Underactive thyroid gland is called as hypothyroidism. It is a term used to describe a condition in which there is a reduced level of thyroid hormone (thyroxine) in the body. This can cause various symptoms, the most common being: tiredness, weight gain, constipation, aches, dry skin, lifeless hair and feeling cold. Thyroxine is a hormone (body chemical) made by the thyroid gland in the neck. It is carried round the body in the bloodstream. It helps to keep the body's functions (the metabolism) working at the correct pace. Many cells and tissues in the body need thyroxine to keep them going correctly.
When thyroid gland is unable to make enough thyroxine it results in hypothyroidism. Hypothyroidism causes many of the body's functions to slow down. Hypothyroidism may also occur if there is not enough thyroid gland left to make thyroxine, eg after surgical removal or injury. (In contrast, if you have hyperthyroidism, you make too much thyroxine. This causes many of the body's functions to speed up.)
When the thyroid gland fails to produce enough hormones it results in hypothyroidism. Hypothyroidism may be due to a number of factors, including:
- Autoimmune disease. People who develop a particular inflammatory disorder known as Hashimoto's thyroiditis suffer from the most common cause of hypothyroidism. Autoimmune disorders occur when your immune system produces antibodies that attack your own tissues. Sometimes this process involves your thyroid gland. Scientists aren't sure why the body produces antibodies against itself. Some think a virus or bacterium might trigger the response, while others believe a genetic flaw may be involved. Most likely, autoimmune diseases result from more than one factor. But however it happens, these antibodies affect the thyroid's ability to produce hormones.
- Hyperthyroidism treatment. People who produce too much thyroid hormone (hyperthyroidism) are often treated with radioactive iodine or anti-thyroid medications to reduce and normalize their thyroid function. However, in some cases, treatment of hyperthyroidism can result in permanent hypothyroidism.
- Surgery of thyroid gland. Removing all or a large portion of your thyroid gland can diminish or halt hormone production. In that case, you'll need to take thyroid hormone for life.
- Radiotherapy. Radiation used to treat cancers of the head and neck can affect your thyroid gland and may lead to hypothyroidism.
- Use of certain medications. A number of medications can contribute to hypothyroidism. One such medication is lithium, which is used to treat certain psychiatric disorders. If you're taking medication, ask your doctor about its effect on your thyroid gland.
Rarely, hypothyroidism may result from one of the following:
- Diseases arising due to birth defects. Some babies are born with a defective thyroid gland or no thyroid gland. In most cases, the thyroid gland didn't develop normally for unknown reasons, but some children have an inherited form of the disorder. Often, infants with congenital hypothyroidism appear normal at birth. That's one reason why most states now require newborn thyroid screening.
- Disorders of pituitary. A relatively rare cause of hypothyroidism is the failure of the pituitary gland to produce enough thyroid-stimulating hormone (TSH) — usually because of a benign tumor of the pituitary gland.
- Pregnancy and related disorders. Some women develop hypothyroidism during or after pregnancy (postpartum hypothyroidism), often because they produce antibodies to their own thyroid gland. Left untreated, hypothyroidism increases the risk of miscarriage, premature delivery and preeclampsia — a condition that causes a significant rise in a woman's blood pressure during the last three months of pregnancy. It can also seriously affect the developing fetus.।
- Deficiency of iodine deficiency. The trace mineral iodine — found primarily in seafood, seaweed, plants grown in iodine-rich soil and iodized salt — is essential for the production of thyroid hormones. In some parts of the world, iodine deficiency is common, but the addition of iodine to table salt has virtually eliminated this problem in the United States. Conversely, taking in too much iodine can cause hypothyroidism.
One is at increased risk to develop hypothyroidism if one or more of following risk factors are present:
- Woman older than age 60
- Autoimmune disease
- Family history of an autoimmune disease
- Treatment with radioactive iodine or anti-thyroid medications
- Having received radiation to your neck or upper chest
- Thyroid surgery (partial thyroidectomy)
- Pregnancy or delivering a baby within the past six months
You may barely notice the symptoms of hypothyroidism at first, such as fatigue and weight gain, or you may simply attribute them to getting older. But as your metabolism continues to slow, you may develop more obvious signs and symptoms. Hypothyroidism signs and symptom may include:
- Unexplained weight gain
- Puffy face
- Increased sensitivity to cold
- Dry skin
- Muscle weakness
- Elevated blood cholesterol level
- Muscle aches, tenderness and stiffness
- Pain, stiffness or swelling in your joints
- Heavier than normal or irregular menstrual periods
- Thinning hair
- Slowed heart rate
- Impaired memory
In untreated hypothyroidism, signs and symptoms can gradually become more severe. Constant stimulation of your thyroid gland to release more hormones may lead to an enlarged thyroid (goiter). In addition, you may become more forgetful, your thought processes may slow, or you may feel depressed.
