Classification Of Idiopathic Inflammatory Myopathies Research Articles

Quid de la détection des anticorps anti-TIF1γ dans les dermatomyosites ?

AbstractThe classification of idiopathic inflammatory myopathies (IBD) is evolving, with the consideration, in addition to clinicopathological criteria, of the presence of autoantibodies specific to myositis for the diagnosis and identification of clinical forms.The diagnosis of dermatomyositis (DM) is based on clinical, histological, imaging criteria and the demonstration of myositis-specific autoantibodies (MSA). Within these antibodies, anti-TIF1γ have a special place due to their high prevalence in juvenile DM and in cancer-associated DM. Anti-TIF1γ antibodies are present in 7-31% of adult DMs. DMs with anti-TIF1γ are associated with cancer in more than half of cases in adults (38-75%), whereas this is not the case in juvenile DMs. The role of the TIF1γ protein in the tumor process and of autoantibodies in the triggering of DM are the subject of numerous hypotheses, but without any definitive conclusion currently.Given the diagnostic and prognostic importance of the presence of anti-TIF1γ antibodies, it is essential to have reliable tests suitable for routine practice to characterize them. The reference technique, immunoprecipitation, is not suitable for the routine laboratory. Immunodots are practical but their performance is not optimal in terms of sensitivity and specificity. Elisa and the particle-based multi-analyte technology (PMAT)-type automated technique seem to present performances close to immunoprecipitation but with a practicability adapted to routine use.

Contribution of Complement, Microangiopathy and Inflammation in Idiopathic Inflammatory Myopathies.

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group characterized by muscle weakness and skin symptoms and are categorized into six subtypes: dermatomyositis (DM), polymyositis (PM), anti-synthetase syndrome (ASS), immune-mediated myopathy (IMNM), inclusion body myopathy (IBM), and overlap myositis. Myositis-specific autoantibodies were detected for the diagnosis and classification of IIM. This review highlights the pathogenic contributions of the complement system, microangiopathy, and inflammation in IIM. Deposition of complement around capillaries and/or the sarcolemma was observed in muscle biopsy specimens from patients with DM, ASS, and IMNM, suggesting the pathomechanism of complement-dependent muscle and endothelial cell injury. A recent study using human muscle microvascular endothelial cells showed that Jo-1 antibodies from ASS induce complement-dependent cellular cytotoxicity in vitro. Based on both clinical and pathological observations, antibody- and complement-mediated microangiopathy may contribute to the development of DM and anti-Jo-1 ASS. Juvenile DM is characterized by the loss of capillaries, perivascular inflammation, and small-vessel angiopathies, which may be related to microinfarction and perifascicular atrophy. Several serum biomarkers that reflect the IFN1 signature and microangiopathy are elevated in patients with DM. The pathological observation of myxovirus resistance protein A (MxA), which suggests a type 1 interferon (IFN1) signature in DM, supports the diagnosis and further understanding of the pathomechanism of IIM. A recent report showed that an increase in triggering receptor expressed on myeloid cells (TREM-1) around perimysial blood vessels and muscles in patients with IIM plays a role in triggering inflammation and promoting the migration of inflammatory cells by secreting proinflammatory cytokines, such as tumor necrosis factor α. The deposition of complement in muscles and capillaries is a characteristic feature of DM, ASS, and IMNM. Microangiopathy plays a pathogenic role in DM, possibly resulting in perifascicular atrophy. Further understanding of the detailed pathomechanism regarding complement, microangiopathy, and inflammation may lead to novel therapeutic approaches for IIM.

Clinicopathological Reclassification of Idiopathic Inflammatory Myopathy to Match the Serological Results of Myositis-Specific Antibodies.

