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Myositis
Myositis refers to any condition causing inflammation in one or more muscles. Weakness, swelling, and pain are the most common myositis symptoms. Myositis causes include infection, injury, autoimmune conditions, and drug side effects. Treatment of myositis varies according to the cause.
Causes of Myositis
Myositis is caused by any condition that leads to inflammation in the muscles. Myositis causes can be divided into several major categories:
Inflammatory conditions causing myositis. Conditions causing inflammation throughout the body may affect the muscles, causing myositis. Many of these causes are autoimmune conditions, in which the body produces damaging antibodies against its own tissues. Inflammatory conditions causing potentially severe myositis include:
- Dermatomyositis
- Polymyositis
- Inclusion body myositis
Other inflammatory conditions tend to cause milder forms of myositis, including:
- Systemic lupus erythematosus (lupus)
- Scleroderma
- Rheumatoid arthritis
Inflammatory conditions are often the most serious myositis causes, requiring prolonged treatment.
Myositis caused by infection. Viral infections are the most common infections causing myositis. Rarely, bacteria, fungi, or other organisms can cause myositis as well. Viruses or bacteria may invade muscle tissue directly, or release substances that damage muscle fibers. Common cold and flu viruses, as well as human immunodeficiency virus (HIV), can cause myositis.
Drugs causing myositis. Many different medications and drugs can cause temporary muscle damage. Because inflammation in the muscles is often not identified, the muscle problem may be called myopathy rather than myositis. Drugs causing myositis and/or myopathy include:
- Statins
- Colchicine
- Plaquenil (hydroxychloroquine)
- Alpha-interferon
- Cocaine
- Alcohol
Myopathy may occur shortly after starting a medication, or may occur after taking a drug for months or years. Severe myositis caused by medications is rare.
Myositis due to injury. Vigorous exercise of untrained muscle groups can lead to muscle pain, swelling, and weakness for hours or days after a workout. Inflammation contributes to these symptoms, technically making this a form of myositis. Myositis symptoms after exercise or injury nearly always resolve completely with rest and recovery.
Myositis and rhabdomyolysis. Rhabdomyolysis occurs when muscle breakdown occurs in large muscle groups. Muscle pain, weakness, and swelling can be symptoms of rhabdomyolysis. The urine may also turn a dark brown or red color.
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