Muscular and extramuscular features of myositis patients with anti-U1-RNP autoantibodies

Myositis-Associated Autoantibodies in Patients With Juvenile Myositis Are Associated With Refractory Disease and Mortality

OBJECTIVE

Myositis-associated autoantibodies (MAAs) have been associated with overlap myositis, certain disease manifestations such as interstitial lung disease (ILD), and worse prognosis in the idiopathic inflammatory myopathies. MAAs overall remain largely uncharacterized in patients with juvenile-onset myositis. Moreover, it is unknown whether the number of MAAs is associated with disease severity.

METHODS

Patients with juvenile myositis in cross-sectional natural history studies who underwent testing for myositis autoantibodies were included. Demographics, myositis autoantibodies, clinical characteristics, medications received, and outcomes of those with and without MAAs were compared. Multivariable logistic regression was performed to determine whether the number of MAAs detected was associated with severe disease features.

RESULTS

Among 551 patients, 36% had an MAA and 13% had more than one MAA. Among those who were MAA positive, there was a higher frequency of overlap myositis (18% vs 5.9%, P < 0.001). MAA positivity was associated with certain clinical features, including Raynaud phenomenon (odds ratio [OR] 2.44, 95% confidence interval [CI] 1.41-4.28) and ILD (OR 3.43, 95% CI 1.75-6.96), as well as a chronic disease course (OR 1.72, 95% CI 1.10-2.72) and mortality (OR 3.76, 95% CI 1.72-8.43). The number of MAAs was also associated with mortality (OR 1.83, 95% CI 1.16-2.86).

CONCLUSION

MAAs were prevalent in a large cohort of patients with juvenile myositis. ILD, refractory disease, and mortality were associated with MAA positivity. Prospective studies are needed to determine whether early detection of MAAs may lead to improved outcomes for patients with juvenile myositis.

Autoantibody evaluation in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIM), generally referred to as myositis is a heterogeneous group of diseases characterized by muscle inflammation and/or skin involvement, diverse extramuscular manifestations with variable risk for malignancy and response to treatment. Contemporary clinico-serologic categorization identifies 5 main clinical groups which can be further stratified based on age, specific clinical manifestations and/or risk for cancer. The serological biomarkers for this classification are generally known as myositis-specific (MSAs) and myositis-associated antibodies. Based on the use of these antibodies, IIM patients are classified into anti-synthetase syndrome, dermatomyositis, immune-mediated necrotizing myopathy, inclusion body myositis, and overlap myositis. The current classification criteria for IIM requires clinical findings, laboratory measurements, and histological findings of the muscles. However, the use MSAs and myositis-associated autoantibodies as an adjunct for disease evaluation is thought to provide a cost-effective personalized approach that may not only guide diagnosis but aid in stratification and/or prognosis of patients. This review provides a comprehensive overview of contemporary autoantibodies that are specific or associated myositis. In addition, it highlights possible pathways for the detection and interpretation of these antibodies with limitations for routine clinical use.

Ro52/TRIM21 - From host defense to autoimmunity

Ro52 (TRIM21) belongs to the ubiquitin ligase family. This protein plays a crucial role in many immunological processes, including antibody-dependent intracellular neutralization, synergy with the complement system, antiviral response, death mediation, oxidative stress response, and protein ubiquitination. Abnormal expression of TRIM21 can break immunological tolerance and lead to the production of autoantibodies against TRIM21. Antibodies against TRIM21 are detected in various autoimmune diseases, including Sjögren's syndrome (SS), systemic lupus erythematosus (SLE), or myositis. However, anti-TRIM21 presence is not limited to autoimmune connective tissue disorders. It was observed in patients with malignancies, various cancerous processes, infectious diseases, and idiopathic interstitial pneumonia. The occurrence of TRIM21 autoantibodies is also associated with clinical features, such as the prevalence of interstitial lung diseases and cardiac or haematological involvement in connective tissue disorders. The purpose of this review was to summarize current knowledge of the immunological functions of TRIM21 and analyze the clinical implications of anti-TRIM21 antibodies in the disease course.

Joint and muscle inflammatory disease: A scoping review of the published evidence

OBJECTIVES

Polyarthritis is commonly reported in idiopathic inflammatory myositis patients, but few studies have focused on the overlap of myositis with rheumatoid arthritis which is a difficult diagnosis in the absence of well-defined diagnostic criteria. The primary objective of this scoping review was to map the field of research to explore the potential diagnoses in patients presenting with both myositis and polyarthritis.

METHODS

Two electronic databases (MEDLINE/PubMed® and Web of Science®) were systematically searched using the terms (myositis OR 'inflammatory idiopathic myopathies') AND (polyarthritis OR 'rheumatoid arthritis') without any publication date limit.

