Subgroup Of Idiopathic Inflammatory Myopathies Research Articles

Where are we moving in the classification of idiopathic inflammatory myopathies?

Discoveries of myositis-specific antibodies, transcriptomic signatures, and clinicoseropathological correlation support classification of idiopathic inflammatory myopathies (IIM) into four major subgroups: dermatomyositis, immune-mediated necrotizing myopathy (IMNM), antisynthetase syndrome (ASS), and inclusion body myositis (IBM) whereas leaving polymyositis as a historical nonspecific diagnosis of exclusion. This review summarizes and comments on recent knowledge regarding the major subgroup of IIM. Type 1 interferon (IFN1) pathway activation is the most prominent in dermatomyositis whereas type 2 interferon (IFN2) pathway activation is high in IBM and ASS; neither pathway is distinct in IMNM. Myxovirus-resistant protein A, IFN1 surrogate marker, is now one of definite dermatomyositis muscle biopsy criteria in the new 2018 European Neuromuscular Centre classification of dermatomyositis; the classification emphasizes on different categorization with and without dermatomyositis-specific antibody result. Novel HLA loci associated with anti-TIF1-γ, anti-Mi-2, and anti-Jo-1 antibodies in Caucasian population are identified. Associations of chaperon-assisted selective autophagy (CASA) and complement-mediated autoimmunity in IMNM as well as highly differentiated T cells in IBM are discovered. Current IIM classification requires integrated clinicoseropathological approaches. Additional information, such as transcriptomics, HLA haplotyping, and potential biomarkers help tailoring categorization that may have future diagnostic and therapeutic implications.

Classification of idiopathic inflammatory myopathies based on clinical manifestations and myositis-specific antibodies

To investigate the classification of idiopathic inflammatory myopathies (IIM) based on clinical manifestations and myositis- specific antibodies using cluster analysis. We retrospectively analyzed the data of patients with IIM admitted in Nanfang Hospital in 2015-2019. The clinical data of the patients including serum creatine kinase (CK), interstitial lung disease (ILD), cancer, and myositis-specific antibodies were collected for two-step cluster analysis to identify the distinct clusters of patients, whose clinical characteristics were subsequently analysed. A total of 71 patients with IIM were included in this study, including 30 (42.3%) with polymyositis (PM), 20 (28.2%) with classic dermatomyositis (DM), 16 (22.5%) with amyopathic dermatomyositis (CADM), and 5 (7.0%) with immune-mediated necrotizing myopathy (IMNM). Two-step cluster analysis identified 3 distinctive subgroups: Cluster 1 of 15 (51.7%) patients characterized by rash, positive anti-MDA5 antibody and hypoproteinemia (P < 0.05) with normal or slightly elevated CK level, mainly corresponding to CADM; Cluster 2 of 4 (57.1%) patients with significantly elevated CK and positive anti-SRP antibody (P < 0.001) corresponding to IMNM; and Cluster 3 of 17 (48.6%) patients consisting primarily of patients with PM, characterized by positivity for anti- aminoacyl transfer RNA synthetases antibodies (P=0.022) corresponding to antisynthetase syndrome (ASS). Patients with IIM can be divided into 3 subgroups based on their clinical and serological characteristics (especially myositis-specific antibodies), and among them ASS may represent an independent IIM subgroup with unique clinical characteristics.

