WHAT ARE MYOPATHIES?
Myopathy is the medical term for muscle disease. A general term meaning inflammation of the muscles, myositis includes the following diseases: dermatomyositis (DM), polymyositis (PM), inclusion body myositis, and juvenile myositis.
WHO GETS MYOPATHIES?
Inflammatory myopathies are rare diseases. Polymyositis and dermatomyositis occur in approximately one person in 100,000. All age groups are affected, with peak incidence between the ages of 5 and 10 in children and between the ages of 40 and 50 in adults. Women are affected about twice as often as men. All ethnic groups are affected.
WHAT CAUSES MYOPATHIES?
We do not know what causes myositis. But because myositis has many forms, it probably has many causes. Some scientists think that myositis results when a person with a certain genetic background is exposed to particular chemicals, viruses, or other infectious agents.
WHAT ARE THE SYMPTOMS OF MYOPATHIES?
Symptoms of myositis may include:
- Difficulty climbing stairs or lifting arms
- Trouble swallowing or breathing
- Muscle pain and soreness that does not resolve after a few weeks
- Known elevations in muscle enzymes by blood tests (CPK)
- Trouble rising from a chair
- Tired feeling after standing or walking
HOW ARE MYOPATHIES DIAGNOSED?
Criteria for diagnosing PM and DM include:
- History of and findings on physical examination of muscle weakness of hip and/or shoulder region
- Elevation of muscle enzymes on laboratory testing
- Evidence for abnormal muscle activity on electromyography testing
- Findings of inflammation on muscle biopsy
- Typical rash of DM
WHAT IS THE RELATION BETWEEN DM AND CANCERS?
Because of the association of DM with cancer, all adult patients diagnosed with this form of myositis should be evaluated for cancer. Most authorities in the field simply recommend that types of cancer most common for the patient age group and gender be screened.
HOW ARE MYOPATHIES TREATED?
Corticosteroids are the treatment of choice for the majority of patients with myositis. The most commonly used medication in this class is oral prednisone, but intravenous forms of corticosteroids can be given to rapidly control the disease during an acute flare.
Immunosuppressive drugs such as methotrexate, azathioprine, cyclosporine, cyclophosphamide, or chlorambucil have been reported to demonstrate efficacy in patients with myositis resistant to prednisone alone or in those unable to taper off prednisone without experiencing a relapse.
In patients with myositis resistant to these standard therapies, intravenous immunoglobulin G has been shown in well designed studies to have a beneficial effect on treating the muscle disease. IV IgG consists of antibodies taken from normal donors at the blood bank and appears to work by blocking abnormal antibodies produced by myositis patients.
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