Definition

Myopathy is a general term for diseases that affect skeletal muscles (the muscles that control voluntary body movements). People with myopathy experience muscle weakness due to impaired function of muscle fibers.

Causes

Based on the causes, myopathy can be divided into:

• Genetic Myopathy: Myopathy present at birth due to genetic mutations passed down from parents. Conditions included in genetic myopathy are:
  • Congenital Myopathy.
  • Mitochondrial Myopathy: Caused by a dysfunction in mitochondria, the energy-producing part of the cell. This may be due to genetic mutations, with or without a family history of the same condition.
  • Metabolic Myopathy: Caused by a gene defect affecting the enzymes required for normal muscle function and movement.
  • Muscular Dystrophy: Occurs due to a lack of abnormality of muscle-supporting proteins, leading to progressive muscle dysfunction or damage. Muscular dystrophy is the most common form of genetic myopathy, with Duchenne and Becker muscular dystrophy affecting 7 in 100,000 people worldwide.

• Acquired Myopathy: Myopathy that develops later in life, possibly caused by certain medical conditions, infections, exposure to certain drugs, or electrolyte imbalances. Conditions include:
  • Autoimmune or Inflammatory Myopathy: Occurs when the body's immune cells attack its tissues, causing muscle dysfunction.
  • Toxic Myopathy: Results from toxins or medications affecting muscle structure or function. Examples include:
    • Toxins: Alcohol and toluene.
    • Medications: Immunotherapies (pembrolizumab, nivolumab), corticosteroids (prednisone), cholesterol-lowering drugs (statins), amiodarone, colchicine, chloroquine, antivirals, and protease inhibitors used in HIV treatment, as well as omeprazole.
  • Endocrine Myopathy: Occurs when hormones affect muscle function. Conditions include:
    • Thyroid disorders: Hypothyroidism (low thyroid hormone levels) is more common, though hyperthyroidism (elevated thyroid hormone) can also cause issues.
    • Parathyroid hormone excess: Leads to increased calcium levels.
    • Adrenal hormone disorders: Such as Addison's disease and Cushing's syndrome. 
  • Infectious Myopathy: Caused by infections affecting muscle function, such as viral infections (HIV, influenza, Epstein-Barr), bacterial infections (pyomyositis), Lyme disease, parasitic infections (toxoplasmosis), and fungal infections (candida).
  • Electrolyte Imbalance: Abnormally high or low potassium or magnesium levels can impact muscle function.
  • Critical Illness Myopathy: Weakness of limb and respiratory muscles, often seen in patients in intensive care units for extended periods. This can also be caused by medications used during treatment, such as muscle relaxants, corticosteroids, and sedatives.

Risk factor

Everyone is at risk of developing myopathy. Some factors that increase the risk include:

• Family history of myopathy.
• Gender: Depending on the type of myopathy, men may have a higher risk. However, inflammatory and endocrine myopathies are more common in women.
• Autoimmune, metabolic, or endocrine disorders.
• Exposure to certain medications or toxins.

Symptoms

Most myopathies share common symptoms, including:

• Muscle weakness, often affecting the upper arms, shoulders, and thighs (more frequently and severely). This weakness is usually symmetrical (occurs on both sides of the body) and primarily affects muscles close to the torso, such as the shoulders, upper arms, hips, and thighs. The muscles of the hands and feet are usually not affected. Muscle weakness in myopathy may cause:
• Difficulty performing daily activities like bathing, dressing, or brushing hair.
• Difficulty standing up from a chair, climbing stairs, or performing tasks that require lifting arms overhead, such as changing a lightbulb.
• Muscle cramps, stiffness, and spasms.
• Fatigue and shortness of breath during activity.
• Low energy.

Additional symptoms may vary depending on the type of myopathy and can include:

• Non-progressive or very slow progressive muscle weakness.
• Fluctuating muscle weakness with periods of normal strength.
• Delayed motor development in children (such as walking, jumping, climbing stairs, holding a spoon or pencil).
• Children may struggle to keep up with peers during sports or play.
• Problems with muscles controlling swallowing and speech, leading to choking or unclear speech.

Diagnosis

Doctors may conduct various tests to determine the specific type of myopathy, including:

• Physical examination.
• Muscle strength tests.
• Electromyography (EMG).
• Ultrasound.
• MRI.
• Genetic testing.
• Muscle biopsy.

The goal is to identify the specific type of myopathy to develop a tailored treatment plan.

Management

While there is no cure for genetic myopathies, there are many treatment options available to manage symptoms. Treatment depends on the underlying cause or specific disease. The most effective treatment for genetic and endocrine myopathies is early diagnosis and management by a specialist medical team.

For acquired myopathies, such as those caused by autoimmune conditions like dermatomyositis and polymyositis, medications can help control symptoms. These include corticosteroids or other immunosuppressive drugs that reduce the immune response and inflammation. Physical therapy, supportive devices like braces for muscle weakness, and sometimes surgery may be considered.

Treatment for metabolic, toxic, and endocrine myopathies typically focuses on addressing the underlying cause. Medications or surgery may be used to manage symptoms.

Complications

In some cases, myopathy can be progressive or worsen over time, leading to severe disability, life-threatening conditions, or even fatality.

Prevention

Most myopathies cannot be prevented. However, if you or your family have myopathy, there are steps you can take to manage the condition, such as:

• Eating a healthy and balanced diet with plenty of fruits and vegetables.
• Staying active with light exercise (consult your doctor before starting any exercise routine).
• Maintaining a healthy weight.
• Taking all prescribed medications.
• Participating in therapies like physical therapy, occupational therapy, and speech therapy.
• Monitoring your body for changes. Keep track of disease progression and symptoms, and see your doctor regularly, or sooner if new symptoms appear, to adjust your treatment plan as needed.

When to see a doctor?

If you experience symptoms of myopathy that concern you, it's best to consult a doctor.

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