Treatment of idiopathic inflammatory myopathies

PURPOSE OF REVIEW: This article reviews the results of recent therapeutic trials in dermatomyositis, polymyositis, and inclusion body myositis and suggests an approach to treating patients with inflammatory myopathy. RECENT FINDINGS: We reviewed 10 double-blind, placebo-controlled therapeutic trials in patients with inflammatory myopathy. Only one, using intravenous immunoglobulin in refractory dermatomyositis, indicated benefit. A brief trial of azathioprine in polymyositis and eight studies using various treatments in inclusion body myositis did not show benefit. SUMMARY: There have been no adequate double-blind, placebo-controlled therapeutic trials of dermatomyositis and polymyositis. It is generally accepted, however, that these disorders respond to immunosuppressive agents. Prednisone is usually the initial treatment. There is no agreement on how prednisone should be administered and even less agreement about other agents. Inclusion body myositis, which now appears to be the most common (in adults), is unresponsive to immunosuppressive and immunomodulating therapies. There are candidate treatments for inclusion body myositis and a need for additional double-blind, placebo-controlled therapeutic trials in all patients with inflammatory myopathy.     

Chemokine-like factor expression in the idiopathic inflammatory myopathies

Objectives –  We evaluated the expression of chemokine-like factor (CKLF) in biopsied muscle fibers in inflammatory myopathies, non-inflammatory myopathies and neurologically diseased controls.
Materials and methods –  We studied the expression of CKLF in 15 polymyositis (PM), five dermatomyositis (DM), 15 non-inflammatory myopathies and nine neurologically diseased patients by immunohistochemistry.
Results –  Chemokine-like factor was mostly expressed in small diameter muscle fibers surrounded by infiltrated lymphocytes of inflammatory myopathies patients. Parts of them were also positive for the staining of the developmental form of myosin heavy chain, a maker of regenerating muscle fibers. Thrombin immunoreactivity was observed in endomysium in PM and perimysium in DM. In vitro differentiation study showed a constitutive expression of CKLF in myoblasts that was abolished in myotubes during differentiation process and was induced again by thrombin. Thrombin regulates CKLF expression through protease-activated receptor-1 in myotubes. Treatment of a protein kinase C inhibitor partially blocked CKLF expression in myoblasts, while it remarkably inhibited that in myotubes.
Conclusion –  Chemokine-like factor expression is differentially regulated in myoblasts and myotubes. Thrombin could be a strong regulator for its expression. As CKLF is immunohistochemically positive in regenerating muscle fibers, we postulate here that CKLF is a useful marker for regenerating muscle fibers in inflammatory myopathies.     

Automatic decomposition electromyography in idiopathic inflammatory myopathies

Automatic decomposition electromyography (ADEMG) is a commercially available software package with installed reference values that enables the objective measurement of motor unit action potentials (MUAPs). To assess the diagnostic yield of this package in idiopathic inflammatory myopathies (IIM) we performed biceps brachii ADEMG in 17 patients with polymyositis, dermatomyositis and inclusion body myositis. Results were compared with those in 12 controls, and with the results of conventional EMG of the biceps and other muscles. Decreased mean values for MUAP duration occurred significantly more frequently in IIM patients than in controls; other MUAP characteristics did not differ. In IIM patients, decreased mean amplitude and increased mean number of turns occurred significantly less frequently on ADEMG than did corresponding abnormalities on conventional biceps EMG. Decreased mean values for duration and amplitude, and increased mean values for number of turns were seen significantly less often on ADEMG than corresponding abnormalities on conventional EMG of four different, individually chosen muscles. Overall evaluation of ADEMG resulted in a diagnosis of possible myopathy in 1 and probable myopathy in 8 patients, whereas overall evaluation of conventional EMG led to a diagnosis suggestive of IIM in 13 patients. We conclude that, although measurement of mean MUAP duration might be valuable in IIM diagnosis, our results do not favour the use of biceps brachii ADEMG and the installed reference values for the diagnosis of IIM. We suggest modifications to improve ADEMG's applicability.     

