Review: Immune-mediated necrotizing myopathies - a heterogeneous group of diseases with specific myopathological features

Statin-induced autoimmune myositis: a proposal of an "experience-based" diagnostic algorithm from the analysis of 69 patients

Statin-induced autoimmune myositis (SIAM) represents a rare clinical entity that can be triggered by prolonged statin treatment. Its pathogenetic substrate consists of an autoimmune-mediated mechanism, evidenced by the detection of antibodies directed against the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR Ab), the target enzyme of statin therapies. To facilitate the diagnosis of nuanced SIAM clinical cases, the present study proposes an "experience-based" diagnostic algorithm for SIAM. We have analyzed the clinical data of 69 patients diagnosed with SIAM. Sixty-seven patients have been collected from the 55 available and complete case records regarding SIAM in the literature; the other 2 patients represent our direct clinical experience and their case records have been detailed. From the analysis of the clinical features of 69 patients, we have constructed the diagnostic algorithm, which starts from the recognition of suggestive symptoms of SIAM. Further steps provide for CK values dosage, musculoskeletal MR, EMG/ENG of upper-lower limbs and, Anti-HMGCR Ab testing and, where possible, the muscle biopsy. A global evaluation of the collected clinical features may suggest a more severe disease in female patients. Atorvastatin proved to be the most used hypolipidemic therapy.

Anti-complement Agents for Autoimmune Neurological Disease

In recent years, there has been increasing recognition of the diversity of autoimmune neurological diseases affecting all levels of the nervous system. A growing understanding of disease pathogenesis has enabled us to better target specific elements of the immune system responsible for the cell dysfunction and cell destruction seen in these diseases. This is no better demonstrated than in the development of complement directed therapies for the treatment of complement mediated autoimmune neurological conditions. Herein, we describe the basic elements of the complement cascade, provide an overview of select autoimmune neurological diseases whose pathogenesis is mediated by complement, the effector system of autoantigen bound autoantibodies, and discuss the complement directed therapies trialed in the treatment of these diseases. Several complement-directed therapies have demonstrated benefit in the treatment of autoimmune neurological diseases; we also review the trials resulting in the approval of these therapies for the treatment of AChR Ab-positive myasthenia gravis (MG) and neuromyelitis spectrum disorder. Finally, on the heels of the recent successes described, we discuss possibilities for the future, including additional targeted therapies with greater ease of administration, improved risk profiles, and other possible uses for therapeutics targeting elements of the complement cascade.

Perivascular and endomysial macrophages expressing VEGF and CXCL12 promote angiogenesis in anti-HMGCR immune-mediated necrotizing myopathy

OBJECTIVES

To study the phenotype of macrophage infiltrates and their role in angiogenesis in different Idiopathic Inflammatory Myopathies (IIMs).

METHODS

The density and distribution of the subpopulations of macrophages subsets (M1, inducible nitric oxide+, CD11c+; M2, arginase-1+), endomysial capillaries (CD31+, FLK1+), degenerating (C5b-9+), and regenerating (NCAM+) myofibers, were investigated by immunohistochemistry in human muscle samples of diagnostic biopsies from a large cohort of untreated patients (n: 81) suffering from anti-3-hydroxy-3-methylglutaryl coenzyme A reductase (anti-HMGCR)+ Immune Mediated Necrotizing Myopathy (IMNM), anti-signal recognition particle (anti-SRP)+ IMNM, seronegative IMNM, Dermatomyositis, Polymyositis, Polymyositis with mitochondrial pathology, sporadic Inclusion Body Myositis, Scleromyositis, and anti-Synthetase Syndrome. The samples were compared with mitochondrial myopathy and control muscle samples.

RESULTS

Compared with the other IIMs and controls, endomysial capillary density (CD) was higher in anti-HMGCR+ IMNM, where M1 and M2 macrophages, detected by confocal microscopy, infiltrated perivascular endomysium and expressed angiogenic molecules such as VEGF-A and CXCL12. These angiogenic macrophages were preferentially associated with CD31+ FLK1+ microvessels in anti-HMGCR+ IMNM. The VEGF-A+ M2 macrophage density was significantly correlated with CD (rS: 0.98; p: 0.0004). Western blot analyses revealed increased expression levels of VEGF-A, FLK1, HIF-1α, and CXCL12 in anti-HMGCR+ IMNM. CD and expression levels of these angiogenic molecules were not increased in anti-SRP+ and seronegative IMNM, offering additional, useful information for differential diagnosis among these IIM subtypes.

CONCLUSION

Our findings suggest that in IIMs, infiltrating macrophages and microvascular cells interactions play a pivotal role in coordinating myogenesis and angiogenesis. This reciprocal crosstalk seems to distinguish anti-HMGCR associated IMNM.

The Significance of Autoantibodies in Juvenile Dermatomyositis

Juvenile dermatomyositis is a chronic and rare autoimmune disorder classified into the spectrum of idiopathic inflammatory myopathies. Although this entity is mainly characterized by the presence of pathognomonic cutaneous lesions and proximal muscle weakness, the clinical manifestation can be highly heterogeneous; thus, diagnosis might be challenging. Current treatment recommendations for juvenile dermatomyositis, based mainly upon case series, include the use of corticosteroids, immunomodulatory, and immunosuppressive agents. Recently, several specific autoantibodies have been shown to be associated with distinct clinical phenotypes of classic dermatomyositis. There is a need to further evaluate their relevance in the formation of various clinical features. Furthermore, while providing more personalized treatment strategies, one should consider diversity of autoantibody-related subgroups of juvenile dermatomyositis.

