Inflammatorische Myopathien

Inflammatory myopathies cover infectious, focal and immunogenic myopathies. This review focuses on the clinical features, diagnostic techniques, pathogenesis and therapy of immunogenic myopathies. Besides myositis associated with other autoimmune disorders, dermatomyositis is the most common immunogenic myopathy. The independent diagnosis of polymyositis has come under debate, since within this group of patients some are now diagnosed as having either hereditary muscular dystrophy with inflammatory signs or inclusion body myositis (IBM). Even more strikingly, patients diagnosed with sporadic IBM may now be diagnosed with either a form of hereditary IBM or with a form belonging to the group of protein aggregate myopathies or myofibrillar myopathies. This re-classification reflects the well-known and clinically evident therapeutic dilemma in many of these patients. Thus the indication for muscle biopsy or rebiopsy requires new consideration and attention.     

Histological data in inflammatory myositis

Inflammatory muscular diseases of adult and child consist of dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM). Muscular biopsy takes a seminal place in their diagnosis, through analysis of the topography and clustering of individual histological lesions: endomysial, perimysial and perivascular inflammation, muscular necrosis with regeneration, fibre modifications, fibrosis, micro-angiopathy. They can be associated with collagen diseases or malignant tumors that usually precede them. IBM seems somewhat apart among inflammatory myopathies, being characterised by the association of neurogenic and myogenic features and the presence of vacuoles containing filaments with an accumulation of proteins previously reported in Alzheimer's disease (beta amyloid protein, tau, ubiquitin,.). Inflammation is of various intensity, lacking in familial IBM (hereditary inclusion body myopathy) that otherwise shares the same histologic characteristics as sporadic forms. Other inflammatory muscular diseases: focal myositis, eosinophilic polymyositis, are less frequent. Macrophagic myofasciitis, viral myositis and drug induced myositis are discussed in other articles.     

New classifications and pathophysiology of the inflammatory myopathies

SCOPE: Review on new classifications of myositis linked with their different pathophysiology. CURRENT SITUATION AND SALIENT POINTS: The classification of myositis refined recently, taking into account clinical (such as isolated muscle involvement or not, association with cancer...), immunological (presence or absence of auto-antibodies) and pathological criteria. This new classification has the ability to separate different clinical and physiopathological entities, having actually different prognosis factors. The most common inflammatory myopathies include dermatomyositis (DM), polymyositis (PM), inclusion body myositis (IBM), but also, overlap myositis (defined, among others, by the presence of auto-antibodies), and myositis associated to cancers. These myopathies may be also distinguished by their histological features which also reflect their different underlying pathogeneses. The mechanism of DM is complement-mediated microangiopathy, the inflammatory infiltrate being secondary to ischaemic damage. In PM the muscle fibres are damaged by cytotoxic CD8 T lymphocytes. IBM may be a degenerative disease with accumulation of a variety of proteins within the fibres. The inflammatory infiltrate, which is similar to that seen in PM, may be secondary to accumulated proteins. PERSPECTIVES: These diseases with different pathogeny and prognosis should be treated by specific approaches. That is the reason why we initiated specific clinical trials for respectively inclusion body myositis and overlap myositis.     

Pathogenesis of the idiopathic inflammatory myopathies

The inflammatory myopathies, commonly described as idiopathic, are a group of acquired diseases characterized by an inflammatory infiltrate of the skeletal muscle. On the basis of clinical and immuno-pathological features, three major diseases can be identified: dermatomiositis (DM), polymyositis (PM) and inclusion body myositis (IBM). Immunopathogenesis mechanisms are crucial for discriminating between the three different subsets of inflammatory myopathies. DM is a complement-mediated microangiopathy affecting skin and muscle. PM and IBM are T cell-mediated disorders, where CD8-positive cytotoxic T cells invade muscle fibres expressing MHC class I antigens. This article summarizes the main immunopathological markers. The impact of this new knowledge must be defined in relation to potential therapeutic targets for idiopathic inflammatory myopathies.     

