Upon completion of the chapter, the reader will be able to:
Explain the major components of the hypothalamic–pituitary–thyroid axis and the interaction among these components.
Discuss the prevalence of thyroid disorders, including subclinical (mild) and overt (typical signs and/or symptoms present) hypothyroidism and hyperthyroidism.
Discuss the relationship between serum thyroid-stimulating hormone (TSH) levels and primary thyroid disease and the advantages for the use of TSH levels over other tests such as serum T4 (thyroxine) and T3 (triiodothyronine) levels.
Identify the typical signs and symptoms of hypothyroidism and the consequences of inadequate treatment.
Describe the clinical use of levothyroxine (LT4) in the treatment of hypothyroidism.
Discuss the issues regarding LT4 product bioequivalence and the advantages of maintaining patients on the same product.
Describe the management of hypothyroidism and hyperthyroidism in pregnant women.
Identify the typical signs and symptoms of Graves' disease and the consequences of inadequate treatment.
Discuss the pharmacotherapy of Graves' disease, including the advantages and disadvantages of antithyroid drugs versus radioactive iodine, adverse effects, and patient monitoring.
Describe the potential effects of amiodarone, lithium, and interferon-α on thyroid function.
The thyroid gland is the largest endocrine gland in the body, residing in the neck anterior to the trachea between the cricoid cartilage and the suprasternal notch. The thyroid gland produces two biologically active hormones, thyroxine (T4) and triiodothyronine (T3). The parafollicular C cells of the thyroid gland produce calcitonin.
In most patients with thyroid hormone disorders, the measurement of a serum thyroid-stimulating hormone (TSH) level is adequate for the initial screening and diagnosis of hypothyroidism and hyperthyroidism. Serum-free thyroxine (FT4) and triiodothyronine (FT3) levels may be helpful in distinguishing subclinical (mild) thyroid disease from overt disease. The target TSH for most patients being treated for thyroid disorders should be the mean normal value of 1.4 milli international units/L (mIU/L) or 1.4 micro international units/mL (μIU/mL) (target range, 0.5 to 2.5 mIU/L or 0.5 to 2.5 μIU/mL), although patients must be individually titrated based on resolution of signs and symptoms as well as biochemical tests. The target TSH may be different in patients being treated with levothyroxine (LT4) for thyroid cancer.
Hypothyroidism can affect virtually any tissue or organ in the body. The most common symptoms, such as fatigue, lethargy, sleepiness, cold intolerance, and dry skin, are nonspecific and can be seen with many other disorders. The classic overt signs, such as myxedema and delayed deep tendon reflexes, are seen uncommonly now because more patients are screened or seek medical attention earlier. Patients with mild (also known as subclinical) hypothyroidism may have subtle symptoms that progress so slowly that they are not noticed easily by the patient or family. The lack of overt or specific signs and symptoms emphasizes the importance of using the serum TSH level to identify patients with hypothyroidism. Treatment of patients ...
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