Exploring necrotizing autoimmune myopathies with a novel immunoassay for anti-3-hydroxy-3-methyl-glutaryl-CoA reductase autoantibodies

Emerging mechanisms and therapeutics in inflammatory muscle diseases

Idiopathic inflammatory myopathies (IIMs), or myositis, are rare diseases marked by immune-driven muscle damage and complications like skin lesions and interstitial lung disease (ILD). Despite advances, challenges in diagnosis and treatment persist, particularly in inclusion body myositis (IBM), where no effective therapy exists. Recent breakthroughs, including transcriptomics and insights into antibody-mediated immunity and interferon (IFN) signaling, have clarified IIM pathophysiology and spurred the development of new therapies, such as chimeric antigen receptor (CAR) T cells and Janus kinase (JAK) inhibitors. We explore the latest findings on the mechanisms underlying adult-onset IIMs, emphasizing IBM pathobiology and its unique immune and degenerative pathways, such as a selective type 2 myofiber damage and severe cell stress. Finally, we highlight the recent advances in transcriptomics, single-cell analysis, and machine learning in transforming IIM research by improving diagnostic accuracy, uncovering therapeutic targets, and supporting the development of personalized treatment strategies.

Prevalence and pathogenic activity of anti-desmocollin-3 antibodies in patients with pemphigus vulgaris and pemphigus foliaceus

BACKGROUND

Desmocollin-3 (DSC3) is a calcium-dependent desmosomal cadherin that plays an essential role in cell-cell adhesion. IgG antibodies (Abs) directed against the extracellular (EC) domain of DSC3 have occasionally been detected in rare types of pemphigus. Investigations into the prevalence of anti-EC-DSC3 IgG Abs and those targeting the intracellular (IC) domain of DSC3 in pemphigus vulgaris and pemphigus foliaceus sera, and their potential pathogenic activity, have yielded conflicting results.

OBJECTIVES

To assess the prevalence and pathogenicity of Abs directed against the EC and IC domains of DSC3 in patients with pemphigus.

METHODS

Anti-DSC3 IgG and IgA directed against the EC and IC domains of DSC3 were assayed in 146 patients with pemphigus using a newly developed addressable laser bead immunoassay. The pathogenicity of these autoAbs was first tested in vitro using a keratinocyte dissociation assay with patients' sera or from C57BL/6 mice immunized with recombinant IC-DSC3. In vivo pathogenicity was tested by passive transfer of an anti-IC-DSC3 monoclonal Ab (mAb) derived from a hybridoma (A9) into neonatal mice.

RESULTS

Anti-EC-DSC3 or anti-IC-DSC3 IgG and/or IgA Abs were detected in 21.2% of sera from patients with pemphigus vs. 4.0% (P < 0.001) and 5.0% (P < 0.001) of sera from healthy donors, respectively. Most anti-DSC3 Abs corresponded to IgA. Anti-IC-DSC3 Abs were detected in 44% of patients with pemphigus whose serum anti-desmoglein (DSG) 1-3 Ab profile was inconsistent with their clinical and histological features, according to compensation theory. Anti-IC-DSC3 IgG and IgA Abs induced a dissociation of the keratinocyte monolayer in vitro, which was abolished by preadsorption of these IgG or IgA fractions with recombinant IC-DSC3. In addition, IgG from mice immunized with recombinant IC-DSC3 induced acantholysis in vitro. Finally, in neonatal mice, the passive transfer of an anti-IC-DSC3 mAb in combination with anti-DSG1-3 Abs exacerbated blister formation.

CONCLUSIONS

Our findings suggest that anti-IC-DSC3 Abs are pathogenic and explain the discordance seen in some patients with regard to their clinical phenotype and their anti-DSG1-3 Ab profile.

Immune-mediated necrotizing myopathy: A comprehensive review of the pathogenesis, clinical features, and treatments

Immune-mediated necrotizing myopathy (IMNM) is a rare and newly recognized autoimmune disease within the spectrum of idiopathic inflammatory myopathies. It is characterized by myositis-specific autoantibodies, elevated serum creatine kinase levels, inflammatory infiltrate, and weakness. IMNM can be classified into three subtypes based on the presence or absence of specific autoantibodies: anti-signal recognition particle myositis, anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase myositis, and seronegative IMNM. In recent years, IMNM has gained increasing attention and emerged as a research hotspot. Recent studies have suggested that the pathogenesis of IMNM is linked to aberrant activation of immune system, including immune responses mediated by antibodies, complement, and immune cells, particularly macrophages, as well as abnormal release of inflammatory factors. Non-immune mechanisms such as autophagy and endoplasmic reticulum stress also participate in this process. Additionally, genetic variations associated with IMNM have been identified, providing new insights into the genetic mechanisms of the disease. Progress has also been made in IMNM treatment research, including the use of immunosuppressants and the development of biologics. Despite the challenges in understanding the etiology and treatment of IMNM, the latest research findings offer important guidance and insights for delving deeper into the disease's pathogenic mechanisms and identifying new therapeutic strategies.

Contribution of Complement, Microangiopathy and Inflammation in Idiopathic Inflammatory Myopathies

PURPOSE OF REVIEW

Idiopathic inflammatory myopathies (IIMs) are a heterogeneous group characterized by muscle weakness and skin symptoms and are categorized into six subtypes: dermatomyositis (DM), polymyositis (PM), anti-synthetase syndrome (ASS), immune-mediated myopathy (IMNM), inclusion body myopathy (IBM), and overlap myositis. Myositis-specific autoantibodies were detected for the diagnosis and classification of IIM. This review highlights the pathogenic contributions of the complement system, microangiopathy, and inflammation in IIM.

RECENT FINDINGS

Deposition of complement around capillaries and/or the sarcolemma was observed in muscle biopsy specimens from patients with DM, ASS, and IMNM, suggesting the pathomechanism of complement-dependent muscle and endothelial cell injury. A recent study using human muscle microvascular endothelial cells showed that Jo-1 antibodies from ASS induce complement-dependent cellular cytotoxicity in vitro. Based on both clinical and pathological observations, antibody- and complement-mediated microangiopathy may contribute to the development of DM and anti-Jo-1 ASS. Juvenile DM is characterized by the loss of capillaries, perivascular inflammation, and small-vessel angiopathies, which may be related to microinfarction and perifascicular atrophy. Several serum biomarkers that reflect the IFN1 signature and microangiopathy are elevated in patients with DM. The pathological observation of myxovirus resistance protein A (MxA), which suggests a type 1 interferon (IFN1) signature in DM, supports the diagnosis and further understanding of the pathomechanism of IIM. A recent report showed that an increase in triggering receptor expressed on myeloid cells (TREM-1) around perimysial blood vessels and muscles in patients with IIM plays a role in triggering inflammation and promoting the migration of inflammatory cells by secreting proinflammatory cytokines, such as tumor necrosis factor α.

SUMMARY

The deposition of complement in muscles and capillaries is a characteristic feature of DM, ASS, and IMNM. Microangiopathy plays a pathogenic role in DM, possibly resulting in perifascicular atrophy. Further understanding of the detailed pathomechanism regarding complement, microangiopathy, and inflammation may lead to novel therapeutic approaches for IIM.

Anti-HMGCR immune-mediated necrotising myopathy: Addressing the remaining issues

The discovery of autoantibodies directed against the 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) enzyme has defined a sub-set of immune-mediated necrotising myopathy (IMNM) which is strongly associated with exposure to statin medications. Although understanding of anti-HMGCR IMNM has grown considerably with the reporting of multiple cohorts in North America, Europe, Asia and Oceania, there remain many unanswered questions. The true incidence of anti-HMGCR IMNM is not known and heterogeneity of phenotype and treatment response within this autoantibody sub-group is being increasingly recognised. Statin-naïve adults and juvenile patients with anti-HMGCR potentially share characteristics distinct from statin-exposed patients, alluding to unique pathogenesis. Conflicting data exists on whether malignancies are associated with anti-HMGCR and further clarification is required to determine the degree of cancer screening required. Treatment approaches to anti-HMGCR IMNM are heterogeneous but generally highlight the efficacy of intravenous immunoglobulin. Even with multimodal immunosuppression, patients with anti-HMGCR remain prone to relapse, with younger patients generally manifesting more refractory disease. In this Review, we aim to summarise the current literature on anti-HMGCR and discuss the remaining issues.

