What causes hypothyroidism?
The most common cause of thyroid hormone deficiency is called Hashimoto's thyroiditis. Hashimoto was the first physician to describe the disorder and hence his name has been applied to this autoimmune disorder. Autoimmune disorders are diseases where the immune system gets "confused" and accidentally attacks one of the body's organs instead of fighting off foreign invaders such as bacteria and viruses that cause pneumonia or other infections. The same body system begins to attack and destroy cells in the thyroid gland, resulting in the failure of the body to produce the necessary amount of thyroid hormone.
Other common causes of hypothyroidism include:
- cases arising after surgery or radioactive iodine therapy for Grave's disease
- silent thyroiditis
- subacute thyroiditis
- postpartum thyroiditis radioactive iodine use
- pituitary gland dysfunction
- hormone resistance
- iodine deficiency
Hypothyroidism due to silent thyroiditis, subacute thyroiditis, or postpartum thyroiditis usually is self-limited and naturally corrects itself within a number of months.
Iodine deficiency is an extremely rare cause of hypothyroidism in people living in North America or Europe, but can still be seen in people living in underdeveloped countries where salt is not routinely supplemented with iodine.
Signs and symptoms
The symptoms of an underactive thyroid can develop slowly and be missed or confused with other illnesses. The heart rate slows, muscles become slow and weak, and often ache, bowels become constipated and body energy levels drops. Cold or drafty rooms become intolerable and people may wear multiple layers of clothing and turn up the heat in their homes in an attempt to keep warm. The slowing of the metabolism will cause an increase in body weight. This weight increase can often occur despite eating less and exercising. Fluid retention occurs and puffiness or edema can be found at the ankles or around the eyes. Hair may begin to fall out and skin will become dry. A depressed mood, poor sleep, and decreased libido (sex drive) may occur. Women may notice their periods become irregular, heavier, or longer. Anemia (low blood count) may develop. In severe cases the voice can become hoarse, or progressive drowsiness to the point of unconsciousness may develop.
How is an underactive thyroid diagnosed?
Thyroid function can be measured easily with a simple blood test. Usually this means measuring a TSH level. When the TSH level is high, the thyroid is generally underactive. Sometimes, additional tests such as a T4 or a T3 blood level will need to be done. Once diagnosed, it is important to determine the cause of the hypothyroidism.
Dr. Richard Bebb, MD
in association with the MediResource Clinical Team
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