Autoantibodies in Autoimmune Myopathy

myositis-specific autoantibodies,” says Dr. Aggarwal. Even at the Pittsburgh Myositis Center, which has an extremely comprehensive myositis lab, he notes that patients only have a positive myositis-specific auto­antibody in about 60–70% of cases. He notes, “I think [that] in the future we will be able to discover these autoantibodies and, hopefully, come up to 90% or more.”

Research into myositis is challenging, partly because the group of conditions is both rare and heterogeneous in its manifestations. Autoantibodies may open up new research avenues as clinicians can bring more uniformity to myositis research. “We still enroll patients with clinical symptoms of polymyositis and dermato­myositis or juvenile myositis or cancer-associated myositis,” notes Dr. Aggarwal. “However, now we are able to do post hoc analyses in clinical studies to see which of the autoantibody subset groups show better outcomes or other unique features.”

For example, in a recent clinical trial, 200 myositis patients with refractory DM, PM and juvenile DM were treated with rituximab.¹⁷ A post hoc analysis allowed researchers to see that patients with antisynthetase syndrome showed the best improvement of all the antibody groups. “Within this heterogeneous group we are able to have some uniformity using autoantibodies,” Dr. Aggarwal explains.

Dr. Aggarwal provides another example from disease-subset-specific treatment in patients positive for the anti-HMGCR antibody.¹⁸ “These patients in a limited data set have been shown to respond very well to IVIG even as a monotherapy.”

When to Get Help

Many general rheumatologists can successfully care for these IIM patients, but Dr. Aggarwal recommends referral in certain situations. If clinicians are struggling with diagnosis or with treatment-resistant disease, expert help may be needed. Dr. Aggarwal adds, “When the patient has severe disease to begin with, for example a patient with severe interstitial lung disease with myositis, I recommend clinicians refer to a more experienced myositis center.”

Ruth Jessen Hickman, MD, is a graduate of the Indiana University School of Medicine. She is a freelance medical and science writer living in Bloomington, Ind.

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