Efgartigimod restores muscle function in a humanized mouse model of immune-mediated necrotizing myopathy

OBJECTIVE

Immune-mediated necrotizing myopathies (IMNMs) are severe forms of myositis often associated with pathogenic anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies (aAbs). Efgartigimod is an engineered human IgG1 Fc fragment that antagonizes the neonatal Fc receptor (FcRn), thereby preventing recycling and promoting lysosomal degradation of IgG, including aAbs. We evaluated the therapeutic effects of IgG reduction by efgartigimod in a humanized murine model of IMNM.

METHODS

Disease was induced in C5-deficient (C5def) or Rag2-deficient (Rag2-/-) mice receiving co-injections of anti-HMGCR+ IgG from an IMNM patient and human complement. C5def mice were treated in a preventive setting with s.c. injections of efgartigimod and Rag2-/- mice in a curative setting after disease was induced by anti-HMGCR+ IgG injections. Anti-HMGCR aAbs levels were monitored in mouse serum and muscle tissue. Histological analysis was performed on muscle sections. Muscle force was assessed by grip test or measurement of gastrocnemius strength upon electrostimulation.

RESULTS

Administration of efgartigimod rapidly reduced total IgG levels, including the level of pathogenic anti-HMGCR aAbs, in both serum (P < 0.0001) and muscle (P < 0.001). In the preventive setting, efgartigimod prevented myofibre necrosis (P < 0.05), thus precluding loss of muscle strength (P < 0.05). In the therapeutic setting, efgartigimod prevented further necrosis and allowed muscle fibre regeneration (P < 0.05). Hence, muscle strength returned to normal (P < 0.01).

CONCLUSION

Efgartigimod reduces circulating IgG levels, including pathogenic anti-HMGCR+ IgG aAbs, in a humanized mouse model of IMNM, preventing further necrosis and allowing muscle fibre regeneration. These results support investigating the therapeutic efficacy of efgartigimod through a clinical trial in IMNM patients.

Clinical and Radiological Features of Korean Patients With Anti-HMGCR Myopathy

BACKGROUND AND PURPOSE

To understand the characteristics of Korean patients with anti-3-hydroxy-3-methylglutaryl-coenxyme A reductase (HMGCR) myopathy, we measured anti-HMGCR antibodies and analyzed the clinical, radiological, and pathological features of patients with anti-HMGCR myopathy.

METHODS

We measured titers of anti-HMGCR antibodies in the sera of 99 patients with inflammatory myopathy, 36 patients with genetic myopathy, and 63 healthy subjects using an enzyme-linked immunosorbent assay. We tested 16 myositis-specific autoantibodies (MSAs) in all patients with anti-HMGCR myopathy.

RESULTS

Positivity for the anti-HMGCR antibody was observed in 17 (4 males and 13 females) of 99 patients with inflammatory myopathy. The median age at symptom onset was 60 years. Ten (59%) of the patients with anti-HMGCR positivity had taken statins. The titer of anti-HMGCR antibodies was significantly higher in the statin-naïve group (median=230 U/mL, interquartile range=170-443 U/mL) than in the statin-exposed group (median=178 U/mL, interquartile range=105-210 U/mL, p=0.045). The most common symptom was proximal muscle weakness in 15 patients (88%), followed by myalgia in 9 (53%), neck weakness in 4 (24%), dysphagia in 3 (18%), and skin lesions in 2 (12%). The median titer of anti-HMGCR antibody was 202 U/mL. We found eight different MSAs in nine (53%) patients. The median disease duration from symptom onset to diagnosis was significantly shorter in the MSA-positive group than in the MSA-negative group (p=0.027).

CONCLUSIONS

Our study was the first to measure anti-HMGCR antibodies in inflammatory myopathy. It has provided new findings, including the suggestion of the coexistence of other MSAs in Korean patients.

Identification of Feature Genes and Key Biological Pathways in Immune-Mediated Necrotizing Myopathy: High-Throughput Sequencing and Bioinformatics Analysis

Background

Immune-mediated necrotizing myopathy (IMNM), a subgroup of idiopathic inflammatory myopathies (IIMs), is characterized by severe proximal muscle weakness and prominent necrotic fibers but no infiltration of inflammatory cells. IMNM pathogenesis is unclear. This study investigated key biomarkers and potential pathways for IMNM using high-throughput sequencing and bioinformatics technology.

Methods

RNA sequencing was conducted in 18 IMNM patients and 10 controls. A combination of weighted gene coexpression network analysis (WGCNA) and differentially expressed gene (DEG) analysis was conducted to identify IMNM-related DEGs. Feature genes were screened out by employing the protein-protein interaction (PPI) network, support vector machine-recursive feature elimination (SVM-RFE), and least absolute shrinkage selection operator (LASSO). Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to verify their differential expression, and the receiver operating characteristic curve (ROC) was used to evaluate their diagnostic efficiency. Functional enrichment analysis was applied to reveal the hidden functions of feature genes. Furthermore, 28 immune cell abundance patterns in IMNM samples were measured.

Results

We identified 193 IMNM-related DEGs that were aberrantly upregulated in the IMNM population and were closely associated with immune-inflammatory responses, regulation of skeletal and cardiac muscle contraction, and lipoprotein metabolism. With the help of the PPI network and the LASSO and SVM-RFE algorithms, three feature genes, LTK, MYBPH, and MYL4, were identified and further confirmed by qRT-PCR. ROC curves among IMNM, dermatomyositis (DM), inclusion body myositis (IBM), and polymyositis (PM) samples validated the LTK and MYL4 genes as IMNM-specific feature markers. In addition, all three genes had a notable association with the autophagy-lysosome pathway and immune-inflammatory responses. Ultimately, IMNM displayed a marked immune-cell infiltrative microenvironment. The most significant correlation was found between CD4 T cells, CD8 T cells, macrophages, natural killer (NK) cells, and dendritic cells (DCs).

Conclusions

LTK, MYBPH, and MYL4 were identified as potential key molecules for IMNM and are believed to play a role in the autophagy-lysosome pathway and muscle inflammation.

Prevention of Anti-HMGCR Immune-Mediated Necrotising Myopathy by C5 Complement Inhibition in a Humanised Mouse Model

Introduction: immune-mediated necrotising myopathy (IMNM) is associated with pathogenic anti-signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibodies, at least partly through activation of the classical pathway of the complement. We evaluated zilucoplan, an investigational drug, and a macrocyclic peptide inhibitor of complement component 5 (C5), in humanized mouse models of IMNM. Methods: purified immunoglobulin G (IgG) from an anti-HMGCR+ IMNM patient was co-injected intraperitoneally with human complement in C57BL/6, C5-deficient B10 (C5def) and Rag2 deficient (Rag2−/−) mice. Zilucoplan was administered subcutaneously in a preventive or interventional paradigm, either injected daily throughout the duration of the experiment in C57BL/6 and C5def mice or 8 days after disease induction in Rag2−/− mice. Results: prophylactic administration of zilucoplan prevented muscle strength loss in C5def mice (anti-HMGCR+ vs. anti-HMGCR+ + zilucoplan: p = 0.0289; control vs. anti-HMGCR+ + zilucoplan: p = 0.4634) and wild-type C57BL/6 (anti-HMGCR+ vs. anti-HMGCR+ + zilucoplan: p = 0.0002; control vs. anti-HMGCR+ + zilucoplan: p = 0.0939) with corresponding reduction in C5b-9 deposits on myofibres and number of regenerated myofibres. Interventional treatment of zilucoplan after disease induction reduced the complement deposits and number of regenerated myofibres in muscles of Rag2−/− mice, although to a lesser extent. In this latter setting, C5 inhibition did not significantly ameliorate muscle strength. Conclusion: Early administration of zilucoplan prevents the onset of myopathy at the clinical and histological level in a humanized mouse model of IMNM.

