start of lifelong treatment avoids or minimizes this damage. Even with early treatment, however, mild problems in memory, attention, and mental processing may persist into adolescence and adulthood.

Effects of Childhood-Onset Hypothyroidism. If hypothyroidism develops in children older than 2 years, mental retardation is not a danger, but physical growth may be slowed and new teeth delayed. If treatment is delayed, adult growth could be affected. Even with treatment, some children with severe hypothyroidism may have attention problems and hyperactivity.

Effects of Hypothyroidism and Childhood X-Ray Treatments

Two million Americans, mostly children, received x-ray treatments to the head or neck between 1920 and 1960 for acne, enlarged thymus gland, recurrent tonsillitis, or chronic ear infections. The risk of developing thyroid nodules and thyroid cancers is increased in these individuals, especially if they have hypothyroidism. Cancer can develop as late as 40 years after the original treatment. Everyone who has had head and neck radiation should be sure to have their thyroid glands examined regularly.

• Review Date: 4/19/2006
• Reviewed By: Harvey Simon, M.D., Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital

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