Beta-chemokine receptor expression in idiopathic inflammatory myopathies

Beta-chemokines attract and activate T cells and monocytes and have a key role in chronic inflammation. Certain beta-chemokines, such as monocyte chemoattractant protein-1 (MCP-1), have been reported to be upregulated in the idiopathic inflammatory myopathies (IIM). We studied the distribution of beta-chemokine receptors in polymyositis (PM), sporadic inclusion-body myositis (sIBM), dermatomyositis (DM), and control samples. CCR1-5 were localized to blood vessels in all samples. In addition, increased endothelial expression of CCR2A was observed in IIM. Subsets of inflammatory cells, identified as macrophages and T cells, in all three types of IIM expressed CCR2A, CCR2B, CCR3, CCR4, and CCR5. In contrast to an earlier report, we found CCR2B to be the most prominent MCP-1 receptor on inflammatory cells in IIM, especially in PM and sIBM. Strong CCR4 expression was present on myonuclei of regenerating muscle fibers. The prominence of the CCR2 receptors further underlines the importance of the interaction with their ligand MCP-1 in the immunopathogenesis of IIM and puts CCR2B forward as a potential target for future therapeutic intervention.     

Increase in transglutaminase 2 in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IMs), including dermatomyositis (DM), polymyositis (PM), and sporadic inclusion body myositis (s-IBM), are characterized by inflammatory cell infiltration in muscle tissue and muscle fiber destruction, which leads to muscle weakness. Although the cause of IMs is unclear, an autoimmune pathogenesis may be involved in initiating the muscle inflammation. Recently, we have found an aberrant expression of transglutaminase 2 (TGase 2) in s-IBM, which is closely associated with insoluble inclusion body formation. TGase 2 is a cross-linking enzyme that generates a conformational change of molecules via a covalent isopeptide bond. The increase in the level of TGase 2 expression and the inappropriate presentation of substrates/cross-linked aggregates to the immune system may contribute to the autoimmune aspects of IMs. We investigated whether or not an increase in TGase 2 expression is a common factor in muscle inflammation. Duchenne muscular dystrophy (DMD) and normal tissues were employed as controls. Using immunocytochemistry and quantitative RT-PCR, the level of TGase 2 expression was found to be specifically increased in PM and DM, but not in DMD and normal controls. Therefore, the targeting of TGase inhibition in IMs will be a challenging therapeutic approach that should be investigated in the near future.     

Local expression of cytokines in idiopathic inflammatory myopathies

H. Lepidi, V. Frances, D. Figarella-Branger, C. Bartoli, A. Machado-Baeta & J-F. Pellissier (1998) Neuropathology and Applied Biology , 24, 73–79
Local expression of cytokines in idiopathic inflammatory myopathies
The idiopathic inflammatory myopathies (IIM), including dermatomyositis (DM), polymyositis (PM), and inclusion body myositis (IBM), are regarded as autoimmune diseases. They are characterized by chronic lymphocytic and macrophagic infiltration in muscle tissue. Of particular importance in understanding the immune response to IIM is the specific pattern of locally produced cytokines. Frozen muscle tissues from IIM (5 DM, 3 PM, and 1 IBM) were used to investigate the cytokine responses. The RT-PCR technique was instrumental to determine the pattern of expression of pro-inflammatory (IL-1β, IL-6, TNF-α), Th1 (IFN-γ IL-2), and Th2 (IL-4) cytokines. Immunohistochemistry was also used to localize morphologically IFN-γ and IL-4. Our results show that pro-inflammatory cytokines and Th1 cytokines are mainly expressed in IIM. The accumulation of mononuclear inflammatory cells and the inflammatory syndrome in IIM are probably related in part to the production of pro-inflammatory cytokines. Moreover, the pattern of local cytokine expression is consistent with a Th1 immune response related to autoimmune diseases.     

