Pathogenic aspects of dermatomyositis, polymyositis and overlap myositis

Pathogenic mechanisms of disease in idiopathic inflammatory myopathies: autoantibodies as clues

Idiopathic inflammatory myopathies (IIMs) encompass a spectrum of autoimmune diseases characterized by muscle inflammation and systemic involvement. This review aimed to synthesize current evidence on the clinical significance and pathogenic mechanisms underlying autoantibodies associated with IIMs. Autoantibodies targeting aminoacyl-tRNA synthetases (ARS) play a pivotal role in antisynthetase syndrome (ASS), highlighting associations with interstitial lung disease (ILD) and distinctive clinical features. Anti-Mi-2 antibodies in dermatomyositis (DM) are hallmarked by characteristic cutaneous manifestations and favorable prognostic outcomes. Conversely, anti-TIF1 antibodies are correlated with DM and a higher risk of malignancies, implicating CD8+ T cells in its pathogenesis. Anti-MDA5 antibodies signify clinically amyopathic DM (CADM) with severe ILD, linked to dysregulated neutrophil extracellular trap (NET) formation. In immune-mediated necrotizing myopathies (IMNMs), anti-SRP and anti-HMGCR antibodies induce complement-mediated myopathy, typically following statin exposure. Additionally, anti-TRIM72 antibodies emerge as potential diagnostic markers in IIMs. Anti-cN1A autoantibodies are linked to inclusion body myositis (IBM) and play a decisive role in muscle protein degradation. Meanwhile, anti-FHL1 autoantibodies are associated with severe disease manifestations and muscle damage, as established in experimental models. Anti-eIF3 autoantibodies, recently identified in polymyositis (PM) patients, are rarely detected (<1%) and associated with a favorable prognosis. Elucidating these autoantibodies is anticipated to not only assist in early diagnosis and disease stratification but also inform targeted therapeutic interventions, emphasizing the intricate interplay between autoimmunity, cellular dysfunction, and clinical outcomes in IIMs.

Revisiting idiopathic eosinophilic myositis: towards a clinical-pathological continuum from the muscle to the fascia and skin

OBJECTIVES

Idiopathic inflammatory myopathies are mainly defined by inflammatory infiltrates within the muscle (lymphocytes and macrophages). Eosinophil muscle infiltration has been described in idiopathic eosinophilic myositis (IEM) and rarely in EF. This study aimed to further delineate the nosological frame of idiopathic eosinophil muscle infiltration through the exhaustive analysis of IEM and EF patients.

METHODS

This multicentre retrospective case series included IEM patients diagnosed between 2000 and 2022. IEM inclusion criteria were eosinophilic muscle infiltration with myositis pathological features, after the exclusion of differential diagnoses. An additional group of EF patients diagnosed between 2016 and 2022 was constituted. Inclusion criteria were an EF diagnosis and fascia thickening with inflammatory infiltrate.

RESULTS

A total of 20 IEM cases and 10 EF cases were included. The median (interquartile range) age at diagnosis was 65 (49-70) years; there were 18 males. Data analysis delineated four subgroups: focal EM (FEM, n = 3), diffuse EM (DEM, n = 6), eosinophilic myofasciitis (EMF, n = 11) and EF (n = 10). FEM represented a limited and benign form of myositis. DEM cases presented objective muscle impairment with eosinophilic muscle infiltration. EMF patients presented subjective muscle impairment (myalgia, 55%), fasciitis (on histology and/or imaging), eosinophilic muscle infiltration and frequent hypereosinophilia (55%). EF patients presented myalgia (50%), muscle lesions on histology with fascia-restricted inflammatory infiltrates with (60%) or without (40%) eosinophils.

CONCLUSIONS

The analysis of IEM and EF patient characteristics delineates four subgroups (FEM, DEM, EMF and EF) in terms of clinical, laboratory, imaging, pathological and outcome specificities, and proposes an adapted diagnostic and care management approach.

