Malignant Hyperthermia


What is malignant hyperthermia?

Malignant hyperthermia is a rare but very serious syndrome that causes a dangerous reaction to anesthesia. Malignant hyperthermia occurs when a patient is given certain types of anesthesia before undergoing surgery or a medical procedure.

Because the patient often does not know that he or she has the syndrome, it may only be discovered once anesthesia is given before surgery and symptoms begin.

Symptoms and Causes

What is the cause of malignant hyperthermia?

Malignant hyperthermia is an inherited syndrome. If one parent has the gene for the syndrome, the baby has a 50 percent chance of inheriting it.

Most cases occur in people in their early 20s. Some studies show that men are more at risk than women to develop malignant hyperthermia.

What are the symptoms of malignant hyperthermia?

The patient may not have any health issues until the symptoms actually occur when he or she receives anesthesia. Symptoms come on quickly, and can include:

  • Rapidly increasing body temperature, sometimes to more than 105 degrees F (40.6 degrees C)
  • Muscle stiffness. The muscles react to the anesthesia by releasing calcium that is normally stored within the muscle cells. Excess calcium causes the muscles to shrink and stiffen.
  • Rapid, and possibly irregular, heartbeat

If it is not treated, malignant hyperthermia can lead to the failure of several organs, internal bleeding, cardiac arrest and possibly death.

Diagnosis and Tests

How is malignant hyperthermia diagnosed?

A patient who is going to have surgery should tell the healthcare providers about his or her family medical history, especially if it is known that one parent has the gene for malignant hyperthermia. If a parent has the gene, then a child is more likely to have it.

If it is suspected that a patient is susceptible to the syndrome, the doctor may recommend special tests and procedures. The doctor may take a muscle biopsy (a small portion of the patient’s muscle) and analyze it for a reaction to an anesthesia gas.

Management and Treatment

How is malignant hyperthermia treated?

The symptoms of malignant hyperthermia must be treated immediately. A drug, usually dantrolene (Dantrium®), is given to relieve symptoms quickly and to stop the excess calcium from getting into the muscles. In addition, to treat the overheating of the body, the patient may be wrapped in a cooling blanket and given intravenous fluids.

What are the complications associated with malignant hyperthermia?

Once it is determined that a patient is suffering from malignant hyperthermia, complications are already rapidly occurring. If treatment does not begin immediately once the body reacts to the anesthesia, several complications can occur, including:

  • Internal bleeding
  • Brain injury/coma
  • Increased acid in the body
  • Fluid in the lungs
  • Cardiac arrest
  • Kidney and liver failure

Children are at a greater risk for these complications.


Can malignant hyperthermia be prevented?

Malignant hyperthermia can be prevented by avoiding the agents that bring it about: succinylcholine (Anectine®) and inhalational agents. Alternatives are readily available and can be substituted easily.

The patient should tell the doctor and other caregivers about his or her family history before any surgeries or medical procedures. The surgeon and anesthesiologist can then plan to use other anesthesia drugs, and can be on the lookout for signs of malignant hyperthermia once the surgery begins.

Outlook / Prognosis

What is the prognosis (outlook) for patients who are at risk for malignant hyperthermia?

If the patient has an abnormal reaction to anesthesia and the symptoms are treated immediately, the prognosis is good. If malignant hyperthermia is not treated, serious medical complications, up to and include death, can occur.

Last reviewed by a Cleveland Clinic medical professional on 10/26/2018.


  • Malignant Hyperthermia Association of the United States. Frequently Asked Questions. ( Accessed 10/29/2018.
  • National Organization for Rare Disorders. Malignant Hyperthermia. ( Accessed 10/29/2018.
  • U.S. National Library of Medicine: Genetics Home Reference. Malignant hyperthermia. ( Accessed 10/29/2018.

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