RESULTS

Among individual records, 280 reports met inclusion criteria after full-text review. There was heterogeneity in the definition of overlap myositis as well as the characteristics of rheumatoid arthritis. In many studies, key data were lacking; rheumatoid factor status was reported in 56.8% (n=151), anti-citrullinated proteins antibodies status in 18.8% (n=50), and presence or absence of bone erosions in 45.1% (n=120) of the studies. Thirteen different diagnoses were found to associate myositis with polyarthritis: antisynthetase syndrome (29.6%, n=83), overlap myositis with rheumatoid arthritis (16.1%, n=45), drug-induced myositis (20.0%, n=56), rheumatoid myositis (7.5%, n=21), inclusion body myositis (1.8%, n=5), overlap with connective tissue disease (20.0%, n=56), and others (5.0%, n=14).

CONCLUSION

The spectrum of joint and muscle inflammatory diseases encompasses many diagnoses including primitive and secondary myositis associated with RA or arthritis mimicking RA. This review highlights the need for a consensual definition of OM with RA to better individualise this entity from the numerous differential diagnoses.

Clinical characteristics of myositis patients with isolated anti-U1 ribonucleoprotein antibody resemble immune-mediated necrotizing myopathy

Background

Anti-U1 ribonucleoprotein (U1RNP) antibodies were associated with connective tissue diseases (CTDs), but the clinical characteristics of this antibody in Chinese myositis patients have not been studied.

Objective

We aim to analyze the clinical features of myositis patients who test positive for anti-U1RNP antibodies and delineate a subgroup of myositis.

Design

This is a retrospective cohort study.

Methods

We reviewed the clinical data of myositis patients with anti-U1RNP antibodies and compared them to those with anti-signal recognition particle (SRP) and hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibody-associated immune-mediated necrotizing myopathy (IMNM).

Results

A total of 30 adult cases were identified; median age was 47.5 years and 24 (80%) were females, and 12 patients did not coexist with myositis-specific antibodies (MSAs) (isolated anti-U1RNP). The serum creatine kinase (CK) was significantly higher in patients with isolated anti-U1RNP (2182.5 U/L versus 289 U/L, p = 0.01), and the number of patients with CK > 2000 U/L was higher compared to that in anti-U1RNP antibody patients coexisting with MSAs (66.7% versus 16.7%, p = 0.009). The prevalence of IMNM in patients' muscle pathology with isolated anti-U1RNP was significantly higher (75%, p = 0.003). Skin rashes were less common in isolated anti-U1RNP group (p < 0.05). Of the 25 individuals with available pulmonary high-resolution CT (HRCT), 14 (56%) were diagnosed with interstitial lung disease (ILD). The incidence of muscular weakness, dysphagia, or levels of CK was not different between the isolated anti-U1RNP antibody individuals and the anti-HMGCR or SRP-IMNM groups (p > 0.05). But the frequency of Raynaud's phenomenon, arthritis, and membrane attack complex (MAC) deposits in myositis patients with isolated anti-U1RNP antibodies were higher than in anti-HMGCR and SRP-IMNM (all p < 0.005). There was no difference between anti-U1RNP patients with and without Ro-52 (p > 0.05). Isolated anti-U1RNP individuals showed marked improvements in muscle strength, and the remission rate in 1 and 2 years was significantly higher than that in anti-HMGCR and SRP-IMNM (p < 0.05).

Conclusions

The clinical and pathological features of myositis patients with isolated anti-U1RNP antibodies were similar to IMNM. Arthritis and ILD are the most common extramuscular clinical features. Most respond well to treatment and have a good prognosis.

Clinical and serological correlation of systemic sclerosis in Moroccan patients

Objective

SSc is a CTD characterized by excessive fibrosis of the skin and internal organs, along with microvascular damage, and is often associated with typical autoantibodies. The aim of this study was to analyse the correlation between specific autoantibody profiles, clinical and paraclinical features in Moroccan patients with SSc.

Methods

We analysed the presence of specific autoantibodies in 46 SSc patients using IIF on HEp-2 cells and immunodot. We then correlated the types of autoantibodies with clinical and laboratory manifestations.

Results

Among our patients, 86.9% were females. The mean age of patients at diagnosis was 50.21 years, with an average delay to diagnosis of 5 years. The main clinical manifestations found were RP (89.2%), sclerodactyly (84.8%), proximal scleroderma (67.4%), gastrointestinal involvement (50%) and interstitial lung disease (30.4%). According to the specific autoantibody profile, 14 patients were anti-topo I positive (30.4%), 8 anti-RNP (68 kDa/A/C) positive (17.4%) and 6 anti-RNA polymerase III positive (13%). We found a significant association of anti-RNA polymerase III with sclerodactyly and pulmonary arterial hypertension (P < 0.05). We also found an association between anti-topo I and interstitial lung disease in 30.4% of patients. There was no significant association between the positivity for the autoantibodies and other diagnosed clinical manifestations.