Beyond Systemic Lupus Erythematosus and Anti-Phospholipid Syndrome: The Relevance of Complement From Pathogenesis to Pregnancy Outcome in Other Systemic Rheumatologic Diseases

Evidence about the relevance of the complement system, a highly conserved constituent of the innate immunity response that orchestrates the elimination of pathogens and the inflammatory processes, has been recently accumulated in many different rheumatologic conditions. In rheumatoid arthritis, complement, mainly the classical pathway, contributes to tissue damage especially in seropositive subjects, with complement activation occurring in the joint. Data about complement pathways in psoriatic arthritis are dated and poorly consistent; among patients with Sjögren syndrome, hypocomplementemia exerts a prognostic role, identifying patients at risk of extra-glandular manifestations. Hints about complement involvement in systemic sclerosis have been recently raised, following the evidence of complement deposition in affected skin and in renal samples from patients with scleroderma renal crisis. In vasculitides, complement plays a dual role: on one hand, stimulation of neutrophils with anti-neutrophil cytoplasmic antibodies (ANCA) results in the activation of the alternative pathway, on the other, C5a induces translocation of ANCA antigens, favouring the detrimental role of antibodies. Complement deposition in the kidneys identifies patients with more aggressive renal disease; patients with active disease display low serum levels of C3 and C4. Even though in dermatomyositis sC5b-9 deposits are invariably present in affected muscles, data on C3 and C4 fluctuation during disease course are scarce. C3 and C1q serum levels have been explored as potential markers of disease activity in Takayasu arteritis, whereas data in Behçet disease are limited to in vitro observations. Pregnancies in women with rheumatologic conditions are still burdened by a higher rate of pregnancy complications, thus the early identification of women at risk would be invaluable. A fine-tuning of complement activation is required from a physiological progression of pregnancy, from pre-implantation stages, through placentation to labour. Complement deregulation has been implicated in several pregnancy complications, such as recurrent abortion, eclampsia and premature birth; low complement levels have been shown to reliably identify women at risk of complications. Given its physiologic role in orchestrating pregnancy progression and its involvement as pathogenic effector in several rheumatologic conditions, complement system is an attractive candidate biomarker to stratify the obstetric risk among women with rheumatologic conditions.

Anti-HMGCR myopathy overlaps with dermatomyositis-like rash: a distinct subtype of idiopathic inflammatory myopathy

OBJECTIVE

To characterize the clinical and pathological features of anti-HMGCR myopathy.

METHODS

The presence of anti-HMGCR antibody in the serum of 227 patients with idiopathic inflammatory myopathy (IIM) and 100 healthy control individuals was assessed by ELISA. All ELISA positive samples were retested by indirect immunofluorescence assay (IIFA) on HEK293 cells. The clinical findings, muscle pathological features, and treatment outcomes of patients with anti-HMGCR myopathy, along with comparisons between anti-HMGCR myopathy with and without dermatomyositis (DM)-like skin rashes, and among MSA-based subgroups were analyzed.

RESULTS

We established an optimized ELISA cutoff for anti-HMGCR antibody positivity as ≥ 5.28 U. The overall concordance between ELISA and IIFA was 96.83%. Twenty-one out of 227 IIM patients were anti-HMGCR-positive by both assays. Of these 21 patients, 9 had DM-like skin rashes, and 16 showed remarkable muscle inflammation; 5 patients were juvenile-onset, and 2 received statin treatment. The muscle biopsies from these patients demonstrated variable muscle necrosis and T cell infiltration. Most anti-HMGCR-positive patients achieved favorable outcomes following prednisone and additional immunotherapies. The anti-HMGCR myopathy patients with DM-like rashes, compared to those without DM-like rashes, were younger and had a shorter disease duration.

CONCLUSIONS

Optimization of cutoff of anti-HMGCR antibody assays with confirmation by alternative assays can result in higher sensitivity and specificity. DM-like skin rashes and lymphocytic infiltrates were not rare in patients with anti-HMGCR myopathy. These findings suggest that while anti-HMGCR myopathy may overlap with DM-like rash, it is pathologically different from classic DM, and should be considered a distinct subgroup of IIM.

Myositis-Specific Antibodies and Myositis-Associated Antibodies in Patients With Idiopathic Inflammatory Myopathies From the PANLAR Myositis Study Group

BACKGROUND

Dermatomyositis (DM) and polymyositis (PM) are forms of idiopathic inflammatory myopathies (IIMs), which are associated with the production of autoantibodies that are useful in the diagnosis and prognosis of the disease.

OBJECTIVE

The aim of this study was to determine the frequency of antinuclear autoantibodies (ANAs), myositis-specific autoantibodies (MSAs), and myositis-associated autoantibodies (MAAs) in 6 Latin American countries.

METHODS

Two hundred ten patients with IIM were included in this cross-sectional study from 2014 to 2017: 112 from Mexico, 46 from Colombia, 20 from Peru, 16 from the Dominican Republic, 10 from Argentina, and 6 from Guatemala. Antinuclear autoantibodies were detected by indirect immunofluorescence on HEp-2 cells. MSAs and MAAs were tested by a line immunoassay method. Mann-Whitney U and χ2 tests were used for statistical analysis.

RESULTS

Of the 210 IIM patients, 139 (66.2%) had DM, 59 (28%) PM, and 12 (5.7%) juvenile DM. The mean age was 43.5 (6-79 years); 158 (75.2%) were female, and 52 (24.8%) were male. The overall frequency of ANA was 60%. The most frequent patterns were fine speckled (AC-4) (78.3%) and cytoplasmic (AC-19) (6.45%). The most frequent MSA were anti-Mi-2 (38.5%) and anti-Jo-1 (11.9%). Anti-Mi-2 was more frequent in patients from Colombia (40.1%). The MAA more frequent were anti-Ro-52/TRIM21 (17.6%) and anti-PM-Scl75 (7.5%).

CONCLUSIONS

This is the first study of ANA, MSA, and MAA in patients from 6 countries from the Panamerican League against Rheumatism myositis study group. We observed a general prevalence of 60% of ANA. In relation to MSA and MAA, anti-Mi-2 was the more frequent (38.5%).

Anti-HMGCR myopathy: clinical and histopathological features, and prognosis

PURPOSE OF REVIEW

This review aims to describe clinical and pathological features, prognosis and treatment in patients with anti-HMGCR antibody positive immune-mediated necrotizing myopathy (HMGCR-IMNM) based on recent findings.

RECENT FINDINGS

Using advances in diagnostic modalities that can confirm the presence of anti-HMGCR antibody, the clinical and pathological manifestations of HMGCR-IMNM were found to be broader than previously reported. Although only a small percentage of HMGCR-IMNM patients present with atypical manifestations, some of these patients show slow disease progression and clinical symptoms, which are similar to those of limb-girdle muscular dystrophies. Other atypical HMGCR-IMNM patients have skin conditions similar to dermatomyositis-like skin rush or dermatological presentations of Jessner-Kanoff disease or cutaneous lymphoma, whose pathological changes including CD8-positive and bcl-2-positive lymphocytic accumulations, similar to Jessner-Kanoff lymphocytic infiltration of skin or low-grade cutaneous lymphoma, which are observed in muscle and skin.

