Clinical characteristics and change in the antibody titres of patients with anti-MDA5 antibody–positive inflammatory myositis

The aim of this study was to evaluate the clinical characteristics of patients with anti-melanoma differentiation-associated gene 5 (MDA5) antibody-positive inflammatory myositis, and the change in anti-MDA5 antibody titres before and after onset.For 105 PM/DM patients, newly diagnosed in our hospital within the period 2008-2016, serum anti-MDA5 antibody levels were measured at diagnosis and after treatment by ELISA using the MESACUP anti-MDA5 test. The relationships between anti-MDA5 antibody levels and clinical manifestations, laboratory data, and mortality were examined.Compared with patients who were anti-MDA5 antibody negative, those who were antibody positive demonstrated more frequent dermatitis, clinically amyopathic DM, interstitial lung disease and rapid-progressive interstitial lung disease, as well as significantly higher serum ferritin, significantly lower creatine kinase and aldolase, and significantly less frequent ANA (⩾1:160) and anti-cytoplasmic pattern of ANA staining positivity. Anti-MDA5 antibody titres were examined before disease onset in two patients; one showed antibody positivity with low titres 2 years earlier, while both exhibited increased titres at onset. Anti-MDA5 antibody titres declined significantly less in survivors than in non-survivors after treatment; however, there was no significant difference between the two groups when the rate was compared at 2 months after treatment.An initial decrease in anti-MDA5 antibody titre after commencement of treatment was observed in most of the patients, including in fatal cases, suggesting that this may not necessarily be a useful marker for treatment of patients with DM.