Hyperthyroidism includes a range of endocrine disorders caused by overactive thyroid glands or thyroid stimulators in the blood. It can result in thyrotoxicosis, an outcome of excessive thyroid hormone.

Hyperthyroidism generally presents with nervousness, fatigue, palpitations, heat intolerance, and weight loss. Clinical signs are warm skin, sweating, tremors of hands and fingers, tachycardia or palpitations, widened pulse pressure, and atrial fibrillation. Myalgia and muscle weakness may occur. It is more prevalent in individuals older than 60 years, but it occurs commonly in patients between 20 and 50 years of age, and it is more likely to occur in women. Elderly patients usually have an atypical presentation and are more likely to present with symptoms of depression or dementia, and for this reason may be easily misdiagnosed. Some patients with very large goiters have temporary facial congestion when they raise their arms above their head (Pemberton's sign).

The most common types are Graves disease, Plummer disease, and toxic adenoma. Primary thyroid hyperfunction is usually related to Graves disease, typically characterized by goiter, exophthalmos (Graves ophthalmopathy), and infiltrative dermopathy (pretibial myxedema). Likely a molecular subtype of Graves disease, thyrotoxic periodic paralysis (TPP) is associated with hyperthyroidism and hypokalemia. Like familial hypokalemic periodic paralysis, TPP is characterized by episodes of painless, often progressive muscle weakness or paralysis precipitated by heavy exercise, fasting, or high-carbohydrate meals or upon awakening. Distinguishing between TTP and familial hypokalemic periodic paralysis is important for prognosis and treatment. Correction of hyperthyroidism also corrects TTP.

Other causes of hyperthyroidism include thyroid nodule(s), thyroiditis, excess iodine, and overmedication for underactive thyroid. Genetic factors may influence the occurrence of hyperthyroidism. Autoimmune thyroid disease generally occurs in families. Some thyroid disorders may be attributed to mutations in the TSHR gene. Some genetic syndromes may be associated with hyperthyroidism. Additionally, exogenous hyperthyroidism may occur due to intentional or accidental ingestion of thyroid hormone.

Treatment is dependent on the severity of the hyperthyroidism and includes antithyroid medications and radioactive iodine to prevent the overproduction of thyroid hormones. In patients with very large goiters or whose hyperthyroidism has recurred after treatment with antithyroid drugs, surgical removal of part or all of the thyroid gland may be indicated. Although hyperthyroidism may have serious complications when ignored, with diagnosis and treatment, the prognosis is generally good.

Note: Thyroid storm is a life-threatening manifestation. The diagnosis is made clinically by the presence of severe symptoms including fever (often > 103° F), tachycardia, hypotension, congestive heart failure, atrial fibrillation or another arrhythmia, altered mental status, and gastrointestinal distress in a patient with hyperthyroidism.