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Malignant hyperthermia

Malignant hyperthermia (MH) is disease passed down through families that causes a fast rise in body temperature (fever) and severe muscle contractions when the affected person gets general anesthesia. This condition is not the same as hyperthermia that is due to medical emergencies such as heat stroke or infection.


Symptoms can include:

  • Bleeding
  • Dark brown urine
  • Muscle ache without an obvious cause, such as exercise or injury
  • Muscle rigidity and stiffness
  • Quick rise in body temperature

Myotonia of the eyelid (a disorder causing the inability to relax voluntary muscle after vigorous effort).


There has been a great improvement in our understanding of the causes of and who is susceptible to malignant hyperthermia. Nearly 40 genetic defects have been linked to the disorder. Malignant hyperthermia susceptibility is an inherited autosomal dominant disorder; this means that only one parent has to carry the disease for a child to inherit the condition. The siblings and children of a patient have a 50% possibility of inheriting the MH gene, and therefore, they could develop a MH reaction when exposed to trigger factors.

Those who are carriers may not be aware of this risk unless they or one of their family members have a life-threatening crisis related to testing or have a severe reaction to anesthesia during a surgical procedure.

It is also important to note that not all carriers of the defected MH gene will develop a critical episode when exposed to triggering anesthetics. The following volatile anesthetic agents are known triggers of MH:

  • Inhaled General Anesthetics
  • Desflurane
  • Enflurane
  • Ether
  • Halothane
  • Isoflurane
  • Methoxyflurane
  • Sevoflurane

Also known to trigger MH is succinylcholine (Anectine), a short-acting depolarizing-type, skeletal muscle relaxant for intravenous (IV) administration.


The use of certain medicines can prevent complications from malignant hyperthermia during surgery. In addition, avoiding the use of stimulant drugs such as cocaine, amphetamines and ecstasy as they can produce problems similar to MH in those persons who are predisposed to this condition.

Genetic testing is recommended for those persons who have a family history of myopathy, muscular dystrophy or malignant hyperthermia.