Immune-mediated necrotizing myopathy (IMNM): A myopathological challenge

This review is focused on the myopathological spectrum of immune mediated necrotizing myopathies (IMNMs) and its differentiation with other, potentially mimicking, inflammatory and non-inflammatory myopathies. IMNMs are a subgroup of idiopathic inflammatory myopathies (IIMs) characterized by severe clinical presentation with rapidly progressive muscular weakness and creatine kinase elevation, often requiring early aggressive immunotherapy, associated to the presence of muscle specific autoantibodies (MSA) against signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Muscle biopsy usually shows unspecific features consisting in prominent necrosis and regeneration of muscle fibres with mild or absent inflammatory infiltrates, inconstant and faint expression of major histocompatibility complex (MHC) class I and variable deposition of C5b-9 on sarcolemma. Several conditions could present similar histopathological findings leading to possible misdiagnosis of IMNM with other IIMs or non-inflammatory myopathies (nIMs) and viceversa. This review analyses the muscle biopsy data in IMNMs through a systematic revision of the literature from the last five decades. Several histopathological variables have been considered in both SRP- and HMGCR-IMNM, and compared to other IIMs - as dermatomyositis (DM) and anti-synthethase syndrome (ASS) - or other nIMs -as toxic myopathies (TM), critical illness myopathy (CIM) and muscular dystrophy (MD) - to elucidate similarities and differences among these potentially mimicking conditions. The major histopathological findings of IMNMs were: very frequent necrosis and regeneration of muscle fibres (93%), mild inflammatory component mainly constituted by scattered isolated (65%) CD68-prevalent (68%) cells, without CD8 invading/surrounding non-necrotic fibres, variable expression of MHC-I in non-necrotic fibres (56%) and constant expression of sarcoplasmic p62, confirming those that are widely considered the major histological characteristics of IMNMs. Conversely, only 42% of biopsies showed a sarcolemmal deposition of C5b-9 component. Few differences between SRP and HMGCR IMNMs consisted in more severe necrosis and regeneration in SRP than in HMGCR (p = 0.01); more frequent inflammatory infiltrates (p = 0.007) with perivascular localization (p = 0.01) and clustered expression of MHC-I (p = 0.007) in HMGCR; very low expression of sarcolemmal C5b-9 in SRP (18%) compared to HMGCR (56%) (p = 0.0001). Milder necrosis and regeneration, detection of perifascicular pathology, presence of lymphocytic inflammatory infiltrates and myofibre expression of MxA help to distinguish DM or ASS from IMNM. nIMs can present signs of inflammation at muscle biopsy. Low fibre size variability with overexpression of both MHC-I and II, associated with C5b-9 deposition, could could be observed in CIM, while increased connective tissue should lead to consider MD, or TM in absence of C5b-9 deposition. Nevertheless, these features are not constantly detected and muscle biopsy could not be diriment. For this reason, muscle biopsy should always be critically considered in light of the clinical context before concluding for a definite diagnosis of IMNM, only based on histopathological findings. More rigorous collection and analysis of muscle biopsy is warranted to obtain a higher quality and more homogeneous histopathological data in inflammatory myopathies.

Clinical Course, Myopathology and Challenge of Therapeutic Intervention in Pediatric Patients with Autoimmune-Mediated Necrotizing Myopathy

(1) Background: Immune–mediated necrotizing myopathy (IMNM) is a rare form of inflammatory muscle disease which is even more rare in pediatric patients. To increase the knowledge of juvenile IMNM, we here present the clinical findings on long-term follow-up, myopathological changes, and therapeutic strategies in two juvenile patients. (2) Methods: Investigations included phenotyping, determination of antibody status, microscopy on muscle biopsies, MRI, and response to therapeutic interventions. (3) Results: Anti-signal recognition particle (anti-SRP54) and anti- 3-hydroxy-3-methylglutarly coenzyme A reductase (anti-HMGCR) antibodies (Ab) were detected in the patients. Limb girdle presentation, very high CK-levels, and a lack of skin rash at disease-manifestation and an absence of prominent inflammatory signs accompanied by an abnormal distribution of α-dystroglycan in muscle biopsies initially hinted toward a genetically caused muscle dystrophy. Further immunostaining studies revealed an increase of proteins involved in chaperone-assisted autophagy (CASA), a finding already described in adult IMNM-patients. Asymmetrical muscular weakness was present in the anti-SRP54 positive Ab patient. After initial stabilization under therapy with intravenous immunoglobulins and methotrexate, both patients experienced a worsening of their symptoms and despite further therapy escalation, developed a permanent reduction of their muscle strength and muscular atrophy. (4) Conclusions: Diagnosis of juvenile IMNM might be complicated by asymmetric muscle weakness, lack of cutaneous features, absence of prominent inflammatory changes in the biopsy, and altered α-dystroglycan.

Statin-Induced Myopathy: Translational Studies from Preclinical to Clinical Evidence

Statins are the most prescribed and effective drugs to treat cardiovascular diseases (CVD). Nevertheless, these drugs can be responsible for skeletal muscle toxicity which leads to reduced compliance. The discontinuation of therapy increases the incidence of CVD. Thus, it is essential to assess the risk. In fact, many studies have been performed at preclinical and clinical level to investigate pathophysiological mechanisms and clinical implications of statin myotoxicity. Consequently, new toxicological aspects and new biomarkers have arisen. Indeed, these drugs may affect gene transcription and ion transport and contribute to muscle function impairment. Identifying a marker of toxicity is important to prevent or to cure statin induced myopathy while assuring the right therapy for hypercholesterolemia and counteracting CVD. In this review we focused on the mechanisms of muscle damage discovered in preclinical and clinical studies and highlighted the pathological situations in which statin therapy should be avoided. In this context, preventive or substitutive therapies should also be evaluated.

