Polymyositis is a disease that causes the skeletal muscles—the muscles that allow your body to move—to become irritated and inflamed. The muscles eventually start to break down and become weak, making even simple movements difficult.

Polymyositis is just one disease in a larger group of similar diseases called inflammatory myopathies. It can affect muscles all over the body.

Another type of myositis, or skeletal muscle inflammation, is called dermatomyositis. Dermatomyositis is a condition that also leads to muscle weakness, but it's also accompanied by a characteristic skin rash.

Facts about polymyositis

Polymyositis rarely strikes people younger than 18. Most of the time, it affects people who are 31 to 60 years old. Experts think that polymyositis is probably related to or triggered by a viral infection or an autoimmune reaction—a response that causes the body to attack its own tissues. In some cases, certain medications may lead to an allergic response that cause muscle irritation and damage. Most of the time, however, doctors aren’t able to uncover the exact cause of polymyositis.

Because polymyositis affects muscles all over the body, it can impair more than the ability to run, walk, or lift objects. It can also affect the muscles that allow you to eat and even breathe.

Some people with polymyositis are able to control their symptoms with medical therapy. In more severe cases, treatment usually isn't as effective. Polymyositis that can't be managed well with treatment can result in severe disabilities—including frequent falls and an inability to swallow or breathe independently.


The muscles that are closest to the center of the body, known as proximal muscles, tend to be affected by polymyositis the most often.

These are common symptoms of polymyositis:

  • Muscle pain and stiffness

  • Muscle weakness—particularly in the abdominal area, shoulders, upper arms, and hips

  • Joint pain and stiffness

  • Difficulty catching your breath

  • Problems with swallowing

  • Irregular heart rhythms, which may develop if the heart muscle becomes inflamed

Polymyositis can make it difficult to do everyday things. You may notice trouble walking up a flight of stairs, lifting up your arms, or even getting out of your chair. As inflammation worsens and extends throughout the body, pain and weakness may affect the ankles, wrists, and lower arm area.

Weight loss and poor nutrition may become a problem as well, if muscle weakness leads to difficulty eating and swallowing.


Your doctor may run a number of different tests to diagnose polymyositis. Elevated muscle protein levels in the blood reflect muscle irritation and can help to establish the diagnosis of polymyositis.

A physical exam and special tests to determine how strong your muscles are can also be helpful.

Polymyositis can also be diagnosed with the help of these tests:

  • MRI scan to help determine whether muscles are inflamed

  • Biopsy of muscle tissue

  • Electromyography, which tests muscle strength and function by examining its electrical activity


Polymyositis can't be cured, but treatments can manage symptoms. Corticosteroid drugs are the primary treatment for polymyositis. Symptoms usually get better within four or six weeks, and your doctor will usually start to cut down on the steroids after that to minimize possible side effects. Some people may need to take steroids permanently to manage the disease and keep symptoms at bay. Steroid medications aren't always effective though. In some instances, a doctor may prescribe special drugs that blunt the immune system and help reduce the inflammation associated with polymyositis.

Physical therapy and regular exercise can also help treat polymyositis and treat symptoms. These approaches can help keep muscles from shrinking, or becoming atrophied, and can help maintain your strength. Using heat therapy on the muscles and taking some time to rest can also help symptoms improve. You may also be able to wear braces or other special devices to help manage polymyositis.

Calling the doctor

If you notice difficulty doing tasks that used to be easy for you, such as getting up from a chair, climbing stairs, or carrying light groceries, you should schedule an appointment with your doctor to find out what could be wrong. If you experience trouble breathing or can't swallow normally, you may need emergency medical attention.


In general, there is no known way to prevent polymyositis, as the exact cause is unknown. In some cases where medications may be to blame, though, avoiding these medications can prevent future episodes of polymyositis.


Serious complications can arise from untreated polymyositis. As the muscles become weaker, you may fall more often and may be limited in your daily activities. You may also lose weight and develop malnutrition and respiratory failure if the muscles in the digestive tract and chest wall are affected by the disease.

Key points to remember

Muscle weakness can be a sign of a serious health condition, including polymyositis. Although it can't be cured, many people successfully manage their polymyositis and enjoy life with few symptoms. Be sure talk with your doctor if you have any concern that you may have polymyositis.