Hyperthyroidism is the reaction to excess production of thyroid hormone.
Graves' disease is the most common form of hyperthyroidism. It is an an autoimmune disease caused by thyroid stimulating immunoglobulins (TSI's) of the IgG class which bind to thyrotropin (TSH) receptors on the thyroid gland. The TSI's mimic the action of TSH and cause excess secretion of T4 and T3.
Large doses of iodine can result in hyperthyroidism. Toxic multinodular goiter is caused by iodine deprivation followed by iodine repletion. The jodbasedow phenomenon refers to thyrotoxicosis in a previously euthyroid patient as a result of exposure to iodine. It typically occurs in areas of endemic iodine deficiency when measures to increase iodine intake are implemented.
Lithium has several effects on intra-thyroidal iodine metabolism, one of which is to inhibit hormone release.
Glucocorticoids causes a decrease in serum thyroid hormone levels due to inhibition of TSH secretion and decreased binding of T4 to TBG. Serum T3 is also decreased, in part because of inhibition of the conversion of T4 to T3. A direct inhibitory action of glucocorticoids on the thyroid may occur in Graves' disease, possibly by inhibition of thyroid-stimulating immunoglobulins. Dexamethasone, in conjunction with iodide, can effect a rapid reduction in the degree of thyrotoxicosis.
Other causes are rare and include TSH-secreting, pituitary tumors, surreptitious ingestion of T4 or T3, and functioning trophoblastic tumors.
Risk factors for hyperthyroidism include: Positive family history; Female sex; and Other autoimmune disorders.
Standard lab tests include measurements of T3, T4, Free thyroxine index (FTI) and TSH Many drugs can alter lab results, including: Anabolic steroids, Androgens, Estrogens, Heparin, Iodine containing compounds, Phenytoin, Rifampin, Salicylates, and Thyroxine.
High titers of antithyroid peroxidase (anti-TPO or antimicrosomal) antibodies or antithyroglobulin antibodies are found in the serum of most patients with Hashimoto's disease and in many with primary thyroprivic hypothyroidism or Graves' disease.
Diagnostic imaging using radioiodine (radioactive iodine uptake or RAIU) can differentiate between GraveÕs disease and toxic multinodular goiter.
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