An update on the pathogenic role of IL-6 in rheumatic diseases

Interleukin (IL)-6 is a pleiotropic cytokine that is involved in the pathogenesis of various rheumatic diseases. Direct inhibition of the IL-6 pathway by an anti-IL-6 receptor or inhibiting the ligand itself has proved to be efficacious in the treatment of these diseases. Juvenile idiopathic arthritis, adult-onset Still's disease, large vessel vasculitis including giant cell arteritis and Takayasu disease, systemic sclerosis, and polymyalgia rheumatica respond well to IL-6 inhibition as expected. However, no clinically meaningful effect has been observed with regard to IL-6 blockade in ankylosing spondylitis, psoriatic arthritis, and systemic lupus erythematosus. This review discusses the current state of IL-6 targeting approaches in various rheumatic diseases other than rheumatoid arthritis.

Altered peripheral helper T cells in peripheral blood and muscle tissue of the patients with dermatomyositis

Peripheral helper T (Tph) cells, phenotypically PD-1hiCXCR5-CD4+, are a recently identified Th cell subset that relates to several autoimmune diseases. Contrary to PD-1hiCXCR5+CD4+ follicular helper T (Tfh) cells, Tph cells are not located in lymphoid organs but accumulate in inflamed tissues. This study investigated Tph cells to determine their involvement in dermatomyositis (DM). The frequency of circulating Tph and Tfh cells was evaluated by flow cytometry at baseline and after glucocorticoid treatment. The expression of Tph and B cells was determined in muscle tissue by immunohistochemistry (IHC). Further, the correlations between circulating Tph cells and clinical characteristics were investigated. Flow cytometry revealed that circulating Tph and Tfh cells were decreased in peripheral blood of DM patients compared with healthy controls (HCs). However, the muscular expression of Tph and B cells was upregulated in patients with DM compared to that in the controls by IHC. Interestingly, the increased B cells accumulated around Tph cells in infiltrated lesions. The frequency of circulating Tph cells was positively correlated with Tfh cells, CD3+ T cells, CD4+ T cells, and CD8+ T cells, whereas negatively correlated with erythrocyte sedimentation rate (ESR), interleukin (IL)-6, and IL-10 levels. Furthermore, the abnormal circulating Tph cells in peripheral blood were recovered after glucocorticoid treatment. These results indicate that Tph cells might be involved in the immunopathogenesis of DM and therefore might provide novel insight for the development of DM therapies.

The altered metabolism profile in pathogenesis of idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are a group of heterogeneous autoimmune diseases characterized by muscle weakness, muscle inflammation and extramuscular manifestations. Despite extensive efforts, the mechanisms of IIMs remain largely unknown, and treatment is still a challenge for physicians. Metabolism changes have emerged as a crucial player in autoimmune diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA). However, little is known about metabolism changes in IIMs. In this review, we focus on the alteration of metabolism profile in IIMs, and the relationships with clinical information. We highlight the potential roles of metabolism in the pathogenesis of IIMs and discuss future perspectives for metabolic checkpoint-based therapeutic interventions.

Biologic therapy in the idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIM) are a group of autoimmune diseases resulting from inflammation of muscle and manifesting as weakness, though a range of extra-muscular manifestations are observed. These are often correlated closely with disease subtype and the presence of myositis-specific/myositis-associated antibodies. IIM are notoriously difficult to treat and often refractory to glucocorticoid therapy and synthetic immunosuppressants. Both the innate and adaptive immune systems are implicated in the pathogenesis of IIM. A growing understanding of the key cytokines as well as the cell-mediated and antibody effectors of disease has identified multiple potential targets for biologic therapy. The most widely used of these is B-cell depletion via rituximab though the tumour necrosis factor inhibitors and other biologic therapies used in diseases such as rheumatoid arthritis, systemic lupus erythematosus and multiple sclerosis have also been trialled. This review summarises the literature thus far on biologic therapy in IIM, highlighting both the significant trials that influence current treatment regimens and also the continuing need for further research to inform more effective therapies.

