MYOSITIS DISORDERS: POLYMYOSITIS, INCLUSION BODY MYOSITIS, AND DERMATOMYOSITIS Myositis Disorders: Polymyositis, Inclusion Body Myositis, and Dermatomyositis

be severely disabling. Weakness is generally first What is myositis? evident in the large muscles around the hips and shoulder girdle. An individual may notice difficulty Myositis is an inflammation of the in walking, rising from a chair or a bed, turning over muscle. Polymyositis, inclusion body in bed, climbing stairs and lifting his or her arms. In myositis and dermatomyositis are some cases, as the disorder progresses, the pattern of walking becomes clumsy and there is a tendency disorders characterized by inflammation to fall. Excessive fatigue may occur, especially after of the voluntary (skeletal) muscles. prolonged standing or walking. These conditions impact the muscle Within each of these disorders, the symptoms leading to weakness and in some vary widely from person to person, with respect to severity, rate of progression and complications. cases, severe disability. In polymyositis, In addition, the three disorders differ markedly in the inflammation is found in many terms of response to treatment. muscles, thus the term “poly”. As the name implies, in inclusion body myositis, What causes myositis? These conditions were initially classified together the muscle is characterized by because they all displayed muscle inflammation. abnormal inclusions – accumulations Although the cause of each of these illnesses of misfolded protein. In dermatomyositis, remains unknown, they are distinct clinical conditions. the muscle inflammation is accom- Polymyositis and inclusion body myositis show some similarities in terms of their pathological panied by a skin rash, therefore the characteristics; dermatomyositis appears to a prefix “dermato,” referring to skin. All different type of disorder altogether. three of these conditions are considered One theory is that there is an autoimmune rare. They are also known as component to these illnesses. In autoimmune disorders, the immunological mechanisms that normally provide inflammatory myopathies. protection against infection and foreign substances are disrupted and instead, attack and injure the body’s own tissues. Researchers are looking into the reasons why What are the symptoms of these disorders? this abnormal response occurs in some people. The primary symptom of these disorders is muscle These are not considered hereditary disorders in the weakness, which is usually progressive and may conventional sense. Cases usually just appear (sporadic)

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and a history of the disorder in the same family is Polymyositis may be associated with other connective unusual. However, a hereditary factor, the presence tissue disorders, vascular disorders or autoimmune of a group of genes associated with a predisposition diseases, such as lupus. Polymyositis may also be to developing an autoimmune disorder, is implicated. associated with infectious disorders, such as HIV-AIDS, Other types of autoimmune disorders may be common or with Lyme disease or toxoplasmosis. in families with a history of myositis. Although polymyositis tends to be progressive, effective treatments are available. Treatments How is the diagnosis made? include medication, physical therapy, exercise, heat In diagnosing muscle conditions, several standard tests therapy (including microwave and ultrasound), are utilized including a blood test of creatine kinase, an orthotics and other assistive devices. The usual electrical test of muscles called an electromyography, and treatment for polymyositis involves the administration a muscle biopsy. Generally speaking, the most useful of a corticosteroid drug, such as prednisone. test for diagnosis is the muscle biopsy, although it Immunosuppressant therapy, such as azathioprine is also the most invasive for the patient. Dermatomyositis and methotrexate, may be used in people who do tends to be a recognizable condition due to the not respond well to prednisone. Another type of characteristic rash. effective therapy involves periodic intravenous Polymyositis may be difficult to distinguish from infusions of antibodies (immunoglobulin) from late onset muscular dystrophy. The most useful test for donors. Response to treatment is variable. this purpose is the muscle biopsy. A biopsy showing widespread degeneration and regeneration of muscle More about Dermatomyositis fibers, extensive inflammation, and no hypertrophic In dermatomyositis, in addition to muscle weakness, a muscle fibers provides strong support for a diagnosis characteristic reddish skin rash develops, typically on of an inflammatory myopathy. The presence of one of the face (cheeks and eyelids), elbows, hands, knees and the autoimmune connective tissue diseases also helps upper chest. The entire skin may take on a reddish hue differentiate polymyositis from muscular dystrophy. In in severe cases. the diagnosis of all acutely progressive cases, viral, bacterial The onset of dermatomyositis occurs rapidly, and parasitic infections of muscle -- all of which can usually measured in weeks or months. It can occur resemble polymyositis -- must be excluded. at any age and in people of either sex. The course of The differentiation between polymyositis and dermatomyositis is often severe and rapidly progressive, inclusion body myositis can be challenging. In some sometimes involving the heart and lungs. It is often cases, a patient is diagnosed and treated for polymyositis. accompanied by degeneration of blood vessels If the patient does not respond to treatment, further (vasculitis) and with the formation of calcium investigation may lead to a re-diagnosis of inclusion deposits (calcinosis) under the skin or in the muscle. body myositis. These deposits can cause pain and infections, and may have to be surgically removed. Some cases of More about Polymyositis dermatomyositis may be accompanied by other Polymyositis is more common in females than males autoimmune disorders such as lupus, scleroderma, and usually begins after age 20. It is characterized by or vasculitis. a rapid onset of widespread muscle inflammation and A range of treatments may be used including weakness. The symptoms of polymyositis are quite medication, physical therapy, exercise, heat therapy, diverse and somewhat difficult to define. orthotics and other assistive devices. The usual

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treatment for dermatomyositis involves the admin- severely affected and require a wheelchair. Unfortunately, istration of a corticosteroid drug, such as prednisone. immunosuppressant drugs have not proved to be an Immunosuppressant therapy, such as azathioprine effective treatment for inclusion body myositis; currently, and methotrexate, may be used in people who do not there is no proven treatment. respond well to prednisone. Another type of effective therapy involves periodic intravenous infusions of What research is being done? antibodies (immunoglobulin) from donors. Muscle research is ongoing; the exact mechanisms Most cases respond to some degree, although the involved in normal muscle function are still poorly disorder tends to be more pervasive than polymyositis understood. Research on the myositis disorders focuses and usually requires ongoing treatment. on the origin, causes and course of these disorders and on improved methods of diagnosis and treatment. A More about Inclusion Body Myositis great deal of research is centered on the steps in the Inclusion body myositis usually affects men more progression of these disorders to help reveal potential than women and usually strikes after 50. Inclusion opportunities for treatment. body myositis displays the same general immune system involvement as seen in polymyositis, however, in inclusion body myositis there is also a progressive Disclaimer: deterioration of the muscle characterized by the This document is intended for general information accumulation of abnormal proteins that is not seen in and awareness. Muscular Dystrophy Canada will polymyositis. Inclusion body myositis is not generally not be held responsible for misuse of information associated with other conditions. It is a progressive or any damages incurred as a result of its use. disease, as seen by the progressive weakening of the This resource is not meant to replace consultations large skeletal muscles of the arms and legs. Approximately with your doctor or to provide medical advice, half of cases develop weakness in swallowing. However, diagnosis or treatment. For information specific the heart and lungs are not usually affected. The degree to the condition affecting you or your family, of disability varies; some remain able to walk, although please consult your physician or neurologist. require a cane for long distances. Others are more

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