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Metabolic Myopathies - Types, Symptoms, Diagnosis, and Treatment

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Our muscles require energy to function well. Any defect in producing energy leads to muscular disorders. Read the article to know more.

Written by

Dr. Gayathri P

Medically reviewed by

Dr. Sugreev Singh

Published At November 16, 2022
Reviewed AtFebruary 28, 2024

Introduction:

Generally, the food we eat is converted to energy by chemical reactions in the body. The carbohydrates and fatty acids are broken down by various enzymes in the body to produce ATP (adenosine triphosphate). Metabolic myopathy happens due to a lack of enzymes that are required in ATP synthesis. This article reviews the different types of metabolic myopathies, their diagnosis, and their management.

What Are Metabolic Myopathies?

Metabolic myopathies are hereditary disorders that disturb the body's energy production process. Therefore, the energy supply to muscles is blocked and does not coordinate well with the bones and joints during the body’s movements.

Usually, it is classified as

  • Myopathies that show exercise-related symptoms: Muscle pain and cramps occur after transient exercise or extended physical activities.

  • Myopathies with fixed symptoms: The patient complains of muscle weakness and is linked with underlying systemic conditions.

What Are the Types of Metabolic Myopathies?

  • Glycogen Storage Disorder (Glycogenosis): The carbohydrate (glucose) in the food is processed into glycogen and is stored in the liver and skeletal muscles. During any physical activity, the glycogen is broken down to produce ATP. Any changes (mutation) in the genes involved in the synthesis or degradation of glycogen leads to a glycogen storage disorder.

  • Lipid Storage Disorder: The fat in the food that we eat is converted to fatty acids, and it provides energy during minimal exercise or fasting. The fatty acids are transferred to mitochondria (the powerhouse of the cell), where it is broken down to produce energy. The short-chain fatty acids pass freely into mitochondria, whereas the long-chain fatty acids bind with carnitine to get into mitochondria. The process of fatty acid transformation is controlled by CPT (carnitine palmitoyltransferase) I and II enzymes. A specific genetic mutation that causes CPT I and II enzyme deficiency gives rise to lipid storage disorders.

  • Mitochondrial Disorder: The mitochondria in the cell do various functions like fat, protein metabolism, and energy production. Various genes are involved in the functioning of mitochondria. Thus, mitochondrial disorder occurs due to the mutation of genes responsible for normal mitochondrial functioning and is passed from parents to offspring.

What Are the Various Glycogen Storage Disorders?

The glycogen storage disorders that arise from several enzyme deficiencies are listed.

Type I: Glucose-6-phosphatase deficiency.

Type II: Pompe disease due to acid-maltase deficiency.

Type III: Cori-Forbes disease; debrancher enzyme deficiency.

Type IV: Anderson disease; brancher enzyme deficiency.

Type V: McArdle disease: muscle phosphorylase deficiency.

Type VI: Liver phosphorylase deficiency.

Type VII: Tarui disease; phosphofructokinase deficiency.

Type VIII: Phosphorylase b kinase deficiency.

Type IX: Phosphoglycerate kinase deficiency.

Type X: Phosphoglycerate mutase deficiency.

Type XII: Lactate dehydrogenase deficiency.

Type XII: Aldolase A deficiency.

The characteristic features of a few glycogen storage disorders on clinical and laboratory examinations are discussed below:

types-of-metabolic-myopathies

What Are the Features of Lipid Storage Disorders?

1) Carnitine Palmitoyltransferase (CPT) Deficiency: The CPT, I, and II enzymes are required for fatty acid metabolism. In childhood, the lipid disorder is severe and mild in adults. The characteristic features include muscle weakness or stiffness and pain. The symptoms occur in episodes and last for several weeks.

The following factors trigger the attacks -

  • Severe exercise.

  • Exposure to cold.

  • Drugs such as Ibuprofen, Diazepam, etc.

  • Infection.

  • Stress.

  • High fat intake.

2) Myoadenylate Deaminase Deficiency (MADD): It is another form of lipid storage disorder, and it causes muscle pain, weakness, stiffness, cramps, and exercise intolerance. Laboratory investigations show increased levels of serum creatine kinase and lactate.