Drug-induced paraspinal myositis mimicking acute bilateral sciatica

Although cocaine induced myopathy and myotoxicity are described in the literature, we report a rare case of cocaine induced paraspinal myositis presenting with acute sciatic symptoms. A 35-year-old man presented with acute left-sided sciatica and was discharged from the emergency department (ED). He subsequently attended ED the following day in severe pain and bilateral sciatic symptoms, but denied symptoms of neurogenic bowel/bladder disturbance. Clinical examination was limited by severe pain: focal midline lumbar tenderness was elicited on palpation, per rectal and limb examinations were within normal limits with no significant neurological deficit. He was admitted for observation and pain management. His blood tests revealed a leucocyte count of 21.5×10⁹/L, C reactive protein of 89 mg/L and deranged renal function with creatinine of 293 μmol/L. An urgent lumbar spine MRI was arranged to rule out a discitis or epidural abscess. Lumbar MRI did not demonstrate any features of discitis but non-specific appearances of paraspinal inflammation raised the suspicion of a paraspinal myositis. Creatinekinase (CK) was found to be 66329 IU/L and a detailed history revealed he was a cocaine user. Paraspinal muscle biopsy confirmed histological features compatible with myositis. Other serological tests were negative, including anti-GBM, ANCA, ANA, Rheumatoid factor, Hep B, Hep C, myositis specific ENA, Treponema pallidum, Borrelia burgdorferi, Rickettsia, Leptospira, EBV and CMV. There was good clinical response to treatment with prednisolone 20 mg OD with an improvement in renal function, CK levels and CRP. He had resumed normal activities and return to work at 6-week follow-up. A detailed social history including substance misuse is important in patients presenting to the ED-especially in cases of severe musculoskeletal pain with no obvious localising features. Drug induced myotoxicity, although rare, can result in symptomatic patients with severe renal failure.

Aminoquinoline antimalarial therapy in dermatomyositis-are we missing opportunities with respect to comorbidities and modulation of extracutaneous disease activity?

It is now widely accepted that long-term aminoquinoline antimalarial therapy with hydroxychloroquine (HCQ) can mitigate one of the most important comorbidities of systemic lupus erythematosus (LE)-atherosclerotic cardiovascular disease (ASCVD). Increasing evidence suggests that idiopathic inflammatory myopathy (IIM) patients have a risk for ASCVD comorbidity that is similar to that of systemic LE. I would like to explore the primary hypothesis that long-term HCQ therapy could provide those with IIM, especially dermatomyositis (DM) patients, an ASCVD comorbidity benefit similar to that of systemic LE. In addition, while HCQ is known to have clinical benefits for the cutaneous manifestations of DM, I would also like to explore the secondary hypothesis that HCQ might have steroid-sparing effects on one or more of the systemic manifestations of DM.

The Immune Response and the Pathogenesis of Idiopathic Inflammatory Myositis: a Critical Review

The pathogenesis of idiopathic inflammatory myositis (IIMs, including polymyositis and dermatomyositis) remains largely enigmatic, despite advances in the study of the role played by innate immunity, adaptive immunity, genetic predisposition, and environmental factors in an orchestrated response. Several factors are involved in the inflammatory state that characterizes the different forms of IIMs which share features and mechanisms but are clearly different with respect to the involved sites and characteristics of the inflammation. Cellular and non-cellular mechanisms of both the immune and non-immune systems have been identified as key regulators of inflammation in polymyositis/dermatomyositis, particularly at different stages of disease, leading to the fibrotic state that characterizes the end stage. Among these, a special role is played by an interferon signature and complement cascade with different mechanisms in polymyositis and dermatomyositis; these differences can be identified also histologically in muscle biopsies. Numerous cellular components of the adaptive and innate immune response are present in the site of tissue inflammation, and the complexity of idiopathic inflammatory myositis is further supported by the involvement of non-immune mechanisms such as hypoxia and autophagy. The aim of this comprehensive review is to describe the major pathogenic mechanisms involved in the onset of idiopathic inflammatory myositis and to report on the major working hypothesis with therapeutic implications.

