Muscle biopsy features of idiopathic inflammatory myopathies and differential diagnosis

Anti-nuclear matrix protein 2 antibody-positive amyopathic dermatomyositis presenting in a patient with prostate cancer: A case report

Nuclear matrix protein (NXP-2) positive amyopathic dermatomyositis (DM) may present without classic symptoms like muscle weakness, dysphagia, and edema, and mimic conditions like cutaneous lupus. Given DM's association with malignancy and interstitial lung disease, prompt and accurate diagnosis is important. Testing for myositis-specific antibodies aids diagnosis in ambiguous cases.

Sporadic Inclusion Body Myositis at the Crossroads between Muscle Degeneration, Inflammation, and Aging

Sporadic inclusion body myositis (sIBM) is the most common muscle disease of older people and is clinically characterized by slowly progressive asymmetrical muscle weakness, predominantly affecting the quadriceps, deep finger flexors, and foot extensors. At present, there are no enduring treatments for this relentless disease that eventually leads to severe disability and wheelchair dependency. Although sIBM is considered a rare muscle disorder, its prevalence is certainly higher as the disease is often undiagnosed or misdiagnosed. The histopathological phenotype of sIBM muscle biopsy includes muscle fiber degeneration and endomysial lymphocytic infiltrates that mainly consist of cytotoxic CD8+ T cells surrounding nonnecrotic muscle fibers expressing MHCI. Muscle fiber degeneration is characterized by vacuolization and the accumulation of congophilic misfolded multi-protein aggregates, mainly in their non-vacuolated cytoplasm. Many players have been identified in sIBM pathogenesis, including environmental factors, autoimmunity, abnormalities of protein transcription and processing, the accumulation of several toxic proteins, the impairment of autophagy and the ubiquitin-proteasome system, oxidative and nitrative stress, endoplasmic reticulum stress, myonuclear degeneration, and mitochondrial dysfunction. Aging has also been proposed as a contributor to the disease. However, the interplay between these processes and the primary event that leads to the coexistence of autoimmune and degenerative changes is still under debate. Here, we outline our current understanding of disease pathogenesis, focusing on degenerative mechanisms, and discuss the possible involvement of aging.

Recurrent Temporal Infections: The Link to Systemic Lupus Erythematosus

BACKGROUND Systemic lupus erythematosus (SLE) is an autoimmune disease with diverse manifestations. The involvement of the musculoskeletal system is very common, and infection is one of the manifestations, which can involve any part of the body. We report a case of a middle-aged woman with recurrent episodes of infection of her left temple. CASE REPORT A 51-year old woman was referred to our clinic following failures to eradicate infection on her left temple for 9 months. Examination revealed facial asymmetry, with diffuse non-tender swelling involving her left temple area, which extended to her cheek. Computed tomography and magnetic resonance imaging (MRI) showed a periosteal reaction of the zygomatic bone. Left temporalis muscle thickening and residual osteomyelitis of the zygomatic bone were also shown by MRI. In view of the unresolved infection with incision and drainage and antibiotics, further blood investigations led to the discovery of SLE. The antinuclear antibody and anti-double-stranded DNA were positive. In addition, low nephelometry markers, C3 (26.7 mg/dL) and C4 (8.24 mg/dL), were observed. This patient was treated with 200 mg of oral hydrochloroquine once daily and 5 mg of oral prednisolone once daily. After 6 months of treatment, the infection subsided, and the structures involved showed remarkable healing. The patient is still taking the same dose and frequency of both drugs at the present time. CONCLUSIONS Temporalis pyomyositis and osteomyelitis of the zygomatic bone could be manifestation of SLE disease; however, the involvement of infection cannot be ruled out.

Muscle fibrosis as a prognostic biomarker in facioscapulohumeral muscular dystrophy: a retrospective cohort study

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant epigenetic disorder with highly variable muscle involvement and disease progression. Ongoing clinical trials, aimed at counteracting muscle degeneration and disease progression in FSHD patients, increase the need for reliable biomarkers. Muscle magnetic resonance imaging (MRI) studies showed that the appearance of STIR-positive (STIR+) lesions in FSHD muscles represents an initial stage of muscle damage, preceding irreversible adipose changes. Our study aimed to investigate fibrosis, a parameter of muscle degeneration undetectable by MRI, in relation to disease activity and progression of FSHD muscles. We histologically evaluated collagen in FSHD1 patients' (STIR+ n = 27, STIR- n = 28) and healthy volunteers' (n = 12) muscles by picrosirius red staining. All patients (n = 55) performed muscle MRI before biopsy, 45 patients also after 1 year and 36 patients also after 2 years. Fat content (T1 signal) and oedema/inflammation (STIR signal) were evaluated at baseline and at 1- and 2-year MRI follow-up. STIR+ muscles showed significantly higher collagen compared to both STIR- (p = 0.001) and healthy muscles (p < 0.0001). STIR- muscles showed a higher collagen content compared to healthy muscles (p = 0.0194). FSHD muscles with a worsening in fatty infiltration during 1- (P = 0.007) and 2-year (P < 0.0001) MRI follow-up showed a collagen content of 3.6- and 3.7-fold higher compared to FSHD muscles with no sign of progression. Moreover, the fibrosis was significantly higher in STIR+ muscles who showed a worsening in fatty infiltration in a timeframe of 2 years compared to both STIR- (P = 0.0006) and STIR+ muscles with no sign of progression (P = 0.02). Fibrosis is a sign of muscle degeneration undetectable at MRI never deeply investigated in FSHD patients. Our data show that 23/27 of STIR+ and 12/28 STIR- muscles have a higher amount of collagen deposition compared to healthy muscles. Fibrosis is higher in FSHD muscles with a worsening in fatty infiltration thus suggesting that its evaluation with innovative non-invasive techniques could be a candidate prognostic biomarker for FSHD, to be used to stratify patients and to evaluate the efficacy of therapeutic treatments.

Antigen-driven T cell-macrophage interactions mediate the interface between innate and adaptive immunity in histidyl-tRNA synthetase-induced myositis

Introduction

Previous work in humans has demonstrated that both innate and adaptive immune signaling pathways contribute to the pathogenesis of idiopathic inflammatory myopathy (IIM), a systemic autoimmune disease targeting muscle as well as extra-muscular organs. To better define interactive signaling networks in IIM, we characterized the cellular phenotype and transcriptomic profiles of muscle-infiltrating cells in our established murine model of histidyl-tRNA synthetase (HRS)-induced myositis.

Methods

Myositis was induced in wild type (WT) and various congenic/mutant strains of C57BL/6 mice through intramuscular immunization with recombinant HRS. Histopathological, immunohistochemical, flow cytometric, and transcriptomic assessments were used to characterize the functional relationship between muscle-infiltrating cell populations in these strains lacking different components of innate and/or adaptive immune signaling.

Results

RAG1 KO mice developed markedly reduced muscle inflammation relative to WT mice, demonstrating a key requirement for T cells in driving HRS-induced myositis. While the reduction of mononuclear cell infiltrates in CD4-Cre.MyD88fl/fl conditional knockout mice and OT-II TCR transgenic mice highlighted roles for both innate and TCR-mediated/adaptive immune signaling in T cells, diminished inflammation in Lyz2-Cre.MyD88fl/fl conditional knockout mice underscored the importance of macrophage/myeloid cell populations in supporting T cell infiltration. Single cell RNA sequencing-based clustering of muscle-infiltrating subpopulations and associated pathway analyses showed that perturbations of T cell signaling/function alter the distribution and phenotype of macrophages, fibroblasts, and other non-lymphoid cell populations contributing to HRS-induced myositis.

Discussion

Overall, HRS-induced myositis reflects the complex interplay between multiple cell types that collectively drive a TH1-predominant, pro-inflammatory tissue phenotype requiring antigen-mediated activation of both MyD88- and TCR-dependent T cell signaling pathways.

