Anti-HMGCR myositis is usually a chronic disease requiring long-term immunosuppression. Although younger patients had more severe disease and a worse prognosis than older patients, they did not have evidence of a known co-existing muscular dystrophy to explain their persistent, and sometimes progressive, muscle weakness.

Objective Patients with immune-mediated necrotizing myopathy (IMNM) often have autoantibodies recognizing the signal recognition particle (SRP) or HMG-CoA reductase (HMGCR). Here, we studied a cohort of anti-SRP patients to identify factors associated with disease severity and clinical improvement; we also compared the severity of weakness in those with anti-SRP versus anti-HMGCR autoantibodies. Methods All anti-SRP patients in the Johns Hopkins Myositis Cohort from 2002 to 2015 were included. Longitudinal information regarding proximal muscle strength, creatine kinase (CK) levels, and immunosuppressive therapy were recorded at each visit. Univariate and multivariate multilevel regression models were used to assess prognostic factors influencing recovery. Strength in the anti-SRP patients was compared to strength in 49 previously described anti-HMGCR subjects. Results Data from 37 anti-SRP patients and 380 total clinic visits was analyzed. Younger age at onset was associated with more severe weakness at the first visit (p=0.02) and all subsequent visits (p=0.002). Only 50% of patients reached near-full or full strength after 4 years of treatment and most of these continued to have elevated CK levels. Rituximab appeared to be effective in 13 of 17 anti-SRP patients. Anti-SRP patients were significantly weaker than those with anti-HMGCR autoantibodies (−1.3 strength points, p=0.001). Conclusions Younger age at onset is associated with more severe weakness in anti-SRP myositis. Furthermore, even among anti-SRP patients whose strength improved with immunosuppression, most had ongoing disease activity as demonstrated by elevated CK levels. Finally, anti-SRP patients were significantly weaker than anti-HMGCR patients, providing evidence that these autoantibodies are associated with distinct forms of IMNM.

Objectives Dermatomyositis (DM) patients typically present with proximal weakness and autoantibodies that are associated with distinct clinical phenotypes. We observed that DM patients with autoantibodies recognizing the nuclear matrix protein NXP-2 often presented with especially severe weakness. The aim of this study was to characterize clinical features associated with anti-NXP-2 autoantibodies. Methods 235 DM patients underwent testing for anti-NXP-2 autoantibodies. Patient characteristics, including muscle strength, were compared between those with and without these autoantibodies. The number of cancer cases observed in anti-NXP-2-positive subjects was compared with the number expected in the general population. Results 56 (23.8%) of the DM patients were anti-NXP-2-positive. There was no significant difference in the prevalence of proximal limb weakness in patients with and without anti-NXP-2. In contrast, anti-NXP-2-positive patients had more prevalent weakness in the distal arms (35% vs. 20%, p=0.02), distal legs (25% vs. 8%, p<0.001), and neck (48% vs. 23%, p<0.001). Anti-NXP-2-positive subjects were also more likely to have dysphagia (62% vs. 35%, p<0.001), myalgia (46% vs. 25%, p=0.002), calcinosis (30% vs. 17%, p=0.02) and subcutaneous edema (36% vs. 19%, p=0.01) than anti-NXP-2-negative patients. Five (9%) anti-NXP-2-positive subjects had cancer-associated myositis, representing a 3.68-fold increased risk (95% confidence interval 1.2-8.6) compared to the expected prevalence in the general population. Conclusions In DM, anti-NXP-2 autoantibodies are associated with subcutaneous edema, calcinosis, and a severe muscle phenotype characterized by myalgia, proximal and distal weakness, and dysphagia. As anti-NXP-2 positive patients have an increased risk of cancer, we suggest they should undergo comprehensive cancer screening.

The rs-fcMRI functional connectivity changes within (intranetwork) and between (internetwork) resting state networks occur after acute ON, indicating immediate cortical responses to focal inflammatory demyelination. Thus, focal white matter injury in the central nervous system acutely results in widespread network alterations that may lead to functional neurologic changes seen in MS.

Objective Although more than a dozen myositis‐specific autoantibodies (MSAs) have been identified, most patients with myositis are positive for a single MSA. The specific overexpression of a given myositis autoantigen in myositis muscle has been proposed as initiating and/or propagating autoimmunity against that particular autoantigen. The present study was undertaken to test this hypothesis. Methods In order to quantify autoantigen RNA expression, RNA sequencing was performed on muscle biopsy samples from control subjects, MSA‐positive patients with myositis, regenerating mouse muscles, and cultured human muscle cells. Results Muscle biopsy samples were available from 20 control subjects and 106 patients with autoantibodies recognizing hydroxymethylglutaryl‐coenzyme A reductase (n = 40), signal recognition particles (n = 9), Jo‐1 (n = 18), nuclear matrix protein 2 (n = 12), Mi‐2 (n = 11), transcription intermediary factor 1γ (n = 11), or melanoma differentiation–associated protein 5 (n = 5). The increased expression of a given autoantigen in myositis muscle was not associated with autoantibodies recognizing that autoantigen (all q > 0.05). In biopsy specimens from both myositis muscle and regenerating mouse muscles, autoantigen expression correlated directly with the expression of muscle regeneration markers and correlated inversely with the expression of genes encoding mature muscle proteins. Myositis autoantigens were also expressed at high levels in cultured human muscle cells. Conclusion Most myositis autoantigens are highly expressed during muscle regeneration, which may relate to the propagation of autoimmunity. However, factors other than overexpression of specific autoantigens are likely to govern the development of unique autoantibodies in individual patients with myositis.

