Myopathy refers to a group of rare diseases that involve injury to the muscles. There are several types of myopathy. The autoimmune myopathies include polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM). These diseases are classified as autoimmune because research suggests that they occur when the body's immune system attacks its muscles. This self-attack causes inflammation of the muscle fibers, or myositis.

The primary symptom of polymyositis, dermatomyositis and inclusion body myositis is muscle weakness. The muscles closest to the trunk of the body are affected most in DM and PM. In PM, muscles farther from the trunk may also be mildly affected. In IBM, muscles closest to and farthest from the trunk are affected about equally. Dermatomyositis is most easily distinguished from PM and IBM by the appearance of a rash. The rash occurs on the eyelids, cheeks and bridge of the nose. The rash also appears on the back or upper chest, elbows, knees and knuckles.

PM, DM and IBM can be difficult to diagnose. The rarity of the diseases creates part of the difficulty in diagnosis. The similarity of the symptoms with other diseases that cause muscle weakness also complicates the diagnosis. Tests, including EMG and muscle biopsy, help distinguish these diseases.

There is currently no treatment that cures PM, DM or IBM. PM and DM can be managed with treatment, but unfortunately, there is no treatment that effectively controls IBM. Most patients with PM and DM respond to corticosteroid medications like Prednisone and immunosuppressant drugs. IVIg, a pooled human gamma globulin product, is sometimes used to treat each of these diseases. IVIg is most effective in treating DM and may be effective in treating PM. IVIg has no affect on IBM.

The course of each disease varies. Many factors affect the disease outcome. These include which disease is present, patient age at diagnosis, gender, and other medical conditions. Most patients with PM and DM have a remission in symptoms with treatment. Patients with IBM may need to use assistive devices such as walkers and wheelchairs as muscle weakness progresses.

Research with DM, PD and IBM is somewhat limited due to the relative rarity of each of these diseases. However, researchers are continuing to study the similarities and differences between DM, PM and IBM. Researchers are also drawing upon many areas of medicine including investigations into other autoimmune diseases to further their understanding of DM, PM and IBM. As understanding of these diseases grows, more effective treatments for each disease can be developed. Hope remains that researchers may even find a cure for them.

References

First published April 1, 2000
Last updated August 1, 2003
Copyright © 2000 Accordant Health Services, Inc. All Rights Reserved.

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