Delayed skeletal muscle repair following inflammatory damage in simulated agent-based models of muscle regeneration

Healthy skeletal muscle undergoes repair in response to mechanically localised strains during activities such as exercise. The ability of cells to transduce the external stimuli into a cascade of cell signalling responses is important to the process of muscle repair and regeneration. In chronic myopathies such as Duchenne muscular dystrophy and inflammatory myopathies, muscle is often subject to chronic necrosis and inflammation that perturbs tissue homeostasis and leads to non-localised, widespread damage across the tissue. Here we present an agent-based model that simulates muscle repair in response to both localised eccentric contractions similar to what would be experienced during exercise, and non-localised widespread inflammatory damage that is present in chronic disease. Computational modelling of muscle repair allows for in silico exploration of phenomena related to muscle disease. In our model, widespread inflammation led to delayed clearance of tissue damage, and delayed repair for recovery of initial fibril counts at all damage levels. Macrophage recruitment was delayed and significantly higher in widespread compared to localised damage. At higher damage percentages of 10%, widespread damage led to impaired muscle regeneration and changes in muscle geometry that represented alterations commonly observed in chronic myopathies, such as fibrosis. This computational work offers insight into the progression and aetiology of inflammatory muscle diseases, and suggests a focus on the muscle regeneration cascade in understanding the progression of muscle damage in inflammatory myopathies.

Paraneoplastic Neurologic Disorders

PURPOSE OF REVIEW

To provide an overview and highlight recent updates in the field of paraneoplastic neurologic disorders.

RECENT FINDINGS

The prevalence of paraneoplastic neurologic disorders is greater than previously reported and the incidence has been rising over time, due to improved recognition in the era of antibody biomarkers. Updated diagnostic criteria that are broadly inclusive and also contain diagnostic risk for clinical presentations (high and intermediate) and diagnostic antibodies (high, intermediate, and low) have replaced the original 2004 criteria. Antibody biomarkers continue to be characterized (e.g., KLHL-11 associated with seminoma in men with brainstem encephalitis). Some paraneoplastic antibodies also provide insight into likely immunotherapy response and prognosis. The rise of immune checkpoint inhibitors as cancer therapeutics has been associated with newly observed immune-mediated adverse effects including paraneoplastic neurological disorders. The therapeutic approach to paraneoplastic neurologic disorders is centered around cancer care and trials of immune therapy. The field of paraneoplastic neurologic disorders continues to be advanced by the identification of novel antibody biomarkers which have diagnostic utility, and give insight into likely treatment responses and outcomes.

Immunoproteasome subunit β5i promotes perifascicular muscle atrophy in dermatomyositis by upregulating RIG-I

BACKGROUND

Perifascicular atrophy is a unique pathological hallmark in dermatomyositis (DM)-affected muscles; however, the mechanism underlying this process remains unclear. In this study, we aimed to investigate the potential role of the immunoproteasome subunit β5i and retinoic acid-inducible gene-I (RIG-I) in DM-associated muscle atrophy.

METHODS

The expression of β5i and RIG-I in the muscles of 16 patients with DM was examined by PCR, western blotting and immunohistochemistry. The associations between β5i and RIG-I expression levels and muscle disease severity were evaluated. Lentivirus transduction was used to overexpress β5i in human skeletal muscle myoblasts (HSMMs) and consequent cell functional changes were studied in vitro.

RESULTS

β5i and RIG-I expression in the muscle of patients with DM was significantly increased and closely associated with muscle disease severity. Immunohistochemistry and immunofluorescence analyses showed the marked colocalised expression of β5i and RIG-I in perifascicular myofibres. β5i overexpression in HSMMs significantly upregulated RIG-I, the muscle atrophy marker MuRF1, type I IFN-related proteins (MxA and IFNβ) and NF-κB pathway-related proteins (pIκBα, pIRF3 and pNF-κBp65). In addition, the viability of HSMMs decreased significantly after β5i overexpression and was partly recovered by treatment with a β5i inhibitor (PR957). Moreover, activation of RIG-I by pppRNA upregulated IFNβ and MuRF1 and reduced the cell viability of HSMMs.

CONCLUSION

The immunoproteasome subunit β5i promotes perifascicular muscle atrophy in DM via RIG-I upregulation; our findings suggest a pathomechanistic role of β5i and RIG-I in DM-associated muscle damage, highlighting these components as potential therapeutic targets for the treatment of DM.

Immune Checkpoint Inhibitor-Associated Myositis: A Distinct Form of Inflammatory Myopathy

ABSTRACT

Research on the relationship between inflammatory myopathy and malignancy has grown considerably within the last century. Now, the burgeoning field of inflammatory myopathy has yet another player in the mix: immune checkpoint inhibitor-associated myositis (ICI myositis). Immune checkpoint inhibitor-associated myositis is indicated by clinical diagnosis of inflammatory myopathy after initiation of immune checkpoint inhibitor for cancer management. Current literature reflects low prevalence but high mortality associated with ICI myositis, especially when involving myasthenia gravis and myocarditis. Immune checkpoint inhibitor-associated myositis tends to have muscle pain along with weakness, infrequent presentation with dermatitis, or interstitial lung disease and is typically seronegative with scattered, endomysial inflammatory infiltrates on biopsy. The differential diagnosis of ICI myositis includes myasthenia gravis and other neurological immune-related adverse events. Therapeutic approach involves high doses of corticosteroids with a choice of steroid-sparing immunomodulating agent(s) that is primarily driven by expert opinion due to lack of robust research to support one agent over another. There is wide variation in the inclusion criteria for ICI myositis used in previous studies. We review previously used inclusion criteria and suggest an expertise-based classification criterion to provide a standardized definition and allow comparability between studies. There is a critical need for prospective translational and clinical studies that elucidate the pathophysiology of ICI myositis in order to improve evaluation and management of these patients.

Extraocular Muscle Biopsy: Surgical Technique and Indications

Extraocular muscle biopsy is a technique used for the histological diagnosis of several orbital diseases; it could bring valuable assistance to the diagnostic process. The purpose of this article is to review the indications, surgical technique, and complications of this biopsy.

Extraocular muscle biopsy is frequently used in tumoral pathology, however, in inflammatory diseases, it is only used when facing a poor reaction to the treatment or in case of chronicity. The surgical procedure must be precise and least traumatic, in order to avoid intra- and post-operative complications, but also to preserve the integrity and function of the muscle. This procedure remains non-standardized and not devoid of complications, hence the need for a careful evaluation of the benefit/risk ratio before considering it.

Autoantibodies in the pathogenesis of idiopathic inflammatory myopathies: Does the endoplasmic reticulum stress response have a role?

Idiopathic inflammatory myopathies (IIMs) are a group of rare, acquired autoimmune diseases characterized by profound muscle weakness and immune cell invasion into non-necrotic muscle. They are related to the presence of antibodies known as myositis-specific antibodies and myositis-associated antibodies, which are associated with various IIM phenotypes and the clinical prognosis. The possibility of the participation of other pathological mechanisms involved in the inflammatory response in IIM has been proposed. Such mechanisms include the overexpression of major histocompatibility complex class I in myofibers, which correlates with the activation of stress responses of the endoplasmic reticulum (ER). Taking into account the importance of the ER for the maintenance of homeostasis of the musculoskeletal system in the regulation of proteins, there is probably a relationship between immunological and non-immunological processes and autoimmunity, and an example of this might be IIM. We propose that ER stress and its relief mechanisms could be related to inflammatory mechanisms triggering a humoral response in IIM, suggesting that ER stress might be related to the triggering of IIMs and their auto-antibodies’ production.

A multidisciplinary approach to the diagnosis of antisynthetase syndrome

Antisynthetase syndrome is a subtype of idiopathic inflammatory myopathy, strongly associated with the presence of interstitial lung disease. Diagnosis is made by identifying myositis-specific antibodies directed against aminoacyl tRNA synthetase, and relevant clinical and radiologic features. Given the multisystem nature of the disease, diagnosis requires the careful synthesis of subtle clinical and radiological features with the interpretation of specialized autoimmune serological testing. This is provided in a multidisciplinary environment with input from rheumatologists, respiratory physicians, and radiologists. Differentiation from other idiopathic interstitial lung diseases is key; treatment and prognosis differ between patients with antisynthetase syndrome and idiopathic interstitial lung disease. In this review article, we look at the role of the multidisciplinary team and its individual members in the initial diagnosis of the antisynthetase syndrome, including the role of physicians, radiologists, and the wider team.