Myxedema is an advanced type of hypothyroidism. It is rare, but when it occurs it can be life-threatening. Signs and symptoms include low blood pressure, decreased breathing, decreased body temperature, unresponsiveness and even coma. In extreme cases, myxedema can be fatal.
Hypothyroidism can be diagnosed by a blood test. A normal blood test will also rule it out if symptoms suggest that it may be a possible diagnosis. One or both of the following may be measured:
- TSH. This hormone is made in the pituitary gland. It is released into the bloodstream. It stimulates the thyroid gland to make thyroxine. If the level of thyroxine in the blood is low, then the pituitary releases more TSH to try to stimulate the thyroid gland to make more thyroxine. Therefore, a raised level of TSH means the thyroid gland is underactive and is not making enough thyroxine.
- Thyroxine (T4). A low level of T4 confirms hypothyroidism.
In some people. TSH level is raised but they have a normal T4 level. This means that you are making enough thyroxine but the thyroid gland is needing extra stimulation from TSH to make the required amount of thyroxine. In this situation you have an increased risk of developing hypothyroidism in the future. Your doctor may advise a repeat blood test every so often to see if you do eventually develop hypothyroidism. Other tests are not usually necessary unless a rare cause of hypothyroidism is suspected. For example, tests of the pituitary gland may be done if both the TSH and T4 levels are low.
Untreated hypothyroidism can lead to :
- An increased risk of developing heart disease. This is because a low thyroxine level causes the blood lipids (cholesterol, etc) to rise.
- An increased risk of developing some pregnancy complications - for example: pre-eclampsia, anaemia, premature labour, low birth weight, stillbirth, and serious bleeding after the birth.
- Chances of developing hypothyroid coma (myxoedema coma) which is a very rare complication.
With treatment, however, the outlook is excellent. With treatment, symptoms usually go, and you are very unlikely to develop any complications.
Hypothyroidism treatment involves daily use of the synthetic thyroid hormone levothyroxine. This oral medication restores adequate hormone levels, reversing the signs and symptoms of hypothyroidism. Post few weeks of starting treatment, you'll notice that you're feeling less fatigued. The medication also gradually lowers cholesterol levels elevated by the disease and may reverse any weight gain. Treatment with levothyroxine is usually lifelong, but because the dosage you need may change, your doctor is likely to check your TSH level every year.
Determining proper dosage may take time. To determine the right dosage of levothyroxine initially, your doctor generally checks your level of TSH after two to three months. Excessive amounts of the hormone can cause side effects, such as:
- Increased appetite
- Heart palpitations
Your doctor may start treatment with a smaller amount of medication and gradually increase the dosage if you have coronary artery disease or severe hypothyroidism. Progressive hormone replacement allows your heart to adjust to the increase in metabolism. Levothyroxine causes virtually no side effects when used in the appropriate dose and is relatively inexpensive. If you change brands, let your doctor know to ensure you're still receiving the right dosage. Also, don't skip doses or stop taking the drug because you're feeling better. If you do, the symptoms of hypothyroidism will gradually return.
As everyone forgets to take their tablets from time to time, don't worry if you miss a tablet as it is not dangerous to miss the odd forgotten levothyroxine tablet. If you forget to take a dose, take it as soon as you remember if this is within 2 or 3 hours of your usual time. If you do not remember until after this time, skip the forgotten dose and take the next dose at the usual time. Do not take two doses together to make up for a missed dose. However, you should try to take levothyroxine regularly each morning for maximum benefit.
Some drugs, supplements and even some foods may affect your ability to absorb levothyroxine. Talk to your doctor if you eat large amounts of soy products or a high-fiber diet or you take other medications, such as:
- Iron supplements
- Aluminum hydroxide, which is found in some antacids
- Calcium supplements
In cases of subclinical hypothyroidism, discuss treatment with your doctor. For a relatively mild increase in TSH, you probably won't benefit from thyroid hormone therapy, and treatment could even be harmful. For a higher TSH level, on the other hand, thyroid hormones may improve your cholesterol level, the pumping ability of your heart and your energy level.