Polymyositis and Dermatomyositis

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KEY POINTS

• Polymyositis and dermatomyositis are rare muscle diseases that cause muscle swelling and irritation, weakness, rashes and pain.
• The most common treatment is steroid medicine to control inflammation and pain.
• Treatment may also include physical therapy and treatment for other symptoms.

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What are polymyositis and dermatomyositis?

Polymyositis and dermatomyositis are rare muscle diseases. Polymyositis (PM) causes muscle inflammation (swelling and irritation) and weakness.

Dermatomyositis (DM) causes inflammation of muscles and blood vessels and can also cause a rash. It’s hard to predict the course of these diseases. You might:

• Have a severe attack and then do well for months or years
• Have frequent flare-ups of the disease but your symptoms don’t get much worse over time

Sometimes these diseases can make the heart muscle weak. Then it is hard for your heart to pump well, and fluid may build up in your lungs and other body tissues. These diseases also may cause heart rhythm problems and a very fast heart rate. If your breathing muscles are affected, you may have lung problems, including pneumonia.

What is the cause?

The exact cause is not known. PM or DM may happen when your body’s immune system attacks your own tissues. Both PM and DM are most common in adults 50 to 70 years old and children 5 to 15 years old. It is more common in women than men and is more common in African Americans.

What are the symptoms?

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

• Weakness, especially in your 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. The rash is most common around the eyes, on joints (knuckles, elbows, knees), and on the upper body.

How is it diagnosed?

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

• Blood tests
• An EMG (also called an electromyogram), which uses needles passed through your skin to send mild electric signals and check how your nerves and muscles respond
• MRI scan, which uses a strong magnetic field and radio waves to show detailed pictures of the affected muscles
• Biopsy, which is the removal of a tiny sample of tissue for testing

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

How is it treated?

There is no known cure for PM or DM. The most common treatment is steroid medicine to control symptoms such as inflammation or pain, and muscle weakness. Using a steroid for a long time can have serious side effects. Take steroid medicine exactly as your healthcare provider prescribes. Don’t take more or less of it than prescribed by your provider and don’t take it longer than prescribed. Don’t stop taking a steroid without your provider's approval. You may have to lower your dosage slowly before stopping it.

If more treatment is needed, you may be prescribed medicine that keeps your body's immune system from attacking your skin and muscles.

Treatment may also include

• Physical therapy to help keep your muscles from getting weaker.
• Treatment for other symptoms, such as shortness of breath or pain
• You may need to see a specialist called a rheumatologist, who treats diseases of the immune system.

How can I help take care of myself?

• Follow the full course of treatment prescribed by your healthcare provider.
• Be sure you get all recommended cancer screening tests, such as mammograms for breast cancer screening and colonoscopy for colon cancer screening. DM and PM can increase the risk of several types of cancer.
• Get regular exercise and physical therapy to help prevent the weakness and loss of the flexibility of your skin and muscles.
• Do what you can to keep your bones healthy. If you are taking steroid medicine, it can weaken your bones. Check with your healthcare provider about taking calcium and vitamin D supplements. You may need other medicines to help prevent loss of bone (osteoporosis).
• Avoid being out in the sun a lot. It could worsen skin symptoms. Ask your health care provider which sunscreen you should use.
• Watch for signs of infection: warmth, redness, swelling, tenderness.
• Ask your provider:
  • How and when you will get your test results
  • How long it will take to recover
  • If there are activities you should avoid and when you can return to your normal activities
  • How to take care of yourself at home
  • What symptoms or problems you should watch for and what to do if you have them
• Make sure you know when you should come back for a checkup.