Frequency and clinical relevance of anti-Mi-2 autoantibody in adult Brazilian patients with dermatomyositis

To analyze the frequency and clinical relevance of anti-Mi-2 autoantibody in a representative sample of patients with dermatomyositis. This longitudinal inception cohort study, from 2001 to 2017, included 87 definite adult dermatomyositis. Anti-Mi-2 analysis was performed using a commercial kit. Seventeen patients (19.5%) had anti-Mi-2 and 70 (80.5%) did not have this autoantibody. The following parameters were equally distributed between the patients with versus without anti-Mi-2: mean age at the disease diagnosis onset, median follow-up time, constitutional symptoms (baseline), cutaneous cumulative lesions, dysphagia, joint and pulmonary involvement. There was also no difference between the groups in relation to follow-up time, disease relapsing, treatment, disease status, deaths and occurrence of neoplasia. In contrast, patients with anti-Mi2 antibodies had higher frequency of elevated serum levels of muscle enzymes at disease onset (median: creatine phosphokinase 6240 [3800-9148] U/L and aldolase 60.0 [35.0-138.0] U/L), lower frequency of pulmonary involvement at disease onset (5.9%), less current glucocorticoid dose (median: 0 [0-10] mg/day), and higher frequency of disease remission during follow-up (58.8%) in comparison with patients without anti-Mi-2 autoantibody (484 [115-4880] and 12.1 [6.3-70.0] U/L, 40.0%, 0 [0-10] mg/day, 27.1%, respectively). The anti-Mi-2 autoantibody was found in one fifth of patients with dermatomyositis. This autoantibody was associated with a lower occurrence of pulmonary involvement, a higher frequency of disease in remission, and elevated levels of muscle enzymes. There was also no correlation regarding the frequency of disease relapsing or neoplasia development.