Hypothyroidism, a clinical state resulting from a deficiency of thyroid hormones due to decreased activity of the thyroid gland. 

Hypothyroidism is the most common disorder of thyroid function.

It is reported to be more common in women than in men. 

In hypothyroidism, there is decreased production and secretion of the thyroid hormones by the thyroid gland.

It is sometimes caused by surgical removal of all or part of the gland. 

An overdose of antithyroid medicine, decreased release of thyroid stimulating hormone by the pituitary gland, or atrophy of the thyroid gland itself can also be responsible. 

Weight gain, sluggishness, dryness of the skin, constipation, arthritis, and slowing of the processes of the body may occur. 

Untreated, hypothyroidism leads to severe facial swelling, coma, and death. 

Treatment is by giving the deficient hormone. Dosage is adjusted to maintain normal levels of thyroid hormones.

The cause of some hypothyroidism is unknown but is thought to be autoimmune in origin.

Other hypothyroidism is caused by destruction of thyroid or pituitary tissue by underlying disease, surgery, or radiation treatment. 

Hypothyroidism is a common disorder that affects all age groups. 

Women between 30 and 60 years of age are most often affected.

It also occurs in approximately 1 of every 4,500 live births. 

The incidence is rising in the elderly population.

When the supply of thyroid hormone is inadequate, a general depression of most cellular enzyme systems and oxidative processes results, reducing the metabolic activity of the cells.

This in turn reduces oxygen consumption, decreases energy production, and lessens body heat. 

Tissues are infiltrated by mucopolysaccharides, carotene is deposited in epidermal layers, adrenergic stimulation is decreased, protein effusion collects in the pericardial and pleural sacs, and proteinaceous ground substances are deposited in tissues.

Signs and symptoms are often insidious in onset. 

They include fatigue and lethargy; mild weight gain; cold, pale, dry, rough hands and feet; reduced attention span with memory impairment, slowed speech, and loss of initiative; swelling in extremities and around the eyes, eyelids, and face; menstrual irregularities; muscle aches and weakness; joint aches and stiffness; clumsiness; hyper stiff reflexes; decreased pulse; decreased blood pressure; agitation; depression; and paranoia.

Myxedema coma is a life-threatening complication of hypothyroidism that requires immediate treatment. 

Other complications include ischemic heart disease, congestive failure, pleural and pericardial effusion, deafness, psychosis, and anemia.

Serum free triiodothyronine and thyroxine are decreased; 

Serum thyroid-stimulating hormone is increased in primary hypothyroidism and decreased in secondary hypothyroidism. 

Oral replacement thyroid hormone; IV form is used for myxedemic coma

Thyroid hormone , thyronine, an iodine-containing compound released by the thyroid gland, mainly as thyroxine (T4), and in smaller amounts as four times more potent triiodothyronine (T3). 

These hormones increase the rate of processing, affect body temperature, regulate protein, fat, and carbohydrate catabolism in all cells. 

They keep up growth hormone release, skeletal maturation, and the heart rate, force, and output. 

They promote central nervous system growth, stimulate the making of many enzymes, and are necessary for muscle tone and vigor. 

All phases of the making and the release of T4 and T3 are regulated by the thyroid-stimulating hormone (TSH) released by the front pituitary gland. 

The production of thyroid hormones is too high in excess thyroid gland activity (hyperthyroidism) and related diseases.

The production is too low in swelling of the face (myxedema), and absent in blocked development (cretinism). 

T4's normal 6 to 7-day half-life in blood is reduced to 3 or 4 days in hyperthyroidism and extended to 9 or 10 days in myxedema. 

T3 has a normal half-life of 2 days or less and, like T4, is used most actively in the liver.

Pharmaceutical preparations of thyroid hormones gotten from animal glands and the synthetic compounds levothyroxine sodium and liothyronine sodium are used as  in patients with hypothyroidism. 

The dosage is initially low. 

It is slowly increased to the optimal level based on the patient's clinical response. 

Over dosage or a rapid increase in the dosage may result in signs of excess thyroid gland activity, as nervousness, tremor, rapid heart beat (tachycardia), irregular heartbeat (cardiac arrhythmia), and menstrual irregularity.

Thyroid stimulating hormone (TSH), also called thyrotropin. A substance released by the front lobe of the pituitary gland. 

It controls the release of thyroid hormone and is necessary for the growth and function of the thyroid gland.

Thyrotropin releasing hormone, thyroid releasing hormone, TSH releasing factor, also called thyrotropin releasing factor (TRF), TSH releasing factor. 

A substance of the hypothalamus that stimulates the release of thyrotropin (thyroid stimulating hormone) from the front pituitary gland.

Signs include swelling of the hands, face, feet, and tissues around the eye. 

The disease may lead to coma and death.

Inflammation of the thyroid gland.

Sudden thyroiditis is caused by infections. 

It is marked by pus and abscess formation. 

It may progress to the less sudden (subacute) disease of the gland. 

Sub acute thyroiditis is marked by fever, weakness, sore throat, and a painfully large gland with tumor like lumps of tissue (granulomas).

Long-term lymphocytic thyroiditis (Hashimoto's disease) is marked by lymphocyte and plasma cell infiltration of the gland and by a larger gland. It seems to be carried as a dominant trait. It may be linked to some autoimmune disorders. 

Another long-term form of thyroiditis is Riedel's struma, a rare progressive formation of fibers (fibrosis) usually of one lobe of the gland but sometimes involving both lobes, the windpipe, and surrounding muscles, nerves, and blood vessels. 

Radiation thyroiditis occasionally occurs 7 to 10 days after the treatment of hyperthyroidism with radioactive iodine 131.