Around 80% of people with DM test positive for ANA and around 30% of people have myositis-specific autoantibodies which include antibodies to aminoacyl-tRNA synthetases (anti-synthetase antibodies), including antibodies against histidine—tRNA ligase (also called Jo-1); antibodies to signal recognition particle (SRP); and anti-Mi-2 antibodies.Magnetic resonance imaging may be useful to guide muscle biopsy and to investigate involvement of internal organs; X-ray may be used to investigate joint involvement and calcifications.A given case of dermatomyositis may be classified as amyopathic dermatomyositis if only skin is affected and no muscle weakness for longer than 6 months is seen according to one 2016 review, or two years according to another. Classification
Dermatomyositis is a form of systemic connective tissue disorder, a class of diseases that often involves autoimmune dysfunction.It has also been classified as an idiopathic inflammatory myopathy, along with polymyositis, necrotizing autoimmune myositis, cancer-associated myositis, and sporadic inclusion body myositis.A form of this disorder that occurs prior to adulthood is known as juvenile dermatomyositis. Treatment
No cure for dermatomyositis is known, but the symptoms can be treated. Options include medication, physical therapy, exercise, heat therapy (including microwave and ultrasound), orthotics and assistive devices, and rest. The standard treatment for dermatomyositis is a corticosteroid drug, given either in pill form or intravenously. Immunosuppressant drugs, such as azathioprine and methotrexate, may reduce inflammation in people who do not respond well to prednisone. Periodic treatment using intravenous immunoglobulin can also improve recovery.
Epidemiology
Incidence of DM peaks at ages 40–50, but the disease can affect people of all ages. It tends to affect more women than men. The prevalence of DM ranges from one to 22 per 100,000 people. History
The diagnostic criteria were proposed in 1975 and became widely adopted. Amyopathic DM, also called DM sine myositis, was named in 2002. People who died with dermatomyositis
Opera singer Maria Callas (1923–1977) allegedly had dermatomyositis from 1975 until her death. Actor Laurence Olivier (1907–1989) had dermatomyositis from 1974 until his death. American football running back Ricky Bell (1955–1984), the runner-up for the Heisman Trophy in 1976, and the number-one pick in the NFL draft in 1977, died at the age of 29 from heart failure caused by this disease. Rob Buckman (1948–2011) a doctor, comedian, author, and the president of the Humanist Association of Canada. Research
As of 2016, research was ongoing into causes for DM, as well as biomarkers;  clinical trials were ongoing for use of the following drugs in DM: ajulemic acid (Phase II), adrenocorticotropic hormone gel (Phase IV, open label), IMO-8400, an antagonist of Toll-like receptor 7,8 and 9 (Ph II), abatacept (Phase IV, open label), and sodium thiosulfate (Phase II). References

 This article incorporates public domain material from NINDS Dermatomyositis Information Page. United States Department of Health and Human Services. Retrieved 12 December 2016. == External links ==