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Malignant Hyperthermia

  • Cynthia M. Johnson, MA
Publication Type:


Malignant Hyperthermia

(Malignant hyperpyrexia; Malignant Hyperthermia Susceptibility)


Malignant hyperthermia (MH) is a fast and harmful rise in body temperature.


MH is often caused by a faulty gene. People who have the gene have malignant hyperthermia susceptibility.

MH can be triggered by certain medicines, mainly anesthesia and muscle relaxers.

Risk Factors

MH is more common in young adults and men. The risk is higher in those who have family membrs with MH.


Symptoms of MH may start after medicine is given. A person may have:

  • Fever higher than 105 degrees Fahrenheit (ºF) (40.6 degrees Celsius [ºC])
  • Stiff muscles
  • Muscle spasms, mainly in the face
  • Fast breathing
  • Fast or uneven heartbeats
  • Dark urine (pee)
  • An uneven skin color
Muscle Fibers.

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MH is an emergency. Diagnosis is based on symptoms and recent anesthesia.

MH susceptibility may be suspected based on a person's medical and family history. Genetic testing and a muscle biopsy may be done to confirm it.


Any medicine causing this problem will be stopped or changed. Medicine may also be given to lower body temperature.

Emergency care will be needed, such as:

  • Oxygen therapy
  • Ending or postponing surgery
  • Supportive care and monitoring


People with past MH or a family history of it should tell their doctors. This is especially important before any surgery or procedure.





  • FAQs: General MH questions. Malignant Hyperthermia Association of the United States website. Available at: http://www.mhaus.org/faqs/category/frequently-asked-questions-about/about-mh/.
  • Hopkins PM, Girard T, et al. Malignant hyperthermia 2020: Guideline from the Association of Anaesthetists. Anaesthesia. 2021;76(5):655-664.
  • Malignant hyperthermia. EBSCO DynaMed website. Available at: https://www.dynamed.com/condition/malignant-hyperthermia.


  • Mark Arredondo, MD
Last Updated:

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.