Malignant hyperthermia is a dangerous, rapid rise in body temperature due to internal issues. It is most often caused by certain medications, especially anesthesia medication.

People can have a tendency to have malignant hyperthermia which is known as malignant hyperthermia susceptibility.


Malignant hyperthermia susceptibility is often caused by a specific gene mutation. Only 1 parent has to have the defective gene for the child to inherit the susceptibility.

A malignant hyperthermia event is caused by abnormal levels of calcium in the muscle. The change in calcium causes an increase in metabolism. Heat is a side-effect of metabolism.

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The abnormal levels of calcium often are triggered by medications used for anesthesia such as:

  • Certain inhaled anesthesia gases
  • Certain muscle relaxants

Risk Factors

Malignant hyperthermia occurs most often in children and people who are Caucasian or of Northern European descent.

The main risk factor is having a family history of malignant hyperthermia.


Symptoms may begin after medication is given and include:

  • Fever - often more than 40.6°C (105°F)
  • Stiff muscles
  • Muscle spasms, especially the facial muscles
  • Fast breathing
  • Fast or irregular heartbeat
  • Dark urine
  • An uneven skin color


Malignant hyperthermia is an emergency. It is often suspected based on symptoms and recent anesthesia administration.

Malignant hyperthermia susceptibility may be suspected based on your medical and family history. If you have a positive family history, then your doctor may test you for the susceptibility with:

  • Genetic testing
  • Muscle biopsy —a sample of muscle tissue is taken and examined under a microscope


If the condition was triggered by a certain anesthetic, it will be stopped and/or changed.

Emergency care will be given and may include:

  • Ending surgery
  • Cooled IV fluids and blankets to reduce your temperature
  • Oxygen therapy to reduce damage caused by high temperature
  • Medications to slow muscle metabolism, control breathing and heart rate.

Kidney and heart tests may also be done to look for any potential complications from the hyperthermia event.


Make sure all of your doctors are aware of your susceptibility to malignant hyperthermia or any family history of malignant hyperthermia.

  • Discuss these facts before any surgery or medical procedure. This will allow your doctor to select medications that are less likely to trigger malignant hyperthermia.
  • Wear a medical alert bracelet to let emergency responders know about your condition. The bracelet will speak for you if you are unable to do so.

If you think there may be malignant hyperthermia susceptibility in your family, talk to your doctor about genetic testing as part of your family planning process.

Revision Information

  • Reviewer: EBSCO Medical Review Board James P. Cornell, MD
  • Review Date: 09/2018 -
  • Update Date: 09/03/2015 -