[Retrospective study on clinical manifestation, thigh MRI and electrophysiology characteristics of immune-mediated necrotizing myopathy].

To summarize the clinical, thigh magnetic resonance (tMRI) and electromyographic (EMG) characteristics in patients with immune-mediated necrotizing myopathy (IMNM). A total of 32 IMNM patients who were admitted to the Department of Neurology from April 2019 to April 2021 were enrolled at the First Medical Centre of Chinese PLA General Hospital. According to the type of antibody, the patients were divided into anti-SRP antibody positive (SRP) group, anti-HMGCR antibody positive (HMGCR) group and seronegative (SN) group. The gender, age, course of disease, myositis antibodies, extramuscular manifestations, EMG were collected and analyzed among three groups. The characteristics of skeletal muscle were assessed by tMRI inflammatory edema and fat infiltration scores. Analysis of variance, Kruskal-Wallis test and Chi-square test were used to compare the differences in different clinical characteristics and tMRI scores among the three groups. When there was a statistical difference among the three groups, the comparison between the two groups was corrected by the Bonferroni method. (1) Of the 32 patients, 20 were females (62.5%).The median age of onset was 47±14 years, 25 (78.1%) patients had an acute or subacute course.There were 17 (53.1%) with SRP, 8 (25.0%) with HMGCR, and 7 (21.9%) with MSAs (myositis specific antibodies) negative. Anti-Ro52 antibody was the most common combined antibody (12/32, 37.5%), among which 10 were in SRPgroup.(2) The CK of all patients were elevated, median was 5 948 (4 229, 7 664) U/L. There was no statistical difference of MMT scores among three groups. The proximal limb score was lower than distal limb (<0.01). The axial muscle score was lower than the distal limb score (<0.05).(3) Extramuscular manifestations of HMGCR group were lower than those of the other two groups (12.5% vs. 71.4% and 76.5%, <0.017). Rash (60.0% vs.14.3%, <0.05) and interstitial pulmonary diseases (70.0% vs. 14.3%, <0.05) were more common in patients with anti-SRP coexistence with anti-Ro52 than those with isolated anti-SRP. Connective tissue disease was more common in SN group (57.1% vs. 11.8% and 0, <0.017).(4) tMRI showed fascial edema of SN group was more obvious than that of the other two groups (<0.017). There was no statistical difference in the degree of fat infiltration and inflammatory edema among three groups, but SRP group had more cases of early fat infiltration.(5) Myotonic potentials (25.0% vs. 0 and 0, <0.017) and compound repetitive discharges (CRDs) (50.0% vs. 5.9% and 0, <0.017) were common in HMGCR group. Proteomic analysis found significantly different expressed proteins in skeletal muscle of patients with myotonic potentials or CRDs were associated with cytoskeleton, cell junction and extracellular matrix. IMNM with pure anti-SRP antibody positive and anti-HMGCR positive were mainly affected by skeletal muscles. Those who were co-positive for anti-SRP antibody and anti-Ro52 antibody had more extramuscular manifestations, which might be a special subtype of SRP group. This study proposed for the first time that myofascial inflammatory edema is an early sign of SN-IMNM injury. EMG of HMGCRgroup were more prone to myotonia potential and CRDs.