Advances in serological tests are transforming the classification of idiopathic inflammatory myopathy (IIM). The new criteria suggested by the 119th European Neuromuscular Center international workshop divide IIM cases into four main diseases according to clinical and pathological findings, adding immune-mediated necrotizing myositis and nonspecific myositis to the classic categories of polymyositis and dermatomyositis. Seventy one cases of IIM with sufficient available clinical and pathological data were reviewed to be reclassified according to the new criteria. Most of the cases previously classified as polymyositis (77.8%, 35/45) were reclassified as immune-mediated necrotizing myopathy. The results of myositis-specific antibodies matched well with the new clinicopathological classification. This new clinicopathological classification for IIM in combination with serological test results could be applied to our previous case series. Adoption of the new criteria will lead to a better understanding of the disease and hence new therapeutic insights.

Performance of the 2017 EULAR/ACR Classification Criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups: a scoping review.

The 2017 EULAR/ACR classification criteria for adult/juvenile idiopathic inflammatory myopathies (IIM) were established using a data-driven approach by an international group of myositis experts to allow classification of IIM and its major subtypes. Since their publication, the performance of the criteria has been tested in multiple cohorts worldwide and significant limitations have been identified. Moreover, the understanding and classification of IIM have evolved since 2017. This scoping review was undertaken as part of a large international project to revise the EULAR/ACR criteria and aims to i) summarise the evidence from the current literature on the performance characteristics of the 2017 EULAR/ACR classification criteria in various cohorts and IIM subtypes, and ii) delineate the factors that need to be considered in the revision of the classification criteria. A systematic search of Medline (via PubMed), Cumulative Index to Nursing and Allied Health Literature, and conference abstract archives was conducted independently by three investigators for studies on the EULAR/ACR criteria published between October 2017 and January 2023. This scoping review of 19 articles and 13 abstracts revealed overall good performance characteristics of the EULAR/ACR criteria for IIM, yet deficiencies in lack of inclusion of certain IIM subtypes, such as immune mediated necrotising myopathy, amyopathic dermatomyositis, antisynthetase syndrome and overlap myositis. Published modifications that may improve the performance characteristics of the criteria for classification of IIM subtypes were also summarised. The results of this review suggest that a revision of the EULAR/ACR criteria is warranted.

Comparison of Muscle Biopsy Features with Myositis Autoantibodies in Inflammatory Myopathies: A Pilot Experience

Abstract Background: Idiopathic inflammatory myopathies (IIM), also called autoimmune myositis, are heterogeneous. These include dermatomyositis (DM), inclusion body myositis, immune mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASS), and overlap polymyositis. Classification of IIM has evolved from clinical to clinico-pathologic to the recent clinico-sero-pathologic with the discovery of myositis-specific antibodies (MSA) and myositis-associated antibodies. The various antibodies have shown association with specific phenotypes. Objective: To analyze muscle biopsy features with respect to each MSA and MAA to understand the frequency of findings in each entity. Materials and Methods: Biopsy-proven cases of IIM where myositis profile was available were included in the study after obtaining Institutional Ethics Committee (IEC) approval. In addition to the stains and enzyme histochemistry, immunohistochemistry with MHC class I and II and MxA was performed. Features like perifascicular atrophy, perifascicular necrosis, scattered necrosis, inflammation, etc. were analyzed. Myositis profile was performed by line-blot technique using a 16-antigen panel. Cases were divided into different autoantibody subgroups. Various clinical, demographic, and muscle biopsy features were studied with respect to each MSA and MAA. Results: There were a total of 64 cases. Mi2 (N = 18) was the most common autoantibody. Some of the salient observations included PFA with perivascular inflammation in Mi2; pediatric cases and microinfarcts in NXP2; no PFA or inflammation in MDA5; perifascicular necrosis in JO1; extensive necrosis with sparse inflammation in SRP; more inflammation in overlap myositis; MxA positivity in DM; and absent in ASS. Conclusion: This is a pilot study documenting differences in biopsy phenotype with each MSA and MAA which is comparable to the literature. These findings can be used to characterize IIM in seronegative biopsies.