SUMMARY

Anti-HMGCR autoantibodies define unique populations of IMNM patients. Recent studies have revealed that clinicopathological manifestations of HMGCR-IMNM, especially extramuscular symptoms and pathological manifestations, are more common than previously recognized.

Immune-mediated necrotizing myopathy: clinical features and pathogenesis

Immune-mediated necrotizing myopathy (IMNM) is a group of inflammatory myopathies that was distinguished from polymyositis in 2004. Most IMNMs are associated with anti-signal recognition particle (anti-SRP) or anti-3-hydroxy-3-methylglutaryl-coA reductase (anti-HMGCR) myositis-specific autoantibodies, although ~20% of patients with IMNM remain seronegative. These associations have led to three subclasses of IMNM: anti-SRP-positive IMNM, anti-HMGCR-positive IMNM and seronegative IMNM. IMNMs are frequently rapidly progressive and severe, displaying high serum creatine kinase levels, and failure to treat IMNMs effectively may lead to severe muscle impairment. In patients with seronegative IMNM, disease can be concomitant with cancer. Research into IMNM pathogenesis has shown that anti-SRP and anti-HMGCR autoantibodies cause weakness and myofibre necrosis in mice, suggesting that, as well as being diagnostic biomarkers of IMNM, they may play a key role in disease pathogenesis. Therapeutically, treatments such as rituximab or intravenous immunoglobulins can now be discussed for IMNM, and targeted therapies, such as anticomplement therapeutics, may be a future option for patients with refractory disease.

Recovery from hypoxemia and Hypercapnia following noninvasive pressure support ventilation in a patient with statin-associated necrotizing myopathy: a case report

Background

Statin-associated necrotizing myopathy (SANM) is a rare autoimmune disorder caused by administration of statins. SANM is characterized by weakness due to necrosis and regeneration of myofibers. Here we report the first case of SANM with acute respiratory failure treated with noninvasive pressure support ventilation in addition to immunosuppressants.

Case presentation

A 59-year-old woman who had been treated with 2.5 mg/day of rosuvastatin calcium for 5 years stopped taking the drug 4 months before admission to our hospital due to elevation of creatine kinase (CK). Withdrawal of rosuvastatin for 1 month did not decrease the level of CK, and she was admitted to our hospital due to the development of muscle weakness of her neck and bilateral upper extremities. Anti-3-hydroxy-3-methylglutaryl coenzyme A reductase antibodies were positive. Magnetic resonance imaging showed myositis, and muscle biopsy from the right biceps brachii muscle showed muscle fiber necrosis and regeneration without inflammatory cell infiltration, suggesting SANM. After the diagnosis, she received methylprednisolone pulse therapy (mPSL, 1 g/day × 3 days, twice) and subsequent oral prednisolone therapy (PSL, 30 mg/day for 1 month, 25 mg/day for 1 month and 22.5 mg/day for 1 month), leading to improvement of her muscle weakness. One month after the PSL tapering to 20 mg/day, her muscle weakness deteriorated with oxygen desaturation (SpO2: 93% at room air) due to hypoventilation caused by weakness of respiratory muscles. BIPAP was used for the management of acute respiratory failure in combination with IVIG (20 g/day × 5 days) followed by mPSL pulse therapy (1 g/day × 3 days), oral PSL (30 mg/day × 3 weeks, then tapered to 25 mg/day) and tacrolimus (3 mg/day). Twenty-seven days after the start of BIPAP, she was weaned from BIPAP with improvement of muscle weakness, hypoxemia and hypercapnia. After she achieved remission with improvement of muscle weakness and reduction of serum CK level to a normal level, the dose of oral prednisolone was gradually tapered to 12.5 mg/day without relapse for 3 months.

Conclusions

Our report provides new insights into the role of immunosuppressants and biphasic positive airway pressure for induction of remission in patients with SANM.

Statin-Associated Autoimmune Myopathy: Current Perspectives

Although generally well tolerated, statin users frequently report muscle-related side effects, ranging from self-limiting myalgias to rhabdomyolysis or the rare clinical entity of statin-associated immune-mediated necrotizing myopathy (IMNM). Statin-associated IMNM is based on the development of autoantibodies against 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), the rate-limiting enzyme in cholesterol synthesis and the pharmacologic target of statins, and leads to a necrotizing myopathy requiring immunosuppressive therapy. This review attempts to recapitulate the diverse aspects of anti-HMGCR IMNM, including clinical presentation, diagnostic modalities, genetic risk associations, therapeutic options and potential pathogenetic pathways.

Severe axial and pelvifemoral muscle damage in immune-mediated necrotizing myopathy evaluated by whole-body MRI

BACKGROUND

Our objective was to define the pattern and severity of muscle damage in immune-mediated necrotizing myopathy (IMNM) and its relationship with clinical and serological features.

METHODS

IMNM patients with a whole-body MRI (n=42) were included and compared to sporadic inclusion-body myositis (s-IBM) patients (n=60). Fat replacement was estimated using the Mercuri score in 55 muscles. Overall lesion load was defined as the sum of all abnormal Mercuri scores (reported in % maximal score) and lesion load quotient was defined as the overall lesion load divided by disease duration. Linear relationships between variables were assessed and multidimensional analysis was performed to define homogenous groups of patients.

RESULTS

IMNM patients were aged 48.1±15.8 years and had a disease duration of 9.8±8.1 years. Most severely affected muscle groups were located in the pelvifemoral and lumbar region. Unsupervised analysis showed two subgroups of patients: one with mild lesion load (15±10%, n=32/42) and another with severe lesion load (60±10%, n=10/42: p<0.001) associated with a mean disease duration of 6.8±6.0 years and 19.5±5.7 years, respectively (p<0.0001). Correlational studies confirmed that disease duration was the most important predictor of muscle damage. Multivariate analyses demonstrated a more severe involvement in select muscle groups in females and seropositive patients. No difference was found in overall lesion load quotient of IMNM compared to IBM (p=0.07) but with a distinct muscle pattern.

CONCLUSION

IMNM is associated with severe axial and pelvifemoral muscle damage. Disease duration is an important predictor of muscle damage. IMNM and s-IBM patients have a comparable damage burden.

Development of a New Classification System for Idiopathic Inflammatory Myopathies Based on Clinical Manifestations and Myositis-Specific Autoantibodies

Importance

Idiopathic inflammatory myopathies are heterogeneous in their pathophysiologic features and prognosis. The emergence of myositis-specific autoantibodies suggests that subgroups of patients exist.

Objective

To develop a new classification scheme for idiopathic inflammatory myopathies based on phenotypic, biological, and immunologic criteria.

Design, Setting, and Participants

An observational, retrospective cohort study was performed using a database of the French myositis network. Patients identified from referral centers for neuromuscular diseases were included from January 1, 2003, to February 1, 2016. Of 445 initial patients, 185 patients were excluded and 260 adult patients with myositis who had complete data and defined historical classifications for polymyositis, dermatomyositis, and inclusion body myositis were enrolled. All patients were tested for anti-histidyl-ARN-t- synthetase (Jo1), anti-threonine-ARN-t-synthetase (PL7), anti-alanine-ARN-t-synthetase (PL12), anti-complex nucleosome remodeling histone deacetylase (Mi2), anti-Ku, anti-polymyositis/systemic scleroderma (PMScl), anti-topoisomerase 1 (Scl70), and anti-signal recognition particle (SRP) antibodies. A total of 708 variables were collected per patient (eg, cancer, lung involvement, and myositis-specific antibodies).

Main Outcomes and Measures

Unsupervised multiple correspondence analysis and hierarchical clustering analysis to aggregate patients in subgroups.

