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Hypothyroidism 

Introduction
Hypothyroidism is a condition that most often occurs when the thyroid gland does not produce enough thyroid hormone.  Your thyroid gland is located at the front of your neck.  Thyroid hormones regulate your body metabolism.  Metabolism refers to all of the chemical processes that take place in your body.  This includes the production of energy and hormones, tissue growth, elimination of waste products, and the distribution of nutrients in the blood.
 
Hypothyroidism can affect all of your body functions.  It generally causes the body’s normal rate of functioning to slow down.  This can result in physical, emotional, and behavioral changes.  Most types of hypothyroidism cannot be prevented, but can be treated.  Untreated hypothyroidism can lead to serious medical problems.

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Anatomy
Your thyroid gland is located in the front lower part of your neck, in front of your windpipe.  Your thyroid primarily produces the thyroid hormone Thyroxine (T4).  This then is converted to the biologically active form called triiodothyronine (T3).  The thyroid hormones are secreted into your blood circulation and travel throughout your body.  These help to regulate the function of practically every cell and tissue in your body.  T4 and T3 are necessary for good health and control of your metabolism and energy levels.
 
The hypothalamus and pituitary gland in your brain regulate T4 and T3 production in the thyroid gland.  When T4 and T3 levels are low, the hypothalamus produces thyrotropin-releasing hormone (TRH) to signal the pituitary gland to produce thyroid-stimulating hormone (TSH).  The TSH travels in the bloodstream and signals the thyroid gland to produce more T4 and T3.  When T4 and T3 levels are high, the pituitary gland stops producing TSH.

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Causes
Your thyroid primarily produces the thyroid hormone Thyroxine (T4). This then is converted to the biologically active form called triiodothyronine (T3).  Hypothyroidism usually develops because of an underactive thyroid gland.  Hypothyroidism most commonly results from problems with the thyroid gland.  Hashimoto’s Thyroiditis is the most common cause of hypothyroidism in the United States.  Hashimoto’s Thyroiditis is an autoimmune disorder.  It occurs when abnormal blood antibodies and white blood cells attack and damage the thyroid cells.  This leaves a low amount of thyroid cells, which are unable to produce adequate amounts of thyroid hormones. 
 
In other parts of the world, a lack of iodine is the most common cause of hypothyroidism.  This is rarely seen in the United States.  In the United States, iodine is added to salt, food, and water.
 
Surgery, radioactive iodine therapy, or radiation treatments that affect part or all of the thyroid gland can also cause hypothyroidism.  The thyroid gland may be surgically removed for the treatment of certain thyroid conditions or cancer.  Radioactive iodine therapy, a treatment for hyperthyroidism, can destroy the thyroid gland.  Radiation treatment, such as external beam radiation used to treat cancer, can also damage the thyroid gland.  Additionally, some women develop hypothyroidism during pregnancy.
 
Less common causes of hypothyroidism include infections, certain medications, such as lithium, and excessive iodine intake.  Some infants are born without a functioning thyroid gland.  All infants in the United States are tested for hypothyroidism at birth.
 
In rare cases, hypothyroidism can occur with a normal thyroid gland.  This often occurs when there is a problem with the hypothalamus or the pituitary gland.  The pituitary gland does not produce enough TSH.  In turn, the thyroid gland cannot produce T4 and T3 without the signal from TSH to do so.

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Symptoms
The symptoms of hypothyroidism usually develop slowly over months or years.  Hypothyroidism causes your metabolic rate to slow down.  You may have a slow pulse and feel tired, sluggish, or weak.  You may want to sleep all of the time.  You may develop high cholesterol.  Your blood pressure may be too high or too low.  In rare severe cases, the heart muscle may weaken, leading to heart failure. 
 
You may feel unusually cold or have cold skin.  You may feel more comfortable in hot weather; however, you may not sweat.  This happens as your body works to conserve heat by redirecting blood away from your skin.  This will also cause you to look pale.  Your skin may develop a yellow color because of a buildup of carotene.  Carotene is normally converted to Vitamin A, but the conversion process is slowed by hypothyroidism. 
 
Your skin may also become dry and flaky.  Skin cracks may develop on your knees and elbows.  Your fingernails may become very brittle and develop lines and grooves.  You may also develop red itchy hives on your skin.
 
Your hair may become thin, coarse, and brittle.  It is common to lose hair, even to the point of balding.  You may also lose your body hair, including hair from your eyebrows, arms, legs, and pubic area. 
 
You may notice some changes in your digestive system because your body has slowed down.  Food may not move through your stomach and intestines as fast as it did before.  This can cause constipation, hard stools, bloating, and heartburn.  Additionally, some people gain weight when their metabolism slows down.
 