MicroRNA and mRNA profiling in the idiopathic inflammatory myopathies

BackgroundThe idiopathic inflammatory myopathies (IIMs) are heterogeneous autoimmune conditions of skeletal muscle inflammation and weakness. MicroRNAs (miRNAs) are short, non-coding RNA which regulate gene expression of target mRNAs. The aim of this study was to profile miRNA and mRNA in IIM and identify miRNA-mRNA relationships which may be relevant to disease.MethodsmRNA and miRNA in whole blood samples from 7 polymyositis (PM), 7 dermatomyositis (DM), 5 inclusion body myositis and 5 non-myositis controls was profiled using next generation RNA sequencing. Gene ontology and pathway analyses were performed using GOseq and Ingenuity Pathway Analysis. Dysregulation of miRNAs and opposite dysregulation of predicted target mRNAs in IIM subgroups was validated using RTqPCR and investigated by transfecting human skeletal muscle cells with miRNA mimic.ResultsAnalysis of differentially expressed genes showed that interferon signalling, and anti-viral response pathways were upregulated in PM and DM compared to controls. An anti-Jo1 autoantibody positive subset of PM and DM (n = 5) had more significant upregulation and predicted activation of interferon signalling and highlighted T-helper (Th1 and Th2) cell pathways. In miRNA profiling miR-96-5p was significantly upregulated in PM, DM and the anti-Jo1 positive subset. RTqPCR replicated miR-96-5p upregulation and predicted mRNA target (ADK, CD28 and SLC4A10) downregulation. Transfection of a human skeletal muscle cell line with miR-96-5p mimic resulted in significant downregulation of ADK.ConclusionMiRNA and mRNA profiling identified dysregulation of interferon signalling, anti-viral response and T-helper cell pathways, and indicates a possible role for miR-96-5p regulation of ADK in pathogenesis of IIM.

AB0610 SEASONAL VARIATION IN IDIOPATHIC INFLAMMATORY MYOPATHIES INCIDENCE AND PRESENTATION: A RETROSPECTIVE STUDY IN BEIJING AND HONG KONG

Background:Seasonal patterns of disease onset and severity in idiopathic inflammatory myopathies (IIMs) as a whole are conflicting [1-3]. In recent years, over 10 myositis-specific antibodies (MSAs) have been identified. They are able to divide patients into homogenous subgroups and inform on prognosis [4].Objectives:The objective of the study was to investigate the seasonal variation of onset of IIMs characterised serologically.Methods:This was a multi-centred retrospective observational study. Consecutive Chinese patients with IIMs admitted to the rheumatology wards of the participating major regional hospitals in Beijing and Hong Kong from July 2013 to June 2018 were recruited. The diagnosis of IIMs was based on the Bohan and Peter’s criteria with definite or probable cases being included [5]. Patients with clinically amyopathic disease must have the typical Gottron’s papules or heliotrope rash as determined by rheumatologists or dermatologists, and with no symptoms or signs of muscle involvement according to Sontheimer [6]. Patients with juvenile myositis, inclusion body myositis, cancer-associated myositis and myositis associated with other connective tissue disease were excluded. A commercial line blot immunoassay kit (EUROLINE) was used to detect the MSAs.Results:All together 495 patients were studied. The mean age of the patients at disease onset was 48.1 years (S.D. 13.3). There was a female predominance (68.3%). The subgroups of IIMs were: dermatomyositis (61.0%), polymyositis (21.8%), clinically amyopathic dermatomyositis (12.9%), immune mediated necrotising myopathy (3.8%) and nonspecific myositis (0.4%). No particular seasonal pattern in disease onset was observed in IIM patients as a whole (Figure 1) or in any classical subgroups. However, significantly more patients with any one MSA had their disease started in the first half of the year (p=0.007) as shown in Figure 2. Patients with either anti-synthetase or anti-MDA5 antibodies, which are associated with interstitial lung disease, had more frequent disease onset from November to February, which might coincide with the local flu season. It was also found that MSA positivity was associated with infection of the patient (p=0.005). Further analyses showed that patients with MSAs which are typically associated with severe skin disease (MDA5, TIF1g, NXP2, SAE) had more hospitalisation from April to September where excessive sun exposure is expected. There were no major differences between the Beijing and Hong Kong subgroups.Conclusion:Apparent seasonal patterns were noticed in our ethno-serologically defined IIM patients. Certain environmental factors, particularly infection or UV exposure, could be potential triggers. Our findings could shed light on the identification of etiologic factors and enhance our understanding of disease pathogenesis.