Results

Among 260 participants (163 [62.7%] women; mean age, 59.7 years; median age [range], 61.5 years [48-71 years]), 4 clusters of patients emerged. Cluster 1 (n = 77) included patients who were male, white, and older than 60 years and had finger flexor and quadriceps weakness and findings of vacuolated fibers and mitochondrial abnormalities. Cluster 1 regrouped patients who had inclusion body myositis (72 of 77 patients [93.5%]; 95% CI, 85.5%-97.8%; P < .001). Cluster 2 (n = 91) regrouped patients who were women and had high creatine phosphokinase levels, necrosis without inflammation, and anti-SRP or anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibodies corresponding to immune-mediated necrotizing myopathy (53 of 91 [58.2%]; 95% CI, 47.4%-68.5%; P < .001). Cluster 3 (n = 52) regrouped patients who had dermatomyositis rash and anti-Mi2, anti-melanoma differentiation-associated protein 5 (MDA5), or anti-transcription intermediary factor-1γ (TIF1γ) antibodies, mainly corresponding with patients who had dermatomyositis (43 of 52 [82.7%]; 95% CI, 69.7%-91.8%; P < .001). Cluster 4 (n = 40) was defined by the presence of anti-Jo1 or anti-PL7 antibodies corresponding to antisynthetase syndrome (36 of 40 [90.0%]; 95% CI, 76.3%-97.2%; P < .001). The classification of an independent cohort (n = 50) confirmed the 4 clusters (Cohen κ light, 0.8; 95% CI, 0.6-0.9).

Conclusions and Relevance

These findings suggest a classification of idiopathic inflammatory myopathies with 4 subgroups: dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy, and antisynthetase syndrome. This classification system suggests that a targeted clinical-serologic approach for identifying idiopathic inflammatory myopathies may be warranted.

Peculiar clinicopathological features of immune-mediated necrotizing myopathies

PURPOSE OF REVIEW

In the past decade, immune-mediated necrotizing myopathies have emerged as a separate entity in the heterogenous group of autoimmune myopathies. This group is characterized by clinical manifestations restricted to the muscle tissue, and until recently, the definition was based on muscular pathological features.

RECENT FINDINGS

It was shown that they are the most severe autoimmune myopathies in term of muscle damages. They have been associated with two myositis-specific antibodies: either anti-signal recognition particle (anti-SRP) or anti-hydroxy-3-methylglutaryl-CoA reductase (anti-HMGCR) antibodies. These two antibodies are now considered as immune-mediated necrotizing myopathy (IMNM) diagnostic criteria. Each antibody delineates a homogenous subgroup of IMNM patients in terms of severity and IMNM without myositis-specific antibodies have a high risk of malignancy. In addition, pathological observations as well as in-vitro experiments suggest the pathogenic role of anti-SRP and anti-HMGCR antibodies.

SUMMARY

IMNM are muscle-specific autoimmune diseases associated with a severe weakness and a risk poor muscle strength recovery. Anti-SRP and anti-HMGCR antibodies are specifically associated with this condition and are crucial for the diagnosis and the prognosis. The muscle biopsy remains necessary for IMNM diagnosis in absence of myositis-specific antibodies.

Myositis-specific autoantibodies, a cornerstone in immune-mediated necrotizing myopathy

Over the past few years, myositis-specific autoantibodies played an increasing role in the inflammatory idiopathic myositis definition. They became the critical immunological marker for immune-mediated necrotizing myopathy diagnosis (IMNM) since the paradigm switch from histological to serological criteria. This review is focused on the key role of the anti-signal recognition particle (anti-SRP) and the anti-3-Hydroxy-3-MethylGlutaryl-Coenzyme A Reductase (anti-HMGCR) antibodies in immune-mediated necrotizing myopathy. Anti-SRP and anti-HMGCR antibodies are robust diagnostic tools in case of both the classical subacute form and the slowly progressive form of IMNM that may mimic muscular dystrophy. Anti-SRP and anti-HMGCR patients share clinical, biological and histological features with some antibody-associated specificity. Anti-SRP patients harbour more severe muscle weakness and atrophy with severe muscle damage on magnetic resonance imaging study. Approximately 10-20% of anti-SRP patients develop extramuscular symptoms, especially lung interstitial disease. Conversely, anti-HMGCR patients are often associated with statin exposure. In both cases, patients have a poor outcome with frequent relapse and the use of combined immunotherapy. Of note, various data suggest a direct pathogenic role of these antibodies reinforcing the interest in targeted therapeutic strategy.

In vivo pathogenicity of IgG from patients with anti-SRP or anti-HMGCR autoantibodies in immune-mediated necrotising myopathy

OBJECTIVES

In autoimmunity, autoantibodies (aAb) may be simple biomarkers of disease or true pathogenic effectors. A form of idiopathic inflammatory myopathy associated with anti-signal recognition particle (SRP) or anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) aAb has been individualised and is referred to as immune-mediated necrotising myopathy (IMNM). The level of aAb correlates with IMNM activity and disease may respond to immunosuppression, suggesting that they are pathogenic. We aimed to evaluate the pathogenicity of IgG from patients with anti-SRP or anti-HMGCR aAb in vivo by developing the first mouse model of IMNM.

METHODS

IgG from patients suffering from anti-SRP or anti-HMGCR associated IMNM were passively transferred to wild-type, Rag2-/- or complement C3-/- mice. Muscle deficiency was evaluated by muscle strength on electrostimulation and grip test. Histological analyses were performed after haematoxylin/eosin staining or by immunofluorescence or immunohistochemistry analysis. Antibody levels were quantified by addressable laser bead assay (ALBIA).

RESULTS

Passive transfer of IgG from patients suffering from IMNM to C57BL/6 or Rag2-/- mice provoked muscle deficiency. Pathogenicity of aAb was reduced in C3-/- mice while increased by supplementation with human complement. Breakage of tolerance by active immunisation with SRP or HMGCR provoked disease.

CONCLUSION

This study demonstrates that patient-derived anti-SRP+ and anti-HMGCR+ IgG are pathogenic towards muscle in vivo through a complement-mediated mechanism, definitively establishing the autoimmune character of IMNM. These data support the use of plasma exchanges and argue for evaluating complement-targeting therapies in IMNM.

Anti-HMGCR myopathy may resemble limb-girdle muscular dystrophy

Objective

To determine the prevalence and clinical features of anti-HMGCR myopathy among patients with presumed limb-girdle muscular dystrophy (LGMD) in whom genetic testing has failed to elucidate causative mutations.

Methods

Patients with presumed LGMD and unrevealing genetic testing were selected based on a few clinico-pathologic features and tested for anti-HMGCR autoantibodies (n = 11). These clinico-pathologic features are peak creatine kinase (CK) greater than 1,000 IU/L and at least 3 of the following features: (1) limb-girdle pattern of weakness, (2) selective involvement of posterior thigh on clinical examination or muscle imaging, (3) dystrophic changes on muscle biopsy, and (4) no family history of muscular dystrophy.

Results

Six patients tested positive for anti-HMGCR autoantibodies. In 4, there was a presymptomatic phase, lasting as long as 10 years, characterized by elevated CK levels without weakness. Muscle biopsies revealed variable degrees of a dystrophic pathology without prominent inflammation. In an independent cohort of patients with anti-HMGCR myopathy, 17 of 51 (∼33%) patients were initially presumed to have a form of LGMD based on clinico-pathologic features but were ultimately found to have anti-HMGCR myopathy. Most of these patients responded favorably to immunomodulatory therapies, evidenced by reduction of CK levels and improved strength.

Conclusions

Anti-HMGCR myopathy can resemble LGMD. Diagnosis of patients with a LGMD-like presentation of anti-HMGCR myopathy is critical because these patients may respond favorably to immunotherapy, especially those with shorter disease duration.

