Hypothyroidism is a condition in which the thyroid gland fails to produce enough of the hormones that are essential for a wide variety of functions in the body, including proper cardiac, nerve, gastrointestinal, and psychologic function.
Hypothyroidism affects about five million Americans. The most common cause worldwide is iodine deficiency. However, in the United States, where iodized salt is commonly used, most cases are due to an autoimmune disease called Hashimoto's thyroiditis. Other causes include drugs (e.g., lithium and amiodarone), genetic factors, neck surgery, and radiation therapy.
Myxedema coma is a life-threatening complication of hypothyroidism that is marked by confusion, disorientation, low blood pressure, low body temperature, decreased breathing rate, and, though rarely, coma. Causes of myxedema coma in patients with hypothyroidism can include infection, heart attack, stroke, trauma (including surgery and burns), low blood sugar, electrolyte disturbances, severe bleeding, noncompliance with thyroid medications, and various drugs (e.g., beta-blockers, sedatives, narcotics, and phenothiazine antipsychotic drugs).
Symptoms can be subtle and nonspecific, including weakness, fatigue, and weight gain. Chronic or severe disease can result in:
- Goiter (a swelling at the base of the neck)
- Dull facial expression
- Drooping eyelids
- Hoarse speech
- Thinning or dry, brittle hair
- Dry skin
- Myxedema (swelling of the skin)
- Menstrual disorders
- Slow heart rate
- Decreased coordination
- Gender: The majority of cases occur in women.
- Age: Risk of hypothyroidism increases with age.
- Genetics: Hypothyroidism is associated with several gene mutations.
Hypothyroidism: Diagnosis and Treatment
- A medical history and physical examination are the first steps in diagnosis. However, because the clinical symptoms are highly variable, diagnosis ultimately relies on laboratory testing.
- Blood testing to measure the blood levels of thyroid hormones will diagnose the disease. However, in some cases, certain conditions can lead to altered thyroid hormone tests in the absence of thyroid disease. These include malnutrition, chronic illness, diabetes, drugs, and pregnancy.
- Because high cholesterol levels can occur in hypothyroidism, most patients should also be tested for cholesterol levels.
- Further laboratory testing may be useful in selected cases. For example, ultrasound of the neck and thyroid is sometimes recommended.
- In some cases, biopsy of the thyroid may be recommended to rule out thyroid cancer.
- In most cases, hypothyroidism requires lifelong thyroid hormone replacement. The usual regimen begins at 50μg/day and increases by 25 to 50 μg/day every four to eight weeks until an appropriate dose is reached. While the dose is being increased, regular blood testing is necessary to monitor the body's response to the medication.
- Iodine deficiency is treated with potassium iodide.
- Myxedema coma is a medical emergency that requires hospitalization, intravenous thyroid hormone and steroids, and fluids.
Hypothyroidism: Nutritional Considerations
The nutritional considerations can help reduce the risk of hypothyroidism or aid in treatment:
- Iodized salt: The use of iodized salt is a well-accepted public health strategy for decreasing the incidence of iodine deficiency disorders, particularly hypothyroidism.
- Gluten-free diet in patients with celiac disease: Hypothyroidism is relatively common in patients with celiac disease. Although evidence is limited, clinical trials found that most celiac disease patients with mild hypothyroidism who strictly followed a gluten-free diet for one year experienced improved thyroid function and a reduced need for thyroid hormone medication.
- Iron supplementation: Iron deficiency may also increase the risk for thyroid disease. Although Western, meat-eating populations have greater iron levels than non-Western populations, some individuals are low in iron. One study revealed that thyroid hormone levels were significantly lower in women with iron-deficiency anemia, compared with women who had normal iron levels. In these patients, iron supplementation (or other treatments for iron deficiency) may be useful. However, iron supplements should be taken apart from thyroid hormone medication (see below).
- When thyroid medication is used, it should be taken on an empty stomach. Meals can decrease the absorption of thyroid hormone, with a particularly noticeable effect from high-fiber meals. Both calcium carbonate and iron supplements can significantly reduce absorption of thyroid hormone and reduce its effectiveness. This may have particular relevance for older women, who are more likely to need thyroid hormone replacement and to be using calcium supplements.