Dysregulated innate immune function in the aetiopathogenesis of idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIMs) are a heterogeneous group of systemic muscle conditions that are believed to be autoimmune in nature. They have distinct pathological features, but the aetiopathogenesis of each subtype remains largely unknown. Recently, there has been increased interest in the complex role the innate immune system plays in initiating and perpetuating these conditions, and how this may differ between subtypes. This article summarises the traditional paradigms of IIM pathogenesis and reviews the accumulating evidence for disturbances in innate immune processes in these rare, but debilitating chronic conditions.

Inflammatory myopathies and lymphoma

The inflammatory myopathies comprise a group of immune-mediated muscle diseases. Lymphoma is a term for a variety of lymphatic system malignancies. Autoimmune diseases and lymphoproliferative malignancies share a complex bidirectional relationship. A causal relationship between inflammatory mypathies and lymphoma has not been established. The diagnosis/treatment of inflammatory myopathy usually precedes the detection/diagnosis of lymphoma. Immune system dysregulation presumably underlies the evolution of lymphoma in patients with inflammatory myopathies. Inflammatory activity with chronic B-cell activation and/or antigen stimulation is deemed the major risk factor for lymphoma in patients with autoimmunity. A "paraneoplastic" phenomenon or the effects of immunosuppressive therapy may be alternative immune-based mechanisms. In chronic lymphocytic leukemia immune system disturbance rarely results in non-hematological autoimmune disease, including inflammatory myopathies.

Comparative Assessment of Female Mouse Model of Graves' Orbitopathy Under Different Environments, Accompanied by Proinflammatory Cytokine and T-Cell Responses to Thyrotropin Hormone Receptor Antigen

We recently described a preclinical model of Graves' orbitopathy (GO), induced by genetic immunization of eukaryotic expression plasmid encoding human TSH receptor (TSHR) A-subunit by muscle electroporation in female BALB/c mice. The onset of orbital pathology is characterized by muscle inflammation, adipogenesis, and fibrosis. Animal models of autoimmunity are influenced by their environmental exposures. This follow-up study was undertaken to investigate the development of experimental GO in 2 different locations, run in parallel under comparable housing conditions. Functional antibodies to TSHR were induced in TSHR A-subunit plasmid-immunized animals, and antibodies to IGF-1 receptor α-subunit were also present, whereas control animals were negative in both locations. Splenic T cells from TSHR A-subunit primed animals undergoing GO in both locations showed proliferative responses to purified TSHR antigen and secreted interferon-γ, IL-10, IL-6, and TNF-α cytokines. Histopathological evaluation showed orbital tissue damage in mice undergoing GO, manifest by adipogenesis, fibrosis, and muscle damage with classic signs of myopathy. Although no inflammatory infiltrate was observed in orbital tissue in either location, the appearances were consistent with a "hit-and-run" immune-mediated inflammatory event. A statistically significant increase of cumulative incidence of orbital pathology when compared with control animals was shown for both locations, confirming onset of orbital dysimmune myopathy. Our findings confirm expansion of the model in different environments, accompanied with increased prevalence of T cell-derived proinflammatory cytokines, with relevance for pathogenesis. Wider availability of the model makes it suitable for mechanistic studies into pathogenesis and undertaking of novel therapeutic approaches.

