Pathogenesis


• Abstract 1102: Autoantigen Expression In Regenerating Muscle Cells
• Abstract 1784: Metabolic Muscle Disorders and Cholesterol-Lowering Drugs
• Abstract 102: Role of Signal Recognition Particle (SRP) autoantibodies

Treatment


• Abstract 1785: Impact of Creatine Supplements on Muscle Function
• Abstract 118: Effects of High-Dose Intravenous Immunoglobulin (IVIg) Treatment

Purpose: Because there are distinct clinical phenotypes in systemic autoimmune diseases such as idiopathic inflammatory myopathies (IIM), yet ubiquitous expression of autoantigens, the authors sought to better define the mechanisms underlying the striking association of targets of the immune response with disease phenotype. Perhaps better understanding of these targets can lead to elucidation of relevant pathogenic and therapeutic pathways.

Methods: Autoantigen expression and markers of muscle cell regeneration were analyzed by immunoblotting and immunocytochemistry in muscle biopsies from controls (n=8) or patients with autoimmune myositis (n=15). Autoantigen expression was also evaluated as a function of differentiation of myoblasts into myotubes in vitro.

Results: Myositis autoantigens were examined in equal protein amounts of detergent lysates of human muscle biopsies, and expression was normalized using vinculin as a loading control. Expression levels of Mi-2, U1-70kDa, histidyl-RNA synthetase and DNA-PK_cs were low in control muscle biopsy lysates, but were sharply increased in patients with autoimmune myositis (U1-70kDa: 34 fold, p<0.002; HRS: 4.3 fold, p<0.045 and DNA-PK_cs: 6.9 fold, p<0.006). Additionally, Mi-2 levels were increased exclusively in dermatomyositis (DM) biopsies (mean of 10-fold, p< 0.045), and not in polymyositis (PM) biopsies (1.2 fold, p=0.9). Immunocytochemistry showed that autoantigen levels were highest in cells with the morphologic features of regenerating cells, marked by positive staining for NCAM or neonatal myosin heavy chain. NCAM staining was undetectable by immunoblotting in control biopsies, but was positive in 75% of biopsies from either DM or PM patients (p=0.013; Fishers exact test). Autoantigen expression changed was significantly higher in myoblasts than myotubes during the in vitro differentiation.

Conclusions: Several myositis autoantigens are differentially expressed during muscle cell differentiation, and that such regenerating cells expressing increased autoantigen levels are present in myositis but not in normal muscle. The studies focus attention on the regenerating muscle cell as the source of antigen that supplies the ongoing immune response in myositis.

Editorial comment: This study represents one of the most significant contributions to understanding the pathogenesis of autoimmune myopathies to date. Indeed it helps to explain the puzzling paradox of why there are distinct clinical phenotypes despite ubiquitous autoantigen expression. This study is provocative and may have clinical applicability, as regulating cell differentiation may provide unique therapeutic prospects in autoimmune myositis.

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Abstract 1784: Metabolic Muscle Disorders and Cholesterol-Lowering Drugs
G. Vladutiu, P. Isackson, R. Wortmann

Purpose: The authors in this study hypothesized that the prevalence of combined or single inherited metabolic gene defects is higher than expected from the general population among patients who suffer from statin myopathies. The authors further suggested that because manifesting carriers for metabolic myopathies exist, one would predict that symptoms in carriers may also be triggered by statins.

Methods: In 132 patients with statin myopathies, muscle biopsies (in 105 patients) or whole blood (in 41 patients) were evaluated for enzyme deficiencies or mutations, respectively, which cause common metabolic myopathies. Mutation analyses were performed for carnitine palmitoyltransferase (CPT) II deficiency, myoadenylate deaminase deficiency, and myophosphorylase deficiency. The diagnosis of statin myopathy was determined by the patients physician.

Results: At least one abnormality was found in 36% of patients, and 30% of patients had more than one abnormality. The increase in carrier frequency of myophosphorylase deficiency was 20-fold in patients with statin myopathies compared to normal controls (p<0.0001). Similarly, CPT II deficiency was 11 times higher in statin myopathy patients compared to normal controls (p<0.0001). A 4-fold increase in myoadenylate deaminase deficiency was also observed. Although 75% of patients with a 10-fold elevation of plasma CK had evidence for a defined underlying metabolic myopathy, affected individuals also were found among those with a wide range of CK levels including normal plasma CK. Significant secondary abnormalities were found as well, with over half of muscle biopsies evaluated for CPT II activity demonstrating secondary deficiencies and 31% demonstrating carnitine abnormalities. Correspondingly, lipid storage was present in 1/3 of these.

