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Goiter

April 17, 2012

Jennifer W.

Introduction

Goiter is the swelling of the thyroid gland and is in the endocrine disease, metabolic disease, and autoimmune disease categories.  The most common cause of goiter worldwide is a lack of iodine in the diet.  In the United States, where most people use iodized salt, goiter is more often due to the over- or underproduction of thyroid hormones or to the nodules that develop in the gland itself.

Pathogenesis

The thyroid gland produces two main hormones, Thyroxine and Tri-iodothyronine (T-3).  These hormones circulate in the bloodstream and help regulate metabolism.  They maintain the rate at which the body uses fats and carbohydrates, helps control the body’s temperature, influences heart rate, and helps regulate the production of proteins.  The thyroid gland also produces calcitonin, which is a hormone that helps regulate the amount of calcium in the blood.

The pituitary gland and hypothalamus controls the rate at which these hormones are produced and released.  The process begins when the hypothalamus signals the pituitary gland to make a hormone known as thyroid-stimulating hormone (TSH).  The pituitary gland releases a certain amount of TSH, depending on how much thyroxine and T-3 are in the blood.  The thyroid gland, in turn, regulates its production of hormones based on the amount of TSH it receives from the pituitary gland.

Etiology

It should be noted that having a goiter doesn’t necessarily mean that the thyroid gland isn’t working normally.  Even when it’s enlarged, the thyroid may produce normal amounts of hormones.  It might also, however, produce too much or too little Thyroxine and T-3.  A number of factors can cause the thyroid gland to enlarge:

Iodine deficiency:  In the developing world, people who live inland or at high elevations are often iodine-deficient and can develop goiter when the thyroid enlarges in an effort to obtain more iodine. Although a lack of dietary iodine is the main cause of goiter in many parts of the world, this is not the case in countries where iodine is routinely added to table salt and other foods.

Graves’ disease:  Goiter can sometimes occur when the thyroid gland produces too much thyroid hormone (hyperthyroidism).  In Graves’ disease, antibodies produced by the immune system mistakenly attack the thyroid gland, causing it to produce excess thyroxine.  This overstimulation causes the thyroid to swell.

Hashimoto’s disease:  Goiter can also result from an underactive thyroid (hypothyroidism).  Like Graves’ disease, Hashimoto’s disease is an autoimmune disorder.  But instead of causing the thyroid to produce too much hormone, Hashimoto’s damages the thyroid so that it produces too little.  Sensing a low hormone level, the pituitary gland produces more TSH to stimulate the thyroid, which then causes the gland to enlarge.

Multinodular goiter:  In this condition, several solid or fluid-filled lumps called nodules develop in both sides of the thyroid, resulting in overall enlargement of the gland.

Solitary thyroid nodules:  In this case, a single nodule develops in one part of the thyroid gland.  Most nodules are noncancerous (benign) and don’t lead to cancer.

Thyroid cancer:  Thyroid cancer is far less common than benign thyroid nodules.  Cancer of the thyroid often appears as an enlargement on one side of the thyroid.

Pregnancy:  A hormone produced during pregnancy, human chorionic gonadotropin (HCG), may cause the thyroid gland to enlarge slightly.

Inflammation:  Thyroiditis is an inflammatory condition that can cause pain and swelling in the thyroid.

Symptoms

Not all goiters cause signs and symptoms.  When signs and symptoms do occur they may include: a visible swelling at the base of the neck, a tight feeling in the throat, coughing, hoarseness, difficulty swallowing, and difficulty breathing.

Diagnosis

A doctor may discover an enlarged thyroid gland simply by feeling the patient’s neck and having them swallow during a routine physical exam.  In some cases, the doctor may also be able to feel the presence of nodules.  The following tests may also help to diagnose a goiter:

A hormone test:  Blood tests can determine the amount of hormones produced by the thyroid and pituitary glands.  If the thyroid is underactive, the level of thyroid hormone will be low.  At the same time, the level of thyroid-stimulating hormone (TSH) will be elevated because the pituitary gland tries to stimulate the thyroid gland to produce more thyroid hormone.  Goiter associated with an overactive thyroid usually involves a high level of thyroid hormone in the blood and a lower than normal TSH level.

An antibody test:  Some causes of goiter involve production of abnormal antibodies.  A blood test may confirm the presence of these antibodies.

Ultrasonography: A wand-like device (transducer) is held over the neck.  Sound waves bounce through the neck and back, forming images on a computer screen.  The images reveal the size of the thyroid gland and whether the gland contains nodules that the doctor may not have been able to feel.

