Efficacy and Safety of Cyclophosphamide Treatment in Severe Juvenile Dermatomyositis Shown by Marginal Structural Modeling

OBJECTIVE: In patients with severe or refractory juvenile dermatomyositis (JDM), second-line treatments may be required. Cyclophosphamide (CYC) is used to treat some connective tissue diseases, but evidence of efficacy in JDM is limited. This study aimed to describe clinical improvement in JDM patients treated with CYC and model efficacy of CYC compared to patients not treated with CYC. METHODS: Clinical data on skin, global and muscle disease were analyzed from patients recruited to the Juvenile Dermatomyositis Cohort and Biomarker Study. Clinical improvement following CYC treatment was described using unadjusted analysis. Marginal structural models (MSMs) were used to model treatment efficacy and adjust for confounding by indication. RESULTS: Compared to CYC start, there were reductions at 6, 12 and 24 months in skin disease (p=1.3×10-10 ), global disease (p=2.4×10-8 ), and muscle disease (p=8.0×10-10 ) for n=56 patients treated with CYC in unadjusted analysis. Limited evidence suggested reduction in glucocorticoid dose (p=0.047) in patients treated with CYC. MSM analysis showed reduced global disease and skin disease in patients who started CYC treatment over 12 months ago compared to patients never or not yet treated with CYC. In these patients, modified disease activity score for skin disease was 1.19 units lower (p=0.0085) and physician's global assessment was 0.66 units lower (p=0.027). Minor adverse events were reported in 3 patients within 1 year of stopping CYC. CONCLUSION: CYC is efficacious with no short-term side-effects seen in this study. Improvements in skin, global and muscle disease were observed. Further studies are required to evaluate longer-term side-effects. This article is protected by copyright. All rights reserved

Muscle biopsy in combination with myositis-specific autoantibodies aids prediction of outcomes in juvenile dermatomyositis

OBJECTIVE: Juvenile dermatomyositis (JDM) is a rare and severe autoimmune condition characterized by rash and proximal muscle weakness. While some patients respond to standard treatment, others do not. We investigated whether histopathology and myositis-specific autoantibodies (MSA) have prognostic significance. // METHODS: Muscle biopsy samples (n=101) from the UK JDM Cohort and Biomarker Study were stained, analyzed and scored. Autoantibodies were measured (n=90) and longitudinal clinical data were collected (median follow-up 4.9 years). Long-term treatment status was modelled using generalized estimating equations. // RESULTS: Muscle biopsy scores differed according to MSA. When effects of MSA were accounted for, increased severity of muscle pathology predicted increased risk of remaining on treatment over time: 1.48-fold higher odds (1.12-1.96, p=0.0058) for the global pathology score (hVAS) and 1.10-fold higher odds (1.01-1.21, p=0.038) for the total biopsy score for the standardized score tool. A protective effect was identified in patients with anti-Mi2 autoantibodies, who had 7.06-fold lower odds (1.41-35.36, p=0.018) of remaining on treatment, despite displaying more severe muscle pathology at biopsy. For patients with anti-NXP-2, anti-TIF1γ autoantibodies or no-detectable autoantibody, increased severity of muscle pathology alone could predict the risk of remaining on treatment, without adjustment for MSA: 1.61-fold higher odds (1.16-2.22, p=0.0040) for hVAS and 1.13-fold higher odds (1.03-1.24, p=0.013) for total biopsy score. // CONCLUSION: Muscle pathology, in combination with MSA, predicts the risk of remaining on treatment in JDM and may be useful for discussing probable treatment length with parents and patients. Understanding these associations may identify patients at greater risk of severe disease

CD19+CD24hiCD38hi B Cells Are Expanded in Juvenile Dermatomyositis and Exhibit a Pro-Inflammatory Phenotype After Activation Through Toll-Like Receptor 7 and Interferon-α

Juvenile dermatomyositis (JDM) is a rare form of childhood autoimmune myositis that presents with proximal muscle weakness and skin rash. B cells are strongly implicated in the pathogenesis of the disease, but the underlying mechanisms are unknown. Therefore, the main objective of our study was to investigate mechanisms driving B cell lymphocytosis and define pathological features of B cells in JDM patients. Patients were recruited through the UK JDM Cohort and Biomarker study. Peripheral blood B cell subpopulations were immunophenotyped by flow cytometry. The results identified that immature transitional B cells were significantly expanded in active JDM, actively dividing, and correlated positively with disease activity. Protein and RNAseq analysis revealed high interferon alpha (IFNa) and TLR7-pathway signatures pre-treatment. Stimulation of B cells through TLR7/8 promoted both IL-10 and IL-6 production in controls but failed to induce IL-10 in JDM patient cells. Interrogation of the CD40-CD40L pathway (known to induce B cell IL-10 and IL-6) revealed similar expression of IL-10 and IL-6 in B cells cultured with CD40L from both JDM patients and controls. In conclusion, JDM patients with active disease have a significantly expanded immature transitional B cell population which correlated with the type I IFN signature. Activation through TLR7 and IFNa may drive the expansion of immature transitional B cells in JDM and skew the cells toward a pro-inflammatory phenotype