The thyroid gland is located in the neck right below the Adam’s apple. The thyroid has a butterfly shape to it with two lobes connected by a bridge known as the isthmus. The thyroid is responsible for making and storing hormones that control and regulate metabolism, body temperature, as well as growth and development. The major hormone that the thyroid gland produces is thyroxine, otherwise known as T4. Thyroxine is converted to triiodothyronine (T3) by removing an atom of iodine (American Thyroid Association). Calcitonin is also produced by the thyroid gland, which sends calcium to bone to help with bone growth and is used in calcium metabolism. Producing too little of these thyroid hormones can result in hypothyroidism and can damage your thyroid due to autoimmune disease. The opposite of this would be producing an excessive amount of thyroid hormone, known as hyperthyroidism. To check for either one of these conditions, one can have a blood test performed to check for an abnormal amount of thyroid stimulating hormone (TSH) in their blood. If high levels of TSH are found, this indicates having a low level of thyroid hormone in the body, which would result in hypothyroidism and having a low level of TSH in the blood would be linked to hyperthyroidism. Iodine is also very important for the thyroid gland and if there is a deficiency of iodine in the body, the thyroid can produce a goiter (swelling of the thyroid). Thyroid problems are very common in the United States, with roughly 27 million people being diagnosed with thyroid disease (Blackwell, 2004).
Hypothyroidism is having low levels of thyroxine (T4) and triiodothyronine (T3) produced by the thyroid gland to provide to the peripheral tissue. Hypothyroidism may be due to a number of factors. The most common cause of hypothyroidism is Hashimoto’s disease, which is an autoimmune disorder. Other causes may include having a thyroidectomy, radiation to the neck, radioiodine thyroid ablation or certain medications (Kohler, et al., 2014). Since the thyroid is not producing enough T3 or T4, the thyroid stimulating hormone(TSH) is then produced by the pituitary gland to control and regulate a sufficient amount of thyroid hormone production. Due to people not being able to produce enough thyroxine or triiodothyronine, many physicians use a replacement dose of levothyroxine to bring TSH levels back up to normal. However, those who have heart problems have to be put on a lower dose due to increasing blood pressure. Giving these patients too high of a dose could cause chest pain. Over the course of six to eight weeks, the dose is increased. An argument that was studied was that six to eight weeks was not long enough for the dose adjustment to change in serum TSH because it has a delayed response compared to serum thyroid levels. However, some researchers say the time should be shorter and some say it should be extended over a longer period of time (Kohler, et al., 2014).
A big concern was that these thyroid hormones could potentially effect kidney function. Having hypothyroidism decreases renal blood flow and creatinine clearance, so these were observed with thyroxine treatments (Kohler, et al., 2014). Blood flow and creatinine are measured as a test of kidney function, so if they were to decrease, a chance of your kidneys shutting down could be possible. After 8 weeks if the TSH levels did not come back to normal, the dose of thyroxine was increased. Once a week blood was drawn to check TSH, T3, T4, and creatinine levels. Studies showed that the average time to achieve normal and stable TSH levels was 3.5 weeks of thyroxine adjustments. It was determined that TSH levels showed thyroid problems much better than the thyroid hormones did. The thyroid hormone affects the central nervous system, cardiovascular system, lipid profile, bone metabolism, energy consumption, and body weight (Kohler, et al., 2014). Many people with hypothyroidism complain of mood swings, weight gain, and decreased cognitive function.
Hypothyroidism affects roughly 3-8% of today’s population (Khandelwal, et al., 2012). Common symptoms produced from having hypothyroidism are fatigue, slow movement, joint aches, constipation, weight gain, depression, etc. Many physicians struggle with the decision of putting someone on a thyroid replacement pill because these symptoms can relate to many other medical conditions, such as cheast paid, excessive sweating, headaches, diarrhea, vomiting, etc . Physicians are now heavily relying on lab work to tell whether or not the patient does have hypothyroidism. In the lab work, thyroid stimulating hormone (TSH), thyroxine (T4), and triiodothyronine (T3) are carefully looked at. However, studies have shown that hypothyroidism is being correlated with the risk of cardiovascular disease (Khandelwal, et al., 2012). Thyroid hormones have been known to control many processes of the cardiovascular system, such as relaxation of vascular smooth muscle, decreased diastolic blood pressure, and even a failing heart (Danzi, et al., 2004). There has been an increased death rate of individuals with heart failure that also have a low functioning thyroid (Khandelwal, et al., 2012). Since cardiovascular problems are the leading cause of death in the United States, thyroid levels are involved with this. When an individual has heart problems, T3 levels are low and this had been related to cardiac dysfunction, although TSH levels can be normal (Khandelwal, et al., 2012). Many physicians are not aware of what causes some of these symptoms that patients are complaining about, so they tend to put them on anti-depressant, muscle-relaxants, stimulants, pain relievers, etc. However, in some cases these medications can make the problems worse by interfering with brain function (Khandelwal, et al., 2012). One of the biggest problems is that many individuals do not know their normal thyroid functioning level, so it is hard to give the accurate amount of TSH to a patient to get their levels back to “regular.”
