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In medicine, hyperpyrexia is an excessive and unusual elevation of body temperature above 42 C (107.6F), or high fever (also called a hyperthermia). Some of the more common causes of hyperpyrexia include excessive exposure to heat or the sun (also called heat hyperpyrexia, a part of heatstroke), bacterial septicemia (a generalized septical infection of the blood, some viral infections, such as mononucleosis, and a thyrotoxic crisis (in hyperthyroidism).

Malignant hyperpyrexia is a particular condition caused by the breakdown of muscle following its over-excitation, in response to certain stimuli, such as extreme exercise (especially in a high ambient temperature), intense and prolonged convulsions, anesthesia, fever or some drugs, such as cocaine, alcohol and aspirin. Malignant hyperpyrexia is accompanied by abnormal heart rhythms (cardiac arrhythmia) and kidney failure. The susceptibility to malignant hyperthermia is an autosomal dominant inherited trait. It is often noted for the first time during a general anesthesia, whereas the patient develops hyperpyrexia and muscle rigidity. Muscle tissue is rapidly destroyed by the hyper-rigidity (rhabdomyolysis) and the break-down products damage the kidneys, leading to renal failure. A dark colored urine is produced in consequence. It can be fatal if not treated rapidly.

See also: Malignant hyperthermia.

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