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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

Diagnosis

Advances in diagnostic methods now make it possible to detect hypothyroidism in almost all cases before severe symptoms develop. Physicians can make the diagnosis of hypothyroidism after completing a history and physical exam of the patient and performing sensitive laboratory tests on the patients blood.

Physical Examination

The physician will check the heart, eyes, hair, skin, and reflexes for signs of hypothyroidism.

Goiter. The presence of a goiter (an enlarged thyroid), especially a rubbery, painless one, may be an indication of Hashimotos disease. If the thyroid is tender and enlarged but not necessarily symmetrical, the physician may suspect subacute thyroiditis. A diffusely enlarged gland may occur in hereditary hypothyroidism, in postpartum patients, or from use of iodides or lithium. Goiters may also develop in people with iodide deficiency.

Thyroid Neck Check. Women who are experiencing menopausal symptoms which may be masking those of hypothyroidism should perform a simple self-examination called the Thyroid Neck Check.

Thyroid Neck Check

  • Hold a mirror in front of the area of the neck where the thyroid gland is located. This area is just below the Adam's apple and right above the collarbone. (Note: The Adam's apple is not the thyroid location.)
  • Tip the head back.
  • Take a drink of water and swallow, watching the neck during the process.
  • Check for any bulging or protrusions. If any is detected, call a physician for a check up.

Thyroid Hormone and Antibody Tests

In diagnosing hypothyroidism, blood tests measuring hormone level are needed to make a correct diagnosis. In some cases, antibody tests are also helpful.

Thyroxine (T4). Hypothyroidism is a condition marked by low thyroxine (T4) hormone levels and they are usually measured. However, the findings from this test are usually inadequate for the following reasons:

  • T4 levels can be normal early in the disease process leading to hypothyroidism. If hypothyroidism is suspected, other tests are needed.
  • T4 levels can be low in patients who do not have hypothyroidism. For instance, thyroxine can be extremely variable in very elderly or seriously ill patients and during pregnancy.

Measuring thyroxine is usually performed using a process called a T3 resin uptake to correct for the presence of medications (e.g., birth control pills, aspirin, and others) that could distort the results. Other tests are needed to confirm a diagnosis of hypothyroidism.

Thyrotropin (Thyroid-Stimulating Hormone or TSH). Measuring TSH is the most sensitive indicator of hypothyroidism. (As with thyroxine levels, however, TSH levels can vary in pregnant women and patients who are ill with other conditions.) In general, results indicate the following:

  • TSH levels over 10mU/L. This is a clear indicator of hypothyroidism if T4 levels are low--and, in most cases, even if they are normal. Patients usually require thyroxine (T4) replacement therapy. They should also be tested for high cholesterol levels and antithyroid antibodies.
  • Levels between 5 mU/l and 10 mU/L. Patients with signs and symptoms of hypothyroidism, usually need thyroxine replacement therapy. Patients without symptoms have subclinical hypothyroidism and should be rechecked annually. Antibody tests should also be performed.
  • TSH levels between 0.5 to 5.0 mU/L. These indicate normal thyroid function. (Abnormally low levels suggest hyperthyroidism.)
  • It should be noted that the specific TSH measurement--even if it is significantly higher than 10 mU/L--is not associated with the severity of the condition. This can be determined only by measuring thyroxine levels and evaluating the patient's symptoms.

Antithyroid Antibodies. If TSH levels suggest hypothyroidism or subclinical hypothyroidism, then physician will usually perform a blood test for specific antithyroid antibodies that act against a factor called thyroperoxidase. Tests may also be performed for antibodies to thyroglobulin. Results depend on the patient's condition:

  • Patients with confirmed hypothyroidism (TSH levels over 10 mU/L). Positive test results in such patients confirm the need for thyroxine replacement therapy. (Even if antibody results are negative, such patients usually require thyroxine replacement therapy). About 90% patients with Hashimotos thyroiditis test positive for antibodies to thyroperoxidase and up to half have thyroglobulin antibodies.
  • In patients with subclinical hypothyroidism (TSH between 5 mU/L 10 mU/L). If antibody levels are high, then thyroxine therapy is usually warranted, since it indicates an underlying autoimmunity condition that poses a high risk for later thyroid failure. If the tests are negative, but patients have thyroid-related problems (e.g., high cholesterol, female infertility) they should be monitored annually with hormone tests.

Of note, about 10% of the American population and 25% of women over 60 years old carry these antibodies and the majority of these women have no thyroid problems. Only about 0.5% have full-blown hypothyroidism and 10% have subclinical hypothyroidism. In one 10-year study, however, people with normal thyroid results and high levels of antibodies still had an annual risk of 2% to 4% for developing hypothyroidism.

Other Hormone Tests Used for Thyroid Function. Other hormone tests are often taken if hyperthyroidism is suspected. They include tests for triiodothyronine (T3) and thyroglobulin (also called thyroid binding globulin). Such measurements, however, may also be helpful in detecting sudden temporary increases in thyroid hormone (thyrotoxicosis) that can precede certain forms of autoimmune thyroiditis.

Imaging Tests

Thyroid Scintigraphy. Thyroid scintigraphy tests scan the thyroid and pick up images highlighted by small amounts of radioactive substances. Thyroid scans can be used to determine whether the thyroid is producing normal amounts of hormone. The patient drinks a small amount of radioactive iodine or technetium and waits until it has been through the thyroid. Images of a properly functioning thyroid would show uniform levels of absorption throughout the gland. Overactive areas would show up white and underactive areas would appear dark. Thyroid scans are usually unnecessary unless the physician needs to rule out suspected cancer.

