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Malignant Hyperthermia: Know the Symptoms for Rapid Detection and Treatment

An illustration of a woman lying down in a hospital bed with her hand over her stomach. She is under anesthesia, administered by an IV drip bag on the left. A red circle surrounds the woman's head, and her cheeks and nose are flushed. There's a small sweat drop on her forehead. She is wearing a green hospital robe, and her brown wavy hair surrounds her head on the pillow. The IV bag is light blue and half-filled with medium blue liquid with bubbles. A dark blue IV tube connects the bag to a port in the woman's right arm.
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Written by Tim Becker, MD.
Resident Physician, The Mount Sinai Hospital
Last updated March 26, 2021

Malignant hyperthermia quiz

Take a quiz to find out if you have malignant hyperthermia.

Malignant hyperthermia is a genetic condition that results in a severe reaction to anesthesia. Symptoms include muscle rigidity and high body temperature.

Malignant hyperthermia quiz

Take a quiz to find out if you have malignant hyperthermia.

Take malignant hyperthermia quiz

What is malignant hyperthermia?


Malignant hyperthermia is a genetic condition (runs in families) that results in a severe reaction to anesthesia. The reaction is caused by genetic abnormalities in proteins that control muscle function.

Symptoms include muscle rigidity, very high body temperature, increased blood acidity, rapid breathing, a faster heart rate and abnormal heart rhythm, degeneration of muscle fibers, and high blood potassium.

Treatments include medication and measures to alleviate symptoms, such as lowering body temperature. Those with this condition are advised to wear a medical I.D. bracelet to avoid complications caused by anesthesia in emergency situations.

Recommended care

Call 911 for an ambulance now. This is a life-threatening condition that needs to be treated at the hospital.

Malignant hyperthermia symptoms

A variety of symptoms may develop if you have malignant hyperthermia, but many of these symptoms can be prevented or mitigated with rapid detection and treatment. They can be experienced throughout the entire body or localized to certain body systems.

Main symptoms

Certain symptoms can be felt throughout or affect the entire body, including:

  • Muscle rigidity: Muscles rapidly become tense, using up a lot of your body's energy.
  • High fever: Your body temperature can rise rapidly, up to very high temperatures, sometimes more than 110 degrees Fahrenheit. These high temperatures can lead to organ dysfunction and blood clotting disorders that can be fatal.
  • Increased acidity of the blood (acidosis): The overuse of energy to make muscles tense leads to extra production of lactic acid in the blood.
  • Breakdown of muscle fibers (rhabdomyolysis): Muscle fibers can degenerate and is usually a later stage of the condition.

Respiratory and chest-related symptoms

Certain symptoms of malignant hyperthermia can be localized to the the respiratory system and heart, including:

  • Rapid breathing: You breathe faster to meet your body's demand for oxygen and restore acid-base balance.
  • Fast heart rate (tachycardia): Your heart rate increases as your body tries to reduce fever and increase available oxygen.
  • High blood potassium (hyperkalemia): Acidosis and rhabdomyolysis can lead to a high potassium level in your blood, which can lead to dangerous heart rhythms.
  • Abnormal heart rhythm (arrhythmia): The muscles exchange acid and electrolytes with the blood, which can cause the heart cells to become unstable, leading to abnormal rhythms.

Malignant hyperthermia quiz

Take a quiz to find out if you have malignant hyperthermia.

Take malignant hyperthermia quiz

Malignant hyperthermia causes

Malignant hyperthermia is rare, occurring once for every 10,000 to 100,000 uses of anesthesia. It can occur regardless of age or ethnic background and has been found to occur more commonly in men and among young people. Causes primarily include genetics and some muscle diseases. An occurrence of malignant hyperthermia requires both an underlying genetic abnormality (such as an RYR1 mutation) and exposure to something that triggers symptoms such as anesthetic medications or extreme heat and exercise.


Abnormalities (mutations) in at least six different genes are known to predispose individuals to malignant hyperthermia.