Coexistence of anti-HMGCR and anti-MDA5 identified by an unlabeled immunoprecipitation assay in a chinese patient cohort with myositis

Myositis-specific autoantibodies are important diagnostic and prognostic markers. The aim of our study is to detect anti-3-hydroxy 3-methylutaryl coenzyme A reductase (anti-HMGCR) antibody using novel unlabeled immunoprecipitation (IP) assay and immunoblotting in Chinese patients with myositis and to clarify the features of anti-HMGCR-positive patients. In the present study, we established novel unlabeled IP assay and immunoblotting of HMGCR C-terminus for anti-HMGCR detection. The presence of anti-HMGCR was screened in 181 Chinese patients with myositis. The sera from 12 of 181 patients were positive for anti-HMGCR. The prevalence of anti-HMGCR autoantibody in our cohorts is about 6.6%. Unexpected, coexistence of anti-HMGCR and anti-melanoma differentiation-associated protein (anti-MDA5) were identified in 4 patients with characteristic rash and interstitial lung disease (ILD), but without myasthenia and elevated serum creatine kinase (CK) levels. Other anti-HMGCR positive patients without anti-MDA5 presented with severe proximal muscle weakness. Mean serum CK levels and lactate dehydrogenase (LDH) were significantly higher in anti-HMGCR-positive patients than in antibody-negative patients (P <.05). Muscle biopsies available from 6 anti-HMGCR-positive patients were characterized with prominent myofiber necrosis and regeneration, little or none of inflammatory cell infiltrates. None of anti-HMGCR positive patients in our cohort was exposed to statins. Our data suggested that anti-HMGCR were found to coexist frequently with anti-MDA5 identified by the established unlabeled IP assay and statin exposure is rare in Chinese myositis patients with anti-HMGCR.

Immune checkpoint inhibitor-related myositis and myocarditis in patients with cancer

OBJECTIVE

To report the clinicopathologic features and outcome of myositis in patients treated with immune checkpoint inhibitors (ICIs) (irMyositis).

METHODS

We retrospectively analyzed patients diagnosed with irMyositis in tertiary centers in Paris, France, and Berlin, Germany, from January 2015 to July 2017. The main outcomes were clinical manifestations and muscle histology, which included major histocompatibility complex class I (MHC-I), C5b-9, CD3, CD4, CD8, CD20, CD68, programmed cell death protein 1 (PD-1), programmed cell death 1 ligand 1 (PD-L) 1, and programmed cell death 1 ligand 2 (PD-L2).

RESULTS

Ten patients with metastatic cancer were included; median age was 73 (range 56-87) years. Median follow-up duration was 48 (range 16-88) weeks. Six patients developed myositis during nivolumab therapy, 1 patient during pembrolizumab, 1 patient during durvalumab, and 2 patients during combined nivolumab and ipilimumab. Median delay between ICI initiation and myositis onset was 25 (range 5-87) days. Clinical manifestations were dominated by acute or subacute myalgia (8 patients) and limb-girdle (7), axial (7), and oculomotor (7) weakness. Four patients had evidence of myocarditis. In all patients, creatine kinase levels were elevated (median 2,668, range 1,059-16,620 U/L), while anti-acetylcholine receptor and myositis-associated antibodies were negative. Electrodiagnostic studies showed myopathic process without decrement in all patients. Muscle biopsy constantly showed multifocal necrotic myofibers, sarcolemmal MHC-I, and endomysial inflammation, consisting mainly of CD68+ cells expressing PD-L1 and CD8+ cells expressing PD-1. ICI treatment was withdrawn in all patients; 9 patients received immunosuppressive therapy, which consistently led to marked clinical improvement.

CONCLUSIONS

irMyositis presents with remarkably homogeneous and unique clinicopathologic features, expanding the nosologic spectrum of inflammatory myopathies in patients with cancer. ICI withdrawal and treatment with corticosteroids improve outcome.

Potential Pathogenic Role of Anti-Signal Recognition Protein and Anti-3-hydroxy-3-methylglutaryl-CoA Reductase Antibodies in Immune-Mediated Necrotizing Myopathies

PURPOSE OF REVIEW

This review provides an overview of the potential pathogenic roles of anti-SRP and anti-HMGCR in IMNM over the past 5 years.

RECENT FINDINGS

Idiopathic inflammatory myopathies (IIM) are a group of acquired autoimmune disorders that mainly affect the skeletal muscle tissue. Classification criteria of IIM are comprised of polymyositis, dermatomyositis, inclusion body myositis and immune-mediated necrotizing myopathies. One important hallmark of autoimmune diseases is the detection of autoantibodies in patient sera. The anti-SRP (signal recognition particle) and anti-HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase) antibodies are specifically associated with IMNM patients, and their detection has been described as related to disease severity. The muscles of IMNM patients are characterized by necrosis, atrophy and regenerating fibres with sparse inflammatory infiltrates. Although an important correlation between autoantibody titres, creatine kinase levels and disease progression/severity has been described in the last few years, the potential pathogenic roles of these autoantibodies have only recently been described.

Necrosis in anti-SRP+ and anti-HMGCR+myopathies

Objective

To characterize muscle fiber necrosis in immune-mediated necrotizing myopathies (IMNM) with anti–signal recognition particle (SRP) or anti–3-hydroxy-3-methylglutarylcoenzyme A reductase (HMGCR) antibodies and to explore its underlying molecular immune mechanisms.

Methods

Muscle biopsies from patients with IMNM were analyzed and compared to biopsies from control patients with myositis. In addition to immunostaining and reverse transcription PCR on muscle samples, in vitro immunostaining on primary muscle cells was performed.

Results

Creatine kinase levels and muscle regeneration correlated with the proportion of necrotic fibers (r = 0.6, p < 0.001). CD68+iNOS+ macrophages and a Th-1 immune environment were chiefly involved in ongoing myophagocytosis of necrotic fibers. T-cell densities correlated with necrosis but no signs of cytotoxicity were detected. Activation of the classical pathway of the complement cascade, accompanied by deposition of sarcolemmal immunoglobulins, featured involvement of humoral immunity. Presence of SRP and HMGCR proteins on altered myofibers was reproduced on myotubes exposed to purified patient-derived autoantibodies. Finally, a correlation between sarcolemmal complement deposits and fiber necrosis was observed (r = 0.4 and p = 0.004). Based on these observations, we propose to update the pathologic criteria of IMNM.

Conclusion

These data further corroborate the pathogenic role of anti-SRP and anti-HMGCR autoantibodies in IMNM, highlighting humoral mechanisms as key players in immunity and myofiber necrosis.

Dermatomyositis and Immune-Mediated Necrotizing Myopathies: A Window on Autoimmunity and Cancer

Autoimmune myopathies (myositides) are strongly associated with malignancy. The link between myositis and cancer, originally noticed by Bohan and Peter in their classification in 1975 (1), has been evidenced by large population-based cohort studies and a recent meta-analysis. The numerous reports of cases in which the clinical course of myositis reflects that of cancer and the short delay between myositis and cancer onset support the notion that myositis may be an authentic paraneoplastic disorder. Thus, cancer-associated myositis raises the question of cancer as a cause rather than a consequence of autoimmunity. Among myositides, dermatomyositis and more recently, although to a lesser extent, immune-mediated necrotizing myopathies are the most documented forms associated with cancer. Interestingly, the current diagnostic approach for myositis is based on the identification of specific antibodies where each antibody determines specific clinical features and outcomes. Recent findings have shown that the autoantibodies anti-TIF1γ, anti-NXP2 and anti-HMGCR are associated with cancers in the course of myositis. Herein, we highlight the fact that the targets of these three autoantibodies involve cellular pathways that intervene in tumor promotion and we discuss the role of cancer mutations as autoimmunity triggers in adult myositis.

Detection of autoantibodies to 3-hydroxy-3-methylglutaryl-coenzyme a reductase by ELISA in a reference laboratory setting

BACKGROUND

We investigated the performance of an ELISA for the detection of 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) IgG antibodies in immune-mediated necrotizing myopathies (IMNM).

