Anti-MDA5 positivity: describing the frequency and spectrum of clinically evident MDA5 disease.

To evaluate experience in a tertiary rheumatology service with melanoma differentiation-association-protein-5 (MDA5) disease and testing, patients with positive autoantibody results were reviewed for the presence of clinical disease. Anti-MDA5 positivity was detected in 2% of myositis-specific antibody tests. Of these, 29% did not have features consistent with anti-MDA5 disease. However, when present, MDA5 disease is severe with a high mortality.