FRI0317 NOVEL CLASSIFICATION OF IDIOPATHIC INFLAMMATORYMYOPATHIES BASED ON DISTINCTIVE FEATURES AND AUTOANTIBODIES: ANALYSIS OF 67 KOREAN PATIENTS

Background SinceBohan and Peter first described their diagnostic criteria foridiopathic inflammatorymyopathies (IIM) in 1975, new discoveries suchas myositis-specific and myositis-associated autoantibodies (Abs) have been made. Objectives To investigate correlations between specificmyositis Abs and their frequenciesand clinical associationsacross different IIM groups, collectively demonstrating theutility of the new clinicoserologic classification in Koreanadult patients with IIM. Methods We conducted a multicenter cohort study including 67adult patients (age≥18 years) who have been diagnosed as IIM by ENMC criteria.Immunoblot assay with Euroline strip(EUROIMMUN, Germany)was performed using the sera of definite deramatomyositis (DM, n=36), definite polymyositis (PM, n=25), amyopathic DM (n=4), DM sine dermatitis (n=1), and immune mediated necrotizing myopathy (IMNM, n=1). Patients were classifiedbased on three classifications: 1) novel clinicoserologic classification suggested by Troyanov et al. in 2017. 2) 2017 EULAR/ACR classification criteria. 3) 2004 European neuromuscular center (ENMC) criteria.Associations ofmyositis Absand clinical subsets of IIM were investigated. Results The distribution of the various IIM differed strikingly from those using the 3 classifications (Fig1). According to the 2004 ENMC classification and 2017 EULAR/ACR classification criteria, DM and PM was the most and the second frequent entities (DM: 55.2%, 56.7%; PM: 35.8%, 37.3%). But, using the new clinicoserologic classification,overlapmyositis(OM) is the major type of IIM and the frequency of PM is significantly decreased.Anti-ARS Abs specificity included anti-Jo-1(16.4%), -OJ(4.6%), -EJ(6.2%) -PL-7(3.1%), and -PL-12(4.6%). Interstitial lung disease was closely associated with anti-MDA5,and anti-ARS Abs, while DM-specific skin lesion was frequently observed in patients with anti-TIF1γ and anti-ARS Abs. Sevenpatients with cancer-associated DM were identified. They were positive for anti-TIFγ (5/7) and anti- SRP(3/7) (table 1). Conclusion Novel classification based on distinctive features and new myositis Absreflects the clinical phenotype of IIM better. Establishment of a system routinely available to screen myositis Abs is needed. Thiswill be beneficial to providemore precise diagnosis and proper management for patients with IIM. Reference: [1] Jean-Luc Senecal, Jean-Pierre Raynauld, Yves Troyanov. A New Classification of Adult Autoimmune Myositis. Arthritis Rheum2017;69:878-884. Disclosure of Interests None declared