AB1237 Diagnostic value of proteasomal and autophagic markers in muscular diseases

Background:Deficient cellular degradation pathways such as autophagy and the ubiquitin proteasome system (UPS) show a correlation with the onset of neurodegenerative diseases. Especially immune-mediated inflammatory myopathies often show therapy-resistant phenotypes with medical need for further understanding of pathogenesis und possible treatment.Objectives:The aim of this work was to study an association of these two degradation pathways in a large group of different muscle entities and to examine a possible influence in the pathogenesis of the investigated muscle diseases. Furthermore, a potential benefit in diagnostics was studied using factors such as ubiquitin, p62, NBR1 and LC3 and their role as adapter molecules.Methods:We examined ubiquitin, p62, NBR1 and LC3 on muscle biopsies from patients with the diagnosis of s-IBM, dermato- and polymyositis, muscular dystrophy, neurogenic atrophy, myotonic dystrophy type II (PROMM) and metabolic myopathies such as Pompe and McArdle disease. Immunohistochemical single and double stainings as well as immunofluorescence stainings were performed on cryosections. Furthermore, Western blot analysis was performed. The use of a histological score, defined as the product of the frequency of positive fibres and staining intensity, was used to investigate possible differences between the diseases in the expression of the investigated factors.Results:Especially in s-IBM, myofibrillar myopathies and Pompe disease, proteasomal and autophagic markers were detected. On the other hand, neurogenic atrophy, McArdle disease and the majority of the myotonic dystrophies type II showed no positive signals, except for p62, which was detected especially in internalized nuclei and regenerative fibres. Overall, in all entities in regenerative and necrotic as well as in atrophic fibres, a positive staining for ubiquitin, p62, NBR1 and LC3 could be shown. Dermatomyositis showed a moderate immunoreactivity for p62 and NBR1 in the area of the perifascicular atrophy. Polymyositis showed a strong endomysial reaction in the area of the attacked muscle fibres, especially in the area of the lymphocytic infiltrates. The histological score showed that ubiquitin was significantly higher in s-IBM than in polymyositis. NBR1 was significantly higher in s-IBM than in dermatomyositis and muscular dystrophies. LC3 and p62 showed a significantly higher level in s-IBM as compared to dermatomyositis and polymyositis. Except for NBR1, a positive correlation of autophagic and proteasomal markers was shown in dermatomyositis. There was also a positive correlation between LC3 and ubiquitin in polymyositis. Using multivariate analysis and recursive partitioning, we could show a predictability of the diagnosis of s-IBM with a LC3 score above 3. On the other hand, a value below 3 excluded the diagnosis of s-IBM.Conclusion:In particular, s-IBM, myofibrillar myopathies and Pompe disease showed a possible involvement disturbed proteasomal and autophagic degradation pathways in their pathogenesis. In addition, p62 and NBR1 seemed to have an important role in the immune response. Furthermore, the altered autophagic and proteasomal degradation pathways may be involved in ageing processes, sarcopenia and disease. In particular, LC3 seems to be suitable as a screening marker to recognize an idiopathic inflammatory myopathy. The other markers, such as p62, LC3, and NBR1, would be able to distinguish between the subgroups of idiopathic inflammatory myopathies. Therefore, LC3 could be included as a marker in the routine of neuropathological diagnostics. Further studies are needed to fully understand the role of proteasomal and autophagic factors in possible immune suppressive and immune modulatory therapies and to assess possible side effects.Disclosure of Interests:Ulrich Drott: None declared, Patrick Harter: None declared, Harald Burkhardt Grant/research support from: Pfizer, Roche, Abbvie, Consultant of: Sanofi, Pfizer, Roche, Abbvie, Boehringer Ingelheim, UCB, Eli Lilly, Chugai, Bristol Myer Scripps, Janssen, and Novartis, Speakers bureau: Sanofi, Pfizer, Roche, Abbvie, Boehringer Ingelheim, UCB, Eli Lilly, Chugai, Bristol Myer Scripps, Janssen, and Novartis, Michel Mittelbronn: None declared

