Anti-SS-A/Ro antibody positivity as a risk factor for relapse in patients with polymyositis/dermatomyositis

Objective: The objective of this study is to elucidate predictors of relapse in patients with polymyositis and dermatomyositis (PM/DM). Methods: Fifty PM/DM patients who achieved disease stabilization at Okayama University Hospital in 2004–2014 were enrolled retrospectively. Candidate predictors such as demographic factors, clinical symptoms, laboratory data, and treatment status were compared. Results: The mean age of enrolled patients was 58 years; 34 were female. The patient groupings were as follows: 21 with PM, 27 with DM, and two with clinically amyopathic DM. During a mean observation period of 685 d, 5 patients (10%) died and 20 (40%) relapsed. The relapsed patients displayed baseline muscle weakness less frequently (85% versus 100%, p =.03) and anti-SS-A/Ro antibody more frequently (65% versus 27%, p =.007). Anti-SS-A/Ro-positive patients exhibited a higher relapse rate than anti-SS-A/Ro-negative patients (log-rank test, p =.03). Anti-SS-A/Ro-positive patients also exhibited higher anti-Jo-1 antibody positivity and lower levels of serum complement. After adjusting anti-Jo-1 antibody positivity, age, sex, CK <500 IU/L, and lung involvement, anti-SS-A/Ro positivity was still an independent risk factor for higher relapse-rate (odds ratio, 5.5; 95% confidence interval, 1.4–25.1). Conclusions: Anti-SS-A/Ro antibody positivity may be a useful biomarker for prediction of relapse.