SAT0297 DISTINCT CLINICAL PROFILES OF CHINESE AND SWEDISH IDIOPATHIC INFLAMMATORY MYOPATHY PATIENTS WITH ANTI-MELANOMA DIFFERENTIATION ASSOCIATED GENE 5 (MDA5) ANTIBODY
Authors: Ho SO, Tak Lung Victor Wong, Maryam Dastmalchi, Valerie Leclair, Fabricio Espinosa-Ortega, Ingrid E. Lundberg
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 Ab) is one of the most clinically important myositis specific antibodies. It has been found to be associated with severe cutaneous and pulmonary complications. Nonetheless, there appears to be geographical variations in the prevalence and phenotypic presentation of the antibody [1]. We conducted the first comparative study of two ethno-geographically different idiopathic inflammatory myopathy (IIM) cohorts focusing on anti-MDA5 Ab, using standardized classification criteria, antibody detection methods and clinical features assessment. <h3>Objectives:</h3> The objectives of the study were to compare the prevalence of the anti-MDA5 Ab and its associated clinical features between Chinese IIM patients in Hong Kong and Caucasian patients in Sweden. <h3>Methods:</h3> This multicenter retrospective cohort study was conducted on IIM patients followed up in the rheumatology clinic or admitted to the rheumatology wards of the participating hospitals in Hong Kong and Sweden with anti-MDA5 Ab tested between September 2015 and August 2018. The diagnosis of IIM was based on the 2017 European League Against Rheumatism/American College of Rheumatology Classification Criteria with definite or probable cases being included. Demographics and clinical features were collected by reviewing the medical records. A commercial line blot immunoassay kit (EUROIMMUN) was used to detect the anti-MDA5 autoantibodies. <h3>Results:</h3> Altogether, 409 patients with IIM (Sweden: 206, Hong Kong: 203) were recruited. The Swedish patients were generally older (mean age 58.1 vs 51.5 years, p&lt;0.001) at diagnosis, and more of them were male (41.4% vs 23.2%, p&lt;0.001). Subgroups of patients were: dermatomyositis 42.9%, polymyositis 39.3%, inclusion body myositis 15.7% and clinically amyopathic dermatomyositis 2.1% in the Swedish cohort, and 39.4%, 39.4%, 0% and 21.2% respectively in the Chinese cohort. Anti-MDA5 Ab was found in 11.8% of the Chinese and 5.83% of the Swedish patients (p=0.032). The Hong Kong Chinese patients were found to have significantly more ILD (52.7% vs 34.7%) and RPILD (9.41% v 3.65%), while the Swedish patients had more dysphagia (55.3% vs 29.7%) and cardiac involvement (14.0% vs 5.3%). Anti-MDA5 Ab was associated with male gender, younger age at diagnosis, amyopathy, refractory rash, ILD and RPILD in the Swedish patients. The same associations were found in the Chinese patients except the young age at diagnosis. Besides, in the Chinese cohort, the antibody was also positively associated with skin ulceration, vasculitis and hoarseness, but negatively associated with cancer, dysphagia and other connective tissue diseases. When comparing only patients with anti-MDA5 Ab, Chinese patients were significantly older at diagnosis (mean age 47.9 vs 36.4 years, p=0.001), more likely to be amyopathic (79.2% vs 18.2%, p=0.002) and had more vasculitic skin changes (65.2% vs 0%, p&lt;0.001) than the Swedish patients. They also had a tendency towards developing more skin ulcers (45.8% vs 18.2%, p=0.15) and less dysphagia (8.33% vs 36.4%, p=0.063). <h3>Conclusion:</h3> The distinct clinical profiles identified in the Chinese and Swedish IIM patients with anti-MDA5 Ab could depend on different genetic or environmental factors, and may enhance our knowledge about the clinical utility of the antibody and help deciphering the pathogenesis of this complex disease. <h3>Reference</h3> [1] So H, Ip R, Wong V, Yip R. Analysis of anti-melanoma differentiation-associated gene 5 antibody in Hong Kong Chinese patients with idiopathic inflammatory myopathies: diagnostic utility and clinical correlations. Int J Rheum Dis2018;21(5):1076-1081. <h3>Disclosure of Interests:</h3> Ho SO: None declared, Tak Lung Victor Wong: None declared, Maryam Dastmalchi: None declared, Valerie Leclair: None declared, Fabricio Espinosa-Ortega: None declared, Ingrid E. Lundberg Grant/research support from: Dr. Lundberg has received honoraria from Bristol Myers Squibb and MedImmune and is currently receiving a research grant from Bristol Myers Squibb and from Astra Zeneca., Consultant for: She is a scientific advisor for Bristol Myers Squibb, and aTyr