The expression of Trim33 (Tif1γ) increases in skeletal muscles during regeneration and decreases upon maturation. Although Trim33 is required for the normal development of other tissues, its role in skeletal muscle is unknown. The current study aimed to define the role of Trim33 in muscle development and regeneration. We generated mice with muscle-specific conditional knockout of Trim33 by combining floxed Trim33 and Cre recombinase under the Pax7 promoter. Muscle regeneration was induced by injuring mouse muscles with cardiotoxin. We studied the consequences of Trim33 knockdown on viability, body weight, skeletal muscle histology, muscle regeneration, and gene expression. We also studied the effect of Trim33 silencing in satellite cells and the C2C12 mouse muscle cell line. Although Trim33 knockdown mice weighed less than control mice, their skeletal muscles were histologically unremarkable and regenerated normally following injury. Unexpectedly, RNAseq analysis revealed dramatically increased expression of cholecystokinin (CCK) in regenerating muscle from Trim33 knockout mice, satellite cells from Trim33 knockout mice, and C2C12 cells treated with Trim33 siRNA. Trim33 knockdown had no demonstrable effect on muscle differentiation or regeneration. However, Trim33 knockdown induced CCK expression in muscle, suggesting that suppression of CCK expression requires Trim33.

BackgroundMyositis patients may be classified as belonging to one of four clinical groups: dermatomyositis (DM), polymyositis (PM), clinically amyopathic dermatomyositis (CADM) or necrotizing myositis (NM). Alternatively, myositis patients may be classified according to myositis autoantibody status.ObjectivesThe aim of this study was to determine whether clinical groups or myositis autoantibodies provide better prognostic categories with regard to muscle involvement in these patients.MethodsAll Johns Hopkins Myositis Center patients from 2002 to 2015 with a myositis specific autoantibody confirmed by two different immunologic techniques were included. Autoantibody groups accounting for less than 2% of the final sample size were excluded. Strength (analyzed as the average of deltoid and hip flexor strength using Kendall's scale) and log transformed CK levels were compared between the different autoantibody groups using multilevel regression models adjusted for age, time from disease onset, sex, race and treatments. Models with different combinations of key variables were compared using the likelihood ratio test to ascertain if autoantibody groups and clinical subgroups provided the same amount of information regarding muscle weakness and CK levels over time.Results483 patients with 4181 visits were included and 10 different autoantibody groups were identified. Muscle weakness and CK levels followed a gradient among both antibody and clinical groups. Anti-SRP patients had the greatest weakness, followed by anti-HMGCR, anti-Mi2 and anti-NXP2, and then anti-Jo1. CK levels were highest in anti-HMGCR patients, followed by anti-SRP, anti-PL7, anti-Jo1 and anti-Mi2. Interestingly, strength and CK levels were dissociated in two groups: anti-NXP2 patients had significant weakness with low CK levels and anti-PL7 patients were relatively strong despite high CK levels. Multilevel regression models showed autoantibody groups explained the strength and the CK variability better than the clinical groups (AIC difference>20). Indeed, adding clinical groups to a model using only autoantibodies did not improve the model's ability to predict strength (p=0.2) and only mildly improved its ability to predict CK (p=0.01). In comparison, adding the autoantibodies to a model using the clinical groups resulted in a marked improvement in predicting both CK and strength (both p<0.001).ConclusionsIn patients with myositis, autoantibody status predicts strength and CK levels better than clinical grouping.Disclosure of InterestNone declared

The chromodomain helicase and DNA binding 4 (CHD4) protein is upregulated in regenerating myofibers. To define the role of CHD4 in muscle differentiation and regeneration, we generated mice with CHD4 ablated in muscle satellite cells (SCs). Embryonic day 18.5 CHD4 KO mice are non-viable, with atrophic intercostal and back muscles and altered expression of muscle contraction genes. Tamoxifen-inducible conditional CHD4 KO in adult mouse SCs diminished myoblast proliferation, induced premature differentiation, and altered expression of muscle contraction genes at the myotube stage. Following cardiotoxin–induced muscle injury, CHD4 KO regenerating myofibers had reduced cross-sectional area. ChIP-Seq analysis revealed that CHD4 binds actin a1, Wnt and b-catenin genes, which are known to play roles in the regulation of myogenesis. Together, our results suggest an important role for CHD4 in the control of embryonic myogenesis, SC differentiation, and the control of muscle fiber size in adult skeletal muscle during regeneration.