What are myopathies?
Myopathy is the medical term for muscle disease. It is a general term meaning muscle inflammation. Myositis includes the following diseases: dermatomyositis (DM), polymyositis (PM), immune-mediated myositis, and juvenile myositis.
Who gets myopathies?
Inflammatory myopathies are considered rare diseases, with approximately one person per 100,000 developing polymyositis and dermatomyositis. All age groups are affected by these diseases, with the highest rates between ages 5-10 in children and between 40-50 in adults. Women are affected approximately twice as often as men, and all ethnic groups can be affected.
What causes myopathies?
We do not know what causes myositis. However, because myositis has many forms, it likely has many causes. Some scientists believe that myositis occurs when a person with a certain genetic background is exposed to specific chemicals, viruses, or other infectious agents.
What are the symptoms of myopathies?
Symptoms of myositis include:
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Difficulty climbing stairs or raising the arm.
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Difficulty swallowing or breathing.
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Muscle pain that does not go away after several weeks.
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Markedly elevated muscle enzymes on blood tests (CPK).
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Problems arising from sitting in a chair for a long time.
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Feeling tired after standing or walking.
How are myopathies diagnosed?
Diagnostic criteria for dermatomyositis (DM) and polymyositis (PM) include:
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History and physical examination findings of muscle weakness in the hip and/or shoulder area.
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Elevated muscle enzyme levels in laboratory tests.
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Evidence of abnormal muscle activity on electromyography (EMG).
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Presence of inflammation on muscle biopsy.
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Presence of the characteristic rash in cases of dermatomyositis.
What is the relationship between dermatomyositis and cancer?
Because dermatomyositis is associated with cancer, all adult patients with this type of myositis should be evaluated for cancer. Most relevant medical authorities recommend simply screening for the most common cancers based on the patient’s age and gender.
How are myopathies treated?
Corticosteroids are the optimal treatment for the majority of patients with myositis. The most common medication in this class is oral prednisone, but forms of corticosteroids can be given intravenously to rapidly control the disease during acute inflammation. Reports indicate that immunosuppressive medications such as methotrexate, azathioprine, cyclosporine, cyclophosphamide, or chlorambucil have proven effective in treating patients with myositis resistant to prednisone or those unable to tolerate prednisone without relapse. For patients with myositis resistant to these standard treatments, intravenous immunoglobulin G has been shown to have a beneficial effect on muscle disease. Intravenous immunoglobulin (IVIG) consists of antibodies taken from healthy donors at blood banks and appears to work by counteracting the abnormal antibodies produced by myositis patients.
