Hypothyroidism is a medical condition that affects many people each year. This condition involves several parts of the body including the thyroid, pituitary gland, and the hypothalamus. The mechanisms of actions that cause this condition will be discussed in detail along with the symptoms that are portrayed. Further discussion will explain diagnosis and assessment, as well as, medication and treatment options for the condition.
Keywords: hypothyroidism, thyroid
The thyroid gland is a part of the body's endocrine system. It is located in the middle of the neck near the trachea and Adam's apple. The function of the thyroid of the thyroid is to produces hormones which regulate the body's metabolism. The thyroid does this by communicating with the pituitary gland and hypothalamus, which are located in the brain. If the thyroid malfunctions and does not release the correct amount of hormones; a person can develop a condition known as hypothyroidism (Cooper, McDermott, & Wartofsky 2004). Buckley & Schub (2011) stated that hypothyroidism affects less than 1% of the population or approximately 11 million people worldwide. The condition mainly affects woman and is more prevalent with increasing age. The risk factors for this condition include age, gender, diet, obesity, genetics, and previous radiation treatment.
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Kapustin (2010) described the process of thyroid hormone production as being controlled by the hypothalamus-pituitary-thyroid axis, or HPA axis. The process of thyroid production starts with the hypothalamus. The hypothalamus starts by secreting thyrotropin (TRH). TRH goes through portal veins and binds to appropriate receptors. When the TRH binds to these receptors, it activates genes that signal thyroid stimulating hormones (TSH) synthesis. When this occurs, the pituitary gland secretes TSH. This is performed in order to provide stimilus for the secretion of thyroid hormones from the thyroid. These hormones are known as thyroxine (T4) and triiodothyronine (T3). T3 and T4 are produced by the thyroid cells using iodine intake from food and the amino acid tyrosine (Cwynar, 2012).
This is considered the normal mechanism of action of the production of thyroid hormones. If this process is altered, different conditions may develop. Hypothyroidism is a condition that occurs when there are too few hormones being produced. Almandoz & Gharib (2012) stated that there are two types of hypothyroidism, primary and central. Primary hypothyroidism occurs when there is a malfunction from the thyroid itself. Central hypothyroidism occurs when there is an issue with the HPA axis communication between the pituitary gland and hypothalamus.
Buckley & Schub (2011) report the most common cause of primary hypothyroidism is Hashimoto's thyroiditis. Hashimoto's thyroiditis is considered an autoimmune disease that occurs when a person's immune system attacks and destroys thyroid tissue. U.S. National Library of Medicine (2012) stated the enzyme thyroid perioxidase (TPO) plays an integral role in the thyroid for producing T3 and T4. During Hashimoto's thyroiditis, antibodies that are supposed to attack foreign substance start to attack TPO which causes a decreased production in thyroid hormones and damage to the thyroid. Cwynar (2012) stated that the tissue being attacked will become inflamed causing the thyroid not to function properly and decrease hormone production. This signals the pituitary gland to produce more TSH to increase thyroid hormone production. The TSH sent to the thyroid causes thyroid cells to continue to expand and eventually cause nodules or bumps on the inflamed thyroid.
Another cause of hypothyroidism that is less common in the United States is iodine deficiency. Buckley & Schub (2011) state that based on the prevalent use of iodized salt in the United States, this cause is not rampant. As stated earlier, thyroid hormones, T3 and T4 are
produced by thyroid cells taking in iodine from food, so based on this fact if a person does not have enough iodine in their diet, this deficiency can lead to decreased production of thyroid hormones.
A third cause of hypothyroidism is linked to radiation treatment for non-thyroid related issues. It has been found that between 10% and 45% of individuals that receive radiation for a head or neck related cancer have a higher prevalence of hypothyroidism (Almandoz & Gharib, 2012).
Buckley & Schub (2011) reported that central hypothyroidism can be due to two different processes. The first process is known as secondary hypothyroidism and it occurs when there is a malfunction of the pituitary gland and the production of TSH. The second process is known as tertiary hypothyroidism and this occurs when there is malfunction of the hypothalamus and the production of TRH. The most common cause of central hypothyroidism is considered to be a type of pituitary tumor. There may be other causes including traumatic brain injury, gene mutation, hemorrhages, lesions, or radiation (Kapustin, 2011).
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An additional type of hypothyroidism that can occur is subclinical hypothyroidism. This condition is diagnosed if there are elevated levels of TSH and normal levels of T4 in the bloodstream. A person that presents with these levels will be asymptomatic; which suggests that they may be in an early stage of primary thyroid failure. Subclinical hypothyroidism usually occurs with Hashimoto's thyroiditis, radiation therapy, or previous surgery on the thyroid. This condition should only be considered if the HPA is working properly, no recent or current severe illnesses, and the levels are consistent over time (Almandoz & Gharib, 2012).
The signs and symptoms for hypothyroidism can vary according to each case. The cause of hypothyroidism can cause different symptoms as well, such as subclinical hypothyroidism being asymptomatic. There are certain signs that are common for individuals with hypothyroidism to develop. These signs usually develop gradually over time and are subtle in nature. However, these symptoms are not unique to hypothyroidism and may be symptoms of many different types of conditions. For this reason, hypothyroidism is difficult to diagnosis without appropriate assessment measures (Kapustin 2010, Cooper, McDermott, & Wartofsky 2004).
The classic symptoms for hypothyroidism include extreme fatigue, dry skin, muscle weakness, constipation, weight gain, sensitivity to extreme temperatures, irregular menstruation, and brittle hair. Additional symptoms may develop later during the course of hypothyroidism. Some of these symptoms include slurred speech, voice hoarseness, edema of the feet and hands, and decreased taste. Some symptoms are unique towards a certain kind of hypothyroidism. Hashimoto's thyroiditis often has symptoms that are distinctive towards it. These symptoms can include sore throat, sensitivity of the throat, enlargement of the thyroid, neck pain, and a fever (Kapustin 2010).
Other than typical physical symptoms, individuals suffering from hypothyroidism may also suffer from symptoms of mental health disorders. Some of these symptoms may match a diagnosis of depression or anxiety. The particular symptoms include nervousness, sadness mood
swings, nightmares, and lack of motivation (Cooper, McDermott, & Wartofsky 2004, Cwynar 2012, Kapustin 2010).
Several different types of assessments can be completed in order to diagnosis hypothyroidism. The first type of assessment that can be completed and is considered required for an accurate diagnosis is laboratory testing. In order for primary hypothyroidism to be diagnosed, a high level of TSH and a low level of T4 hormones need to be found in the laboratory tests. However, if there are low levels of TSH and T4 hormones, then the diagnosis would be associated with central hypothyroidism. Subclinical hypothyroidism is diagnosed if there is an elevated TSH level and normal T4 hormones levels. In addition to testing TSH and T4 levels, it would be helpful to measure TPO antibodies as well to assist with more accurate diagnosis (Almandoz & Gharib 2012, Kapustin 2010).
If an individual's laboratory tests come back positive for hypothyroidism or subclinical hypothyroidism, the next step would be to have a physical assessment of the throat. This assessment is completed in order to check the size of the thyroid due to the thyroid becoming enlarged and swollen during hypothyroidism. This assessment is also completed in order to check the thyroid for nodules (Kapustin, 2010).