Intravenous Immune Globulin in Amyopathic Dermatomyositis - Report of Two Cases and Review of the Literature

Amyopathic dermatomyositis (ADM) is a rare subtype of dermatomyositis which is often recalcitrant to immune suppressing treatments. Intravenous immunoglobulin (IVIG) has been used in the treatment of refractory dermatomyositis. We present two patients with severe ADM, who were treated with IVIG at 2 g/kg every four weeks. Both patients had a successful response and were able to taper the dosage of prednisone. We present both cases in describing IVIG as a rescue and maintenance steroid-sparing agent in the treatment of severe refractory ADM. We also review the treatment of refractory ADM with IVIg in the English literature.

Clinico pathological study of adult dermatomyositis: Importance of muscle histology in the diagnosis

AIMS

To study the histological features on muscle biopsy and correlate them with clinical features, other laboratory data in adult patients to make a diagnosis of dermatomyositis (DM), applying the European Neuromuscular center (ENMC) criteria.

MATERIALS AND METHODS

Adult patients who fulfilled clinical, laboratory, and muscle biopsy findings according to ENMC criteria for DM during the period 2010-2013 were included in the study. Cryostat sections of muscle biopsy were reviewed with emphasis on Perifascicular atrophy (PFA), perivascular/endomysial inflammation. Muscular dystrophies and metabolic myopathies were excluded by appropriate immunohistochemistry and special stains.

RESULTS

The diagnosis of adult DM was made in 45 patients out of 170 clinically suspected idiopathic inflammatory myopathies. These included 33 definite, 4 probable, 7 possible sine dermatitis, and 1 amyopathic DM. All patients with definite DM had typical rash and proximal muscle weakness and muscle biopsy showed PFA with or without inflammation. Thirteen patients had quadriparesis, neck muscle weakness, dysphagia/dysphonia at presentation. Patients with probable DM had rash and showed perivascular/endomysial inflammation with no PFA. Possible DM sine dermatitis showed PFA with perivascular/endomysial infiltrates. One patient of amyopathic DM had typical heliotrope rash and characteristic skin biopsy.

CONCLUSIONS

Histological features are important for the diagnosis of DM. Relying on PFA for diagnosis of definite DM underestimates the true frequency of DM.

Innate immune-response mechanisms in dermatomyositis: an update on pathogenesis, diagnosis and treatment

Dermatomyositis (DM) is an autoimmune disease mainly affecting muscle and skin. Typical clinical and laboratory findings include muscle weakness with elevated muscle enzymes, characteristic skin lesions (e.g., Gottron papules, heliotrope erythema, Shawl sign), and specific serum autoantibodies. Recent studies have highlighted the activation of the innate immune system, including high expression of interferons (IFNs) and IFN-regulated proteins, as an important pathological hallmark of DM. These findings have changed our understanding of the disease fundamentally, since inappropriate activation of the innate immune system with secondary dysregulation of the adaptive immune response is now considered to be a central pathogenetic feature of DM. In this article, we review current guidelines and standards in diagnosis and treatment. We detail evidence-based and pathophysiology-based treatment strategies, with a focus on skin as well as on muscle lesions. Particularly, we discuss how the recent advances in the understanding of the pathomechanisms of DM have altered our conception of the mode of action of established drugs such as chloroquine and methotrexate. Finally, we outline possible future treatment strategies, with a focus on the innate immune system, e.g., targeting the IFN system with the anti-IFN-α antibody sifalimumab.

Myofiber HLA-DR expression is a distinctive biomarker for antisynthetase-associated myopathy

Objectives

To assess the value of major histocompatibility complex (MHC) class II antigen (HLA-DR) expression to distinguish anti-synthetase myopathy (ASM) from dermatomyositis (DM).

Methods

Muscle biopsies from patients with ASM (n = 33), DM without anti-synthetase antibodies (ASAb) (n = 17), and normal muscle biopsy (n = 10) were first reviewed. ASAb included anti-Jo1 (26/33), anti-PL12 (4/33), anti-PL7 (2/33), and anti-EJ (1/33). Immunohistochemistry was performed for MHC-I/HLA-ABC, MHC-II/HLA-DR, membrane attack complex (C5b-9), neural cell adhesion molecule (NCAM)/CD56 expression, and inflammatory cell subsets. Twenty-four ASM and 12 DM patients from another center were added for HLA-DR evaluation.