Muscle biopsy in myositis: What the rheumatologist needs to know

The appropriate analysis of skeletal muscle tissues is a key element in many diagnostic procedures and can deliver valuable information about the organ that is affected. Although arguably the frequency of muscle biopsy may be declining in certain domains where genetic analysis is now the first line of diagnostic evaluation, it still has an important role in assessment of patients with neuromuscular disorders such as congenital myopathies, muscular dystrophies, metabolic and inflammatory diseases. Here, we have comprehensively discussed the aspects of a modern and fruitful approach to muscle biopsy histopathological studies in rheumatological disorders. We have focussed on the neuromuscular involvement in myositis and its differential diagnoses in both adult and paediatric settings. We have also covered the clinical indications for the biopsy, technical aspects and practical points relevant for the rheumatologists. Finally, we have critically discussed the current and future opportunities that a muscle biopsy may offer and its limitations.

The Evolution of Complex Muscle Cell In Vitro Models to Study Pathomechanisms and Drug Development of Neuromuscular Disease

Many neuromuscular disease entities possess a significant disease burden and therapeutic options remain limited. Innovative human preclinical models may help to uncover relevant disease mechanisms and enhance the translation of therapeutic findings to strengthen neuromuscular disease precision medicine. By concentrating on idiopathic inflammatory muscle disorders, we summarize the recent evolution of the novel in vitro models to study disease mechanisms and therapeutic strategies. A particular focus is laid on the integration and simulation of multicellular interactions of muscle tissue in disease phenotypes in vitro. Finally, the requirements of a neuromuscular disease drug development workflow are discussed with a particular emphasis on cell sources, co-culture systems (including organoids), functionality, and throughput.

The Mitochondrial Epigenome: An Unexplored Avenue to Explain Unexplained Myopathies?

Mutations in either mitochondrial DNA (mtDNA) or nuclear genes that encode mitochondrial proteins may lead to dysfunctional mitochondria, giving rise to mitochondrial diseases. Some mitochondrial myopathies, however, present without a known underlying cause. Interestingly, methylation of mtDNA has been associated with various clinical pathologies. The present study set out to assess whether mtDNA methylation could explain impaired mitochondrial function in patients diagnosed with myopathy without known underlying genetic mutations. Enhanced mtDNA methylation was indicated by pyrosequencing for muscle biopsies of 14 myopathy patients compared to four healthy controls, at selected cytosines in the Cytochrome B (CYTB) gene, but not within the displacement loop (D-loop) region. The mtDNA methylation patterns of the four healthy muscle biopsies were highly consistent and showed intriguing tissue-specific differences at particular cytosines with control skin fibroblasts cultured in vitro. Within individual myopathy patients, the overall mtDNA methylation pattern correlated well between muscle and skin fibroblasts. Despite this correlation, a pilot analysis of four myopathy and five healthy fibroblast samples did not reveal a disease-associated difference in mtDNA methylation. We did, however, detect increased expression of solute carrier family 25A26 (SLC25A26), encoding the importer of S-adenosylmethionine, together with enhanced mtDNA copy numbers in myopathy fibroblasts compared to healthy controls. To confirm that pyrosequencing indeed reflected DNA methylation and not bisulfite accessibility, mass spectrometry was employed. Although no myopathy-related differences in total amount of methylated cytosines were detected at this stage, a significant contribution of contaminating nuclear DNA (nDNA) was revealed, and steps to improve enrichment for mtDNA are reported. In conclusion, in this explorative study we show that analyzing the mitochondrial genome beyond its sequence opens novel avenues to identify potential molecular biomarkers assisting in the diagnosis of unexplained myopathies.

Role of MRI in idiopathic inflammatory myopathies: a review article

Idiopathic inflammatory myopathies are a rare heterogeneous group of chronic, autoimmune conditions characterized by the slow, progressive weakness of the skeletal muscles and inflammatory infiltrates in the muscle tissue. The predominant role of magnetic resonance imaging (MRI) in myositis imaging is to assess disease activity and to identify the target site for biopsy. Its role in phenotyping the disease is less explored. The aim of the present review was to examine the role of MRI in differentiating between the common inflammatory myopathies, i.e. dermatomyositis, polymyositis, and sporadic inclusion body myositis, and to describe the specific spectrum of MRI findings in various inflammatory myopathies.

Diagnostic Dilemma of Paraneoplastic Rheumatic Disorders: Case Series and Narrative Review

Paraneoplastic rheumatic disorder (RD) is a disorder that may present before, concurrent with, or after the diagnosis of malignancy. Paraneoplastic RDs are a clinical expression of occult cancer that is not directly related to a tumor or metastasis and manifests as rheumatoid symptoms. The RD is determined by the organ system affected by articular, muscular, cutaneous, vascular, or miscellaneous symptoms. Each case is challenging to diagnose because cancer may present with similar symptoms as a common rheumatic disorder. Of note, the majority of cases have minimal responsiveness or no responsiveness to standard rheumatoid treatment. Therefore, it is imperative to recognize and treat the underlying cancer accordingly. Herein, we present four different diagnostic dilemma cases of RD: case #1 - leukocytoclastic vasculitis and C3 glomerulopathy, case #2 - scleroderma, case #3 - Raynaud’s syndrome and possible lupus-like syndrome, and case #4 - inflammatory myositis. Institutional IRB approval was obtained for this case series. We will discuss and review the literature on each topic. In addition, we will mention a review of paraneoplastic rheumatoid arthritis. As rheumatic disease is associated with the use of immune checkpoint inhibitors (ICIs) for cancer treatment, we will briefly discuss some of the most common rheumatic presentations in the setting of these drugs. This case review aims to inform clinicians about the atypical presentation of paraneoplastic RD and to highlight the need for interdisciplinary management between rheumatologists, oncologists, and primary care practitioners.

Physical activity in idiopathic inflammatory myopathies: two intervention proposals based on literature review

Idiopathic inflammatory myopathies (IIM) are rare diseases affecting skeletal muscles and leading to progressive muscle weakness and disability. Thanks to the better understanding of their pathogenesis, the management of IIM has been noteworthily implemented in recent years. Current therapeutic strategies include pharmacological and non-pharmacological interventions, among which physical exercise represents a useful option, able to ameliorate disease activity without worsening muscle inflammation. The aim of this narrative review is therefore to provide an updated overview of the benefits of physical exercise in patients with IIM and to suggest plausible training programs to be applied in patients with dermatomyositis, polymyositis, necrotizing myopathy, and inclusion body myositis. In this regard, a combined strategy mixing aerobic and resistance exercises could positively affect the pro-inflammatory and metabolic pathways occurring in skeletal muscles, while promoting muscle fiber regeneration and repair.

Lymphocyte immunophenotyping in inflammatory myositis: a review

PURPOSE OF REVIEW

This is a comprehensive review of the current knowledge on predominant immune cell phenotypes involved in idiopathic inflammatory myopathies (IIM).

RECENT FINDINGS

Major circulating immune cell subpopulations described in IIM encompass the lymphocyte compartment. An unbalance in T cell subsets seems to consistently affect the peripheral and muscle compartment, with a predominance of CD4+ T and B cells in dermatomyositis, CD8+ T cells in polymyositis/inclusion body myositis (IBM) and novel findings highlighting novel proinflammatory T subsets, that is, CD8+Tbet+ and CD28- T cells across different IIM subsets. On the other hand, an impairment in Treg cells number and function has been described especially across polymyositis/dermatomyositis and IBM. Total T follicular helper (Tfh) cells, increased in immune-mediated necrotizing myopathy, skewed toward Tfh2 and Tfh17 in dermatomyositis, polymyositis, and juvenile dermatomyositis. B cell compartment is more rarely described in IIM, yet an unbalance in this pool is as well likely. Evidence of plasma cells increased in polymyositis, dermatomyositis, IBM, and Bregs decreased in dermatomyositis have been reported. Perturbations in the memory and naïve subsets are common in dermatomyositis/polymyositis and antisynthetase syndrome.

