Date Updated: 04/07/2020


Malignant hyperthermia is a severe reaction to certain drugs used for anesthesia. This severe reaction typically includes a dangerously high body temperature, rigid muscles or spasms, a rapid heart rate, and other symptoms. Without prompt treatment, the complications caused by malignant hyperthermia can be fatal.

In most cases, the defective gene that puts you at risk of malignant hyperthermia is inherited, though sometimes it's the result of a random genetic defect. Genetic testing can reveal whether you have an abnormal gene. This genetic disorder is called malignant hyperthermia susceptibility (MHS).

Treatments for malignant hyperthermia include the medication dantrolene (Dantrium, Ryanodex, Revonto), ice packs and other measures to cool body temperature, as well as supportive care.


In most cases, no signs or symptoms of susceptibility to malignant hyperthermia exist until you're exposed to certain drugs used for anesthesia.

In rare cases, people at risk of malignant hyperthermia have shown signs of a reaction after intense physical activity during excessive heat or humidity, during a viral illness, or when taking statin medication.

If you're at risk of malignant hyperthermia and you don't have a serious reaction during your first exposure to certain anesthesia drugs, you're still at risk if you receive these drugs in the future. Other anesthesia medications that don't trigger a reaction can be used instead.

Signs and symptoms of malignant hyperthermia may vary and can occur during anesthesia or during recovery shortly after surgery. They can include:

  • Severe muscle rigidity or spasms
  • Rapid, shallow breathing and problems with low oxygen and high carbon dioxide
  • Rapid heart rate
  • Abnormal heart rhythm
  • Dangerously high body temperature
  • Excessive sweating
  • Patchy, irregular skin color (mottled skin)

When to see a doctor

If someone in your family is known to be at risk of malignant hyperthermia and you need to have anesthesia, it's important to tell your doctor and anesthesia specialist (anesthesiologist). Other drugs may be used instead.


Malignant hyperthermia susceptibility (MHS) is caused by a genetic defect (mutation). The abnormal gene increases your risk of malignant hyperthermia when you're exposed to certain anesthesia medications that trigger a reaction. The abnormal gene is most commonly inherited, usually from one parent who also has it. Less often, the abnormal gene is not inherited and is the result of a random gene mutation.

Different genes can cause the disorder. The most commonly affected gene is RYR1. More rarely affected genes include CACNA1S and STAC3.

Risk factors

Your risk of having malignant hyperthermia disorder is higher if someone in your family has it.

  • If one of your parents has the abnormal gene, you have a 50% chance of having it too (autosomal dominant inheritance pattern).
  • If you have other relatives with this genetic disorder, your chance of having it is also increased.

Your risk of having malignant hyperthermia is also higher if you or a close relative has:

  • A history of an event that is suspected to be malignant hyperthermia during anesthesia
  • A history of muscle tissue breakdown called rhabdomyolysis, which can be triggered by exercise in extreme heat and humidity or when taking a statin drug
  • Certain muscle diseases and disorders caused by inherited abnormal genes


If not treated promptly, malignant hyperthermia can result in major complications, such as:

  • Muscle injury that breaks down muscle tissue and releases contents into the blood (rhabdomyolysis)
  • Kidney damage or failure
  • Problems with clotting and bleeding
  • Death


If you have a family history of malignant hyperthermia or a relative who has problems with anesthesia, tell your doctor or anesthesiologist before surgery or any procedure that requires anesthesia.

Evaluating your risk of malignant hyperthermia allows your anesthesiologist to avoid certain anesthesia drugs.


Malignant hyperthermia is diagnosed based on signs and symptoms, monitoring during and immediately after anesthesia, and lab tests to identify complications.


Susceptibility testing

Testing to find out if you're at increased risk of malignant hyperthermia (susceptibility testing) may be recommended if you have risk factors. Testing may include genetic testing or a muscle biopsy test.

  • Genetic testing. The abnormal gene that makes you susceptible to malignant hyperthermia is identified using genetic testing. A sample of your blood is collected and sent to a lab for analysis. Genetic testing can reveal changes (mutations) in your genes that may make you susceptible to malignant hyperthermia.
  • Muscle biopsy (contracture test). In some cases, the doctor may recommend a muscle biopsy if you're at risk of malignant hyperthermia. During this test, a small piece of muscle tissue is surgically removed for lab analysis. In the lab, the specimen is exposed to triggering chemicals for malignant hyperthermia to determine how the muscle contracts.

If you or someone in your family has malignant hyperthermia and you need to have anesthesia, it's important to tell your doctor and anesthesiologist. Drugs that do not trigger malignant hyperthermia may be used as part of your anesthesia.

Immediate treatment of malignant hyperthermia includes:

  • Medication. A drug called dantrolene (Dantrium, Ryanodex, Revonto) is used to treat the reaction by stopping the release of calcium into the muscle. Other medications may be given to correct your body's metabolic imbalance and treat complications.
  • Oxygen. You may have oxygen through a face mask. In most cases, oxygen is given through a tube placed in the windpipe (trachea).
  • Body cooling. Ice packs, cooling blankets, a fan with cool mist and chilled intravenous (IV) fluids may be used to help reduce body temperature.
  • Extra fluids. You may also get extra fluids through an IV line.
  • Supportive care. You may need to stay in the hospital in intensive care for a day or two to monitor your temperature, blood pressure, heart rate, breathing and response to treatment. Several lab tests will be done frequently to check the extent of the muscle breakdown and kidney damage. A stay in the hospital is usually required until lab values start to return to normal.

Malignant hyperthermia usually resolves within a few days with treatment.

Follow-up care

If you've experienced malignant hyperthermia due to certain anesthesia drugs, exercising during excessive heat and humidity could trigger another reaction. Talk to your doctor about any precautions you should take.

Also, check with your doctor to see if you should have genetic testing to determine if you have an abnormal gene that puts you at risk of malignant hyperthermia. Ask if close family members should also consider genetic testing.

If you have the abnormal gene that puts you at risk of malignant hyperthermia, wear a medical alert bracelet or necklace. This lets health care providers know of your risk, especially in an emergency, when you may not be able to talk.

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