Females may experience irregular menstrual periods that are heavier and last longer.  In some women, the ovaries stop producing eggs, which can cause infertility.  You may also overproduce prolactin.  Prolactin is the hormone responsible for milk production.  Your breasts may produce discharge, even if you are not currently breastfeeding.  Too much prolactin can also interfere with menstruation and ovulation. 
 
You may experience muscle aches and cramps.  The pain may be severe enough to wake you up at night.  You may lose your coordination and feel clumsy.  You may feel a “pins and needles” sensation and develop carpal tunnel syndrome. 
 
Hypothyroidism can cause memory problems, poor concentration, and depression.  Depression is a real medical condition that can be treated.  Symptoms of depression include continually feeling sad, irritable, tired, and uninterested in activities that used to be enjoyable.  Other common symptoms of depression include changes in appetite, sleep difficulties, moving the body at a much slower pace, and not being able to remember things or concentrate as easily as before.  Memory problems, poor concentration, and depressive symptoms in older adults can be similar to those of dementia or Alzheimer’s Disease.  It is important for people with cognitive changes to get a thyroid function test. 
 
Your thyroid may enlarge if it is inflamed and especially if you have Hashimoto’s Thyroiditis.  Your vocal cords may be affected by the enlarged thyroid gland.  This can cause your voice to sound hoarse. 
 
Hypothyroidism rarely occurs in infants and children.  If it is treated in the first month of life, the child can grow and develop normally.  If untreated, hypothyroidism can cause brain damage, mental retardation, developmental delays, and slowed physical growth and sexual development.

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Diagnosis
It is important that you tell your doctor about your symptoms.  Your doctor can begin to diagnose hypothyroidism or subclinical hypothyroidism by reviewing your medical history, conducting a physical examination, and with blood tests.  Subclinical hypothyroidism is hypothyroidism that has not progressed very far and has not yet caused symptoms.  If subclinical hypothyroidism is detected, it can be treated before symptoms develop. 
 
Your doctor can determine if you have hypothyroidism by testing your blood.  The most common blood tests are the Thyroid-stimulating hormone (TSH) assay and the Thyroxine (T4) measurement.  The Thyroid-stimulating hormone (TSH) assay is used to determine if the thyroid gland is functioning properly.  It can identify if an underactive gland is caused by a problem with the pituitary gland, hypothalamus, or a damaged thyroid gland.  The Thyroxine (T4) measurement assesses thyroid functioning by testing how much T4 is in the blood.  If the Thyroid-stimulating hormone (TSH) assay and the Thyroxine (T4) measurement are not normal, an Antithyroid Antibody Test is used to determine the presence of Hashimoto’s Disease.
 
On occasion, a doctor may order a Thyroid Ultrasound or a Thyroid Scan and Radioactive Iodine Uptake (RAIU) Test.  Thyroid scans can detect problems with the thyroid gland.  They can identify how the thyroid gland is functioning and specify areas of overactivity or underactivity.  Further, they can determine if thyroid nodules or cancer are present. 
 
Additional blood tests and medical imaging tests are done to diagnose rare forms of hypothyroidism caused by diseases affecting the hypothalamus or pituitary gland in the brain.  A blood test called the Thyrotropin-Releasing Hormone (TRH) Stimulation Test measures the amount of TRH produced by the hypothalamus.  TRH is the hormone that signals the pituitary gland to produce TSH.  A Computed Tomography (CT) Scan or Magnetic Resonance Imaging (MRI) Scan is used to view the brain structures.  CT scans provide a view in layers, like the slices that make up a loaf of bread.  The MRI scan is very sensitive.  It provides detailed images.  The CT and MRI scans are painless procedures.

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Treatment

Hypothyroidism is easy to treat.  Your doctor will prescribe a type of thyroid replacement hormone for you to take each day.  The purpose of treatment is to replace the absent thyroid hormone and alleviate symptoms. 

Hypothyroidism is generally treated with prescription thyroid hormone replacement medication.  There are a few types of these medications including Synthroid (levothyroxine) which contains T4 and its generic counterpart.  The majority of patients are well controlled with levothyroxine.  However, some patients may require the "natural" thyroid medication that is derived from dry (dessicated) pig (porcine) thyroid gland containing both T4 and T3.

You should follow your doctor's instructions carefully for taking the medication.  Your symptoms may start to improve within the first week with medication.  Symptoms usually disappear within a few months.  People that are in poor health and older adults may take longer for symptoms to go away.

If your thyroid gland was surgically removed, you will need to receive thyroid replacement medication for the rest of your life.  People that received radiation therapy or have Hashimoto's Disease may also need to take medication for the rest of their lives.  In some cases of thyroid dysfunction the thyroid gland function returns on its own. This can happen in instances of hypothyroidism caused by Hashimoto's disease, serious illnesses, infection, and medications.

