McArdle's Disease

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Welcome to PT 635 Pathophysiology of Complex Patient Problems This is a wiki created by and for the students in the School of Physical Therapy at Bellarmine University in Louisville KY. Please do not edit unless you are involved in this project, but please come back in the near future to check out new information!!

Original Editors - Ed Foring as part of Bellarmine University's Pathophysiology of Complex Patient Problems project.

Top Contributors - Edward Foring, Kaylynn Schwamb, Michael Helton, Lucinda hampton, Elaine Lonnemann, Kim Jackson, Admin, 127.0.0.1, Simone Potts and WikiSysop   Read more.

 

Definition/Description

McArdle’s Disease, also referred to as Myophosphorylase Deficiency, or Type V Glycogen Storage Disease, was first described in 1951 by Dr. Brian McArdle while he was practicing in London, England. The condition is a recessive inherited disorder that presents as an inability to metabolize glycogen, the storage form of glucose. This results in a variety of symptoms affecting the musculoskeletal and urinary systems. Patients afflicted by McArdle’s Disease most commonly suffer from muscle fatigue.

Refer to the model below to see how muscle contraction differs in an unaffected muscle compared to one with McArdle’s Disease.

How Skeletal Muscle Normally Contract	A McArdle's Diease Model
	Image:Energy_2.gif

1. Acetylcholine is released from a motor nerve. This causes an entry of calcium into the muscle cell.	1. Acetylcholine is released from a motor nerve. This causes an entry of calcium into the muscle cell.
2. Calcium activates phosphorylase kinase – the first protein kinase discovered by Fischer and Krebs.	2. Calcium activates phosphorylase kinase – the first protein kinase discovered by Fischer and Krebs.
3. Phosphorylase kinase phosphorylates phosphorylase, which is activated	3. Phosphorylase kinase phosphorylates phosphorylase, which is missing or otherwise non-functional
4. Glycogen is broken to glucose. This is used to generate ATP	4. Glycogen is unable to be broken down, creating glucose (and ATP) shortage.
5. The muscle works and requires energy in the form of ATP	5. Motor proteins attach to muscle fibers require ATP for movement.
6. The muscle contains muscle cells	6. Muscles stop responding in absence of ATP .
7. Contractile proteins in the muscle are activated by calcium	7. Because ATP is required to both contract and relax muscles, injury can occur.

Prevalence

• McArdle's Disease is rare and affects approximately 1 in 100,000 people. However, it is one of the most common disorders affecting muscle metabolism.
• The disease presents more often in men than women.
• It is believed that many people remain undiagnosed.
• It presents in the second to third decade of life with symptoms reported at childhood.

Characteristics/Clinical Presentation

• The earliest and most common signs and symptoms of McArdle’s Disease are exercise intolerance and fatiguability.
• Other signs and symptoms may include myalgia, muscle contractures, stiffness, cramping, rhabdomyolysis, myoglobinuria, and second wind.
• Symptoms typically present 10 seconds after beginning strenuous exercise. This is when skeletal muscle relies on the conversion of glycogen to glucose to produce ATP, the main energy source for muscular contraction.
• The inability of the skeletal muscles to metabolize glycogen into glucose with strenuous activity leads to an abrupt feeling of exhaustion or fatigue and an increase in heart rate. This is known as premature exhaustion. Individuals may complain of difficulty with any moderate activity including walking, jogging, or ascending and descending steps.
• Muscle failure occurs under extreme stress when the muscle no longer can produce contraction regardless of the effort made. Muscle failure leads to cramping (electrically silent contractions), which are very painful and can lead to muscle damage.
• The body begins to break down muscle to provide the cells with a tertiary energy source in the form of protein. This process, referred to as rhabdomyolysis, releases creatine kinase and myoglobin into the blood, and excretes those proteins with urination.
• Myoglobinuria is the symptom that refers to the reddish coloration of urine due to the high protein concentration, ultimately leading to kidney dysfunction and failure.
• Muscle damage caused by rhabdomyolysis can lead to fixed weakness, or persistent muscle weakness, that makes it extremely difficult to make strength gains.
• “Second Wind” is the phenomenon that has been observed in patients with McArdle’s Disease, in which the metabolic pathway switches from glycolytic to oxidative phosphorylation.
• After 10 seconds, all of the readily available glucose in the system is depleted and the patient begins to fatigue.
• From 10 seconds to about 8 minutes of exercise, the patient will experience moderate to severe pain from the muscles breaking down in order to compensate for the inability to breakdown glycogen.
• After 8-10 minutes, the second wind will kick in and the patient should be able to continue exercising for 45 minutes without pain and with an appropriate heart rate response, depending on their level of physical fitness.
• Second wind can be monitored through a patient’s heart rate. After reaching an inappropriate peak, the heart rate will lower and level off, signifying the start of the second wind.
• Second wind is not a systemic effect, and must be achieved in each muscle group independently.
• This does not relieve muscle failure symptoms for intense exercise, but offers some relief for light to moderate exercise.
  

