What Are Myopathies?

Medically Reviewed by Poonam Sachdev on August 22, 2022
4 min read

If your doctor has suggested that you may have a myopathy, you likely have a lot of questions. There are many types of myopathies with different causes and outlooks.

Myopathies are a class of diseases that attack your skeletal muscles. These diseases make your muscles weak by targeting the muscle fibers. Myopathies can be inherited or acquired, and they often cause difficulty performing everyday tasks.

Skeletal muscles are the muscles in your body that are connected to your skeletal system. Most of the muscles in your body are skeletal muscles. These muscles are voluntary, meaning you can control what they do. But because most of your muscles are skeletal muscles, myopathies can cause many problems throughout your body.

Inherited myopathies are myopathies that you’re born with when you inherit a genetic mutation from one of your parents. Inherited myopathies include:

Congenital myopathies. People with congenital myopathies often start to show symptoms when they're a baby or child. These myopathies often involve developmental delays in learning motor skills, such as crawling or walking. It's common for congenital myopathies to affect all of the skeletal muscles, and it often does not progress.

Mitochondrial myopathies. Mitochondrial myopathies are caused by mutations in the mitochondria, which are the “powerhouses” or energy-producing parts of the body's cells. In addition to muscle weakness, they may also cause problems with the heart, brain, or gastrointestinal tract. Examples of mitochondrial myopathies include:

  • Kearns–Sayre syndrome
  • Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome
  • Myoclonic epilepsy with ragged red fibers (MERRF) Syndrome

Muscular dystrophies. Muscular dystrophies are characterized by progressive weakness in skeletal muscles. These types of diseases are caused by the degeneration of muscular tissue due to structural support protein abnormalities. 

Metabolic myopathies. Metabolic myopathies are characterized by episodic muscle weakness that's sometimes random but is often caused by exercise or muscle exertion. These myopathies are caused by defects in the genes that code for certain enzymes.

Acquired myopathies are myopathies that are acquired later in life. Examples of acquired myopathies include:

  • Autoimmune/inflammatory myopathy. This type of myopathy causes issues with muscular function due to an autoimmune condition.
  • Toxic myopathy. Toxic myopathy is myopathy caused by toxins — for example, alcohol — and certain medications.
  • Endocrine myopathies. An endocrine myopathy is a myopathy caused by issues with the endocrine system, which controls hormone production. Endocrine myopathies can be caused by thyroid or adrenal diseases.
  • Infectious myopathies. Infectious myopathies are myopathies caused by a viral, bacterial, parasitic, or fungal infection.
  • Critical illness myopathy. Critical illness myopathy may develop while a person is in the intensive care unit. It's thought to be caused by long periods of immobility. This type of myopathy affects the muscles you use to breathe.

All myopathy is characterized by muscle weakness, most commonly in the upper arms, shoulders, and thighs. Other general symptoms you may have with myopathy include:

  • Muscle cramps and stiffness
  • Muscle spasms
  • Low energy
  • Being easily fatigued, especially with activity

Myopathy may make it difficult to do routine tasks, such as getting dressed, bathing, brushing your teeth or hair, climbing stairs, or getting out of bed.

Some myopathies have other specific symptoms. For example, in muscular dystrophies, the muscle weakness is progressive and often begins in the face, hips, and shoulders. Some types of muscular dystrophies may start as an inability to relax certain muscles.

Because there are so many conditions that can affect your body’s nerves and muscles, you may have to go through a wide range of diagnostic testing to be diagnosed with myopathy. These tests may include: 

  • Genetic testing. Genetic testing looks for issues in your genes using a blood or saliva sample.
  • Biochemical genetic testing. Biochemical genetic testing looks for abnormal enzymes from blood, urine, spinal, or amniotic fluid samples.
  • Computerized tomography (CT). CT scans combine several X-ray images taken from several angles to give a more complete picture of what’s going on with your bones, blood vessels, and soft tissue.
  • Lumbar puncture. Also known as a spinal tap, a lumbar puncture extracts cerebrospinal fluid for testing. Your doctor will perform this by inserting a needle between two vertebrae in your lower back.
  • Magnetic resonance imaging (MRI). MRIs use a magnetic field and computer-generated radio waves to create an image of your organs, tissues, and skeletal system.
  • Nerve and muscle biopsy. When a doctor takes a biopsy, they remove tissue or a sample of a certain area for examination and testing.
  • Nerve conduction studies. In a nerve conduction study, a medical professional will place electrodes on your skin. Those electrodes will then stimulate your nerves and record the electrical activity. These tests will help your doctor rule out nerve disorders.
  • Electromyography. Electromyography measures the electrical activity of your muscles. Your doctor will insert electrodes into specific muscles and monitor the activity while you perform certain tasks like contracting or moving the muscle.

The type of treatment your doctor will prescribe for your myopathy depends on the type of myopathy you have. 

Most inherited myopathies don’t have a cure. Instead, treatment involves symptom management, such as physical therapy. Some inherited myopathies, like Duchenne muscular dystrophy and Pompe disease, a type of metabolic myopathy, are treatable with medication.

Treating acquired myopathies usually means treating the cause of the myopathy. For example, endocrine myopathy would be treated by stabilizing your hormone levels. Depending on the severity of the myopathy, you may still need physical therapy.