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Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

What Is It?

Malignant hyperthermia is a severe reaction to a dose of anesthetics. The reaction is sometimes fatal. It is caused by a rare, inherited muscle abnormality. Infrequently, extreme exercise or heat stroke can trigger malignant hyperthermia in someone with the muscle abnormality.

In people with the muscle abnormality, muscle cells have an abnormal protein on their surfaces. The protein does not affect muscle function significantly. That is, until the muscles are exposed to a drug that can trigger a reaction.

When a person with this condition is exposed to one of these drugs:

  • Calcium stored in muscle cells is released

  • The muscles contract and stiffen at the same time

  • There is a dramatic and dangerous increase in body temperature (hyperthermia)

Malignant hyperthermia usually occurs during or after surgery. But it can occur wherever anesthetic medications are used. This includes:

  • Emergency rooms

  • Dental offices

  • Surgeons' offices

  • Intensive care units

Symptoms of malignant hyperthermia usually occur within the first hour after exposure to the trigger medication. However, the symptoms can be delayed for up to 12 hours.

Most cases occur in children and adults younger than 30.

The muscle abnormality that can lead to malignant hyperthermia is caused by one of several genetic mutations. The most common mutation causes about half of all cases. A person with this mutation has a one in two chance of passing the gene to any of his or her children.

Family members can have different levels of sensitivity to medications that trigger the problem. In some cases, reactions are mild. A person may be exposed to high-risk medications several times before experiencing a recognizable reaction.

This condition sometimes occurs in people who also have muscular dystrophy. It also occurs with other muscle diseases associated with genetic mutations.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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