Characteristics of idiopathic inflammatory myopathies with novel myositis-specific autoantibodies.

BACKGROUND In recent years, many novel myositis-specific autoantibodies (MSAs) have been identified. However, their links with the pathogenesis and clinical manifestations of inflammatory myopathies remain uncertain. OBJECTIVES To characterize the population of adult dermatomyositis (DM) and polymyositis (PM) patients treated at our center for autoimmune diseases using clinical and laboratory measures. MATERIAL AND METHODS According to the Bohan and Peter criteria, we retrospectively analyzed patients who fulfilled diagnostic criteria for DM or PM. Myositis-specific autoantibodies and myositis-associated autoantibodies (MAAs) were identified using immunoblot assays. RESULTS Fifty-one PM (71% women) and 36 DM (67% women) Caucasian patients with a median age of 58 (range: 21-88) years who met the definite or probable diagnostic criteria for myositis were included in the study. Myositis-specific autoantibodies were identified in 63 (72%) patients, whereas MAAs were observed in 43 (49%) of them. Interstitial lung disease (ILD) was characteristic of PM patients (67%, χ2 with Yates's correction (χc2) = 13.8078, df = 1, p = 0.0002), being associated with anti-Jo-1 or anti-PL-12 antibodies (fraction comparison test (FCT) 6.4878, p < 0.0001, 6.8354, p = 0.0003, respectively). Interestingly, among patients with anti-MDA5 antibodies (n = 8, 9.2%), all but one had an amyopathic form, with more frequent ILD, skin changes and arthralgias than observed in other patients (FCT 4.7029, p = 0.0228 and p = 7.7986, p = 0.0357, p = 4.7029 and p = 0.0228, respectively). Anti-signal recognition particle (SRP) was strongly associated with the Raynaud's phenomenon (FCT 4.1144, p = 0.0289) and the highest muscle injury markers (Mann-Whitney U test, z = 2.5293, p = 0.0114). Malignancy was recorded in 14 (16%) patients and was equally common in those with PM and DM. The anti-TIF-1γ was the most frequently related to cancer χ2 = 14.7691, df = 1, p < 0.0001). The anti-Mi-2α, similarly prevalent in DM and PM, was typically accompanied by skin changes (FCT 7.7986, p = 0.0357) but not ILD (FCT 8.7339, p = 0.0026). CONCLUSIONS Identification of MSAs might help to predict the clinical course of the autoimmune myopathy and malignancy risk. However, these antibodies were absent in about 30% of patients with typical PM or DM manifestations, which encourages further research in this area.