Conclusion

Some clinical manifestations of SSc might be positively correlated with the presence of specific autoantibodies. Environmental factors, ethnicity and gene interaction might also influence this correlation.

Marked Efficacy of a Therapeutic Strategy in a Patient With Necrotizing Myopathy Associated With Anti-signal Recognition Particle (SRP) Autoantibodies

Necrotizing autoimmune myopathy (NAM) is a rare muscular disorder characterized by severe proximal muscle weakness. Risk factors include statin use, malignancy, and connective tissue diseases. The current study presents the first case of NAM in Saudi Arabia in a 26-year-old female who presented with proximal upper and lower limb weakness, dysphagia, dysarthria, and dyspnea with no previous medical or surgical history and was not on medication. Targeted myopathic antibody analysis revealed antibodies to signal recognition particles (SRP), and the serum creatinine kinase level reached 9308 U/L. A diagnosis of NAM was made, and the patient was started on the management plan. We discussed an interesting case progression and adverse effect challenges, as well as the management of these difficult-to-treat conditions.

Myositis autoantibodies detected by line blot immunoassay: clinical associations and correlation with antibody signal intensity

The aim of this study is to assess the relationship between myositis specific (MSA) and myositis associated (MAA) antibodies and diagnosis (including idiopathic inflammatory myopathies [IIM] and other systemic autoimmune diseases [SAID]), and to explore the impact of antibody signal intensity in diagnostic accuracy. We retrospectively reviewed all the serum samples obtained from patients tested for MSA/MAA by line immunoassay (LIA) between 01/01/2018 and 31/12/2020 in Ramón y Cajal University Hospital (Spain). Clinical true positive (CTP) MSAs and MAAs were defined as those patients with IIM or SAID with phenotypes expected of that MSA/MAA. Patients who did not have a phenotype compatible with that antibody were classified as clinical false positive (CFP). One hundred and thirty positive samples were analysed. Forty-six patients (33.38%) were classified as IIM, forty-two (32.3%) as SAID and forty-two (32.3%) as non-IIM/SAID. Among these 130 patients, 164 MSA/MAA were detected. Eighty-five (51.8%) positive MSA/MAA were classified as CTP, and seventy-nine (48.2%) as CFP. Strongly positive antibodies were more frequently CTP (35/47, 74.5%) than weak positives (54/68, 36.8%), (p ˂ 0.001). Antibodies classified as CTP had a higher signal intensity than CFP (36.77 AU vs 20.00 AU, CI95% 7.79-22.09, p ˂ 0.001). The probability of a CFP was associated to negative ANA, low ANA titer, and multiple positive MSA/MAA (p ˂ 0.001). In this study, we confirmed that CFP results using LIA are frequent, and are associated with low signal intensity MSA/MAA, negative ANA, lower titer ANA, and with multiple positive samples.

Gastrointestinal Tract Considerations Part I

The upper gastrointestinal (GI) tract is frequently involved in systemic sclerosis (SSc) and may impact quality of life, physical function and survival. Although we are currently very proactive in terms of screening for heart and lung involvement, patients with SSc are not routinely screened for GI involvement. This review details the available investigations for common upper GI symptoms in SSc, including dysphagia, reflux and bloating and provides advice as to how to integrate these investigations into current clinical care.

Scleromyositis: A distinct novel entity within the systemic sclerosis and autoimmune myositis spectrum. Implications for care and pathogenesis

Systemic sclerosis and autoimmune myositis are both associated with decreased quality of life and increased mortality. Their prognosis and management largely depend on the disease subgroups. Indeed, systemic sclerosis is a heterogeneous disease, the two predominant forms of the disease being limited and diffuse scleroderma. Autoimmune myositis is also a heterogeneous group of myopathies that classically encompass necrotizing myopathy, antisynthetase syndrome, dermatomyositis and inclusion body myositis. Recent data revealed that an additional disease subset, denominated "scleromyositis", should be recognized within both the systemic sclerosis and the autoimmune myositis spectrum. We performed an in-depth review of the literature with the aim of better delineating scleromyositis. Our review highlights that this concept is supported by recent clinical, serological and histopathological findings that have important implications for patient management and understanding of the disease pathophysiology. As compared with other subsets of systemic sclerosis and autoimmune myositis, scleromyositis patients can present with a characteristic pattern of muscle involvement (i.e. distribution of muscle weakness) along with multisystemic involvement, and some of these extra-muscular complications are associated with poor prognosis. Several autoantibodies have been specifically associated with scleromyositis, but they are not currently integrated in diagnostic and classification criteria for systemic sclerosis and autoimmune myositis. Finally, striking vasculopathic lesions at muscle biopsy have been shown to be hallmarks of scleromyositis, providing a strong anatomopathological substratum for the concept of scleromyositis. These findings bring new insights into the pathogenesis of scleromyositis and help to diagnose this condition, in patients with subtle SSc features and/or no autoantibodies (i.e. "seronegative" scleromyositis). No guidelines are available for the management of these patients, but recent data are showing the way towards a new therapeutic approach dedicated to these patients.

