Some types of autoimmune disease attack the muscles of the body. The “myositis-specific antibodies” (MSA) can assist in the diagnosis of polymyositis and dermatomyositis in those patients who have the diseases. About 50% of patients with polymyositis or dermatomyositis have specific MSA or myositis associated antibodies (MAA). MSA are almost never found in patients without myositis, even if they have other muscle diseases of autoimmune diseases. This means that when the physician’s examination and initial testing suggest the possibility of polymyositis or dermatomyositis, a positive test for an MSA can be strong supporting evidence for the diagnosis.
For a long time the testing for these antibodies was only available in research studies, but it is now possible to obtain this testing clinically. The Myositis Profile* performed at the OMRF Clinical Immunology Laboratory includes tests for 12 of the MSAs and MAAs. Additional antibodies may be detectable using this profile. Dr. Ira Targoff is the consultant to the Clinical Immunology Laboratory regarding this testing. As with the Reichlin Profile for lupus, patients with a particular antibody may have distinctive clinical pictures with certain associated problems. Identifying certain antibodies can help characterize the condition more fully. Research continues in our lab, and others around the world, to determine the nature of the relationship between the various MSAs and polymyositis and dermatomyositis.
*Lab-developed test (LDT) development and performance characteristics were determined by the OMRF Myositis Testing Laboratory to perform clinical high-complexity testing. Lab-developed tests have not been cleared or approved by the FDA. Lab-developed tests are accredited by the College of American Pathologists (CAP). References available upon request.