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If you have difficulty with physical activity (often known as “exercise intolerance” in medical terms) then McArdle disease is one of many conditions which might be the cause of it.

As McArdle’s is an ultra rare condition the odds are stacked against it being the cause of your symptoms. We think that about 1 person in 100,000 might have the condition, but to date even in Western countries fewer than that has actually been diagnosed. (One paper calculated that the true incidence may be nearer 1 in 25,000.) Some other neuromuscular conditions are much more common, for example Becker and Duchenne muscular dystrophy (approximately 1 in 17,000 and 3,500 respectively) or fibromyalgia (approximately 1 in 50).


If there is any history of McArdle’s in previous generations of the families of either of your parents then the risk is significantly increased - maybe more like 1 in 1,000. If you have a sibling who is already diagnosed with McArdle’s, and you have both parents in common, then the risk is increased to 1 in 4. Many people with McArdle’s can look back at their childhood and recognize signs of the condition from ages as young as 3 or 4, and almost all before the age of 10. This might include the inability to keep up with siblings and friends in playground games, having aching legs at night, disliking physical education and sports at school, being told off for not completing school runs, occasionally having muscle cramps that lasted hours or days, and being called lazy or unfit. If this is typical of your childhood then it would be worth investigating further.


Most people who turn out to have McArdle’s have been told as a child by their family doctor that they are unfit, are lazy and/or have “growing pains”. There is an average delay of approximately 20 years from first seeing a doctor to achieving a correct diagnosis, although this is improving. This delay is due to the ultra rare nature of the condition and the fact that people with the condition appear normal when physically examined. We need to remember that only about one GP in 200 will ever see a case of McArdle’s.


Compare your experience with this list of typical McArdle symptoms. You can also read more about these symptoms and about second wind elsewhere on this web site.

  • Do you have difficulty with activity/exercise within a minute or two of starting?

  • Do you find that activity/exercise gets a bit easier after about 10 minutes? Or do you perhaps just recognize being better later on in a day of activity? (This is known as “second wind”.)

  • Do you often need to stop for a rest on even a slight incline? Or do you struggle with more than two flights of stairs?

  • Do you have days when you feel as though you just can’t “get going” and feel exhausted?

  • Have you ever experienced a muscle or group of muscles being cramped up so that they are rigid and swollen, and stay like that for hours or days?

  • Has your hand ever cramped such that your fingers are curled up and will not open?

  • Have you ever noticed that your urine is a dark reddish brown color after getting a muscle cramp?


Again due to the ultra rare nature of the condition, misdiagnosis is common (about 90% are initially misdiagnosed). Laziness, polymyositis, exercise induced asthma, fibromyalgia and Chronic Fatigue Syndrome are common errors; but kidney, liver, and heart conditions are also often investigated.


If you recognize most of the symptoms above then a good first step is to ask your family doctor for a simple blood test for Creatine Kinase (CK or CPK). This is a low cost and quick test. The top of the normal CK range is around 200 iu/L although ranges vary slightly by age, gender and laboratory. People with McArdle’s tend to have levels of at least double that and the average for McArdle people is about 2,400 iu/L. If your CK level is raised above the top of the reference range without any particular muscle injury, it can indicate that there is a neuromuscular problem. McArdle’s is one of the possibilities.


Excerpt from: “McArdle disease: a clinical review”. 
R Quinlivan, J Buckley, M James, et al. Journal of Neurology, Neurosurgery and Psychiatry, doi: 10.1136/jnnp.2009.195040

“...the serum CK is almost always raised in McArdle disease. Any patient presenting with a history of muscle cramps affecting any skeletal muscle during exercise should lead the doctor to suspect a metabolic myopathy. A history of painful cramps that occur within a few minutes of initiating exercise and which subside rapidly with rest in conjunction with a raised serum CK is highly suggestive of McArdle disease. If the individual continues to exercise to the point of contracture, there will be a history of painful rigidity, which may persist for several hours; this will almost always be accompanied by muscle swelling and myoglobinuria. A history of a second wind should be specifically looked for, but may not always be recognised by patients. However, during exercise assessment the second wind is a universal finding...”


Around the world the arrangements vary but you will usually be referred to a neurologist with a special interest in neuromuscular diseases. As McArdle’s is so rare many neurologists will only see one or two cases in their whole career. For this reason they cannot get a full understanding of the management of the condition so once diagnosed it is best to be referred to a leading McArdle expert. Our “Directory” on the ”Medical” menu may help.


There is published guidance available for medical professionals considering a diagnosis of McArdle disease (GSD5) or Tarui disease (GSD7). The people seeking a diagnosis may also find it helpful. The paper has a diagnostic flowchart which may assist in pointing to other conditions if it is not either of these. The paper is available under Open Access and we have published a booklet containing the paper and its supplementary material. The booklet can be downloaded from this page.

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