Hyperthyroidism is rare, however, it is on the rise of diagnoses reported. Hyperthyroidism can occur when the body is producing an excessive amount of thyroid hormones. The main thyroid hormones, thyroxine and triiodothyronine, are transported by a thyroid hormone binding globulin (TBG). Symptoms of hyperthyroidism include but are not limited to, heat intolerance, increased bowel movements, rapid heart rate, and weight loss (Priatna, et al., 2017). Some individuals with mild hyperthyroidism and those who are over the age of 70 generally do not express any symptoms. Thyroxine (T4) is converted to triiodothyronine (T3) after being released into the blood by the thyroid gland (Priatna, et al., 2017). T3 regulates the metabolism of other cells throughout our body. The thyroid gland is regulated by the pituitary gland and that is then regulated by the hypothalamus. The hypothalamus releases thyrotropin releasing hormone (TRH) which then triggers the pituitary to release thyroid stimulating hormone (TSH), which then releases thyroid hormones from the thyroid (Priatna, et al., 2017). Hyperthyroidism results from having an overproduction of any of these hormones.
Another way to check for this disorder is by using invasive and non-invasive methods. An invasive method is having a biopsy performed and non-invasive methods are radiology imaging, such as nuclear medicine exams and ultrasounds (Priatna, et al., 2017). Another way to check for thyroid problems is by having a nuclear medicine radioiodine scan by giving a pill of radioactive iodine-123. Radioactive iodine collects in the thyroid before it is excreted into the urine (Priatna, et al., 2017). Sodium Iodide (I-123) is absorbed from the gastrointestinal tract and then distributed to the extracellular fluid of the body. A radioiodine scan shows the uptake and activity of the tissue in the thyroid gland (GE Healthcare). An individual is given a radioactive pill and is then scanned roughly 24 hours later, looking for a thyroid problem. Normal uptake is 15-30%. Anything above 30% would classify the patient as being hyperthyroid. There is also a radioactive iodine-131 (I-131), which is generally more harmful than the 123. I-131 is not commonly used for the scan because the pill is much more expensive due to its high-energy collimators. The I-123 has less radiation than the 1-131 due to its pure gamma emission and short life of 13 hours (Mandel, et al., 2001). Most thyroid problems were shown more efficiently with use of the I-123 scan rather than the I-131 scan.
Thyroid gland function can be influenced by thyroid autoimmunity, which occurs in a two-step process. Stage one has an increased amount of intra-thyroid antigen presenting cells (APC) which transport thyroid auto-antigens to T-helper (Th) cells (De Groot, et al., 2000). The second stage has lymphocytes that interact with the auto-antigens that generate an increase of CD4+ Th lymphocytes, CD8+ T-cytotoxic (Tc) lymphocytes, and antibody-producing B lymphocytes that infiltrate the thyroid (De Groot, et al., 2000). In autoimmune diseases, there is a large amount of Th1 cytokines, which increases the amount of T lymphocyte immunity that causes damage to the immune system of the thyroid cells and results in hypothyroidism (De Groot, et al., 2000). In Graves’ Disease, there is a large amount of Th2 inflammatory cytokines and B lymphocyte immunity that result in high levels of immunoglobulin antibodies that activate the thyroid-stimulating hormone receptor causing hyperthyroidism (De Groot, et al., 2000).
Over an individual’s lifetime they can develop both diseases, hypothyroidism and hyperthyroidism. Hypothyroidism results from low levels of thyroxine and triiodothyronine and high levels of thyroid stimulating hormone (Kohler, et al., 2014). On the other hand, hyperthyroidism is a result of high levels of thyroxine and triiodothyronine and low levels of thyroid stimulating hormone (Priatna, et al., 2017). There are many tests that are still being researched that can help diagnose both of these diseases but as of now, blood tests are the most efficient way. It is important to have a normal level of all these hormones, as they regulate body temperature, organ function, and energy use of the body (American Thyroid Association). Hyperthyroidism is sometimes controlled by having a thyroidectomy (removal of the thyroid) which then causes hypothyroidism because of a lack of thyroid hormones. However, giving the patient a high dose of radioactive I-131 to “kill off” the overactive gland is the most common method (Mandel, et al., 2001). The risk factors are far less than undergoing surgery. The patient is simply followed by watching thyroid hormone levels after taking the I-131 pill. Once the levels have plateaued, the physician can decide if they need to take a thyroid replacement hormone (Danzi, et al., 2004). Physicians would then start you on a thyroid medication to help regulate these thyroid hormone levels. In the future, research could be done to invent a pill that would help better regulate levels of both thyroxine and triiodothyronine. The I-131 and I-123 pills could also be researched more to see if there is a better way to do these tests and not expose the patient to as much radiation. As of now, the I-131 and I-123 thyroid uptake scans are the most efficient way to determine thyroid diseases other than performing a blood test (American Thyroid Association).
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