Hypothyroidism is a condition in which the body lacks sufficient thyroid hormone. Hypothyroidism is also known as an underactive thyroid. It occurs when the thyroid gland does not make enough thyroxine. Many of the symptoms of hypothyroidism are very subtle and are experienced by people without thyroid disease. Thus, a lot of physicians overlook the symptoms of fatigue, weight gain and depression and attribute them to other causes. It is a relatively common disease in purebred domestic dogs as well, and can have a hereditary basis in dogs. The risk of developing hypothyroidism tends to increase with age; older women have the highest risk. There are several distinct causes for chronic hypothyroidism in human beings, the most common being Hashimoto's thyroiditis (an autoimmune disease) and radioiodine therapy for hyperthyroidism. The thyroid gland, located in the front of the neck just below the larynx, secretes hormones that control metabolism. Because thyroid hormone affects growth, development, and many cellular processes, inadequate thyroid hormone has widespread consequences for the body. Women, especially those older than 50, are more likely to have hypothyroidism than men are. In rare cases, hypothyroidism occurs in infants and children.

In hypothyroidism, the thyroid is under active, with too little of the thyroid hormones being released. The thyroid is situated just below your "Adams apple" or larynx. The severity of hypothyroidism varies widely. Patients are classified as "subclinical hypothyroid" if diagnostic findings show thyroid hormone abnormalities, but they do not exhibit any symptoms. Others have moderate symptoms that can be mistaken for other diseases and states. The two most important thyroid hormones are thyroxine (T4) and triiodothyronine (T3), which account for 99.9% and 0.1% of thyroid hormones present in the blood respectively. Untreated hypothyroidism in infants can cause brain damage, leading to mental retardation and developmental delays. Every state in the United States tests newborns for hypothyroidism. The hypothalamus is a brain structure that normally signals the pituitary gland to make thyroid stimulating hormone (TSH), which causes the thyroid to make thyroid hormones. Some medical problems can affect either the hypothalamus or the pituitary gland, and interrupt the chain of signals from the brain to the thyroid. Decreased thyroid hormone effect can cause increased levels of total cholesterol and low-density lipoprotein (LDL) cholesterol and a possible change in high-density lipoprotein (HDL) cholesterol. In addition, hypothyroidism may result in an increase in insulin resistance.

Causes of Hypothyroidism

The common causes and risk factor's of Hypothyroidism include the following:

The most common cause of hypothyroidism is Hashimoto's thyroiditis, a disease of the thyroid gland where the body's immune system attacks the gland.

Lymphocytic Thyroiditis After Hyperthyroidism.

Thyroid Destruction (from radioactive iodine or surgery).

External beam radiation, which is used to treat some cancers, such as Hodgkin's lymphoma. This radiation treatment can destroy the thyroid gland.

An operation to remove part of the thyroid gland (usually for thyrotoxicosis ), often years earlier.

Radioactive iodine treatment for thyrotoxicosis.

Drugs such as amiodarone, interferon alpha, thalidomide, and stavudine have also been associated with primary hypothyroidism.

Use of radioactive iodine for treatment of Graves disease generally results in permanent hypothyroidism within one year of therapy. The frequency is much lower in patients with toxic nodular goiters and those with autonomously functioning thyroid nodules.

Symptoms of Hypothyroidism

Some sign and symptoms related to Hypothyroidism are as follows:

A puffy face.

Tendency to feel cold.

Joint or muscle pain.

Hoarse voice.

An elevated blood cholesterol level.

Fatigue.

Feeling sluggish and tired.

Weakness.

Choking sensation or difficulty swallowing.

Goiter (enlarged thyroid causing a lump in the neck).

Coarseness or loss of hair.

Shortness of breath with a shallow and slow respiratory pattern.

Treatment of Hypothyroidism

Here is list of the methods for treating Hypothyroidism:

If you have coronary artery disease or severe hypothyroidism, your doctor may start treatment with a smaller amount of medication and gradually increase the dosage.

Hypothyroidism is treated with replacement doses of thyroid hormones. Synthetic forms of these hormones are used, including levothyroxine (Synthroid, Levoxyl and other brand names), liothyronine (Cytomel) or liotrix (Thyrolar).

It is treated by replacing the amount of hormone that your own thyroid can no longer make, to bring your T4 and TSH back to normal levels.

The average dose of T4 replacement in adults is approximately 1.6 micrograms per kilogram per day.

Progressive hormone replacement allows your heart to adjust to the increase in metabolism.

Supportive therapy?(oxygen, assisted ventilation, fluid replacement) and intensive-care nursing may be indicated.

Permanently decreased metabolism requires lifelong treatment with thyroxine tablets.