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Inflammatory myopathies are a group of muscle diseases that cause
inflammation and degeneration of the skeletal muscle tissues. The cause of these
diseases is unknown, but they are thought to be autoimmune disorders, disorders
that cause the body’s tissues to be attacked by its own immune system.
For
people with inflammatory myopathies, inflammatory cells surround, invade, and
destroy normal muscle fibers as though they were defective or foreign to the
body. This eventually results in noticeable muscle weakness. This muscle
weakness usually affects both sides of the body and might develop over weeks,
months, or even years. Inflammatory myopathies affect women nearly twice as often
as they affect men.
The two most common inflammatory myopathies are dermatomyositis and
polymyositis. Both diseases share the common symptom of muscle weakness, which
usually affects those muscles that are closest to the trunk of the body
(proximal). Eventually, patients might have difficulty rising from a sitting
position, climbing stairs, lifting objects, or reaching overhead. In some cases,
distal muscles (those not close to the trunk of the body) might be affected later
in the course of the disease. Patients with these diseases might also feel fatigued
and experience weight loss or a low-grade fever. Although all of these diseases
result in similar muscle weakness, each is unique in its development and
treatment.
Dermatomyositis is more rare than polymyositis, affecting 10 people out
of every 1 million. While there is a juvenile form of this disease that begins
between the ages of 5 and 15, it most commonly begins between the ages of 40
and 60. Dermatomyositis has a sub-acute (somewhat short and relatively severe)
onset, usually worsening over a period of days or weeks, although it might also last
for months.
The distinguishing characteristic of dermatomyositis is a rash accompanying,
or more often, preceding muscle weakness. The rash is described as patchy,
bluish-purple discolorations on the face, neck, shoulders, upper chest, elbows,
knees, knuckles, and back. Some patients might also develop hardened bumps of
calcium deposits under the skin. Trouble with swallowing (dysphagia) might also
occur. In about one-fourth of adult cases, muscles ache and are tender to the
touch. In the juvenile form, this percentage can be as high as 50 percent.
Polymyositis also causes varying degrees of decreased muscle function.
The disease has a more gradual onset compared to dermatomyositis and generally begins
in the second decade of life. Polymyositis rarely affects people under age 18.
Like dermatomyositis, difficulty with swallowing occurs but is more common with
polymyositis, which can affect nutrition as well as increase the risk of
aspiration pneumonia. Aspiration pneumonia can result from food or liquid
entering the lungs. About one-third of patients with polymyositis experience
muscle tenderness. However, the discomfort is generally mild.
Diagnosis
Because both polymyositis and dermatomyositis are relatively rare,
there is not a clearly defined approach to diagnosing these conditions. The
diagnosis is further complicated by the similarity of these diseases to other,
more common diseases and disorders. Both polymyositis and dermatomyositis are
often diagnosed by ruling out other conditions.
Tests your doctor might order to help with the diagnosis of polymyositis
and dermatomyositis include an electromyogram (EMG), a test that records muscle
activity and nerve conduction, and a muscle biopsy. A muscle biopsy involves
collecting a
small sample of muscle tissue that is then analyzed in a laboratory.
Treatment and management
Currently there is no cure for inflammatory myopathies. However,
there are several approaches to treating them and helping patients maintain as
close to a normal lifestyle as possible.
Medicines:
Several immunosuppressant medicines have been shown to be quite effective
in treating dermatomyositis and polymyositis. Immunosuppressants work in
patients with inflammatory myopathies by causing the body to produce fewer of
the cells that destroy the muscle fibers and tissue. Corticosteroids can also
work as immunosuppressant medicines. One corticosteroid, prednisone, has
been 75 percent effective in treating these diseases.
Physical therapy:
Physical therapy is important in helping patients manage the muscle weakness
associated with inflammatory myopathies. A physical therapist will assist a
patient in designing an appropriate exercise program, as well as help the patient
make progress throughout the program. Some patients might require assistive
devices such as a walker, and a physical therapist will assist in determining
the most suitable device.
Speech therapy:
Some patients who have swallowing problems need the assistance of a speech
therapist. A speech therapist can recommend exercises that might improve
swallowing, as well as provide general tips and guidance for overcoming
swallowing difficulties.
As with many other conditions, education about inflammatory myopathies and
local support groups can be the greatest tools for managing the disorder and
preventing complications. The following organizations can provide additional
information about inflammatory myopathies:
Myositis Association of America
755 Cantrell Avenue, Suite C
Harrisonburg, VA 22801
(540) 433-7686
www.myositis.org
Muscular Dystrophy Association
3300 E. Sunrise Drive
Tucson, AZ 85718
(800) 572-1717
www.mda.org
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