Inflammatory Myopathies

This article outlines the salient clinical, serologic, electrophysiologic, imaging, and histopathologic findings and treatment options for the idiopathic inflammatory myopathies, including those related to immune checkpoint inhibitors and SARS-CoV-2. The classification of idiopathic inflammatory myopathies has improved with the integration of myositis-specific antibodies and histopathologic findings. Characteristic features of immune checkpoint inhibitor-related myositis have been identified, allowing early recognition and treatment of the syndrome. The COVID-19 pandemic has had a profound impact on the care of patients with idiopathic inflammatory myopathies, and several mechanisms of virus-related muscle injury have been proposed. A comprehensive evaluation including clinical examination, EMG, imaging, antibody testing, muscle biopsy, and cancer screening, when appropriate, can lead to an earlier accurate diagnosis and an individualized treatment approach for patients with idiopathic inflammatory myopathies.

AN UNCOMMON PRESENTATION OF ANTISYNTHETASE SYNDROME-RELATED INTERSTITIAL LUNG DISEASE IN A YOUNG INDIAN MALE

AN UNCOMMON PRESENTATION OF ANTISYNTHETASE SYNDROME-RELATED INTERSTITIAL LUNG DISEASE IN A YOUNG INDIAN MALE

Performance of the 2017 European Alliance of Associations for Rheumatology/American College of Rheumatology Classification Criteria in Patients With Idiopathic Inflammatory Myopathy and Anti-Melanoma Differentiation-Associated Protein 5 Positivity.

This study aimed to evaluate whether the 2017 European Alliance of Associations for Rheumatology (EULAR)/American College of Rheumatology (ACR) classification criteria for adult and juvenile idiopathic inflammatory myopathies (IIMs) could appropriately classify the diagnosis in adult patients with anti-melanoma differentiation-associated protein 5 (anti-MDA-5)-positive IIM. In addition, this study sought to determine whether a status of anti-MDA-5 positivity could be incorporated into the EULAR/ACR IIM classification criteria set and whether the recently modified criteria based on the presence of myositis-specific autoantibodies (MSAs) could be used to appropriately classify the diagnosis in patients with anti-MDA-5-positive IIM. Consecutive adult patients clinically diagnosed as having anti-MDA-5-positive IIM from 10 hospitals in Hong Kong were retrospectively recruited; patient characteristics were obtained from electronic medical records. We used a commercial line blot immunoassay to detect MSAs. We also determined a proposed set of phenotypic-serologic classification criteria specific for anti-MDA-5. In the patient cohort (n=120; 31.7% with dermatomyositis, 68.3% with clinically amyopathic dermatomyositis [CADM]), the diagnosis could be classified with the EULAR/ACR criteria in 86 patients (71.7%) and with the Bohan and Peter criteria in 49 patients (40.8%). However, when combined with criteria specifically modified for CADM, the diagnosis could be classified by the Bohan and Peter criteria in 76.7% of patients. We observed that the sensitivity of the EULAR/ACR criteria could be improved to 98.3% if anti-MDA-5 antibody-positive status was considered as one of the criteria. The MSA-based criteria had 100% sensitivity. When we applied our proposed specific phenotypic-serologic criteria for the classification of patients with anti-MDA-5 antibodies, 97.5% of patients were able to be classified as having IIM. In this cohort of patients with anti-MDA-5-positive IIM, the diagnosis could not be classified by the EULAR/ACR criteria in almost 30% of patients. We suggest incorporating anti-MDA-5 antibody positivity as a criterion into existing criteria sets or developing specific criteria for patients with anti-MDA-5-positive IIM.

Integrated analysis of plasma and urine reveals unique metabolomic profiles in idiopathic inflammatory myopathies subtypes.