Performance of the new EULAR/ACR classification criteria for idiopathic inflammatory myopathies (IIM) in a large monocentric IIM cohort

BackgroundIn 2017, the European League Against Rheumatism (EULAR) and the American College of Rheumatology (ACR) published new classification criteria for idiopathic inflammatory myopathies (IIM). ObjectivesTo [1] assess the performance of the EULAR/ACR criteria in a monocentric cohort of consecutive patients with IIM, compare them with the Bohan and Peter (BP) criteria, and with the physician's diagnosis; and [2] evaluate the effect of including the presence of interstitial lung disease (ILD) as variable in the criteria. Methods439 consecutive patients with a diagnosis of IIM followed at the Rheumatology Clinic, Karolinska University Hospital, Sweden were enrolled. The patients were diagnosed as IIM and subclassified by expert physicians. Clinical, laboratory, serological and histopathological data were collected from existing databases (Euromyositis registry and Swedish Rheumatology quality registry) and clinical charts of the patients. The sensitivity of the EULAR/ACR and the BP criteria was calculated. ResultsThe EULAR/ACR criteria had a higher sensitivity (87.7%) compared to the BP criteria (80.4%). The concordance between the two sets of criteria was low (k = 0.253 p<0.001). The EULAR/ACR criteria showed a very high specificity (>98%) for the major IIM subgroups polymyositis, dermatomyositis, and inclusion body myositis. The sensitivity was variable and was high in inclusion body myositis (98%), dermatomyositis (90%) and lower in polymyositis (73%). When including ILD in the variables of the criteria, six more patients were classified as IIM cases (1.3%). ConclusionThe EULAR/ACR criteria for IIM are applicable with high sensitivity and specificity using data available from existing databases and clinical charts and represent a major step forward from the previous criteria for IIM and its subgroups. Their application will improve the quality of clinical trials and research studies with IIM patients.

Interferon-signature in idiopathic inflammatory myopathies.

The present review describes the interferon (IFN)-signature currently emerging as a tool for the diagnosis of idiopathic inflammatory myopathies (IIMs), and aims at presenting the interests and limitations of this recent tool for the clinics and the research. Recent in-vivo and in-vitro transcriptomic studies have evidenced the involvement of IFNs in the pathogenesis of IIMs. A correlation between the IFN-signature and the clinical severity of IIMs has been established. Moreover, studies pointed out differences in the IFN-signature regarding the IIM subgroup (dermatomyositis, polymyositis, inclusion body myositis, anti-synthetase syndrome, immuno-mediated necrotizing myopathies), raising the hypothesis of several pathogenic processes in IIMs. IIM pathogenesis remains partially understood. IFN-signature represents one of the main recent advances in the field. IFN-signature was identified thanks to transcriptomic analyses of tissues or cells from IIM patients (muscle, skin, blood cells, muscle cells) and should allow to establish new diagnosis and better monitoring of IIM patients. It also provides a tool for investigation of IIM pathogenesis. Nevertheless, IFN-signature still requires accurate definition in order to standardize its use, notably in the clinical practice.

P.18Comparing histological features and molecular gene expression in anti-Jo1-, anti-PL-7 and anti-PL-12 antibody-positive patients