The Role of Anti-U1 RNP Antibody in Connective Tissue Disease-Associated Pulmonary Arterial Hypertension: A Systematic Review and Meta-Analysis

Connective tissue disease (CTD) patients may suffer from pulmonary arterial hypertension (PAH), a serious complication, and anti-U1 ribonucleoprotein (RNP) antibodies can be used as a potential indicator for the development and prognosis of CTD-associated PAH (CTD-PAH). However, there are still some controversies; thus, a systematic review and meta-analysis were performed. We searched PubMed, Embase, Cochrane Library, and Scopus for eligible studies and assessed their quality using Newcastle−Ottawa scales or Agency for Healthcare Research and Quality indicators according to the type of research. Odds ratio (OR) was adopted as a measure of effect in risk factor analysis, and hazard ratio (HR) was adopted for prognostic factor analysis. Publication bias was evaluated using the Egger’s test. Thirteen studies were finally included. Anti-U1 RNP antibody was proved as a risk factor for PAH among CTD patients (OR = 5.30, 95%CI 2.96−9.48, p < 0.05) and a protective factor against mortality among CTD-PAH patients (HR = 0.55, 95%CI 0.36−0.83, p < 0.05). CTD patients with positive anti-U1 RNP antibodies are at high risk for PAH, so routine screening examinations, including echocardiography, are recommended. Additionally, anti-U1 RNP positivity has been linked to decreased mortality in patients with CTD-PAH.

Inflammatory Myopathies

PURPOSE OF REVIEW

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.

RECENT FINDINGS

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.

SUMMARY

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.

Nephrotic Syndrome as an Extramuscular Manifestation of Anti-EJ Antibody-Positive Dermatomyositis: A Case Report and Review of the Literature

Renal involvement is underestimated as an extramuscular manifestation of dermatomyositis (DM). Here, we describe a 67-year-old woman with anti-glycyl-transfer ribonucleic acid synthetase (anti-EJ) antibody and anti-ribonucleoprotein antibody-positive DM complicated by systemic sclerosis, who developed nephrotic syndrome concurrently with the exacerbation of DM, as indicated by incremental serum creatine kinase levels, high-intensity lesions on muscle magnetic resonance imaging, and active interstitial pneumonitis on chest computed tomography. Renal biopsy revealed the presence of immune-deposition in the glomerulus by immunofluorescence. To our knowledge, this is the first report describing the coexistence of anti-EJ antibody-positive DM and nephrotic syndrome. More reports of similar cases are warranted to substantiate the association.

Clinical and histopathological features of myositis in systemic lupus erythematosus

Objective

The objectives of this study were to compare the clinical features of patients with SLE with and without myopathy and to describe the muscle biopsy features of patients with SLE myopathy.

Methods

This nested case–control study included all subjects enrolled in the Hopkins Lupus Cohort database from May 1987 to June 2016. Subjects with elevated creatine kinase along with evidence of muscle oedema on MRI, myopathic electromyography and/or myopathic muscle biopsy features were defined as having SLE myopathy. Demographic, serological and clinical features were compared between patients with SLE with and without myopathy. Muscle biopsies were histologically classified as polymyositis, dermatomyositis, necrotising myopathy or non-specific myositis.

Results

From among 2437 patients with SLE, 179 (7.3%) had myopathy. African American patients were more likely to develop myositis than Caucasian patients (p<0.0001). Compared with those without myopathy, patients with SLE myopathy were more likely to have malar rash (OR 1.67, 1.22–2.29), photosensitivity (OR 1.43, 1.04–1.96), arthritis (OR 1.81, 1.21–2.69), pleurisy (OR 1.77, 1.3–2.42), pericarditis (OR 1.49, 1.06–2.08), acute confusional state (OR 2.07, 1.09–3.94), lymphopaenia (OR 1.64, 1.2–2.24), anti-double-stranded DNA antibodies (OR 1.52, 1.09–2.13), lupus anticoagulant (OR 1.42, 1–2), cognitive impairment (OR 1.87, 1.12–3.13), cataract (OR 1.5, 1.04–2.18), pulmonary hypertension (OR 1.98, 1.13–3.47), pleural fibrosis (OR 2.01, 1.27–3.18), premature gonadal failure (OR 1.9, 1.05–3.43), diabetes (OR 1.92, 1.22–3.02) or hypertension (OR 1.45, 1.06–2). Among 16 muscle biopsies available for review, the most common histological classifications were necrotising myositis (50%) and dermatomyositis (38%).

