Autoantibody testing in idiopathic inflammatory myopathies

Immunosuppressive and immunomodulatory therapies for idiopathic inflammatory myopathies

This is a protocol for a Cochrane Review (intervention). The objectives are as follows:

This protocol is for two separate reviews to assess the effects (benefits and harms) of immunosuppressant and immunomodulatory treatments for the idiopathic inflammatory myopathies.  

Coexistence of Multiple Myositis-Specific Antibodies in Patients with Idiopathic Inflammatory Myopathies

The mutual exclusivity of myositis-specific antibodies (MSAs) has been reported before, but the coexistence of 2 or more MSAs was still found in a few case reports. This study aims to confirm the existence and prevalence of double MSAs in patients with idiopathic inflammatory myopathy (IIM) and to clarify the clinical features of these patients. One hundred fifty-one patients with IIM diagnosed from 1 July 2018 to 31 July 2022, at National Cheng Kung University Hospital, Taiwan, were enrolled and divided into two groups, patients with ≤1 MSA (n = 128, 84.8%) and those with ≥2 MSAs (n = 23, 15.2%) according to the initial serology results. After being re-examined by ANA-IIF assay, 8 out of 23 patients were confirmed to have ≥2 MSAs. The demographic data and clinical features were presented. The prevalence of double-positive MSAs among IIM was 5.3% in this cohort. The coexistence of two MSAs in an IIM patient does exist but is rare. Patients with two MSAs belonging to two distinct IIM subtypes presented clinical features skewed to one subtype instead of "mixed phenotypes". No apparent difference in clinical severity was found between patients with ≥2 MSAs and ≤1 MSA. Longer follow-ups and more studies are required to characterize the patients of IIM with ≥2 MSAs.

Weakness in the intensive care unit

When asked to assess patients in an intensive care unit (ICU) who have respiratory muscle weakness, oropharyngeal weakness and a vulnerable airway, our immediate thought may be of Guillain-Barré syndrome or myasthenia gravis, but there are many other possible causes. For example, previously unrecognised chronic neurological conditions may decompensate and require ICU admission. Clinicians can use various clinical clues to help recognise them and need to understand how patterns of weakness reflect differing causes of reduced consciousness on ICU. Additionally, patients admitted to ICU for any reason may develop weakness during their stay, the most likely cause being ICU-acquired weakness. Assessing patients in ICU is challenging, hampered by physical barriers (machines, tubes), medication barriers (sedatives) and cognitive barriers (delirium, difficulty communicating). Nonetheless, we need to reach a clinical diagnosis, organise appropriate tests and communicate clearly with both patients and ICU colleagues.

Pathophysiological Mechanisms and Treatment of Dermatomyositis and Immune Mediated Necrotizing Myopathies: A Focused Review

Idiopathic inflammatory myopathies (IIM), collectively known as myositis, are a composite group of rare autoimmune diseases affecting mostly skeletal muscle, although other organs or tissues may also be involved. The main clinical feature of myositis is subacute, progressive, symmetrical muscle weakness in the proximal arms and legs, whereas subtypes of myositis may also present with extramuscular features, such as skin involvement, arthritis or interstitial lung disease (ILD). Established subgroups of IIM include dermatomyositis (DM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASyS), overlap myositis (OM) and inclusion body myositis (IBM). Although these subgroups have overlapping clinical features, the widespread variation in the clinical manifestations of IIM suggests different pathophysiological mechanisms. Various components of the immune system are known to be important immunopathogenic pathways in IIM, although the exact pathophysiological mechanisms causing the muscle damage remain unknown. Current treatment, which consists of glucocorticoids and other immunosuppressive or immunomodulating agents, often fails to achieve a sustained beneficial response and is associated with various adverse effects. New therapeutic targets have been identified that may improve outcomes in patients with IIM. A better understanding of the overlapping and diverging pathophysiological mechanisms of the major subgroups of myositis is needed to optimize treatment. The aim of this review is to report on recent advancements regarding DM and IMNM.

Epidemiology of Idiopathic Inflammatory Myopathies in Africa: A Contemporary Systematic Review

BACKGROUND

The epidemiology of idiopathic inflammatory myopathies (IIMs) has been extensively studied in America, Europe, and Asia, but remains unclear in Africa.

OBJECTIVE

The aim of this review was to summarize available data on the epidemiology of IIMs in Africa.

METHODS

We searched MEDLINE, EMBASE, and African Journals Online for studies published up to December 30, 2020, and reporting epidemiological data on IIMs in Africa. Data were combined through narrative synthesis. The review protocol was registered with PROSPERO, CRD42020186781.

