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People affected by McArdle disease may at times present for urgent medical care. This will usually be due to suspected rhabdomyolysis, with attendant risks of acute renal failure and/or compartment syndrome. Here we provide information on McArdle episodes, most of which will apply also to the other muscle GSDs we cover.

  • Guidance for McArdle patients.
  • An alert for emergency doctors.

(The doctor will treat each episode according to the individual circumstances.)

  • Background information about episodes. 
Please be aware that for other languages automated translation from English is available (see Languages button above). Please read our medical disclaimer here.

We have produced a flowchart on the above link, which will help guide you in your decision about whether you need to seek urgent medical care. Please use that flowchart, and then if you decide you need to seek medical attention, return here.


You should:

  • Drink plenty of water to help flush your kidneys.

  • Go to hospital promptly for medical assessment.

  • If possible, take a urine sample with you to show on arrival.


Remember to take your card with you, and if possible the “At hospital with McArdle’s” leaflet. 


McArdle Disease (GSD5) [1] is a rare metabolic myopathy. Patients experience physical activity/exercise intolerance and muscle cramps. They are at risk of rhabdomyolysis [2], which can lead to acute renal failure.


Patients may appear well but have a muscle cramp, myoglobinuria or feel unwell/have fever after activity/exercise. There may be an extreme muscle contracture with swelling and often severe pain.


Urgent assessment for possible rhabdomyolysis. Creatine Kinase usually grossly raised. Consider urine analysis for myoglobinuria and full chemistry panel (including CK, glucose, calcium and bone profile, urea and electrolytes).


Consider fluid bolus followed by IV saline at 2x maintenance and (unless diabetic) possibly 10% dextrose to keep blood glucose >3.5 mmol/L. Episodes require monitoring of urine output, CK and electrolyte status.


Oliguria can occur requiring prompt referral for haemodialysis. In rare cases compartment syndrome [3] has developed, requiring surgical referral.


Section 6 of the Clinical Practice Guidelines covers emergencies, and section 5.3 covers laboratory testing. Go to the Clinical Practice Guidelines page.


Medical Overview
is available to browse on the following page.


Clinical Practice Guidelines from an international study group available here, free of charge.




It is likely that you will have a fixed contracture (spasm) in one or more muscles. This is when the muscle contracts and then fails to relax again. It becomes hard or stiff, swells up and usually becomes very painful. You must NOT try to force the muscle - e.g. do not try to forcibly uncurl the fingers of a “clawed” hand. This may tear the muscle and cause a lot more damage. Cooling the affected muscle, for example with an ice pack, may slow the development of symptoms. If the muscle is not in a fixed contracture but just sore and enlarged, some very gentle massage may also help.


Myoglobinuria (myoglobin protein in your urine) is a product of rhabdomyolysis (broken down muscle). If you think you may be having an episode, urinate into a clear or white container so that you can easily monitor the colour of your urine. The depth of colour will depend on the amount of muscle damage you have done. That is, how severe the contracture is and the size of the affected muscle/s. It will also appear darker if you are dehydrated as it will not be so diluted in your urine. The darkness of the colour is what matters, not the length of time that the myoglobinuria lasts. Do not wait to see if it grows paler, if it is dark get to hospital.

Myoglobin gets into your blood from the damaged muscle and can then block the kidneys as they filter your blood to produce urine. Your kidneys not only remove excess fluids but also regulate various chemicals in your blood. Having your kidneys blocked by myoglobin (acute renal failure) can be life threatening.


Immediately start drinking water at the rate of roughly 500ml (1 pint) per hour to flush through your kidneys and dilute your urine. Remember that over-hydrating can also be dangerous. If available, add a pinch of table salt and a level teaspoon of sugar.


You should go straight to hospital, not to a family doctor. If you are not producing much urine, immediately on arrival tell them that you are suffering rhabdomyolysis which may be causing acute renal failure. If you can take a urine sample, show this to the triage (assessment) nurse/doctor as soon as possible. A dark urine sample will immediately highlight to them that urgent treatment is required.

You may hold a stand-by letter from your McArdle specialist for such emergency situations - if so, take that with you, or take your McArdle Information Card. But failing that, draw the attention of the emergency doctor to the above notes.