Associated Co-morbidities

• Renal Failure: Kidney dysfunction and failure are associated with rhadbomyolysis and myoglobinuria.
• Gout: Inhibited ATP production leads to the production or purine metabolites. These metabolites are converted to uric acid, which can lead to hyperuricemia. The most common place for gout to form is the first metatarsal; however it can be found in the insteps, ankles, heels, knees, wrist, fingers, and elbows as well.

 

Medications

There are currently no medications used to treat McArdle's Disease.

Supplements

• Vitamin B6 (mixed evidence): Izume (2010) found decreased fatigue and increased glycogenolysis as seen on the ischemic forearm test with B6 supplementation. Beynon (1998) found no significant improvements compared to a placebo treatment. However, approximately 80% of vitamin B6 binds to myophyphoralyse, so patients with McArdle’s Disease may need to supplement B6 to avoid deficiency.
• Ramipril: 2.5 mg orally daily showed some subjective improvement in participants with the D/D ACE polymorphism
• Creatine supplements: Vorgerd (2000, 2002) found an increase in exercise tolerance of workload and depletion in phosphocreatine with low levels of creatine supplementation, but an increase in symptoms with high levels of creatine supplementation.
• Oral Sucrose: Vissing (2003) concluded that oral ingestion of sucrose can significantly improve exercise tolerance in McArdle’s Disease. However, overtime this supplementation may cause weight gain and is contraindicated for any individual with diabetes.
• There is a lack of evidence to show benefit from supplementation with branched chain amino acids, depot glucagon, dantrolene sodium, verapamil or, high-dose oral ribose.
  
  

Diet

Tarnopolsky’s diet recommendations

• Carbohydrate-rich diet: (20% fat, 15% protein and 65% carbohydrate)
• Anderson (2008) found that this diet, compared to a protein rich diet (55% protein, 30% carbohydrate and 15% fat), resulted in a significant drop in heart rate and work effort with a 25% increase in maximal oxygen uptake.
• A low carbohydrate is not recommended because it will deplete liver glycogen and reduce the amount of glucose released into the blood stream. This will lead to hypoglycemia (low blood sugar) when the person becomes active.
• It is recommended to consume a sugary drink or snack before participating in strenuous activity to provide the body with immediate energy before the second wind is achieved.
  

Diagnostic Tests/Lab Tests/Lab Values

Creatine Phosphokinase Test 

If lab work is conducted than the patient will have an elevated CPK test. This alone does not conclude the individual has McArdle's disease because CPK values will be elevated due to any muscle breakdown in the system. When the brain, heart or skeletal muscle has significant damage it releases an enzyme called creatine phosphokinase. In McArdle's disease the inability of glycogen to turn into glucose for energy; the muscle breaks down itself releasing this enzyme into the blood stream.

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 slightly 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.

This test has now been replaced by the non-ischemic forearm test.

Non-Ischemic Forearm Test

This test is done in the same manor as the ischemic forearm test but without the blood pressure cuff. Click here to learn more.

Muscle Biopsy
The biopsy looks for the presence of myophosphorylase activity, which is absent in and can confirm diagnosis of McArdle’s disease. Click here to view biopsy images of McArdle's Disease.

 

Etiology/Causes

McArdle’s Disease has been shown to have an autosomal recessive inheritance pattern, requiring two defective copies of the gene for the condition to manifest. The defect exists as mutation of the gene for myophosphorylase (PYGM), which occurs on chromosome 11. Myophosphorylase is an enzyme that helps break down glycogen into glucose during exercise. Carriers of the gene are not known to have symptoms of the disease.

Systemic Involvement

There has not been any long term studies that have found long term effects on the general health on individuals with McArdle's Diease. Typically individuals with this disease are in excellent health as long as the disease is managed properly. If the disease is unmanaged, resulting in constant cases of rhabdomyolysis, it can lead to kidney and liver dysfunctions. 

Precaution: Any patient with McArdle's disease that has cardiovascular complication could be on a statin medication. Statin's increase the potential risk for rhabdomyolysis. Therefore physical activity should be keep to an absolute minimum.

Medical Management (current best evidence)

Quinlivan R, Martinuzzi A, Schoser B. Pharmacological and nutritional treatment for McArdle disease (Glycogen Storage Disease type V). Cochrane Database of Systematic Reviews 2010, Issue 12. Art. No.: CD003458. DOI: 10.1002/14651858.CD003458.pub4

Physical Therapy Management (current best evidence)

The physical therapist has an important role in keeping the patient active and avoiding inactivity due to fatigue.