RESULTS

We included 39 studies reporting 683 cases (71.7% adults) of IIMs. Incidence rates of ~7.5/1,000,000 person-years and 1.2/1,000,000 person-years were estimated for dermatomyositis (DM), whereas polymyositis (PM) had an incidence rate of 8.8/1,000,000 person-years. Prevalence estimates of 11.49/100,000 and 11/100,000 (95% confidence interval, 0-32) were provided for IIMs and the PM subtype, respectively. Mean age at diagnosis ranged from 7.9 to 57.2 years, and 50% to 100% of the patients were females. Main subtypes of adult-onset IIMs were DM (21%-93%) and PM (12%-79%), whereas the commonest juvenile subtype was juvenile DM (5.8%-9%). Skeletal muscle involvement (56%-100%) was the main disease feature, and esophagus was the most commonly affected internal organ (6%-65.2%). Anti-Jo1/histidyl tRNA synthetase (7%-100%) and anti-Mi2 (17%-45%) antibodies were the most frequent myositis specific antibodies. Early mortality was high (7.8%-45%), and main death causes were infections, cancers and organ damage in respiratory and cardiovascular domains.

CONCLUSIONS

Apart from a potential younger age at onset of adult IIMs in Africa, current sparse data mostly suggest a similar epidemiology between Africa and other regions. Further high-quality studies are required to validate these findings.

OptimisAtion of Diagnostic Accuracy in idioPathic inflammaTory myopathies (ADAPT study): a protocol for a prospective diagnostic accuracy study of multimodality testing in patients suspected of a treatable idiopathic inflammatory myopathy

INTRODUCTION

Idiopathic inflammatory myopathies (IIMs) excluding inclusion body myositis (IBM) are a group of heterogeneous autoimmune disorders characterised by subacute-onset and progressive proximal muscle weakness, which are frequently part of a multisystem autoimmune disorder. Reaching the diagnosis can be challenging, and no gold standard for the diagnosis of IIM exists. Diagnostic modalities include serum creatine kinase activity, muscle imaging (MRI or ultrasound (US)), electromyography (EMG), myositis autoantibody testing and muscle biopsy. Several diagnostic criteria have been developed for IIMs, varying in reported sensitivity and specificity.

HYPOTHESIS

We hypothesise that an evidence-based diagnostic strategy, using fewer and preferably the least invasive diagnostic modalities, can achieve the accuracy of a complete panel of diagnostic tests, including MRI, US, EMG, myositis-specific autoantibody testing and muscle biopsy.

METHODS AND ANALYSIS

The OptimizAtion of Diagnostic Accuracy in idioPathic inflammaTory myopathies study is a prospective diagnostic accuracy study with an over-complete study design. 100 patients suspected of an IIM excluding IBM will be included. A reference diagnosis will be assigned by an expert panel using all clinical information and all results of all ancillary tests available, including 6 months of follow-up. Several predefined diagnostic strategies will be compared against the reference diagnosis to find the optimal diagnostic strategy.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the medical ethics committee of the Academic Medical Centre, University of Amsterdam, The Netherlands (2019-814). The results will be distributed through conference presentations and peer-reviewed publications.

TRIAL REGISTRATION NUMBER

Netherlands trial register; NL8764.

Paraneoplastic neurological syndromes: a practical approach to diagnosis and management

Paraneoplastic neurological syndromes (PNS) are the immune-mediated effects of a remote cancer and are characterised by an autoantibody response against antigens expressed by the tumour. Classically, well-characterised 'onconeuronal' antibodies target intracellular antigens and hence cannot access their antigens across intact cell membranes. The pathogenic mediators are likely to be neuronal-specific T cells. There is a variable response to immunotherapies and the clinical syndrome helps to direct the search for a specific set of tumours. By contrast, many newly emerging autoantibodies with oncological associations target cell surface epitopes and can exert direct pathogenic effects on both the central and peripheral nervous systems. Patients with these cell-surface directed autoantibodies often clearly respond to immunotherapies. Overall, the clinical, serological and oncological features in an individual patient helps determine the clinical relevance of the syndrome and hence guide its management. We summarise current knowledge and a practical approach to the investigation, diagnosis, treatment and outcomes of patients with suspected PNS.

The reliability of immunoassays to detect autoantibodies in patients with myositis is dependent on autoantibody specificity

Objectives

In order to address the reliability of commercial assays to identify myositis-specific and -associated autoantibodies, we aimed to compare the results of two commercial immunoassays with the results obtained by protein immunoprecipitation.

Methods

Autoantibody status was determined using radio-labelled protein immunoprecipitation for patients referred to our laboratory for myositis autoantibody characterization. For each autoantibody of interest, the sera from 25 different patients were analysed by line blot (Euroline Myositis Antigen Profile 4, EuroImmun, Lübeck, Germany) and dot blot (D-Tek BlueDiver, Diagnostic Technology, Belrose, NSW, Australia). Sera from 134 adult healthy controls were analysed.