Magnetic resonance imaging criteria for distinguishing between inclusion body myositis and polymyositis

OBJECTIVE: To develop diagnostic imaging criteria for polymyositis (PM) and sporadic inclusion body myositis (sIBM). METHODS: We investigated 220 patients with suspected inflammatory myopathies by magnetic resonance imaging (MRI). Findings were compared with the results of clinical and biological examinations and muscle biopsy. PM and IBM were diagnosed in 25 patients each. Quantitative and qualitative MRI analysis of the 3 muscle groups of the 2 thighs included fatty infiltration, atrophy, inflammation, and the type and distribution of the lesions. RESULTS: MRI was abnormal in all patients. Fatty infiltration and atrophy were more frequent in patients with sIBM (p < 0.05). Inflammation as the sole abnormality was preferentially encountered in PM (p = 0.05). Widespread abnormalities were more frequent in sIBM (p < 0.01). Abnormalities in PM tended to be distributed along the fascia. Involvement of the anterior group, an asymmetrical distribution, and a distal predominance were all more frequent in sIBM (p < 0.001). CONCLUSION: Despite some overlap in MRI findings between the 2 diseases, MRI was useful for distinguishing PM from sIBM.     

Use of muscular MRI in inflammatory myopathies

PURPOSE: Inflammatory myopathies include polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM) which differ in terms of clinical, immuno-histological presentations, evolution and treatment. Diagnosis is based on the muscular biopsy but histological distinction between PM and IBM can be difficult; biopsies can be insufficient as well as during follow-up to detect active areas within the muscle. CURRENT KNOWLEDGE AND KEY POINTS: Muscular MRI is an important tool both in the diagnosis and the follow-up of IMM in the following circumstances: Distinction between PM and IBM: fatty infiltration and involvement of the anterior group of the thighs are characteristic of IBM whereas isolated inflammation and involvement of the three thighs or posterior muscle groups are characteristic of PM. Biopsy guidance on the inflammatory lesions depicted on the STIR sequence either initially or after a non-conclusive biopsy. To differentiate, active disease from steroid myopathy. FUTURE PROSPECTS AND PROJECTS: Several multicentric trials are in development both in spectro and morphologic MRI to study hypoxic phenomenon in early course of IMM and muscular volume evaluation both in normal subjects, congenital or acquired myopathies.     

Anti-PM-Scl antibodies in a patient with inclusion body myositis

SIR, The term inclusion body myositis (IBM) was coined in 1971by Yunis and Samaha [1] to describe a subset of patients withrefractory chronic myositis whose muscle biopsies showed, inaddition to inflammation, abnormal muscle fibers containingvacuoles and characteristic filamentous inclusions in the cytoplasmand nuclei. A sporadic and a hereditary form have been recognized[2]. The cause of sporadic IBM is not known and it is consideredan idiopathic inflammatory myopathy     

Limited effects of high-dose intravenous immunoglobulin (IVIG) treatment on molecular expression in muscle tissue of patients with inflammatory myopathies

OBJECTIVES: The study was conducted with the aim of achieving an improved understanding of the molecular mechanisms of high-dose intravenous immunoglobulin (IVIG) in inflammatory myopathies by investigating the effects on muscle function and immunological molecules in skeletal muscle of polymyositis (PM), dermatomyositis (DM) and inclusion body myositis (IBM) patients. METHODS: Thirteen treatment-resistant patients, 6 PM, 4 DM, 2 IBM and 1 juvenile DM, were treated with 2 g/kg of IVIG, three times at monthly intervals. Functional Index in Myositis and serum creatinine kinase (CK) levels were determined, and muscle biopsies were performed before treatment and after the third IVIG infusion. Immunological molecules were also studied in biopsies taken 24-48 h after the first infusion. RESULTS: Improved muscle function was observed in three patients (1 PM, 1 DM and 1 IBM) and CK levels decreased in five. T cells, macrophages, major histocompatibility complex (MHC) class I antigen on muscle fibres, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression and membranolytic attack complex (MAC) deposits on capillaries were present to an equal degree in biopsies before and after IVIG treatment. No correlation between the clinical response and molecular changes was found. CONCLUSIONS: The clinical effects of high-dose IVIG on muscle function in patients with refractory inflammatory active myositis did not correspond to effects on any of the investigated molecules in our study. T cells, macrophages, phenotypical changes in muscle fibres and endothelial cell activation were still present after treatment. These observations question a role for IVIG as an immune-modulating therapy in patients with inflammatory myopathies.     