Results

Ubiquitous myofiber HLA-ABC expression was equally observed in ASM and DM (93.9% vs 100%, NS). In contrast, myofiber HLA-DR expression was found in 27/33 (81.8%) ASM (anti-Jo1: 23/26, 88.5%; others: 5/7, 71.4%) vs 4/17 (23.5%) DM patients (p < 0.001). HLA-DR was perifascicular in ASM, a pattern not observed in DM. In addition, C5b-9 deposition was observed on sarcolemma of non-necrotic perifascicular fibers in ASM, while, in DM, C5b-9was mainly detected in endomysial capillaries. CD8 cells were more abundant in ASM than in DM (p < 0.05), and electively located in perimysium or in perifascular endomysium. HLA-DR expression correlated positively with the CD8+ cells infiltrates. Strictly similar observations were made in the confirmatory study.

Conclusion

ASM is characterized by strong myofiber MHC-II/HLA-DR expression with a unique perifascicular pattern, not described so far. HLA-DR detection must be included for routine myopathological diagnosis of inflammatory/dysimmune myopathies. HLA-DR expression in ASM may indicate a specific immune mechanism, possibly involving IFNγ.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0154-2) contains supplementary material, which is available to authorized users.

Inflammatory myopathies: One-center experience

OBJECTIVE

Our aim was to report our experience with inflammatory myositis.

MATERIAL AND METHODS

In total, 60 patients were evaluated retrospectively, and 43 of them (71.7%) were female. The median age was 45 (17-81). Of all patients, 33 (55%) were diagnosed as polymyositis, 22 (36.6%) as dermatomyositis (classical, amyopathic, and malignancy-associated), and 5 (8.33%) as undifferentiated myositis. The 3 patients with malignancy-associated dermatomyositis had lung cancer, nasopharyngeal carcinoma, and endometrial cancer. Two patients with polymyositis had a history of low-grade gastric mixed tumor and thymoma but were diagnosed 7 and 12 years ago, and no recurrences have been reported during the routine controls.

RESULTS

All patients, other than two with malignancy-associated dermatomyositis, were treated via immunosuppressive agent, and the third patient with lung cancer was diagnosed later and gave up immunosuppressive therapy. Thirty-nine (65%) of the patients were treated via oral low-dose steroid, and 19 (31.7%) were treated via intravenous high-dose pulse steroid therapy. All patients were treated with steroid, which was tapered by time, and 23 (38.3%) were treated with azathioprine, 6 (10%) were treated with cyclophosphamide, 3 (5%) were treated with methotrexate, and 6 (10%) were treated with isolated steroid therapy at the time of diagnosis. The median follow-up period was 37 (2-135) months. Six patients (10%) have died-3 due to myocardial infarction, 1 due to septic shock, 1 due to malignancy, and 1 with an unknown reason. The 5-year survival rate was 76.9%, and the 10-year survival rate was 40%.

CONCLUSION

Other than the high ratio of PM in our series, all other results were compatible with the literature. We faced few resistant diseases; therefore, biologic agents were used rarely.

Meta-analysis of the association of dermatomyositis and polymyositis with cancer

BACKGROUND

Although some features of dermatomyositis (DM) and polymyositis (PM) have been reported as possible prognostic indicators for cancer development, previous studies were small in size and were unable to establish a definitive relationship between neoplasms and DM and PM.

OBJECTIVES

To evaluate risk factors for developing malignancies in patients with DM and PM.

METHODS

Meta-analysis of the studies reported in the literature was performed to unveil risk factors for developing cancer among patients with DM and PM. The included studies were either cohort or retrospective case-control studies with information on cancer status. Risk for malignancy was determined as the odds ratio (OR) or weighted mean difference (WMD) with a 95% confidence interval (CI), determined by fixed and random effects models. Stata 10.0 software was used to identify possible publication bias.