Results

Overall commercial assays performed reasonably well, with high agreement (Cohen’s κ >0.8). Notable exceptions were the detection of rarer anti-synthetases with κ < 0.2 and detection of anti-TIF1γ, where κ was 0.70 for the line blot and 0.31 for dot blot. Further analysis suggested that the proportion of patients with anti-TIF1γ may recognize a conformational epitope, limiting the ability of blotting-based assays that utilize denatured antigen to detect this clinically important autoantibody. A false-positive result occurred in 13.7% of samples analysed by line blot and 12.1% analysed by dot blot.

Conclusion

The assays analysed do not perform well for all myositis-specific and -associated autoantibodies and overall false positives are relatively common. It is crucial that clinicians are aware of the limitations of the methods used by their local laboratory. Results must be interpreted within the clinical context and immunoprecipitation should still be considered in selected cases, such as apparently autoantibody-negative patients where anti-synthetase syndrome is suspected.

Late-onset myopathies: clinical features and diagnosis

Late-onset myopathies are not well-defined since there is no clear definition of 'late onset'. For practical reasons we decided to use the age of 40 years as a cut-off. There are diseases which only manifest as late onset myopathy (inclusion body myositis, oculopharyngeal muscular dystrophy and axial myopathy). In addition, there are diseases with a wide range of onset including 'late onset' muscle weakness. Well-known and rather frequently occurring examples are Becker muscular dystrophy, limb girdle muscular dystrophy, facioscapulohumeral dystrophy, Pompe disease, myotonic dystrophy type 2, and anoctamin-5-related distal myopathy. The above-mentioned diseases will be discussed in detail including clinical presentation - which can sometimes lead someone astray - and diagnostic tools based on real cases taken from the author's practice. Where appropriate a differential diagnosis is provided. Next generation sequencing (NGS) may speed up the diagnostic process in hereditary myopathies, but still there are diseases, e.g. with expansion repeats, deletions, etc, in which NGS is as yet not very helpful.

Initial seronegative immune-mediated necrotising myopathy with subsequent anti-HMGCR antibody development and response to rituximab: case report

Background

Immune-mediated necrotising myopathy (IMNM) is characterised by severe muscle weakness and necrosis with a paucity of inflammation on muscle biopsy. Around 60% of cases are associated with antibodies to the signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR); the remainder are seronegative. IMNM is more treatment resistant than inflammatory myopathies.

Case presentation

A 69-year-old woman with previous statin exposure presented aged 63 with muscle weakness and raised creatinine kinase (CK). Anti-SRP and anti-HMGCR antibodies were not detected, but muscle biopsy revealed changes consistent with necrotising myopathy. Statins were discontinued, and she was treated with prednisolone and methotrexate achieving disease remission. Clinical and biochemical parameters were largely stable until 6 years after diagnosis she experienced a rapid deterioration. This was found to be associated with new development of anti-HMGCR antibody. Rituximab was commenced, resulting rapidly in remission. She has remained in remission since, following 2 cycles of rituximab.

Conclusions

To our knowledge, this is the first reported case of serologically negative IMNM whose subsequent rapid deterioration was associated with development of anti-HMGCR antibody. The response to rituximab and subsequent sustained remission suggests a role for early use of rituximab in aggressive cases of anti-HMGCR myopathy.

Muscle biopsy: what and why and when?

Skeletal muscle biopsy remains an important investigative tool in the diagnosis of a variety of muscle disorders. Traditionally, someone with a limb-girdle muscle weakness, myopathic changes on electrophysiology and raised serum creatine kinase (CK) would have a muscle biopsy. However, we are living through a genetics revolution, and so do all such patients still need a biopsy? When should we undertake a muscle biopsy in patients with a distal, scapuloperoneal or other patterns of muscle weakness? When should patients with myositis, rhabdomyolysis, myalgia, hyperCKaemia or a drug-related myopathy have a muscle biopsy? What does normal muscle histology look like and what changes occur in neurogenic and myopathic disorders? As with Kipling's six honest serving men, we hope that by addressing these issues we can all become more confident about when to request a muscle biopsy and develop clearer insights into muscle pathology.

How to investigate: Suspected systemic rheumatic diseases in patients presenting with muscle complaints

Muscular symptoms, which may be due to multiple causes, are one of the most common early complaints in a rheumatology practice. Musculoskeletal symptoms in rheumatic conditions are very varied, ranging from mechanical problems to muscular symptoms derived from inflammatory and systemic autoimmune diseases. Several drugs commonly used by different specialists and certain drugs used in rheumatology can also cause a wide variety of muscle symptoms. A description of different systemic autoimmune diseases follows to describe the different forms of involvement of the musculoskeletal system that they cause, as well as the main causes with which a differential diagnosis should be made. In this chapter, we will try to give some clues to reach an early diagnosis using clinical criteria, particularly based on a directed anamnesis and physical examination, discussing possible guidelines for the complimentary tests that may be required in patients with muscle complaints.

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.