Eosinophils in hereditary and inflammatory myopathies

It is not known whether eosinophilic myositis is a specific histopathological feature of limb girdle muscular dystrophy 2A (LGMD2A).Number and location of eosinophils in skeletal muscle biopsies (n=100) was analysed by Giemsa and modified hematoxylin/eosin staining in patients with genetically confirmed myopathies (LGMD2A, LGMD2B, LGMD2L, facioscapulohumeral muscular dystrophy, dystrophinopathy), histologically confirmed idiopathic inflammatory myopathies (sporadic inclusion body myositis (sIBM), dermatomyositis (DM), polymyositis), amyotrophic lateral sclerosis (neurogenic control), and normal controls.The number of eosinophils/mm2 was significantly higher in LGMD2A, PM, DM, and sIBM compared to controls but not significantly higher than other myopathies. A large overlap in the number of eosinophils/mm2 between all groups was seen. In all disease groups eosinophils were mainly found endomysially (46- 88%) and intra- and perivascularly (4-37%). There was no correlation between the numbers of eosinophils/mm2 and (i) age at biopsy and (ii) the duration of the disease. The extent of myopathic, fibrotic, and inflammatory changes did not differ in samples with high and low eosinophil count.Eosinophils seem to represent an unspecific histological finding in hereditary and inflammatory myopathies, but also amyotrophic lateral sclerosis.Key words: Eosinophil, inflammatory myopathy, hereditary myopathy, limb girdle muscular dystrophy, calpainopathy, Giemsa staining, amyotrophic lateral sclerosis     

Muscle biopsy findings in inflammatory myopathies

The inflammatory myopathies encompass a heterogeneous group of acquired muscle diseases characterized clinically, by muscle weakness, and histologically, by inflammatory infiltrates within the skeletal muscles. The group of these myopathies comprise three major and discrete subsets: polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM). Each subset retains its characteristic clinical, immunopathologic, and morphologic features regardless of whether it occurs separately or in connection with other systemic diseases. Although the diagnosis of these disorders is based on the combination of clinical examination, electromyographic data, serum muscle enzyme levels, various autoantibodies, and the muscle biopsy findings, the muscle biopsy offers the most definitive diagnostic information in the majority of the cases. This article summarizes the main histologic features that characterize PM, DM, or IBM and emphasizes the main pitfalls associated with interpretation of the biopsies.     

Utility of magnetic resonance imaging in the evaluation of patients with inflammatory myopathies

Magnetic resonance imaging (MRI) and P-31 magnetic resonance spectroscopy (P-31 MRS) provide unique, quantitative data that cannot be obtained from routine laboratory tests. MRI is the method of choice for imaging of muscle abnormalities. It is also a very sensitive technique for localizing nonhomogenous inflammation in inflammatory myopathies such as dermatomyositis, juvenile dermatomyositis, amyopathic dermatomyositis, polymyositis, and inclusion body myositis. During treatment of inflammatory myopathies, the extent and severity of inflammation may decrease at varying rates, but weakness and fatigue remain serious clinical problems. The metabolic abnormalities detected with P-31 MRS are more persistent and can be used for objective patient evaluation after the disappearance of inflammation and normalization of serum levels of muscle enzymes. With P-31 MRS, biochemical defects are quantitated, including low levels of ATP and phosphocreatine (PCr) and elevated concentrations of ADP and inorganic phosphate (Pi), which may all be related to weakness and fatigue. Thus, MRI and P-31 MRS are useful in assessing the status of patients with inflammatory myopathies during treatment with prednisone and immunosupressive drugs.     

Histological and molecular alterations in inflammatory myopathies

The histological findings in muscle biopsies of inflammatory myopathies have been divided into 2 groups: A) Endomisial infiltrates mainly by T CD8+, CD4+ and macrophages and B) Perivascular infiltrates by CD4+, B cells and macrophages. The first kind of infiltrate suggests an immune reaction against muscle fibers very common in PM and inclusion body myositis, On the other hand the perivascular infiltrate is a hallmark of DM. It has ben shown that autoantigens related with myopathies such as Mi-2, Jo-1, OJ, PL12, Ku, PM/Scl are able to suffer proteolytic cleavage by granzyme B and other stimulus induced by cytotoxic T cells. In this chapter we will review the histological and molecular findings of inflammatory myopathies but we will also discuss a special group of myopathies related to the presence of antibodies against the SRP complex, in particular the SRP72 and SRP54 antibodies, which are associated with a poor prognosis and clinical outcome and present an inadequate response to conventional treatment.     

