What Is Malignant Hyperthermia?

Medically Reviewed by Carmelita Swiner, MD on July 07, 2023
Written by WebMD Editorial Contributors
3 min read

Malignant hyperthermia is when you have an extremely high body temperature caused by certain chemicals or other triggers. If left untreated, malignant hyperthermia can cause death.

Hyperthermia is a medical emergency that happens when your overall body temperature is too high. Your body loses control of functions, like sweating, which usually keep it at about 98 degrees Fahrenheit. With hyperthermia, your body goes over 104 degrees Fahrenheit. 

‌Hyperthermia usually happens when you’re in a high-heat situation. This could include wearing clothes that are too heavy or warm, not drinking enough water, or being outside for too long on a hot day.‌

Malignant hyperthermia is when certain kinds of anesthetics (or sometimes intense exercise or high air temperature) cause hyperthermia. Anesthetics are drugs that temporarily take away feeling and/or consciousness. They’re useful in surgeries and other treatments that would be extremely painful otherwise. 

‌Malignant hyperthermia most often happens after using certain anesthetics or other medications. The anesthetics that trigger malignant hyperthermia are: 

  • Inhaled general anesthesia
  • Desflurane
  • Enflurane
  • Ether
  • Halothane
  • Isoflurane
  • Methoxyflurane
  • Sevoflurane
  • Succinylcholine

These chemicals can trigger malignant hyperthermia even in people who have used them before without problems.

Intense exercise or high air temperatures can sometimes trigger malignant hyperthermia. When this happens, it's called “awake” hyperthermia.

‌Malignant hyperthermia shares most symptoms with general hyperthermia. The symptoms will most likely appear while you’re under anesthesia, or immediately after. These symptoms include:

  • Muscle spasms (quick, sudden movements or twitches)
  • Blood becoming acidic
  • Muscle stiffness
  • Higher carbon dioxide levels in breath
  • Irregular heartbeat
  • Red, splotchy skin
  • Breathlessness or other breathing problems
  • Extreme sweating
  • Very high body temperature (usually appears after other symptoms)
  • Death, in severe cases‌

People with malignant hyperthermia may never know it. The symptoms usually only appear after you take certain medicines.

‌Genetic defects (errors in the code of your DNA) increase your risk of experiencing malignant hyperthermia. These defects may be present in your genetic code from birth. They may also activate later in life.

Scientists have found over 80 different genetic code defects that can cause malignant hyperthermia. These genetic defects often run in families. Parents and siblings of someone who has malignant hyperthermia are more likely to have it themselves.‌

Malignant hyperthermia is more common in males than females.

‌Two medical tests can help you figure out if you have a genetic defect that causes malignant hyperthermia. 

Genetic blood test. A lab can use a sample of your blood to look at the genetic code in your blood cells. These tests can find a defect that occurs in about half of people with malignant hyperthermia. 

These blood tests aren’t 100% accurate. Some genetic defects that can cause malignant hyperthermia haven’t been discovered yet. People with known genetic defects don’t always get malignant hyperthermia.‌

Muscle biopsy. A sample of your muscle tissue can help figure out if you’re at risk of malignant hyperthermia. A doctor or other professional will remove a very small part of your muscle, likely from your leg. A lab will test the muscle’s reaction to the chemicals that trigger malignant hyperthermia. 

Muscle biopsy tests are more accurate and harder to access than genetic tests. You need to have certain symptoms and family history to get a muscle biopsy test. Fewer labs can perform a muscle biopsy test than a blood test for malignant hyperthermia.

‌Malignant hyperthermia usually happens during or after a medical treatment involving anesthesia. To reverse the hyperthermia, doctors must immediately stop using the trigger medication. They may also:

  • Use a cooling blanket
  • Put ice packs on your groin, underarms, or other areas
  • Give you cold fluids through an IV
  • Inject the medication dantrolene
  • Call a malignant hyperthermia hotline

A doctor may take you to another part of the hospital to closely watch your symptoms afterward. 

‌There’s no treatment to reverse the genetic defect that causes malignant hyperthermia. Knowing if you have the genetic defect can help you avoid emergencies. 

Tell your doctor if you’re at risk of experiencing malignant hyperthermia. They’ll make sure to use safe anesthetics during medical treatments. ‌

A doctor will pay close attention to your temperature and other basic measurements during a procedure with anesthesia. Responding early to changes in these measurements can help prevent malignant hyperthermia emergencies.