• Optimal exercise programs for managing McArdle’s Disease are aerobic based; they provide light resistance along with a cardiovascular component.
• A plan of care incorporating low to moderate intensity aerobic physical activity can improve symptoms and reduce susceptibility to injury of the muscle.
• The goal is to achieve the "second wind" for each muscle group that is being worked.
• Light to moderate resistance training can also help, but allow adequate time to rest in between sets.
• As a rule, do not work the muscles to absolute fatigue, and be sure to target larger muscle groups.
• If strenuous activity must be done use a 6 second rule, only do that activity for 6 seconds prior to resting to ensure that only the phosphagen energy system is used in anaerobic activity.

Physical therapists can promote flexibility in order to prevent muscle contractures and reduce pain.

• Stretching should be very light because maximal stretching will work the muscle anaerobically by inducing a protective contraction from the Golgi tendon. This strong protective contraction can lead to muscle damage.
• Stretching following walking may offer immediate and dramatic pain relief to individuals with McArdle’s Disease.
• For active individuals, stretching should take place very frequently to help reduce cramping. If not, muscles may become tight due to the toxic build up throughout activity and stretching can become painful.
• Physical therapists should encourage a stretch that feels sufficient without causing pain.

Physical therapists should promote active participation by patients in managing their disease.

• Individuals with McArdle’s Disease can easily over exert themselves and become injured without even realizing it.
• It is important that they be conscious of their energy levels, blood sugar, heart rate, and general well-being.
• These individuals have a place in physical therapy to improve aerobic capacity, strength, and flexibility.
• During any low to moderate intensity activities, patients with McArdle’s Disease should warm up properly until they achieve the "second wind. Strenuous activities should be limited to six seconds to ensure the use of the phosphagen system.

Alternative/Holistic Management (current best evidence)

Massage
o Individuals with McArdle’s Disease claim that massage therapy can be beneficial in maintaining an active lifestyle.
o Any massage should be light and fluid using effleurage techniques. Deep and hard massage for trigger point or myofascial release can be damaging to the muscle and should be avoided.
o Massages help push fatigue causing toxins out of the muscles and into the blood stream where they can be excreted from the body. It is recommended that individuals with McArdle’s Disease take in plenty of fluids following a massage to help flush the body of toxins.
o Pain with massage is a sign that rhabdomyolysis may be occurring. Do not continue massage therapy with pain.

Differential Diagnosis

Rhabdomyolysis: a clinical and biochemical syndrome resulting from skeletal muscle injury that alters the integrity of the muscle cell membrane sufficiently to allow the release of the muscle cell content into the plasma. Due to the quick breakdown of the skeletal muscle there is a big accumulation of the breakdown products which can cause renal failure. Although rhabdomyolysis is a symptom of McArdle’s disease, it can be a symptom of other conditions, or it can exist independently.

Fibromyalgia: a syndrome characterized by widespread chronic unabated pain in addition to a host of several additional co-morbidities that can severely impact and disrupt a person’s daily life. The symptoms associated with fibromyalgia may originate from abnormal central nervous system output. Fibromyalgia isn't just one condition; it's a complex syndrome involving many different factors. McArdle’s Disease and Fibromyalgia share many symptoms, but they have different causes, so their treatments differ.

Muscular Dystrophy: a group of more than 30 inherited diseases. They all cause muscle weakness and muscle loss. Some forms of MD appear in infancy or childhood. Others may not appear until middle age or later. The different types can vary in whom they affect, which muscles they affect, and what the symptoms are. All forms of MD grow worse as the person's muscles get weaker. Most people with MD eventually lose the ability to walk. McArdle’s Disease and Muscular Dystrophy share many symptoms, such as weakness and muscles loss.

Myositis: Myositis means inflammation of the muscles that you use to move your body. An injury, infection, or autoimmune disease can cause it. Two specific kinds are polymyositis and dermatomyositis. Polymyositis causes muscle weakness, usually in the muscles closest to the trunk of your body. Dermatomyositis causes muscle weakness, plus a skin rash. Because Myositis also causes muscle weakness, it can present similarly to McArdle’s Disease.

Tarui's Disease: A condition in which there exists a deficiency of the phosphofructokinase enzyme which is needed to facilitate the breakdown of glucose into energy in muscle during exercise. Tarui’s Disease is also a glycogen storage deficiency, so it has many similarities to McArdle’s Disease. Consequently, they are treated in a similar manner.

Case Reports/ Case Studies

Haller Ronald G and John Vissig.The Effects of Oral Sucrose on Exercise Tolerance in Patients with McArdle's Disease. The New England Journal of Medicine. 2003 349;26 pg 2503-2509

• Please refer to PubMed and Association of Glycogen Storage UK for additional Case Reports and Case Studies

Recent Related Research (from Pubmed)

see tutorial on Adding PubMed Feed

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Resources

• Association for Glycogen Storage Disease UK 
• Association for Glycogen Storage Disease US
• Image:Facebook_icon.gif Join the Facebook Group: McArdle's Disease
• File:Nord.gif Support Community

• www.McArdlesDisease.org 

References

see adding references tutorial.

Special thank you to Andrew Wakelin, McArdle Disease (GSD Type V) Coordinator for AGSD UK for review and insight towards this page.