Inflammatory Myopathies

father and son fishing

Fast Facts

  • Polymyositis and dermatomyositis occur in about one person per 100,000.
  • All ages can get these diseases.
  • Weakness in the large muscles around the neck, shoulders and hips.
  • Myopathy almost always causes loss of muscle strength.
  • Some patients also have rashes or breathing problems, or both.
  • Treatment is most often effective. Following your doctor’s treatment plan is key to having a good outcome.

The two inflammatory myopathies include polymyositis and dermatomyositis. Muscle inflammation and weakness occur in both conditions while patients with dermatomyositis also have a rash. Proper diagnosis and treatment raise the chance of living life fully despite this illness.

What are myopathies?

Myopathy is the medical term for muscle disease. Some muscle diseases occur when the body's immune system attacks muscles. The result is misdirected inflammation, hence the name inflammatory myopathies. This damages muscle tissue and makes muscles weak. 

People with inflammatory myopathies may have these features:

  • Weakness in the large muscles around the neck, shoulders and hips
  • Trouble climbing stairs, getting up from a seat, or reaching for objects overhead
  • Little, if any, pain in the muscles
  • Choking while eating or aspiration (intake) of food into the lungs
  • Shortness of breath and cough

The inflammatory myopathies include polymyositis and dermatomyositis. Muscle inflammation and weakness occur in both conditions while patients with dermatomyositis also have a rash. This rash of dermatomyositis most often appears as purple or red spots on the upper eyelids or as scaly, red bumps over the knuckles, elbows or knees. Children with the disease also may have white calcium deposits in the skin called calcinosis.

Sometimes patients can have the rash with no sign of muscle disease. Doctors call this form of the disease amyopathic dermatomyositis. People with dermatomyositis may also have lung inflammation that causes cough and shortness of breath. Children with the disease may have an inflammation of the blood vessels (vasculitis) that can result in skin lesions.

What causes myopathies and who gets them?

There are many causes of muscle disease other than inflammation. They include infection, muscle injury due to medicine, inherited diseases that affect muscle function, disorders of electrolyte levels, and thyroid disease. It is unknown what causes inflammatory myopathies. A top theory is that something goes wrong in the immune system, which leads to attack of the “self” and muscle inflammation.

Inflammatory myopathies are rare. Polymyositis and dermatomyositis occur in about one person per 100,000.

All ages can get these diseases. The peak time to get them, though, is ages 5 to 10 in children, and 40 to 50 in adults. Women get inflammatory myopathies about twice as often as men. These diseases affect all ethnic groups. No one can predict who will get an inflammatory myopathy.

How are myopathies diagnosed?

A doctor suspects myopathy when patients complain of trouble doing tasks that require muscle strength, or when they get certain rashes or breathing problems. Most people with myopathy have little or no pain in their muscles. A doctor will do a muscle strength exam to find if true muscle weakness is present. The following test may then be needed:

  • A blood test to measure the level of various muscle enzymes and myositis-specific antibodies
  • An electromyogram - often referred to as an EMG - to gauge electrical activity in muscle
  • A biopsy of a weak muscle (a small piece of muscle tissue is removed for testing)
  • Magnetic resonance imaging - more often called MRI - to try to show abnormal muscle

In adults, dermatomyositis and, to a much lesser extent, polymyositis at times may be linked to cancer. Therefore, all adults with these diseases should have tests to rule out cancer.

How are myopathies treated?

Corticosteroids: Often, the first treatment is an oral (by mouth) corticosteroid, such as prednisone, at a high dose. This reduces inflammation. Blood muscle enzymes tend to return to normal about 4 - 6 weeks after treatment starts. Most patients regain muscle strength in 2−3 months. The side effects of corticosteroids include weight gain and redistribution of body fat, thinning of the skin, osteoporosis, and cataracts. Even muscle weakness can be a side effect. Because patients taking prednisone are at risk for osteoporosis, they should receive proper treatment to prevent it.

Disease Modifying Antirheumatic Drugs (DMARDs) Your doctor likely will add another drug to your treatment plan: methotrexate or azathioprine. This gives better long-range control of the disease and helps avoid long-term side effects of corticosteroids. Patients whose disease is severe or who do not respond to standard treatment have other options. They include intravenous immunoglobulin - sometimes referred to as IVIg, cyclosporine (Neoral,Sandimmune), tacrolimus (Prograf), mycophenolate mofetil (CellCept), and rituximab (Rituxan).

Physical therapy: Physical therapy can help patients with muscle disease lead active lives. Physical therapy and exercise are important in the treatment of muscle disease.

Living with myopathy

Myopathies are chronic (long-term) diseases. To help control your illness, it is important to practice good health measures. Eat a healthy, well-balanced diet, exercise and try to keep a healthy weight.

If you have a dermatomyositis rash, protect yourself from the sun. This is because the rash gets worse after sun exposure, for reasons that are not clear. Therefore, limit time outdoors, and put on sunscreen when you go outside.

If you have trouble swallowing, eat soft or semisolid foods, or puree your solid foods. To prevent choking if you are bedbound, you should be seated up in bed to eat.

People with myopathy may look healthy and normal. It is important for employers, teachers and family members to understand the limits that muscle weakness causes in people with myopathy.

Updated March 2017 by Ziv Paz, MD and reviewed by the American College of Rheumatology Committee on Communications and Marketing.

This information is provided for general education only. Individuals should consult a qualified health care provider for professional medical advice, diagnosis and treatment of a medical or health condition.

© 2017 American College of Rheumatology