What Are the Types of Mitochondrial Disorders?

Mostly all mitochondrial disorders possess symptoms like exercise intolerance due to fatigue from mild exercise. But, the classic features of glycogenosis, like muscle stiffness and cramps, are not present. Certain mitochondrial syndromes are listed below -

  • Kearns-Sayre Syndrome (KSS): The symptoms and signs develop before the age of 20, and it includes pigmentary retinopathy (a degenerative disorder of the retina), extraocular muscle weakness, and ataxia (lack of coordination).

  • MELAS: Mitochondrial encephalopathy, lactic acidosis, and stroke-like epilepsy syndrome (MELAS) affect the brain, muscles, and nervous system. It is genetically transferred to offspring from their mothers.

How Are Metabolic Myopathies Diagnosed?

  • Laboratory Examination - On blood investigation, decreased red blood cells and low creatine kinase is observed.

  • Muscle Biopsy - A sample of muscle tissue is surgically removed for investigation. Mitochondrial disease like KSS shows ragged blue fibers on staining.

  • Genetic Testing - It is done to determine the mutation of genes responsible for causing specific enzyme deficiency.

How to Treat Metabolic Myopathies?

There is no effective treatment available for metabolic myopathies. However, the following measures help in relieving the symptoms.

  • Low-fat diet: Intake of foods rich in carbohydrates, vegetables, and fruits and less fat are found to be helpful.

  • Avoid severe or prolonged exercise.

  • Vitamin supplements are also suggested to improve energy production.

  • Enzyme replacement therapy: intravenous administration of deficient enzymes is done to relieve the patient from symptoms like fatigue, muscle pain, etc.

  • Physical training: A therapist provides special training to get relief from muscle pain. They also aid in doing mild exercise to manage body weight.

Conclusion:

Every muscle in the body requires energy to be active and function well. Metabolic myopathies are a rare genetic disorder that disturbs energy production, and muscles become weak. A detailed clinical and laboratory investigation is necessary to identify the exact type of metabolic myopathy and differentiate it from other genetic disorders. It also provides a clear view of deciding the treatment plan.

Frequently Asked Questions

1.

Which Specialist Treats Metabolic Myopathy?

A rheumatologist diagnoses inflammatory myopathy, whereas a metabolic neurologist diagnoses metabolic myopathy.

2.

Can Myopathies Be Cured?

Inherited and genetic myopathies do not have any treatment. They are not completely curable, but symptoms can be treated and resolved.

3.

Does Exercise Help Myopathy?

Physical exercises are effective for patients with myopathies. Exercise to improve muscular strength, endurance, and cardiovascular fitness has a major role for patients with myopathy. 

4.

Which Disorders Cause Myopathy?

Many conditions, like inflammatory conditions, can cause myopathies, and genetic factors can also result in myopathy. Some systemic conditions can also result in myopathies like thyroid disorders, rheumatoid arthritis, lupus, sarcoidosis, Sjogren’s syndrome, amyloidosis, or another critical illness. 

5.

Can Viruses Cause Myopathy?

Infectious myopathies can occur as a result of infections that affect muscle function. The viruses that cause viral myopathies are HIV, influenza, and Epstein-Barr.

6.

What Are the Blood Tests to Diagnose Myopathies?

The blood tests to diagnose myopathy are for muscle enzymes like creatine kinase (CK) or aldolase, which may be elevated in some cases of myopathy due to the breakdown of muscle fibers. Other tests include electrolytes like magnesium, sodium, potassium, phosphorous, and calcium.

7.

Does Myopathy Last Forever?

Myopathy is a chronic condition that lasts for a long time. Myopathy has no cure, but the symptoms can be managed through medicines.

8.

What is Myopathy?

Myopathy is a skeletal muscle disorder due to an abnormality in the muscle structure or metabolism. It may be from a variety of causes. Some may be inherited, and some may be acquired during their lifetime.

9.

Can Myopathy Cause Pain?

Myopathies can cause chronic inflammation. They can also cause muscle weakness and pain in some patients.
Source Article IclonSourcesSource Article Arrow
Dr. Sugreev Singh
Dr. Sugreev Singh

Internal Medicine

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