CHARACTERISATION OF SWEDISH MYOSITIS PATIENTS WITH ANTI-MDA5 AUTOANTIBODIES AND CORRELATION OF CLINICAL FEATURES WITH AUTOANTIBODY LEVELS

• The association between anti-melanoma differentiation association protein 5 autoantibodies (aMDA5) and rapidly progressive interstitial lung disease (RP-ILD) in clinically amyopathic dermatomyositis is well established in Asian population cohorts. In western cohorts, ILD has been strongly associated with aMDA5 but data regarding RP-ILD have been more conflicting. It is also suggested that western cohorts have more pronounced myopathic features than Asian.ObjectivesTo characterise the disease manifestations of a Swedish aMDA5 positive idiopathic inflammatory myositis (IIM) cohort and to explore antigen reactivity of the MDA5 protein.MethodsFirst available serum samples collected from 28 consecutive patients with IIM and positive aMDA5 ever tested by ELISA, Line Blot (LB) or Immunoprecipitation, attending Karolinska University Hospital between 1999 and 2021, were included. Clinical data including presence of anti-SSA autoantibodies by ELISA or LB was retrieved retrospectively. An in-house ELISA was used to screen serum samples for reactivity against a recombinant MDA5 protein (rMDA5, aa A110-D1025, UniProt ID Q9BYX4) and seven MDA5-derived constructs containing different domains. Correlations between aMDA5 reactivity levels and clinical data were explored.ResultsNine patients showed no reactivity to any of the rMDA5 constructs by ELISA and were excluded from further analysis.Reactivity against rMDA5 was confirmed by ELISA in 19 patients (median 184.7 µg/mL (interquartile range (IQR) 277.07). The cohort included 13 male and 6 female patients, 94% Caucasian, with mean age at diagnosis of 41.05 years (standard deviation (SD) 10.5). Median disease duration at time of sampling was 0 months (IQR 1). All patients except one had signs of muscle involvement (muscle weakness, elevated muscle enzymes, muscle oedema or muscle biopsy consistent with myositis). At diagnosis 63.2% of patients reported muscle weakness (21.1 % had a manual muscle test 8 score <75). Dermatological findings were observed in 17/19 (89.7 %). During disease course nine patients (47.4%) had confirmed arthritis.ILD was diagnosed in 16/19 patients (84.2%), four of these (25%) developed a RP-ILD. One patient passed away due to RP-ILD and one required a lung transplant. Patients with ILD had a statistically significant higher mean age at diagnosis than those without (42.8.5 (SD 10.3) vs 31.3 (SD 4.7) years, p=0.02). Patients developing RP-ILD were not significantly older than patients with chronic ILD. Respiratory symptoms were reported by 75% of patients with ILD at time of diagnosis. The mean total lung capacity (TLC) of the ILD cohort was 68% (SD 17), mean diffusion capacity of carbon monoxide (DLCO) was 59% (SD 15) and mean forced vital capacity (FVC) was 62% (SD 19). There was a higher proportion of patients with CRP ≥ 3 times the reference range at diagnosis amongst patients with FVC <70 % than patients with FVC >70 % (88.9 % vs 16.7 %, p= 0.01).Ten patients (52.6%) had anti-SSA autoantibodies, all had ILD. Anti-SSA positive patients had a statistically significant lower TLC than those without (62% vs 79% respectively, p=0.04) and a lower FVC (57% vs 76% respectively, p=0.05).We found a weak non-statistically significant negative correlation between titres of aMDA5 and TLC, DLCO and FVC (Pearson coefficients -0.187, -0.289, -0.130 respectively). Frequency of ILD was higher in patients with aMDA5 titres >100 µg/mL than those with titers <100, but not statistically significant (81.3% vs 18.8%, respectively).ConclusionIn this Caucasian cohort of aMDA5 positive IIM patients, ILD was present in over 80% of patients, of these, one quarter had RP-ILD. Older patients were more likely to present with ILD. Anti-SSA positivity and higher CRP levels were associated with worse lung function. We found a weak negative correlation between aMDA5 titres and lung function tests, as well as a trend of higher frequency of ILD in patients with higher aMDA5 titres. Muscle and skin involvement were found in a high proportion of patients.AcknowledgementsD. Demirdal & E. Van Gompel contributed equally to this abstract.Disclosure of InterestsDeniz Demirdal: None declared, Eveline Van Gompel: None declared, Edvard Wigren: None declared, Maryam Dastmalchi: None declared, Begum Horuluoglu: None declared, Angeles Shunashy Galindo-Feria: None declared, Susanne Gräslund: None declared, Karine Chemin: None declared, Ingrid E. Lundberg Shareholder of: Roche and Novartis., Consultant of: Consulting fees from Corbus Pharmaceuticals Inc, Astra Zeneca, Bristol Myer´s Squibb, Corbus Pharmaceutical, EMD Serono Research & Development Institute, Argenx, Octapharma, Kezaar, Orphazyme, and Janssen, Grant/research support from: Research grants from Astra Zeneca, Antonella Notarnicola Speakers bureau: compensation for lecture at conference sponsored by Boehringer Ingelheim.

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