Malignant Hyperthermia                     MHANZ Logo

Patient Information

What is Malignant Hyperthermia?

Malignant Hyperthermia (malignant hyperpyrexia, MH) is a syndrome that can occur in susceptible people when they are given certain anaesthetic drugs. It occurs very rarely and is genetically inherited (i.e. runs in a family). It can result in a very high temperature and muscle rigidity developing during an anaesthetic that can be deadly if not recognised and treated.

How do I know if I have it?

You may have had a reaction under general anaesthetic which had some or all of the features of MH. Your anaesthetist may have referred you to the MH testing centre. You may have a family member who has been found to be susceptible to MH.
The only way we currently know to diagnose MH is by muscle biopsy. If someone in your family has it we will usually test all membersí, as half of them may be susceptible. For some people genetic tests (blood tests) may be available.

How will it affect me if I have a positive diagnosis for MH?

If the biopsy results are positive this will alter the types of anaesthetics that you can safely be given. The anaesthetist must not use potent volatile anaesthetic agents or a drug called suxamethonium. These are the only drugs that have been shown to trigger MH and they would not be given in any other situation than an anaesthetic or emergency situation (i.e. your GP would not prescribe them). There are other available alternatives to these drugs. Therefore you can have adequate anaesthesia for future operations.
Being susceptible to MH only affects the type of anaesthetic drugs you can receive safely. In general it does not effect any other aspect of your health.

Will my family have to be tested?

If you have a positive muscle biopsy it would be prudent to test all of your relatives. If they do not have the diagnosis they can rest assured of no problems with triggering of malignant hyperthermia during anaesthesia, but if they test positive much can be done to avoid life-threatening problems intra-operatively. Such testing may involve the IVCT or genetic testing.

Can MH be treated?

Since the 1970ís a drug has been available that can help in the treatment of MH. It is called dantrolene and it helps to relax muscle. It has been very effective in decreasing the death rate from MH if used early in the developing syndrome. It is not a cure but rather a treatment and should therefore not be relied upon if the diagnosis of MH has been made prior to surgery.
  Does previous uneventful anaesthesia mean Iím safe?

Unfortunately, on average, patients found to be susceptible to MH have had 3 previous uneventful anaesthetics so this is no guarantee that you are not susceptible.

How many people have this syndrome?

MH occurs in approximately 1 in 15,000 to 1 in 50,000 anaesthetics. Recent European studies have suggested a genetic predisposition of about 1 in 5,000 persons.

What Anaesthetics are safe?

Local anaesthetics, spinal, epidural and other regional (numbing) anaesthetics are safe. General anaesthesia with intravenous maintenance is also safe as is the gas, nitrous oxide.

What is a muscle biopsy?

This is a relatively small, day case surgical procedure that involves a cut - under regional or non-triggering general anaesthetic - to the outer thigh. A sample of muscle is removed which is then delivered to the anaesthetic laboratory where it is tested. There may be some residual soreness in the area of the biopsy for a few days but the procedure is low risk. You will usually need 2 to 3 days off work.

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