The term hyperthyroidism refers to an overproduction of hormone by the thyroid gland. The resulting physiologic syndrome of excess thyroid hormone is termed thyrotoxicosis, although the two terms should not be used synonymously. Hyperthyroidism should be used to describe conditions associated with a sustained overproduction of thyroid hormone, such as Graves' disease or toxic multinodular goiter (TMNG). Several other conditions or situations result in transient increases in circulating thyroid hormone, which may result in thyrotoxicosis, but they do not cause hyperthyroidism in the strict sense of the term (Table 3-1). This chapter reviews the epidemiology, clinical presentation, evaluation, and management of patients with hyperthyroidism, focusing on surgical management.
Table 3-1. Causes of Thyrotoxicosis
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Table 3-1. Causes of Thyrotoxicosis
|Hyperthyroidism (sustained hormone excess)|
|Toxic multinodular goiter|
|Iodine-induced hyperthyroidism (Jod-Basedow effect)|
|TSH-secreting pituitary tumors|
|Metastatic functioning thyroid carcinoma|
|Thyrotoxicosis (transient hormone excess)|
|Iatrogenic hormone overreplacement|
Hyperthyroidism is present in approximately 0.5% of the population.1,2 An additional 0.8% of the population has mildly suppressed or undetectable serum thyroid-stimulating hormone (TSH) levels but circulating thyroid hormone levels in the normal range.2 Additionally, the rate of development of the various causes of hyperthyroidism varies according to geographic location and is believed to be related to the iodine intake of the population. For example, an epidemiologic survey comparing an area of normal iodine intake to one with insufficient iodine intake found that Graves' disease accounted for 80% of cases of hyperthyroidism in the iodine-sufficient population but toxic uninodular and multinodular goiter accounted for the majority of cases in the iodine-deficient population.3
The clinical presentation of this disorder involves multiple symptoms that vary depending on the degree of hormone excess, the duration of illness, and the presence of other medical comorbidities. Additionally, the patient's age may affect the clinical presentation because elderly patients with thyrotoxicosis often have minimal clinical symptoms, a phenomenon termed apathetic hyperthyroidism.4 Thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3), are involved in the production of heat and energy; the development of the nervous system; the regulation of somatic growth and puberty; and the coordination of the synthesis of proteins involved in normal hepatic, cardiovascular, neurologic, and muscular functions. The wide range of actions of T3 and T4 on multiple organ systems accounts for the number and variability of symptoms that may accompany thyrotoxicosis (Table 3-2). Typically, patients complain of nervousness or anxiety, restlessness, palpitations, weight loss, and sensitivity to heat. Women may have irregular menses or problems with decreased fertility, and men may develop painful gynecomastia or reduced libido.5,6
Table 3-2. Common Signs and Symptoms of Thyrotoxicosis...
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