Inflammatory myopathies: update on diagnosis, pathogenesis and therapies, and COVID-19-related implications

The inflammatory myopathies constitute a heterogeneous group of acquired myopathies that have in common the presence of endomysial inflammation. Based on steadily evolved clinical, histological and immunopathological features and some autoantibody associations, these disorders can now be classified in five characteristic subsets: Dermatomyositis (DM) Polymyositis (PM), Necrotizing Autoimmune Myositis (NAM), Anti-synthetase syndrome-overlap myositis (Anti-SS-OM), and Inclusion-Body-Myositis (IBM). Each inflammatory myopathy subset has distinct immunopathogenesis, prognosis and response to immunotherapies, necessitating the need to correctly identify each subtype from the outset to avoid disease mimics and proceed to early therapy initiation. The review presents the main clinicopathologic characteristics of each subset highlighting the importance of combining expertise in clinical neurological examination with muscle morphology and immunopathology to avoid erroneous diagnoses and therapeutic schemes. The main autoimmune markers related to autoreactive T cells, B cells, autoantibodies and cytokines are presented and the concomitant myodegenerative features seen in IBM muscles are pointed out. Most importantly, unsettled issues related to a role of autoantibodies and controversies with reference to possible triggering factors related to statins are clarified. The emerging effect SARS-CoV-2 as the cause of hyperCKemia and potentially NAM is addressed and practical guidelines on the best therapeutic approaches and concerns regarding immunotherapies during COVID-19 pandemic are summarized.

[Myositis: From classification to diagnosis]

Idiopathic inflammatory myopathies, or IIM, are a group of acquired diseases that affect the muscle to a certain extent, and may also affect other organs. They include dermatomyositis, which can affect the muscle eventualy, with a typical skin rash; inclusion body myositis, with a purely muscular expression resulting in a slow progressive deficit; and the former group of "polymyositis", a misnomer that actually includes other categories of IIM, such as immune-mediated necrotizing myopathies, with a severe muscle involvement often presents from the onset of the disease; antisynthetase syndrome, which combines muscle damage, joint involvement and a potentially life-threatening lung disease; and overlapping myositis, which combines muscle damage with other organs involvement connected to another autoimmune disease. The diagnosis of IIM is based on rigorous clinical examination and interrogation, electromyographic data and immunological testing for myositis specific antibodies. This antibody dosage must be extended or repeated if necessary to classify correctly the muscle disease under investigation, as the available tests may not perform well enough. Muscle biopsy, although very informative, is not anymore systematically recommended when the clinic and the antibodies are typical. However, some forms of IIM are sometimes difficult to classify; in these cases, muscle biopsy plays a crucial role in the precise etiological diagnosis.

Influenza A (H3N2) infection followed by anti-signal recognition particle antibody-positive necrotizing myopathy: A case report

A 60-year-old Japanese woman presented with subacute progressive muscle pain and weakness in her proximal extremities. She was diagnosed with influenza A (H3N2) infection a week before the onset of muscle pain. At the time of admission, she exhibited weakness in the proximal muscles of the upper and lower limbs, elevated serum liver enzymes and creatinine kinase, and myoglobinuria. She did not manifest renal failure and cardiac abnormalities, indicating myocarditis. Electromyography revealed myogenic changes, and magnetic resonance imaging of the upper limb showed abnormal signal intensities in the muscles, suggestive of myopathy. Muscle biopsy of the biceps revealed numerous necrotic regeneration fibers and mild inflammatory cell infiltration, suggesting immune-mediated necrotizing myopathy (IMNM). Necrotized muscle cells were positive for human influenza A (H3N2). Autoantibody analysis showed the presence of antibodies against the signal recognition particle (SRP), and the patient was diagnosed with anti-SRP-associated IMNM. She was resistant to intravenous methylprednisolone pulse therapy but recovered after administration of oral systemic corticosteroids and immunoglobulins. We speculate that the influenza A (H3N2) infection might have triggered her IMNM. Thus, IMNM should be considered as a differential diagnosis in patients with proximal muscle weakness that persists after viral infections.

Patients with Interstitial Lung Disease Secondary to Autoimmune Diseases: How to Recognize Them?

The diagnostic assessment of patients with Interstitial Lung Disease (ILD) can be challenging due to the large number of possible causes. Moreover, the diagnostic approach can be limited by the severity of the disease, which may not allow invasive exams. To overcome this issue, the referral centers for ILD organized Multidisciplinary Teams (MDTs), including physicians and experts in complementary discipline, to discuss the management of doubtful cases of ILD. MDT is currently considered the gold standard for ILD diagnosis, but it is not often simple to organize and, furthermore, rheumatologists are still not always included. In fact, even if rheumatologic conditions represent a common cause of ILD, they are sometimes difficult to recognize, considering the variegated clinical features and their association with all possible radiographic patterns of ILD. The first objective of this review is to describe the clinical, laboratory, and instrumental tests that can drive a diagnosis toward a possible rheumatic disease. The secondary objective is to propose a set of first-line tests to perform in all patients in order to recognize any possible rheumatic conditions underlying ILD.

