Malignant Hyperthermia

What is malignant hyperthermia?

Malignant hyperthermia (MH) is a rare medical emergency that can happen when you receive certain general anesthetic medications or another medicine called succinylcholine.

Patients at risk for MH often have an inherited gene change (mutation) that was passed down from a parent. This is called malignant hyperthermia susceptibility (MHS). Most people with MHS do not have symptoms unless they get a medicine that triggers an MH reaction. Also, not all people with MHS develop an acute episode of malignant hyperthermia with triggering medicines.

MH can be life-threatening if it is not treated quickly.

Child with oxygen mask lying on bed in operating room — Before your child has surgery, your health care team will ask whether anyone in the family has had severe reactions to anesthesia. This information will help the doctor choose the best anesthesia for your child.

Symptoms of malignant hyperthermia

Signs and symptoms of MH usually happen during or shortly after getting anesthesia and may include:

Fast breathing
Fast heartbeat
Sweating
Severe muscle stiffness or muscle spasms
Increase in body temperature or high body temperature
Patchy irregular skin color (mottling)

Causes of malignant hyperthermia

A change in either the RYR1 or CACNA1S gene is most often linked to MHS. These gene changes affect how muscles respond to some medicines commonly used during anesthesia. These include certain inhaled general anesthesia medicines and succinylcholine, a medicine that relaxes muscles.

A change in the RYR1 or CACNA1S gene is usually inherited from a parent. In rare cases, a new gene change can happen by chance, meaning the patient is the first in their family to have it.

Risk factors for malignant hyperthermia

Your child may have a higher risk for MH if they have:

A change in the RYR1 or CACNA1S gene
Had an MH reaction before
A close family member who had MH or a serious reaction related to anesthesia

Tell your child’s care team if your child has any of these risk factors. The team can choose anesthesia medicines that do not cause an MH reaction.

Tests for malignant hyperthermia

Genetic testing

A genetic test can show gene changes linked to MH. The results help your child’s care team understand your child’s inherited risk for MH. They can choose anesthesia medicines that are less likely to trigger a reaction.

Genetic testing may not find every gene change linked to MH. Your child's care team will explain what the results mean and if more testing is needed.

If your child’s test results show an increased risk for MH, certain anesthesia medicines may trigger an MH reaction. About 2 in 10,000 people are in this group. Be sure to let all of your child’s doctors know about this result.

There may be other genetic changes related to malignant hyperthermia that cannot be detected with current testing.

Muscle biopsy

During a muscle biopsy, a small sample of your child's muscle is taken for testing. This test is called a caffeine halothane contracture test. It looks at whether the muscle tissue reacts to certain chemicals.

Because the sample must be tested right away, this test is only done at special testing centers.

Treatment of malignant hyperthermia

MH is a medical emergency. If your child has signs of an MH reaction, the care team will stop the triggering anesthesia medicines and begin treatment right away. Treatment may include:

Dantrolene, a medicine that relaxes muscles
Ice packs to cool the body
IV (intravenous) fluids
Medicines to keep your child comfortable
Supportive care for symptoms and side effects as needed

Your child may want to wear a medical alert bracelet or carry a wallet card that informs others of this condition. In an emergency, doctors can use this information to help make decisions about medicines.

Questions to ask your care team

Is my child at risk for malignant hyperthermia?
Should my child have genetic testing for malignant hyperthermia?
If my child is at risk for malignant hyperthermia, which medicines should be avoided?
Should my child wear a medical alert bracelet or carry information about MH susceptibility?
What should I tell other health care providers before my child has anesthesia?
Should other family members be tested for MH susceptibility?

Key points about malignant hyperthermia

Malignant hyperthermia (MH) is a rare but serious reaction to certain general anesthesia medicines and succinylcholine.
Patients often have a change in the RYR1 or CACNA1S gene. This is called malignant hyperthermia susceptibility (MHS).
Most people with MHS do not have symptoms until they get a medicine that triggers the reaction.
Let your child’s health care providers know if your child develops a high fever after they receive anesthesia.
Genetic testing can help the care team understand your child’s risk for MH.
Your child’s care team can choose medicines that are less likely to trigger an MH reaction.
Let all of your child’s health care providers know if your child or a close family member has had MH or a serious reaction to anesthesia.
Wearing a medical alert bracelet or other medical ID can help make health care providers aware of the risk for malignant hyperthermia in an emergency.