Clinical Characteristics of Immune-Mediated Necrotizing Myopathy with Autoantibodies Recognizing the Signal Recognition Particle: A Retrospective Study of a Chinese Cohort

Abstract Objective: Immune-mediated necrotizing myopathy (IMNM) with autoantibodies recognizing the signal recognition particle (SRP) patients tend to have prominent proximal weakness and infrequent extra-muscular involvement, especially interstitial lung disease (ILD). However, we reported a Chinese cohort of anti-SRP IMNM patients with relatively more frequent ILD.Methods: Anti-SRP IMNM patients from September 2016 to November 2019 were included according to the most recent European Neuromuscular Center criteria for IMNM. All sera for anti-SRP autoantibody and other myositis-related autoantibodies detection were obtained before the treatment initiation. Muscle strength, coexisting autoimmunity, complications including ILD, treatment and follow-up outcomes were also recorded. Univariate logistic regression was performed to determine variables predicting bad outcomes.Results: Of 271 patients with idiopathic inflammatory myopathy tested, we diagnosed 23 (8.5%) patients with anti-SRP IMNM. Muscle weakness was presented in 23 patients (100%) and generally worse in the lower limbs. ILD was observed in 50% anti-SRP IMNM patients. Predictor of bad outcomes identified by univariate logistic regression analysis was complicated ILD (odds ratio, 3.8).Conclusion: ILD tends to be more frequent in this Chinese anti-SRP IMNM cohort from Hunan province. Complicated ILD represents a risk factor for bad outcomes for anti-SRP IMNM.