Eosinophilic granulomatosis with polyangiitis presenting with myositis: case based review

Eosinophilic granulomatosis with polyangitis (EGPA) is a systemic necrotizing small-vessel vasculitis that presents heterogeneously as a multi-organ disease. EGPA evolves through three phases: (1) prodromic phase with asthma, atopy and sinusitis, (2) eosinophilic phase characterized by peripheral eosinophilia and eosinophilic infiltration without necrosis, and (3) vasculitic phase involving organ damage. EGPA often presents with asthma, mononeuritis multiplex, lung infiltrates, sinusitis and constitutional symptoms. Although myalgias are common, EGPA rarely presents with true weakness with elevated creatinine kinase (CK). We describe a rare case of a patient presenting with eosinophilic myositis, who subsequently developed fulminant EGPA. The patient's diagnosis was supported by an initial clinical presentation of weakness and elevated CK, followed by fleeting pulmonary infiltrates and mononeuritis multiplex, peripheral eosinophilia, and strongly positive myeloperoxidase anti-cytoplasmic antibody (MPO-ANCA). Muscle biopsy revealed eosinophilic myositis. The patient responded well to high-dose glucocorticoids and cyclophosphamide with improved symptoms and biochemical markers. Based on our literature review, there are only seven similar cases reported of EGPA presenting with myositis and confirmatory muscle biopsies. There is significant heterogeneity in their clinical findings, histopathology and treatments that were used. Our case report and literature review highlights the importance of recognizing myositis as an initial presenting symptom of EGPA, providing an opportunity for early diagnosis and treatment to reduce risk of further disease progression and morbidity.

Thrombospondin-1 mediates muscle damage in brachio-cervical inflammatory myopathy and systemic sclerosis

Objective

To describe the clinical, serologic and histologic features of a cohort of patients with brachio-cervical inflammatory myopathy (BCIM) associated with systemic sclerosis (SSc) and unravel disease-specific pathophysiologic mechanisms occurring in these patients.

Methods

We reviewed clinical, immunologic, muscle MRI, nailfold videocapillaroscopy, muscle biopsy, and response to treatment data from 8 patients with BCIM-SSc. We compared cytokine profiles between patients with BCIM-SSc and SSc without muscle involvement and controls. We analyzed the effect of the deregulated cytokines in vitro (fibroblasts, endothelial cells, and muscle cells) and in vivo.

Results

All patients with BCIM-SSc presented with muscle weakness involving cervical and proximal muscles of the upper limbs plus Raynaud syndrome, telangiectasia and/or sclerodactilia, hypotonia of the esophagus, and interstitial lung disease. Immunosuppressive treatment stopped the progression of the disease. Muscle biopsy showed pathologic changes including the presence of necrotic fibers, fibrosis, and reduced capillary number and size. Cytokines involved in inflammation, angiogenesis, and fibrosis were deregulated. Thrombospondin-1 (TSP-1), which participates in all these 3 processes, was upregulated in patients with BCIM-SSc. In vitro, TSP-1 and serum of patients with BCIM-SSc promoted proliferation and upregulation of collagen, fibronectin, and transforming growth factor beta in fibroblasts. TSP-1 disrupted vascular network, decreased muscle differentiation, and promoted hypotrophic myotubes. In vivo, TSP-1 increased fibrotic tissue and profibrotic macrophage infiltration in the muscle.

Conclusions

Patients with SSc may present with a clinically and pathologically distinct myopathy. A prompt and correct diagnosis has important implications for treatment. Finally, TSP-1 may participate in the pathologic changes observed in muscle.

Anti-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) antibody in necrotizing myopathy: treatment outcomes, cancer risk, and role of autoantibody level

Objective: To evaluate clinical associations of anti-hydroxy-3-methylglutaryl-coenzyme A reductase (anti-HMGCR) antibody (Ab) and statin exposure in necrotizing myopathy (NM) patients. Methods: NM without a known myositis-specific autoantibody (MSA) was ascertained from a large single-centre myositis database between 1985 and 2012. A comparison NM cohort included 32 anti-SRP⁺ autoantibody patients, and other control groups included 74 non-NM myositis patients and 21 non-myositis controls. Sera from all cases and controls were tested using a validated anti-HMGCR enzyme-linked immunosorbent assay. Clinical features including statin use and anti-HMGCR Ab status were compared between cases and controls. Results: Of the 256 NM muscle biopsies reviewed, only 48 subjects with available sera were identified as traditional MSA-negative NM. Anti-HMGCR positivity was significantly (p < 0.001) associated with MSA-negative NM [48% (23/48)] compared to all of the myositis and non-myositis controls [5% (6/127)]. Most anti-HMGCR Ab-positive NM patients had high titres of anti-HMGCR (83%) and a history of statin exposure (78%), along with severe muscle weakness, high creatine kinase (CK) levels (90% ≥ 5000 IU/L), a paucity of other organ manifestations, and the need for immunosuppression with prednisone and methotrexate, but generally favourable outcomes. Anti-HMGCR serum levels were associated with baseline CK levels but not muscle weakness. Conclusion: HMGCR Ab-positive NM patients are associated with statin exposure, have severe muscle weakness and high CK at presentation, lack other organ manifestations, and generally have favourable outcomes from immunosuppression. Anti-HMGCR Abs should be assessed in MSA-negative NM patients, particularly those with a history of statin exposure.

