AB0671 HISTOPATHOLOGICAL, CLINICAL AND SEROLOGICAL FEATURES IN IIM PATIENTS FROM A SINGLE CENTER COHORT

Background Idiopathic inflammatory myositis (IIM) is a group of heterogeneous autoimmune diseases, characterized by myositis-specific (MSA) or myositis-associated autoantibodies (MAA). Muscle biopsy the diagnostic gold standard, but correlations with elevated creatine level (CK) MSA/MAA are unclear. Objectives To evaluate association between specific histological findings and clinical and/or serological features in IIM patients from single tertiary Rheumatology referral center. Methods We retrospectively analyzed demographic data medical charts, 184 affected followed-up for >1 year. biopsies 89 were retrieved deltoid, biceps quadriceps muscle, snap-frozen stored at -80°C processed routine histology histochemistry. Results The majority our muscle cohort was represented Dermatomyositis (DM) (39.3%), Polymyositis (PM) (29.2%) Anti-synthetase syndrome (ASS) (13.5%), whereas rest composed Overlap Syndrome (OS), Immune-Mediated Necrotizing Myopathy (IMNM) Inclusion-Body Myositis (IMB) (13.5%, 2.2% respectively). DM presented perifascicular atrophy 85% cases perivascular infiltration only 40% cases, similar to other types IIMs. overall finding minimal inflammation necrosis major atrophy. In comparison, showed more endomysial (Table 1). ASS 83% perimysial 67% cases. Those characteristics observed both anti-Jo-1+ (13.9%) as well non-Jo-1+ (13.2%). Non-Jo-1+ infiltration, invading enveloping fibers (not present anti Jo-1+) (p: 0.036), addition rimmed vacuoles aspecific presentation. Moreover, DM, anti-Mi2+ antibodies (9.3%) significantly associated regeneration comparison anti-TIF1γ+ (5.8%) anti-NXP2+ (4.6%). No significant histopathological found anti-Ro52 (37.2%), that most frequent MAA cohort. Table 1. BIOPSY CHARACTERISTICS 12 (%) PM 35 26 p [OR] vs diffuse 3 (25) 34 (97.1) 8 (30.8) <0.0001 [0.010 (0.001-0.106)] [76.5 (8.8-660.6)] perifascicolar degeneration ---- 29 (82.9) 15 (57.7) 0.044 [3.544 (1.09-11.5)] prevalent 10 (28.6) 1 (3.8) 0.017 [10 (1.19-84)] Jo1 (% ) PL7/PL12 5 (invading fibers) 0 (60) 0.015 [inf] Mi2 TIF1γ NXP2 4 (100) (20) 0.007 0.002 infiltrate (surrounding 6 (75) 0.061 Conclusion associations emerged CK levels, different MSA. Some seem define subtypes DM. A precise definition autoantibody profile could not phenotype also damage distribution. Disclosure Interests None declared