AB0446 DEMOGRAPHIC AND CLINICAL FEATURES OF IDIOPATHIC INFLAMMATORY MYOSITIS AND PREVALENCE OF MYOSITIS-RELATED ANTIBODIES
Authors: G. K. Yardimci, E. Erul, B. Farisoğullari, G. Ayan, L. Kiliç, O. Karadag, Ş. A. Bilgen
Journal: Annals of the Rheumatic Diseases (2021)

Background: Idiopathic inflammatory myopathies (IIM) are heterogeneous groups of connective tissue diseases. Diagnosis of IIM is sometimes challenging, but newly defined myositis specific autoantibodies (MSAs) are helpful in diagnosing of IIM and revealing the clinical signs [1]. Objectives: To describe demographic and clinical features of IIMs and to evaluate the frequency and clinical associations of myositis-specific and myositis associated antibodies (MAAs) in IIM. Methods: Samples obtained from patients tested for MSA/MAA as of 2017 to 2020 were retrospectively evaluated. Patients were diagnosed with IIM according to clinician diagnosis. The prevalence and clinical associations of myositis-related antibodies were assessed with univariate and multivariate analysis. Results: 152 patients (70.4% female) were tested for myositis-related antibodies during the study period. 81 patients were diagnosed with IIM (38 DM, 43PM). DM patients were diagnosed at an earlier age and its association with malignancy was more relevant, although the relationship with malignancy was not statistically significant. Differences of clinical characteristics between DM and PM patients were skin features which were more frequent in DM, and interstitial lung disease which was more common in PM patients. MSAs/MAAS were found in 65.4% and 43.2% in IIM patients, more frequently than patients without IIM (p=0.000 and 0.0225, respectively). MSAs were equally frequent in both IIM groups, whereas MAAs were more common in the PM group (although no significant difference in overlap with other connective tissue diseases within these two diseases). The most common MSAs in DM were anti-TIF1-γ (23%), anti-MDA5 (16%), anti-NXP2 (13%) and in PM were anti-Jo-1 (28%), anti-MDA5 (12%), anti-ku (12%), anti-PL7 (12%) respectively. Predictors of ILD in IIM were Anti-Jo-1 positivity and age (RR:10 [CI:2-41] p=0.003 and RR:1.07 [CI:1.02-1.12] p=0.04 respectively) Conclusion: The general characteristics of DM and PM patients and the frequencies of myositis-specific autoantibodies were similar to the literature, except that anti-TIF1-γ antibodies (14%) were more common in our Turkish cohort [2]. References: [1]Cruellas, M.G., et al., Myositis-specific and myositis-associated autoantibody profiles and their clinical associations in a large series of patients with polymyositis and dermatomyositis. Clinics (Sao Paulo), 2013. 68 (7): p. 909-14. [2]Gonzalez-Bello, Y., et al., Myositis-Specific Antibodies and Myositis-Associated Antibodies in Patients With Idiopathic Inflammatory Myopathies From the PANLAR Myositis Study Group. J Clin Rheumatol, 2020. Table 1. Baseline characteristics of the patients with DM and PM DM (n=38) PM (n=43) P Female, n (% ) 27 (71.1) 29 (67.4) 0.457 Age at onset, years 33 (15-48) 47 (38-58) 0.002 Skeletal muscle features Muscle weakness, n (% ) 34 (89.5) 37 (86.0) 0.451 Myalgia, n (% ) 23 (60.5) 30 (69.8) 0.261 Artritis, n (% ) 8 (21.1) 9 (20.9) 0.601 Skin features, n (% ) Heliotrope rash, n (% ) 18 (47.4) 0 (0) &lt;0.001 Gottron papules, n (% ) 25 (65.8) 0 (0) &lt;0.001 Gottron sign, n (% ) 18 (47.4) 0 (0) &lt;0.001 Generalize erythema, n (% ) 10 (26.3) 0 (0) &lt;0.001 Calcinosis, n (% ) 4 (10.5) 1 (2.3) 0.143 Dysphagia, n(% ) 10 (26.3) 12 (27.9) 0.537 Interstitial lung disease (ILD), n (% ) 8 (21.1) 20 (47.6) 0.012 Other connective tissue diseases overlap, n (% ) 6 (15.8) 13 (30.2) 0.102 Malignancies, n (% ) 5 (13.5) 3 (7) 0.275 Laboratory data Creatine kinase (IU/L ) 505 (110-3616) 801 (402-1868) 0.655 C-reactive protein (mg/dl ) 0.3 (0.1-0.8) 1.2 (0.5-2.8) &lt;0.001 ESR (mm/h ) 19 (8-27) 25 (17-48) 0.005 MAAs (Ro-52, pm-scl 100, pm-scl75), n (% ) 11 (28.9) 24 (55.8) 0.013 MSAs, n (% ) 28 (73.7) 25 (58.1) 0.108 Anti- TIF1- γ, n (% ) 9 (23.7) 2 (4.7) 0.014 Anti-Jo-1, n (% ) 2 (5.3) 12 (27.9) 0.007 Anti-PL-7, n (% ) 0 5 (11.6) 0.038 Disclosure of Interests: None declared.