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Myositis

Symptoms of Myositis

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.

Dermatomyositis, polymyositis, and other inflammatory myositis conditions tend to cause weakness that gets worse slowly over weeks or months. The weakness affects large muscle groups, including the neck, shoulders, hips, and back. Muscles on both sides are usually affected.

The weakness from myositis can lead to falls and make it difficult to get up from a chair or after a fall. Other myositis 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.

Some people with myositis have muscle pain, but many do not.

Most muscle pain is not caused by myositis, but by strain injuries, or ordinary illnesses like colds and flu. These and other ordinary muscle pains are called myalgias.

Diagnosis of Myositis

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. A scanner using a high-powered magnet and a computer creates images of the muscles. An MRI scan can help identify areas of myositis and changes in the muscles over time.

EMG. By inserting needle electrodes into muscles, a doctor can test the response of muscles to electrical nerve signals. 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.

There are many causes of muscle weakness and pain more common than myositis, and testing for myositis is not a straightforward process. For these reasons, the process of diagnosing myositis can be long.

Treatment of Myositis

Myositis treatment varies according to the cause.

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

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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WebMD Medical Reference

Reviewed by Melinda Ratini, DO, MS on April 23, 2013

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