What Is Inflammatory Muscle Disease?
Inflammatory muscle disease is an autoimmune disorder of unknown cause (idiopathic) which results in muscle weakness. The muscles involved are the "skeletal" muscles, that is, the muscles of the limbs making movement difficult. Sometimes the muscles of swallowing or phonation, or even breathing may be involved. Rarely, facial muscles are involved with weakness, as opposed to myasthenia gravis which frequently involves muscles of the eyes and face. In inflammatory muscle disease, the cardiac muscle may be involved, resulting in cardiac failure or arrhythmias. The term "myositis" is given to these muscle diseases. Myositis can occur at any age and even occurs in children. Both men and women may develop the disorder. Sometimes, myositis may occur without other manifestations of disease, or myositis may be a part of a more full-blown autoimmune disorder, such as systemic lupus erythematosus.
Are There Different Types Of Inflammatory Muscle Disorders?
There is a classification of types of myositis which help the physician and patient understand prognosis and management.
Polymyositis (described above)
Dermatomyositis (associated with a characteristic skin rash)
Dermatomyositis associated with malignancy (oftentimes the cancer is hidden, or occurs after the onset of the muscle disease)
Childhood polymyositis of dermatomyositis
Polymyositis associated with another connective tissue disease
Inclusion body myositis (characterized by specific changes on muscle biopsy)
Miscellaneous types, such as, eosinophilic, localized.
What Else Can Cause Symptoms Of Muscle Disease?
Muscle weakness, muscle stiffness, and muscle pain can be associated with many other conditions, which should be considered when evaluating symptomatology. For example, many medications can cause muscle symptoms, such as cholesterol lowering drugs. Infections can result in muscle disease, such as trichinosis, influenza, or HIV. Some endocrine disorders like thyroid disease, diabetes, or Addison's disease can be manifested by muscle abnormalities. Neurologic diseases such as myasthenia, or ALS, or muscular dystrophy can cause muscle weakness.
How Is The Diagnosis Of Inflammatory Muscle Disease Made?
The first step in any medical evaluation is a good and thorough medical history. It is important for the patient to describe as best as he/she can the exact nature of the symptoms. Past medical history and family history is extremely important. The reporting of all medications, and even supplements and over-the-counter medications is important. After the thorough history, the physician should conduct a full physical examination. As noted above, sometimes myositis is associated with a malignancy, and examining the appropriate body systems is necessary. Laboratory testing is an essential part of the examination. General health screens are performed such as blood count, sugar, liver profile, etc. But specialized muscle enzyme testing is necessary, including creatine kinase and aldolase levels. Certain autoantibodies can be associated with polymyositis and dermatomyositis, such as the ANA, JO-1 anitbody, Pm-Scl antibody, or Mi-2 antibody. These are serologic measure of autoimmune activity which can be associated with myositis.
After these tests, the physician will order an electromyogram(EMG). This is a needle test of the muscle to judge the electrical activity of the muscle by analyzing wave forms on an oscilloscope. The skeletal muscles are very active electrically, and disturbances in muscle function, physiology, and microscopic anatomy can sometimes be seen on EMG. Depending on the EMG results, the physician may recommend a muscle biopsy. The muscle biopsy is performed under local anesthesia and the muscle studied will depend on the judgment of the physician. Sometimes it will be the biceps (arm) or quadriceps (thigh). (It should never be the muscle which had the EMG!) The muscle tissue is submitted for several staining procedures which look for the infiltration of inflammatory cells or other abnormal cells, "inclusions" in cells, deterioration of the muscle fiber, inflammation around blood vessels, etc. At this point, the neuromuscular pathologist can usually categorize the abnormalities seen so that a diagnosis is rendered.
How Is Myositis Treated?
The treatment of myositis is individualized according to the patient's needs and after careful consultation and planning with his/her physician. One of the standards of treatment is corticosteroids. Corticosteroids are powerful anti-inflammatory and immunomodulatory medications. Fortunately, most cases of myositis will respond to corticosteroids alone. These medications may need to be taken over several months to years in order to control the disease and prevent relapse. Sometimes, steroids are not enough by themselves, and the addition of "disease-modifying" drugs are necessary, for example, methotrexate, azathioprine, or even cyclophosphamide. A newer treatment option is to use intravenous gamma globulin for refractory cases. Sometimes, combinations of medications are necessary. There is ongoing research in muscular diseases to develop more effective and safer treatment. The newer biologic agents (anti-tumor necrosis factor agents) may be helpful in controlling disease.
Authored by: Carolyn Smith, M.D.