Some subgroups of idiopathic inflammatory myopathies are defined by myositis-specific autoantibodies, like the anti-synthetase syndrome (ASyS). These specific antibodies describe subsets of patients with distinct clinical phenotypes reflecting an underlying antigen-driven process, e.g. Jo-1 myositis is characterized by perifascicular necrosis, inflammation with MHC expression and unique myonuclear actin inclusions. The most frequently detected antibodies other than Jo1 are PL-7 and PL-12 also affecting a considerable proportion of patients. However, beyond some clinical descriptions there exist no in-depth characterization of PL-7/PL-12 ASyS. Therefore, we focused on the detailed description of these subgroups, analyzing 40 patients using modern histopathology, qPCR, and electron microscopy to describe the disease more precisely. Besides clinical information, e.g. muscle affection, lung involvement, we quantified various morphological features like atrophy, necrosis, regeneration, MHC expression and cell infiltration. Of special interest are invading B and P cells, which we aim to characterize in combination with their attracting chemokines like CXCL13 or CXCR4. All three groups show similar histological features, but it became apparent that Jo1+ patients show a worse and more acute picture than PL-7/PL-12+ patients. In line with this results of the underlying immune response experiments with qPCR showed an upregulation of genes involved in a pro-inflammatory immune response in Jo1 (like strong upregulation of IFNG), whereas PL-7/PL-12 show a significantly increased expression of genes that are rather anti-inflammatory (e.g. upregulation of IL4R, TGFB). In conclusion, Jo1+ patients show different clinical features and appear more acute regarding the ongoing inflammation than PL-7/PL-12. Since the latter groups appeared very similar in terms of severity and accessory symptoms, they should be treated differently than Jo1+ patients regarding diagnostics and therapy.

T-cell transcriptomics from peripheral blood highlights differences between polymyositis and dermatomyositis patients

BackgroundPolymyositis (PM) and dermatomyositis (DM) are two distinct subgroups of idiopathic inflammatory myopathies, a chronic inflammatory disorder clinically characterized by muscle weakness and inflammatory cell infiltrates in muscle tissue. In PM, a major component of inflammatory cell infiltrates is CD8+ T cells, whereas in DM, CD4+ T cells, plasmacytoid dendritic cells, and B cells predominate. In this study, with the aim to differentiate involvement of CD4+ and CD8+ T-cell subpopulations in myositis subgroups, we investigated transcriptomic profiles of T cells from peripheral blood of patients with myositis.MethodsTotal RNA was extracted from CD4+ T cells (PM = 8 and DM = 7) and CD8+ T cells (PM = 4 and DM = 5) that were isolated from peripheral blood mononuclear cells via positive selection using microbeads. Sequencing libraries were generated using the Illumina TruSeq Stranded Total RNA Kit and sequenced on an Illumina HiSeq 2500 platform, yielding about 50 million paired-end reads per sample. Differential gene expression analyses were conducted using DESeq2.ResultsIn CD4+ T cells, only two genes, ANKRD55 and S100B, were expressed significantly higher in patients with PM than in patients with DM (false discovery rate [FDR] < 0.05, model adjusted for age, sex, HLA-DRB1*03 status, and RNA integrity number [RIN]). On the contrary, in CD8+ T cells, 176 genes were differentially expressed in patients with PM compared with patients with DM. Of these, 44 genes were expressed significantly higher in CD8+ T cells from patients with PM, and 132 genes were expressed significantly higher in CD8+ T cells from patients with DM (FDR < 0.05, model adjusted for age, sex, and RIN). Gene Ontology analysis showed that genes differentially expressed in CD8+ T cells are involved in lymphocyte migration and regulation of T-cell differentiation.ConclusionsOur data strongly suggest that CD8+ T cells represent a major divergence between PM and DM patients compared with CD4+ T cells. These alterations in the gene expression in T cells from PM and DM patients might advocate for distinct immune mechanisms in these subphenotypes of myositis.

Myositis autoantibody profiles and their clinical associations in Greek patients with inflammatory myopathies.