Conclusions

Patients with SLE myopathy have a higher prevalence of numerous SLE disease manifestations. Necrotising myopathy and dermatomyositis are the most prevalent histopathological features in SLE myopathy.

Therapeutic plasma exchange for the treatment of refractory necrotizing autoimmune myopathy

Introduction

Necrotizing autoimmune myopathy (NAM) is strongly associated with pathognomonic autoantibodies targeting 3‐hydroxy‐3‐methylglutaryl‐coenzyme A reductase (HMGCR) or signal recognition particle (SRP), whose levels in turn are correlated with serum creatine kinase (CK) and necrosis. Thus, NAM may be amenable to therapeutic plasma exchange (TPE) to remove pathogenic antibodies and improve patient symptoms.

Methods

A retrospective case series and literature review of patients presenting with NAM and undergoing treatment with TPE was performed. Clinical data including patient demographics, symptoms, physical exam findings, muscle biopsy, lower extremity imaging, prior therapy, and duration from diagnosis to TPE initiation were collected retrospectively for adult patients with NAM treated with TPE after failing to respond to immunomodulatory therapy. Laboratory data including change in CK levels and myositis‐specific antibody titers from baseline were measured in some patients.

Results

Six patients (median age at diagnosis 52.5 years, interquartile range [IQR] 35.8‐64.5 years, four male/two female) underwent a median of 7.5 (IQR: 5‐10) TPE procedures with 5% albumin as replacement. All patients exhibited a statistically significant reduction in CK level from pre‐TPE baseline (range: 43.0%‐58.7% reduction). Responses in this cohort were best in patients with antibodies targeting HMGCR and SRP, which are most strongly associated with NAM. These results compare favorably to a literature review of NAM patients (n = 19) treated with TPE, who also exhibited positive clinical and laboratory responses across varying treatment lengths.

Conclusion

TPE can play a role in the management of NAM, particularly in patients with HMGCR or SRP antibodies who are refractory to pharmacologic immunosuppression.

Disease criteria of systemic lupus erythematosus (SLE); the potential role of non-criteria autoantibodies

Patients with SLE show a broad spectrum of more than 200 autoantibodies. They can be pathogenic, predictive, prognostic or even an epiphenomenon. Here, we discuss different autoantibodies that have not been included in EULAR/ACR 2019 classification criteria. Most of them have been addressed to monitor and detect disease activity and not specifically as classification criteria. Indeed, markers to assess disease activity fluctuate as compared with classification criteria and their validation is different. The development of new methods will probably bring new clinical associations and be evaluated as potential classification criteria.

•

Most of the autoantibodies described in SLE are of utility in monitoring disease activity.

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The validation of activity biomarkers is different from classification criteria biomarkers.

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The new methods coming into the clinical routine will bring new associations and potentially classification criteria.

Immune-mediated necrotizing myopathy (IMNM): A myopathological challenge

This review is focused on the myopathological spectrum of immune mediated necrotizing myopathies (IMNMs) and its differentiation with other, potentially mimicking, inflammatory and non-inflammatory myopathies. IMNMs are a subgroup of idiopathic inflammatory myopathies (IIMs) characterized by severe clinical presentation with rapidly progressive muscular weakness and creatine kinase elevation, often requiring early aggressive immunotherapy, associated to the presence of muscle specific autoantibodies (MSA) against signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Muscle biopsy usually shows unspecific features consisting in prominent necrosis and regeneration of muscle fibres with mild or absent inflammatory infiltrates, inconstant and faint expression of major histocompatibility complex (MHC) class I and variable deposition of C5b-9 on sarcolemma. Several conditions could present similar histopathological findings leading to possible misdiagnosis of IMNM with other IIMs or non-inflammatory myopathies (nIMs) and viceversa. This review analyses the muscle biopsy data in IMNMs through a systematic revision of the literature from the last five decades. Several histopathological variables have been considered in both SRP- and HMGCR-IMNM, and compared to other IIMs - as dermatomyositis (DM) and anti-synthethase syndrome (ASS) - or other nIMs -as toxic myopathies (TM), critical illness myopathy (CIM) and muscular dystrophy (MD) - to elucidate similarities and differences among these potentially mimicking conditions. The major histopathological findings of IMNMs were: very frequent necrosis and regeneration of muscle fibres (93%), mild inflammatory component mainly constituted by scattered isolated (65%) CD68-prevalent (68%) cells, without CD8 invading/surrounding non-necrotic fibres, variable expression of MHC-I in non-necrotic fibres (56%) and constant expression of sarcoplasmic p62, confirming those that are widely considered the major histological characteristics of IMNMs. Conversely, only 42% of biopsies showed a sarcolemmal deposition of C5b-9 component. Few differences between SRP and HMGCR IMNMs consisted in more severe necrosis and regeneration in SRP than in HMGCR (p = 0.01); more frequent inflammatory infiltrates (p = 0.007) with perivascular localization (p = 0.01) and clustered expression of MHC-I (p = 0.007) in HMGCR; very low expression of sarcolemmal C5b-9 in SRP (18%) compared to HMGCR (56%) (p = 0.0001). Milder necrosis and regeneration, detection of perifascicular pathology, presence of lymphocytic inflammatory infiltrates and myofibre expression of MxA help to distinguish DM or ASS from IMNM. nIMs can present signs of inflammation at muscle biopsy. Low fibre size variability with overexpression of both MHC-I and II, associated with C5b-9 deposition, could could be observed in CIM, while increased connective tissue should lead to consider MD, or TM in absence of C5b-9 deposition. Nevertheless, these features are not constantly detected and muscle biopsy could not be diriment. For this reason, muscle biopsy should always be critically considered in light of the clinical context before concluding for a definite diagnosis of IMNM, only based on histopathological findings. More rigorous collection and analysis of muscle biopsy is warranted to obtain a higher quality and more homogeneous histopathological data in inflammatory myopathies.

