_________________________________________________________________________ Thyroid Dysfunction
the level of thyroid hormone in the blood and increases or decreases the amount of TSH released, which then regulates the amount of thyroid hormone in the blood. This cycle con- stantly measures and redeploys hormones in response to the amounts measured [1; 4]. Persons with a normally functioning thyroid gland are described as being in a state of euthyroidism. As noted, the two main categories of thyroid dysfunction are hypothyroidism, or decreased secretion of thyroid hormones, and hyperthyroidism, the overproduction of these hormones. Most dysfunctional situations involving the thyroid gland are included in these two categories. Diagnosis of suspected thyroid problems can be determined by laboratory testing to measure the amount of TSH, T3, and free T4. Overt hypothyroidism is evidenced by an increase in TSH levels and a decrease in T3 and T4 levels. (Actual numbers vary from laboratory to laboratory.) Subclinical (also referred to as borderline or mild) hypothyroidism may show an increased but normal level of TSH with normal levels of T3 and T4. Low-normal or decreased TSH with increased levels of T3 and T4 is indicative of hyperthyroidism. Subclinical hyperthyroidism is characterized by a decreased but normal levels of TSH, T3, and T4 [4]. Subclinical hypothyroidism or hyperthyroidism may be over- looked due to the lack of symptomatology, but it is appropriate to do testing because evidence shows that even mild changes can be significant. In cases of subclinical hypothyroidism, myocardial performance is adversely influenced; both systolic and diastolic function may be affected. Similarly, subclinical hyperthyroidism may lead to increased risk of developing atrial fibrillation, tachycardia, congestive heart failure, thromboem- bolism, and stroke [4]. HYPOTHYROIDISM Hypothyroidism is not a disease itself, but rather a clinical manifestation of the underproduction of thyroid hormones. There are many potential causes for this underactivity, includ- ing genetic factors, age, smoking status, congenital absence of the thyroid gland, surgical removal of the gland, pharma- ceutical overtreatment of hyperthyroidism, lack of iodine in the diet, environmental issues, radiation therapy to the head or neck, and autoimmune disorders such as Hashimoto thy- roiditis [2; 7] . As mentioned, thyroid disease affects more than 20 million Americans and is frequently undiagnosed. Worldwide, hypo- thyroidism is considered epidemic. It is estimated that 35% of the world’s population is affected by hypothyroidism, and congenital hypothyroidism is a primary cause of intellectual disability [3; 7; 10] .
INTRODUCTION The thyroid gland is part of the endocrine system, which is composed of multiple glands that control all body systems. When one gland in the endocrine system malfunctions, it has a cascading effect to all the other glands. If the thyroid is excreting an excess of hormones or has a deficit of hormones, the ramifications can be felt in every part of the body. It has been estimated that nearly 200 million individuals worldwide have been diagnosed with a thyroid disorder. In the United States, approximately 10% of the population will develop a thyroid disorder in their lifetime, and more than 20 million people in the United States (5%) have some type of thyroid dysfunction (greater than the number of Americans with cancer). However, up to 60% of those with thyroid dys- function are unaware of their condition. Among those with thyroid dysfunction, approximately 4.6% have hypothyroidism, and approximately 1.2% have hyperthyroidism [1; 2; 3] . These statistics indicate that nurses and other healthcare workers frequently encounter patients with thyroid dysfunction. Thy- roid problems are common and often lifelong conditions, but they are treatable. It is important for healthcare providers to be aware of signs and symptoms of thyroid conditions and to have an understanding of the disease process, diagnosis, treat- ment, and management that will ultimately affect quality of life. ANATOMY AND PHYSIOLOGY The thyroid gland is located in the anterior portion of the neck, inferior to the larynx. It consists of two lobes joined by an isthmus and is often described as being shaped like the letter “H” or a butterfly. Often embedded behind the four corners, or points, of the H shape are the parathyroid glands; in some cases, parathyroid glands may be found in the subglandular fat of the chest. These glands are visually indistinguishable from the surrounding thyroid tissue except by microscopic examination and are often inadvertently affected by treatments to the thyroid. The thyroid gland operates as part of a feedback mechanism involving the hypothalamus and the pituitary gland. Using iodine originating in the diet and blood, the gland makes thyroid hormones that are critical to several bodily functions. First, the hypothalamus sends a signal to the pituitary gland through thyrotropin-releasing hormone (TRH). When the pitu- itary gland receives this signal, it releases thyroid-stimulating hormone (TSH) to the thyroid gland. Upon receiving TSH, the thyroid responds by releasing two hormones, thyroxine (T4) and triiodothyronine (T3), which then enter the bloodstream and affect the metabolism of the muscles as well as the heart, liver, and other organs. Finally, the pituitary gland monitors
81
Book Code: ANCCTX2027
EliteLearning.com/Nursing
Powered by FlippingBook