Metabolic Myopathies: Types, Symptoms, Treatment

Overview

Metabolic myopathies are a group of genetic diseases that can affect the body’s muscles. Metabolic refers to chemical reactions that provide energy, nutrients and substances necessary for health and growth.

Like all cells, muscle cells depend on metabolism to function correctly. Muscle cells convert sugar and fat into adenosine triphosphate (ATP), through the work of enzymes. Metabolic myopathies occur when genetic mutation causes insufficient levels of a particular enzyme that is used in this process, leading to the abnormal function of muscle cells.

Metabolic myopathies are rare but treatable. However, they are sometimes misdiagnosed as muscular dystrophies or inflammatory myopathies. Definite diagnosis is important for prompt treatment.

Causes

As described above, metaboly myopathies are diseases caused by certain genetic mutation.

Types

According to the enzyme that is deficient or missing, there are usually three types of metabolic myopathies:

  • Glycogen metabolism disorders.

Glycogen metabolism disorders are caused by impairment in the body’s ability to convert glucose stores into usable energy. They consist of 14 subtypes, the most common of which are McArdle disease and Pompe disease. McArdle disease is due to lack of an enzyme that assists in carbohydrate metabolism. Pompe disease is caused by acid maltase deficiency.

  • Lipid metabolism disorders.

Skeletal muscle breaks down lipids in the form of fatty acids in order to produce energy at rest and with exercise. Disability to break down these fatty acids can produce muscle weakness and pain during periods of prolonged exercise.

  • Mitochondrial myopathies.

This type results from lack of a particular enzyme normally present in the mitochondria, the energy-producing parts of cells.

Symptoms

Signs and symptoms of metabolic myopathies vary among individuals. In fact, some people with the condition may live symptom-free because their cells have found a different pathway for creating energy to power muscles. If occurring, general signs and symptoms include:

  • Fatigue
  • Muscle weakness or cramping
  • Exercise intolerance
  • Heart problems
  • Difficulty breathing if the disease affects muscles involved in respiration
  • Rhabdomyolysis, a painful breakdown of muscle tissue that can cause kidney damage

Diagnosis

The diagnosis of metabolic myopathies begins with a detailed medical history and physical examination. Most often, physicians diagnose metabolic myopathies by testing a sample of muscle biopsy, which is taken through a needle or with a small incision under local anesthesia.

Other diagnostic tests that can be used to confirm or rule out specific metabolic myopathies include:

  • Blood tests to detect genetic differences and signs of muscle tissue breakdown
  • Electromyography (EMG) to rule out muscular dystrophy and other disorders
  • Exercise testing
  • Genetic testing

Treatment

Treatment options for metabolic myopathies vary depending on myopathy types, because the nature of the disorder and the symptoms can be different. Basically, treatment for metabolic myopathies are the combination of medications, modifications in activity, dietary changes, and nutritional supplements to reduce symptoms and prevent complications.

Patients should work with their doctors to determine a treatment plan. Rehabilitation specialists can help determine appropriate exercise and stretching regimens to prevent muscle loss and maximize activity. Genetic counseling can help to determine the risk of inheritance in other family members, as well as the risks and benefits of genetic testing.

If needed, other physicians, such as pulmonologists, orthopedic surgeons, and cardiologists, will be consulted to provide expert advice on management of extra-muscular symptoms and complications.


Keywords: metabolic myopathies.

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What is Pompe Disease and its Prognosis?

What is Mito Disease?

What is Nemaline Myopathy?

Bethlem Myopathy: Symptom, Diagnosis, Treatment

Why Do I Feel Muscle Weakness Frequently?

* The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.