ObjectivesIdiopathic inflammatory myopathies (IIM) are a class of autoimmune diseases with high heterogeneity that can be divided into different subtypes based on clinical manifestations and myositis‐specific autoantibodies (MSAs). However, even in each IIM subtype, the clinical symptoms and prognoses of patients are very different. Thus, the identification of more potential biomarkers associated with IIM classification, clinical symptoms, and prognosis is urgently needed.MethodsPlasma and urine samples from 79 newly diagnosed IIM patients (mean disease duration 4 months) and 52 normal control (NC) samples were analysed by high‐performance liquid chromatography of quadrupole time‐of‐flight mass spectrometry (HPLC‐Q‐TOF‐MS)/MS‐based untargeted metabolomics. Orthogonal partial least‐squares discriminate analysis (OPLS‐DA) were performed to measure the significance of metabolites. Pathway enrichment analysis was conducted based on the KEGG human metabolic pathways. Ten machine learning (ML) algorithms [linear support vector machine (SVM), radial basis function SVM, random forest, nearest neighbour, Gaussian processes, decision trees, neural networks, adaptive boosting (AdaBoost), Gaussian naive Bayes and quadratic discriminant analysis] were used to classify each IIM subtype and select the most important metabolites as potential biomarkers.ResultsOPLS‐DA showed a clear separation between NC and IIM subtypes in plasma and urine metabolic profiles. KEGG pathway enrichment analysis revealed multiple unique and shared disturbed metabolic pathways in IIM main [dermatomyositis (DM), anti‐synthetase syndrome (ASS), and immune‐mediated necrotizing myopathy (IMNM)] and MSA‐defined subtypes (anti‐Mi2+, anti‐MDA5+, anti‐TIF1γ+, anti‐Jo1+, anti‐PL7+, anti‐PL12+, anti‐EJ+, and anti‐SRP+), such that fatty acid biosynthesis was significantly altered in both plasma and urine in all main IIM subtypes (enrichment ratio > 1). Random forest and AdaBoost performed best in classifying each IIM subtype among the 10 ML models. Using the feature selection methods in ML models, we identified 9 plasma and 10 urine metabolites that contributed most to separate IIM main subtypes and MSA‐defined subtypes, such as plasma creatine (fold change = 3.344, P = 0.024) in IMNM subtype and urine tiglylcarnitine (fold change = 0.351, P = 0.037) in anti‐EJ+ ASS subtype. Sixteen common metabolites were found in both the plasma and urine samples of IIM subtypes. Among them, some were correlated with clinical features, such as plasma hypogeic acid (r = −0.416, P = 0.005) and urine malonyl carnitine (r = −0.374, P = 0.042), which were negatively correlated with the prevalence of interstitial lung disease.ConclusionsIn both plasma and urine samples, IIM main and MSA‐defined subtypes have specific metabolic signatures and pathways. This study provides useful clues for understanding the molecular mechanisms, searching potential diagnosis biomarkers and therapeutic targets for IIM.

Nailfold capillaroscopy changes with disease activity in patients with inflammatory myositis including overlap myositis, pure dermatomyositis, and pure polymyositis.

ObjectivesNailfold capillaroscopy (NFC) is useful in the evaluation of connective tissue diseases. There are few capillaroscopy examinations in patients with idiopathic inflammatory myopathies (IIMs) using the 2017 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) classification. We evaluated the clinical, laboratory, and NFC in patients with IIMs using 2 classifications.Material and methodsIn this cross-sectional study, 150 patients with IIMs were selected based on the EULAR/ACR classification and the Troyanov and Senécal classification. Nailfold capillaroscopy, laboratory tests, clinical manifestations, and disease activity were evaluated.ResultsThe subgroups were as follows: 81 patient with dermatomyositis (DM), 25 with amyopathic dermatomyositis (ADM), 25 with juvenile dermatomyositis (JDM), 19 with polymyositis (PM),53 with pure DM, 11 with pure PM, and 51 with overlap myositis (OM). Eight (42%) patients with PM and 28 (34.5%) patients with DM were categorized as OM. The scleroderma pattern was the dominant capillaroscopy pattern in the DM (72.8%), JDM (72%), ADM (76%), pure DM (75.4%), and OM (78.4%) subgroups, respectively. In the DM, ADM, JDM, and OM subgroups, scleroderma pattern had an association with high skin Visual Analogue Scale (VAS) score (p < 0.05). In OM patients, the association between scleroderma pattern and high global VAS was also detected (p < 0.05).ConclusionsThe scleroderma pattern was the dominant capillaroscopy pattern in all groups except for PM and pure PM. Some of patients with PM could be categorized as OM. In the DM and pure DM subgroups, there was a significant association between global and skin activity and higher NFC score. Adding the NFC to the classification of IIM is probably helpful in more detailed classifications.