METHODS

Patients positive for HMGCR antibodies (n=61) or negative (n=78) by protein immunoprecipitation (IP), and healthy controls (n=100) were used to evaluate the ELISA. Unique consecutive serum samples (n=155) received at ARUP Laboratories for HMGCR IgG testing by ELISA were also investigated and analysed for serum muscle enzymes (aldolase, creatine kinase, and myoglobin). The ELISA's sensitivity, specificity, and percentage agreement were assessed relative to IP. Correlation between specific muscle enzyme concentration and the presence of HMGCR antibody was determined.

RESULTS

Overall agreement between ELISA and IP was 93.4%. Using the IP as reference, the sensitivity and specificity of the ELISA was 95.1%, and 100%, respectively. Inter- and intra-assay coefficient of variation of the ELISA was <10.0%, and ≤15.0%, respectively. In the consecutive cohort, 21 (13.6%) samples tested positive for HMGCR IgG. Concentrations of aldolase, creatine kinase, and myoglobin were significantly higher (all p<0.0001) in patients positive for HMGCR antibodies at the time of evaluation.

CONCLUSIONS

We confirm significant reliability of HMGCR antibodies as measured by the ELISA for the evaluation of IMNM.

Statin-associated immune-mediated myopathy: biology and clinical implications

PURPOSE OF REVIEW

In the last 6 years, our understanding of statin-associated myopathy expanded to include not only a toxic myopathy with limited and reversible side-effects but also an autoimmune variety in which statins likely induce an autoimmune myopathy that is both associated with a specific autoantibody and responsive to immunosuppression and immune modulation. This review widens the reader's understanding of statin myopathy to include an autoimmune process.

RECENT FINDINGS

Statin-associated immune-mediated myopathy provides an example of an environmental trigger (statins) directly implicated in an autoimmune disease associated with a genetic predisposition as well as potential risk factors including concomitant diseases and specific statins. Given a median exposure to statins of 38 months, providers should be aware that anti-3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR) myopathy may occur even after several years of statin exposure.

SUMMARY

It is important for the reader to understand the clinical presentation of statin-associated immune-mediated myopathy and the difference in its clinical presentation to that of statins as direct myotoxins. Prompt recognition of such an entity allows the clinician to immediately stop the offending agent if it has not already been discontinued as well as to recognize that statin rechallenge is not a likely option, and that prompt treatment with immunosuppression and/or immunomodulation is usually of enormous benefit to the patient in restoring muscle strength and physical function. VIDEO ABSTRACT.

A Case of Statin-Associated Autoimmune Myopathy

A 70-year-old previously independent man developed progressive proximal leg weakness resulting in a fall at home suffering traumatic brain injury. He was prescribed a statin medication two years prior, but this was discontinued on admission to the hospital due to concern for statin myopathy. His weakness continued to progress while in acute rehabilitation, along with the development of dysphagia requiring placement of gastrostomy tube and respiratory failure requiring tracheostomy. Corticosteroids and intravenous immunoglobulin were administered without response. Nerve conduction study demonstrated no evidence of neuropathy; electromyography revealed spontaneous activity suggestive of myopathy. A muscle biopsy was performed and demonstrated myonecrosis. Serology was positive for autoantibodies to 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), verifying our diagnosis of statin-associated autoimmune myopathy (SAM). The patient was subsequently treated with rituximab and methotrexate and demonstrated mild clinical improvement. He was eventually liberated from the ventilator. However, later in the course of treatment, he developed respiratory distress and required ventilator support. The patient was discharged to long-term acute care two months after his initial presentation and died due to ventilator-acquired pneumonia three months later. Since their introduction 30 years ago, statin medications have been widely prescribed to prevent cardiovascular diseases. Myalgias and/or myopathic symptoms are among the most recognized side effects of the medication. Statin-associated autoimmune myopathy is a very rare complication of statin use and estimated to affect two to three for every 100,000 patients treated. Clinically, the condition presents as progressive symmetric weakness, muscle enzyme elevations, necrotizing myopathy on muscle biopsy, and the presence of autoantibodies to HMGCR. These findings will often persist and even progress despite discontinuation of the statin. Very few cases of SAM have been described in the literature. Describing this rare condition and the ultimately fatal outcome of our patient, we aim to further understanding of SAM, its presentation and clinical course to promote earlier diagnosis and prompt management.

Immune-mediated necrotizing myopathy

BACKGROUND

Immune-mediated necrotizing myopathy (IMNM) is a newly identified subgroup of idiopathic inflammatory myopathies. It is defined as a rare and severe disease, with symmetrical and proximal muscle weakness and a characteristic histology. An autoimmune aspect of IMNM is suggested by its association with autoantibodies directed against signal recognition particle (SRP) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) in the majority of patients. Statin use is strongly associated with anti-HMGCR-positive IMNM. The pathophysiological mechanisms of this disease are still poorly understood, and as a result, no therapeutic strategy has been validated to date.

OBJECTIVE

The aim of this article is to provide an overview of the current knowledge about epidemiology, clinical features, and pathophysiology of IMNM, as well as treatment strategies.

RESULTS AND CONCLUSION

IMNM is a subject of widespread interest, with quick and meaningful advances being made. In recent years, huge progress has been made in terms of diagnosis and patient management. However, the understanding of pathophysiological mechanisms and treatment strategies still requires further investigation.

Anti-HMGCR antibodies in systemic sclerosis

The objective of this study was to investigate the frequency of autoantibodies to hydroxymethylglutaryl coenzyme A reductase (HMGCR) in systemic sclerosis (SSc) and associations with inflammatory myositis and statin exposure.This was a cross-sectional, multicenter study of 306 subjects from the Canadian Scleroderma Research Group cohort who had complete data on statin exposure and serology for anti-HMGCR antibodies assayed by an addressable laser bead immunoassay (ALBIA). Descriptive statistics were used to summarize the baseline characteristics of the patients and to compare subjects with and without anti-HMGCR antibodies.Four (1.3%) subjects had anti-HMGCR antibodies. None of the subjects with anti-HMGCR antibodies titers had a history of an inflammatory myositis or overlap with polymyositis/dermatomyositis, compared to 8.6% and 2.0% of those without anti-HMGCR antibodies, respectively. In addition, none of the subjects with anti-HMGCR antibodies had past or current exposure to statins compared to 12% of those with negative titers.Anti-HMGCR antibodies are rare in SSc and are not associated with inflammatory myopathy or statin exposure. Larger studies will be required to confirm these preliminary observations. Nevertheless, we conclude that anti-HMGCR antibodies are unlikely to play a major role in inflammatory myopathy in SSc and anti-HMGCR antibodies can be present in subjects without exposure to statins.

Autoimmune Myopathies: Where Do We Stand?

Autoimmune diseases (AIDs) as a whole represent a major health concern and remain a medical and scientific challenge. Some of them, such as multiple sclerosis or type 1 diabetes, have been actively investigated for many decades. Autoimmune myopathies (AIMs), also referred to as idiopathic inflammatory myopathies or myositis, represent a group of very severe AID for which we have a more limited pathophysiological knowledge. AIM encompass a group of, individually rare but collectively not so uncommon, diseases characterized by symmetrical proximal muscle weakness, increased serum muscle enzymes such as creatine kinase, myopathic changes on electromyography, and several typical histological patterns on muscle biopsy, including the presence of inflammatory cell infiltrates in muscle tissue. Importantly, some AIMs are strongly related to cancer. Here, we review the current knowledge on the most prevalent forms of AIM and, notably, the diagnostic contribution of autoantibodies.

