hyperthyroidism

/huy'peuhr thuy"roy diz'euhm/, n. Pathol.

1. overactivity of the thyroid gland.

2. a condition resulting from this, characterized by increased metabolism and exophthalmos.

[1895-1900; HYPER- + THYROID + -ISM]

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▪ pathology

also called  thyrotoxicosis 

      excess hormone production by the thyroid gland.

      Hyperthyroidism is usually caused by Graves disease; however, it may also be caused by a benign thyroid tumour (adenoma), multinodular goitre, thyroid inflammation ( thyroiditis), or high doses of thyroid hormone.

      Most patients with hyperthyroidism have an enlarged thyroid gland (goitre), with varying characteristics. Patients with Graves disease have generalized thyroid enlargement (diffuse goitre), but so also do patients with thyroiditis, which may be painless or painful. Other patients have a single hyperfunctioning thyroid nodule or multiple hyperfunctioning thyroid nodules. The increased thyroid hormone production results in an increase in the function of many organ systems. It causes an increase in cardiac output, tachycardia (rapid heartbeat), atrial fibrillation (rapid irregular heart rhythm), palpitations (pounding in the chest due to forceful contraction of the heart), and shortness of breath. Neuromuscular symptoms and signs include nervousness, hyperactivity and restlessness, anxiety and irritability, insomnia, tremor, and muscle weakness. Other common symptoms and signs are weight loss despite normal or even increased appetite, increased perspiration and intolerance of heat, increased frequency of bowel movements, and irregular menstrual periods and decreased menstrual blood flow in women. The most severe form of hyperthyroidism is thyroid storm, which is characterized by very rapid heartbeat, fever, disorientation, shortness of breath, and weakness, all of which may lead to heart failure, a drop in blood pressure, and death.

      Hyperthyroidism is diagnosed on the basis of these symptoms and signs, and the diagnosis is confirmed by finding high serum total and free thyroxine (and triiodothyronine) concentrations and low serum thyrotropin (thyroid-stimulating hormone, TSH) concentrations. In serum, thyroxine (and triiodothyronine) exists in two forms, one of which is bound to several proteins, and the other of which, a very small amount, is free. Serum thyroxine can be measured as serum total thyroxine or free thyroxine; the latter is preferable because it is the form of thyroxine that is readily available to the cells of the body and, therefore, is metabolically active. Measurements of serum total thyroxine are high in patients with thyroid disease and in patients producing more of the proteins that bind to thyroxine.

      Hyperthyroidism is usually a chronic, even lifelong, disorder. It can be treated with an antithyroid drug, radioactive iodine, or surgery (thyroidectomy). There are three widely used antithyroid drugs—methimazole, carbimazole (which is rapidly converted to methimazole in the body), and propylthiouracil. These drugs block the production of thyroid hormone but have no permanent effect on either the thyroid gland or the underlying cause of the hyperthyroidism. Patients with hyperthyroidism caused by Graves disease are often treated (therapeutics) with an antithyroid drug for one to two years, in the hope that they will have a remission of the disease and remain well after the drug is stopped; this occurs in 30 to 50 percent of patients. Radioactive iodine is taken up by thyroid cells in the same way as is nonradioactive iodine, but the radiation destroys the cells, thereby reducing thyroid hormone production and also reducing the size of the thyroid gland. It is highly effective, but it results ultimately in hypothyroidism in most patients. It is suitable for patients with Graves disease and is the preferred treatment for patients with a nodular goitre, in whom hyperthyroidism is a lifelong condition. The removal of the thyroid by thyroidectomy is rarely performed today, except in the case of patients with a large goitre. When caused by thyroiditis, hyperthyroidism is transient, usually lasting only four to six weeks, and no treatment or only symptomatic treatment with a beta-adrenergic (adrenergic drug) antagonist drug ( beta-blocker) is needed.

Robert D. Utiger

 

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