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Thyroid hormone affects all organ systems, and is responsible for increasing metabolic rate, heart rate, ventricle contractility, as well as muscle and central nervous system excitability. Two major types of thyroid hormones are thyroxine (T4) and triiodothyronine (T3). T4 is the major form of thyroid hormone. The ratio of T4 to T3 released in the blood is 20:1. Peripherally, T4 is converted to the active T3, which is three to four times more potent than T4.

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Hyperthyroidism refers to excess circulating hormone resulting only from thyroid gland hyperfunction whereas thyrotoxicosis refers to excess circulating thyroid hormone originating from any cause (including thyroid hormone overdose).

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Thyroid storm is the extreme manifestation of thyrotoxicosis. This is an acute, severe, life-threatening state of thyrotoxicosis caused either by adrenergic hyperactivity or altered peripheral response to thyroid hormone following the presence of one or more precipitants.

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In the U.S., the overall incidence of hyperthyroidism is estimated to be between 0.05% to 1.3%, with the majority being subclinical in terms of presentation.1 Among hospitalized thyrotoxicosis patients, the incidence of thyroid storm has been noted to be <10%.2

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The mortality of thyroid storm without treatment is between 80% and 100%, and with treatment, it is between 15% and 50%.

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Causes of hyperthyroidism can be divided into primary and secondary causes (as depicted in Tables 224-1 and 224-2).

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Table Graphic Jump Location
Table 224-1 Causes of Hyperthyroidism: Primary and Secondary Hyperthyroidism 
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Figure 224-0.1.
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Pathology specimen of Graves disease: most common cause of hyperthyroidism. Diffuse swelling is evident. (Courtesy of the University of Malaya Pathology Museum.)

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Figure 224-0.2.
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Pathology specimen of multinodular goiter: second most common cause of hyperthyroidism. Multinodular appearance could be seen. (Courtesy of the University of Malaya Pathology Museum.)

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Table Graphic Jump Location
Table 224-2 Other Causes of Hyperthyroidism 

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