ABS1110 CLINICAL CHARACTERISTICS AND EVOLUTION OF INTERSTITIAL LUNG DISEASE IN A RETROSPECTIVE ANALYSIS OF PATIENTS WITH ANTISYNTHETASE SYNDROME, ANTI-MDA5 SYNDROME, AND SCLEROMYOSITIS

Background: Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of connective tissue diseases characterized by muscle inflammation and frequent multisystem involvement. Interstitial lung disease (ILD) is the most common extra-muscular manifestation, especially in antisynthetase syndrome (AsyS), anti-melanoma differentiation-associated protein 5 (MDA5) syndrome, and scleromyositis, contributing significantly to IIM morbidity and mortality. ILD can progress even when muscular and cutaneous symptoms resolve, a phenomenon that we termed "post-myopathic ILD." This progression poses diagnostic and therapeutic challenges due to its unpredictable clinical trajectory. While IIM-ILD epidemiology is well-documented, post-myopathic ILD remains poorly understood. Objectives: To characterize clinical phenotypes, treatment regimens, and ILD trajectories in AsyS, anti-MDA5 syndrome, and scleromyositis within a British Columbia (BC) myositis cohort and explore the features of post-myopathic ILD. Methods: A retrospective review of IIM patients seen at the Mary Pack Arthritis Centre (March 2019–June 2024) was conducted. Patients were categorized into AsyS, anti-MDA5 syndrome, and scleromyositis based on clinical and serologic criteria. Data collected included demographics, myositis-specific antibodies, treatments, and clinical courses. ILD activity, including post-myopathic ILD, was assessed through multidisciplinary evaluations involving clinical history, high-resolution computed tomography (HRCT), pulmonary function tests (PFTs), and 6-minute walk tests. Ethical approval was obtained (UBC REB H24-01298). Results: Of 268 IIM patients, 114 met inclusion criteria (AsyS: 49.1%, scleromyositis: 25.4%, anti-MDA5 syndrome: 22.8%) (Table 1). The cohort was predominantly female (68.4%) with a median age of 51 years at diagnosis and a follow-up duration of 35.5 months. IIM-ILD was present in 82.5% of patients; 13.2% had post-myopathic ILD. ILD rates were highest in AsyS (89.3%; post-myopathic ILD: 18.0%) and anti-MDA5 syndrome (84.6%; post-myopathic ILD: 22.7%), while scleromyositis had the lowest ILD rates (65.5%) and no post-myopathic ILD cases (Figure 1). The most common antibodies were anti-Ro52 (41.2%), anti-Jo-1 (33.3%), anti-MDA5 (25.4%), and anti-PM/Scl (15.8%). At follow-up, 72.8% of ILD cases were in remission, 16.7% had active disease, 9.6% were deceased, and 4.4% had undergone lung transplantation. The majority of patients received a median of 2 disease-modifying antirheumatic drugs (DMARDs). Biological or targeted synthetic (b/ts) DMARDs were used in 35.1% of patients. Patients with post-myopathic ILD had higher b/ts DMARD usage (53.3%). Conclusion: This study highlights the heterogeneity of IIM-ILD across AsyS, anti-MDA5 syndrome, and scleromyositis in the largest BC myositis cohort. Post-myopathic ILD was prevalent in AsyS and anti-MDA5 syndrome but absent in scleromyositis, suggesting pathophysiological differences. The increased b/ts DMARD use in patient with post-myopathic ILD underscores the need for intensive therapeutic strategies. The unique progression of post-myopathic ILD, independent of musculoskeletal or cutaneous disease activity, emphasizes the importance of multidisciplinary care and further research into its clinical trajectory. REFERENCES: NIL . Figure 1Proportion of patients with ILD and post-myopathic ILD in each syndrome. Table 1Clinical characteristics and demographics of 114 patients at last follow-up appointment.VariablesValuesAge (years) at diagnosis, median (IQR)51 (41-62)Age (years) at last follow-up, median (IQR)56.5 (47-67)Duration of disease (months), median (IQR)35.5 (17-70.5)Sex, n (%)Female78 (68.4)Male36 (31.6)Clinical Phenotype, n (%)AsyS56 (49.1)Scleromyositis29 (25.4)Anti-MDA5 syndrome26 (22.8)Other3 (2.6)Myositis-associated antibodies, n (%)Anti-MDA529 (25.4)Anti-Jo-138 (33.3)Anti-EJ8 (7.0)Anti-PL-77 (6.1)Anti-PL-125 (4.4)Anti-Ro5247 (41.2)Anti-PM/Scl18 (15.8)Anti-Ku7 (6.1)Anti-Mup443 (2.6)Anti-Mi-22 (1.8)Anti-TIF-11 (0.9)Anti-SRP1 (0.9)Diagnosis of ILD, n (%)Yes94 (82.5)No20 (17.5)Clinical status, n (%)Active19 (16.7)Remission83 (72.8)Deceased11 (9.6)Unknown1 (0.9)Post lung transplant5 (4.4)Post-myopathic ILD15(13.2)Number of DMARDs trialed* (median), n (IQR)Total (n=114)2 (2-4)Active (n=19)2 (2-3)Remission (n=83)2 (2-4)Deceased (n=11)1 (1-2)Post lung transplant (n=5)2 (1.5-3.5)Post-myopathic ILD (n=15)2 (2-4)Number of patients currently on b/tsDMARDs**, n (%)Total (n=114)40 (35.1)Active (n=19)9 (47.4)Remission (n=83)29 (34.9)Deceased (n=11)2 (18.2)Post lung transplanted (n=5)1 (20.0)Post-myopathic ILD (n=15)8 (53.3)*excluding glucocorticoids, IVIG, and hydroxychloroquine. DMARDs: disease modifying anti-rheumatic drugs. **b/ts DMARDs: biological/targeted synthetic disease modifying anti-rheumatic drugs. Acknowledgements: We thank the support from Fresenius Kabi and Pfizer in this investigator initiated clinical research project. Disclosure of Interests: Julia (JJ) Clark: None declared, Dora Chan: None declared, Makshada Kowlessur: None declared, Jan Dutz: None declared, Kun Huang Fresenius Kabi, Novartis, Abbvie, I have received $10,000 Canadian from Fresenius Kabi and Pfizer each for Investigator initiated clinical research. © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.

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