SUMMARY

Protean immune cell abnormalities characterize different IIM subsets, reflecting the complexity of these autoimmune conditions. A deeper understanding of B-cell and T-cell immunophenotyping may promote early diagnosis and identification of new potential therapeutic targets.

Rituximab as a glucocorticoid-sparing agent in idiopathic inflammatory myopathies: a retrospective single-center cohort study

BACKGROUND

Idiopathic inflammatory myopathies (IIM) are essentially treated aiming to improve muscle function and extra muscular disease manifestations. Rituximab is potentially a glucocorticoid-sparing agent which was reviewed in multiple studies with small sample sizes due to the rarity of the disease. Higher statistical power can enhance the trustworthiness of alternative treatment modalities yielding the main objective of this study.

METHODS

This retrospective study was conducted at a tertiary rheumatology center. Patients were diagnosed with an idiopathic inflammatory myopathy (dermatomyositis (DM), polymyositis (PM)) and were treated with rituximab to be included in this study. Parameters of disease activity including acute phase reactants, muscle enzyme levels, and disease-specific autoantibodies were analyzed. The primary study endpoint was the improvement of the patient symptoms. The secondary endpoint was the decrease in the creatinine kinase level.

RESULTS

The study includes 26 patients (19 DM, 7 PM). The age of diagnosis was 42.04 ± 15.22 years; the follow-up duration was 64.84 ± 71.91 months. The mean corticosteroid dose decreased from 32.895 ± 24.399 to 8.44 ± 11.29 (p < 0.001). Other treatment methods were methotrexate (n = 18), intravenous immunoglobulin (IVIG) (n = 7), and cyclophosphamide (n = 2). Two patients were lost to follow-up.

CONCLUSION

Rituximab is shown to be effective in treating myositis along with corticosteroids as well as a corticosteroid-sparing agent in retrospective studies and open-label clinical trials; however, lack of statistical power should be underlined. Long-term decrease in steroid use and decrease in disease activity markers hint the effective use of rituximab as a glucocorticoid-sparing agent as well as its safety with minimal side effects. Key Points • Long-term decrease in steroid use and decrease in disease activity markers hint the effective use of rituximab as a glucocorticoid-sparing agent as well as its safety with minimal side effects.

Pathomechanisms and biomarkers in facioscapulohumeral muscular dystrophy: roles of DUX4 and PAX7

Facioscapulohumeral muscular dystrophy (FSHD) is characterised by progressive skeletal muscle weakness and wasting. FSHD is linked to epigenetic derepression of the subtelomeric D4Z4 macrosatellite at chromosome 4q35. Epigenetic derepression permits the distal-most D4Z4 unit to transcribe DUX4, with transcripts stabilised by splicing to a poly(A) signal on permissive 4qA haplotypes. The pioneer transcription factor DUX4 activates target genes that are proposed to drive FSHD pathology. While this toxic gain-of-function model is a satisfying "bottom-up" genotype-to-phenotype link, DUX4 is rarely detectable in muscle and DUX4 target gene expression is inconsistent in patients. A reliable biomarker for FSHD is suppression of a target gene score of PAX7, a master regulator of myogenesis. However, it is unclear how this "top-down" finding links to genomic changes that characterise FSHD and to DUX4. Here, we explore the roles and interactions of DUX4 and PAX7 in FSHD pathology and how the relationship between these two transcription factors deepens understanding via the immune system and muscle regeneration. Considering how FSHD pathomechanisms are represented by "DUX4opathy" models has implications for developing therapies and current clinical trials.

Pervasive inflammatory activation in patients with deficiency in very-long-chain acyl-coA dehydrogenase (VLCADD)

OBJECTIVES

Very-long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a disorder of fatty acid oxidation. Symptoms are managed by dietary supplementation with medium-chain fatty acids that bypass the metabolic block. However, patients remain vulnerable to hospitalisations because of rhabdomyolysis, suggesting pathologic processes other than energy deficit. Since rhabdomyolysis is a self-destructive process that can signal inflammatory/immune cascades, we tested the hypothesis that inflammation is a physiologic dimension of VLCADD.

METHODS

All subjects (n = 18) underwent informed consent/assent. Plasma cytokine and cytometry analyses were performed. A prospective case analysis was carried out on a patient with recurrent hospitalisation. Health data were extracted from patient medical records.

RESULTS

Patients showed systemic upregulation of nine inflammatory mediators during symptomatic and asymptomatic periods. There was also overall abundance of immune cells with high intracellular expression of IFNγ, IL-6, MIP-1β (CCL4) and TNFα, and the transcription factors p65-NFκB and STAT1 linked to inflammatory pathways. A case analysis of a patient exhibited already elevated plasma cytokine levels during diagnosis in early infancy, evolving into sustained high systemic levels during recurrent rhabdomyolysis-related hospitalisations. There were corresponding activated leukocytes, with higher intracellular stores of inflammatory molecules in monocytes compared to T cells. Exposure of monocytes to long-chain free fatty acids recapitulated the cytokine signature of patients.

CONCLUSION

Pervasive plasma cytokine upregulation and pre-activated immune cells indicate chronic inflammatory state in VLCADD. Thus, there is rationale for practical implementation of clinical assessment of inflammation and/or translational testing, or adoption, of anti-inflammatory intervention(s) for personalised disease management.

Long-term Follow-up and Muscle Imaging Findings in Brachio-Cervical Inflammatory Myopathy

OBJECTIVE

To report on a cohort of patients diagnosed with brachio-cervical inflammatory myopathy (BCIM), with specific focus on muscle MRI and follow-up data.

METHODS

Clinical, histopathologic, serologic, and pre- and post-treatment MRI findings of patients diagnosed with BCIM were retrospectively evaluated.

RESULTS

Six patients, all females with a mean age at onset of 53 years (range 37-62 years), were identified. Mean diagnostic delay was 17 months, and mean follow-up was 35 months. Most common clinical features encompassed predominant involvement of neck and proximal upper limb muscles, followed by distal upper limb, facial, and bulbar muscle weakness with different severity. Lower limb involvement was rare, although present in severe cases. Muscle biopsies showed a heterogeneous degree of perivascular and endomysial inflammatory changes. Myositis-specific antibodies were absent in all patients, whereas all resulted positive for antinuclear antibodies; half of the patients had anti-acetylcholine receptor antibodies without evidence of muscle fatigability. MRI showed disproportionate involvement of upper girdle and neck muscles compared with lower limbs, with frequent hyperintensities on short-tau inversion recovery sequences. Partial clinical and radiologic improvement with steroid and immunosuppressant therapy was obtained in most patients, especially in proximal upper limb muscles, whereas neck weakness persisted.

CONCLUSION

BCIM is an inflammatory myopathy with a peculiar clinical and radiologic presentation and a relatively broad spectrum of severity. Long-term follow-up data suggest that appropriate and early treatment can prevent chronic muscle function impairment. MRI characterization can be helpful in reducing diagnostic and treatment delay with positive consequence on clinical outcome.

Nonimmune mechanisms in idiopathic inflammatory myopathies

PURPOSE OF REVIEW

This review encompasses the main novelties regarding nonimmune mechanisms implicated in the pathogenesis of idiopathic inflammatory myopathies (IIM).