Conclusions: These data indicate that patients with statin-induced myopathies display an increased risk of having underlying metabolic muscle diseases and, in some cases, carrier status alone appears to add to the increased risk.

Editorial comment: Although the mechanism of statin myopathy is not clearly understood, some investigators speculate that interference with cholesterol metabolism disrupts the mitochondrial membrane, in which cholesterol in a necessary component. As nearly 100 million people worldwide are now taking HMG-coA reductase inhibitors (statins) for lipid lowering and cardio-protection, it is worthwhile knowing what mechanisms contribute to the phenomenon of statin myopathy. This study sheds light on the possible underlying pathogenesis of this problem. Ideally, it would be advantageous to be able to predict which patients will develop statin myopathies and therefore avoid this class of drugs if possible. As for clinical applicability, routine screening for metabolic myopathy carrier status is not cost effective or widely available and may not make sense on a population level.

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Abstract 102: Histopathological Features of Myopathies in Patients with Anti-SRP Autoantibodies
Michito Hirakata, Tetsuya Takada, Akira Suwa, Shinji Sato, Tadayuki Ishihara, Jun Shimizu, John A. Hardin

Purpose: These investigators were interested in further exploring the role of Signal Recognition Particle (SRP) autoantibodies.

Methods: Among 2,700 patients with polymyositis/dermatomyositis and other connective tissue diseases with myositis as a clinical feature, these investigators identified 23 Japanese patients with these antibodies. Anti-SRP antibodies were found using radioimmunoprecipitation assays. Histologic analysis was performed on 12 of these patients muscle biopsies and included alkaline phosphatase, myosin ATPase , and modified Gomori trichrome staining techniques.

Results: 21 patients had an inflammatory myopathy and 43% of these required cytotoxic agents or intravenous immunoglobulin therapy in addition to steroids. The remaining patients in the study had rheumatoid arthritis, two of whom had no clinical features of myositis. Muscle biopsy specimen of twelve patients were examined histologically in detail. All 12 had muscle fiber necrosis and regeneration but only one demonstrated an inflammatory infiltrate.. Six of the 12 (50%) patients showed type I fiber predominance by ATPase staining (a feature related to resistance to steroid treatment).

Conclusion: These studies suggest that anti-SRP autoantibodies are most likely to be associated with myopathies without histopathologic inflammation.

Editorial comment: This study sheds some further evidence that some autoimmune myopathies are not, in fact, associated with inflammation. This may explain why they are often resistant to corticosteroid therapy. The methodology in this study is unclear in that it does elaborate on why only 12 of the 23 patients underwent muscle biopsy. The patient numbers in this study are small; however, anti-SRP antibodies are found in less than 1% of inflammatory myopathy patients. Thus, this study draws attention the emerging opinion that inflammation may in fact be an epiphenomenona in some inflammatory myopathies. Indeed, inflammation may be distinct from the autoimmune processes, including upregulation of Class I MHC and generation of autoantibodies.

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Abstract 1785 Creatine Supplements Improve Idiopathic Inflammatory Myopathy (IIM) in a 6-month Double-Blind, Randomized Placebo-Controlled Trial
H. Alexanderson, N. Pipitone, Y-L Chung, M. Dastmalchi, C. Sthl-Hallengren, S. Richards, C. Morrison, J. Bell, IE Lundberg, DL Scott.

Purpose: The authors sought to test their hypothesis that creatine and exercise are more effective than exercise alone in improving muscle function in idiopathic inflammatory myopathies (IIM). This was a randomized double-blind controlled trial conducted for 6 months at two centers.

Methods: This was a 6- month study with a 1-month observational period followed by 5 months treatment (creatine vs. placebo). Treatment consisted of oral creatine supplements (8 days 20gm/day then 3gm/day) or placebo combined with a home exercise program. The creatine supplements utilized were distributed from a single source and were 99% pure. All study patients had greater than 6 months IIM, stable disease, received steroids with/without cytotoxic drugs and had muscle weakness. They were assessed at baseline and after 1, 3 and 6 months. The two primary outcomes were functional index (FI) and Aggregate functional performance score (AFPT) consisting of four items (50-fet walk, ascending a flight of stairs, timed up and go, and descending a flight of stairs). Manual muscle testing (MMT) was a secondary outcome. Patients at one center also had MR-spectroscopy assessed muscle phospho-creatine and other high-energy phosphate levels.