  • RYR1: This is a gene that provides instructions for making the protein that helps inform muscles when to become tense (contract) via signaling with calcium ions. RYR1 abnormalities are the most common genetic risk factor for malignant hyperthermia. The gene is inherited in an Autosomal Dominant pattern, meaning that if you have a parent, sibling, or child with the mutation, there is a 50 percent chance that you also have it.
  • CACNA1S: This is a gene related to RYR1 that also helps make muscles contract. This is a much less common cause of malignant hyperthermia.

Muscle diseases

Certain rare muscle diseases are also associated with an increased risk of malignant hyperthermia, including:

  • Central core disease
  • Multiminicore disease

Anesthetic Medications

Most commonly, malignant hyperthermia is triggered by medications that are used so that you do not feel pain during invasive procedures or surgery. This may include:

  • Inhaled gases: Such as halothane, isoflurane, sevoflurane, and desflurane
  • Muscle relaxants: Such as succinylcholine

Unfortunately, safely experiencing anesthesia does not rule out predisposition to malignant hyperthermia. Although malignant hyperthermia can occur during your first exposure to anesthetics, people with the susceptibility do not experience symptoms until their third anesthetic exposures, on average.Fortunately, safe alternative medications can be used.

Extreme heat and strenuous exercise

Extreme heat and strenuous exercise can also cause malignant hyperthermia. However, these cases are very rare.

Treatment options and prevention for malignant hyperthermia

If not treated promptly, malignant hyperthermia can be fatal. However, malignant hyperthermia usually occurs during or immediately after surgery and can often be detected and treated immediately by anesthesia specialists. Treatments include:

  • Medications: Dantrolene relaxes tense muscles and is used to treat the reaction.
  • Supportive treatments: Ice packs, cooling blankets, fluids, and fans can be used to decrease body temperature. After an episode of malignant hyperthermia, you are typically closely monitored for at least 24 hours.
  • Medical alert bracelets: Since the triggering anesthetics are used in emergency departments and urgent surgeries, a medical alert bracelet could help medical personnel prevent an episode of malignant hyperthermia.

Ready to treat your malignant hyperthermia?

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Malignant hyperthermia quiz

Take a quiz to find out if you have malignant hyperthermia.

Take malignant hyperthermia quiz

When to seek further consultation for malignant hyperthermia

You should seek medical attention if you or a family member has malignant hyperthermia or you have a family history of malignant hyperthermia, especially if either of you are preparing for surgery.

If a family member has had malignant hyperthermia

You can discuss with your physician the risks and benefits of pursuing testing to determine if you are also at risk of the condition [10]. Historically, the most effective way of determining susceptibility involves removing a small piece of muscle and examining it in a laboratory (muscle biopsy). Recently, blood tests that identify genetic mutations linked to malignant hyperthermia have become available. These tests are less invasive and less expensive, but do not yet detect all forms of the disorder.

If you are preparing for surgery

It is imperative to share if you or a family member has suffered from malignant hyperthermia in the past with your surgeon and anesthesiologist. The anesthesiologist can select specific medications to make sure you stay safe during and after the surgery. You may not experience malignant hyperthermia during your first surgery. Even if you have safely been under anesthesia before, any family history is still important to report.

Questions your doctor may ask to determine malignant hyperthermia

  • Have you been feeling more tired than usual, lethargic or fatigued despite sleeping a normal amount?
  • Are you sick enough to consider going to the emergency room right now?
  • Have you lost your appetite recently?
  • Do you have a cough?
  • Have you experienced any nausea?

Self-diagnose with our free Buoy Assistant if you answer yes on any of these questions.

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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Rothschild has been a faculty member at Brigham and Women’s Hospital where he is an Associate Professor of Medicine at Harvard Medical School. He currently practices as a hospitalist at Newton Wellesley Hospital. In 1978, Dr. Rothschild received his MD at the Medical College of Wisconsin and trained in internal medicine followed by a fellowship in critical care medicine. He also received an MP...
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