RECENT FINDINGS

In recent years, growing data support a role for endoplasmic-reticulum (ER) stress as a propagator of muscular damage, together with the release of interferon type I and reactive oxygen species in hypoxemic muscle fibers. Other studies evaluating the relationship between autophagy and Toll-like receptors (TLRs) in IIM subtypes have shown increased TLR3 and TLR4 expression in fibers of IIM patients and colocalization with LC3, an autophagy marker, submitting autophagy as a likely player in IIM pathogenesis. Most novel evidences concern the potential role of denervation of the neuromuscular junction in IIM, possibly connected to hyperexpression of MHC-I, and trafficking of extracellular vesicles, which may represent a connection between nonimmune and immune-mediated mechanisms of muscle inflammation and damage.

SUMMARY

Nonimmune mechanisms contribute to the pathogenesis of IIM, likely cooperating with immune-mediated inflammation. Consistent data were released for ER stress, autophagy, mitochondrial dysfunction and hypoxia; in addition to, neuromuscular denervation and extracellular vesicles have been proposed as thoughtful links between muscle inflammation, damage and atrophy. Further understanding of nonimmune abnormalities and potential reversible pathways is needed to improve the management of IIM.

Mitochondrial dysfunction underlying sporadic inclusion body myositis is ameliorated by the mitochondrial homing drug MA-5

Sporadic inclusion body myositis (sIBM) is the most common idiopathic inflammatory myopathy, and several reports have suggested that mitochondrial abnormalities are involved in its etiology. We recruited 9 sIBM patients and found significant histological changes and an elevation of growth differential factor 15 (GDF15), a marker of mitochondrial disease, strongly suggesting the involvement of mitochondrial dysfunction. Bioenergetic analysis of sIBM patient myoblasts revealed impaired mitochondrial function. Decreased ATP production, reduced mitochondrial size and reduced mitochondrial dynamics were also observed in sIBM myoblasts. Cell vulnerability to oxidative stress also suggested the existence of mitochondrial dysfunction. Mitochonic acid-5 (MA-5) increased the cellular ATP level, reduced mitochondrial ROS, and provided protection against sIBM myoblast death. MA-5 also improved the survival of sIBM skin fibroblasts as well as mitochondrial morphology and dynamics in these cells. The reduction in the gene expression levels of Opa1 and Drp1 was also reversed by MA-5, suggesting the modification of the fusion/fission process. These data suggest that MA-5 may provide an alternative therapeutic strategy for treating not only mitochondrial diseases but also sIBM.

Paraneoplastic Necrotizing Myopathy Post Lumpectomy and Chemotherapy for Early Breast Cancer

Our case report describes a 60-year-old female patient with a past medical history of Stage IB breast cancer, status post lumpectomy and adjuvant chemotherapy, admitted to our hospital with the chief complaints of fever, myalgia, and muscle weakness. A physical exam revealed proximal muscle weakness and a facial rash. A full workup was done, and the muscle biopsy showed evidence of a necrotizing myopathic process, which confirmed our diagnosis. This led to a diagnosis of necrotizing myopathy, deemed to be paraneoplastic after other possible differentials were ruled out. The patient showed improvement after a five-day course of intravenous immunoglobulin (IVIG) and high-dose steroids. Necrotizing myopathy, as a paraneoplastic process, has been scarcely described. In the context of our case, we review the characteristics and relevant existing literature about paraneoplastic necrotizing myopathy as well as emphasize the need to include it as a differential in the setting of malignancy.

Efficacy and Safety of Rituximab in Korean Patients with Refractory Inflammatory Myopathies

BACKGROUND

Rituximab (RTX), a monoclonal antibody that selectively binds to CD20+ B cells, showed favorable outcomes in patients with idiopathic inflammatory myopathies (IIM) in small case series, but the evidence is still not enough. Our goal was to determine the efficacy and safety of RTX for Korean patients with refractory IIM.

METHODS

We retrospectively analyzed the medical records of 16 patients with refractory IIM treated with RTX in seven tertiary rheumatology clinics in the Korea. The efficacy of RTX was evaluated with the improvement of serum creatine phosphokinase (CPK) level and physician's global assessment (PGA), and daily corticosteroid dose reduction. A > 25% decrease in CPK level, corticosteroid dose, or PGA was considered significant. A complete response (CR) was designated by meeting three efficacy criteria and a partial response (PR) by only two criteria.

RESULTS

Sixteen patients with IIM were evaluated (13 female; median age, 51.8 years). All patients had received at least one conventional immunosuppressive agent (median, 3.6 [2.0-5.0]) and concomitant corticosteroids. The median CPK level and median dose of prednisolone was 421.0 units/L and 20.0 mg/day respectively. Eleven patients were treated with intravenous immunoglobulin. Seven patients received 2,000 mg of RTX and the others received lower dose. Twenty-four weeks after RTX treatment, 11 patients achieved a > 25% reduction in corticosteroid dose and CPK levels, and nine showed improved PGA. The overall response rate was 68.8% (11 patients). At the end of follow-up (median 24 weeks), 12 (75.0%) patients responded overall: four (25.0%) and eight (50.0%) patients achieved CR and PR, respectively. Baseline muscle enzyme levels were higher in responders than non-responders, but disease duration, RTX dose, ESR and serum CRP were not significantly different between the two groups. The rate of adverse event was 25.4/1,000 person-years.

CONCLUSION

RTX could be an effective and relatively safe therapeutic option in patients with refractory IIM.

Edematous myositis: a clinical presentation first suggesting dermatomyositis diagnosis

AIMS

Edema of the limbs is uncommon in idiopathic inflammatory myopathies (IIM). The few reported cases have been associated with severe and refractory dermatomyositis (DM), sometimes in association with cancers. We aimed to determine if edematous myositis is a homogeneous subtype based on clinical, serological and pathological features.

METHODS

This is a retrospective observational study performed between 2008 and 2015 in the French national referral center for myositis. All adult patients with an inflammatory muscle biopsy and upper limbs edema were included as well as IIM cases without limb edema as controls. Clinical, biological and pathological features were collected.

RESULTS

Seventeen edematous myositis were included and compared to 174 IIM without edema, including 50 DM controls. Edema was the first manifestation in 23% of patients. Muscle weakness was severe and symmetric, 71% of patients presented dysphagia and a restrictive ventilatory pattern was found in 40%. Fifty-two percent of patients had a typical DM skin rash and 23% had cancer within 3 years of diagnosing myositis. Fifty-three percent of patients presented a myositis specific antibody and only DM-specific antibodies were detected. Classic pathological DM features (perifascicular atrophy, perifascicular/perimysial perivascular inflammation) were uncommon but capillary C5b-9 deposition and MxA expression were seen in 79% and 73% of cases, respectively. A perimysial edema was found in 82% of cases. Seventeen percent of patients died (median follow up of 18 months). Edematous myositis demonstrated more marked capillary C5b-9 deposition compared to IIM controls. There was no clinical, biological or pathological difference with DM controls except for limb edema.

CONCLUSION

Our study underlines that limb edema could be a symptom of IIM and that edematous myositis are mostly DM. The vasculopathy seems to play a key role in its pathophysiology. Limb edema associated with muscle impairment should suggest the diagnosis of DM in clinical settings.

