Hypothyroidism: Too Little Thyroid Hormone

Part 1: Introduction, Causes, and Symptoms of Hypothyroidism

Hypothyroidism is a condition in which the body lacks sufficient thyroid hormone. Since the main purpose of thyroid hormone is to "run the body's metabolism," it is understandable that people with this condition will have symptoms associated with a slow metabolism. The estimates vary, but approximately 10 million Americans have this common medical condition. In fact, as many as 10% of women may have some degree of thyroid hormone deficiency.   Hypothyroidism is more common than you would believe, and millions of people are currently hypothyroid and don't know it. For an overview of how thyroid hormone is produced and how its production is regulated, check out our thyroid hormone production page.

Learn More about Hypothyroidism

Causes of Hypothyroidism

There are two fairly common causes of hypothyroidism. The first is a result of previous (or currently ongoing) inflammation of the thyroid gland, which leaves a large percentage of the cells of the thyroid damaged (or dead) and incapable of producing sufficient hormone. The most common cause of thyroid gland failure is called autoimmune thyroiditis (also called Hashimoto's thyroiditis), a form of thyroid inflammation caused by the patient's own immune system.

The second major cause is the broad category of "medical treatments."  The treatment of many thyroid conditions warrants surgical removal of a portion or all of the thyroid gland. If the total mass of thyroid producing cells left within the body are not enough to meet the needs of the body, the patient will develop hypothyroidism. Remember, this is often the goal of the surgery for thyroid cancer.

But at other times, the surgery will be to remove a worrisome nodule, leaving half of the thyroid in the neck undisturbed. Sometimes, this remaining thyroid lobe and isthmus will produce enough hormone to meet the demands of the body. For other patients, however, it may become apparent years later that the remaining thyroid just can't quite keep up with demand.

Similarly, goiters and some other thyroid conditions can be treated with radioactive iodine therapy. The aim of the radioactive iodine therapy (for benign conditions) is to kill a portion of the thyroid to prevent goiters from growing larger or  producing too much hormone (hyperthyroidism).

Occasionally, the result of radioactive iodine treatment will be that too many cells are damaged so the patient often becomes hypothyroid within a year or two. However, this is usually greatly preferred over the original problem.

There are several other rare causes of hypothyroidism, one of them being a completely "normal" thyroid gland that is not making enough hormone because of a problem in the pituitary gland. If the pituitary does not produce enough thyroid stimulating hormone (TSH) then the thyroid simply does not have the "signal" to make hormone. So it doesn't.

Symptoms of Hypothyroidism

  • Fatigue
  • Weakness
  • Weight gain or increased difficulty losing weight
  • Coarse, dry hair
  • Dry, rough pale skin
  • Hair loss
  • Cold intolerance (you can't tolerate cold temperatures like those around you)
  • Muscle cramps and frequent muscle aches
  • Constipation
  • Depression
  • Irritability
  • Memory loss
  • Abnormal menstrual cycles
  • Decreased libido

Each individual patient may have any number of these symptoms, and they will vary with the severity of the thyroid hormone deficiency and the length of time the body has been deprived of the proper amount of hormone.

You may have one of these symptoms as your main complaint, while another will not have that problem at all and will be suffering from an entirely different symptom. Most people will have a combination of these symptoms. Occasionally, some patients with hypothyroidism have no symptoms at all, or they are just so subtle that they go unnoticed.

If you have these symptoms, you need to discuss them with your doctor. Additionally, you may need to seek the skills of an endocrinologist.  If you have already been diagnosed and treated for hypothyroidism and continue to have any or all of these symptoms, you need to discuss it with your physician. 

Potential Dangers of Hypothyroidism

Because the body is expecting a certain amount of thyroid hormone the pituitary will make additional thyroid stimulating hormone (TSH) in an attempt to entice the thyroid to produce more hormone. This constant bombardment with high levels of TSH may cause the thyroid gland to become enlarged and form a goiter (termed a "compensatory goiter").

Left untreated, the symptoms of hypothyroidism will usually progress. Rarely, complications can result in severe life-threatening depression, heart failure, or coma.

Hypothyroidism can often be diagnosed with a simple blood test. In some persons, however, it's not so simple and more detailed tests are needed.  Most importantly, a good relationship with a good endocrinologist will almost surely be needed.   

Hypothyroidism is completely treatable in many patients simply by taking a small pill once a day. However, this is a simplified statement, and it's not always so easy.  There are several types of thyroid hormone preparations and one type of medicine will not be the best therapy for all patients.  Many factors will go into the treatment of hypothyroidism and it is different for everybody.