- An abnormality of the thyroid gland in which secretion of thyroid hormone is usually increased and is no longer under regulatory control of hypothalamic-pituitary centers; characterized by a hypermetabolic state, usually with weight loss, tremulousness, elevated plasma levels of thyroxin and/or triiodothyronine, and sometimes exophthalmos; may progress to severe weakness, wasting, hyperpyrexia, and other manifestations of thyroid storm; often associated with exophthalmos (Graves disease). SEE ALSO: thyrotoxicosis. SYN: hyperthyrea, thyroidism (1), thyrointoxication.- hereditary h. a rare inherited (autosomal dominant) disorder with constitutive stimulation of the thyrocytes.- iodine-induced h. SYN: Jod-Basedow phenomenon.- masked h. h. occurring without the usual manifestations, especially lack of hyperactivity and eye findings, often with hypoactivity, even somnolence. Manifestation can be limited to heart failure.- primary h. h. due to a disorder originating within the thyroid gland, in contrast to one of pituitary origin; may be due to generalized overactivity of the gland, to a localized hyperactive nodule, or to circulating antibody, which stimulates the gland (long-acting thyroid stimulator).- secondary h. h. due to stimulation of the thyroid gland by an excess of thyrotrophin secreted by the pituitary gland.
* * *hy·per·thy·roid·ism -.rȯid-.iz-əm, -rəd- n excessive functional activity of the thyroid gland also the resulting condition marked esp. by increased metabolic rate, enlargement of the thyroid gland, rapid heart rate, and high blood pressure called also thyrotoxicosis see GRAVES' DISEASE
* * *n.overactivity of the thyroid gland, either due to a tumour, overgrowth of the gland, or Graves's disease. See thyrotoxicosis.
* * *hy·per·thy·roid·ism (hi″pər-thiґroid-iz-əm) a condition caused by excessive production of iodinated thyroid hormones; characteristics include goiter, tachycardia or atrial fibrillation, widened pulse pressure, palpitations, fatigability, nervousness and tremor, heat intolerance and excessive sweating, warm, smooth, moist skin, weight loss, muscular weakness, excessive defecation, emotional lability, and ocular signs such as stare, slowing of eyelid movements, photophobia, and sometimes exophthalmos. Called also hyperthyroidosis. See also Graves disease and thyrotoxicosis.
Medical dictionary. 2011.