Polymyositis: does it really exist as a distinct clinical subset?

PURPOSE OF REVIEW

To summarize information on polymyositis; diagnosis, definitions, published data and opinions.

RECENT FINDINGS

Polymyositis originally referred to inflammatory muscle diseases presenting with muscle weakness and inflammatory cell infiltrates on muscle tissue visible by microscopy. Over time and with improved technology to immunophenotype infiltrating inflammatory cells and characterize muscle fibres, the meaning of polymyositis changed and became more specific. There is ongoing controversy over the term polymyositis, with proponents for a strict definition based on histopathological and immunohistochemical features on muscle biopsies whereas others advocate for a broader clinical and histopathological phenotype. Over the past decades, the discovery of several myositis-specific autoantibodies together with distinct histopathological features have enabled the identification of new subsets previously labelled as polymyositis notably the antisynthetase syndrome and the immune-mediated necrotizing myopathies thus reducing the number of patients classified as polymyositis.

SUMMARY

There are still a small number of patients among the idiopathic inflammatory myopathies that can be classified as polymyositis as discussed in this review but the entity is now considered relatively rare.

Biomarker und Histologie bei idiopathischen inflammatorischen Myopathien

Die idiopathischen inflammatorischen Myopathien (IIM) sind eine Gruppe entzündlicher Muskelerkrankungen für deren Diagnosestellung, Verlaufsbeurteilung, Prognoseabschätzung und Risikostratifizierung Biomarker eine jeweils essentielle Rolle spielen. Biomarker in diesem Kontext können sowohl „herkömmliche“ serologische Marker wie Muskelenzyme oder Autoantikörper, histologische Marker wie entitätsspezifische inflammatorische Muster, aber auch genomische und genetische Marker sein. Der vorliegende Artikel gibt einen Überblick über bewährte und innovative Marker.

Polymyositis: is there anything left? A retrospective diagnostic review from a tertiary myositis centre

OBJECTIVE

The current classification criteria for idiopathic inflammatory myopathy (IIM) retain PM as a major disease subgroup. However, evolution in the understanding of IIM has suggested that many of these patients could be better described as having an alternative diagnosis. In the present study, we apply the latest understanding of IIM subtyping to retrospectively review PM diagnoses in a large cohort of IIM patients.

METHODS

Within a previously reported cohort of 255 patients from a UK tertiary myositis clinic, 37 patients classified as PM according to both the EULAR/ACR IIM criteria and expert opinion were identified. Clinical data and complementary tests were reviewed, and consensus decisions regarding final classification were reached in each case.

RESULTS

Nine (9/37, 24.3%) patients remained classified as PM, 3.5% (9/255) of the original cohort; these PM patients were seronegative for myositis antibodies, responsive to immunosuppression, and in 4/7 (57.1%) patients where muscle biopsy was performed had HLA-1 upregulation and endomysial inflammatory infiltrates. Immune-mediated necrotizing myopathy (5/37, 13.5%) and connective tissue disease overlap myositis (7/37, 19%) were the main alternative diagnoses. The remaining patients were diagnosed as: unspecified myopathy (6/37, 16%), dermatomyositis (2/37, 5%), cancer-associated myopathy (3/37, 8.1%), and non-inflammatory myopathy (1/37, 3%, myofibrillar myopathy). Four patients (4/37, 10%) had insufficient data available to confidently reclassify.