Myositis-specific (MSAs) or-associated autoantibodies (MAAs) have been linked to particular clinical phenotypes of idiopathic inflammatory myopathies (IIM) and appear to aid diagnosis. The objective of this study was to analyze the prevalence of MSAs and MAAs and their possible clinical associations in Greek IIM patients. This study comprised 95 IIM patients classified based on the 2017 EULAR/ACR classification criteria. All patients had MSAs and MAAs measured in their sera by line immunoblot assay. Dermatomyositis was the most prevalent IIM clinical subtype. MSAs were found in 44% of the patients, whereas MAAs in 23%. The most frequently detected MSA was anti-Jo-1 (22%), while the most frequently detected MAA was anti-Ro-52 (30%). The distributions of MSAs/MAAs did not differ between the five IIM subgroups, except for anti-Mi-2 which was only detected in dermatomyositis patients. Patients with at least one MSA and/or MAA positivity showed more frequently IIM characteristic skin rashes, while those presenting solely MAA positivity had more often puffy hands and Raynaud's phenomenon. Anti-Jo1-positive patients presented more frequently lung disease, while anti-Ro52 positivity related to mechanic's hands. Anti-Ro-52 and anti-Jo-1 strongly associated with one another. Prevalence of IIM subtypes and of MSAs/MAAs in our patients is in line with published reports in populations of similar geographic distribution. While MSA and/or MAA positivity did associate with particular clinical manifestations, it did not predict in our cohort specific IIM subgroup as defined by the latest EULAR/ACR classification criteria. Future studies are warranted to conclusively decide if these autoantibodies, measured with a standardized method, should or not be incorporated in every day clinical practice to aid IIM diagnosis.

18F-FDG PET/CT and MRI in Necrotizing Autoimmune Myopathy

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.

2017 European League Against Rheumatism/American College of Rheumatology Classification Criteria for Adult and Juvenile Idiopathic Inflammatory Myopathies and Their Major Subgroups.

To develop and validate new classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIM) and their major subgroups. Candidate variables were assembled from published criteria and expert opinion using consensus methodology. Data were collected from 47 rheumatology, dermatology, neurology, and pediatric clinics worldwide. Several statistical methods were utilized to derive the classification criteria. Based on data from 976 IIM patients (74% adults; 26% children) and 624 non-IIM patients with mimicking conditions (82% adults; 18% children), new criteria were derived. Each item is assigned a weighted score. The total score corresponds to a probability of having IIM. Subclassification is performed using a classification tree. A probability cutoff of 55%, corresponding to a score of 5.5 (6.7 with muscle biopsy) "probable IIM," had best sensitivity/specificity (87%/82% without biopsies, 93%/88% with biopsies) and is recommended as a minimum to classify a patient as having IIM. A probability of ≥90%, corresponding to a score of ≥7.5 (≥8.7 with muscle biopsy), corresponds to "definite IIM." A probability of <50%, corresponding toa score of <5.3 (<6.5 with muscle biopsy), rules out IIM, leaving a probability of ≥50-<55% as "possible IIM." The European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification criteria for IIM have been endorsed by international rheumatology, dermatology, neurology, and pediatric groups. They employ easily accessible and operationally defined elements, and have been partially validated. They allow classification of "definite," "probable," and "possible" IIM, in addition to the major subgroups of IIM, including juvenile IIM. They generally perform better than existing criteria.

Acute digital ischemia: A rare presentation of antisynthetase syndrome.

Antisynthetase syndrome (ASS) is recognized as a subgroup of idiopathic inflammatory myopathies (IIMs). It is associated with autoantibodies directed against aminoacyl-transfer ribonucleic acid (tRNA) synthetase enzymes. We report the first case of anti-PL-7/anti-SSA 52kD ASS presenting as acute digital ischemia, an association not described previously. Occlusive vasculopathy is a rare but serious manifestation that can be seen at presentation in patients with ASS and may herald the onset of severe interstitial lung disease (ILD). Comprehensive evaluation should be performed to confirm the presence of subclinical myositis. Extensive myositis-specific antibody testing is strongly recommended even if initial screening autoimmune serologies are unrevealing.

The Correlation of Muscle Biopsy Scores with the Clinical Variables in Idiopathic Inflammatory Myopathies.

