Polymyositis & Dermatomyositis
Medical Author: William C. Shiel Jr., MD, FACP, FACR
Medical Editor: Dennis Lee, MD
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Myositis (Muscle Inflammation)...Check the Meds!
Medical Author: William
C. Shiel Jr., MD, FACP, FACR
 I am a rheumatologist—an internal medicine
specialist who is trained to evaluate, diagnose, and treat diseases that involve
the muscles and joints. Because rheumatologists have a keen interest in
undiagnosed conditions, I see a number of patients every week who are seeking a
first diagnosis.
It is commonplace for doctors to refer patients to a
rheumatologist for the evaluation of painful muscles. There are many diseases
that are associated with inflammation of muscles. Furthermore, many conditions
may appear to involve muscles but may actually be a result of disease of the
tendons, joints, or bones.
By way of illustration, I want to call viewers'
attention to a patient that I just saw in the office this week. I feel that this
patient is very representative of a muscle condition that is under appreciated nowadays. I also know that patients and doctors should have a heightened
awareness of this condition since it is easily managed when discovered early.
When discovered late, it can lead to serious injury—not only to the muscles
but also potentially to the kidneys and heart.
Mr. Jones is a 75-year-old man who was referred by a
cardiologist because of pains and stiffness in the muscles of his arms,
shoulders, thighs, and buttocks. He has been taking Lipitor (atorvastatin) for
six months to control elevated cholesterol levels in his blood. Mr. Jones
reported muscle aching for the past eight weeks. He was also weak in the
locations of pain. Blood testing for the muscle enzyme, CPK, was mildly
elevated.
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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 typically those closest to the trunk or torso. This results in weakness that can be severe. Polymyositis is a chronic illness with periods of increased symptoms, called flares or relapses, and minimal or no 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 20s. 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, referred to as 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.
Researchers from Sweden at the national meeting of the American College of Rheumatology in 2007 reported their findings that T-cells of the immune system in some polymyositis or dermatomyositis patients reacted against cytomegalovirus (CMV) and that detectable antibodies against CMV were present. Their conclusion was that there may be subsets of patients who develop their disease, in part, because of infection with this particular virus.
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, called statins), 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).
Next: What are symptoms of polymyositis? »
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