Hypothyroidism; secondary

Causes and Risks:
The thyroid gland is an important organ of the endocrine system, located in the front of the neck just below the larynx. The thyroid gland secretes the hormones thyroxine ( T4 ), triiodothyronine ( T3 ), and calcitonin , which control body metabolism and regulate calcium balance. The secretion of T3 and T4 by the thyroid is controlled by an endocrine feedback system involving the pituitary gland and the hypothalamus in the brain. Calcitonin is regulated by the amount of calcium in the blood and acts in conjunction with the parathyroid gland to control calcium levels. Since the thyroid gland is regulated by the pituitary gland and the hypothalamus, thyroid disorders may result not only from defects in the gland itself, but also from disruption of the control system. Thyroid disorders caused by overproduction of thyroid hormones are called hyperthyroidism , and underproduction of these hormones is known as hypothyroidism .

The causes of secondary hypothyroidism are failure of the pituitary gland to secrete a hormone to stimulate the thyroid gland, or failure of the hypothalamus. Hypothyroidism or underactivity of the thyroid gland may cause a variety of symptoms and may affect all body functions. The body's normal rate of functioning slows causing mental and physical sluggishness. The symptoms may vary from mild to severe, with the most severe form called myxedema which is a medical emergency. Risk factors include being over 50 years old, being female, and having a history of pituitary or hypothalamic dysfunction . The incidence is 2 out of 1,000 people.

Prevention:
This condition may not be preventable. Awareness of risk may allow early diagnosis and treatment.

Symptoms:
Early symptoms:

Late symptoms:



Signs and Tests:
A physical exam that reveals a small thyroid gland. Vital signs (temperature, pulse , rate of breathing, blood pressure ) reveal a slow heart rate , low blood pressure , and low temperature.

A chest X-ray reveals an enlarged heart.

Laboratory tests to determine thyroid function include:

Additional laboratory abnormalities may include:



Treatment:
The purpose of treatment is to replace the deficient thyroid hormone. Levothyroxine is the most commonly used medication, but others are available. The lowest dose effective in relieving symptoms is used. Life-long therapy is indicated as relapses will occur if therapy is interrupted. Medication must be continued even when symptoms subside.

After replacement therapy has begun, report any symptoms of increased thyroid activity ( hyperthyroidism ), such as restlessness , rapid weight loss , and sweating .

A high-fiber , low-calorie diet and moderate activity will help relieve constipation and promote weight loss.

Myxedema coma is treated by intravenous thyroid replacement and steroid therapy. Supportive therapy of oxygen, assisted ventilation, fluid replacement, and intensive care nursing may be indicated.

Prognosis:
With early treatment, return to the normal state is usual. However, relapses will occur if the medication is not continued. Myxedema coma can result in death.

Complications:
Myxedema coma, the most severe form of hypothyroidism , is rare. It may be caused by an infection, illness, exposure to cold or certain medications.

Symptoms and signs of myxedema coma include:

Other complications include:



Call Your Healthcare Provider:
Call your health care provider if signs of hypothyroidism are present, or if chest pain or rapid heart beat occur.

Call your health care provider if restlessness , rapid weight loss , sweating , or other symptoms occur after beginning treatment for this disorder.