Different phenotypic manifestations between Brazilian and Japanese anti-MDA5 antibody-positive dermatomyositis: an international tricentric longitudinal study.

Objectives: Anti-MDA5 autoantibodies are strongly associated with interstitial lung disease (ILD) and rapidly progressive ILD (RP-ILD) in Asian patients with dermatomyositis (DM) or amyopathic DM (ADM). However, this association has not yet been established in Brazilian patients with anti-MDA5(+) DM/ADM. This study aimed to investigate the phenotypic differences between Brazilian and Japanese patients with anti-MDA5(+) DM/ADM, with a particular focus on ILD.

Methods: This was an international, tricentric, retrospective cohort study conducted in one Brazilian and two Japanese tertiary centres. Patients diagnosed with anti-MDA5(+) DM/ADM at the three centres were enrolled. Clinical characteristics and outcomes were collected using a pre-standardised protocol and compared between Brazilian and Japanese patients.

Results: Thirty-four Brazilian and 65 Japanese patients were analysed. Brazilian patients were younger at the time of diagnosis than Japanese patients. The prevalence of muscle weakness, myalgia, dysphagia, heliotrope rash, V-sign, calcinosis, Raynaud's phenomenon, and digital ulcers was higher in Brazilian patients, whereas mechanic's hands were more prevalent in Japanese patients. The prevalence of ILD was significantly lower in Brazilian patients than in Japanese patients (50.0% vs. 98.5%, P<0.001). RP-ILD was observed in 34 (52.3%) Japanese patients and in only one (3.3%) Brazilian patient (P<0.001). Outcomes including overall survival and the frequency of relapses and complications, such as severe infection and malignancy, were comparable between the two populations.

Conclusions: Brazilian patients with anti-MDA5(+) DM/ADM had a higher prevalence of skin and muscle involvement, whereas the prevalence of ILD and RP-ILD was significantly lower than in Japanese patients.