Frequency, mutual exclusivity and clinical associations of myositis autoantibodies in a combined European cohort of idiopathic inflammatory myopathy patients

Myositis autoantibodies: recent perspectives

PURPOSE OF REVIEW

To provide an overview of recent discoveries related to myositis-specific autoantibodies (MSAs) and assays used for their measurement.

RECENT FINDINGS

New autoantibody specificities have been reported including a MSA directed against eukaryotic initiation factor 3 and a myositis-associated autoantibody directed against heat shock factor 1. The association of anti-TIF1γ with cancer-associated dermatomyositis dependent on age has been confirmed in several large cohorts. Despite MSAs being almost entirely mutually exclusive, several myositis autoantigens are overexpressed in regenerating muscle and do not correlate with the corresponding MSA in any one patient. Further mechanisms may determine the final MSA specificity and are likely to include the need for autoantigen processing and presentation with adaptive T-cell help. The presence of CD4-positive T cells specific for histidyl tRNA synthetase protein in bronchial lavage fluid from antisynthetase patients lends support to this view. Finally, it is widely held that MSA do play an important role in clinical practice among some evidence and concern about commercial assay reliability.

SUMMARY

MSAs continue to provide important tools for clinical diagnosis and management as well as insights into disease mechanisms. Further improvement in the standardization and reliability of routine detection of MSAs is a high priority.

MDA-5 dermatomyositis complicated by interstitial lung disease and cutaneous ulcers: successful treatment with corticosteroids, mycophenolate mofetil and intravenous immunoglobulin

Antimelanoma differentiation-associated gene 5 (MDA-5) dermatomyositis is a subtype of dermatomyositis that is associated with rapidly progressive interstitial lung disease (RP-ILD), as well as with a variety of cutaneous manifestations. Patients with MDA-5 dermatomyositis tend to have a poor prognosis that is often attributed to the high rates of concurrent RP-ILD. Given the severity of disease, early diagnosis and aggressive management is pivotal. We present a case of a 40-year-old woman diagnosed with MDA-5 dermatomyositis who presented with weakness, painful cutaneous ulcerations and interstitial lung disease. She was treated with monthly intravenous Ig (IVIg), weight-based prednisone and mycophenolate mofetil (MMF). After approximately 2 years of treatment, her interstitial lung disease remains stable and she has had significant improvement in weakness and cutaneous ulcerations. Our case provides evidence for early and aggressive treatment of MDA-5 dermatomyositis with a combination of weight-based prednisone, MMF and IVIg.

Identification of a novel autoantigen eukaryotic initiation factor 3 associated with polymyositis

Objectives

To describe the prevalence and clinical associations of autoantibodies to a novel autoantigen, eukaryotic initiation factor 3 (eIF3), detected in idiopathic inflammatory myositis.

Methods

Sera or plasma from 678 PM patients were analysed for autoantigen specificity by radio-labelled protein immunoprecipitation (IPP). Samples immunoprecipitating the same novel autoantigens were further analysed by indirect immunofluorescence and IPP using pre-depleted cell extracts. The autoantigen was identified through a combination of IPP and MALDI-TOF mass spectrometry, and confirmed using commercial antibodies and IPP-western blots. Additional samples from patients with DM (668), DM-overlap (80), PM-overlap (191), systemic sclerosis (150), systemic lupus erythematosus (200), Sjogren’s syndrome (40), rheumatoid arthritis (50) and healthy controls (150) were serotyped by IPP as disease or healthy controls.

Results

IPP revealed a novel pattern in three PM patients (0.44%) that was not found in disease-specific or healthy control sera. Indirect immunofluorescence demonstrated a fine cytoplasmic speckled pattern for all positive patients. Mass spectrometry analysis of the protein complex identified the target autoantigen as eIF3, a cytoplasmic complex with a role in the initiation of translation. Findings were confirmed by IPP-Western blotting. The three anti-eIF3-positive patients had no history of malignancy or interstitial lung disease, and had a favourable response to treatment.

