To investigate the clinical features of dermatomyositis (DM) and clinically amyopathic DM (CADM) patients with the presence of anti-melanoma differentiation-associated gene 5 (anti-MDA-5) antibodies.
We screened the serum anti-MDA-5 antibody levels of 140 patients with various connective tissue diseases (CTDs), including 32 with DM and 32 with CADM, or idiopathic pulmonary fibrosis (IPF). The clinical courses of DM/CADM patients with a positive expression of anti-MDA-5 antibodies were delineated.
Anti-MDA-5 antibodies were detected at a significantly higher frequency in CADM patients than in DM patients (12 of 32 versus 3 of 32; P = 0.016), but were not detected in patients with other CTDs or IPF and healthy controls. Patients with a positive expression of anti-MDA-5 antibodies developed significantly more skin ulcerations (12 of 15 versus 4 of 49; P < 0.001) and interstitial lung disease (ILD; 15 of 15 versus 31 of 49 [P = 0.003]) than those without anti-MDA-5 antibodies. High-resolution computed tomography scores of the MDA-5-positive subset were increased compared with the MDA-5-negative group (mean ± SD 117.7 ± 76.3 versus 54.4 ± 50.7; P = 0.004), and the scores correlated well with anti-MDA-5 antibody levels (r(2)  = 0.582, P = 0.029). The respiratory symptoms as well as skin ulcerations were dramatically improved in patients with anti-MDA-5 antibody levels <500 units/ml after treatment, whereas patients with anti-MDA-5 antibody levels >500 units/ml were resistant to the treatment and died of respiratory failure in a short period of time.
Anti-MDA-5 antibody levels closely correlate with the severity of skin ulcerations, ILD, and the prognosis of the disease. Dynamic observation of serum anti-MDA-5 antibody levels would be helpful in predicting the course of ILD and facilitating better therapeutic targeting.