Anti-signal Recognition Particle Antibody-positive Necrotizing Myopathy with Secondary Cardiomyopathy: The First Myocardial Biopsy- and Multimodal Imaging-proven Case

A 69-year-old Japanese woman was admitted to our hospital with progressive muscle weakness and dysphagia. She was taking pitavastatin for dyslipidemia. Her serum creatine kinase was 6,300 U/L. Pitavastatin was stopped, but her symptoms deteriorated, and cardiac congestion appeared. A muscle biopsy showed necrotizing myopathy (NM), and anti-signal recognition particle (SRP) antibody was positive. ¹⁸F-fluorodeoxyglucose-positron emission tomography showed an abnormal uptake, and magnetic resonance imaging showed abnormal gadolinium enhancement in the left ventricular wall. An endomyocardial biopsy revealed inflammatory cardiomyopathy. Steroid, tacrolimus, and intravenous immunoglobulins were effective against the symptoms. This is the first case of biopsy-proven secondary cardiomyopathy due to anti-SRP-positive NM.

Whole-body MRI and pathological findings in adult patients with myopathies

Magnetic resonance imaging (MRI) is considered the most sensitive and specific imaging technique for the detection of muscle diseases related to myopathies. Since 2008, the use of whole-body MRI (WBMRI) to evaluate myopathies has improved due to technical advances such as rolling table platform and parallel imaging, which enable rapid assessment of the entire musculoskeletal system with high-quality images. WBMRI protocols should include T1-weighted and short-tau inversion recovery (STIR), which provide the basic pulse sequences for studying myopathies, in order to detect fatty infiltration/muscle atrophy and muscle edema, respectively. High signal intensity in T1-weighted images shows chronic disease with fatty infiltration, whereas high signal intensity in STIR indicates an acute stage with muscle edema. Additional sequences such as diffusion-weighted imaging (DWI) can be readily incorporated into routine WBMRI study protocols. Contrast-enhanced sequences have not been done. This article reviews WBMRI as an imaging method to evaluate different myopathies (idiopathic inflammatory, dystrophic, non-dystrophic, metabolic, and channelopathies). WBMRI provides a comprehensive estimate of the total burden with a single study, seeking specific distribution patterns, including clinically silent involvement of muscle areas. Furthermore, WBMRI may help to select the "target muscle area" for biopsy during patient follow-up. It may be also be used to detect related and non-related pathological conditions, such as tumors.

Statin-induced myopathy: a case report

Background

Statins are one of the most frequently used drug groups among patients with cardiovascular disease. Muscle pain is very frequent among patients using statins. It is important to distinguish patients with benign muscle pain without significant biochemical correlates from patients with serious myopathies.

Case summary

We present the case of a 68-year-old woman taking atorvastatin in the past 8 months after a coronary bypass grafting, presenting with proximal muscle weakness and pain. Biochemical analysis showed a markedly elevated creatine kinase (CK) (24,159 U/L). Despite discontinuation of the statin and therapy for rhabdomyolysis (IV fluid, mannitol, and sodium bicarbonate), CK levels did not drop as much as expected. Muscle biopsy showed mild inflammatory changes and few necrotic muscle fibres, suggestive for an immune-mediated necrotizing myopathy (IMNM). Serology showed a high anti-HMG-CoA reductase antibody (anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase antibody) titre, diagnostic for an IMNM induced by statins. The patient was treated with corticosteroids and methotrexate. Creatine kinase levels, muscle weakness, and pain gradually improved over the following months.

Discussion

IMNM induced by statins is a relatively new entity. It is important to be recognized because it is not a self-limiting adverse effect such as the frequent benign muscle pains caused by statins. Beside discontinuation of the causative statin, aggressive immunosuppressive therapy is mandatory in IMNM. Therefore, it is important to test for anti-HMGCR antibodies and if necessary perform a muscle biopsy in patients taking statins, presenting with muscle weakness, and CK elevations not improving after discontinuation of the statin.

Histological heterogeneity in a large clinical cohort of juvenile idiopathic inflammatory myopathy: analysis by myositis autoantibody and pathological features

Aim

Juvenile idiopathic inflammatory myopathies have been recently reclassified into clinico‐serological subgroups. Myopathological correlates of the subgroups are incompletely understood.

Methods

We studied muscle biopsies from 101 children with clinically and serologically defined juvenile idiopathic inflammatory myopathies from the UK JDM Cohort and Biomarker Study by applying the international JDM score tool, myopathological review and C5b‐9 complement analysis.

Results

Autoantibody data were available for 90/101 cases with 18/90 cases positive for anti‐TIF1γ, 15/90 anti‐NXP2, 11/90 anti‐MDA5, 5/90 anti‐Mi2 and 6/90 anti‐PmScl. JDM biopsy severity scores were consistently low in the anti‐MDA5 group, high in the anti‐Mi2 group, and widely distributed in the other groups. Biopsies were classified histologically as perifascicular atrophy (22/101), macrophage‐rich necrosis (6/101), scattered necrosis (2/101), clustered necrosis (2/101), inflammatory fibre invasion (2/101), chronic myopathic change (1/101), diffuse endomysial macrophage infiltrates (40/101) and minimal change (24/101). MDA5 cases segregated with the minimal change group and showed no capillary C5b‐9‐deposition. The Mi2 group displayed high severity scores and a tendency towards sarcolemmal complement deposition. NXP2 and TIF1γ groups showed a variety of pathologies with a high proportion of diffuse endomysial macrophage infiltrates and a high proportion of capillary C5b‐9 deposition.

