10Idiopathic inflammatory myositis
Section snippets
Advances in diagnosis
The diagnosis of idiopathic inflammatory myopathy (IIM) has traditionally been based on a clinical presentation with skeletal muscle weakness, elevated serum levels of muscle enzymes including creatine kinase (CK) and the myopathic triad (fibrillations with sharp positive waves, polyphasic motor units with low amplitude and short duration and spontaneous high-frequency discharges) on electromyography together with characteristic histopathological changes on muscle biopsy. Antibodies, both
Antisynthetase antibodies
Aminoacyl transfer RNA (tRNA) synthetases (ARSs) are a group of cytoplasmic enzymes, each of which catalyse the binding of a specific amino acid to the cognate tRNA during protein synthesis. Antibodies directed to these enzymes (anti-ARS) interact with conformational epitopes in conserved regions of the enzyme to inhibit enzyme activity [2]. The anti-ARS are highly specific, can be detected preceding disease onset and are thus considered to be critical in disease pathogenesis [11].
Antibodies
cN1A antibody
Antibodies to cytoplasmic 5′-nucleotidase 1A (cN1A), a 43-kDa muscle autoantigen, have recently been identified in patients with IBM, supporting a role for B-cell-mediated humoral immunity in its pathogenesis [54], [55], ∗[56]. Anti-cN1A antibodies have high specificity for IBM, but they may also be found in patients with other autoimmune diseases, for example, systemic lupus erythematosus (SLE) or Sjögren's syndrome [54], ∗[56], [57], [58]. In a South Australian cohort of patients with
Myositis-associated antibodies
Antibodies to Ro52 are the most commonly detected MAAs [4], [39], and they have been found in the sera of 35/147 (23.8%) myositis patients from an Australian cohort [65], 30/155 (19%) patients from a French cohort [66], 30/100 (30%) Canadian patients [4] and 104/417 (25%) patients in a European cohort [39]. Importantly, when tested with Ro60 (SSA) by ELISA using a combination of the two antigens, up to 20% of anti-Ro52 antibodies are missed. As reactivity to Ro52 and Ro60 represents two
Muscle histopathology
A muscle biopsy is essential to confirming IIM, distinguishing between disease subsets and excluding other conditions. The cardinal histological feature common to DM, PM and IBM is mononuclear inflammatory cell infiltrate in skeletal muscle. These infiltrates consist of lymphocytes and macrophages within and/or around muscle fascicles and may invade muscle fibres [78]. Despite this unifying thread, distinct histopathological differences separate the subsets of IIM, reflecting underlying
Treatment of IIM
Therapeutic strategies for IIM have evolved over the years, particularly with the increasing availability of biologic agents, but they remain largely consensus driven rather than being based on randomised controlled trials. The rarity of these conditions, together with the varied classification criteria and outcome measures used, has made comparisons between trials difficult. More recent studies have incorporated better disease classification and IMACS core set measures.
The natural history and
Tools for research and future directions
IIM encompasses a heterogeneous group of disorders defined by clinical phenotype, serology and histology. The best approach to classifying IIM remains unclear. Universally accepted histopathological criteria are lacking, and a number of patients lack currently recognised MAA or MSA. Advances are being made in the development of clinico-serological and histologic classification, definitions of disease activity and damage and treatment strategies. As this occurs, longitudinal cohorts will be well
Summary
International collaborative efforts have made important advances in multiple facets of IIM. Increasing availability of testing for MSAs and MAAs have led to better definition of antibody profiles in patients with IIM and greater recognition of their clinical and prognostic significance. We now have a greater understanding of the correlations between MAAs and MSAs, histopathological findings and clinical subtypes. Moreover, there is increasing awareness of the association between antibody
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Muscle pathological features and extra-muscle involvement in idiopathic inflammatory myopathies with anti-mitochondrial antibody
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2021, Ultrasound in Medicine and BiologyCitation Excerpt :A broader spectrum of acute and sub-acute muscle disorders includes infectious myositis (viral, bacterial, fungal and parasitic), muscle infarction, granulomatous myositis, drug-induced rhabdomyolysis and alloimmune polymyositis after allogeneic stem cell transplantation, polyneuropathy-related myositis and myositis owing to congenital disorders (Schulze et al. 2009; Michelle and Mammen 2015). The diagnosis of myositis is based on clinical signs and symptoms; laboratory tests including creatine kinase (CK), aldolase and antibodies; electromyography; and, increasingly, magnetic resonance imaging (MRI) (Dalakas 2015; Lundberg 2016; Tieu et al. 2016; Tomas et al. 2019). MRI is non-invasive and can detect early muscular abnormalities in the presence of only mild or no clinical symptoms and unrevealing laboratory tests.
Inpatient burden and resource utilization of polymyositis and dermatomyositis: A 10-year study of national inpatient sample
2021, Revue du Rhumatisme (Edition Francaise)Inpatient burden and resource utilization of polymyositis and dermatomyositis: A 10-year Study of National Inpatient Sample
2020, Joint Bone SpineCitation Excerpt :Polymyositis (PM) and dermatomyositis (DM) are the two most common subtypes of idiopathic inflammatory myositis, characterized by inflammation of proximal skeletal muscle although extra-muscular organs, including skin (in the case of DM), lungs, heart and esophagus, are also frequently affected [1–3].
Inflammatory muscle disease – An update
2020, Best Practice and Research: Clinical RheumatologyCitation Excerpt :As more studies are conducted in larger myositis cohorts, additional insights into the clinical phenotypes associated with each antisynthetase antibody will become apparent. Anti-Mi2 is associated with classical cutaneous features of DM such as Gottron's papules, heliotrope rash, shawl sign, V-neck sign, periungual erythema with cuticular hypertrophy and photosensitivity [10,20]. ( Table 2).
The spectrum of idiopathic inflammatory myopathies in Western Australia: epidemiological characteristics and mortality over time
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