Conclusion

We report a novel autoantibody in 0.44% of PM patients directed against a cytoplasmic complex of proteins identified as eIF3. Although our findings need further confirmation, anti-eIF3 appears to correlate with a good prognosis and a favourable response to treatment.

Generation and validation of recombinant antibodies to study human aminoacyl-tRNA synthetases

Aminoacyl-tRNA synthetases (aaRSs) have long been viewed as mere housekeeping proteins and have therefore often been overlooked in drug discovery. However, recent findings have revealed that many aaRSs have noncanonical functions, and several of the aaRSs have been linked to autoimmune diseases, cancer, and neurological disorders. Deciphering these roles has been challenging because of a lack of tools to enable their study. To help solve this problem, we have generated recombinant high-affinity antibodies for a collection of thirteen cytoplasmic and one mitochondrial aaRSs. Selected domains of these proteins were produced recombinantly in Escherichia coli and used as antigens in phage display selections using a synthetic human single-chain fragment variable library. All targets yielded large sets of antibody candidates that were validated through a panel of binding assays against the purified antigen. Furthermore, the top-performing binders were tested in immunoprecipitation followed by MS for their ability to capture the endogenous protein from mammalian cell lysates. For antibodies targeting individual members of the multi-tRNA synthetase complex, we were able to detect all members of the complex, co-immunoprecipitating with the target, in several cell types. The functionality of a subset of binders for each target was also confirmed using immunofluorescence. The sequences of these proteins have been deposited in publicly available databases and repositories. We anticipate that this open source resource, in the form of high-quality recombinant proteins and antibodies, will accelerate and empower future research of the role of aaRSs in health and disease.

Line blot immunoassays in idiopathic inflammatory myopathies: retrospective review of diagnostic accuracy and factors predicting true positive results

Background

Line blot immunoassays (LIA) for myositis-specific (MSA) and myositis-associated (MAA) autoantibodies have become commercially available. In the largest study of this kind, we evaluated the clinical performance of a widely used LIA for MSAs and MAAs.

Methods

Adults tested for MSA/MAA by LIA at a tertiary myositis centre (January 2016–July 2018) were identified. According to expert-defined diagnoses, true and false positive rates were calculated for strongly and weakly positive autoantibody results within three cohorts: idiopathic inflammatory myopathy (IIM), connective tissue disease (CTD) without myositis, and non-CTD/IIM. Factors associated with true positivity were determined.

Results

We analysed 342 cases. 67 (19.6%) had IIM, in whom 71 autoantibodies were detected (50 strong positives [70.4%], 21 weak positives [29.6%]). Of the strong positives, 48/50 (96.0%; 19 MSAs, 29 MAAs) were deemed true positives. Of the weak positives, 15/21 (71.4%; 3 MSAs, 12 MAAs) were deemed true positives.

In CTD without myositis cases (n = 120), 31/61 (51.0%; 5 MSAs, 26 MAAs) autoantibodies were strongly positive, with 24/31 (77.4%; 0 MSAs, 24 MAAs) true positives. 30/61 (49.2%; 13 MSAs, 17 MAAs) were weakly positive, with 16/30 (53.3%; 0 MSAs, 16 MAAs) true positives. In non-CTD/IIM cases (n = 155), all 24 MSAs and 22 MAAs were false positives; these results included 17 (37.0%; 7 MSAs, 10 MAAs) strong positives.

Individual autoantibody specificities were > 98.2 and > 97.5% for weakly and strongly positive results, respectively. True positivity was associated with high pre-test for IIM (odds ratio 50.8, 95% CI 13.7–189.2, p < 0.001) and strong positive (versus weak positive) results (4.4, 2.3–8.3, p < 0.001).

Conclusions

We demonstrated the high specificity of a myositis LIA in a clinical setting. However, a significant burden of false positive results was evident in those with a low pre-test likelihood of IIM and for weakly positive autoantibodies.

