Malignant hyperthermia (MH) is a rare, inherited condition that causes muscle rigidity, high fever, fast heart rate, and abnormal muscle contractions when someone with the disease receives general anesthesia. These complications can include or lead to rhabdomyolysis, high blood potassium, and death. MH has a low incidence and high mortality rate. 

Hyperthermia means high body temperature, but this condition is not the same as hyperthermia from other medical emergencies such as heat stroke or infection.

Patients with MH can experience life-threatening complications, called a MH crisis, if they are exposed to trigger agents, such as certain anesthetics that are used to put patients to sleep for surgery.

Trigger agents currently in use in the United States include most of the inhalational anesthetic gases and the muscle relaxant, Succinylcholine. These agents do not necessarily trigger a crisis every time a susceptible patient comes in contact with them. That means an uneventful anesthetic in the past does not rule out MH-susceptibility.

Recent evidence indicates that individuals with MH-susceptibility may develop MH with exercise or heat exposure. 

Malignant Hyperthermia Symptoms

A MH crisis can occur when a susceptible patient is exposed to triggering agents.

This exposure can lead to muscle rigidity, very high fever, failure of other organs (kidney, lung), abnormal blood clotting and other life-threatening complications.

If treatment is not started promptly, up to 7 out of 10 patients may die from a MH crisis and its complications.

Malignant Hyperthermia Diagnosis

In general, testing for MH-susceptibility is recommended in 2 groups of patients:

  1. Anyone who experienced a MH crisis or questionable MH crisis during anesthesia that involved trigger agents.
  2. Anyone with a close relative who tested positive for MH or who experienced a MH crisis. Children of an affected person have a 50 percent chance of inheriting MH from their parents.

Tests may include:

  • Blood clotting studies
  • Blood work
  • Genetic testing
  • Muscle biopsy

Muscle Biopsy for Malignant Hyperthermia

Watch a video on muscle biopsy and caffeine halothane contracture testing (CHCT) performed at Wake Forest Baptist Medical Center. 

Our Malignant Hyperthermia Team

Thomas Pranikoff, MD
Thomas Pranikoff, MD
Alan Glenn Woodruff, MD
Alan Woodruff, MD
Marina Lin
Marina R Lin, MS, Biochemist

Malignant Hyperthermia Crisis Management

Preventing a MH crisis is the key. If you are MH-susceptible, safe anesthesia agents will be used and the risk of a MH crisis can be avoided.

If you experience a MH crisis, there is treatment available – a drug called dantrolene. However, effectiveness is greatest when given early. Dantrolene is given through an intravenous line and is thought to reverse the effects of triggering agents on muscle function. If dantrolene is started promptly in a MH crisis, together with rapid cooling, discontinuing triggering agent, and hyperventilating with oxygen, the risk of complications or death is substantially reduced.

Life with Malignant Hyperthermia

Individuals known to be susceptible to MH can safely undergo anesthesia for any type of surgical or dental procedure as long as trigger agents are avoided. Below are some frequently asked questions for individuals who may be MH-susceptible.