Conclusion

We have shown that juvenile idiopathic inflammatory myopathies have a spectrum of histopathological phenotypes and show distinct complement attack complex deposition patterns. Both correlate in some cases with the serological subtypes. Most cases do not show typical histological features associated with dermatomyositis (e.g. perifascicular atrophy). In contrast, more than half show relatively mild histopathological changes.

Interstitial lung disease and inflammatory myopathy in antisynthetase syndrome with PL-12 antibody

We report the case of an 80-year-old Caucasian man with PL-12 antibody positive antisynthetase syndrome. He presented with progressive dyspnoea and weight loss, later developing dysphagia, mild proximal muscle weakness and mild sicca symptoms. Investigations revealed interstitial lung disease, inflammatory myopathy and an immunology profile consistent with PL-12 antisynthetase syndrome. Prednisolone and cyclophosphamide resulted in a significant improvement of all his symptoms.

Statin-naïve anti-HMGCR antibody-mediated necrotizing myopathy in China

This study aimed to clarify the phenotypes and therapeutic responses of statin-naïve anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) antibody-mediated necrotizing myopathy. Anti-HMGCR antibodies were tested with ELISA methodology in the sera sample of 98 patients meeting the idiopathic inflammatory myopathy criteria and with negative anti-signal recognition particle (SRP) antibody. Twenty-one statin-naïve patients with anti-HMGCR antibody were detected (21.4%), with onset age from 6 to 67 years old. Proximal weakness and neck flexion weakness was the core neurological feature. The average maximal creatine kinase (CK) level was 7968.6 ± 4408.7U/L. Muscle MR imaging showed edema (88.2%), moderate or severe fatty replacement (70.6%) and muscle atrophy (88.2%) in lower limbs. Fatty replacement was significantly more prominent in the medial and posterior musculature than the anterior musculature (p = 0.0013). Seven (33.3%) patients were treated with mono-glucocorticoid, and thirteen (61.9%) patients needed adjuvant immunosuppressant. Eight (38.1%) patients experienced symptom relapse. The early-onset patients (<50 years old) were found with higher CK levels, shorter duration course, poorer response to adjuvant immunosuppressant and more recurrent weakness than the late-onset patients (≥50 years old). As a conclusion, Statin-naïve anti-HMGCR antibody-mediated necrotizing myopathy may not be rare. Compared with late-onset statin-naïve patients with anti-HMGCR antibody-mediated necrotizing myopathy, early-onset patients presented severer clinical features and worse therapeutic responses.

Idiopathic inflammatory myopathies overlapping with systemic diseases

A muscle biopsy is currently requested to assess the diagnosis of an idiopathic inflammatory myopathy overlapping with a systemic disease. During the past few years, the classification of inflammatory myopathy subtypes has been revisited progressively on the basis of correlations between clinical phenotypes, autoantibodies and histological data. Several syndromic entities are now more clearly defined, and the aim of the present review is to clarify the contribution of muscle biopsy in a setting of idiopathic inflammatory myopathies overlapping with systemic diseases.
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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.

Current Classification and Management of Inflammatory Myopathies

Inflammatory disorders of the skeletal muscle include polymyositis (PM), dermatomyositis (DM), (immune mediated) necrotizing myopathy (NM), overlap syndrome with myositis (overlap myositis, OM) including anti-synthetase syndrome (ASS), and inclusion body myositis (IBM). Whereas DM occurs in children and adults, all other forms of myositis mostly develop in middle aged individuals. Apart from a slowly progressive, chronic disease course in IBM, patients with myositis typically present with a subacute onset of weakness of arms and legs, often associated with pain and clearly elevated creatine kinase in the serum. PM, DM and most patients with NM and OM usually respond to immunosuppressive therapy, whereas IBM is largely refractory to treatment. The diagnosis of myositis requires careful and combinatorial assessment of (1) clinical symptoms including pattern of weakness and paraclinical tests such as MRI of the muscle and electromyography (EMG), (2) broad analysis of auto-antibodies associated with myositis, and (3) detailed histopathological work-up of a skeletal muscle biopsy. This review provides a comprehensive overview of the current classification, diagnostic pathway, treatment regimen and pathomechanistic understanding of myositis.

A rare cause of proximal muscle weakness: immune necrotising myopathy

Background Immune-mediated necrotising myopathies are characterised clinically by the subacute onset of proximal limb weakness, accompanied by elevated creatinine kinase levels. They are distinguished from other myopathies by the absence of prominent infiltration of the muscle with inflammatory cells in the biopsies. Case presentation A 44-year-old man presented with upper extremity weakness and dysphagia. Laboratory tests included a creatinine kinase level of 4362 U/L (normal: 52-336 U/L). Rheumatological markers were all negative. A muscle biopsy showed multiple necrotic fibres with minimal inflammatory infiltration. One gram of methylprednisolone (IV) was given, followed by 1 mg/kg of methylprednisolone daily by the oral route. Intravenous immunoglobulin (0.4 mg/kg/day) was given for five days. Muscle weakness regressed and dysphagia disappeared with treatment. The patient remains well in the 23rd month of treatment, taking 5 mg/day prednisolone and monthly intravenous immunoglobulin. Conclusion Treatment of immune-mediated necrotising myopathy can be challenging as evidence-based therapeutic options are limited. It is generally accepted that early and extensive immunosuppression, including glucocorticoids as first-line agents, may be required.

