Department of Pediatrics

Polymyositis is a progressive disease of the muscles. It usually affects the muscles closest to the trunk of the body (called proximal muscles), but it may affect muscles anywhere in the body. These muscles become inflamed or swollen and cause discomfort. The disease starts slowly, and if untreated, gradually the muscles become weaker and weaker and pain in the muscles increases.

Front Muscles of Trunk  

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This rare disease is believed to be an autoimmune disorder. Your immune system is your body’s defense system. It fights diseases and infections. An autoimmune disease is a condition in which your body's immune system mistakenly attacks your own body. With polymyositis, your immune system attacks your own healthy muscle tissue.

The sooner the disease is treated, the more favorable the outcome. If you suspect you have this condition, contact your doctor.

The cause of polymyositis is unknown. Factors that may contribute to polymyositis include:

• Genetics
• A virus that sets off the condition
• A reaction to certain drugs that set off the condition

A risk factor is something that increases your chance of getting a disease or condition.

The following factors increase your chance of developing polymyositis:

• Age: 50-70 years old
• Sex: women are more likely to develop polymyositis than men

If you experience any of these symptoms, do not assume it is due to polymyositis. These symptoms are quite common and may be caused by other, less serious, health conditions. If you experience any one of them, see your physician.

Symptoms include:

• General weakness (lethargy)
• Weakness in the muscles of the hips and shoulders that occurs slowly and gradually over a period of weeks or even months
  • This gradual muscle weakness is often the first sign of the disease
• Achy, tender muscles
• Weight loss
• Fatigue after standing or walking
• Trouble rising from a chair
• Great effort needed to climb stairs
• Struggle to lift objects
• Difficulty reaching overhead (eg, unable to comb your hair)
• Trouble with swallowing (when muscles in the front of the neck and throat become involved)–rare
• Difficulty breathing (if it affects the lungs or chest muscles)–quite rare

Polymyositis is not easy to diagnose because the symptoms vary from person-to-person. It is often a matter of ruling out other diseases and conditions to arrive at the diagnosis. Your doctor will ask about your symptoms and medical history, and perform a physical exam.

Tests may include the following:

• Blood test—to check for autoantibodies (antibodies that attack parts of your body)
• Creatine kinase test—blood test that looks for elevated levels of muscle proteins or enzymes called creatine kinase (CK) (when a muscle is damaged, CK is released into the bloodstream)
• Aldolase test—a blood test that looks for elevated levels of aldolase (a substance released into the bloodstream when a muscle is damaged)
• Electromyogram (EMG) —measures activity of your muscles, often used to help find causes of muscle weakness or damage
• Muscle biopsy —a small piece of muscle tissue is removed and examined to see if the muscle is damaged in some way
• Magnetic resonance imaging (MRI) —noninvasive scan, using magnetic waves, of your muscles to see if any muscles are inflamed

There is no cure for polymyositis, but treatment can improve your muscle strength and function. Talk with your doctor about the best treatment plan for you. Treatment options include the following:

• Corticosteroids—These medications, taken orally, reduce inflammation of the muscles. These are often the first medications doctors use to treat the symptoms of polymyositis.
• Immunosuppressants—nonsteroidal anti-inflammatory drugs (NSAIDS)
• Exercise—exercising your muscles is essential, which includes a regular stretching routine for muscles in weakened arms and legs. Light strengthening exercises can be done as the pain lessens and function returns.
  • Physical therapy may be recommended by your physician to prevent permanent muscle damage.
  • Your doctor may also suggest whirlpool baths, heat, and massages for treating muscles.
• Rest—to manage your condition, it is important to get enough rest by taking frequent breaks and limiting your activity.

There is nothing that you can do to prevent developing polymyositis.