What is metabolic myopathy?

Metabolism is the process through which our cells convert fuel sources — for instance, sugar — into usable energy.

Like all cells, muscle cells depend on metabolism to function correctly. Muscle cells convert sugar and fat into adenosine triphosphate, or ATP, through the work of enzymes. ATP enables muscles to contract and function normally.

Metabolic myopathies occur when genetic differences cause insufficient levels of a particular enzyme that is used in this process. When this happens, the affected muscles cannot convert fuel into energy and thus cannot function.

Metabolic Myopathy Types

Different forms of metabolic myopathies are distinguished by which enzyme is deficient or missing.

For instance, McArdle disease is due to a lack of enzyme that assists in carbohydrate metabolism. A different kind of metabolic myopathy caused by acid maltase deficiency is called Pompe disease.

Mitochondrial metabolic myopathy is another type that results from a lack of a particular enzyme normally present in the mitochondria, the energy-producing parts of cells.

Metabolic Myopathy Symptoms

Metabolic myopathy symptoms vary among individuals. In fact, some people with the condition my live symptom-free because their cells have found a different pathway for creating energy to power muscles.

In other cases, symptoms may appear, depending on which enzyme is missing. Symptoms of metabolic myopathy include:

• Fatigue and exercise intolerance (energy returns after rest)

• Muscle cramping

• Heart problems

• Difficulty breathing if the disease affects muscles involved in respiration

• Rhabdomyolysis, a painful breakdown of muscle tissue that can cause kidney damage, may result from too-strenuous exercise, illness, stress, exposure to cold, or going too long without food.

Metabolic Myopathy Diagnosis

Metabolic myopathies can have symptoms that are similar to those of many other conditions. A muscle biopsy can help determine the cause of muscle weakness.

A blood test can detect genetic differences and also signs of muscle tissue breakdown. Blood tests may be conducted in conjunction with intense or moderate exercise to look for evidence in the bloodstream that muscle damage has occurred.

Electromyography (EMG) may be used to rule out muscular dystrophy and other disorders.

Metabolic Myopathy Treatment  

People with metabolic myopathies must avoid acute muscle breakdowns that release muscle proteins into the bloodstream and cause severe kidney damage.

Individuals should work with doctors and other members of the care team to develop a plan for managing physical activities. In some cases, care providers may recommend a program of light aerobic training.

A cardiologist familiar with metabolic myopathies can screen for any damage to the heart muscle

Diet can be a factor in avoiding symptoms and complications. Depending on which enzyme(s) are affected by a metabolic myopathy, a high-protein or low-fat diet may be helpful.

For one type of metabolic myopathy called Pompe disease, a new treatment replaces missing acid maltase enzyme with a synthetic version.

It’s important for anyone affected by metabolic myopathy to rely on the expertise of their physician and follow their recommended diet and treatment plan.

More Information on Metabolic Myopathy 

Read about other types of neuromuscular disease in the Health Library