Diaphragmatic dysfunction in patients with idiopathic inflammatory myopathies

Polymyositis, dermatopolymyositis, and inclusion body myositis imply chronic inflammation of skeletal muscles. Pulmonary complications include aspiration pneumonia, interstitial pneumonitis, or respiratory muscle myositis. This study aims at better describing their impact on respiratory muscle. Twenty-three consecutive patients (12 PM, 5 DM, 6 IBM) were studied (static inspiratory and expiratory pressures; diaphragm function in terms of the mouth and transdiaphragmatic pressure responses to bilateral phrenic stimulation). Pulmonary parenchymatous abnormalities were mild (6 cases) or absent. The mouth pressure produced by phrenic stimulation was 6.83+/-3.01 cm H2O, with 18 patients (78%) diagnosed with diaphragm weakness (<10 cm H2O) and lower values in DM (4.35+/-1.48 cm H2O) than in IBM and in PM (P<0.05). Diaphragm weakness is frequent and probably overlooked in inflammatory myopathies. Further studies are needed to delineate the clinical relevance of these results.     

Targeted immunotherapy trials for idiopathic inflammatory myopathies

The idiopathic inflammatory myopathies (IIM) are a group of muscle diseases with complex immunopathogenesis that varies between disease subgroups, and possibly between patients within the same subgroup. There exists no universal consensus on optimum management, so that no “standard” therapy has been developed. Treatment-refractive IIM remains a clinical challenge. Progress in the development and application of molecular biology techniques and biological therapeutics are evolving into a new scientific frontier in the management of autoimmune diseases. This review offers an update on those components of the humoral and cellular immunity deemed potential targets for biological therapeutics (monoclonal antibodies and fusion proteins) that have been approved by the US FDA for treatment of immunological disorders. A futuristic approach is envisioned in which each individual will receive targeted therapy tailored to patient-specific immune mechanisms. Risk–benefit and cost analyses should determine whether such targeted therapy is appropriate and feasible for refractive and/or newly diagnosed disease.     

Expression and distribution of the nitric oxide synthases in idiopathic inflammatory myopathies

Different immune effector mechanisms have been characterised in the idiopathic inflammatory myopathies (IIM): in polymyositis (PM) and sporadic inclusion body myositis (sIBM), T-cell-mediated cytotoxicity targets nonnecrotic muscle fibres, whereas in dermatomyositis (DM) the complement-mediated immune response is directed against the microvasculature. As nitric oxide (NO) has an important function in cell signalling and in the cytotoxicity displayed by activated macrophages, it is potentially involved in the immunopathogenesis of IIM. Using immunohistochemical, in situ hybridisation and Western blotting techniques, we visualised the three isoforms of NO synthase (NOS) in muscle tissues from normal controls and from patients diagnosed with IIM. The levels of both constitutive isoforms of NOS (endothelial, i.e., eNOS, and neuronal, i.e., nNOS) were unchanged in IIM as compared with normal muscle. Both protein and mRNA of the inducible form (iNOS) were detected in half of the control biopsies. Constant and increased iNOS protein expression was found in endomysial infiltrates of PM and sIBM, whereas perimysial inflammatory cells in DM were largely negative. We developed a quantitative Western blotting protocol which confirmed the constitutive nature of nNOS and eNOS and the significant induction of iNOS in PM. Our results appoint iNOS with a dual function: a limited and transient role in normal muscle physiology and an active cytotoxic role in PM and sIBM.     

