Ab0249 a Comparative Case-Control Analysis of Paraneoplastic Versus Non-Paraneoplastic Inflammatory Myopathies

Background: Idiopathic inflammatory myopathies (IIM) constitute a heterogeneous group of systemic rheumatic diseases characterized by chronic muscle weakness and the infiltration of mononuclear cells into muscle tissue. The etiology is unknown; however, the association between IIM and neoplastic processes is recognized, being more pronounced in dermatomyositis (DM) compared to polymyositis (PM). Nonetheless, the nature and extent of this association are not fully elucidated. Objectives: To analyze the clinical phenotype and compare the clinical and serological characteristics of patients with neoplasia-associated inflammatory myopathy. Methods: An observational retrospective case-control study was conducted at a single center from 2016 to 2023, including patients diagnosed with IIM. The case group consisted of patients with paraneoplastic DM and those with non-neoplasia-associated IIM as controls; demographic, serological, clinical variables, and outcomes were assessed. Patients with less than 12 months of disease progression were excluded. Results: A total of 52 patients were analyzed, of which 9 (17.3%) had paraneoplastic DM and 43 (82.7%) had non-neoplasia-associated IIM. The median age in the paraneoplastic cohort was 67 years (CI) 50-92), while in the non-paraneoplastic cohort it was 62 years (CI 21-90). The paraneoplastic IIM group was 66.7% female, compared to 76.7% in the non-paraneoplastic group. The average follow-up was 3 years (CI 1-43) for patients with paraneoplastic DM and 4 years (CI 1-31) for those without neoplasms. Several autoantibodies, in addition to those already known to be associated with paraneoplastic IIM, were observed in the case group, with 66.67% (n=6) positive for anti-Ro52, 33.3% (n=3) positive for anti-TIF1 gamma, and 11.1% (n=1) for anti-NXP2, anti-MDA5, anti-Mi2-b, anti-Jo1, anti-PL7, anti-PL12, and anti-SAE antibodies. In contrast, the control group showed a more variable representation of other positive autoantibodies. The median number of positive autoantibodies in both groups was 2 per patient. The rest of the clinical, analytical, and demographic variables are shown in Table 1. Regarding serological markers, no statistically significant differences were observed between the two groups in any of the measured variables (Table 1). Notable variables include the initial ESR, which had a median of 29 mm/h (CI 2-104) for paraneoplastic IIM and 22 mm/h (CI 1-90) for non-paraneoplastic IIM (p = 0.796). Similarly, the final ESR was 20 mm/h (CI 3-94) versus 20 mm/h (CI 2-88) respectively (p = 0.969). As for CPK, the median peak value in the case group was 1234 U/L (CI 159-10000) compared with 1998 U/L (CI 159-9980) in the control group (p = 0.178), and the post-treatment CPK was 135 U/L (CI 42-800) versus 174 U/L (CI 41-1230), respectively (p = 0.079). Table 1. Demographic, clinical, and analytical variables of patients with inflammatory myopathies. Conclusion: Notable disparities were evident between the groups when evaluating the spectrum of autoantibodies associated with idiopathic inflammatory myopathies. The case group predominantly consisted of patients positive for multiple autoantibodies, prominently including anti-Ro52, as well as autoantibodies such as anti-TIF1 gamma and anti-NXP2, which are classically linked to neoplastic conditions. Interestingly, similar autoantibody positivity was observed among control group patients, despite the absence of any malignant neoplastic correlation. Serological variables did not demonstrate statistically significant differences across the cohorts, underscoring the complexity of correlating serological markers with neoplastic associations in IIM.neoplasms. No statistically significant differences were observed regarding serological variables in both groups. REFERENCES: 1 Selva-O'Callaghan A, Pinal-Fernandez I, Trallero-Araguás E, Milisenda JC, Grau-Junyent JM, Mammen AL. Classification and management of adult inflammatory myopathies. Lancet Neurol. 2018 Sep;17(9):816-828. 2 McHugh NJ, Tansley SL. Autoantibodies in myositis. Nat Rev Rheumatol. 2018 Apr 20;14(5):290-302. Acknowledgements: NIL. Disclosure of Interests: None declared.