Mitochondrial Dysfunction: A Common Hallmark Underlying Comorbidity between sIBM and Other Degenerative and Age-Related Diseases

Sporadic inclusion body myositis (sIBM) is an inflammatory myopathy associated, among others, with mitochondrial dysfunction. Similar molecular features are found in Alzheimer's disease (AD) and Type 2 Diabetes Mellitus (T2DM), underlying potential comorbidity. This study aims to evaluate common clinical and molecular hallmarks among sIBM, AD, and T2DM. Comorbidity with AD was assessed in n = 14 sIBM patients by performing neuropsychological and cognitive tests, cranial magnetic resonance imaging, AD cerebrospinal fluid biomarkers (levels of amyloid beta, total tau, and phosphorylated tau at threonine-181), and genetic apolipoprotein E genotyping. In the same sIBM cohort, comorbidity with T2DM was assessed by collecting anthropometric measures and performing an oral glucose tolerance test and insulin determinations. Results were compared to the standard population and other myositis (n = 7 dermatomyositis and n = 7 polymyositis). Mitochondrial contribution into disease was tested by measurement of oxidative/anaerobic and oxidant/antioxidant balances, respiration fluxes, and enzymatic activities in sIBM fibroblasts subjected to different glucose levels. Comorbidity of sIBM with AD was not detected. Clinically, sIBM patients showed signs of misbalanced glucose homeostasis, similar to other myositis. Such misbalance was further confirmed at the molecular level by the metabolic inability of sIBM fibroblasts to adapt to different glucose conditions. Under the standard condition, sIBM fibroblasts showed decreased respiration (0.71 ± 0.08 vs. 1.06 ± 0.04 nmols O2/min; p = 0.024) and increased anaerobic metabolism (5.76 ± 0.52 vs. 3.79 ± 0.35 mM lactate; p = 0.052). Moreover, when glucose conditions were changed, sIBM fibroblasts presented decreased fold change in mitochondrial enzymatic activities (-12.13 ± 21.86 vs. 199.22 ± 62.52 cytochrome c oxidase/citrate synthase ratio; p = 0.017) and increased oxidative stress per mitochondrial activity (203.76 ± 82.77 vs. -69.55 ± 21.00; p = 0.047), underlying scarce metabolic plasticity. These findings do not demonstrate higher prevalence of AD in sIBM patients, but evidences of prediabetogenic conditions were found. Glucose deregulation in myositis suggests the contribution of lifestyle conditions, such as restricted mobility. Additionally, molecular evidences from sIBM fibroblasts confirm that mitochondrial dysfunction may play a role. Monitoring T2DM development and mitochondrial contribution to disease in myositis patients could set a path for novel therapeutic options.

A new in vitro model of polymyositis reveals CD8+ T cell invasion into muscle cells and its cytotoxic role

Objectives

The hallmark histopathology of PM is the presence of CD8⁺ T cells in the non-necrotic muscle cells. The aim of this study was to clarify the pathological significance of CD8⁺ T cells in muscle cells.

Methods

C2C12 cells were transduced retrovirally with the genes encoding MHC class I (H2K^b) and SIINFEKL peptide derived from ovalbumin (OVA), and then differentiated to myotubes (H2K^bOVA-myotubes). H2K^bOVA-myotubes were co-cultured with OT-I CD8⁺ T cells derived from OVA-specific class I restricted T cell receptor transgenic mice as an in vitro model of PM to examine whether the CD8⁺ T cells invade into the myotubes and if the myotubes with the invasion are more prone to die than those without. Muscle biopsy samples from patients with PM were examined for the presence of CD8⁺ T cells in muscle cells. The clinical profiles were compared between the patients with and without CD8⁺ T cells in muscle cells.

Results

Analysis of the in vitro model of PM with confocal microscopy demonstrated the invasion of OT-I CD8⁺ T cells into H2K^bOVA-myotubes. Transmission electron microscopic analysis revealed an electron-lucent area between the invaded CD8⁺ T cell and the cytoplasm of H2K^bOVA-myotubes. The myotubes invaded with OT-I CD8⁺ T cells died earlier than the uninvaded myotubes. The level of serum creatinine kinase was higher in patients with CD8⁺ T cells in muscle cells than those without these cells.

Conclusion

CD8⁺ T cells invade into muscle cells and contribute to muscle injury in PM. Our in vitro model of PM is useful to examine the mechanisms underlying muscle injury induced by CD8⁺ T cells.

Muscular Sarcocystosis in Sheep Associated With Lymphoplasmacytic Myositis and Expression of Major Histocompatibility Complex Class I and II

Sarcocystosis is a protozoal disease affecting a wide range of animals. The aims of this study were to characterize the following in sheep: (1) the muscle pathology in Sarcocystis infection, (2) the inflammatory infiltrate and its relationship to severity of infection, and (3) immune markers expressed by parasitized muscle fibers and parasitic cysts. Skeletal muscle samples from 78 sheep slaughtered in southern Italy were snap frozen and analyzed by histopathology, immunohistochemistry, and immunofluorescence. Polymerase chain reaction (PCR) and sequencing were used for Sarcocystis species identification. All 40 muscle samples tested were PCR-positive for Sarcocystis tenella. Histologically, cysts were identified in 76/78 cases (97%), associated with an endomysial infiltrate of lymphocytes and plasma cells. The T cells were predominantly CD8+, with fewer CD4+ or CD79α+ cells. Eosinophils were absent. Notably, sarcolemmal immunopositivity for major histocompatibility complex (MHC) I and II was found in 76/78 cases (97%) and 75/78 cases (96%), respectively, both in samples with and in those without evident inflammatory infiltrate. The number of cysts was positively correlated with inflammation. In addition, MHC I was detected in 55/78 cyst walls (72%), and occasionally co-localized with the membrane-associated protein dystrophin. The findings suggest that muscle fibers respond to the presence of cysts by expression of MHC I and II. The possible role of MHC I and II in the inflammatory response and on the cyst wall is also discussed.

Scurfy Mice Develop Features of Connective Tissue Disease Overlap Syndrome and Mixed Connective Tissue Disease in the Absence of Regulatory T Cells

Due to a missense mutation in the Foxp3 gene, scurfy mice are deficient in functional regulatory T cells (Treg). The consequent loss of peripheral tolerance manifests itself by fatal autoimmune mediated multi-organ disease. Previous studies have outlined the systemic inflammatory disease and demonstrated production of anti-nuclear antibodies (ANA) in scurfy mice. However, specific autoantibody targets remained to be defined. ANA are immunological markers for several connective tissue diseases (CTD) and target a large number of intracellular molecules. Therefore, we examined scurfy sera for the presence of different ANA specificities and further assessed the organ involvement in these animals. Indirect immunofluorescence was used as a screen for ANA in the sera of scurfy mice and dilutions of 1/100 were considered positive. Addressable laser bead immunoassays (ALBIA) were used to detect specific autoantibody targets. Subsequent histological tissue evaluation was verified by hematoxylin and eosin (H&E) staining. In our study, we observed that nearly all scurfy mice produced ANA. The most prevalent pattern in scurfy sera was nuclear coarse speckled, also known as the AC-5 pattern according to the International Consensus on ANA Patterns. U1-ribonucleoprotein (U1RNP) was found to be the most common target antigen recognized by autoantibodies in scurfy mice. Additionally, scurfy mice exhibited a mild myositis with histological characteristics similar to polymyositis/dermatomyositis. Myopathy-specific autoantibody profile revealed significantly increased levels of anti-SMN (survival of motor neuron) as well as anti-Gemin3 antibodies in scurfy sera. Overall, we demonstrate that the impaired peripheral tolerance in the absence of regulatory T cells in scurfy mice is associated with features of mixed connective tissue disease (MCTD). This includes, along with our previous findings, very high titers of anti-U1RNP antibodies and an inflammatory myopathy.

MRI of skeletal muscles in patients with idiopathic inflammatory myopathies: characteristic findings and diagnostic performance in dermatomyositis

Objective

To define the characteristic findings on MRI of skeletal muscles in patients with dermatomyositis (DM) relative to those in patients with other idiopathic inflammatory myopathies (IIMs) and to assess their diagnostic performance in DM.

Methods

Thirty-six patients with DM, 17 patients with amyopathic DM, 19 patients with polymyositis and 16 patients with non-IIM classified by the 2017 European League Against Rheumatism/American College of Rheumatology criteria were included in this study. The following MRI findings (short-tau inversion recovery [STIR] and gadolinium-enhanced fat-suppressed T1-weighted imaging [Gd-T1WI]) for proximal limb muscles were compared between the disease groups and between myositis-specific autoantibodies/myositis-associated autoantibodies (MSAs/MAAs)-positive and MSAs/MAAs-negative groups: structures with high signal intensity (HSI) (subcutaneous, fascia, muscle); distributions of HSI areas in muscle (diffuse, patchy, peripheral) and patterns of HSI in muscle (honeycomb, foggy, strong HSI). Univariate, multivariate and receiver-operating characteristic [ROC] analyses were performed to assess the diagnostic performance of MRI in DM.

