What is malignant hyperthermia?

Malignant hyperthermia (MH) is a severe reaction to certain medications used for anesthesia. These medications eliminate feelings of pain and relax your muscles during surgeries and other medical procedures. Not all medications cause the reaction associated with this condition.

Susceptibility to MH is passed down through genetics. If someone in your family has it, consider getting tested. The condition can lead to severe health outcomes.

Learn more: What is a drug allergy? »

Symptoms: What happens?

MH can occur during or after the administration of particular anesthetics or succinylcholine type muscle relaxants. You may encounter these medications in a variety of medical settings, including hospitals, outpatient clinics, and dental offices.

If you have the genes for MH, your body will trigger a reaction when exposed to these medications.

Some of the ways your body may respond include:

  • muscle rigidity, often first occurring in the jaw
  • a high fever that can reach 110°F (43.3°C) and above
  • faster body metabolism
  • rapid heart rate
  • rapid breathing
  • muscle spasms
  • breakdown of muscle fibers
  • climbing acid levels in the blood and elsewhere in the body

You may experience these symptoms in your first exposure to the medication. It’s also possible to experience a reaction after multiple uses despite no previous symptoms. In some instances, people with MH have experienced these serious symptoms during intense physical activity or in extreme heat.

Causes

MH is more likely to occur in people with muscle cells that contain unusual proteins. This causes an abnormal release of calcium in your body when your muscle cells are triggered. Triggers include certain medications, extreme heat, or strenuous physical exercise. MH can occur with this release of calcium in the body.

Only certain medications cause MH. One category of medication that can cause symptoms is known as volatile anesthetic agents. These include:

  • halothane
  • isoflurane
  • sevoflurane
  • desflurane
  • enflurane
  • ether
  • methoxyflurane

A muscle relaxant called succinylcholine can also cause symptoms.

Risk factors

MH is an inherited condition. People who are prone to MH have an altered gene in their cells that can react when exposed to particular medications.

You have a 50 percent chance of inheriting this condition if your parent or a sibling has the condition. You have a 25 percent chance of having the condition if any of your aunts, uncles, or grandparents have it. You may not know you have this condition unless a family member has MH during surgery or another event.

Some conditions are tied to MH, such as central core disease and multiminicore disease. Both of these are genetic conditions.

Incidence

The U.S. Library of Medicine states that MH occurs in 1 of every 5,000 to 50,000 people exposed to trigger medications. The Malignant Hyperthermia Association of the United States estimates that 1 in every 100,000 adults undergoing surgery encounters the condition. And in children, it occurs in 1 out of every 30,000 surgeries.

The estimates of people who have it are wide-ranging because not all people encounter the triggering medications in their lives. You may not know you have MH unless you are administered the specific drugs that cause it.

Testing

It’s possible to be tested for MH. Tests include genetic testing as well as muscle biopsies. You should get tested if you have a family member who has had MH. Knowing if you have the gene will help you manage future surgical procedures with your doctor.

Testing and diagnosis begins with a visit to your doctor. They will review your family history and determine the best course of action to diagnose the condition.

Tests include:

  • ECG
  • blood tests
  • urine tests

Your doctor may also order a muscle biopsy to conduct the caffeine halothane contracture test. This test measures your muscle response to halothane and caffeine.

Testing is not the only way to diagnose the condition. You may be diagnosed when exposed to the medications that trigger it during a medical procedure.

How it’s treated

Your doctor will need to work quickly to control symptoms if you experience MH during a medical event. Some actions the doctor may take include:

  • applying ice packs, cooling blankets, and fans to cool the body
  • using cold isotonic saline through an intravenous drip to reduce your body temperature
  • administering dantrolene (Dantrium)

The best way to treat the condition is to avoid all exposure to the medications that cause it. This can only be done if you’re diagnosed prior to exposure.

Recovery

The symptoms and outcomes of MH are serious. Recovery may require medical interventions like intubation, paralysis, or induced coma. Despite early interventions at the first signs of MH, the condition can be life-threatening.

Complications

The severe symptoms of MH can lead to serious outcomes, such as:

Outlook

MH is a serious medical condition. You should get tested if a family member has experienced the symptoms when exposed to trigger medications. Your doctor can help you manage the condition to avoid medications that may trigger MH during medical procedures. If you have been diagnosed with MH, it’s important to tell your family members so they can tell their own doctors. This will ensure that they prepare for the possibility of also having MH.