Ultrasound. Ultrasound has limited value, but it can visualize the thyroid and specific abnormalities, such as nodules. (It cannot measure the thyroid glands function, however.)

Thyroid ultrasound Click the icon to see an image of thyroid ultrasound.

More Advanced Imaging Tests. If laboratory tests suggest that a pituitary or hypothalamus problem is causing hypothyroidism, the physician will usually order brain imaging procedures using computed tomography (CT) scans or magnetic resonance imaging (MRI). MRIs may also be used for determining the extent of thyroid cancers and of goiters. MRIs are also being used for investigating hypothyroidism in infants and for determining widespread effects of autoimmune thyroiditis (such as Hashimoto's hypothyroidism).

Needle Aspiration Biopsy

Needle aspiration biopsy is used to obtain thyroid cells for microscopic evaluation. It may be useful to rule out thyroid cancer in patients with suspected Hashimotos hypothyroidism, especially if they have difficulty swallowing or develop a goiter. Much like drawing blood, the physician injects a small needle into the thyroid gland and draws cells from the gland into a syringe. The cells are put onto a slide, stained, and examined under a microscope.

Other Blood Tests

Cholesterol levels need to be checked. Other blood tests may be performed to detect levels of calcitonin, calcium, prolactin, and thyroglobulin and to check for anemia and liver function, all of which may be affected by hypothyroidism.

Screening Recommendations for Hypothyroidism

Screening in Older Adults

Some physicians believe that because thyroid problems are so common in the elderly and thyroid hormone tests are so inexpensive, blood tests for thyroid function should be routine. Undiagnosed hypothyroidism in elderly patients can develop into a serious and even life-threatening situation. Hyperthyroidism also poses many health risks. In fact, during the period around menopause, the symptoms of menopause and hypothyroidism are similar and can easily be confused with each other.

Professional organizations differ widely on screening recommendations. Most do not recommend widespread screening for healthy adults:

  • The American College of Physicians recommends that women over 50 years old be screened for thyroid disorders every five years. The American Academy of Family Physicians believes that adults do not have to be screened until they are over 60.
  • The American Thyroid Association, however, recommends that all adults, both men and women, begin their screening at age 35 and every five years afterward. Experts in this organization argue that such early screening is inexpensive and would prevent progression to hypothyroidism, and therefore possibly heart disease, in people with subclinical hypothyroidism. Such an approach would also eliminate the need for expensive anti-cholesterol drugs.

Screening in Pregnant Women

Untreated hypothyroidism in a pregnant woman, particularly in the first trimester, may have adverse neurologic effects on the unborn child. All pregnant women should be tested for thyroid function. It should be noted, however, that the elevated levels of estrogen that occur during pregnancy cause thyroid hormone levels to rise. Therefore, if a woman had low thyroid levels before pregnancy, test results for thyroxine after she gets pregnant may actually be normal. In addition, diagnosing and treating hypothyroidism even early in the pregnancy may still not prevent birth defects in the infant. Some experts go further, then, and propose that screening be done on any woman who is planning a pregnancy to help determine those who may be at increased risk for hypothyroidism and, if needed, begin treatment as early as possible during the critical first trimester.

Screening in Infants

It is very difficult to diagnose hypothyroidism in newborns by symptoms alone. Fortunately, almost all newborns with hypothyroidism are identified shortly after birth through an effective national screening program using a thyroid blood test. Each year over 1,500 children are now saved from subnormal intelligence.

Ruling Out Other Disorders

The symptoms of hypothyroidism are so similar to common conditions, including just aging, it often makes diagnosis difficult.

Conditions That Cause Thyroid Abnormalities. Some conditions may cause thyroid abnormalities without symptoms and must be differentiated from subclinical hypothyroidism. They include, although are not limited to, the following:

  • Inadequate response to thyroid therapies in people with hypothyroidism.
  • Recovery from a severe illness that is unrelated to thyroid disorders.
  • Chronic kidney failure.
  • Failure of the adrenal gland.

Aging-Related Disorders. Some symptoms of hypothyroidism and aging are very similar. Menopausal symptoms often resemble hypothyroidism. Many other problems related to aging, such as vitamin deficiencies, Parkinsons and Alzheimers diseases, and arthritis, also have characteristics that can mimic hypothyroidism.

Obesity. Many people who are overweight believe that they have an underactive thyroid gland, but only a very small percentage of obese people actually have hypothyroidism. Hypothyroid patients generally show only a moderate weight increase of five to 10 pounds, mainly from accumulation of fluid, and in fact they often have a decreased appetite.

Depression. A lack of interest in personal relationships, drowsiness, an increase in sleep, slowing of speech, and general apathy are signs of clinical depression as well as hypothyroidism. The two disorders, in fact, often coexist, particularly in older women, so diagnosing one does not rule out the presence of the other.

Diseases of Muscles and Joints. Joint and muscle aches may be the first symptoms of hypothyroidism. Most likely, however, such pain is not caused by hypothyroidism if other thyroid symptoms remain absent. Numerous conditions can cause muscle and joint pain, and if thyroid levels are normal the physician should look for other causes.

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