What is Malignant Hyperthermia (MH)?
MH is a reaction to commonly used anaesthetic drugs where the body produces too much heat. If it is not recognised and treated in its early stages, MH can lead to death. When someone is known to be at risk of developing MH, there are safe alternative anaesthetic drugs that can be used. The risk of developing MH is associated with a change in the genes that are responsible for controlling the release of calcium in skeletal muscle cells. A person at risk of MH can be diagnosed by removing a small piece of muscle (using safe anaesthesia) in an operation called a muscle biopsy, and then exposing small strips of their muscle to the anaesthetic gases under carefully controlled conditions in our MH laboratory.
Is MH common?
No. An MH reaction is a rare event, occurring in about one in every ten thousand general anaesthetics. Possibly about 1 in every 500 persons in the population is potentially susceptible (has a genetic change that may make them more likely to have MH).
I have had an uneventful anaesthetic in the past. Does this mean I do not have MH?
No. Triggering anaesthetics do not necessarily cause an MH crisis every time someone at risk is given them. There is one patient who had 13 general anaesthetics before they had an MH reaction, although on average, a person develops a reaction on the third exposure.
Who gets MH and why?
MH is hereditary; it is passed on through the family. It affects males and females equally, and can occur in every ethnicity.
A person with MH has a 50% chance of passing that risk on to each child that they have.
MH is not contagious.
How do I know if I have MH?
A specialised muscle biopsy which is called an In Vitro Contracture test (IVCT) is currently the only certain test for MH. In some families a DNA (gene) test can be used to identify those at high risk, and these people do not need to have the muscle biopsy. A negative DNA test does not exclude MH.
Is there a cure?
There is no cure for the predisposition to MH. The management of MH involves avoiding the triggering agents during anaesthesia. Safe anaesthesia can be given if the doctors know a person is at risk.
Can MH be treated?
Since the 1970’s a drug has been available that can help in the treatment of MH. It is called Dantrolene. It has been very effective in treating MH if used early in the MH crisis. It is not a cure for MH and is only for use in emergencies as it does not completely stop the events.
What Anaesthetics are safe?
Non-triggering general anaesthesia with intravenous anaesthesia agents is safe. Nitrous oxide gas is safe. Local anaesthetics are safe. Spinal, epidural and other regional (numbing) anaesthetics are safe.
The only drugs necessary to avoid are volatile anaesthetics and a muscle relaxing drug called suxamethonium (succinylcholine).
Apart from when I have surgery, what effect will MH have on my lifestyle?
You can still lead an active life with no restrictions on normal activity including sports, such as rugby, netball and running marathons.
Can I choose not to be tested?
Yes, absolutely. The decision to have a muscle biopsy is up to you. You will be provided with as much information as you need to help you reach your decision. If you decide not to be tested, then you would have to be assumed to be at risk of MH should you require an anaesthetic. The anaesthetist needs to know your MH status for safety, and this may lead to postponement of non-life saving surgery or increased risk of complications during emergency surgery.
Also, if you choose not to be tested, your children (and possibly other relatives), will be assumed to be at risk of MH and would need to undergo testing which could be unnecessary if you had a test and were shown to not be at risk.
Should I be worried about further anaesthetics if I am at risk of MH?
No. It is important to realise that operations can be performed safely and effectively for patients at risk of MH. All anaesthetists in Australia and New Zealand and most developed countries are aware of this condition. However, in order to anaesthetise you safely, anaesthetic equipment needs to be specially prepared and a more experienced anaesthetist will often be called as some anaesthetists are less familiar with the alternative anaesthetics.
Although the condition will be documented in your notes, and an alert placed on the national patient database system (if you are in New Zealand), it is important for you to inform the anaesthetist of your MH status before any operation. We advise that you keep an MH warning card in your wallet or purse. We also advise that you wear a medical alert bracelet or similar in case you are brought into hospital unconscious after an accident or illness.
Can I travel overseas if I have MH?
Most developed countries have well trained anaesthetists and the necessary anaesthetic drugs and equipment to manage patients at risk of MH. In less developed countries, safe anaesthesia for patients at risk of MH cannot be guaranteed. Hospitals in those countries are also unlikely to be able to afford Dantrolene which is the antidote to MH. Any of the Malignant Hyperthermia Units in Australia or New Zealand can give specific advice for your situation.
What do I do if I am negative and I need an operation in the future?
If you are negative, you can receive anaesthesia without any specific precautions. You should give the results of your muscle biopsy test to all treating doctors.
Do I need to inform any family members?
Yes. If you receive a negative result, all your children and their children will be considered negative and do not require any special precautions. MH cannot “skip generations”.