Objectives: To compare the muscle pathology findings among subgroups of idiopathic inflammatory myopathies (IIM) patients, and to determine the correlations of muscle biopsy scores with muscle power and creatine kinase (CK).Methods:The medical records of IIM patients consisting of the demographic data, clinical parameters and laboratory conducted were retrospectively reviewed. Their initial muscle biopsies were reviewed, and four domains were scored: inflammation, vascular, muscle, and connective tissue.Results: Ninety-five IIM patients (28 patients with idiopathic polymyositis (PM) 9 idiopathic dermatomyositis (DM), 5 DM associated with malignancy, and 53 PM/DM associated with connective tissue disease) with median (IQR: Q1, Q3) disease duration of 1.2 (0.5, 3.1) months were included. No significant differences in initial muscle pathology findings and muscle pathology score among the subgroups were found. Muscle degeneration and endomysial fibrosis scores were negatively correlated with muscle power (r=-0.23 and-0.24, respectively, p<0.05) and positively correlated with CK (r=0.27 and 0.39, respectively, p<0.01). No significant correlation was detected either inflammation or vasculitis scores with muscle power and CK levels.Conclusion:In this study, muscle biopsy cannot be used to differentiate among subgroups of IIM patients. In addition, we found only modest correlation of muscle biopsy scores with muscle power and CK. Further study is necessary to confirm our findings.

Immune-mediated necrotizing myopathy.

Immune-mediated necrotizing myopathy (IMNM) is a newly identified subgroup of idiopathic inflammatory myopathies. It is defined as a rare and severe disease, with symmetrical and proximal muscle weakness and a characteristic histology. An autoimmune aspect of IMNM is suggested by its association with autoantibodies directed against signal recognition particle (SRP) and 3-hydroxy-3-methylglutaryl-coenzymeA reductase (HMGCR) in the majority of patients. Statin use is strongly associated with anti-HMGCR-positive IMNM. The pathophysiological mechanisms of this disease are still poorly understood, and as a result, no therapeutic strategy has been validated to date. The aim of this article is to provide an overview of the current knowledge about epidemiology, clinical features, and pathophysiology of IMNM, as well as treatment strategies. IMNM is a subject of widespread interest, with quick and meaningful advances being made. In recent years, huge progress has been made in terms of diagnosis and patient management. However, the understanding of pathophysiological mechanisms and treatment strategies still requires further investigation.

Immune-Mediated Necrotizing Myopathy: An Often Misdiagnosed Entity

Immune-mediated necrotizing myopathies (IMNM) are recognized as a subgroup of idiopathic inflammatory myopathies (IIM). IMNM are defined based on a combination of clinical presentation and laboratory studies, requiring a specific myopathological pattern on muscle biopsy for diagnosis. The authors describe a case of a patient with necrotizing myopathy, thought to be immune mediated, highlighting the challenge of its differential diagnosis. As clinical assessment and diagnostic tools sometimes fail to determine whether a necrotizing myopathy is immune mediated, leading to misdiagnosis and a compromise of the optimal therapeutic approach, distinguishing between IMNM and other myopathies is crucial.

G.P.73: Necrotizing autoimmune myopathy: Clinical and histopathological features of 6 patients

