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What is polymyositis?

Polymyositis is a disease that causes muscles to become irritated and inflamed. The muscles eventually start to break down and become weak. The condition can affect muscles all over the body. This can make even simple movements difficult. Polymyositis is one disease in a group of diseases called inflammatory myopathies.

What causes polymyositis?

The exact cause of polymyositis is not known. It most often happens in people ages 31 to 60. It rarely occurs in people younger than 18. Experts think that polymyositis may be related to or triggered by a virus or an autoimmune reaction. An autoimmune reaction is when the body attacks its own tissues. In some cases, a medication may lead to an allergic response that causes muscle irritation and damage. But in most cases, health care providers aren’t able to find the exact cause of the condition.

What are the symptoms of polymyositis?

The condition affects muscles all over the body, and can impair more than the ability to run, walk, or lift objects. It can also affect the muscles that allow you to eat and breathe. The muscles that are closest to the center of the body tend to be affected the most often. These are known as proximal muscles.

The common symptoms of polymyositis include:

  • Muscle pain and stiffness
  • Muscle weakness, particularly in the abdomen, shoulders, upper arms, and hips
  • Joint pain and stiffness
  • Trouble catching your breath
  • Problems with swallowing
  • Irregular heart rhythms, if the heart muscle becomes inflamed

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

Weight loss and poor nutrition may become a problem if muscle weakness leads to trouble eating and swallowing.

How is polymyositis diagnosed?

The process starts with a medical history and a physical exam. The exam will include seeing how strong your muscles are. Tests may also be done, such as:

  • Blood tests. These are done to look for signs of muscle inflammation. They also check for abnormal proteins that form in autoimmune disease.
  • Electromyelogram (EMG). This may be done to find abnormal electrical activity in affected muscles.
  • MRI. This test uses large magnets and a computer to look for inflammation in the body.
  • Muscle biopsy. Tiny pieces of tissue are taken to be checked with a microscope.

How is polymyositis treated?

Treatment will depend on your symptoms, your age, and your general health. It will also depend on how severe the condition is. There's no cure for polymyositis, but the symptoms can be managed. You may need more than one kind of treatment. And your treatment may need to be changed over time. In severe cases, some treatments are not as effective. Treatments include:

  • Anti-inflammatory medications. These are steroid drugs, or corticosteroids. They ease inflammation in the body. Symptoms usually get better within 4 to 6 weeks. Your health care provider may lower the dose of steroids after that to lessen side effects. Some people may need to take steroids ongoing to manage the disease and reduce symptoms.
  • Immunosuppressive drugs. These are drugs that block or slow down your body's immune system.
  • Physical therapy. Special exercises help to stretch and strengthen the muscles. These can help keep muscles from shrinking.
  • Heat therapy and rest. These can help lessen muscle symptoms.
  • Braces or other special devices. These can help to support muscles and help with movement.

Talk with your health care providers about the risks, benefits, and possible side effects of all medications.

What are the complications of polymyositis?

If polymyositis is not treated, it can lead to severe complications. As the muscles become weaker, you may fall often and be limited in your daily activities. If the muscles in the GI tract and chest wall are affected, you have respiratory failure, malnutrition, and weight loss. Polymyositis that is treated but can't be managed well can cause in severe disability. This includes an inability to swallow or breathe without help.

Can polymyositis be prevented?

There is no known way to prevent polymyositis, as the exact cause is not known. In some cases where medications may be to blame, avoiding these medications can prevent future episodes of the condition.

When should I call my health care provider?

If your symptoms get worse or you notice new symptoms, notify your health care provider. If you have trouble breathing or can't swallow normally, you may need emergency medical help.

Key points

  • Polymyositis causes muscles to become irritated and inflamed. The muscles start to become weak. This can make even simple movements difficult.
  • The condition can affect swallowing and breathing.
  • Although it can't be cured, the symptoms of polymyositis can be managed.

Next steps

Tips to help you get the most from a visit to your health care provider:

  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.
Online Medical Reviewer: Foster, Sara, RN, MPH
Online Medical Reviewer: Freeborn, Donna, PhD, CNM, FNP
Date Last Reviewed: 1/30/2014
© 2000-2016 The StayWell Company, LLC. 780 Township Line Road, Yardley, PA 19067. All rights reserved. This information is not intended as a substitute for professional medical care. Always follow your healthcare professional's instructions.