If you receive a positive result, we advise you to inform blood relatives of your diagnosis and ask them to contact the Malignant Hyperthermia Unit for advice regarding testing.
In particular, your children have a 50% chance of having inherited MH from you, and it is likely that you inherited the condition from one of your parents. Your brothers and sisters should be considered at risk of MH as well.
Can I still have a local anaesthetic at the dentist?
Yes. All local anaesthetics are safe to use. It is still important to inform your dentist, especially if you need to be referred on for surgical dentistry, e.g. wisdom teeth removal. Some dentists use sedation with midazolam and laughing gas (Nitrous oxide) – this is safe in MH patients.
Can I still take medicine to treat a cold?
Yes. All cold and flu remedies are safe in MH. The only triggering drugs for MH are a muscle relaxing drug called Suxamethonium, and the volatile anaesthetic gases.
I am pregnant. Can I have a muscle biopsy?
No. Pregnancy affects the result of the muscle biopsy. We usually wait until six months after you have given birth to your baby.
I have MH and now I am pregnant. Do I need to do anything special?
You should inform your doctor or midwife that you have MH so you can be referred to the hospital for a clinic visit. You can still have a normal birth, but your midwife should inform the operating theatre at your hospital when you come in to hospital in labour. That way if you need any help at delivery, equipment will be prepared for you.
If you have MH and we have been able to find a DNA mutation in your blood, we may be able to take a blood sample from your baby’s umbilical cord at birth. This is painless for the baby. We need some advance warning to get the special blood tubes to your local hospital or birthing centre beforehand. Contact your MH centre to organise this.
How old do my children have to be before they can be tested?
Children must be at least 10 years of age and weigh more than 30kg before they can be tested. In practice we usually wait until they are 12.
What is recommended in terms of work/exercise after the muscle biopsy?
This depends on the type of work you do. A more physical job may require a longer period off work, but usually no more than a week is required.
In terms of exercise we would recommend you gradually return to your normal activities after your surgery and be guided by your level of comfort. Depending on the type and intensity of exercise you do, it can take between 2–6 weeks to get back to normal.
How long should I avoid driving?
There is no set time to avoid driving. However, you cannot drive home from your biopsy and we advise you do not drive until you have the strength to comfortably perform an emergency stop.
What if my local doctor has no knowledge of MH?
Within two weeks of your biopsy, your general practitioner and your referring doctor will be sent a copy of your results. You will also be given a copy of your results for your records. We are available to speak to any doctor who wishes to discuss your management or future anaesthetics.
A relative of mine wants to be tested for MH, what should I do?
There is a referral form on the website which you will need to fill in with your general practitioner. Alternatively their doctor can contact their local MH unit and get advice.
I have been told I have Malignant Hyperpyrexia – is this the same condition?
Yes, malignant hyperpyrexia is an old name for malignant hyperthermia.
THE MUSCLE BIOPSY
I have been told I need a muscle biopsy. Why?
There are three common reasons for being referred to the Malignant Hyperthermia Unit for a muscle biopsy.
- You experienced a reaction to an anaesthetic that raised the suspicion of MH.
- MH has been found in your family and there is no DNA test available in your family.
- MH has been found in your family, a DNA test is available in your family but you have had a negative DNA test.
Other reasons for being referred to the MH Unit for biopsy
- You, or a relative have a muscle disease that may be associated with a risk of MH, such as central core disease.
- You developed heat stroke after exercise or muscle cell breakdown after exercise (rhabdomyolysis) and your neurologist has recommended a biopsy
I live a long way from a testing centre; can I have the test done at my local hospital?
No. The laboratory tests are highly specialised and the muscle samples need to be taken to the lab within 15 minutes of the muscle biopsy in order for the tests to be reliable.
The four geographical locations available for testing in Australia and New Zealand are:
Westmead, New South Wales
Perth, Western Australia
Palmerston North, New Zealand
What does the muscle biopsy involve?
The muscle biopsy involves taking a small sample of muscle from the outer part of your thigh. The biopsy is a surgical procedure through an incision (cut) in the skin which is usually 5–7 cm long.
The procedure is performed in the operating theatre and usually takes no more than 45 minutes to one hour.
You meet an anaesthetist before surgery who will check your health status and discuss the procedure in detail, giving you the opportunity to ask any questions. You may be offered a choice of general or regional (spinal, epidural or nerve block) anaesthesia but the procedure cannot be done with local anaesthetic only. Different institutions will have slightly different instructions so please click on the link to download instructions relevant to your institution.
Specific instructions for patients at Palmerston North Hospital
Specific instructions for patients at Royal Melbourne Hospital
Specific instructions for patients at Westmead Hospital
Specific instructions for patients at Royal Perth Hospital
How do I look after my wound?