Once you begin taking prescription thyroid replacement medication, regular doctor visits are required for blood tests to make sure that you receive the correct dose of medication.  Doses may need to change over time because of a variety of reasons, including weight changes, underlying disease or conditions, and change in thyroid gland function.  Most people that take prescription thyroid replacement medication need to be monitored for the rest of their lives.

Surgery may be necessary to treat gland enlargement or Hashimoto's disease.  Surgery may be used to treat people that do not respond well to medications.  Surgery to remove the thyroid gland is called thyroidectomy.  Depending on the situation, part of or the entire gland may be removed.  After thyroidectomy, you may need to take medication for the rest of your life.

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Prevention
Most cases of hypothyroidism in the United States are caused by Hashimoto’s Disease and cannot be prevented.  You should watch for the signs and be tested if you are at risk for hypothyroidism or experience symptoms.  Early diagnosis enables early treatment and the prevention of symptoms.
 
It is important that you attend all of your doctor appointments.  Medication should be taken as directed.  It may take some time to determine the right dose of medication for you.  Once your thyroid levels return to normal, you will need to be re-checked every 6 to 12 months. 
 
Children with hypothyroidism need to see their doctor regularly.  A child’s dose of medication will need to change as he or she grows.  Untreated hypothyroidism in children and infants can have severe developmental consequences, such as brain damage, mental retardation, developmental delays, and impaired growth and sexual development.  All infants in the United States are tested for hypothyroidism at birth.  If treated within the first month of life, the child can grow and develop normally.

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Am I at Risk

Risk factors may increase your likelihood of developing hypothyroidism.  People with all of the risk factors may never develop the condition; however, the chance of developing hypothyroidism increases with the more risk factors you have.  You should tell your doctor about your risk factors and discuss your concerns. 

Risk factors for hypothyroidism: 
•  Older adults are more likely to develop hypothyroidism than younger people.
•  Women are more likely than men to develop thyroid disease.
•  A family history of hypothyroidism increases your risk.
•  Medical conditions including diabetes, vitiligo (an autoimmune disease that causes light colored patches of skin), pernicious anemia, and premature gray hair are associated with hypothyroidism.
•  An iodine deficiency can cause hypothyroidism.  This is more common in the developing world.
•  Some medications can interfere with normal thyroid function.  These include lithium carbonate, amiodarone, and interferon alpha.
•  Radiation treatments, radioactive iodine therapy, or removal of all or part of the thyroid gland can affect its function and cause hypothyroidism.

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Complications
If untreated, hypothyroidism can lead to health problems.  Untreated hypothyroidism can result in a condition called myxedema.  Myxedema consists of tissue swelling, fluid buildup in the heart and lungs, slowed muscle reflexes, and problems with thinking skills. 
 
You should call emergency medical services if you or a person you know develops signs of myxedema coma.  Myxedema coma is a rare life-threatening condition.  It occurs when thyroid hormone levels are extremely low.  Symptoms of myxedema coma include loss of consciousness or unresponsiveness, extreme tiredness and weakness, severe breathing problems, a slow heart rate (less than 60 beats per minute), low blood pressure, and a low body temperature (95° F or below).  Myxedema coma can also cause mental processing changes.  A person may become confused or apathetic.  They may become psychotic and hear or see things that actually are not there.
 
Untreated hypothyroidism can cause several other conditions.  It may cause cholesterol levels to rise, increasing the risk of coronary artery disease and stroke.  Pericardial effusion, a fluid build up around the heart, can occur.  It can contribute to sleep apnea, a condition in which breathing stops for 10 seconds or longer during sleep.  Finally, it can lead to forgetfulness and dementia.

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This information is intended for educational and informational purposes only. It should not be used in place of an individual consultation or examination or replace the advice of your health care professional and should not be relied upon to determine diagnosis or course of treatment.

The iHealthSpot patient education library was written collaboratively by the iHealthSpot editorial team which includes Senior Medical Authors Dr. Mary Car-Blanchard, OTD/OTR/L and Valerie K. Clark, and the following editorial advisors: Steve Meadows, MD, Ernie F. Soto, DDS, Ronald J. Glatzer, MD, Jonathan Rosenberg, MD, Christopher M. Nolte, MD, David Applebaum, MD, Jonathan M. Tarrash, MD, and Paula Soto, RN/BSN. This content complies with the HONcode standard for trustworthy health information. The library commenced development on September 1, 2005 with the latest update/addition on April 13th, 2016. For information on iHealthSpot’s other services including medical website design, visit www.iHealthSpot.com.