RESULTS

Twenty studies with 380 patients and 1575 controls were included in the analysis. The factors that may increase the risk of cancer in patients with DM and PM were older age (WMD 11·41, 95% CI 9·84-12·98), male sex (OR 1·92, 95% CI 1·49-2·48), cutaneous necrosis (OR 5·52, 95% CI 3·49-8·74) and dysphagia (OR 2·41, 95% CI 1·50-3·86), whereas those that may provide protection against cancer included arthritis (OR 0·38, 95% CI 0·24-0·61) and interstitial lung disease (OR 0·32, 95% CI 0·20-0·51).

CONCLUSIONS

Our data suggest that age, sex, cutaneous necrosis, dysphagia, arthritis and lung complications may influence susceptibility to cancer in patients with DM and PM.

A new paradigm: innate immune sensing of viruses via the unfolded protein response

The immune system depends upon combinations of signals to mount appropriate responses: pathogen specific signals in the context of co-stimulatory “danger” signals drive immune strength and accuracy. Viral infections trigger anti-viral type I interferon (IFN) responses by stimulating endosomal and cytosolic pattern recognition receptors (PRRs). However, viruses have also evolved many strategies to counteract IFN responses. Are there intracellular danger signals that enhance immune responses to viruses? During infection, viruses place a heavy demand on the protein folding machinery of the host endoplasmic reticulum (ER). To survive ER stress, host cells mount an unfolded protein response (UPR) to decrease ER protein load and enhance protein-folding capacity. Viruses also directly elicit the UPR to enhance their replication. Increasing evidence supports an intersection between the host UPR and inflammation, in particular the production of pro-inflammatory cytokines and type I IFN. The UPR directly activates pro-inflammatory cytokine transcription factors and dramatically enhances cytokine production in response to viral PRR engagement. Additionally, viral PRR engagement may stimulate specific pathways within the UPR to enhance cytokine production. Through these mechanisms, viral detection via the UPR and inflammatory cytokine production are intertwined. Consequently, the UPR response is perfectly poised to act as an infection-triggered “danger” signal. The UPR may serve as an internal “co-stimulatory” signal that (1) provides specificity and (2) critically augments responses to overcome viral subterfuge. Further work is needed to test this hypothesis during viral infections.

Diagnosis and treatment of the idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIMs) are rare disorders with the unifying feature of proximal muscle weakness. These diseases include polymyositis(PM), dermatomyositis (DM) and inclusion body myositis (IBM) as the most common. The diagnosis is based on the finding of weakness on exam, elevated muscles enzymes, characteristic histopathology of muscle biopsies, electromyography abnormalities and rash in DM. Myositis-specific antibodies have been helpful in defining subsets of patients with different responses to treatment and prognosis. The cornerstone of therapy is corticosteroids with the addition of other immunosuppressives in severe or refractory disease or patients with intolerable side effects. IBM is particularly difficult to treat but is more slowly progressive as compared with PM or DM. There is still a great need to find more effective and less-toxic therapies.

Diagnosis and treatment of inflammatory myopathy: issues and management

The idiopathic inflammatory myopathies include polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM). The specific etiologies of these muscle diseases are not well known and are thought to involve components of the humoral and cellular immune system as well as other nonimmune factors. Diagnosing these myopathies involves a laboratory evaluation, imaging studies, multidisciplinary consultations, histologic examination and potentially genetic studies. Despite all that we currently know about inflammatory muscle disease with these studies, we find that our current concept of muscle disease is changing. In the cases of immune-mediated necrotizing myopathy and inclusion body myositis, the concept of inflammation needs to be rethought. Moreover, the classification schemes for these idiopathic myopathies may need updating to include current research findings that relate to pathogenesis. With ongoing discoveries, classification and appropriate treatment is becoming increasingly challenging. This paper discusses the inflammatory myopathies, the challenges to diagnosis, classification controversies and potential treatment options.

