Hypothyroidism is treated by replacing the thyroid hormone that the body is not producing.  Untreated hypothyroidism and over-treated hypothyroidism can be harmful. 

There are three types of hypothyroidism:

• Primary hypothyroidism occurs when the thyroid gland fails to produce thyroxine (T-4) and triiodothyronine (T-3).
  
  
• Secondary hypothyroidism occurs when the pituitary fails to secrete adequate thyroid-stimulating hormone (also known as TSH or thyrotropin).
  
  
• Tertiary hypothyroidism occurs when the hypothalamus fails to deliver thyrotropin releasing-hormone (TRH) to the pituitary gland.

Primary hypothyroidism accounts for over 99 percent of cases. Primary hypothyroidism may be the end result of:

• Hashimoto's thyroiditis (an autoimmune disease where the body produces antibodies that attack and damage the thyroid)
  
  
• Complications of thyroid surgery or surgical removal of the thyroid
  
  
• Radioiodine therapy or anti-thyroid medications to treat hyperthyroidism
  
  
• Radiation used to treat cancers of the head and neck
  
  
• Certain types of thyroid inflammation or viral infections
  
  
• Certain medications, such as lithium (used to treat certain psychiatric disorders)
  
  
• A congenital thyroid defect (occurs in 1 in 4,000 babies)
  
  
• Postpartum thyroiditis that causes the thyroid to go through a period of hyperthyroidism followed by a period of hypothyroidism
  
  
• Iodine deficiency.  (This is a problem in some parts of the world but not in the U.S. because of our use of iodized salt.)

Primary hypothyroidism can also occur for no apparent reason (called spontaneous onset).

Diagnosis of primary hypothyroidism is based on characteristic symptoms and physical signs and the results of blood tests that measure your level of thyroid-stimulating hormone (TSH) and sometimes your level of the thyroid hormone thyroxine (T4). A low level of thyroxine and high level of TSH indicate an underactive thyroid. That is because your pituitary produces more TSH in an effort to stimulate your thyroid gland into producing more thyroid hormone.¹   The most commonly used test is the measurement of thyroid-stimulating hormone (TSH).  What is considered normal?   Traditionally, a TSH value of less than 0.5 was considered hyperthyroid (overactive thyroid), while a TSH value of more than 5.5 was considered hypothyroid (underactive thyroid).  In 2002 the American Association of Clinical Endocrinologists (AACE) recommended a narrower TSH reference range of 0.3 to 3.0.  Ask your doctor what values your lab uses.

Your doctor may order other tests to determine the cause of your hypothyroidism, including one for thyroid autoantibodies to identify autoimmune thyroiditis (Hashimoto's thyroiditis) or imaging tests such as ultrasound or radioactive scanning  to look for physical and functional abnormalities.    

The American Association of Clinical Endocrinologists (AACE) also recommends that people routinely perform a simple self-examination called the Neck Check™.  Go to http://www.aace.com/public/awareness/tam/2006/pdfs/NeckCheckCard.pdf for step-by-step instructions.    

The goal of treatment for hypothyroidism is to bring your thyroxine (T4) level back into balance and achieve a TSH level between the AACE reference range of 0.3 to 3.0.  A synthetic hormone called levothyroxine (brand names include Levothroid, Levoxyl, Synthroid, and Unithroid) is standard.  Your doctor will choose the dosage based on your age, weight and any co-existing medical conditions and other medications or supplements you may be taking.  The dose of thyroid hormone is based upon lean body mass, not total body weight.  Doctors tend to ask patients remain on the same brand of thyroid hormone because even minor variations of equivalency brand to brand may have a significant impact.

It can take several weeks for your hypothyroid symptoms to improve after you start taking thyroid hormone medicine.  You will need to keep track of your symptoms and be alert to any signs of over-replacement or under-replacement.  Read the introductory page for this topic for an overview of hyperthyroidism and hypothyroidism symptoms.  Your doctor will have your TSH levels tested periodically to get to the dosage that is right for you.  It can be a long process for some.  Issues that can interfere include inconsistency in how you take your levothyroxine (it should be the same time every day an on an empty stomach to maximize absorption), missed doses, other medications, supplements or certain foods that may interfere with absorption, changes in estrogen levels (if you are approaching menopause) and changes in brand. 

Since most cases of hypothyroidism are permanent and often progressive, your doctor will continue routine checks on your TSH levels throughout your life. In general, we need about 20% less thyroid hormone by the time we are in our 70's and older.  With careful management, people with hypothyroidism can live healthy, normal lives.

¹ American Association of Clinical Endocrinologists.


Learn more about Hypothyroidism:

Key Point 1: The thyroid gland is a critical part of your body's regulatory system and affects your physical and mental health.  Symptoms caused by too little or too much thyroid hormone can greatly affect your daily life.