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

Alternative Names

Autoimmune Thyroiditis; Hashimoto's Thyroiditis


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. It should be noted, however, that iodine deficiency and goiter are still major problems in less developed nations, causing 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 (e.g., sedatives, pain killers, narcotics, amiodarone, and lithium) may increase the risk. Emergency treatment is required. Mortality rates are high (between 30% and 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 thus helping to keep them open so blood may flow smoothly through them.

Hypothyroidism is associated with unhealthy cholesterol levels, mild high blood pressure, impaired heart muscle contraction, and heart failure in people with existing heart disease. There is some evidence that even subclinical hypothyroidism increases the rates of heart disease and heart attacks in older women.

Cholesterol and Lipid Levels. Hypothyroidism is significantly associated with high 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. (Some experts are suggesting, in fact, that patients with high cholesterol should be assessed for thyroid function before they are given cholesterol-lowering agents, although this is controversial.) Even subclinical hypothyroidism poses a higher risk for unhealthy cholesterol levels. Research is mixed, however, on whether this association has any significance and justifies treating this mild condition.

High Blood Pressure (Hypertension). Hypothyroidism may slow the heart rate to less than 60 beats per minute, reduce the hearts 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 a three-fold increased risk of hypertension. Blood flow may even be affected in patients with subclinical hypothyroidism. All patients with chronic hypothyroidism, especially pregnant women, should have their blood pressures checked regularly.

Homocysteine. Studies are finding that hypothyroidism is associated with elevated levels of homocysteine, an amino acid that is a suspect in heart disease. High levels can be prevented with supplements of vitamins B6, B12, and folic acid.

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. In one study, both triiodothyronine (T3) and L-tryptophan (a chemical important in depression) appeared to be taken up by the same portion of red blood cells. Interesting implications of the study are that alterations in one substance may affect the other. Adding thyroid hormones to antidepressants, in fact, hastens a depressed patients 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.
  • Glaucoma. Some research has associated hypothyroidism with an increased risk for glaucoma.
  • Headache. Hypothyroidism may also worsen headaches in people predisposed to them.
  • Thyroid lymphoma. Patients with Hashimoto's thyroiditis are at higher risk for this cancer, which is still very rare.

Effects of Hypothyroidism on Infertility and Pregnancy

Most women with hypothyroidism fail to produce eggs, and, in fact, 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 remain hypothyroid 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 other 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 two 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. Cancer can develop as late as 40 years after the original treatment. This risk is increased in people who develop hypothyroidism.Everyone who has had head and neck radiation should be sure to have their thyroid glands examined regularly.


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