包涵体肌炎的临床和病理分析

目的探讨包涵体肌炎的临床和病理特点。方法分析20例包涵体肌炎患者的临床、骨骼肌活检组织化学染色及电镜病理特点。结果骨骼肌活检组织化学染色病理特点：肌周膜、肌内膜、血管周围炎性细胞浸润,肌纤维大小不等,散在变性、坏死和再生肌纤维,结缔组织增生,肌纤维内可见边缘空泡,空泡周边淀粉样物质沉积,可伴破碎红纤维、肌纤维类型或分布异常。电镜：肌原纤维结构紊乱,Z线排列不整或消失,肌浆包涵体内可见大量髓磷脂小体和吞噬空泡聚集,周边可见脂滴、糖原颗粒。结论包涵体肌炎临床诊断、鉴别诊断困难,骨骼肌活检病理分析是确诊本病的可靠标准。     

Inclusion body myositis in a patient with long standing rheumatoid arthritis treated with anti-TNFα and rituximab

Adult inflammatory myopathies are rare conditions. Amongst them, inclusion body myositis (IBM) is considered to be the most common acquired myopathy in adults above 50 years of age, follows a slowly progressive course, and ultimately leads to severe disability. The case of a 57-year-old patient with long standing rheumatoid arthritis (RA) who developed muscle wasting and weakness of the quadriceps femoris after initiation of anti-TNFα treatment is presented. Further workup including muscle biopsy revealed IBM. Initiation of rituximab for continuing synovial inflammation led to remission of RA, but no amelioration of muscle weakness was noted. Although cases of IBM in patients with autoimmune disorders have occasionally been reported and are believed to more favourably respond to immunosuppressive treatment, our patient was unresponsive to glucocorticoids. Furthermore, deterioration of muscle strength was noted with both adalimumab and etanercept treatment. Rituximab, not previously used in IBM, successfully controlled RA, but showed no effect on muscle strength. The present case underlines the therapeutic difficulties in IBM and suggests that anti-TNFα therapy might even be deleterious. While an early trial of the lymphocyte-depleting antibody alemtuzumab in IBM showed promising results, selective anti-B-cell-therapy remained without effect in our patient.     

Provision of an explanation for the inefficacy of immunotherapy in sporadic inclusion body myositis: Quantitative assessment of inflammation and β‐amyloid in the muscle

Objective

In sporadic inclusion body myositis (IBM), inflammation and accumulation of β‐amyloid–associated molecules cause muscle fiber damage. We undertook this study to determine why intravenous immunoglobulin (IVIG) and prednisone are not effective in sporadic IBM despite their effectiveness in other inflammatory myopathies.

Methods

Relevant inflammatory and degeneration‐ associated markers were assessed by quantitative polymerase chain reaction and immunohistochemistry in repeated muscle biopsy specimens from patients with sporadic IBM treated in a controlled study with IVIG and prednisone (n = 5) or with prednisone alone (n = 5). Functional effects were assessed in a muscle cell culture model.

Results

In muscle biopsy specimens, messenger RNA (mRNA) expression of the proinflammatory chemokines CXCL9, CCL3, and CCL4 and of the cytokines interferon‐γ (IFNγ), transforming growth factor β, interleukin‐10 (IL‐10), and IL‐1β was significantly reduced after treatment in both groups. No consistent changes were observed for tumor necrosis factor α, IL‐6, inducible costimulator (ICOS), its ligand ICOSL, and perforin. Messenger RNA expression of the degeneration‐associated molecule ubiquitin and the heat‐shock protein αB‐crystallin was also reduced, but no changes were noted for amyloid precursor protein (APP) or desmin. By immunohistochemistry, a significant down‐modulation of chemokines was observed, but not of inducible nitric oxide (NO) synthase, nitrotyrosine, IL‐1β, APP, and ubiquitin; β‐amyloid was reduced in 6 of 10 patients. Pronounced staining of IgG was observed in the muscle after treatment with IVIG, indicating penetration of infused IgG into the muscle and a possible local effect. In muscle cells exposed to IFNγ plus IL‐1β, IgG and/or prednisone down‐regulated mRNA expression of IL‐1β 2.5‐fold. Accumulation of β‐amyloid, overexpression of αB‐crystallin, and cell death were prevented. In contrast, NO‐associated cell stress remained unchanged.

