Benefits of adjunct plasma exchange in idiopathic inflammatory myopathy with anti-signal recognition particle antibodies：a real-world study

OBJECTIVES: To compare the efficacy of adjunct plasma exchange (PE) therapy with standard therapy in idiopathic inflammatory myopathy (IIM) with anti-signal recognition particle (SRP) antibodies. METHODS: Anti-SRP-positive myositis patients were consecutively enrolled and followed up. Two-way ANOVA was performed to compare the pre- and post-treatment changes of myositis disease activities between the two groups. The Kaplan-Meier method was performed to compare the composite end point of all-cause death and relapse after propensity score matching (PSM) and inverse probability weighting (IPW) analyses. Cox regression analyses were performed to screen long-term prognostic factors. RESULTS: In total, 53 patients were included (35 received standard therapy, 18 received adjunct PE therapy). The PE therapy group tended to have severer muscle weakness (p = 0.027), higher levels of anti-SRP antibody titers (p = 0.001), and CK (p < 0.001), as well as higher doses of corticosteroid administration (p = 0.038). At the 4-week follow-up point, both groups achieved remarkable remission as indicated by significant improvements in the six core set measures (CSMs), and the changes in the six CMSs were more prominent in the PE therapy group (all p < 0.001). During a median follow-up of 15 months, 26 patients reached the composite end point, and the PE therapy group had significantly better prognosis after IPW analysis (p = 0.029). In the multivariate cox regression analyses, PE therapy (HR: 0.14 [0.03-0.57], p = 0.006) and interstitial lung disease (HR: 4.82 [1.22-19.12], p = 0.025) turned out to be independent predictors for long-term prognosis. CONCLUSION: Adjunct PE therapy provided quick remission and sustaining benefits for IIM with anti-SRP antibodies.