The association between myositis-specific autoantibodies and muscle pathologies in idiopathic inflammatory myopathies

OBJECTIVE

To investigate specific muscle pathologies of different kinds of myositis-specific autoantibodies (MSAs) in idiopathic inflammatory myopathy (IIM) patients.

METHODS

One hundred eleven Chinese patients from Xiangya Hospital, Central South University diagnosed with IIMs according to European Neuromuscular Centre (ENMC) criteria were included. Clinical manifestation, myositis-specific autoantibodies, and histologic findings were evaluated to explore the pattern of necrosis, regeneration, and perifascicular atrophy, inflammatory cells in IIM patients with different MSAs.

RESULTS

Anti-SRP group has the lowest muscle strength scores, the highest creatine kinase levels, the most severe degree of necrosis and regeneration (1.90[0.80-3.95], 1.00[0.30-1.71]), and the lowest positive rate of MHC-I staining (35.71%). The anti-MDA5 group demonstrates the mildest pathological changes, with the fewest necrotic and regenerated muscle fibers (0.00[0.00-0.50], 0.00[0.00-0.00]), and the fewest inflammatory cell infiltration, and the highest muscle strength scores. The anti-NXP2 group has the most frequent inflammatory infiltrates, especially CD4+ T cells (31.14[15.00-39.00]). The patients with anti-NXP2 and the anti-TIF1γ antibodies show higher frequency of punched-out fibers (1.50[0.00-3.70], 0.00[0.00-1.00]) and perifascicular atrophy (71.43%, 55.56%). As for anti-synthetase antibodies (ASAs), the anti-Jo-1 group shows the most frequent rate of perifascicular necrosis (60%), while other ASA groups do not show perifascicular necrosis.

CONCLUSIONS

Of the MSAs, the anti-SRP antibody leads to the most severe muscle involvement, while the anti-MAD5 antibody the mildest. The anti-NXP2 and anti-TIF1γ groups have the most typical "DM" pathology. Key Points • Anti-SRP group shows severe muscle pathology while anti-MDA5 group shows the mildest. • Anti-NXP2 group has the most frequent inflammatory infiltrates. Pouch-out fibers and perifascicular atrophy are more prevalent in anti-NXP2 and anti-TIF1γ groups. • Anti-Jo-1 group is often accompanied by perifascicular necrosis, while other anti-synthetase antibody groups are not.

Extended myositis-specific and -associated antibodies profile in systemic sclerosis: A cross-sectional study

OBJECTIVE

In systemic sclerosis (SSc) and idiopathic inflammatory myopathies (IIM), auto-antibodies are used in daily practice as potent biomarkers of clinical phenotypes. This study aimed at estimating the prevalence of myositis-specific (MSA) and myositis-associated (MAA) auto-antibodies in a well-characterised SSc patients cohort using two different immunoblot assays, and studying their clinical associations.

METHODS

In this cross-sectional study, the sera of 300 consecutive patients were tested at the same time with myositis antibodies Euroimmun® and D-tek® immunoblot assays.

RESULTS

Prevalence of MSA/MAA, MSA and MAA were 17.0%, 8.0% and 9.7%, respectively. When combining results of both tests, anti-PM/Scl 100 were found in 5.0% (95% confidence interval 2.8; 8.1); anti-PM/Scl 75 and anti-TIF1γ in 3.7% (1.8; 6.5); anti-Ku 3.0% (1.4; 5.6); anti-MDA5 in 1.3% (0.4; 3.4); anti-Mi-2 β, anti-NXP2, anti-PL-7 and anti-SRP in 0.7% (0.08; 2.4); anti-EJ and anti-PL-12 in 0.3% (0.01; 1.8) of patients. No reactivity against SAE1, Jo-1 or OJ was observed. Anti-PM/Scl 75 antibodies were associated with interstitial lung disease (80% vs. 42%) and myositis (27% vs. 3%); anti-Ku antibodies were associated with myositis (33% vs. 3%).

