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Hyperthyroidism: Overview and Risk Factors

Hyperthyroidism is a condition of excess thyroid hormone. It may be caused by intrinsic thyroid dysfunction (primary hyperthyroidism) or by excessive stimulation of the thyroid gland by an autonomous source of thyroid–stimulating hormone (TSH, secondary hyperthyroidism). Hyperthyroidism may also be caused by excessive ingestion of exogenous thyroid hormone.

Approximately 85% of cases of primary hyperthyroidism result from Graves’ disease, in which autoantibodies to the TSH receptor continually stimulate the thyroid gland to overproduce thyroid hormone. Other causes of primary hyperthyroidism include toxic adenoma, toxic multinodular goiter, and thyroiditis. Secondary hyperthyroidism is usually caused by a TSH–secreting anterior pituitary adenoma. Hyperthyroidism may be associated with autoimmune diseases, including Addison’s disease and type 1 diabetes mellitus.

Clinical manifestations of hyperthyroidism vary significantly. The most common signs and symptoms include tachycardia, palpitations, heat intolerance, weight loss, and menstrual irregularities. Less common are nausea, vomiting, restlessness, anxiety, tremor, and atrial fibrillation. Further signs and symptoms depend on the etiology and severity of hyperthyroidism. In Graves’ disease, for example, typical symptoms are a diffuse, symmetric goiter; ophthalmopathy (including lid lag and irreversible exophthalmos); and dermopathy (including pretibial myxedema, a thickening and redness of the pretibial skin).

The most severe form of hyperthyroidism is thyroid storm, which can be precipitated by thyroidectomy, acute stress (eg, infection, trauma, nonthyroid surgery), or an acute iodine load. Presentation may include extreme fever (up to 40ºC–41ºC/104ºF–106ºF), severe nausea, vomiting, jaundice, rigidity, agitation, or delirium; these symptoms may progress to seizures and coma, tachycardia, and congestive heart failure, and frank shock.

Risk Factors

Hyperthyroidism is more common in females. There may also be a genetic component of risk, as individuals with certain HLA–D subtypes have an increased risk for Graves’ disease.

 

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Hyperthyroidism: Diagnosis and Treatment >>