Polymyositis is a disease of the muscles. It usually affects the muscles closest to the trunk of the body. However, it may affect muscles anywhere in the body. The muscles become inflamed or swollen. This causes pain. The disease is progressive and starts slowly. If untreated, the muscles gradually become weaker. The pain in the muscles also increases.

Front Muscles of Trunk

Trunk Core Muscles
© 2009 Nucleus Medical Art, Inc.

This rare disease is believed to be an autoimmune disorder. Your immune system is your body’s defense system. It fights diseases and infections. In this case your immune system attacks your own muscle tissue by mistake.

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


The cause 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

Risk Factors

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. They may be caused by other, less serious, health conditions. If you experience any one of them, see your doctor.

Symptoms include:

  • General weakness (lethargy)
  • Weakness in the muscles of the hips and shoulders—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


This diagnosis is not easy. Symptoms vary from person to person. It is often a matter of ruling out other diseases and conditions. Your doctor will ask about your symptoms and medical history. A physical exam will be done.

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. Treatment can improve your muscle strength and function. Talk with your doctor about the best plan for you. Treatment options include the following:


  • Corticosteroids—taken by mouth to reduce inflammation of the muscles (often the first medications used)
  • Immunosuppressants—nonsteroidal anti-inflammatory drugs (NSAIDS)


Exercising your muscles is vital and may include:

  • A regular stretching routine for weakened arms and legs
  • Light strengthening as the pain lessens and function returns
  • Physical therapy—to prevent permanent muscle damage


  • Your doctor may also suggest whirlpool baths, heat, and massages
  • It is important to get enough rest:
    • Take frequent breaks
    • Limit your activity when needed


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