Polymyositis and Dermatomyositis

What are polymyositis and dermatomyositis?

Polymyositis (PM) is a chronic disease that causes muscle inflammation and weakness. Dermatomyositis (DM) is a related disease that causes inflammation of blood vessels, which can also cause muscle problems. It may also cause a rash and other problems. The heart muscle is affected in about half of the people who have PM or DM.

Both of these diseases are rare. They are different from polymyalgia rheumatica, which is a much more common and more painful condition. It causes sore joints and muscles but does not actually weaken or damage the muscles.

How do they occur?

PM or DM probably happens because your immune system attacks your own tissues. It is not known why this happens. PM or DM occurs most often in adults 50 to 70 years old and children 5 to 15 years old. Sometimes the disease seems to be associated with a cancer, but doctors don’t know if this means that some cancers cause PM or DM.

What are the symptoms?

PM or DM can begin suddenly or slowly. Symptoms may include:

• weakness, especially in the hips, thighs, upper arms, and shoulders
• muscle and joint pain
• weight loss
• tiredness
• fever
• tremors of the hands
• shortness of breath, even at rest
• problems swallowing

If you have dermatomyositis, you may also have a purple or dark red rash.

How are these diseases diagnosed?

Your healthcare provider will ask about your medical history and your symptoms and examine you. Tests may include:

• Removal of a small sample of muscle to check for inflammation (a biopsy).
• An electromyogram (EMG) to check your muscle strength and function.
• Blood tests to check for
  • certain enzymes that are a sign of damaged muscle
  • substances called autoantibodies that can help your provider know how to treat your symptoms
• MRI scans of muscles to see the pattern and extent of damage

You may have tests for other problems that can cause muscle weakness or muscle pain. For example, low thyroid hormone over a long time can cause muscle weakness, and some drugs can cause muscle pain.

How are they treated?

There is no known cure for PM or DM. Treatment might include:

• Physical therapy to prevent more weakness.
• Treatment for other symptoms, such as shortness of breath or pain.
• Prednisone or other anti-inflammatory drugs. These drugs work better for some people than for others. If more treatment is needed, powerful drugs that interfere with the body's immune system may be used. These more powerful drugs must be used very carefully.

You may need to see a specialist in diseases of connective tissue (a rheumatologist).

How long will the effects last?

It is difficult to predict the course of this disease. You might:

• have a severe attack and then do well
• have ongoing flare-ups of the disease, but not much worsening of your symptoms
• have trouble with your breathing or heart caused by the disease

If the inflammation affects the heart muscle, it can weaken your heart. Then it is hard for the heart to squeeze well, and congestive heart failure may develop. This means that fluid is building up in the lungs and other body tissues. The disease also may cause heart rhythm problems and a very fast heart rate. Inflammation of the sac that surrounds the heart may cause some fluid buildup inside the sac (a problem called pericarditis or pericardial effusion).

If the inflammation affects your heart or the lungs, causing lots of shortness of breath, you will need to work very closely with your healthcare provider to manage your disease.

How can I help take care of myself?

• Carefully follow your healthcare provider’s instructions for any medicines you are taking or other treatments.
• Regular exercise and physical therapy can help prevent loss of the flexibility of your skin and muscles.
• Do what you can to keep your bones healthy. If you are taking steroid medicine, such as prednisone, it can weaken your bones. Check with your healthcare provider about taking calcium and vitamin D supplements. You may need other medicines, such as alendronate, to help prevent loss of bone (osteoporosis).
• Dermatomyositis and polymyositis can increase the risk of several types of cancer. Be sure you stay up to date on all recommended cancer screening tests, such as mammograms for breast cancer screening and colonoscopy for colon cancer screening.
• Avoid being out in the sun a lot.
• Watch for signs of infection. Medicines like prednisone can suppress the immune system and make easier for you to have infections. Call your healthcare provider if you have high fever, shaking chills, or other symptoms of infection.
• Call your provider right away if you have shortness of breath and trouble swallowing.