Definition

Myositis is an inflammatory condition affecting the body's skeletal muscles. It can be caused by various factors, including muscle fiber damage, muscle infections, or autoimmune diseases. This inflammation damages the muscle fibers, leading to muscle weakness and impaired muscle contraction.

This condition is often long-term and affects the musculoskeletal system. Prolonged muscle inflammation can cause muscle wasting and disability.

Myositis is a common condition, with a higher incidence in women than men (2:1). It can occur in all age groups, from as young as 5 years old to those over 50.

There are four main types of myositis: polymyositis, dermatomyositis, inclusion body myositis, and necrotizing autoimmune myopathy. Dermatomyositis is more common in children aged 5-14, while inclusion body myositis usually affects those over 50.

Causes

Several common causes of myositis include:

• Autoimmune diseases that attack the muscles, causing inflammation.
• Allergic reactions due to exposure to toxic substances or certain medications.
• Viral, bacterial, or fungal infections that cause muscle inflammation.
• Severe muscle injuries.
• Rhabdomyolysis, a complication from muscle tissue breakdown.

Risk Factor

While myositis can affect both children and adults, several risk factors may increase the risk of developing this condition:

• Age: Myositis, particularly when caused by autoimmune diseases, is more common in individuals over 50.
• Gender: Women are more likely to develop myositis than men.
• Genetic disorders: Genetic issues can increase the risk of polymyositis and dermatomyositis.
• UV exposure: This factor can increase the risk of polymyositis and dermatomyositis, especially in individuals with genetic abnormalities.
• Autoimmune diseases: Long-term autoimmune conditions, such as arthritis or lupus, can increase the risk of myositis.

Symptoms

The primary symptom of myositis is progressive muscle weakness due to inflammation that damages the muscle fibers. This inflammation affects the arteries and veins that run through the muscles.

Other symptoms of myositis can include fatigue after walking or standing, frequent falls, and difficulty swallowing and breathing. Some individuals may also experience muscle pain, particularly when the muscles are touched.

Symptoms of myositis can also vary depending on the type:

• Polymyositis
  This type has a range of symptoms, making it difficult to diagnose. It generally affects both sides of the body and occurs between ages 30-60. Without treatment, it can cause difficulty swallowing, speaking, rising from a chair, climbing stairs, lifting objects, and reaching overhead. Additional symptoms may include arthritis, shortness of breath, irregular heartbeat, or heart failure.
• Dermatomyositis
  This type is characterized by a skin rash that appears alongside muscle weakness. The rash is usually small and red or purple and spreads to the eyelids and muscles around the joints. It can appear on the face, neck, chest, upper back, or back and worsens with sun exposure. Other symptoms may include weight loss, fever, lung inflammation, and photosensitivity.
• Inclusion Body Myositis
  This type is marked by muscle weakness, particularly in individuals over 50. Early signs include frequent falls and stumbling, with gradual weight loss. It commonly affects the upper limbs and can occur on one or both sides of the body. This condition can coexist with Alzheimer's or other age-related nerve diseases.
• Necrotizing Autoimmune Myopathy
  This rare condition presents symptoms similar to polymyositis, such as weakness in the upper and lower skeletal muscles on both sides. Symptoms can arise suddenly and worsen over days or weeks, often following a viral infection, cancer near the muscles, or after taking cholesterol-lowering medications.
• Childhood Inflammatory Myopathy
  This type affects children between 2 and 15 years old, presenting with muscle weakness in the upper legs, swelling, muscle pain, skin rashes, abdominal pain, fever, and muscle shortening due to inflammation of the muscles and surrounding tissues. Without treatment, it can lead to difficulty swallowing and breathing.

Diagnosis

The doctor will ask about your symptoms and medical history. Myositis is often suspected based on its primary symptoms, but additional tests are required for confirmation, such as:

• Electromyography (EMG): Measures electrical activity in muscles during contraction and rest.
• MRI: Identifies structural abnormalities in the muscles.
• Ultrasound: Detects muscle inflammation.
• Blood tests: Check muscle enzyme levels, like creatine kinase, and can indicate autoimmune diseases.
• Muscle biopsy: Examines muscle tissue for long-term inflammation, muscle fiber abnormalities, or vascular changes.

Management

Myositis treatment depends on its cause. Most cases are due to autoimmune diseases, and while myositis can't be cured in adults, several treatments can improve symptoms:

• Immunosuppressive drugs: Medications that reduce inflammation in myositis, such as corticosteroids, azathioprine, methotrexate, and other immunosuppressants
• Physical rehabilitation therapy
• Exercise: Maintains muscle strength and flexibility
• Orthotic devices
• Heat therapy

Complications

Untreated myositis can lead to several potentially serious complications. The condition can worsen and cause damage to the heart muscles. Possible complications include:

• Difficulty swallowing, potentially leading to malnutrition
• Increased risk of falls
• Breathing difficulties
• Increased susceptibility to infections
• Respiratory failure
• Heart failure

When to See a Doctor?

Myositis is a serious condition. If you experience progressive muscle weakness, you should see a doctor immediately. Prompt treatment can significantly improve myositis symptoms.

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