Results

The characteristic MRI findings in patients with DM were subcutaneous HSI, fascial HSI, peripheral distribution and honeycomb pattern. The MRI findings in the MSAs/MAAs-positive group included more frequent fascial HSI but less frequent foggy pattern compared with the MSAs/MAAs-negative group. Likelihood of DM score ≥ 3 (obtained by counting the number of characteristic MRI findings in patients with DM) showed good diagnostic performance in DM (STIR: sensitivity 72.2%, specificity 88.5%, area under ROC curve [AUC] 84.9%; Gd-T1WI: sensitivity 81.2%, specificity 91.5%, AUC 89.9%).

Conclusion

The characteristic MRI findings of skeletal muscles can predict patients with DM as well as patients with MSAs/MAAs.

Interleukin-37 (IL-37) Suppresses Pertussis Toxin-Induced Inflammatory Myopathy in a Rat Model

Background

Recent data have demonstrated the potential immunosuppressive roles of interleukin-37 (IL-37) in several diseases, but whether it is involved in the pathogenesis of inflammatory myopathy has not been elucidated.

Material/Methods

An experimental autoimmune myositis (EAM) model was built by subcutaneous injections of pertussis toxin (PTX) and purified rabbit myosin (10mg/kg) emulsified with an equal volume of conventional complete Freund’s adjuvant (CFA) in a Lewis model. Autoimmune myositis Lewis model rats were divided into 3 groups: group A rats (control group) were injected with CFA in saline weekly; group B (IL-37 group) rats were injected with saline with IL-37 and CFA in saline weekly; and group C (IL-37 + SIS3 group) rats were injected with IL-37, CFA, and SIS3. ELISA was also used to assess the expressions of TNF-α, IL-6, IL-1β, TGF-β1, and CK. HE staining was performed to assess pathological changes in lung and muscle tissues.

Results

The expressions of TNF-α, IL-6, IL-1β, TGF-β1, and CK significantly increased in autoimmune myositis Lewis model rats. After IL-37 treatment, the expression of TNF-α, IL-6, IL-1β, TGF-β1, and CK was significantly reduced, as were the inflammatory responses of lung and muscle. However, SIS3 reduced the effects of IL-37 on the autoimmune myositis Lewis model rats.

Conclusioans

These findings indicate that IL-37 protects against inflammatory response via regulating Smad3 in autoimmune myositis Lewis model rats.

Immunohistochemical and ultrastructural analysis of sporadic inclusion body myositis: a case series

Sporadic inclusion body myositis (s-IBM) is a progressive, skeletal muscle disease with poor prognosis. However, establishing the final diagnosis is difficult because of the lack of clear biomarkers in the blood serum and very slow development of clinical symptoms. Moreover, most other organs function normally without any disturbance. Here, in patients with this untreatable disease, we have underlined the importance of immunohistochemical and ultrastructural assessment of skeletal muscle in patients diagnosed with s-IBM. The goal of this study was to identify the distribution of specific antigens and to determine morphological features in order to localize pathological protein aggregates, rimmed vacuoles, and loss of myofibrils, which are key elements in the diagnosis of s-IBM. All studied patients were between 48 and 83 years of age and were hospitalized in the Department of Rheumatology and Internal Medicine between 2011 and 2016. Anamneses revealed an accelerated progression of muscle atrophy, weakness of limb muscles, and difficulties with climbing stairs. Based on histopathology and transmission electron microscopy examination, inflammatory infiltrations consisting of mononuclear cells, severe atrophy and focal necrosis of myofibers, splitting of myofilaments, myelinoid bodies and rimmed vacuoles were observed. Primary antibodies directed against CD3, CD8, CD68, cN1A, beta-amyloid, Tau protein and apolipoprotein B made it possible to identify types of cells within infiltrations as well as the protein deposits within myofibers. Using a combination of immunohistochemistry and electron microscopy methods, we were able to establish the correct final diagnosis and to implement a specific treatment to inhibit disease progression.

Effect of CTLA4-Ig (abatacept) treatment on T cells and B cells in peripheral blood of patients with polymyositis and dermatomyositis

We aimed to evaluate in vivo effects of abatacept on phenotypes of T and B cells in the circulation of myositis patients in a sub-study of the ARTEMIS trial. Twelve patients with paired frozen PBMCs before and after 6-month abatacept treatment were included in this sub-study where mass cytometry (CyTOF) was chosen as a technology to be tested for its utility in a real-life clinical immune monitoring setting. Using CyTOF, the peripheral T cell phenotypes demonstrated considerable variation over time and between individuals precluding the identification of treatment-specific changes. We therefore conclude that studies of patient cohorts displaying wide clinical heterogeneity using mass cytometry must be relatively large in order to be suited for discovery research and immune monitoring. Still, we did find some correlations with functional muscle outcome, namely positive correlations between the ratio of CD4⁺ T cells and CD8⁺ T cells (CD4/CD8) in peripheral blood samples both at baseline and after treatment with muscle endurance improvement as assessed by the functional index-2 (FI-2) test. Our data suggest that the CD4/CD8 ratio in circulation at time of active disease may be a predictor of treatment efficacy in myositis patients.

Mediators and Patterns of Muscle Loss in Chronic Systemic Inflammation

Besides its primary function in locomotion, skeletal muscle (SKM), which represents up to half of human's weight, also plays a fundamental homeostatic role. Through the secretion of soluble peptides, or myokines, SKM interacts with major organs involved in metabolic processes. In turn, metabolic cues from these organs are received by muscle cells, which adapt their response accordingly. This is done through an intricate intracellular signaling network characterized by the cross-talking between anabolic and catabolic pathways. A fine regulation of the network is required to protect the organism from an excessive energy expenditure. Systemic inflammation evokes a catabolic reaction in SKM known as sarcopenia. In turn this response comprises several mechanisms, which vary depending on the nature of the insult and its magnitude. In this regard, aging, chronic inflammatory systemic diseases, osteoarthritis and idiopathic inflammatory myopathies can lead to muscle loss. Interestingly, sarcopenia may persist despite remission of chronic inflammation, an issue which warrants further research. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) system stands as a major participant in muscle loss during systemic inflammation, while it is also a well-recognized orchestrator of muscle cell turnover. Herein we summarize current knowledge about models of sarcopenia, their triggers and major mediators and their effect on both protein and cell growth yields. Also, the dual action of the JAK/STAT pathway in muscle mass changes is discussed. We highlight the need to unravel the precise contribution of this system to sarcopenia in order to design targeted therapeutic strategies.

Myositis, Ganglioneuritis, and Myocarditis with Distinct Perifascicular Muscle Atrophy in a 2-Year-Old Male Boxer

A 2-year-old male, intact Boxer was referred for chronic diarrhea, hyporexia, labored breathing, weakness and elevated creatine kinase, and alanine aminotransferase activities. Initial examination and diagnostics revealed a peripheral nervous system neurolocalization, atrial premature complexes, and generalized megaesophagus. Progressive worsening of the dog's condition was noted after 36 h; the dog developed aspiration pneumonia, was febrile and oxygen dependent. The owners elected humane euthanasia. Immediately postmortem biopsies of the left cranial tibial and triceps muscles and the left peroneal nerve were obtained. Postmortem histology revealed concurrent myositis, myocarditis, endocarditis, and ganglioneuritis. Mixed mononuclear cell infiltrations and a distinct perifascicular pattern of muscle fiber atrophy was present in both muscles. This is a novel case of diffuse inflammatory myopathy with a distinct perifascicular pattern of atrophy in addition to endocarditis, myocarditis, and epicarditis.

