MYOSITIS

Myositis refers to any condition causing inflammation in muscles. Weakness, swelling, and pain are the most common myositis symptoms.

Causes of Myositis

  • Infection. Viral infections are the most common infections causing myositis. Rarely, bacteria, fungi, or other organisms can cause myositis as well.
  • Autoimmune conditions, in which the body attacks its own tissues. Inflammatory conditions causing potentially severe myositis include:
    • Dermatomyositis
    • Polymyositis
    • Inclusion body myositis
    • Lupus
    • Scleroderma
    • Rheumatoid arthritis
  • Drugs. Many different medications and drugs can cause temporary muscle damage.
    • Statins
    • Colchicine
    • Plaquenil (hydroxychloroquine)
    • Alpha-interferon
    • Cocaine
    • Alcohol
  • Injury. Vigorous exercise 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.
  • Rhabdomyolysis. Rhabdomyolysis occurs when muscles break down quickly. Muscle pain, weakness, and swelling are symptoms of rhabdomyolysis. Urine may also turn a dark brown or red color.

The main symptom of myositis is muscle weakness. The weakness may be noticeable or may only be found with testing. Muscle pain (myalgias) may or may not be present.

The weakness from myositis can lead to falls and make it difficult to get up from a chair or after a fall. Other symptoms that may be present with inflammatory conditions include:

  • Rash
  • Fatigue
  • Thickening of the skin on the hands
  • Difficulty swallowing
  • Difficulty breathing

People with myositis caused by a virus usually have symptoms of a viral infection, such as runny nose, fever, cough and sore throat, or nausea and diarrhea. But the symptoms of viral infection may go away days or weeks before myositis symptoms begin.

DIAGNOSIS

A doctor may suspect myositis based on a person’s symptoms of muscle weakness or other evidence of myositis. Tests for myositis include:

  • Blood tests. High levels of muscle enzymes, such as creatine kinase, may mean there is muscle inflammation. Other blood tests check for abnormal antibodies that may identify an autoimmune condition.
  • MRI scan. An MRI scan can help identify areas of myositis and changes in the muscles over time.
  • EMG. EMG can identify muscles that are weak or damaged by myositis.
  • Muscle biopsy. This is the most accurate test for diagnosing myositis. A doctor identifies a weak muscle, makes a small incision, and removes a small sample of muscle tissue for testing. Muscle biopsy leads to a final diagnosis in most people with myositis.

 

RECOMMENDED MEDICATIONS

Myositis treatment varies according to the cause.

Inflammatory conditions causing myositis may require treatment with drugs that suppress the immune system, including:

  • Prednisone
  • Azathioprine (Imuran)
  • Methotrexate

Myositis caused by infection is usually due to a virus, and no specific treatment is necessary. Myositis caused by bacteria is uncommon and usually requires antibiotics to prevent life-threatening spread of the infection.

Although rhabdomyolysis rarely results from myositis, it can cause permanent kidney damage. People with rhabdomyolysis are hospitalized in order to receive continuous intravenous fluids in large amounts.

Myositis related to a drug is treated by stopping the medication. In cases of myositis caused by statin drugs, muscle inflammation usually subsides within a few weeks after stopping the medicine.

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