Polymyositis and Dermatomyositis


Polymyositis and dermatomyositis are disorders of the body's connective tissues, which include tendons, ligaments and the dense sheets of collagen-based tissue that cover the ends of the muscles.

These diseases cause swelling and tenderness in the muscles (polymyositis) and sometimes the skin (dermatomyositis). The disease causes weaknesses in the arms and legs.


Both Polymyositis and dermatomyositis have symptoms in common with sclerosis or sometimes lupus.

Signs of these conditions may appear suddenly and severely or gradually and more mildly. Symptoms are more likely to be gradual in older people. Sometimes a person may have a serious infection before the symptoms begin.

The symptoms include:

  • Muscle weakness. This is usually not noticeable until the disease is advanced and about half the muscle fibers have been destroyed. A person may have difficulty raising his or her arms above the shoulders, climbing steps or rising from sitting. If the neck muscles are seriously affected, it may not be possible for the person to lift his or her head from the pillow. If the muscles of the throat are affected, the person may have difficult using his or her voice.
  • Contraction of the arms and legs. While the hands, feet and face are usually not affected by this condition, the arms and legs may tighten up in the late stages of the disease.
  • Shortness of breath. This is caused by gradual damage and weakness of the chest wall and the muscles that move the diaphragm during breathing.
  • Difficulty swallowing. This may occur when the muscles of the throat and esophagus (the tube that connects the mouth to the stomach) are involved
  • Muscle tenderness or pain
  • Raynaud's phenomenon
  • Fever
  • Feeling tired
  • Weight loss

Compared to lupus or sclerosis, there is relatively little organ involvement with polymyositis. Sometimes, however, the effect on specific organs may be the first symptoms. These include breathing problems, heart disorders involving irregular rhythms or electrical signals, kidney failure or digestive tract ulcers.

If dermatomyositis occurs along with polymyositis, symptoms may also include:

  • Skin rash. This can be either raised and smooth or scaly. It may appear on the forehead, the neck, shoulders, chest and back, forearms and lower legs, elbows and knees or the joints of the fingers, toes, wrists and ankles.
  • Swelling around the eye. This may look purplish and bruised.
  • Swelling at the base and sides of the fingernails
  • Splitting of the skin of the fingers

While the skin eruptions often completely fade away, some leave behind brownish spots, scars or smooth white patches.

Causes and Risk Factors

It is not known what causes these conditions. It may be an immune reaction of the body against its own tissues. Viruses may play a role. A tumor may spark an immune reaction against both tumor and the muscle tissue.

Polymyositis and dermatomyositis occur almost two times often in women than men.

While it can occur at any age, it usually appears in people between the ages of five to 15 or 40 to 60.


A doctor will base his or her diagnosis on the presence of:

  • Muscle weakness
  • A characteristic skin rash
  • Increased levels of a particular muscle enzyme in the blood

To confirm the diagnosis, a doctor may order:

  • A muscle biopsy. This involves taking a small sample of muscle tissue to check under a microscope for changes in the muscle fiber. A muscle biopsy is required to confirm the diagnosis and rule out other conditions that may have similar symptoms.
  • An electromyogram. This test records electrical signals between the muscles and nerves when they are stimulated.
  • Sometimes a magnetic resonance image (MRI) is done to identify what parts of the muscle are most swollen and inflamed before a biopsy is done.

A doctor should also check for any cancerous tumors in an adult with dermatomyositis.


A person should limit his or her physical activities until signs of inflammation have gone away. Doctors usually prescribe corticosteroids such as prednisone at first to control the inflammation. The patient's progress will be monitored with blood tests for six to 12 weeks. During this time, the patient's muscle strength should improve. Once the blood enzyme levels return to normal, the corticosteroid dose will be slowly lowered. The drugs may be increased again if the blood enzyme levels start to rise again.

Some people may need to stay on corticosteroids indefinitely. Some patients appear to recover completely after several years of taking the corticosteroids. Taking high doses of corticosteroids for a long time may also cause muscle weakness. If the myositis is associated with tumors that can't be removed surgically or that have spread from other parts of the body, it may not respond as well to corticosteroids.

When corticosteroids cannot be used, drugs that suppress the body's immune system may be used instead. These include methotrexate, cyclophosphamide, chlorambucil, azathioprine and cyclosporine. If a tumor is associated with polymyositis, sometimes removing the tumor causes the polymyositis to go away.

In children, it may be possible to discontinue prednisone after a year if the polymyositis appears to disappear.

Polymyositis tends to be more severe and difficult to treat if the disease affects the patient's heart or lungs. However, relatively long periods of time without symptoms (remission) or even apparent recovery do occur, especially in children.

Severe muscle weakness that continues to get worse can become life threatening if it causes difficulty swallowing, malnutrition or respiratory difficulties or failure.

© 2000-2022 The StayWell Company, LLC. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.
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