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.
Keywords: dermatomyositis; idiopathic inflammatory myopathies; myositis-specific antibodies; polymyositis.