The role of interferons type I, II and III in myositis: A review.

The classification of idiopathic inflammatory myopathies (IIM) is based on clinical, serological and histological criteria. The identification of myositis‐specific antibodies has helped to define more homogeneous groups of myositis into four dominant subsets: dermatomyositis (DM), antisynthetase syndrome (ASyS), sporadic inclusion body myositis (sIBM) and immune‐mediated necrotising myopathy (IMNM). sIBM and IMNM patients present predominantly with muscle involvement, whereas DM and ASyS patients present additionally with other extramuscular features, such as skin, lung and joints manifestations. Moreover, the pathophysiological mechanisms are distinct between each myositis subsets. Recently, interferon (IFN) pathways have been identified as key players implicated in the pathophysiology of myositis. In DM, the key role of IFN, especially type I IFN, has been supported by the identification of an IFN signature in muscle, blood and skin of DM patients. In addition, DM‐specific antibodies are targeting antigens involved in the IFN signalling pathways. The pathogenicity of type I IFN has been demonstrated by the identification of mutations in the IFN pathways leading to genetic diseases, the monogenic interferonopathies. This constitutive activation of IFN signalling pathways induces systemic manifestations such as interstitial lung disease, myositis and skin rashes. Since DM patients share similar features in the context of an acquired activation of the IFN signalling pathways, we may extend underlying concepts of monogenic diseases to acquired interferonopathy such as DM. Conversely, in ASyS, available data suggest a role of type II IFN in blood, muscle and lung. Indeed, transcriptomic analyses highlighted a type II IFN gene expression in ASyS muscle tissue. In sIBM, type II IFN appears to be an important cytokine involved in muscle inflammation mechanisms and potentially linked to myodegenerative features. For IMNM, currently published data are scarce, suggesting a minor implication of type II IFN. This review highlights the involvement of different IFN subtypes and their specific molecular mechanisms in each myositis subset.

Comparison of the 2017 EULAR/ACR Criteria with Clinicoserologic Criteria for the Classification of Idiopathic Inflammatory Myopathies in Korean Patients.

PurposeTo investigate correlations between myositis-specific autoantibodies (MSA) or myositis-associated antibodies (MAA) and clinical features, thereby demonstrating the utility of clinicoserologic classification in idiopathic inflammatory myopathies (IIM) patients.Materials and MethodsWe conducted a multicenter study of 108 adult patients (age ≥18 years) who were diagnosed with IIM by Peter and Bohan criteria or 2004 European Neuromuscular Centre (ENMC) criteria. Clinical data were obtained by medical record review. Immunoblot assay with Euroline strip (EUROIMMUN, Germany) was performed using the sera of dermatomyositis (DM, n=56), polymyositis (PM, n=45), amyopathic DM (n=5), DM sine dermatitis (n=1), and immune mediated necrotizing myopathy (n=1) patients. Patients were classified based on two classifications: 2017 EULAR/ACR and novel clinicoserologic classification.ResultsAccording to 2017 EULAR/ACR criteria, DM and PM were the most and the second most frequent entities. Overlap myositis was the major entity of IIM, and the frequency of PM was significantly lower when applying clinicoserologic classification criteria. Sixty-nine (63.9%) patients had one or more MSA, and 61 (56.5%) patients had one or more MAA. Interstitial lung disease was closely associated with anti-MDA5 and anti-ARS, and DM-specific skin lesions were frequently observed in patients with anti-TIF1γ, anti-SRP, and anti-MDA5.ConclusionThe clinicoserologic criteria based on MSA/MAA positivity could reflect more precise clinical features of IIM. Establishment of a laboratory system routinely available to screen for MSA/MAA status will be beneficial to provide precise diagnosis and proper management of IIM patients.

The significance of myositis autoantibodies in idiopathic inflammatory myopathy concomitant with interstitial lung disease.