Results: Of the 60 patients screened, 37 met inclusion criteria and were randomized to creatine (19) vs. placebo (18). Twenty-nine patients completed the trial. Thirty patients were evaluated at 6 months and 37 at 3 months comprising 16 females/ 3 males and 15 females/ 3 males in the creatine/exercise group (CE) and the control group (C) respectively. Mean age was 59 / 50 years (CE/C), mean disease duration was 9.2 / 8.6 years (CE/C). After 6 months there were significant improvements in FI and AFPT in the creatine/exercise group compared to controls (Table 1). The MMT showed significant improvements in the creatine/exercise group by 3 months in right and left shoulder abduction and hip flexion compared to controls (p<0.05). There were significant increases in phosphocreatine/ATP ratios with creatine treatment (p<0.05) but not controls. Creatine supplements were not associated with any clinically relevant adverse events.

Conclusions: Creatine supplements seem to be a safe, effective and inexpensive adjunct to conventional drugs.

Editorial comment: Thus trial is one of the largest 6-month RCTs in IIM to demonstrate that oral creatine supplements combined with home exercises improves muscle strength and function without significant adverse events. The outcome measures in this trial included functional scoring indices; however newer indices defining clinical improvement have recently been published and will most likely be utilized for future clinical trials. It is worth noting that the quality-controlled creatine utilized in this trial may differ from commercially available creatine supplements found in a health-food store in the U.S, as purity cannot be guaranteed. Notably, patients in this study taking creatine did not report an increase in diarrhea or other side effects occasionally reported with creatine supplementation. It appears to be a safe and effective adjunct agent along with traditional therapy and exercise.

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Abstract 118: Limited Effects of High-Dose Intravenous Immunoglobulin (IVIg) Treatment on Clinical Parameters and on Muscle Tissue Characteristics in Patients with Refractory Inflammatory Myopathies
Sevim Barbasso, Maryam Dastmalchi, Helene Alexanderson, Mona Esbjrnsson-Liljedahl, Bjrn Lindvall, Ingrid E. Lundberg

Objective: This study investigated the molecular mechanisms of high-dose intravenous immune globulin (IVIg) treatment in inflammatory myopathies by studying its effect on: muscle function, immunological molecules and fiber type characteristics in skeletal muscle tissue of idiopathic inflammatory myopathy (IIM) patients refractory to traditional immunosuppressive therapy.

Methods: Eleven treatment- resistant patients ( 5 PM, 3 DM, 2 IBM, and 1 JDM) were treated with 2g/kg of IVIg, 3 times with a monthly interval. Assessments were carried out before the first IVIg infusion and 2 weeks after the third IVIg infusion. These included muscle function measured by the Functional Index (FI) in myositis, serum creatinine kinase (CK)-levels and muscle biopsies. Muscle biopsies were evaluated for presence of T cells (CD3), activated macrophages (CD163), major histocompatibility complex (MHC) class I on muscle fibers, expression of intercellular adhesion molecule (ICAM)-1 and the membrane attack complex (MAC) (C5b-9) deposits on capillaries. Fiber-type composition was determined by ATP-ase staining. Clinical improvement was defined as an increase of greater than 15% on the FI.

Results: Clinically relevant improvement was defined as greater than 15% improvement in functional index (FI) observed in 3 patients or 30% decrease in CK levels - a finding observed in 5 of the 9 patients with elevated CK. T cells, macrophages, MHC class I antigen expression on muscle fibers, expression of ICAM-1 and MAC deposits on capillaries were present in all 11 biopsies before and after IVIg treatment. The relative frequency of type I- and type IIA-C fibers showed an inconsistent pattern before and after treatment. Of the 3 patients with clinical improvement, decreased expression of inflammatory cells and ICAM-1 was observed in only one patient. MHC class I antigen presence on muscle fibers was unchanged in all 3 patients who improved, while expression of MAC deposits on capillaries was contradictory.

Conclusions: High-dose IVIg had limited effect on muscle function in patients with active refractory inflammatory myositis. T cells, macrophages, MHC class I antigen on muscle fibers and endothelial cell activation were still present after treatment.

Editorial comment: The authors were unable to confirm the previously reported positive effects of IVIg treatment on clinical parameters or on immunological molecules in skeletal muscle tissue. This study not only investigated clinical improvement but also immunologic effects of IVIg. There was no direct correlation reported between clinical improvement (either by FI or CK scoring) and immunologic changes. One must keep in mind, however, that this population was treatment-resistant at baseline and therefore represents a severe subset of myopathies. Additionally, the pathogenesis of myopathies at the immunologic level, including the role of MHC Class I, is not fully understood.

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