HYPERTHYROIDISM

abnormal bodily condition characterized by excessive secretion of thyroid hormones and caused by overactivity of the thyroid gland. The thyroid gland's oversecretion of hormones is usually accompanied by enlargement of the gland itself, thus forming the swelling, known as a goitre, in the neck region. The increased levels of thyroid hormones cause an increased metabolic rate and hyperactivity of the autonomic nervous system. These syndromes result in an increased heart rate, heart palpitations and fibrillations, and such symptoms as shortness of breath, excessive sweating, nervousness, excitability and hyperactive behaviour, tremors, increased appetite, and protruding eyes. The most common type of hyperthyroidism is Graves' disease (q.v.). This is an autoimmune disorder caused by the body's production of antibodies to the thyroid gland. Another type of hyperthyroidism is toxic multinodular goitre, or Plummer's disease, which results from a benign tumour (adenoma) of the thyroid gland. Hyperthyroidism is treated by drugs that block or suppress the thyroid gland's production of hormones, or by surgical removal of part of the gland.