Conclusion

IVIG and prednisone reduce some inflammatory and degenerative molecules in muscle of patients with sporadic IBM and in vitro, but do not sufficiently suppress myotoxic and cell stress mediators such as NO. The data provide an explanation for the resistance of sporadic IBM to immunotherapy and identify markers that may help to design novel treatment strategies.

     

Autoantibodies in Polymyositis and Dermatomyositis

Inflammatory myopathies are a group of acquired diseases, characterized by immunoflogistic processes primarily involving the skeletal muscle. According to recent classification criteria, four major diseases have been identified: polymyositis (PM), dermatomyositis (DM), sporadic inclusion body myositis (IBM), and necrotizing autoimmune myositis (NAM). Autoantibodies can be found in the sera of most patients with myositis. Myositis-specific autoantibodies (MSAs) are markers of very specific disease entities within the spectrum of myositis, and target proteins involved in key processes of protein synthesis. Myositis autoantigens comprise the well-defined aminoacyl-tRNA synthetases, the Mi-2 helicase/histone deacetylase protein complex, and the signal recognition particle (SRP) ribonucleoprotein, together with novel targets such as TIF1-γ, MDA5, NXP2, SAE, and HMGCR. Recent studies suggest that autoantigens drive a B cell antigen-specific immune response in muscles. Interestingly, an increased expression of Jo-1 and Mi-2 in regenerating fibers in muscle biopsies from PM and DM patients compared to normal was demonstrated. Myositis autoantigen up-regulation was observed in neoplastic tissues, thus representing a potential link between cancer and autoimmunity in myositis. Non-immunological mechanisms seem to participate to the pathogenesis of inflammatory myopathies; induction of endoplasmic reticulum stress response in response to abnormal muscle regeneration and inflammation has recently been reported in patients with myositis. This review article provides an update of new emerging insights about the clinical and pathophysiologic role of principal autoantibodies in myositis.     

Myositis: an update on pathogenesis

PURPOSE OF REVIEW: The etiology and much about the pathogenesis of the inflammatory myopathies remain a mystery. In this review, we investigate recent research efforts to understand the pathogenesis of the diverse entities of polymyositis (PM), dermatomyositis (DM), and inclusion body myositis (IBM), diseases that result from interactions between environmental risk factors and genetic susceptibility. RECENT FINDINGS: Over the past year, there has been considerable progress toward better understanding of IBM, with relatively few developments toward understanding PM and DM. Although these diseases may share some common clinical phenotypic and serologic components, they differ on a molecular and cellular level. SUMMARY: The need for definitive, safer therapies in these diseases makes vital the search for defining detailed pathogenesis of inflammation and muscle fiber damage at the molecular level.     

Incidence and prevalence of idiopathic inflammatory myopathies in South Australia: a 30‐year epidemiologic study of histology‐proven cases

Aim: To describe the epidemiology of biopsy‐proven idiopathic inflammatory myopathies (IIM) in South Australia (SA). Methods: Cases of IIM were ascertained by review of all muscle biopsy reports from the Neuropathology Laboratory, Hanson Institute (wherein all adult muscle biopsies in SA are reported) from 1980 to 2009. Clinical correlation of these patients by review of medical records was undertaken. SA population denominator numbers were obtained from the Australian Bureau of Statistics. Results: Three hundred and fifty‐two biopsy‐proven cases of IIM were identified between 1980 and 2009. The overall annual incidence of IIM appeared to be rising with a mean incidence of eight cases per million population (95% CI: 7.2–8.9). This corresponded with an increasing annual incidence of inclusion body myositis (IBM) (prevalence of 50.5 cases per million population in 2009, 95% CI: 40.2–62.7). A female preponderance was noted in both dermatomyositis (DM) (F : M = 2.75 : 1.00) and polymyositis (PM) (F : M = 1.55 : 1.00) but gender distribution was almost equal in IBM (F : M = 1.1 : 1.0). Mean age at diagnosis for IBM (67.5 years) was higher than for DM (55.1 years) and PM (59.0 years). A higher proportion of DM patients reported living in urban dwellings and DM patients tended to be predominantly professionals. Conclusions: In SA there is an increasing incidence of IBM and the prevalence is one of the highest reported to date. This may reflect an increase in the number of biopsies performed, improved histological techniques or a genuine increase in incidence.