Another option is to wear a MedicAlert bracelet, which will be engraved with your medical conditions and an emergency phone number for doctors. The call center will hold what medical records you wish. See MedicAlert's website.


You should have blood and urine samples taken straight away. You may be put on an intravenous drip (a bottle of fluid connected to a needle in a vein in your arm). This will ensure you have sufficient fluids to flush your kidneys. Your urine output will be monitored and this may involve having a urinary catheter (a drainage tube inserted into the bladder and attached to a clear collection bag) so that your urine is continuously collected and can be easily monitored.


Your test results may take an hour or two to come back. The three things which are of particular interest to the doctors are:

1) Myoglobin in the urine
If present this confirms that you are having an episode of rhabdomyolysis.

2) Creatine Kinase (CK) level
The normal range for unaffected people is about 100 to 200 iu/L. However, people with McArdle's have a base level of an average of 2,500 iu/L. The higher the level the more muscle damage you have incurred. Figures over about 20,000 may require you to stay in hospital until the level has fallen again.

3) Kidney function tests
These will help the doctors assess how well your kidneys are dealing with the myoglobin produced by your muscle breakdown and released into your blood.


The CK (also known as CPK) results in these circumstances can be very greatly raised. It is common to see levels of 40,000 and sometimes as high as several hundred thousand. The CK tends to peak at about 24 hours after the injury was incurred, so the doctors may well want to take samples regularly until the peak has passed. After that they may sample just once every 12 to 24 hours. After the peak the CK level starts to drop by about 30% to 50% in each 24 hour period, so you might see a pattern such as: 12 hours 20k, 24 hours 50k; 36 hours 35k; then each day thereafter 24k, 16k, 11k, 7k. Once below about 20k and on a downward trend the hospital may be prepared for you to be discharged.


Most people find fixed muscle contractures extremely painful and you should be offered pain relief. However, when recovery is well under way you will want to start moving the affected muscles again. At this time it is important not to take regular pain relief which masks the sensations/pain experienced when using the muscles. You need this feedback from the muscles to tell you when you are overdoing it.


The biggest worry is anuria (not producing urine) or oliguria (producing significantly less urine than you are taking in as fluid), which indicate acute kidney failure. If left untreated this can lead to multiple organ failure and can be life threatening. So it is very important that you go to hospital urgently if you have either of these symptoms, and that you make sure that the hospital treats you promptly.

Without anuria you may still experience acute renal failure. The signs for this are the kidney function tests (from a blood sample) and if you are producing less urine than your fluid intake. This only happens in a percentage of cases (probably less than 30%). The more muscle damage you have done the higher the risk. This needs to be treated by going onto dialysis. As long as this is done promptly, there is normally a full recovery of kidney function.

In a very small number of people something called “compartment syndrome” has developed. This is caused by muscle swelling which leads to increased pressure within the fascia (strong membrane) around the affected muscle group. If left untreated it can permanently damage the muscle and affect the circulation. Surgical intervention is usually required to relieve the pressure.


Depending on the level of muscle damage caused, after being discharged from medical care you need to have at least a few days rest and not use the damaged muscle very much until it feels fully recovered. As your body heals, you will need to re-introduce activity and exercise slowly.  This may take a few weeks to re-condition the muscles that were damaged.

As long as you follow the guidelines above, especially about getting prompt attention if you have acute renal failure, there is every reason to expect a full recovery. Kidney function usually returns to normal once the by-products of muscle breakdown have been flushed through. The muscles are very good at recovering, although less so as we get older. However, repeated episodes of major muscle damage should be avoided as they are believed to cause cumulative damage if repeated over many years.


It should be our aim to avoid emergency episodes by working to improve our aerobic capacity and by learning strategies to cope with life without putting ourselves at risk. We have information available to help you adapt activity to avoid injury.

Building aerobic capacity is probably the best protection against these painful, inconvenient and costly episodes. If you do not already recognize and use the “second wind” there is information available to help you do that. If you are very de-conditioned, undertaking a careful program of gentle aerobic activity/exercise, gradually increasing in length and intensity, is the ideal way to achieve a good aerobic capacity. When some isometric activity can‘t be avoided (like lifting something heavy), adhering to the “six second rule” will help to protect you against injury.

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