Skeletal Muscle Involvement in Antisynthetase Syndrome

Importance

Antisynthetase syndrome, characterized by myositis, interstitial lung disease, skin rash, arthropathy, and Raynaud phenomenon, is a clinical entity based on the presence of aminoacyl transfer RNA synthetase (ARS) antibodies in patients' serum. However, antisynthetase syndrome is not included in the histological subsets of idiopathic inflammatory myopathies.

Objective

To elucidate the clinical features of myositis in patients with antisynthetase syndrome.

Design, Setting, and Participants

In this cohort study, muscle biopsy and blood samples were collected from 460 patients with idiopathic inflammatory myositis from various regional referral centers throughout Japan between October 2010 and December 2014. Data were analyzed in March 2016.

Exposures

Six different anti-ARS antibodies were detected in serum by RNA immunoprecipitation. Line blot assay and protein immunoprecipitation were also performed. HLA-DRB1 alleles were genotyped.

Main Outcomes and Measures

The main outcomes were muscle manifestations and histological findings. Predisposing factors, extramuscular symptoms, and follow-up information were also studied.

Results

Of 460 patients with idiopathic inflammatory myopathies, 51 (11.1%) had anti-ARS antibodies. Of this subset, 31 (61%) were women, with a mean (SD) age at disease onset of 60.2 (16.1) years. Among 6 different anti-ARS antibodies, only 1-the anti-OJ antibody-was not detected by line blot assay but by RNA immunoprecipitation. There were no significant HLA-DRB1 alleles associated with anti-ARS antibodies. All 51 patients presented with muscle limb weakness; 14 (27%) had severe limb weakness, 17 (33%) had neck muscle weakness, 15 (29%) had dysphagia, and 15 (29%) had muscle atrophy. Although patients with anti-OJ antibodies showed severe muscle weakness, the clinical presentations of antisynthetase syndrome were relatively homogeneous. In histology, perifascicular necrosis, the characteristic finding of antisynthetase syndrome, was found in 24 patients (47%). Myositis with anti-ARS antibodies responded to the combination of immunosuppressive therapy with favorable outcomes. Interstitial lung disease, found in 41 patients (80%), was more closely associated with mortality than myositis.

Conclusions and Relevance

Although clinical presentations of antisynthetase syndrome were relatively homogeneous, anti-OJ antibodies were associated with severe muscle involvement. Antisynthetase syndrome is a clinical and histological subset among idiopathic inflammatory myopathies.

Progressive hypoventilation due to mixed CD8+ and CD4+ lymphocytic polymyositis following tremelimumab - durvalumab treatment

BACKGROUND

The combination of CTLA-4 and PD-L1 inhibitors has a manageable adverse effect profile, although rare immune-related adverse events (irAE) can occur.

CASE PRESENTATION

We describe an autoimmune polymyositis following a partial response to combination tremelimumab and durvalumab for the treatment of recurrent lung adenocarcinoma. Radiography revealed significant reduction in all metastases; however, the patient developed progressive neuromuscular hypoventilation due to lymphocytic destruction of the diaphragmatic musculature. Serologic testing revealed a low level of de novo circulating antibodies against striated muscle fiber. Immunohistochemistry revealed type II muscle fiber atrophy with a mixed CD8+ and CD4+ lymphocyte infiltrate, indicative of inflammatory myopathy.

CONCLUSIONS

This case supports the hypothesis that muscle tissue is a target for lymphocytic infiltration in immune checkpoint inhibitor-associated polymyositis. Further insights into the autoimmune mechanism of PM will hopefully contribute to the prevention and treatment of this phenomenon.

Paraneoplastic Necrotizing Autoimmune Myopathy in a Patient Undergoing Laparoscopic Pancreatoduodenectomy for Distal Cholangiocarcinoma

A 73-year-old male presented with jaundice and severe muscle weakness. He was diagnosed with distal cholangiocarcinoma and paraneoplastic necrotizing autoimmune myopathy (NAM). Treatment of NAM consisted of dexamethasone pulse therapy, prednisone, and single-dose intravenous immunoglobulin. The distal cholangiocarcinoma was resected through a total laparoscopic pancreatoduodenectomy. After hospital discharge, muscle strength initially increased postoperatively; however, pneumonia resulted in the deterioration of his general condition and death 5 months after the diagnosis of paraneoplastic NAM.

Clinical features and prognosis in anti-SRP and anti-HMGCR necrotising myopathy

OBJECTIVE

To elucidate the common and distinct clinical features of immune-mediated necrotising myopathy (IMNM), also known as necrotising autoimmune myopathy associated with autoantibodies against signal recognition particle (SRP) and 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR).

METHODS

We examined a cohort of 460 patients with idiopathic inflammatory myopathies (IIMs) through a muscle biopsy-oriented registration study in Japan. Study entry was strictly determined by the comprehensive histological assessment to exclude other neuromuscular disorders. Anti-SRP and anti-HMGCR antibodies were detected by RNA immunoprecipitation and ELISA, respectively.

RESULTS

Of 460 patients with IIM, we diagnosed 73 (16%) as having inclusion body myositis (IBM). Of 387 patients with IIMs other than IBM, the frequencies of anti-SRP and anti-HMGCR antibodies were 18% and 12%, respectively. One patient had both autoantibodies. Severe limb muscle weakness, neck weakness, dysphagia, respiratory insufficiency and muscle atrophy were more frequently observed in patients with anti-SRP antibodies than in those with anti-HMGCR antibodies. Serum creatine levels were markedly higher in the patients with autoantibodies than in those without. Histology was characterised by necrosis and regeneration of muscle fibres and was consistent with IMNM except in 1 HMGCR-positive IBM patient. Most patients were initially treated with corticosteroids; however, additional immunosuppressive drugs were required, especially in the patients with anti-SRP antibodies. Rates of unsatisfactory neurological outcome were similar in the 2 autoantibody groups.

