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.

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 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.

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.

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 gene change (mutation) 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 identify the gene change that shows you have the genetic disorder called malignant hyperthermia susceptibility (MHS).
• Muscle biopsy (contracture test). In some cases, your health care provider 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. Because this test must be done on muscle tissue immediately after removing it, travel to a specialized muscle biopsy center is necessary.

If you or someone in your family has MHS or you think you may be at risk of malignant hyperthermia, it's important to tell your health care provider and anesthesiologist before you get anesthesia. 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, Revonto, Ryanodex) is used to treat the reaction by stopping the release of calcium into muscles. Other medications may be given to correct problems with a balance of the body's chemicals (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 any muscle breakdown and possible kidney damage. A stay in the hospital is usually needed until lab test results start to return to a standard range.

With treatment, malignant hyperthermia usually resolves within a few days.

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 health care provider about any precautions you should take.

Also, check with your health care provider to see if you should have genetic testing to determine if you have a genetic disorder that puts you at risk of malignant hyperthermia. Ask if close family members should also consider genetic testing.

If you have the genetic disorder MHS 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.