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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. It can make even simple movements hard to do. Polymyositis is a 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 age 18. Experts think that polymyositis may be linked 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 medicine may lead to an allergic response that causes muscle irritation and damage. In most cases, healthcare 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 affect 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.

The common symptoms of polymyositis include:

  • Muscle pain and stiffness

  • Muscle weakness, particularly in the belly (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 health history and a physical exam. The exam will include seeing how strong your muscles are. You may need tests, such as:

  • Blood tests. These are done to look for signs of muscle inflammation. They also check for abnormal proteins that form in an autoimmune disease.

  • Electromyelogram (EMG). This test 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 looked at 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 known 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 don't work as well. Treatments include:

  • Anti-inflammatory medicines. These are steroid medicines or corticosteroids. They ease inflammation in the body. Symptoms usually get better within 4 to 6 weeks. Your healthcare provider may lower the dose of steroids after that to ease side effects. Some people may need to take steroids ongoing to manage the disease and reduce symptoms.

  • Immunosuppressive medicines. These are medicines that block or slow down your body's immune system.

  • Physical therapy. This treatment includes special exercises that help to stretch and strengthen the muscles. They can help keep muscles from shrinking.

  • Heat therapy and rest. These can help ease muscle symptoms.

  • Braces or other special devices. These can help to support muscles and help with movement.

Talk with your healthcare provider about the risks, benefits, and possible side effects of all medicines.

What are possible 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 digestive tract and chest wall are affected, you may have problems breathing (respiratory failure), malnutrition, and weight loss. Polymyositis that is treated but can't be managed well can cause severe disability. It can lead to an inability to swallow or breathe without help.

Can polymyositis be prevented?

There is no known way to prevent polymyositis because the exact cause is not known. In some cases where medicines may be to blame, stopping these medicines can prevent future episodes of the condition. Don't stop taking any medicine without your healthcare provider's approval.

When should I call my healthcare provider?

If your symptoms get worse or you notice new symptoms, call your healthcare provider.

If you have trouble breathing or can't swallow normally, call 911. You may need emergency medical help.

Key points about polymyositis

  • Polymyositis causes muscles to become irritated and inflamed. The muscles start to become weak, making even simple movements hard to do.

  • The condition can affect swallowing and breathing.

  • Although polymyositis can't be cured, its symptoms can be managed.

Next steps

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

  • Know the reason for your visit and what you want to happen.

  • 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 name of a new diagnosis and any new medicines, treatments, or tests. Also write down any new directions your provider gives you.

  • Know why a new medicine or treatment is prescribed and how it will help you. Also know what the side effects are.

  • Ask if your condition can be treated in other ways.

  • Know why a test or procedure is recommended and what the results could mean.

  • Know what to expect if you do not take the medicine or have the test or procedure.

  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.

  • Know how you can contact your healthcare provider if you have questions.

Online Medical Reviewer: Dan Brennan MD
Online Medical Reviewer: Diane Horowitz MD
Online Medical Reviewer: Raymond Kent Turley BSN MSN RN
Date Last Reviewed: 7/1/2023
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