Medical Minute; McArdle Disease

By: Robert Baker

Often during strenuous exercise muscle cramps and fatigue can occur, but when could it raise concern?

This pivots our discussion towards a Glycogen Storage Disorder known as McArdle Disease.

Common presentation among patients includes painful cramps during exercise due to a build of glycogen.

The enzyme myophosphorylase is the culprit in the autosomal recessive disease effecting the skeletal muscles manifesting in symptoms of fatigue, exercise intolerance and pure myopathy. Four common features can be seen in this disease.

1. Muscle Intolerance at a young age

2. High Serum CK (Creatine Kinase) Levels

3. One or more higher levels of CK after intense exercise

4. Second Wind Phenomenon*

*An ability to continue exercise despite excessive fatigue, breathlessness and tachycardia.

The diagnosis is often made through a muscle biopsy of the vastus lateralis in the thigh combined with an exercise tolerance test to measure lactic acid. Recommendation towards oral ingestion of sucrose has shown to improve exercise intolerance and reduce the risk of myoglobinuria as well as avoidance of intense anaerobic exercise.

Although there is no cure for this condition, lifestyle changes in the intensity of exercise and diet can aid in living with this condition.