CONCLUSION

In this cross-sectional study of 300 SSc patients, the prevalence of MSA/MAA, MSA and MAA using immunoblot assays were 17.0%, 8.0% and 9.7%, respectively. MAA positivity was associated with ILD and myositis, but this study did not highlight any clinical associations with MSA positivity.

The promise, perceptions, and pitfalls of immunoassays for autoantibody testing in myositis

Background

A myositis-specific autoantibody can now be identified in the majority of patients with myositis. They identify homogeneous patient subgroups and are key tools in developing a personalized approach to disease management. There is substantial clinical interest in exploiting myositis autoantibodies as biomarkers, and consequently, a large number of commercial assays have been developed for their detection. These assays are already in widespread clinical use. In order to better understand perceived concerns from the international myositis community in relation to the reliability of these assays and how they are being used, we conducted a survey of international myositis experts, all of whom were members of the International Myositis Assessment and Clinical Studies group.

Results

We collected data on the types of assay used, manufacturers, and the nature of the report provided by different laboratories and received 111 complete responses. Respondents also provided information on how they used the different assays, their confidence in the results, and how this influenced their clinical practice. Enzyme immunoassay/ELISA was the most popular assay method used worldwide followed by line blot. Line blot was the most popular method used in Europe. Despite concerns from over 80% of respondents regarding false-positive and false-negative results with the assay used by their laboratory, over 80% reported that the identification of a myositis autoantibody influenced their diagnostic confidence, the information they provided to a patient, and their recommended treatment.

Conclusions

In spite of ongoing concerns from the majority of users regarding the reliability of the results, myositis-specific autoantibody testing, using commercial immunoassays, is being used globally to inform clinical decision-making. These findings highlight the need for urgent guidance on the use of myositis autoantibody testing and on the interpretation of results. Knowledge of the reliability of currently available assays is essential given the importance already placed on myositis-specific autoantibodies as clinical decision-making tools.

Refractory Myositis Affecting the Intrinsic Muscles of the Hand

Myositis generally affects the proximal muscles. However, we herein report a case of a 48-year-old woman with intractable myositis affecting the intrinsic muscles of the hands. Her myositis, which developed in childhood, was refractory to treatment with steroids and several immunosuppressants, causing walking disability. After experiencing pain and swelling in the hands for six months, she was diagnosed with myositis of the intrinsic muscles of the hands and tested positive for the anti-signal recognition particle antibody. Intravenous immunoglobulin therapy improved the myositis of the hands. This case suggests that inflammation caused by intractable myositis can extend to the hands.

The spectrum of idiopathic inflammatory myopathies in South Africa

INTRODUCTION

There are many reports on idiopathic inflammatory myopathies (IIM) but little information from sub-Saharan Africa. We conducted a retrospective study of IIM in a multi-ethnic cohort seen at a single centre in Durban, South Africa.

METHOD

The study included patients who fulfilled the Bohan and Peter or European League Against Rheumatism/American College of Rheumatology criteria for IIM. The information recorded included demographic data, clinical findings, results of investigations, treatment and outcome. Patients with overlap myositis (OM) had myositis and criteria for another connective tissue disease.

RESULTS

There were 104 patients with IIM; 82.7% female and 70.2% African blacks. They included 41 (39.4%) with OM, 26 (25%) polymyositis (PM), 26 (25%) dermatomyositis (DM), six (5.8%) juvenile dermatomyositis and five (4.8%) cancer-associated myositis. Our patients had a younger mean age at diagnosis (36.8 ± 14.7 years) compared with 45-55 years in most other studies. Scleroderma-myositis overlap accounted for 26 (63.4%) of the patients with OM. Patients with OM were significantly younger than PM (p = 0.004) and DM (p = 0.044) and had lower, but not statistically significant, creatine kinase levels at diagnosis compared with PM (p = 0.052) and DM (p = 0.073). Interstitial lung disease was more common in OM (p = 0.001) and PM (p = 0.024) than DM. Oropharyngeal weakness was more common in DM than OM (p = 0.001) and PM (p = 0.032). African blacks were younger (p = 0.028) at diagnosis and had more cardiac abnormalities (p = 0.034) than Indians.