Necrotizing autoimmune myopathy (NAM) is a relatively newly recognized subgroup of idiopathic inflammatory myopathies. Classically, patients present with a subacute severe proximal myopathy, associated with a markedly elevated creatine kinase level, usually greater than 10 times the upper limit of normal, and electromyography shows myopathic changes. Muscle biopsy is required for diagnosis, revealing active necrosis of the muscle fibers without inflammatory invasion and variable upregulation of MHC class 1. The other causes of necrotizing myopathy should be excluded such as toxic myopathies, muscular dystrophies. The clinical presentation is highly variable, often similar to the other inflammatory myopathies. We herein report the clinical and histopathological features of 6 patients with NAM. Age of onset ranged from 35 to 69 years (mean 56.8 years), and 5 of them were female. All of the patients presented with subacute onset proximal limb weakness, 4 with myalgia. Serum CK levels ranged from 1041 to 7900 IU/L. Needle EMG revealed myopathic changes in all. Muscle biopsies showed mainly necrotic and/or regenerative muscle fibers in all 6 patients. There were focal (in 4) or diffuse (in 2) major histocompatibility complex class 1 expression in sarcolemma or cytoplasm of muscle fibers among necrotic muscle fibers. Screening for cancer revealed negative or normal results in all. Two patients received statins previously. Three patients had diabetes mellitus and 1 patient had SLE. All treated with steroids and/or immunosuppressive drugs. The clinical characteristics of these patients, pathologic findings, associated risk factors and response to immunosuppressive therapies are discussed.

Acquired necrotizing myopathies

Necrotizing myopathy exhibits a specific histological pattern, characterized by significant necrosis, with simultaneous muscle fiber regeneration, but without or with little inflammation. This histological pattern may be observed in acquired myopathies but also in muscular dystrophy. Acquired necrotizing myopathy can be secondary to drugs or toxics agents, and if not, autoimmune mechanisms have to be suspected. Necrotizing autoimmune myopathy (NAM) is now recognized as a subgroup of idiopathic inflammatory myopathies. This review aims to further describe the different acquired myopathies, with special focus on NAM since specific autoantibodies have been discovered. Usually, acquired myopathy has an acute onset, but a slower progression may sometimes be observed that could lead to erroneous diagnosis of muscular dystrophy. NAM may be associated with specific autoantibodies against signal recognition particle, or, as more recently described, against 3-hydroxy-3-methylglutaryl-coenzyme A reductase, especially in statin-exposed patients. Their presence permits affirmation that muscular necrosis is immune-mediated. The antibody titer is correlated to the disease activity. NAMs are now considered as a new entity, treatable by immunosuppressants, and should not be misdiagnosed as a muscular dystrophy.

P.21.1 Autophagy as a link between immunity and inflammation in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of immune-mediated muscle disorders characterized by muscle inflammation and weakness. They comprise inclusion body myositis (IBM), polymyositis (PM), juvenile dermatomyositis (JDM) and adult dermatomyositis (DM). Autophagic pathway impairment has been well documented in sporadic IBM, where it has been suggested to be responsible for the accumulation of multiple-protein aggregates, typical of the myopathy. The main candidates responsible for this impairment are suggested to be TLRs. We evaluated the autophagic process also in PM and DM, in particular the interaction between autophagosome maturation and innate immune system. LC3 and other autophagic molecules, together with TLR3, TLR4, HSP60 and HMGB1/2 were analyzed in IIM and control muscles by qPCR, immunohistochemistry and immunoblot. Myoblasts and myotubes from PM, DM and control muscle biopsies were analyzed to evaluate changes in TLR and HMGB1/2 expression after induction or inhibition of autophagy. Gene expression analysis showed a dysregulation of autophagy in all IIM subgroups. A tight correlation between autophagy and innate immunity in myopathic muscles compared to controls was highlighted by confocal microscopy; activation of stress response and the presence of bacterial infection were observed connected with an abnormal accumulation of autophagosomes in IIM myofibers. These findings demonstrate the involvement of the autophagic process in the pathogenesis of all subtypes of IIMs; it is not clear if this mechanism represents a consequence or a cause of the induction of immune response and inflammation. Autophagic machinery components might represent a possible target for new therapeutic approaches for IIM.

SAT0207 Epidemiological Data of Patients with Idiopathic Inflammatory Myopathy from a Hungarian Myositis Centre

BackgroundThe idiopathic inflammatory myopathies (IIM) are systemic autoimmune disease characterised with proximal muscle weakness. The epidemiology of these multifactorial diseases is partially known. These are rare diseases and Immunological or...