RESUMO
AIM: To compare the prevalence of the anti-melanoma differentiation-associated gene 5 antibody (anti-MDA5 Ab) in Hong Kong Chinese patients with dermatomyositis (DM) and polymyositis (PM); in addition, to examine the association of anti-MDA5 Ab and the clinical characteristics of these patients. METHODS: Twenty consecutive existing patients with DM being followed up at the Rheumatology Clinic of Kwong Wah Hospital, Hong Kong were recruited. Twenty patients with PM were recruited from the same clinic as the controls. A commercial line blot immunoassay was used to detect the anti-MDA5 Ab in all the participants. The frequencies of anti-MDA-5 Ab in the two groups were compared. The clinical characteristics of the patients with and without the antibody were analyzed. RESULTS: Anti-MDA5 Ab was found in 30% of patients with DM but not in patients with PM. All patients with the antibody exhibited the clinically amyopathic DM (CADM) phenotype. These patients were predominantly male, younger and with shorter disease duration. Anti-MDA5 Ab was significantly associated with rapidly progressive interstitial lung disease (RP-ILD) and digital ulcers. No statistically significant association was found between other disease or treatment variables and the antibody. CONCLUSION: Anti-MDA5 Ab is found exclusively in DM patients of the CADM subtype and is associated with RP-ILD and digital ulcers, suggesting that examination of this antibody is clinically useful in Hong Kong Chinese patients with idiopathic inflammatory myopathies. However, further studies are required to assess its prognostic significance, and to explore the difference of its presentations in various populations.
