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Polymyositis

By Jonas Wilson, Ing. Med.

Myositis is inflammation of the muscle and polymyositis denotes that that inflammation affects not one, but many muscles.

Polymyositis is a fairly uncommon condition that leads to increasing weakness of the skeletal muscles (those muscles involved in movement) and it can affect the body bilaterally (on both sides).

People with this inflammatory disease usually find it difficult to do basic everyday maneuvers such as rising from a seated position, climbing stairs or lifting objects overhead.

Polymyositis is characterized by:

  • Progressive muscle weakness that usually starts in those muscles closest to the body’s trunk (i.e. proximal muscles).
  • Difficulty in swallowing and speaking (dysphagia and dysarthria, respectively)
  • Shortness of breath
  • Heart beat irregularities
  • Arthritis

In some cases as the disease progresses, the muscles that are furthest away from the trunk of the body (i.e. distal muscles), such as those in the forearms and ankles, may become affected. Furthermore, patients may have other symptoms including but not limited to a low-grade fever and peripheral adenopathy (enlargement of lymph nodes).

Pathophysiology

The cause of polymyositis has not been identified yet. However, it is speculated that it may be linked to viral agents and autoimmune factors.

Cytotoxic T cells with an unknown autoantigen mediate the inflammatory process seen in the muscles of patients with polymyositis. It is also believed that cancer may be a potential trigger for the condition through an immune pathway that involves attacking the cancer cells as well as the muscles.

Polymyositis is most commonly seen to affect adults between their third and fifth decades of life. Moreover, it is more prevalent women as opposed to men and in blacks than in white.

Associated Conditions

Associated conditions include infectious diseases, such as HIV-AIDS and collagen-vascular or autoimmune disorders (e.g. lupus). Polymyositis and its other associated muscles diseases tend to increase the risk of developing cancer.

Factors that contribute to this increase incidence of cancer include:

  • Male sex
  • Older age
  • Cutaneous necrosis
  • Vasculitis
  • Elevated inflammatory markers in blood such as ESR, CRP and CK.

Arthritis and Raynaud’s syndrome are also contributing factors that increase one’s chance of developing a malignancy.  The specific malignancies associated with polymyositis are lung cancer, nasopharyngeal cancer and non-Hodgkins lymphoma.

Treatment and prognosis

Polymyositis has no cure. However, there are several available treatment options for the symptoms. These are not just limited to pharmacotherapy, but include physical and heat therapy as well as exercise and the use of assistive devices. The homestay of treatment for polymyositis is systemic corticosteroid drugs such as prednisolone.

Immunosuppressive agents, for example methotrexate, may also be used to reduce inflammation. Intravenous immunoglobulins have also been used to help alleviate the symptoms. Heat therapy involves the use of ultrasound and microwaves, while physical therapy is generally recommended to avoid muscles wasting away due to inactivity.

Most patients tend to respond very well to the current therapies used; however, response varies across the board and those with severe disease presentation have a bad prognosis. Although rare, patients with severe disease may develop pneumonia and respiratory failure.

Therapy aims at improving muscle strength and function and thereby enabling a good quality of life. Current research being done on polymyositis is exploring the possibility of targeting gene expression and is also looking into the role of viral infection in the development of the condition.

Reviewed by BPharm

Further Reading

    Last Updated: Jun 8, 2016

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