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Disease Profile


Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

1-9 / 100 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.


Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable



Connective tissue diseases


Polymyositis is a type of inflammatory myopathy, which refers to a group of muscle diseases characterized by chronic muscle inflammation and weakness. The muscles affected by polymyositis are the skeletal muscles (those involved with making movements) on both sides of the body. Although the disease can affect people of all ages, most cases are seen in adults between the ages of 31 and 60 years. The disease is more common among women and among black individuals.[1] 

The exact cause of polymyositis is unknown. The disease shares many characteristics with autoimmune disorders, which occur when the immune system mistakenly attacks healthy body tissues. In some cases, the disease may be associated with viral infectionsconnective tissue disorders, or an increased risk for malignancies (cancer). Diagnosis is based on a clinical examination that may include laboratory tests, imaging studies, electromyography, and a muscle biopsy.[2] Although there is no cure for polymyositis, treatment with corticosteroids or immunosuppressants can improve muscle strength and function.[1][2]


Polymyositis is characterized by chronic muscle inflammation and weakness involving the skeletal muscles (those involved with making movements) on both sides of the body.[1] Weakness generally starts in the proximal muscles (those closest to the chest and abdomen, such as muscles of the upper arm and shoulder and the upper leg and hip). The symptoms of polymyositis may continue to worsen from the time the disease presents over a period of weeks or months. The muscle weakness can cause difficulties climbing stairs, rising from a seated position, lifting objects, or reaching overhead.[1] In some cases, the distal muscles (those further away from the chest and abdomen including the lower arms, hands, lower legs, and feet) may also be affected as the disease progresses.[1]

Other symptoms of polymyositis include arthritisshortness of breath, difficulty swallowing and speaking, mild joint or muscle tenderness, fatigue, and heart arrhythmias. People with polymyositis may have an increased risk to develop cancer.[1][2] 


The exact cause of polymyositis is unknown. The disease is thought to be related to problems with the immune system, and the disease shares many similarities with autoimmune diseases. An autoimmune disease occurs when the immune system mistakenly attacks healthy body tissues. It appears that the cells of the muscles (muscle fibers) of individuals with polymyositis are not protected from the body’s immune system. Therefore, the immune system can attack the muscle fibers, which causes them to become damaged, inflamed, and weakened.[2] 

For some people, symptoms of polymyositis may be associated with connective tissue disordersviral infections such as HIV-AIDS, other autoimmune diseases, or diseases that affect the ability to breathe.[2][3][4] This means that individuals who have any of these diseases are at a higher risk to develop polymyositis.[1][2]


A diagnosis of polymyositis is often suspected in people with proximal muscle weakness and other signs and symptoms associated with the disease. Additional testing can then be ordered to confirm the diagnosis and rule out other diseases that may cause similar features. The testing may include:[2][5][6]


The treatment of polymyositis is based on the signs and symptoms present in each person. Although there is currently no cure, symptoms of the disease may be managed with the following:[2][7]

  • Medications such as corticosteroids, corticosteroid-sparing agents, or immunosuppressive drugs
  • Physical therapy to improve muscle strength and flexibility
  • Speech therapy to address difficulties with swallowing and speech
  • Intravenous immunoglobulin: an infusion of healthy antibodies that are given to block damaging autoantibodies that attack the muscle

Mescape Reference offers more specific information regarding the diagnosis and treatment of polymyositis.


Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

Organizations Supporting this Disease

    Organizations Providing General Support

      Learn more

      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      Where to Start

      • The Mayo Clinic Web site provides further information on Polymyositis.
      • MedlinePlus was designed by the National Library of Medicine to help you research your health questions, and it provides more information about this topic.
      • The National Institute of Neurological Disorders and Stroke (NINDS) collects and disseminates research information related to neurological disorders. Click on the link to view information on this topic.

        In-Depth Information

        • Medscape Reference provides information on this topic. You may need to register to view the medical textbook, but registration is free.
        • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
        • PubMed is a searchable database of medical literature and lists journal articles that discuss Polymyositis. Click on the link to view a sample search on this topic.


          1. Polymyositis Information Page. National Institute of Neurological Disorders and Stroke (NINDS). 2018; https://www.ninds.nih.gov/Disorders/All-Disorders/Polymyositis-Information-Page.
          2. Pappu R & Seetharaman M. Polymyositis. Medscape Reference. February 12, 2018; https://emedicine.medscape.com/article/335925-overview.
          3. Bhansing KJ, Vonk-Noordegraaf A, Oosterveer FPT, van Riel PLCM, and Vonk MC. Pulmonary arterial hypertension, a novelty in idiopathic inflammatory myopathies: insights and first experiences with vasoactive therapy. RMD Open. 2017; 3(1):https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5574416/.
          4. Svensson J, Holmgvist M, Lundberg IE, and Arkema EV. Infections and respiratory tract disease as risk factors for idiopathic inflammatory myopathies: a population-based case-control study. Annals of the Rheumatic Diseases. August 30, 2017; https://www.ncbi.nlm.nih.gov/pubmed/28855175.
          5. Miller ML. Diagnosis and differential diagnosis of dermatomyositis and polymyositis in adults. UpToDate. September 18, 2016; https://www.uptodate.com/contents/diagnosis-and-differential-diagnosis-of-dermatomyositis-and-polymyositis-in-adults.
          6. Burlina P, Billings S, and Albayda J. Automated diagnosis of myositis from muscle ultrasound: Exploring the use of machine learning and deep learning methods. PLoS One. August 30, 2017; 12(8):https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0184059.
          7. Miller ML. Initial treatment of dermatomyositis and polymyositis in adults. UpToDate. June 13, 2017; https://www.uptodate.com/contents/topic.do?topicKey=RHEUM/5160.
          8. Polymyositis (PM). Muscular Dystrophy Association. https://www.mda.org/disease/polymyositis. Accessed 9/17/2017.
          9. Hajj-ali RA. Polymyositis and Dermatomyositis. Merck Manual. June 2013; https://www.merckmanuals.com/home/bone,-joint,-and-muscle-disorders/autoimmune-disorders-of-connective-tissue/polymyositis-and-dermatomyositis.

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