Diagnosis of McArdle’s Disease

Diagnosis of McArdle’s Disease

Many people with McArdle’s disease have been diagnosed only as adults, as for a number of reasons the condition often seems to escape diagnosis in children. People who have the disease can appear quite healthy, and as such the symptoms can be confused with poor conditioning or laziness.

Following evaluation by a neurologist or other physician, diagnosis for McArdle’s disease can be made in one of two ways:

Ischemic Forearm Test

This test is a valuable diagnostic test for a number of metabolic diseases. Speaking generally, the test measures concentration of lactic acid in the blood before and after local exertion of a muscle group. The following protocol description is taken from the University of Florida School of Medicine website:

The test is performed by contracting the forearm to fatigue with a blood pressure cuff inflated to greater than systolic pressure. Antecubital blood samples for lactate and ammonia are collected before and following exercise at 0, 1, 2, 5, and 10 minutes. Ischemia blocks oxidative phosphorylation and ensures dependence on anaerobic glycogenolysis lactate normally rises at least fourfold within 1 to 2 minutes of exercise ammonia rises fivefold within 2 to 3 minutes.

Lactate concetration will rise several-fold under ischemic conditions in normal subjects (o-o-o). There will be no or minimal rise in patients with myophosphorylase deficiency (McArdle’s disease.)

The ischemic forearm test is only moderately uncomfortable to undergo, involving blood samples, a pressure cuff, and a device to squeeze with the hand for forearm muscle contraction, but takes a few hours in order to get blood samples at a resting metabolic rate.

Muscle Biopsy

The following is a description of a muscle biopsy performed in order to diagnose McArdle’s disease in an elderly patient. It involves microscopic muscle fiber examination to identify, among other characteristics, large deposits of glycogen:

Biopsy of Left quadriceps was performed. The biopsy showed subsarcolemmal vacuoles in many fibers with no abnormal contents on hematoxylin and eosin (fig. 1A), Masson’s trichrome (fig. 1B) or Gomori stains (Fig.1C). Increased glycogen content (Fig. 2A) was present in several fibers on PAS stain (diastase sensitive). Myophosphorylase activity was absent using enzyme histochemistry (fig. 2B) with a positive control (Fig. 2C). Mild to moderate myopathic features were present including increased fiber size variation and internal nucleation (Fig. 3A) with scattered myofiber hypertrophy and occasional fiber splitting (fig. 3B). Type I fiber smallness was suggested on ATPse stains (fig. 3C). Decreased oxidative enzymes staining with “moth-eaten” appearance was present, mostly in type 1 fibers (fig. 4A) with linearization of the intermyofibrillar architecture in type II fibers (Fig. 4B). Neurogenic atrophy was minimal.

The biopsy looks for the presence of myophosphorylase activity, which is absent in and can confirm diagnosis of McArdle’s disease.

Diagnosis of McArdle’s disease should be made by a physician familiar with metabolic disease of the muscle. To find a Muscular Dystrophy Association clinic near you, click here.

16 thoughts on “Diagnosis of McArdle’s Disease

  1. Joyce Hamilton-Whitson

    I have done the forearm ischemic muscle test and was in pain and very much weaker for about 4 days afterward.

    My results came back and it showed that my lactate levels doubled while my ammonia levels tripled. They did not mention my pyruvate levels at all. I have yet to hear and/or see the actual lab results.

    Also, my EMA levels in urine were elevated at 7 (range 0-4). It is my understanding that this EMA LEVEL IN URINE could be indicative of Short Chain Acyl CoA Dehydrogenase Deficiency.
    I am seeing my regular PCP, who apparently doesn’t know too much… a second rheumatologist and a first neurologist. My biggest hang up is that no one is really giving me any answers and I am struggling badly with all of this and need faster results and a doctor who is a bit more humble and doesn’t think he/she knows everything and that we’re all just crazy!
    I realize that the results I have here may not be linked to Mcgardles disease… but it’s gotta be something!

  2. cheryle j foster

    i was 49 years old, i awakened one morning and I could not raise my head up. My chin was on my chest so my friend took me to an E.R. and for the next 9 months they ran every type test you’ve all most likely been through coming up with nothing. They thought I had M.S. like my brother but I didnt then they thought it was Miasthynia Gravis but it was not so I was sent to a university where after another 8 months a muscle biopsy was done and the M.D. diagnosis was confirmed. I am no longer able to hold my head up w/o the brace and im quite familiar with the severe muscle cramping however magnesium drastically helps with those at 1,000 mg a day ,it really works! I am now 52 and appear to be once again going through more physical changes that I believe are linked to this disease, a lot of general weakness ,I had just a few months ago been able to (slowly) walk 1-2 mi a day now i cannot go 2 short blocks . I also can no longer drive it is to physically taxing as of this past month. So its back to the drawing board for me. I wish the best for all of you out there living with Mcardles

  3. Karen S

    I have had one doctor send me to another for evaluation of what he thinks is late onset McArdles; the symptoms match all too well. My question is I have not seen any mention of the use of EMG to diagnose. The doctor I have been referred to is scheduling one before he sees me for my fist appointment. Is this uncommon?