CONCLUSION

The spectrum of IIM in our cohort of mainly African blacks is similar to other studies, with OM being the most frequent subtype. Key Points • As there is limited information on idiopathic inflammatory myopathies (IIM) in sub-Saharan Africa, this study reports the spectrum of IIM in a South African cohort of predominantly African blacks. • Our patients were younger at diagnosis, and overlap myositis was the most common phenotype. • Comparisons with other studies show similarities in the manifestations of IIM.

Pitfalls in the diagnosis of myositis

The idiopathic inflammatory myopathies are a group of heterogeneous autoimmune connective tissue diseases. Despite increase in the understanding of these conditions, securing a timely diagnosis and accurate subtype classification remains difficult in some cases. This has important implications for patients, where delayed or inappropriate treatments can have a negative effect on outcomes. Several conditions can mimic myositis, including metabolic myopathies, genetic myopathies and neurological disease. In addition, the heterogeneity within the idiopathic inflammatory myopathy spectrum can also create diagnostic confusion, referred to here as 'myositis chameleons'. This includes inclusion body myositis, immune-mediated necrotizing myopathy, hypomyopathic variants of anti-synthetase syndrome and overlap disease. We highlight the importance of a thorough diagnostic workup, refer to updated classification criteria and emphasize the importance of myositis autoantibody testing. Where diagnostic doubt exists, the involvement of a specialist centre and a multidisciplinary team is vital.

Inflammatory Myopathy-Related Interstitial Lung Disease: From Pathophysiology to Treatment

Inflammatory myopathies (IM) are auto-immune connective tissue diseases characterized by muscle involvement and by extramuscular manifestations. As such, pulmonary manifestations, which mainly include interstitial lung disease (ILD), often darken two out of four distinct IM, namely dermatomyositis and overlapping myositis. Being the initiation site of the disease and being the leading cause of morbidity and mortality, ILD is of major importance in this context. ILD has a heterogeneous expression among the patients, with various onset mode, various radiological pattern, various severity and finally with different prognoses, which are particularly difficult to predict at the time of IM diagnosis. Therefore, ILD is a challenging issue. Treatments are based on steroids and immunosuppressive or targeted therapies. Their respective place is yet poorly codified however and remains often based on clinician expertise. Dedicated clinical trials are lacking to date and are also difficult to build, due to difficulty of constituting large and homogeneous patient groups and to rigorously evaluate disease outcomes. Indeed, pulmonary function tests alone are being regularly defeated in IM, in which respiratory muscles are often involved. Composite scores, bringing together several lung parameters, should thus be developed and validated in the future, to better assess the disease response to treatment. This review aims to describe the current knowledge of IM immuno-pathogenesis, the clinical features associated with IM related-ILD, focusing of both severity and prognosis, and the actual therapeutic approaches.

Juvenile Dermatomyositis-Clinical Phenotypes

PURPOSE OF REVIEW

Juvenile dermatomyositis is a heterogeneous disease with variable clinical outcomes. Here, we describe the recognised subtypes of idiopathic inflammatory myositis which occur in children, with particular reference to disease-associated autoantibodies.

RECENT FINDINGS

Large cohort studies have demonstrated that myositis autoantibodies are common in juvenile dermatomyositis and can be found in the majority of patients. They identify homogenous clinical subgroups and inform prognosis, particularly the risks of developing interstitial lung disease. Descriptions of immune-mediated necrotising myositis in juvenile patients have highlighted a rare but important clinical subset typically associated with severe muscle disease and treatment resistance. It is increasingly apparent that autoantibodies can provide detailed information on prognosis and the likely disease associations in those with juvenile dermatomyositis. Further work is needed to establish how this knowledge should influence our approach to treatment.

