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Polymyositis is a condition that causes inflammation and weakness in many different muscles of the body.

What is going on in the body?
This condition is thought to be an autoimmune disorder. An autoimmune disorder is one in which a person's immune system attacks his or her own body.

When a person has polymyositis, the immune system attacks the muscles. This causes muscular inflammation and weakness. Other organs in the body can also be affected by this condition.

What are the signs and symptoms of the condition?
Signs and symptoms can begin slowly or suddenly. They commonly include: What are the causes and risks of the condition?
The exact cause of this condition is unknown. It occurs most often among women between 40 to 60 years old. However, men and children can also be affected.

A person has a higher than normal risk of developing polymyositis if he or she has another autoimmune disorder, such as:
  • systemic lupus erythematosus. This disorder causes problems with many body organs, including joints, lungs, kidneys, skin, and heart.
  • systemic sclerosis, or scleroderma, which causes skin hardening and tightness
Sometimes, cancer can cause polymyositis for unknown reasons.

What can be done to prevent the condition?
There is no known way to prevent this condition.

How is the condition diagnosed?
Polymyositis is often suspected after a history and physical examination are done. Blood tests are commonly done to help make the diagnosis. When a person has this condition, the immune system often makes certain antibodies. These can be measured with a test called an antibody titre. Certain muscle proteins often increase in the blood due to muscle damage. For example, creatine phosphokinase and aldolase levels commonly rise. Another blood test, called an erythrocyte sedimentation rate, is also usually abnormal.

When these blood tests are abnormal, two other tests are commonly done to confirm the diagnosis:
  • Electromyography (EMG) involves attaching wires to the skin and measuring the electrical activity in the muscles. The response of the muscles to small shocks is also measured.
  • A muscle biopsy involves using a special tool to remove a small piece of muscle. The muscle tissue can then be sent to the laboratory for examination and testing.
What are the long-term effects of the condition?
The muscles can shrink and become very weak in this condition. If the muscles become too weak, the person can die from breathing or swallowing troubles. Heart or lung damage can also occur and may be severe enough to cause permanent disability or death.

In other cases, a person may get better with treatment or the disease may go away completely. Children are more likely to get better than adults.

Other long-term effects may occur if this condition is due to other autoimmune disorders or cancer. For example, cancer may result in death.

What are the risks to others?
This condition is not contagious.

What are the treatments for the condition?
Medications called corticosteroids, such as prednisone, are the most common treatment. These medications suppress the immune system and reduce the inflammation. Azathioprine and methotrexate may be used to suppress the immune system.

If a tumour or cancer is the cause of this condition, removing or treating the tumour may improve or stop symptoms in the muscles.

What are the side effects of the treatments?
Medications that suppress the immune system raise the risk of infections, which can be serious. Corticosteroids may cause emotional problems, weight gain, and bone thinning. These medications may even cause muscle weakness, one of the symptoms they are being used to treat. If muscle weakness occurs, other medications must be used.

What happens after treatment for the condition?
Physiotherapy can help strengthen muscles after treatment. People often get better with treatment. This is especially true of children. But this condition is unpredictable. Some people die from complications of it.

How is the condition monitored?
Repeated blood tests are sometimes used to measure the level of muscle proteins in the blood. When the levels are high, the treatment medication dose is increased because the muscles are still being damaged. Any new or worsening symptoms should be reported to the doctor.

Author: Jorge Allende, MD
Reviewer: HealthAnswers Australia Medical Review Panel
Editor: Dr David Taylor, Chief Medical Officer HealthAnswers Australia
Last Updated: 1/10/2001
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.


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