_________________________________________________________________________ Thyroid Dysfunction
Cardiovascular changes are also common. Increased vascular resistance can result in decreased cardiac output and brady- cardia, leading in turn to pericardial effusion, left ventricular enlargement, and nonspecific ST changes with a prolonged QT interval. Renal vasoconstriction may lead to diastolic hyperten- sion and decreased glomerular filtration rate, decreased tubular reabsorption of electrolytes, and peripheral edema [7; 15]. Some patients may develop decreased peristalsis, leading to chronic constipation and impaired absorption of nutrients. Impaired iron absorption can cause anemia. In many hypothy- roid patients, there is an unexplained weight gain despite no change in oral intake. Some patients may display hematologic changes, such as easy bruising, macrocytic anemia, or normo- cytic normochromic anemia [7; 15]. Due to vasoconstriction associated with decreased thyroid function, the skin may become pale, jaundiced-appearing, dry, and cold. Nails become thick and brittle; hair is dry, coarse, and brittle. Hypothyroidism is one of the main causes of female hair loss [7; 15]. Reproductive problems include an increased rate of mis- carriage, stillbirth, and fetal death. Women also may have menorrhagia, irregular periods, and decreased libido. When present in men, hypothyroidism can result in impotence and decreased libido [7; 15] . DIAGNOSTIC TESTING Whenever there is a suspicion of thyroid imbalance, and even routinely when there is no suspicion, laboratory testing can assist in diagnosing the condition. As noted, three hormone levels are assessed when thyroid function is being evaluated. Serum TSH levels increase when there is an underfunctioning thyroid gland. T4 levels are normal to depressed in cases of overt or subclinical hypothyroidism. Finally, serum T3 levels will appear as decreased in hypothyroidism [4] . TREATMENT Treatment for hypothyroidism is relatively straightforward. A single daily dose of levothyroxine, given as a tablet, can supple- ment the missing natural hormone. Treatment most commonly begins with a lower dose and increases gradually as follow-up blood tests indicate. Because most cases of hypothyroidism are permanent and progressive, it is usually necessary to receive lifelong treatment [14]. It is important to teach patients that they should be consistent in their use of medication. Levothyroxine should be taken at the same time daily, with a full glass of water and on an empty stomach. Various brands of the medication should not be sub- stituted for the prescribed agent as there are slight differences among them and consistency of dosage is important.
Thyroid hormone replacement doses are based on laboratory testing rather than symptoms. Tablets are available in numer- ous strengths (i.e., 25 mcg, 50 mcg, 75 mcg, 88 mcg, 100 mcg, 112 mcg, 125 mcg, 137 mcg, 150 mcg, 175 mcg, 200 mcg, 300 mcg), and the typical initial oral dose is less than 200 mcg daily. This dose is increased by 50–100 mcg every one to four weeks until the desired result is achieved. Doses greater than 300 mcg per day are rare [14; 16] . When initiating treatment with levothyroxine, caution should be used in older patients with underlying heart disease. Patients should be instructed to notify the prescriber if their pulse is faster than 100 beats per minute at rest or if symptoms of hyperthyroidism develop. As noted, medication should be taken at the same time daily. Most patients take it upon waking in the morning. Patients taking thyroid hormone replacement therapy should avoid the use of aluminum hydroxide antacids as they may prevent full absorption. Thyroid hormone can also affect the action of tricyclic antidepressants, aminophyl- line, theophylline, warfarin, phenytoin, carbamazepine, beta blockers, digoxin, and testosterone [14; 16] . There have been some claims that the use of coconut oil may be a useful treatment, or even cure, for hypothyroidism. However, there is no evidence to support this use; in fact, some research suggests that coconut oil can have a negative impact on thyroid production [17] . It is important for clinicians to make their patients aware of this fallacy.
CONDITIONS ASSOCIATED WITH HYPOTHYROIDISM Hashimoto Thyroiditis
Hashimoto thyroiditis, also referred to as autoimmune or chronic lymphocytic thyroiditis, is the most common cause of hypothyroidism in the United States in patients 6 years of age and older. It is estimated that 14 million Americans have this disorder. It is 10 to 15 times more common in women than men [18] . This autoimmune disorder destroys the thyroid gland by way of antithyroid antibodies. Although the immune system normally acts to protect the body from bacteria, viruses, or other foreign invaders, in this instance it attacks normal thy- roid tissue. The immune system mistakenly recognizes normal thyroid cells as foreign substances and, in response, produces antibodies designed to destroy the cells. The cause of this autoimmune response is not well understood, but studies have shown that the development of Hashimoto thyroiditis may be influenced by genetic and/or environmental factors [19; 20] . Hashimoto thyroiditis may be present for a number of years before symptoms appear. In many cases, the symptoms that do arise are the same as those seen in hypothyroidism; however, some symptoms occur more commonly with Hashimoto thy- roiditis, including fatigue, lethargy, forgetfulness, brittle hair and nails, increased sensitivity to medications, enlargement of the thyroid gland (goiter), constipation, sore muscles, and weight gain [18; 19] .
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