CONCLUSION

Our study confirms that PM can now be considered a rare IIM subgroup. A thorough examination, complete myositis autoantibody panel, and careful interpretation of the biopsy results is recommended to confirm the correct IIM sub-type.

Histopathological features of systemic sclerosis-associated myopathy: A scoping review

BACKGROUND

Scleromyositis (SM) is an emerging subset of myositis associated with features of systemic sclerosis (SSc) but it is currently not recognized as a distinct histopathological subset by the European NeuroMuscular Center (ENMC). Our aim was to review studies reporting muscle biopsies from SSc patients with myositis and to identify unique histopathological features of SM.

METHODS

A scoping review was conducted and included all studies reporting histopathological findings in SSc patients with myositis searching the following databases: PubMed, MEDLINE, EMBASE, CINAHL and EBM-Reviews. Clinical, serological, and histopathological data were extracted using a standardized protocol.

RESULTS

Out of 371 citations, 77 studies that included 559 muscle biopsies were extracted. Fifty-seven percent (n = 227/400) had inflammatory infiltrates, predominantly T cells, which were endomysial (49%), perimysial (42%) and perivascular (41%). Few studies (18%, n = 8/44) evaluated the presence of B-cells. Myofiber atrophy was present in 48% (n = 104/218) of biopsies, and was predominantly perifascicular in 19% (n = 6/31), with necrosis reported in 56% (n = 162/290) of cases. Sarcolemmal MHC-I upregulation was found in 72% (n = 64/89) of biopsies. Non-specified C5b-9 deposition was described in 39% of muscle biopsies (n = 28/72). Neurogenic features were present in 23% (n = 44/191); endomysial fibrosis was reported in 35% (n = 120/340); and rimmed vacuoles were observed in 32% (n = 11/34) of biopsies. Capillaropathy, such as capillary dropout and/or ultrastructural endothelial abnormalities, was reported in 33% (n = 43/129) of cases. Reported ENMC categories were mainly polymyositis (21%), non-specific myositis (19%), immune-mediated necrotizing myopathy (16%), and dermatomyositis (8%). Histopathological features were analyzed according to serological subtypes in 28 studies, including anti-PM-Scl (n = 48), -Ku (n = 23) and -U1RNP (n = 90). Most of these biopsies demonstrated inflammatory infiltrates (range 49-85%) as well as MHC-I expression (range 63-81%). Necrosis was associated with anti-Ku (85%) and anti-U1RNP (73%), while anti-Ku was also associated with neurogenic features and rimmed vacuoles in 57% and 25% of cases, respectively.

CONCLUSION

Our review suggests that SM is characterized by heterogeneous pathological features using definitions included in current histopathological criteria. Whether a distinct histopathological signature exists in SM remains to be determined. SSc-specific and SSc-associated autoantibodies may help define more homogeneous histopathological subsets.

The phenotype of myositis patients with anti-Ku autoantibodies

OBJECTIVES

To define the clinical features of anti-Ku-positive myositis patients and to determine the reliability of the Euroline assay to detect anti-Ku autoantibodies.

METHODS

Serum samples were screened for anti-Ku autoantibodies by Euroline and positive samples were confirmed by ELISA. The prevalence and severity of clinical features at onset and during follow-up in patients with anti-Ku-positive myositis were compared to those with dermatomyositis, immune-mediated necrotizing myopathy (IMNM), the antisynthetase syndrome (AS), inclusion body myositis (IBM), anti-U1-RNP-positive myositis, and anti-PM/Scl-positive myositis.

RESULTS

72 (2.9%) of 2475 samples were anti-Ku positive by Euroline using the manufacturer's recommended cutoff of >15. Just 17 (23.6%) of these were confirmed by ELISA and considered anti-Ku-positive for the analysis. Comparators included 169 IMNM, 168 AS, 387 IBM, 20 anti-U1-RNP-positive, and 47 anti-PM/Scl-positive patients. Muscle weakness was a presenting feature in 38% of anti-Ku-positive patients; 81% developed weakness during follow-up. Anti-Ku-positive patients had increased distal weakness compared to the non-IBM comparators. Interstitial lung disease (ILD) was present in 19% of anti-Ku-positive patients at the first visit and eventually developed in 56% of them. Throughout the course of disease, Gottron's papules and/or heliotrope rashes were less common in anti-Ku-positive patients (19%) compared to those with dermatomyositis (94%) or anti-PM/Scl-positive myositis (89%). Anti-Ku-positive patients never developed calcinosis.

CONCLUSIONS

The phenotype of anti-Ku positive myositis is distinguished by distal weakness, frequent ILD, infrequent rash, and no calcinosis. When used according to the current manufacturer's instructions, the Euroline assay has a high false-positive rate for anti-Ku autoantibodies.