18F-FDG PET/CT and MRI in Necrotizing Autoimmune Myopathy: "The Scarface Sign"

Necrotizing autoimmune myopathy (NAM) is a relatively newly recognized subgroup of idiopathic inflammatory myopathies. The common histopathologic features are myocyte necrosis without significant inflammation. Necrotizing autoimmune myopathy can be associated with connective tissue disorders but can also be triggered by viral infections such as human immunodeficiency virus or malignancy, be statin-induced NAM, or be idiopathic. Here, the authors present the case of a 58-year-old man who was referred to our PET unit for a suspected paraneoplastic syndrome in a context of NAM. Complementary contrast-enhanced CT and 3-dimensional T1-weighted MRI were carried out subsequently in order to resolve the PET/CT abnormalities.

Inflammatory Myopathy in Horses With Chronic Piroplasmosis

Horses affected by chronic piroplasmosis may develop poor performance and muscle atrophy. Here we investigate the pathological and immunopathological aspects of myopathy occurring in chronic equine piroplasmosis. The study included 16 horses serologically positive for equine piroplasms presenting with clinical signs and supporting serum biochemical evidence of a myopathy. Skeletal muscle was evaluated by histopathology, immunohistochemistry, indirect immunofluorescence, and molecular detection of piroplasms and inflammatory cytokines in skeletal muscle. Histologic lesions included muscle fiber atrophy (100% of cases), degenerative changes (13/16, 81%), and perivascular perimysial and endomysial lymphocytic infiltrates (81% of cases). In 15 cases (94%), muscle fibers had strong immunostaining for major histocompatibility complex classes I and II. T lymphocyte populations were mainly CD3+, CD8+, and CD4+ in equal proportions, with a lower number of CD79α+ cells. The serum from affected horses was tested by indirect immunofluorescence for binding of IgG, IgM, or IgA to sections of normal equine muscle to detect circulating autoantibodies against muscle antigen(s). In all cases, distinct sarcolemmal staining was detected in sections incubated with serum from affected horses, in contrast to sections incubated with phosphate-buffered saline or equine control sera. Reverse transcription polymerase chain reaction (RT-PCR) testing of muscles from affected animals revealed a significant increase of interferon-γ, interleukin-12, and tumor necrosis factor-α gene expression compared to healthy controls. Theileria equi or Babesia caballi was not detected in samples of affected muscle by RT-PCR. Thus, inflammatory myopathy associated with equine piroplasmosis may involve an autoimmune pathogenesis with upregulation of inflammatory cytokines that may cause myofiber atrophy and degeneration.

Sutureless Extraocular Muscle Biopsy Technique

Purpose

To describe a simple and novel technique of obtaining an extraocular muscle (EOM) biopsy.

Methods

Our sutureless method involves obtaining a full-thickness 3-mm EOM specimen using a disposable punch biopsy.

Results

The procedure was performed successfully, with no worsening of eye movement, muscle weakness, or cosmetic defects postoperatively. The acquired full-thickness specimen was sufficient for analysis.

Conclusions

This technique to obtain an EOM biopsy allows a straightforward sutureless method, providing an adequate sample for tissue scrutiny.

Development and evaluation of a standardized ELISA for the determination of autoantibodies against cN-1A (Mup44, NT5C1A) in sporadic inclusion body myositis

PURPOSE

Sporadic inclusion body myositis (sIBM) is an autoimmune degenerative disease of the muscle, with inflammatory infiltrates and inclusion vacuoles. Its pathogenesis is not fully understood and the diagnosis is hampered by its imprecise characteristics, at times indistinguishable from other idiopathic inflammatory myopathies such as polymyositis and dermatomyositis. The diagnosis may be assisted by the detection of autoantibodies targeting Mup44, a skeletal muscle antigen identified as cytosolic 5'-nucleotidase 1A (cN-1A, NT5C1A). A novel standardized anti-cN-1A IgG ELISA was developed and its diagnostic performance was evaluated by two reference laboratories.

METHODS

Recombinant human full-length cN-1A was expressed and purified, and subsequently utilized to set up a standardized ELISA. To evaluate the novel assay, laboratory A examined sera from North American patients with clinically and pathologically diagnosed definite sIBM (n = 17), suspected sIBM (n = 14), myositis controls (n = 110), non-myositis autoimmune controls (n = 93) and healthy subjects (n = 52). Laboratory B analyzed a Dutch cohort of definite sIBM patients (n = 51) and healthy controls (n = 202).

RESULTS

Anti-cN-1A reactivity was most frequent in definite sIBM (39.2-47.1%), but absent in biopsy-proven classic polymyositis or dermatomyositis. Overall diagnostic sensitivity and specificity amounted to 35.5 and 96.1% (laboratory A) and 39.2 and 96.5% (laboratory B).

CONCLUSIONS

Anti-cN-1A autoantibodies were detected by ELISA with moderate sensitivity, but high specificity for sIBM and may therefore help diagnose this infrequent and difficult-to-diagnose myopathy. The novel anti-cN-1A IgG ELISA can improve and accelerate the diagnosis of sIBM using sera where muscle biopsy is delayed or unfeasible.

The immunoproteasomes are key to regulate myokines and MHC class I expression in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are diseases with muscle weakness, morphologically characterized by inflammatory infiltration and increased expression of MHC class I molecule on myofibers. Immunoproteasome, as a proteolytic complex that shapes the repertoire of antigenic peptides, has been previously demonstrated to be over-expressed in IIMs at mRNA level. In this study, we investigated the expression and the function of the immunoproteasome in IIMs in more detail. As shown by immunofluorescence staining, expression of relevant players of the immunoproteasome was detectable in the inflamed skeletal muscle tissue from IIM patients. In fact, two subunits of the immunoproteasome, β1i or β5i were upregulated in sporadic inclusion body myositis, immune-mediated necrotizing myopathies and dermatomyositis muscle biopsies and co-localized with the MHC class I expressing myofibers. Double immunofluorescence revealed that both myofibers and muscle infiltrating cells, including CD8⁺ T-cells and CD68 ⁺ macrophages in IIMs expressed β1i or β5i. In addition, we have also investigated the role of the immunoproteasome in myoblasts during in vitro inflammatory conditions. Using human primary myoblasts cultures we found that pro-inflammatory cytokines, TNF-α or IFN-γ upregulate β1i or β5i. Selective inhibition or depletion of β5i amplified the TNF-α or IFN-γ mediated expression of cytokines/chemokines (myokines) in myoblasts. Furthermore, we demonstrated that specific inhibitors of β1i or β5i reduced the cell surface expression of MHC class I in myoblasts induced by IFN-γ. Taken together, our data suggest that the immunoproteasome is involved in pathologic MHC class I expression and maintenance of myokine production in IIMs. Thus, induction of the immunoproteasome was identified as a pathomechanism underlying inflammation in IIMs.

Mitochondrial DNA disturbances and deregulated expression of oxidative phosphorylation and mitochondrial fusion proteins in sporadic inclusion body myositis

Sporadic inclusion body myositis (sIBM) is one of the most common myopathies in elderly people. Mitochondrial abnormalities at the histological level are present in these patients. We hypothesize that mitochondrial dysfunction may play a role in disease aetiology. We took the following measurements of muscle and peripheral blood mononuclear cells (PBMCs) from 30 sIBM patients and 38 age- and gender-paired controls: mitochondrial DNA (mtDNA) deletions, amount of mtDNA and mtRNA, mitochondrial protein synthesis, mitochondrial respiratory chain (MRC) complex I and IV enzymatic activity, mitochondrial mass, oxidative stress and mitochondrial dynamics (mitofusin 2 and optic atrophy 1 levels). Depletion of mtDNA was present in muscle from sIBM patients and PBMCs showed deregulated expression of mitochondrial proteins in oxidative phosphorylation. MRC complex IV/citrate synthase activity was significantly decreased in both tissues and mitochondrial dynamics were affected in muscle. Depletion of mtDNA was significantly more severe in patients with mtDNA deletions, which also presented deregulation of mitochondrial fusion proteins. Imbalance in mitochondrial dynamics in muscle was associated with increased mitochondrial genetic disturbances (both depletion and deletions), demonstrating that proper mitochondrial turnover is essential for mitochondrial homoeostasis and muscle function in these patients.