Specific autoantibodies in dermatomyositis: a helpful tool to classify different clinical subsets

Autoantibodies are important in the diagnosis of dermatomyositis. They can be divided in two different groups: myositis-associated autoantibodies (MAA) prevailing in overlap syndromes, and myositis-specific autoantibodies (MSA), with diagnostic specificity exceeding 90%. Our purpose was to detect retrospectively the prevalence of the most common MSAs in a group of 19 adult DM patients (13 women, 6 men). A severe DM (SDM), with extensive cutaneous and muscular manifestations, dysphagia, and sometimes pneumopathy, was detected in ten cases. Three patients had a mild DM (MDM), with little muscle and skin impairment, and a short course. Four patients suffered from amyopathic DM (ADM), two from paraneoplastic DM (PDM). Each serum was tested for ANA, ENA, MAAs, MSAs. Myositis-specific autoantibodies were detected in 15 cases. The most frequent was anti-TIF1γ, associated with SDM or PDM in four out of seven cases. Anti-MDA5 antibodies were recorded in a SDM and in a ADM with lung fibrosis. Anti-Mi2 and anti-SRP antibodies were both detected in a MDM and in a SDM, whereas anti-SAE1 in a amyopathic form. Other antibodies (anti-NXP2, -Jo1, -PL7, -PL12, -OJ) were found in single patients with SDM. Our series confirmed that specific autoantibodies could be helpful to classify different clinical subsets, particularly in the case of paraneoplastic forms or association with pneumopathy. Moreover, they can help in predicting the disease evolution and influence therapeutic strategies. A greater number of cases should be useful to highlight the clinical and pathogenic role of these antibodies, and develop a homogeneous protocol for diagnosis and treatment.