  4. Tina

    I had that blood test and I am sorry but it was very painful for me. In fact it landed me in the emergency room! They treated me for a blood clot and the pain in my arm went away! I have been having troubles with my legs for 3 yrs now. I was over weight & was working on losing the weight. I worked upto jogging 3 miles a day. When one day I started getting these horrible leg cramps. I tried everything under the sun. 6 pairs of diff. shoes, more bananas, more strecthing. It has gotten worse for me. I have seen 2 family dr’S A Rheumatologist, 2 neurologists i have had 2 emg’s which have test positive for myopathic potential. All my bld work is normal. Except the contraversy of if I have Mcardles. Ihave muscle twitches every where now. I actually count them lol at night. I can count up to 31 twiches in just my lower legs in 30 minutes. Walking up a flight of stairs leaves me winded and out of breath. I am not able to exercise at all anymore. I feel so weak and my muscles feel so tired all the time. They are now saying I might need a muscle biopsy & may need to see a 3rd neurologist. I just want an answer to what is happening to my body!

  5. Diane

    I posted a question under “The only realistic treatment for McArdle’s” earlier and then I’m finding all of these other areas people chatting and questioning. I was asking if anyone knew a McArdle’s patient who has had knee replacement? It is posted under “Diane”.

    Also, wanted to add…I was diagnosed through an ischemic forearm test many years ago, and it was very debilitating. My Doctor had no idea how much pain I would under go, and he cried with me. Hopefully, it is not as painful now, and the blood test for the enzyme sounds great!


  6. Shanan Macpherson

    I am so glad I found this website. I have recently been diagnosed with McArdle’s. I have to say that like many of you I am relieved to find out what has been wrong with me my whole life. I have been embarrassed about something I have had no control over. I too would love to slap my PE teachers and say “SEE” !!! I wasn’t being lazy !! My diagnosis started with a swollen lymph gland and some blood work. The results of the blood work was a CK level at 9,870 and no reason for it to be that high. (the lymph gland had nothing to do with anything)So, I will continue to avoid hilly walks, jogging, and be cautious of my limitations.

  7. Jim Ottesen

    Site Admin,

    Thanks for your comments. What you’ve posted makes enormous scientific
    sense. In fact, I am going to look at creatine as my energy could
    use all the help it can get. Often, I feel wasted without doing what
    one might consider exhausting. Of course we are all different, but
    I’m going to give creatine an experimental effort. I’ll report back
    with my results. Jim Ottesen

  8. Site Admin Post author

    The fundamental problem with any oral supplements is once they’re in your stomach, your body does with them as it pleases. Just because one ingests something doesn’t mean that the body will transport it to the right location for ready access at the right time. A big dose of sugar may temporarily spike the concentration of glucose within the cell but only temporarily, because the body works just as quickly to store as fat what it thinks is extra energy. There are other hormonal reactions to a big dose of sugar which also contribute to feeling miserable.

    Creatine has promise for people with McArdle’s disease. Theoretically, extending the window of energy you have from a resting state and allowing you to replenish that ATP quicker should offer relief to someone with a carbohydrate metabolism bottleneck like McArdle’s disease. Up the cell’s creatine phosphate concentrations and you might extend that energy window. The problem is that it’s only a useful experiment when completely controlled.

    And again – since the body is a host of interdependent equilibrium reactions, upsetting any one concentration has implications elsewhere, some harmless and some not.

  9. Jim Ottesen

    Hi Folks,

    Over a period of years, some have mentioned the value of ATP, amino acids,L-Carnitine, ribose, etc. As an “M” patient, I am curious to
    know from some of you as to whether any of you have received advice
    from a neurologist as to the value of any of the aforementioned. If
    there is a diet, vitamin, mineral, supplement or whatever, perhaps more
    could benefit. I have been told and read that B-6 is essential so I take 100 mg every day. Too often, we take “stuff” that others
    say is that “one thing.” In reality, we need those in neuromuscular
    research to suggest those “things” that have the most value
    for our “M” bodies. Any thoughts on these ideas? Most neurologists
    could give us a “suggested diet or possible supplements and things”,
    but I don’t have one – do you? Jim Ottesen

  10. Jim Ottesen

    @Sally B
    Sally, Did you ever get an answer as to the name of the blood test
    that can clearly identify the bad “M?” I have heard of such a test,
    but I’ve not heard of any experts using it as THE TEST for “M.” Matt
    Field, you started this, please help us to help others. I would appreciate any verified info on this. Help! Jim Ottesen

  11. Site Admin Post author

    The ischemic forearm test measures blood lactates before, after and during muscular contractions intense enough to produce fatigue symptoms (but hopefully not cramping.) Zero lactic acid production means there’s a glucose bottleneck, which if other symptoms are present (chronic episodes of exercise-induced failure and cramping, dark urine, etc.) indicates that glycogen is not being metabolized into glucose.

    This test is probably no worse than other standard blood labs, as far as the discomfort it imposes. Memorize these words: ischemic forearm test.

  12. Gail Williams

    I am a 63 yr. old woman that has just stumbled onto this information abot McArdle disease. Wow, the symptoms I’ve been reading are what I have had as far back as I can remember. It started before I could walk–when I started to walk I dragged my left leg. The doctors said it was a habit that I would out grow. So many of the things I’m reading on this web site such as back pain,cramps in the legs and feet,what I refer to as “running out of gas”and very little endurance and also the spots and crazy eye symptoms, are quite enlightening. What kind of a doctor should I contact to see if this what I have? Thanks to whoever lets me know.

  13. jim harrison


    I’d like more information on this blood test. Can you share exactly what type of blood test?

  14. Matt Field

    I was finally diagnosed in december of 2007…but people should know that there is another way to determine if you have mcardles….I live in greensboro north carolina and i went to wake forest university medical center….my doctor did a specific kind of blood test and it was sent to buffalo, new york of all places to be read. it showed that i lack the enzyme to break glycogen into glucose…therefore letting us know i have mcardles….im 28 now and im relieved to know im not “lazy” as all my physical education teachers thought!


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