The thyroid gland is an important endocrine gland that controls the body’s metabolism. It is a small butterfly-shaped gland located in the front of the neck just below the Adam’s apple. The thyroid gland produces the hormones tetraiodothyronine (T4) and triiodothyronine (T3).
Together these hormones regulate how your cells use energy. The pathways by which cells use energy is called metabolism. Your body’s general metabolism determines blood pressure, heart rate, and weight.
Hypothyroidism is a condition where your thyroid gland does not make enough thyroid hormone.
Low levels of thyroid hormone interfere with the body’s ability to perform normal metabolic functions such as efficient use of energy from food products, regulation of many chemical reactions in the body, and maintenance of healthy cells, bones and muscles, to name a few.
There is no known prevention for hypothyroidism, nor is there a cure. Once you have it, you have it for life.
What Causes Hypothyroidism?
The most common causes are surgical removal of your thyroid, autoimmune diseases, and radiation treatment.
This may be necessary to treat hyperthyroidism, or tumors of the thyroid gland. Hypothyroidism will occur when the entire gland is removed.
These diseases cause the production of antibodies that attack your thyroid gland. Autoimmune thyroiditis, which can appear suddenly or develop over several years, is more common in women.
Hashimoto’s thyroiditis and atrophic thyroiditis are the most common types.
Radiation treatment for Hodgkin lymphoma and cancers of the head and neck can injure the thyroid gland. If this occurs, the gland cannot produce enough thyroid hormone to keep your metabolism running smoothly.
Radioactive iodine (I-131) destroys the thyroid gland and can be used to treat people with Grave’s disease and thyroid cancer. Grave’s disease is an autoimmune disease that causes hyperthyroidism.
What are the symptoms of hypothyroidism?
The symptoms of hypothyroidism are often subtle. They are not specific (which means they can mimic the symptoms of many other conditions) and are often attributed to aging.
Patients with mild hypothyroidism may have no signs or symptoms. The symptoms generally become more obvious as the condition worsens and the majority of these complaints are related to a metabolic slowing of the body.
Common symptoms are listed below:
- Modest weight gain
- Cold intolerance
- Excessive sleepiness
- Dry, coarse hair
- Dry skin
- Muscle cramps
- Increased cholesterol levels
- Decreased concentration
- Vague aches and pains
- Swelling of the legs
As the disease becomes more severe, there may be puffiness around the eyes, a slowing of the heart rate, a drop in body temperature, and heart failure.
In its most profound form, severe hypothyroidism may lead to a life-threatening coma (myxedema coma). In a severely hypothyroid individual, a myxedema coma tends to be triggered by severe illness, surgery, stress, or traumatic injury.
This condition requires hospitalization and immediate treatment with thyroid hormones given by injection.
Properly diagnosed, hypothyroidism can be easily and completely treated with thyroid hormone replacement. On the other hand, untreated hypothyroidism can lead to an enlarged heart (cardiomyopathy), worsening heart failure, and an accumulation of fluid around the lungs (pleural effusion), or an accumulation of fluid around the heart (pericardial effusion).
Other Causes of Hypothyroidism
Some children are born without a thyroid gland or they may have one that doesn’t function properly.
Viral or Autoimmune Thyroiditis
When antibodies or viruses attack your thyroid, thyroid hormones can leak out. Sometimes all of the thyroid’s hormones are released into your blood at one time.
When this happens, symptoms of thyroid excess or hyperthyroidism occur.
Lithium (used to treat bipolar disease), amiodarone (medication with high iodine content used to treat serious ventricular arrhythmias, interleukin 2 (anti-viral and anti-cancer agent), and interferon alpha (anti-viral agent) are medications that can cause hypothyroidism.
This is more likely to occur in people who have a genetic tendency for autoimmune thyroid disease.
The pituitary is the master gland that signals the thyroid how much hormone it needs to produce. If the pituitary is damaged by trauma, stroke, or tumor, the signal to release thyroxine can stop.
This causes the thyroid to stop making thyroid hormone.
Not Enough or Too Much Iodine
The thyroid gland needs iodine to make T3 and T4. Iodine had to be obtained in the diet. Too little iodine can cause hypothyroidism and, ironically, too much iodine can
block the thyroid’s ability to make thyroid hormone.
Diseases like amyloidosis can cause the thyroid to become overwhelmed by abnormal proteins where the cells cannot function normally.
Groups at Higher Risk for Hypothyroidism
The following groups are at a greater risk for developing hypothyroidism:
- women over age 50.
- people with autoimmune diseases or a parent or grandparent with an autoimmune disease.
- people given radioactive iodine or radiation therapy
- people treated with antithyroid medication
- those with a history of radiation to the neck and upper chest people with a partial thyroidectomy (removal of the thyroid)
- post-partum females
How is hypothyroidism diagnosed?
A diagnosis of hypothyroidism can be suspected in patients with fatigue, cold intolerance, constipation, and dry, flaky skin. A blood test is needed to confirm the diagnosis.
When hypothyroidism is present, the blood levels of thyroid hormones can be measured directly and are usually decreased. However, in early hypothyroidism, the level of thyroid hormones (T3 and T4) may be normal.
Therefore, the main tool for the detection of hyperthyroidism is the measurement of the TSH, the thyroid stimulating hormone.
As mentioned earlier, TSH is secreted by the pituitary gland. If a decrease of thyroid hormone occurs, the pituitary gland reacts by producing more TSH and the blood TSH level increases in an attempt to encourage thyroid hormone production.
This increase in TSH can actually precede the fall in thyroid hormones by months or years (see the section on Subclinical Hypothyroidism below). Thus, the measurement of TSH should be elevated in cases of hypothyroidism.
However, there is one exception. If the decrease in thyroid hormone is actually due to a defect of the pituitary or hypothalamus, then the levels of TSH are abnormally low.
As noted above, this kind of thyroid disease is known as “secondary” or “tertiary” hypothyroidism. A special test, known as the TRH test, can help distinguish if the disease is caused by a defect in the pituitary or the hypothalamus.
This test requires an injection of the TRH hormone and is performed by an endocrinologist (hormone specialist).
The blood work mentioned above confirms the diagnosis of hypothyroidism, but does not point to an underlying cause.
A combination of the patient’s clinical history, antibody screening (as mentioned above), and a thyroid scan can help diagnose the precise underlying thyroid problem more clearly.
If a pituitary or hypothalamic cause is suspected, an MRI of the brain and other studies may be warranted. These investigations should be made on a case by case basis.
Treatment Options for Hypothyroidism
A common treatment is to replace thyroxine with a specific synthetic thyroid hormone (levothyroxine). This hormone is safe and affordable, but determining the right dosage often takes time. Your metabolic rate has to be returned to normal.
Raising it too quickly can cause palpitations and make some medical problems like coronary artery disease and atrial fibrillation worse. Symptoms of thyroid hormone excess are:
- shakiness or tremors
- increased appetite
Diets rich in soy and high fiber can interfere with levothyroxine absorption. Medications and supplements also can reduce absorption. These include:
- calcium supplements
- iron supplements
- aluminum hydroxide (present in some antacids)