High frequency of muscle activity relapses in anti-synthetase syndrome

Background To date, no study has analyzed muscular activity relapses in anti-synthetase syndrome (ASyS), underscoring the necessity for this investigation. Methods . This single-center retrospective cohort study, conducted between 2010 and 2014, included patients with anti-Jo-1 ASyS. Results . A total of 95 patients with ASyS were identified. However, we excluded patients with anti-aminoacyl-tRNA-synthetase non-Jo-1 antibodies (n = 26), or myositis-associated autoantibodies (n = 25), without muscle involvement (n = 10), and those with incomplete data (n = 2). Consequently, a total of 48 anti-Jo-1 ASyS patients were evaluated with a median age of 44 (interquartile range: 35–54) years, predominantly female (81.3%), and of white ethnicity (79.2%). The median follow-up period was 80 (26–126) months. Twenty patients (41.7%) experienced second muscle activity during follow-up, whereas 10 (20.8%) and four (10.4%) experienced third and fourth muscle relapses, respectively. Compared to those without muscle relapse (n = 20), patients with at least one muscle relapse (n = 28) were younger (48 vs . 39 years, respectively; P = 0.020), exhibited a higher median creatine phosphokinase level (4144 vs . 8124U/L; P = 0.019), and demonstrated lower rates of pulmonary involvement, specifically ground-glass opacity (P = 0.006) and lung fibrosis (P = 0.003). There was no significant difference in treatment between patients with and without muscle relapse, except for cyclophosphamide, which was more frequently utilized in patients without muscle relapse (5.0% vs . 32.9%; P = 0.031). Conclusion . A high frequency of muscle activity relapse was observed in patients with ASyS, particularly among younger individuals with high initial creatine phosphokinase levels and reduced pulmonary involvement. A small subset of patients experienced more than three muscle relapses.