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MEDICAL CONDITIONS

• What is polymyositis?
• What causes polymyositis?
• What are symptoms of polymyositis?
• How does the doctor identify polymyositis?
• How is polymyositis treated?
• Polymyositis At A Glance

What is polymyositis?

Polymyositis is a disease of muscle featuring inflammation of the muscle fibers. The cause of the disease is not known. It begins when white blood cells, the immune cells of inflammation, spontaneously invade muscles. The muscles affected are mostly those closest to the trunk or torso. This results in weakness which can be severe. It is a chronic illness with periods of increased symptoms, called flares or relapses, and decreased symptoms, known as remissions.

Polymyositis is slightly more common in females. It affects all age groups, although its onset is most common in middle childhood and in the twenties. Polymyositis occurs throughout the world. Polymyositis can be associated with skin rash and is then referred to as "dermatomyositis." It also can affect other areas of the body and is, therefore, a systemic illness. Occasionally, it is associated with cancer , or with other diseases of connective tissue (see systemic lupus erythematosus , scleroderma and rheumatoid arthritis ).

What causes polymyositis?

To date, no cause of polymyositis has been isolated by scientific researchers. There are indicators of heredity (genetic) susceptibility that can be found in some patients. There is indirect evidence of infection by a virus that has yet to be identified in a form of polymyositis that is particularly resistant to treatment, called inclusion body myositis. This form of polymyositis is diagnosed by the pathologist, a physician specialist who interprets the microscope findings of muscle tissue. The muscle tissue in this form of polymyositis displays clear areas within the muscle cells (called vacuoles) when viewed under the magnification of a microscope.

Aside from diseases with which polymyositis can be associated (as mentioned above), many other diseases and conditions can mimic polymyositis. These include nerve-muscle diseases (such as muscular dystrophies), drug toxins (such as alcohol, cocaine, steroids, colchicine, hydroxychloroquine, and cholesterol lowering drugs), metabolic disorders (where muscle cells are unable to process chemicals normally), hormone disorders (such as abnormal thyroid), calcium, and magnesium conditions), and infectious diseases (such as influenza virus, AIDS, streptococcus and Lyme bacteria, pork tapeworm and schistosomiasis).

What are symptoms of polymyositis?

Weakness of muscles is the most common symptom of polymyositis. The muscles involved usually are those that are closest to the trunk of the body. The onset can be gradual or rapid. This results in varying degrees of loss of muscle power and atrophy. The loss of strength can be noticed as difficulty getting up from chairs, climbing stairs or lifting above the shoulders. Trouble with swallowing and weakness lifting the head from the pillow can occur. Occasionally, the muscles ache and are tender to the touch (25% of patients).

Patients can also feel fatigue, a general feeling of discomfort and have weight loss and/or low-grade fever.

With skin involvement (dermatomyositis), the eyes can be surrounded by a violet discoloration with swelling. There can be scaly reddish discoloration over the knuckles, elbows and knees (Gottron's sign). There can also be reddish rash on the face, neck and upper chest. Hard lumps of calcium deposits can develop in the fatty layer of the skin, most commonly in childhood dermatomyositis.

Heart and lung involvement can lead to irregular heart rhythm and shortness of breath.

Because polymyositis can present in combination with other illnesses (see related articles on systemic lupus erythematosus, scleroderma and rheumatoid arthritis), it can also have overlap features with them. These illnesses are discussed elsewhere.

Both polymyositis and dermatomyositis can sometimes be associated with cancers, including lymphoma, breast, lung, ovarian, and colon cancer . The cancer risk is reported to be much greater with dermatomyositis than polymyositis.

How does the doctor identify polymyositis?

When a patient first sees the doctor, the recent symptoms especially concerning weakness will be discussed. The condition of many other body areas might be reviewed, for example, the skin, heart, lungs and joints. An examination will further focus on these and other systems. Various measures of strength might be noted.

Blood testing usually reveals abnormally high levels of muscle enzymes, CPK or creatinine phosphokinase, aldolase, SGOT, SGPT, and LDH. These enzymes are released into the blood by muscle that is being damaged by inflammation. They can also be used as measures of the activity of the inflammation. Other routine blood and urine tests can also look for internal organ abnormalities. Chest X-rays, mammograms, PAP smears and other screening tests might be considered.

An electromyograph (EMG) and nerve conduction velocity are electrical tests of muscle and nerves that can show abnormal findings typical of polymyositis as well as exclude other nerve-muscle diseases.

A muscle biopsy is used to confirm the presence of muscle inflammation typical only of polymyositis. This is a surgical procedure whereby muscle tissue is removed for analysis by a pathologist, a specialist in examining tissue under a microscope. Muscles often used for biopsy include the quadriceps muscle of the front of the thigh, the biceps muscle of the arm and the deltoid muscle of the shoulder.

How is polymyositis treated?

Initially, polymyositis is treated with high doses of corticosteroids. These are medications related to cortisone and can be given by mouth or intravenously. They are given because they can have a powerful effect to decrease the inflammation in the muscles. They usually are required for years and their continued use will be based on what the doctor finds related to symptoms, examination and muscle enzyme blood test.

Corticosteroids have many predictable and unpredictable side effects. In high doses they commonly cause increase in appetite and weight, puffiness of the face and easy bruising. They can also cause sweats, facial hair growth, upset stomach, sensitive emotions, leg swelling, acne , cataracts , osteoporosis , high blood pressure , worsening of diabetes and increased risk of infection. A rare complication of cortisone medications is severe bone damage (avascular necrosis) which can destroy large joints, such as the hips and shoulders. Further, abruptly stopping corticosteroids can cause flares of the disease and result in other side effects including nausea, vomiting and decreased blood pressure.

Corticosteroids do not always adequately improve polymyositis. In these patients immunosuppressive medications are considered. These medicines can be effective by suppressing the immune response which attracts the white blood cells of inflammation to the muscles. Many types are now commonly used and others are still experimental. Methotrexate can be taken by mouth (Rheumatrex, Trexall) or by injection into the body. Azathioprine (Imuran) is an oral drug. Both can cause liver and bone marrow side effects and require regular blood monitoring. Cyclophosphamide (Cytoxan), chlorambucil (Leukeran) and cyclosporine (Sandimmune) have been used for serious complications of severe disease. These also can have severe side effects which must be considered with each patient individually. Treatment with intravenous infusion of immunoglobulins (IVIG) has been shown to be effective in severe cases of polymyositis.

Physical therapy is an important part of the treatment of polymyositis. When to begin, and the continued degree of exercise and range of motion of extremities is customized for each patient.

Patients can ultimately do well, especially with early medical treatment of disease and disease flares. The disease frequently becomes inactive, and rehabilitation of atrophied muscle becomes a long- term project. As mentioned above, the form of polymyositis called inclusion body myositis is often more resistant to treatment than the usual form of disease. As scientists better define the specific causes of the different forms of polymyositis, treatment will be more accurately aimed at cure of this disease.

Polymyositis At A Glance

• Polymyositis and dermatomyositis (PM/DM) are chronic inflammatory diseases of muscle.
• Muscle weakness is the most common symptom of PM/DM.
• The cause of PM/DM is unknown.
• Diagnosis of PM/DM involves physical examination of muscle strength, blood tests for muscle enzymes, electrical tests of muscle and nerves, and confirmed by muscle biopsy.
• Treatment of PM/DM involves high doses of cortisone-related medications, immune suppression, and physical therapy.

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