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

Treatments for malignant hyperthermia include the medication dantrolene (Dantrium, Revonto, Ryanodex), 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.

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
  • Irregular heart rhythm
  • Dangerously high body temperature
  • Excessive sweating
  • Patchy, irregular skin color (mottled skin)

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 used to lower cholesterol.

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 drugs that don't trigger a reaction can be used instead.

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 health care provider and anesthesia specialist (anesthesiologist). Other drugs may be used instead.


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

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

Risk factors

Your risk of having the genetic disorder MHS is higher if someone in your family has it.

  • You only need to inherit one changed gene from a parent to be affected by this disorder (autosomal dominant inheritance pattern). If one of your parents has the gene change that causes MHS, you have a 50% chance of having MHS too.
  • If you have other relatives with MHS, 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 (rab-doe-my-OL-ih-sis), 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 gene changes


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

  • A rare condition that causes muscle cells to break down (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 health care provider or anesthesiologist before surgery or any procedure that requires anesthesia.

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

May 13, 2022

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