Complement in the immunopathogenesis of rheumatic disease

The complement system has vital protective functions as a humoral component of the innate immune system and also through interactions with the adaptive immune system; however, when inappropriately activated or regulated, complement can cause inflammation and organ damage, and such processes are involved in the pathogenesis of many inflammatory conditions, not least rheumatic diseases. Furthermore, states of complement deficiency can predispose not only to infections, but also to autoimmune disorders, including rheumatic diseases such as systemic lupus erythematosus. In this Review, the mechanisms behind the pathogenic activities of complement in rheumatic diseases are discussed. Potential approaches to therapeutic intervention that focus on regulating complement activities in these disorders are also considered.

Acquired immune and inflammatory myopathies: pathologic classification

PURPOSE OF REVIEW

We discuss pathology-based characterization and classification of acquired immune and inflammatory myopathies (IIMs).

RECENT FINDINGS

Several types of IIMs do not fit well into the typical IIM subclassifications: dermatomyositis, polymyositis and inclusion body myositis (IBM). Myopathologic features that can provide additional diagnostic clarification in IIM are types of muscle fiber pathology; immune changes (cellular and humoral); and tissues with distinctive involvement (connective tissue, vessels and muscle fibers). Pathologic classification categories include immune myopathies with perimysial pathology (IMPP), a group that can be associated with antisynthetase antibodies; myovasculopathies, including childhood dermatomyositis; immune polymyopathies, active myopathies with little inflammation such as the myopathy with signal recognition particle antibodies; immune myopathies with endomysial pathology (IM-EP), illustrated by brachio-cervical inflammatory myopathy (BCIM); histiocytic inflammatory myopathies, like sarcoid myopathy; and inflammatory myopathies with vacuoles, aggregates and mitochondrial pathology (IM-VAMP), which have inclusion body myositis as a pathologic subtype and are poorly treatable. Some myopathologic features, like B-cell foci and alkaline phosphatase staining of capillaries or perimysium, are more likely to be present in treatable categories of IIM.

SUMMARY

Myopathology can be used to classify IIM. Identification of distinctive myopathologic changes in IIM can improve diagnostic and prognostic accuracy and focus treatment, therapeutic trials and studies of pathogenic factors.

The role of angiopoietin-like protein 2 in pathogenesis of dermatomyositis

Dermatomyositis (DM) is an autoimmune disease marked by chronic inflammation of skin and muscle tissues and characterized clinically by proximal muscle weakness and skin eruption, including heliotrope rash, and Gottron's sign. Treatment with a non-specific immunosuppressive agent or anti-inflammatory corticosteroids is beneficial, although some patients are resistant to these therapies. Proinflammatory cytokines derived from infiltrating inflammatory cells and activated resident cells within skin and muscle tissues likely promote chronic inflammation in DM pathogenesis; however, molecular mechanisms underlying the disease are not completely defined. Here we show that mRNA and protein levels of angiopoietin-like protein 2 (Angptl2), a recently identified chronic inflammation mediator, are abundant in keratinocytes from DM patients' skin eruptions. To examine whether skin cell-derived Angptl2 promotes DM manifestations, we analyzed transgenic (Tg) mice expressing Angptl2 driven by the keratinocyte specific promoter K14 (K14-Angptl2) and therefore constitutively expressing Angptl2 in skin tissue. We found that K14-Angptl2 Tg mice exhibited skin phenotypes similar to those observed in DM patients. In addition, treatment of keratinocytes with exogenous Angptl2 activated the NF-κB inflammatory cascade, resulting in increased expression of the proinflammatory cytokines IL-1β and IL-6. We propose that keratinocyte-derived Angptl2 functions in DM pathogenesis by inducing chronic inflammation in skin tissue.