[Myositis: From classification to diagnosis]

Idiopathic inflammatory myopathies, or IIM, are a group of acquired diseases that affect the muscle to a certain extent, and may also affect other organs. They include dermatomyositis, which can affect the muscle eventualy, with a typical skin rash; inclusion body myositis, with a purely muscular expression resulting in a slow progressive deficit; and the former group of "polymyositis", a misnomer that actually includes other categories of IIM, such as immune-mediated necrotizing myopathies, with a severe muscle involvement often presents from the onset of the disease; antisynthetase syndrome, which combines muscle damage, joint involvement and a potentially life-threatening lung disease; and overlapping myositis, which combines muscle damage with other organs involvement connected to another autoimmune disease. The diagnosis of IIM is based on rigorous clinical examination and interrogation, electromyographic data and immunological testing for myositis specific antibodies. This antibody dosage must be extended or repeated if necessary to classify correctly the muscle disease under investigation, as the available tests may not perform well enough. Muscle biopsy, although very informative, is not anymore systematically recommended when the clinic and the antibodies are typical. However, some forms of IIM are sometimes difficult to classify; in these cases, muscle biopsy plays a crucial role in the precise etiological diagnosis.

Immune-mediated necrotizing myopathy: clinical features and pathogenesis

Immune-mediated necrotizing myopathy (IMNM) is a group of inflammatory myopathies that was distinguished from polymyositis in 2004. Most IMNMs are associated with anti-signal recognition particle (anti-SRP) or anti-3-hydroxy-3-methylglutaryl-coA reductase (anti-HMGCR) myositis-specific autoantibodies, although ~20% of patients with IMNM remain seronegative. These associations have led to three subclasses of IMNM: anti-SRP-positive IMNM, anti-HMGCR-positive IMNM and seronegative IMNM. IMNMs are frequently rapidly progressive and severe, displaying high serum creatine kinase levels, and failure to treat IMNMs effectively may lead to severe muscle impairment. In patients with seronegative IMNM, disease can be concomitant with cancer. Research into IMNM pathogenesis has shown that anti-SRP and anti-HMGCR autoantibodies cause weakness and myofibre necrosis in mice, suggesting that, as well as being diagnostic biomarkers of IMNM, they may play a key role in disease pathogenesis. Therapeutically, treatments such as rituximab or intravenous immunoglobulins can now be discussed for IMNM, and targeted therapies, such as anticomplement therapeutics, may be a future option for patients with refractory disease.

Pericarditis in Systemic Rheumatologic Diseases

PURPOSE OF REVIEW

We review the epidemiology, pathophysiology, and management of pericarditis most commonly complicating autoimmune and autoinflammatory conditions.

RECENT FINDINGS

Typically, pericarditis occurs in the context of a systemic flare of the underlying disease but infrequently, it is the presenting manifestation requiring a high index of suspicion to unravel the indolent cause. Pericardial involvement in rheumatic diseases encompasses a clinical spectrum to include acute, recurrent and incessant pericarditis, constrictive pericarditis, asymptomatic pericardial effusion, and pericardial tamponade. Direct evidence on the pathophysiology of pericarditis in the context of rheumatic diseases is scant. It is theorized that immune perturbations within pericardial tissue result from the underlying central immunopathology of the respective autoimmune or autoinflammatory disease. Pericarditis management depends on acuity, the underlying cause and epidemiological features such as patient's immune status and geographic prevalence of infections such as tuberculosis. Immunosuppressive medications including biologics such as interleukin 1 blockers emerge as possible steroid sparing agents for pericarditis treatment.

Arthritis in Idiopathic Inflammatory Myopathies

PURPOSE OF REVIEW

Arthritis is a well-recognized symptom of idiopathic inflammatory myopathies (IIM). We provide a summary of available data regarding the epidemiology, clinical characteristics, and autoantibody associations of joint involvement in various forms of IIM.

RECENT FINDINGS

Arthritis is reported in 18-55% of patients with IIM. It is particularly frequent (20-70%) in those with antisynthetase syndrome (ASS); highest prevalence is associated with anti-Jo-1 positivity. Most common manifestation is non-erosive polyarthritis. X-ray erosions may be found occasionally in ASS, particularly in patients with overlap with rheumatoid arthritis (RA). Arthritis is often present at the time of IIM diagnosis and it may even precede the onset of muscle weakness. Arthritis may in some cases be the main disease manifestation responsible for the disease burden in patients with IIM. Arthritis is a frequent symptom of IIM. Polyarthritis of small joints of the hands is the most frequent clinical manifestation. Arthritis may be the first or dominant symptom in IIM and therefore patients may be initially misdiagnosed as having RA. Particularly in seronegative RA patients with interstitial lung disease or Raynaud's phenomenon, the possibility of IIM should be considered.