Diagnostic value of MHC class I staining in idiopathic inflammatory myopathies

BACKGROUND: Identification of mononuclear cellular infiltrates in skeletal muscle tissue is the histological cornerstone of the diagnosis of idiopathic inflammatory myopathy (IIM). However, these infiltrates are not always present. OBJECTIVE: To determine whether MHC class I antigen expression on the sarcolemma, which is absent in normal muscle tissue, is upregulated in IIM and could serve as an additional diagnostic test. METHODS: Expression of MHC class I antigens was studied in 224 muscle samples of 61 adult patients with IIM (9 dermatomyositis, 23 polymyositis, 29 inclusion body myositis) and 163 controls (normal subjects and patients with various neuromuscular disorders) in a prospective blinded manner. RESULTS: The sensitivity of the test for diagnosing IIM was 78% (95% confidence interval (CI), 66% to 88%), with a specificity of 95% (91% to 98%). The sensitivity before the start of immunosuppressive treatment was 89% (76% to 96%). The sensitivity was not changed by including all patients who had been on immunosuppressive treatment for less than four weeks before muscle biopsy (sensitivity 90% (79% to 97%)). False positive results were found in only seven controls (4%), six of whom had a muscular dystrophy. CONCLUSIONS: Detection of sarcolemmal MHC class I is a valid test for IIM. It is not affected by the short term use of immunosuppressive agents (less than four weeks) and it should be incorporated in the histological evaluation when the diagnosis of IIM is under consideration or needs to be excluded.     

Distribution of glucocorticoid receptor alpha and beta subtypes in the idiopathic inflammatory myopathies

In contrast with dermatomyositis and polymyositis, inclusion body myositis is unresponsive to glucocorticoid treatment. Glucocorticoid action is mediated through an active glucocorticoid receptor-alpha and negatively regulated by another glucocorticoid receptor isoform. In several autoimmune diseases glucocorticoid receptor-beta up-regulation is involved in glucocorticoid resistance. We studied glucocorticoid receptor distribution in normal and inflammatory myopathy muscle and investigated whether differences in glucocorticoid receptor-alpha and glucocorticoid receptor-beta protein expression are involved in the differential glucocorticoid sensitivity in inclusion body myositis versus polymyositis. Multistep immunofluorescence and Western blotting on fractionated cytoplasmic or nuclear muscle samples were used. Glucocorticoid receptor-alpha was the predominant receptor subtype in muscle and occurred abundantly in myonuclei of control and diseased muscle alike. Glucocorticoid receptor-beta was constitutively expressed on a subset of endothelial cells. No differences between dermatomyositis and the other idiopathic inflammatory myopathies were observed. Increased nuclear glucocorticoid receptor that has dissociated from heat shock protein 90 was found in glucocorticoid treated subjects. Glucocorticoid receptor-alpha and -beta isoform levels were unaltered in muscle tissues from control subjects that had received glucocorticoid treatment prior to biopsy. No differences in relative glucocorticoid receptor-alpha and glucocorticoid receptor-beta protein expression were seen in inclusion body myositis versus polymyositis specimens. Our study indicates that the different glucocorticoid sensitivity in the idiopathic inflammatory myopathies is not related to up- or down-regulation of a given glucocorticoid receptor isoform at the protein level.     

Magnetic resonance imaging of skeletal muscles in idiopathic inflammatory myopathies of adults

The purpose of the study was to describe typical MRI findings in various types of idiopathic inflammatory myopathies in adulthood and to correlate the MRI with histopathological and electromyographic findings, and the serum creatine kinase (CK) activity. A third goal was to assess the diagnostic value of the use of gadolinium-DTPA (Gd-DTPA). Fifty-eight patients (35 women, 23 men), aged 21–83 years (median age 59 years), suffering from idiopathic myositides (13 with acute and 45 chronic diseases; 25 with polymyositis, 14 with dermatomyositis, 8 with granulomatous and 11 with inclusion body myositides) were examined with MRI. Seventeen of them received an intravenous infusion of Gd-DTPA. Histopathological and MRI findings of 21 muscles of 18 patients were compared. MRI of skeletal muscles showed abnormal signal intensities in 56 (96.6%) of the 58 patients. MRI abnormalities were found more often than elevated CK activity (P < 0.001). The hyperintensity of T2-weighted images was more conspicuous than on T1-weighted images in 26 (44.8%) patients, indicating oedema-like abnormalities. MRI of 50 (86.2%) patients showed fat replacement. In acute myositides, oedema-like abnormalities were more often visible and in muscle lipomatosis less often visible than in chronic diseases (P < 0.05 each). In dermatomyositis oedema-like abnormalities were more and lipomatosis less frequent than in the other types of myositis (P < 0.005) and correlated with the acuteness of the disease. In 3 of 17 patients in whom contrast-enhanced T1-weighted images were obtained in addition to plain T1- and T2-weighted images, T2-weighted images were more sensitive in the detection of oedema-like abnormalities than the contrast-enhanced T1-weighted images. In no patient was the opposite true. Thus, contrast-enhanced T1-weighted images did not provide more information than T2-weighted images. Nine patients with poly-, dermato- and inclusion body myositis showed clearly asymmetrical findings. Imaging of the thighs and legs was of similar sensitivity. The different types of myositides showed typical but not specific distributions of the mesenchymal abnormalities in MRI. The findings indicate that MRI of skeletal muscles in myositides can visualize the presence and distribution of oedema-like abnormalities and intramuscular lipomatosis and is suitable for the assessment of the chronicity and severity of the disease.     