This study identified factors associated with interstitial lung disease (ILD) in patients with idiopathic inflammatory myopathy (IIM) based on the latest classification and recent advances in autoantibody serology. We retrospectively analyzed data of 173 patients who underwent complete myositis autoantibody serology examination in a medical center in Taiwan from July 2018 to February 2020. After exclusion of patients who did not receive a final diagnosis of IIM, clinical features, serology data, concomitant diseases, treatment, presence of respiratory failure, and mortality rate of the remaining 97 patients were analyzed. Of IIM patients in our cohort, 47.4% had ILD. ILD was significantly associated with subtypes of IIM, older age of onset, presence of mechanic's hand, and presence of anti-Jo-1 and anti-Ro52 antibodies. Among five IIM subtypes, overlap myositis (OM) and dermatomyositis (DM) were significantly associated with a higher prevalence rate of ILD (67.5% in OM and 53.3% in DM). Among patients with OM, the presence of anti-Jo-1 (100%), anti-PL-7 (100%), and anti-EJ antibodies (77.8%) was most significantly associated with ILD. The latest classification of IIM, older age of onset, presence of mechanic's hand, and presence of anti-Jo-1 and anti-Ro52 antibodies were significantly associated with ILD. Among five IIM subtypes, OM and DM had higher prevalence rate of ILD. Among OM patients, the presence of anti-Jo-1, anti-EJ, and anti-PL-7 antibodies was significantly associated with ILD. The study results may help physicians to timely screen and monitor pulmonary function in high-risk groups.

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 &lt; 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 &lt; 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.

Can machine learning unravel the complex IIM spectrum?

Idiopathic inflammatory myopathies (IIMs) are heterogeneous conditions, and the optimal way to classify patients and divide them into subgroups remains unclear. Could machine learning techniques be the answer to the problem of defining homogeneous disease phenotypes, enabling stratified treatment approaches and the formulation of future IIM classification criteria?

Classification of idiopathic inflammatory myopathies: pathology perspectives

Idiopathic inflammatory myopathies (IIM) are rare diseases with heterogenous clinicopathological features. In recent years, new classification systems considering various combinations of clinical, serological, and pathological information have been proposed. This review summarizes recent clinicoseropathological development in major subgroups of IIM. Considering clinicoseropathological features, IIM are suggestively classified into four major subgroups: dermatomyositis, immune-mediated necrotizing myopathy (IMNM), antisynthetase syndrome (ASS), and inclusion body myositis (IBM). Many historically diagnosed polymyositis have been mainly reclassified as IBM, IMNM, and ASS. Different types of myositis-specific antibodies (MSA) suggest distinct clinicopathological subsets of IIM. Excluding IBM, at least one-third of the IIMs have no known associated MSA. MSA are crucial for IIM classification but can be negative. Thus, IIM should be universally classified using stepwise or integrated information on clinical, serological, and pathological findings.

The Role of Autoantibodies in Idiopathic Inflammatory Myopathies

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of autoimmune muscle diseases with systemic involvement. Patients with IIM present with varying degrees of muscle disease, cutaneous manifestations, and internal organ involvement. The diagnosis and classification of IIM is based primarily on the classification system composed of clinical features, laboratory value and muscle biopsy. In addition, the identification and characterization of myositis-related autoantibodies can help diagnosis and classification. Recently, many studies have also demonstrated that the physician can define the clinical syndromes, establish treatment strategy and predict outcomes based on the patients’ myositis-specific autoantibodies (MSA) and myositis-associated antibodies (MAA) profiles. MSAs are found exclusively in IIMs and facilitate the identification of subsets of patients with relatively homogeneous clinical features. MAAs are frequently found in association with other MSA; however, they may also be detected in various connective diseases. (J Rheum Dis 2019;26:165-178)

Development of a New Classification System for Idiopathic Inflammatory Myopathies Based on Clinical Manifestations and Myositis-Specific Autoantibodies

