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Last updated May 5, 2018

Approved by: Maulik P. Purohit MD, MPH

Polymyositis is a rare inflammatory condition which causes muscle weakness. Polymyositis is progressive and it typically worsens over time.

What are the other Names for this Condition? (Also known as/Synonyms)

  • Idiopathic Inflammatory Myopathy (due to Polymyositis)

What is Polymyositis? (Definition/Background Information)

  • Polymyositis is a rare inflammatory condition which causes muscle weakness. Polymyositis is progressive and it typically worsens over time
  • The onset of the condition most commonly occurs during middle-age, with women being affected more than men
  • The cause of Polymyositis is unknown; however, scientific research indicates that it may be caused by immune system abnormalities
  • The condition results in a progressive weakening of the muscles, difficulty bending the knees when getting up from a seated position, and trouble raising one’s head after lying down
  • The combination of these signs and symptoms form the basis of diagnosis of Polymyositis. If necessary, a tissue biopsy and blood test may be conducted
  • The treatment measures include the use of physical therapy and corticosteroids. The prognosis of Polymyositis varies, and it depends on the severity of one’s signs and symptoms

Who gets Polymyositis? (Age and Sex Distribution)

  • The estimated incidence rate of Polymyositis is one in every 250,000 cases
  • The condition typically affects adults aged 20 years or older. The onset most commonly occurs between the ages 45 and 60 years. Nevertheless, the onset can occur anytime from infancy up to the age of 80 years
  • Women have a higher rate of incidence than men, with the female-male ratio being 2:1
  • All racial and ethnic groups are affected; but, individuals of African-American heritage are at a higher risk for developing Polymyositis

What are the Risk Factors for Polymyositis? (Predisposing Factors)

There are currently no known risk factors for Polymyositis. However, the following may increase an individual's risk for the condition:

  • Individuals between the ages of 45 to 60 years seem to be at a higher risk for developing Polymyositis
  • Women seem to be at a higher risk for developing Polymyositis than men
  • Individuals of African-American descent

It is important to note that having a risk factor does not mean that one will get the condition, A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Polymyositis? (Etiology)

  • According to current scientific research, the definitive cause of Polymyositis is unknown
  • Scientific experts believe that it may be caused by an immune system dysfunction

What are the Signs and Symptoms of Polymyositis?

The signs and symptoms associated with Polymyositis may include:

  • Progressive weakness in the muscles of the hip and thigh, the upper arm, upper back, the shoulder area, and the muscles that move the neck
  • Difficulty bending the knees when getting up from a seated position, or while rising from a chair
  • Difficulty in lifting one’s head after lying down
  • Difficulty breathing; chronic dry cough
  • Difficulty swallowing (dysphagia)
  • General fatigue; tiredness

How is Polymyositis Diagnosed?

Polymyositis is diagnosed using the following tools:

  • Complete medical history and a thorough physical examination
  • Assessment of signs and symptoms
  • The following examinations may be considered to aid in the diagnosis of Polymyositis:
    • Blood analysis: To check for the levels of two muscle enzymes types - creatine phosphokinase and aldolase; as well as, to check for antibodies that attack healthy/normal cells (autoantibodies)
    • Muscle biopsy, in order to look for inflammation
    • Magnetic resonance imaging (MRI) scans to detect muscle abnormalities
    • EMG (electromyography), to record electrical impulses that control the muscles

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the Possible Complications of Polymyositis?

The potential complications due to Polymyositis include:

  • Emotional stress due to impaired mobility
  • Chronic pain due to progressive muscle weakness
  • Difficulty swallowing due to weakness in the esophageal muscles. This can lead to individuals inhaling pieces of food or liquid, which may cause aspiration pneumonia
  • Also, a difficulty in consuming food can lead to weight loss and malnutrition
  • Breathing difficulties due to weakness in the chest muscles

Additionally, the following conditions are associated with Polymyositis:

  • Congestive heart failure
  • Lung infections
  • Cancers, especially of the breast, lung, and bladder
  • Pericarditis, swelling of the thin membranes surrounding the heart

How is Polymyositis Treated?

There is no cure for Polymyositis; however, providing appropriate treatment may help in improving muscle strength. The treatment measures may include the following:

  • Corticosteroids, either oral or topical, may be given to reduce the quantity of inflammation-causing antibodies. As corticosteroids should not be taken for an extended period due to their potential side effects, the healthcare provider may later prescribe other medications to suppress the immune system
  • Physical and speech therapy to aid the individual in mobility and speech, and to compensate for muscle weakness
  • Dietetic assessment to aid the individual in selecting an appropriate diet
  • Intravenous immunoglobulin: A treatment method in which healthy antibodies are introduced into the bloodstream by infusion through a vein, to block the damaged antibodies that attack the muscles

How can Polymyositis be Prevented?

  • Presently, there are no specific methods or guidelines to prevent Polymyositis, as there is no known cause for the condition
  • Excessive exercise may increase the signs and symptoms. Consult your healthcare professional before planning an exercise schedule
  • Periodic follow-ups can help control/regulate the activity of the muscles

What is the Prognosis of Polymyositis? (Outcomes/Resolutions)

  • The prognosis of Polymyositis depends on the severity of the signs and symptoms, the response to treatment, as well as the promptness of diagnosis
  • Individuals, who respond well to treatment, have a better prognosis than individuals who do not respond well to treatment
  • Nevertheless, typically Polymyositis is a progressive condition that continues to worsen with time. Morbidity is known to be caused by cancer and/or lung complications 

Additional and Relevant Useful Information for Polymyositis:

Please visit our Rare Diseases & Disorders Health Center for more physician-approved health information:


What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

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Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: July 12, 2017
Last updated: May 5, 2018