Cutaneous manifestations of dermatomyositis characterized by myositis-specific autoantibodies

Dermatomyositis (DM) is an inflammatory myopathy with characteristic skin manifestations, the pathologies of which are considered autoimmune diseases. DM is a heterogeneous disorder with various phenotypes, including myositis, dermatitis, and interstitial lung disease (ILD). Recently identified myositis-specific autoantibodies have been associated with distinct clinical features. For example, anti-melanoma differentiation-associated protein 5 antibodies have a high specificity for clinically amyopathic DM presenting rapidly progressive ILD. Furthermore, anti-transcriptional intermediary factor 1γ antibodies found in patients with juvenile and adult DM are closely correlated with malignancies, especially in elderly patients. Finally, patients with anti-aminoacyl-transfer RNA synthetase antibodies share characteristic clinical symptoms, including myositis, ILD, arthritis/arthralgia, Raynaud’s phenomenon, and fever; thus, the term “anti-synthetase syndrome” is also used. With a focus on the characteristic cutaneous manifestations in each subgroup classified according to myositis-specific autoantibodies, we introduce the findings of previous reports, including our recent analysis indicating that skin eruptions can be histopathologically classified into myositis-specific autoantibody-associated subgroups and used to determine the systemic pathologies of the different types of antibody-associated DM.

Autoantibodies in Myositis. How to Achieve a Comprehensive Strategy for Serological Testing

Myopathies are a rare type of acquired, chronic autoimmune diseases of the skeletal muscles and affect both children and adults. The hallmark symptoms of idiopathic inflammatory myopathies (IIM) are muscle inflammation, proximal muscle weakness and disability, arthritis, cutaneous rashes, calcinosis, ulceration, malignancy and interstitial lung disease (ILD). Subforms of IIM include polymyositis, dermatomyositis, cancer-related myositis and sporadic inclusion body myositis. Autoantibodies function as biomarkers for diagnosis of IIM and can be used to delimit clinically distinguishable IIM subforms. To maximise the diagnostic information it is essential to perform comprehensive multiparametric serological testing including both screening and confirmation tests.

Frequencies and clinical associations of myositis-related antibodies in The Netherlands: A one-year survey of all Dutch patients

Idiopathic inflammatory myopathies (IIM) are a heterogeneous group of connective tissue diseases, collectively known as myositis. Diagnosis of IIM is challenging while timely recognition of an IIM is of utter importance considering treatment options and otherwise irreversible (severe) long-term clinical complications. With the EULAR/ACR classification criteria (2017) considerable advancement has been made in the diagnostic workup of IIM. While these criteria take into account clinical parameters as well as presence of one autoantibody, anti-Jo-1, several autoantibodies are associated with IIM and are currently evaluated to be incorporated into classification criteria. As individual antibodies occur at low frequency, the development of line blots allowing multiplex antibody analysis has improved laboratory diagnostics for IIM. The Euroline myositis line-blot assay (Euroimmun) allows screening and semi-quantitative measurement for 15 autoantibodies, i.e. myositis specific antibodies (MSA) to SRP, EJ, OJ, Mi-2α, Mi-2β, TIF1-γ, MDA5, NXP2, SAE1, PL-12, PL-7, Jo-1 and myositis associated antibodies (MAA) to Ku, PM/Scl-75 and PM/Scl-100. To evaluate the clinical significance of detection and levels of these autoantibodies in the Netherlands, a retrospective analysis of all Dutch requests for extended myositis screening within a 1 year period was performed. A total of 187 IIM patients and 632 non-IIM patients were included. We conclude that frequencies of MSA and MAA observed in IIM patients in a routine diagnostic setting are comparable to cohort-based studies. Weak positive antibody levels show less diagnostic accuracy compared to positive antibody levels, except for anti-NXP2. Known associations between antibodies and skin involvement (anti-MDA5, anti-TIF1-γ), lung involvement (anti-Jo-1), and malignancy (anti-TIF1-γ) were confirmed in our IIM study population. The availability of multiplex antibody analyses will facilitate inclusion of additional autoantibodies in clinical myositis guidelines and help to accelerate diagnosing IMM with rare but specific antibodies.