Myositis means inflammation of the muscles and represents a group of chronic disorders, also known as inflammatory myopathies. Certain forms of myositis are believed to be autoimmune disorders, which occur when the immune system malfunctions and creates autoantibodies that attack and cause damage to a part of the body. In myositis, autoantibodies attack the skeletal or voluntary muscles, those involved in active movement. In one type of myositis, the skin is also affected. In some forms the autoantibody is identifiable and in others, it is not. There are a few main types: polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM).
Symptoms of Myositis
Symptoms of myositis depend on the type, but most begin with weakness in the proximal muscles, those that are closest to the trunk (torso) of the body. In PM and DM, weakness is symmetrical (same on both sides of the body) but in IBM it is not. Weakness in proximal muscles makes getting up from a chair, climbing stairs and lifting arms overhead difficult. Muscle ache and pain are also common.
In dermatomyositis, the skin is frequently affected, hence its name (dermato = skin), although rash can be absent. If present, the rash is patchy and reddish-purple and may precede or follow the muscle weakness. It can be found anywhere but more commonly on the eyelids and the joints used to extend such as knuckles, knees and elbows. Calcium deposits may also form under the skin and appear as hard, white bumps. Difficulty swallowing occurs in about one-third of all cases.
In IBM, weakness can be proximal as well as distal. Initial symptoms can be weak hand grasp, resulting in difficulty buttoning a shirt and dropping things. Upon biopsy, the muscle will show inclusions, or plaque. As the disease progresses, difficulty swallowing is also common.
Diagnosing myositis can be difficult, as initial symptoms are often ignored because they are mild and may be attributed to something else.
Diagnostic testing may include:
- Muscle biopsy – magnetic resonance imaging (MRI) may be obtained to help determine which muscles to biopsy.
- Electromyography (EMG) to measure muscle activity.
- Blood work to evaluate muscle enzymes (CK, LD, AST and ALT) that are frequently elevated in myositis, as well as anti-Jo-1 antibody that may be present in DM.
Treatment of myositis may include steroids and immunosuppressants such as methotrexate, azathioprine, and cyclosporine. These two therapies are considered first-line therapy for PM and DM. Immune globulin therapy administered into the blood stream intravenously (IVIG) and rituximab (e.g., Rituxan®)are considered if there is poor response to the first-line therapies. Early treatment results in a better prognosis. With the right treatment, PM and DM can be controlled and can even go into remission. Unfortunately at this time, there is no treatment for IBM. Some studies show IVIG may provide a short-term benefit for IBM in some people, particularly those with difficulty swallowing.
This content is not intended to substitute professional medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
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