Idiopathic inflammatory myopathies are heterogeneous in their pathophysiologic features and prognosis. The emergence of myositis-specific autoantibodies suggests that subgroups of patients exist. To develop a new classification scheme for idiopathic inflammatory myopathies based on phenotypic, biological, and immunologic criteria. An observational, retrospective cohort study was performed using a database of the French myositis network. Patients identified from referral centers for neuromuscular diseases were included from January 1, 2003, to February 1, 2016. Of 445 initial patients, 185 patients were excluded and 260 adult patients with myositis who had complete data and defined historical classifications for polymyositis, dermatomyositis, and inclusion body myositis were enrolled. All patients were tested for anti-histidyl-ARN-t- synthetase (Jo1), anti-threonine-ARN-t-synthetase (PL7), anti-alanine-ARN-t-synthetase (PL12), anti-complex nucleosome remodeling histone deacetylase (Mi2), anti-Ku, anti-polymyositis/systemic scleroderma (PMScl), anti-topoisomerase 1 (Scl70), and anti-signal recognition particle (SRP) antibodies. A total of 708 variables were collected per patient (eg, cancer, lung involvement, and myositis-specific antibodies). Unsupervised multiple correspondence analysis and hierarchical clustering analysis to aggregate patients in subgroups. Among 260 participants (163 [62.7%] women; mean age, 59.7 years; median age [range], 61.5 years [48-71 years]), 4 clusters of patients emerged. Cluster 1 (n = 77) included patients who were male, white, and older than 60 years and had finger flexor and quadriceps weakness and findings of vacuolated fibers and mitochondrial abnormalities. Cluster 1 regrouped patients who had inclusion body myositis (72 of 77 patients [93.5%]; 95% CI, 85.5%-97.8%; P < .001). Cluster 2 (n = 91) regrouped patients who were women and had high creatine phosphokinase levels, necrosis without inflammation, and anti-SRP or anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies corresponding to immune-mediated necrotizing myopathy (53 of 91 [58.2%]; 95% CI, 47.4%-68.5%; P < .001). Cluster 3 (n = 52) regrouped patients who had dermatomyositis rash and anti-Mi2, anti-melanoma differentiation-associated protein 5 (MDA5), or anti-transcription intermediary factor-1γ (TIF1γ) antibodies, mainly corresponding with patients who had dermatomyositis (43 of 52 [82.7%]; 95% CI, 69.7%-91.8%; P < .001). Cluster 4 (n = 40) was defined by the presence of anti-Jo1 or anti-PL7 antibodies corresponding to antisynthetase syndrome (36 of 40 [90.0%]; 95% CI, 76.3%-97.2%; P < .001). The classification of an independent cohort (n = 50) confirmed the 4 clusters (Cohen κ light, 0.8; 95% CI, 0.6-0.9). These findings suggest a classification of idiopathic inflammatory myopathies with 4 subgroups: dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy, and antisynthetase syndrome. This classification system suggests that a targeted clinical-serologic approach for identifying idiopathic inflammatory myopathies may be warranted.

Biologics for idiopathic inflammatory myopathies.

As treatment of refractory cases of idiopathic inflammatory myopathies (IIMs) has been challenging, there is growing interest in assessing novel biologics that target various pathways implicated in the pathogenesis of IIM. In the largest clinical trial in adult and juvenile IIM assessing the effectiveness of rituximab, the primary outcome was not met but 83% of this refractory group of IIM patients met a predefined definition of improvement and rituximab demonstrated a significant glucocorticoid-sparing effect. Antitumor necrosis factor utility in IIM is generally limited by uncertain efficacy data along with recent reports suggesting their potential for inducing systemic autoimmune disease including IIM. Further research is required to evaluate the role of newer therapies such as tocilizumab (anti-interleukin-6), abatacept (inhibition of T-cell costimulation), sifalimumab (anti-interferonα) and ruxolitinib, (Janus kinase inhibitor) given their biological plausibility and encouraging recent small case series results. Future clinical trials should consider the targeting of biomarkers implicated in the etiopathogenesis of IIM, predictive factors of treatment response, recent revisions in IIM classification criteria, as well as newly developed data-driven response criteria which employ validated core set measures.