A thyroid scan: During a thyroid scan, a radioactive isotope is injected into the vein on the inside of the elbow.  The patient then lies on a table with their head stretched backward while a special camera produces an image of the thyroid on a computer screen.  The time needed for the procedure may vary, depending on how long it takes the isotope to reach the thyroid gland.  Thyroid scans provide information about the nature and size of the thyroid, but they’re more invasive, time-consuming and expensive than the ultrasound tests.

A biopsy:  During a fine-needle aspiration biopsy, ultrasound is used to guide a needle into the thyroid to obtain a tissue or fluid sample for testing.

Treatment

Goiter treatment depends on the size of the goiter, the signs and symptoms, and the underlying cause.   The following are possible treatments for goiter. 

Observation:  If the goiter is small and doesn’t cause problems, and the thyroid is functioning normally, the doctor may suggest a wait-and-see approach.

Medications:  If hypothyroidism is an option, thyroid hormone replacement with levothyroxine (Levothroid, Synthroid) will resolve the symptoms of hypothyroidism as well as slow the release of thyroid-stimulating hormone from the pituitary gland, often decreasing the size of the goiter.  For inflammation of the thyroid gland, the doctor may suggest aspirin or a corticosteroid medication to treat the inflammation.  For goiters associated with hyperthyroidism, medications to normalize hormone levels may be suggested.

Surgery:  Removing all or part of the thyroid gland (total or partial thyroidectomy) is an option if a large goiter that is uncomfortable or causes difficulty breathing or swallowing is present, or if there is a nodular goiter causing hyperthyroidism.  Surgery is also a treatment option for thyroid cancer.

Radioactive iodine:  In some cases, radioactive iodine is used to treat an overactive thyroid gland.  The radioactive iodine is taken orally and reaches the thyroid gland through the bloodstream, destroying thyroid cells.  The treatment results in diminished size of the goiter, but eventually may also cause an underactive thyroid gland.  Hormone replacement with the synthetic thyroid hormone levothyroxine then becomes necessary, usually for life.

Incidence/Mortality

Most goiters are benign (as stated earlier) and cause only cosmetic disfigurement.  The stats available are in reference to a thyroidectomy. 

About 5% of the people in the U.S. have a goiter as according to http://www.freemd.com/endemic-goiter/incidence.htm http://www.freemd.com/endemic-goiter/incidence.htm

The mortality after a thyroid operation for nontoxic goiter was 0.02 percent for patients less than the age of 50 years but increased with age to 0.66 percent for those 70 years and older (as taken from http://www.ncbi.nlm.nih.gov/pubmed/625682).   

Research, Charities, and Support Groups

The American Thyroid Association (ATA) was founded in 1923.  The ATA is dedicated to scientific inquiry, clinical excellence, public service, education, and collaboration and is the leading worldwide organization dedicated to the advancement, understanding, prevention, diagnosis and treatment of thyroid disorders and thyroid cancer.  ATA is an international individual membership organization with over 1,600 members from 43 countries around the world.  More info about this research organization can be found on www.thyroid.org

Currently there is not a charity for goiters specifically, but the ATA takes donations, which would help to better their research.

www.dailystrength.org is an online support group that contains posts and discussion forums about goiter. 

www.inspire.com is another online support group that has posts about what goiter is and how to live with it. 

Resources

AACE/AME. American Association of Clinical Endocrinologists and Associazione Medici Endocrinologi medical guidelines for clinical practice for the diagnosis and management of thyroid nodules. Endocr Pract. 2006; 12(1):63-102.

American Association for Clinical Chemistry. Lab Tests Online. Thyroid Diseases. Access date: 04/10/12 www.labtestsonline.org    

American Thyroid Association (04/05/12); Goiter. Copyright 2008 www.thyroid.org

Ladenson P, Kim M. Thyroid. In: Goldman L and Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders; 2007: chap 244.

Merck Sharp & Dohme Corp. The Merck Manuals Online Medical Library. Endocrine and Metabolic Disorders. Thyroid Disorders: Simple Nontoxic Goiter (Euthyroid Goiter) Access date: 04/08/12 www.merck.com  

Schlumberger MJ, Filetti S, Hay ID. Nontoxic diffuse and nodular goiter and thyroid neoplasia. In: Kronenberg HM, Melmed S, Polonsky KS, Larsen PR, eds. Williams Textbook of Endocrinology. 11th ed. Philadelphia, Pa: Saunders Elsevier; 2008: chap 13.

Understanding Goiter, the basics. Last reviewed March 19th, 2012 Access date: 04/06/12 www.webmd.com

Vanderpas J. Nutritional epidemiology and thyroid hormone metabolism. Ann Rev Nutr. 2006; 26:293-322.

All images taken from www.google.com

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