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.
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).
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.
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
The mortality of thyroid storm without treatment
is between 80% and 100%, and with treatment, it
is between 15% and 50%.
Causes of hyperthyroidism can be divided into primary and secondary causes
(as depicted in Tables 224-1 and 224-2).
Table 224-1 Causes
of Hyperthyroidism: Primary and Secondary Hyperthyroidism |Favorite Table|Download (.pdf)
Table 224-1 Causes
of Hyperthyroidism: Primary and Secondary Hyperthyroidism
|Graves disease (toxic diffuse goiter) (Figure 224-0.1)||Most common of all hyperthyroidism (85% of all cases)|
|Associated with diffuse goiter, ophthalmopathy, and local
|Toxic multinodular goiter||Second most common cause of hyperthyroidism|
|Toxic nodular (adenoma) goiter (Figure 224-0.2)||An enlarged thyroid gland that contains a small rounded mass
or masses called nodules with overproduction of thyroid hormone|
|Thyrotropin-secreting pituitary adenoma||Thyroid gland stimulated to produce hormones|
|Thyroiditis||Inflammation of the thyroid gland.|
|Hashimoto thyroiditis||Initially gland is overactive (hyperthyroidism state) but
this is usually followed by a state of hypothyroidism|
|Subacute painful thyroiditis (de Quervain thyroiditis)|
|Subacute painless thyroiditis|
Pathology specimen of Graves disease: most common cause
of hyperthyroidism. Diffuse swelling is evident. (Courtesy of the
University of Malaya Pathology Museum.)
Pathology specimen of multinodular goiter: second most
common cause of hyperthyroidism. Multinodular appearance could be
seen. (Courtesy of the University of Malaya Pathology Museum.)
Table 224-2 Other Causes
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