High risk of cancer in autoimmune necrotizing myopathies: usefulness of myositis specific antibody

Cancer can occur in patients with inflammatory myopathies. This association is mainly observed in dermatomyositis, and myositis-specific antibodies have allowed us to delineate patients at an increased risk. Malignancy is also reported in patients with necrotizing autoimmune myopathies, but the risk remains elusive. Anti-signal recognition particle or anti-HMGCR antibodies have been specifically associated with necrotizing autoimmune myopathies. We aimed at screening the incidence of cancer in necrotizing autoimmune myopathies. A group of patients (n = 115) with necrotizing autoimmune myopathies with or without myositis-specific antibodies was analysed. Malignancy occurred more frequently in seronegative necrotizing autoimmune myopathies patients and in HMGCR-positive patients compared to anti-signal recognition particle positive patients. Synchronous malignancy was diagnosed in 21.4% and 11.5% of cases, respectively, and incidence of cancer was higher compared to the general population in both groups. No specific type of cancer was predominant. Patients suffering from a synchronous cancer had a decreased median survival time. Cancer screening is necessary in seronegative necrotizing autoimmune myopathies and in HMGCR-positive patients but not in anti-signal recognition particle-positive patients.

Serological subsets of juvenile idiopathic inflammatory myopathies--an update

In this review we explore the different characteristics of the serological phenotypes identified in juvenile-onset myositis and consider how the serological sub-classification of patients with juvenile myositis can be advantageous both in terms of reaching what can be a difficult diagnosis and informing on prognosis. Recent studies have described the autoantibody associated disease phenotypes and outcome for those with juvenile-onset disease and include analyses of large juvenile-onset myositis cohorts. Here we describe the autoantibody associated disease features for patients within juvenile-onset myositis in detail and discuss the expanding opportunities and strategies for myositis specific autoantibody testing in clinical practice.

Clinical Characteristics of Anti-3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Antibodies in Chinese Patients with Idiopathic Inflammatory Myopathies

Objective

The objective of this study was to detect the prevalence of anti-3-hydroxyl-3- methylglutaryl coenzyme A reductase (anti-HMGCR) antibodies in Chinese patients with idiopathic inflammatory myopathies (IIMs), and to analyze the clinical features of the antibody-positive IIM patients.

Methods

The presence of anti-HMGCR antibodies was detected in 405 patients with IIMs, 90 healthy controls, and 221 patients with other rheumatic diseases by using an ELISA kit. Clinical data from anti-HMGCR antibody-positive and -negative patients were compared. Long-term follow-up of the anti-HMGCR antibody-positive patients was conducted to evaluate the role of anti-HMGCR antibody in IIM disease prognosis.

Results

Of the 405 IIM patients, 22 (5.4%) were found to carry the anti-HMGCR antibody. These IIM patients were predominantly female (73%), and only 3 anti-HMGCR antibody-positive patients with IIM were exposure to statins. Most patients experienced progressive onset, and presented with muscular weakness. Dysphagia was observed in half of the patients (p < 0.01), and 15% of these patients experienced the complication of interstitial lung disease (ILD) (p > 0.05). Mean creatine kinase (CK) levels were higher in antibody-positive patients than in antibody-negative patients (p < 0.05). Muscle biopsies were available from 12 anti-HMGCR antibody-positive patients, eight who experienced myofiber necrosis and showed very little or no evidence of inflammatory cell infiltrates in their muscle biopsies. Of these eleven patients who were followed-up 2.5- to 29-month, 73% experienced improvement after treatment. A cross-sectional study showed that anti-HMGCR antibody levels were significantly associated with CK levels (r = 0.486, p = 0.026) as well as with Myositis Disease Activity Assessment (MYOACT) scores (r = -0.67, p = 0.003) during the initial visit. However, changes in serum anti-HMGCR antibody levels did not correlate with changes in CK levels, Manual Muscle Testing 8 (MMT-8) scores or MYOACT scores in long-term follow-up.

Conclusion

The major clinical features of anti-HMGCR antibody-positive Chinese IIM patients were muscle weakness and dysphagia, which were seen in patients with and without statin exposure. This subtype of patients were responsive to immunosuppressive treatment and received good prognoses after treatment, but serum levels of the anti-HMGCR antibody do not correlate with disease activity.

Statins and myositis: the role of anti-HMGCR antibodies

Muscle toxicity is a recognized adverse effect of statin use. Recently, a new myositis syndrome was described in association with antibodies directed against the pharmacologic target of statins, anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR antibody). The patient's genetic background, characteristic histologic patterns (immune-mediated necrotizing myopathy), and presence of anti-HMGCR antibodies define the syndrome. In most patients, statin discontinuation is insufficient to reverse the myositis symptoms, and immunosuppressive therapy is needed. The mechanisms by which these antibodies may lead to disease are not fully elucidated. Several important questions remain unsolved and warrant further research.

Myopathy with anti-HMGCR antibodies: Perimysium and myofiber pathology

Objective:

To analyze clinical features and myopathology changes in muscle fibers, connective tissue, and vessels in 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody–associated myopathies.

Methods:

Retrospective review of records and myopathologic features of 49 consecutive patients with myopathies and serum HMGCR antibodies.

Results:

Clinical features included onset age from 12 to 83 years, female predominance (67%), proximal, symmetric weakness (84%), muscle discomfort (78%), dysphagia (35%), systemic features, including skin rash and interstitial lung disease (37%), statin use (38%), and a high serum creatine kinase (83%). Myopathology included muscle fiber necrosis or regeneration (66%), myonuclear pathology (43%), perimysial connective tissue damage (61%), and lymphocytic foci (27%).

Conclusions:

Patients with HMGCR antibody–associated myopathies present with weakness and muscle discomfort and often have damage to both perimysial connective tissue and muscle fibers, with necrosis and myonuclear pathology. Only a minority of patients with HMGCR antibody–associated myopathies have a history of statin exposure.

Statins and myotoxic effects associated with anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase autoantibodies: an observational study in Japan

Statins have a variety of myotoxic effects and can trigger the development of inflammatory myopathies or myasthenia gravis (MG) mediated by immunomodulatory properties. Autoantibodies to 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) have been identified in patients with statin-associated myopathy. The purpose of the present study is to develop an enzyme-linked immunosorbent assay (ELISA) of anti-HMGCR antibodies and to elucidate the clinical significance of anti-HMGCR antibodies in Japanese patients with inflammatory myopathies or MG. We enrolled 75 patients with inflammatory myopathies, who were all negative for anti-signal recognition particle and anti-aminoacyl transfer RNA synthetase antibodies. They were referred to Keio University and National Center of Neurology and Psychiatry between October 2010 and September 2012. We also studied 251 patients with MG who were followed at the MG Clinic at Keio University Hospital. Anti-HMGCR antibodies were detected by ELISA. We investigated demographic, clinical, radiological, and histological findings associated with anti-HMGCR antibodies. We established the anti-HMGCR ELISA with the recombinant protein. Protein immunoprecipitation detected autoantigens corresponding to HMGCR. Immunohistochemistry using muscle biopsy specimens revealed regenerating muscle fibers clearly stained by polyclonal anti-HMGCR antibodies and patients' serum. Anti-HMGCR autoantibodies were specifically detected in 8 patients with necrotizing myopathy. The seropositivity rate in the necrotizing myopathy patients was significantly higher than those in the patients with other histological diagnoses of inflammatory myopathies (31% vs 2%, P = 0.001). Statins were administered in only 3 of the 8 anti-HMGCR-positive patients. Myopathy associated with anti-HMGCR antibodies showed mild limb weakness and favorable response to immunotherapy. All 8 patients exhibited increased signal intensities on short T1 inversion recovery of muscle MRI. Of the 251 patients with MG, 23 were administered statins at the onset of MG. One late-onset MG patient experienced MG worsening after 4-wk treatment with atorvastatin. However, anti-HMGCR antibodies were not detected in the 251 MG patients except for one early-onset MG patient with no history of statin therapy. Anti-HMGCR antibodies are a relevant clinical marker of necrotizing myopathy with or without statin exposure, but they are not associated with the onset or deterioration of MG.