Tumor necrosis factor-alpha as a potential therapeutic target in idiopathic inflammatory myopathies

The cytokine, tumor necrosis factor alpha (TNFα), has been implicated in many aspects of immune system development, immune response regulation, and T cell-mediated tissue injury. TNFα plays a less well-defined role in the pathogenesis of the idiopathic inflammatory myopathy (IIM) group of disorders, and has been considered a potential therapeutic target. Observational studies of TNFα-blockade in (mostly refractory) IIM have yielded inconsistent beneficial results so that administration of these biological agents is presently deemed an unreliable alternative treatment strategy. Moreover, anti-TNFα therapy has the rare potential to trigger myositis in patients with rheumatoid arthritis, hinting at a pre-existing “overlap disorder”. The full potential of TNFα-antagonism will be realized only if randomized controlled trials ascertain appropriate treatment regimens and identify patient subgroups most likely to benefit from such therapy.     

Localization of the alpha-chemokine SDF-1 and its receptor CXCR4 in idiopathic inflammatory myopathies

We studied the distribution of stromal cell-derived factor 1 isoforms alpha and beta, and their receptor CXCR4, in polymyositis, sporadic inclusion body myositis and dermatomyositis using in situ hybridization, immunohistochemistry, immunofluorescence and Western blotting. In control muscle, polymyositis and sporadic inclusion body myositis, stromal cell-derived factor-1alpha expression was noted in muscle fibers, while stromal cell-derived factor-1beta and CXCR4 were predominantly localized to capillaries and arterioles. In dermatomyositis, stromal cell-derived factor-1beta immunoreactivity of blood vessels was focally increased. The vast majority of inflammatory cells in idiopathic inflammatory myopathies were CXCR4 positive. A subset of helper T-cells and macrophages expressed stromal cell-derived factor-1alpha, while only rare inflammatory cells expressed stromal cell-derived factor-1beta. A significant increase of stromal cell-derived factor-1alpha and CXCR4 was observed in protein extracts of idiopathic inflammatory myopathies in comparison with normal controls. The abundance of both CXCR4 and its ligand stromal cell-derived factor-1 implicates their interaction in the pathogenesis of idiopathic inflammatory myopathies and identifies these proteins as possible targets for selective immune therapy.     

Myositis specific autoantibodies as a new diagnostic criterion for idiopathic inflammatory myopathies

Myositis specific autoantibodies (MSA) are the most specific diagnostic criteria for idiopathic inflammatory myopathies (IIM). There is no evidence of MSA presence in patients with other neuromuscular or connective tissue diseases. MSA are associated with homogeneous clinical syndromes: antisynthetases with antisynthetase syndrome, anti-SRP with severe, resistant to treatment myositis, anti-Mi-2 with classic, benign dermatomyositis. Therefore it is important to include the myositis specific antibodies into routine diagnostic scheme of IIM.