The wound is covered with a clear dressing. It is safe to shower with this dressing on, but you should not bathe or go swimming. In about 2–3 days the dressing will start to peel off around the edges. You will receive a second dressing in your discharge pack, remove the old dressing and cover the wound with the second one. As it starts to peel off, it can be removed and does not need to be replaced.
What if my wound starts to get more painful, reddened or yellow discharge appears?
Wound infection is an uncommon complication, occurring in less than 1% of muscle biopsies. You will need to see your GP for a check and probably start on antibiotics.
When will I get the result of my biopsy?
We will have your results the same day as the biopsy. A member of the MH team will visit you before you leave the hospital and explain the result and what steps need to be taken.
What do I do if my result is negative?
A negative result means you are not at risk of developing MH. For any future operations, no specific precautions relating to MH need be taken.
If you were having the biopsy because you suffered a suspected MH reaction, other family members can be reassured that they are not at risk of developing MH.
However, if you are having the biopsy because a family member had a reaction and you have a negative result, while you and your immediate descendants (children and grandchildren) are fine, other blood relatives may still need to be tested. It is better to check with the doctor at the time of the biopsy.
What do I do if my result is positive?
A positive result means you are at risk of developing MH. The anaesthetist will explain in detail what this means for you. You will have the opportunity to ask any questions and be given more information to take away with you explaining more about MH.
A positive result does not mean that you cannot have surgery, it means that your anaesthetist will need to take extra precautions to prepare the anaesthetic machine for you, and that alternative safe anaesthetic drugs must be used.
Because MH is a genetic condition there is a 50% chance that your children may inherit MH from you.
You should wear or carry some form of alert about your condition so that people are aware of it in an emergency. The unit you attend for your biopsy will help you with this.
There is an association between exertional heat stroke and MH, so we advise against extreme sporting events in high temperatures.
Will I have pain following the biopsy?
If you have a spinal anaesthetic, the local anaesthetic will last for around six hours, and you will have weakness and numbness of your legs for this period. As this wears off you will start to experience some pain and discomfort around the site of the muscle biopsy. If you chose a general anaesthetic, you will still be comfortable from the pain relief given in theatre initially but will require more once this wears off. Pain killers will be prescribed to ease this, and you will be given a script for analgesia on discharge. The pain is similar to a torn muscle and is usually managed with routine painkillers. Paracetamol and Ibuprofen are given most commonly. As some people are unable to tolerate Ibuprofen due to asthma or stomach ulcers, an alternative such as Tramadol or Codeine will be prescribed for the first couple of days.
How long will the pain last?
This varies between patients. Patients experience pain for an average of six days (ranging from 0–60 days) and use pain killers for an average of three days.
How big will my scar be?
The scar is usually 5–7cm long and is located midway on the outer thigh. In a survey of muscle biopsy patients, 96% described their scar as either hardly noticeable or acceptable. 4% described their scar as poor.
Are there any complications of the muscle biopsy?
All surgical procedures carry the small risk of infection.
Many patients have some numbness around the scar initially. This usually gets better within a week or two but can take up to 6 months to fully resolve. Very rarely the numbness persists.
Rarely the area of the biopsy can bleed, resulting in swelling and pain at the site. This will usually settle with compression bandages.
Post-operative pain is usually well controlled with simple analgesics and rest.
Most people can return to work in less than a week unless their job is very strenuous.
THE GENETIC TEST
MH is a genetically inherited disorder. This means that it can be transferred from parent to child. In some families with MH, there is a change (mutation) in their DNA (the blueprint of body makeup) and this can be identified with a blood test. There are many different mutations that have been found to cause MH.
If you are the first person in your family to be diagnosed with MH, with your permission, at the time of your muscle biopsy you will have some blood taken and examined for all currently known MH genetic changes.
If one of these changes is found in your DNA your family members can access a genetic test for MH.
If no changes mutations are identified, your blood and muscle will be stored in our laboratory and tested as new genetic mutations are identified in the MH community.
A consent form for this process and future research is available for download here.(please supply)
If you are a relative of a person who has already had a positive blood test, your blood will be examined to determine whether or not you have the same genetic change. If you have the same change (mutation) you can be diagnosed as Malignant Hyperthermia Susceptible (MHS) without the need for a muscle biopsy.
If you do not have the same change as your relative, you will still need a muscle biopsy to rule out malignant hyperthermia. This is because a negative genetic result is not a 100% guarantee that you are not at risk of MH.
Here is a flowchart for MH testing which summarises genetic testing and muscle biopsy:
Reference: Br J Anaesth. 2015 Oct;115 (4):531-9. doi: 10.1093/bja/aev225. Epub 2015 Jul 18