POS0875 MYOSITIS-SPECIFIC ANTIBODIES IN A RETROSPECTIVE SINGLE-CENTER OBSERVATIONAL STUDY
Authors: J. Álvarez Troncoso, S. Carrasco Molina, J. Valdivieso, P. Nozal, Á. Robles Marhuenda, E. Martínez Robles, C. Soto Abánades, J. J. Rios, A. Noblejas Mozo, F. Arnalich Fernández
Journal: Annals of the Rheumatic Diseases (2021)

Background: Myositis-specific antibodies (MSA) are highly specific and useful to classify patients as having syndromes with distinct clinical features and prognosis. MSA are almost always mutually exclusive and quite specific, adding value as a useful biomarker for diagnosis. Although individual autoantibodies aren’t sensitive enough to detect the full spectrum of idiopathic inflammatory myopathies (IIM), the sensitivity of a myositis panel is increasing as more autoantibodies are discovered, and as better assays become available. Objectives: We aimed to analyze the usefulness of a myositis-specific immunoblot for the diagnosis of IIM in a hospital cohort from January 2019 to December 2020. We also seek to correlate immunological findings with the risk of associated interstitial lung disease (ILD), cancer, or death. Methods: Retrospective single-center observational study conducted in a Spanish tertiary hospital. In patients with high clinical suspicion of IIM, a myositis immunoblot was performed including Jo1, PL-7, PL-12, EJ, SRP, Mi2, Ku, MDA-5, TIF1-γ, HMGCR, PM-Scl and Ro52 antibodies. The demographic characteristics, the risk of ILD, cancer and death were analyzed. Results: In a cohort of 313 patients with high suspicion of IIM, 87 patients (27.8%) presented a positive MSA (MSA+ve). The mean age at diagnosis was 56.7±16.9 years, with no significant differences between MSA+ve and MSA-ve (p=0.597). Most of the patients were women with significant differences between both groups (80.5% MSA+ve vs 68.1% MSA-ve, p=0.030). IIM were classified as antisynthetase syndrome (ARS) (38%), dermatomyositis (DM) (31%), overlap myopathy (OM) (16.9%) and necrotizing myopathy (NM) (14.1%) according to the manifestations and MSA found (Jo1, PL-12, PL-7, EJ in ARS; Mi-2, MDA-5 and TIF1-γ in DM; Ku and PM-Scl in OM; HMGCR and SRP in NM). The most frequent MSA were anti-Jo1 (16.9%), TIF1-γ (15.5%), Ku (12.7%), Mi-2 (9.9%), PL-7 (9.9%), HMCGR (8.5%), PL-12 (7%), MDA-5 (5.6%), SRP (5.6%) and EJ (4.2%). The presence of Ro52 associated with other MSA was found in 20 patients (22.9%). ILD was the most frequent manifestation (45.2% of the MSA+ve). Non-specific interstitial pneumonia (NSIP) was the most frequent ILD (39.5%), followed by usual interstitial pneumonia (34.2%). The main risk factors associated with IIM-ILD were some subtypes of the MSAs (p&lt;0.001), the association of Ro52 (p&lt;0.001), and older age (p=0.027). Among the IIM, ARS and OM (p&lt;0.001) were more frequently associated with IIM-ILD. The MSAs most associated with IIM-ILD were Jo1, PL-7, PM-Scl, Ku and SRP (p&lt;0.001). Cancer was found in 9.6% of MSA+ve patients. The most frequent tumors were gynecological (37.5%), followed by gastrointestinal (25%) and breast cancer (12.5%). Factors associated with cancer were age (p=0.010), TIF1-γ (p&lt;0.001), SRP (p=0.004), PL-12 (p=0.013), PL-7 (p=0.047) and HMGCR (p=0.027). The mortality of these patients was 3.5%. There were no differences regarding MSA+ve/-ve (p = 0.911). However, MDA-5 (p=0.033) and older age (p=0.001) were associated with higher mortality. There were no significant differences between the IIM classifications, the associated SAD, the presence of cancer or ILD. However, longer follow-up periods and future studies are necessary to confirm these results. Conclusion: The use of a myositis blot allowed classifying, stratifying the risk of ILD, the risk of cancer and the risk of mortality in IIM. IIM-ILD was the most frequent complication, usually manifested as NSIP. The associated risk factors were ARS, OM, some MSAs, Ro52+ and older age. Cancer was a serious and frequent manifestation in these patients, especially in patients with TIF1-γ and other MSAs, so it is essential to know the risk factors and perform an early screening, especially in older patients. A better knowledge of the serological profiles of IIM will provide more individualized approaches and better risk stratification, helping in the management and treatment of these patients. References: [1]Satoh et al. Clin Rev Allergy Immunol. 2017 Feb;52(1):1-19. [2]Betteridge et al. J Intern Med. 2016 Jul;280(1):8-23. Disclosure of Interests: None declared