CONCLUSIONS

Anti-SRP antibodies are associated with severe neurological symptoms, more so than are anti-HMGCR antibodies. Although these autoantibodies are independent serological markers associated with IMNM, patients bearing either share common characteristics.

Treatment and outcomes in necrotising autoimmune myopathy: An Australian perspective

Necrotising Autoimmune Myopathy (NAM) presents as a subacute proximal myopathy with high creatine kinase levels. It is associated with statin exposure, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibody, connective tissue diseases, signal recognition particle (SRP) antibody and malignancy. This case series presents our Western Australian NAM patient cohort: comparing the subgroup presentations, biopsy appearance and treatment outcomes. We retrospectively collected data on patients diagnosed with NAM at the Western Australian Neuroscience Research Institute between the years 2000 and 2015. We identified 20 patients with Necrotising Autoimmune Myopathy: 14 with anti-HMGCR antibodies; two with anti-SRP antibodies; three with connective tissue disease; two as yet unspecified. Median creatine kinase level was 6047units/L (range 1000-17000). The statin naïve patients with HMGCR antibodies and patients with SRP antibodies were the most severely affected subgroups, with higher creatine kinase levels, and were more resistant to immunotherapy. Two or more immunotherapy agents were required in 90%; eight patients required IVIG and rituximab. Steroid weaning commonly precipitated relapses. Four patients had complete remission, and the remaining patients still require immunotherapy. Necrotising Autoimmune Myopathy is a potentially treatable myopathy, which can be precipitated by statin therapy and requires early, aggressive immunotherapy, usually requiring multiple steroid sparing agents for successful steroid weaning.

Immunotherapies for Immune-Mediated Myopathies: A Current Perspective

Until recently, the treatment of immune-mediated inflammatory myopathies has largely been empirical with glucocorticoids, steroid-sparing immunosuppressive drugs, and intravenous immunoglobulin. However, a proportion of patients are only partially responsive to these therapies, and there has been a need to consider alternative treatment approaches. In particular, patients with inclusion body myositis are resistant to conventional immunotherapies or show only a transient response, and remain a major challenge. With increasing recognition of the different subtypes of immune-mediated inflammatory myopathies, and improved understanding of their pathogenesis, more targeted treatments are now being trialled. The overall approach to treatment, and novel therapies targeting B cells, T cells, and specific cytokines are discussed in this review.

An overview of muscle diseases presenting in adulthood

Patients with muscle disease present not only to neurologists, but also to rheumatologists and general physicians. This article provides a framework of how to approach patients with suspected muscle disease, and reviews the clinical features of the most frequently encountered acquired and genetic conditions in adult practice.

An overview of polymyositis and dermatomyositis

Polymyositis and dermatomyositis are inflammatory myopathies that differ in their clinical features, histopathology, response to treatment, and prognosis. Although their clinical pictures differ, they both present with symmetrical, proximal muscle weakness. Treatment relies mainly upon empirical use of corticosteroids and immunosuppressive agents. A deeper understanding of the molecular pathways that drive pathogenesis, careful phenotyping, and accurate disease classification will aid clinical research and development of more efficacious treatments. In this review we address the current knowledge of the epidemiology, clinical characteristics, diagnostic evaluation, classification, pathogenesis, treatment, and prognosis of polymyositis and dermatomyositis.

Myositis mimics: how to recognize them

PURPOSE OF REVIEW

To help clinicians to distinguish between myositis (and other immune-mediated and immunosuppressant-responsive disorders) and its many clinical mimics.

RECENT FINDINGS

Increasing experience has shown that findings from conventional investigations, such as muscle biopsy, can be misleading. More specialist investigations, notably autoantibody screening, immunocytochemical techniques, and evolving DNA technologies, are powerful tools but experience is currently largely limited to specialist centres - and even these techniques are open to misinterpretation.

SUMMARY

Misdiagnosis is hazardous to the patient. Treatable conditions may be missed, or patients subjected inappropriately to potentially toxic drug treatments. Judicious use of clinical skills alone should help reduce these risks.

Inflammatory myopathy with anti-signal recognition particle antibodies: case series of 100 patients

Background

Anti-signal recognition particle (SRP) antibodies are used as serological markers of necrotizing myopathy, which is characterized by many necrotic and regenerative muscle fibers without or with minimal inflammatory cell infiltration. The clinical spectrum associated with anti-SRP antibodies seems to be broad.

Objective

To describe the clinical characteristics, autoantibodies status, and neurological outcome associated with anti-SRP antibody.

Methods

We studied clinical and laboratory findings of 100 patients with inflammatory myopathy and anti-SRP antibodies. Anti-SRP antibodies in serum were detected by the presence of 7S RNA using RNA immunoprecipitation. In addition, enzyme-linked immunosorbent assays (ELISAs) using a 54-kD protein of SRP (SRP54) and 3-hydroxyl-3-methylglutatyl-coenzyme A reductase (HMGCR) were also conducted.

Results

The mean onset age of the 61 female and 39 male patients was 51 years (range 4–82 years); duration ≥ 12 months before diagnosis was seen in 23 cases. All patients presented limbs weakness; 63 had severe weakness, 70 neck weakness, 41 dysphagia, and 66 muscle atrophy. Extramuscular symptoms and associated disorders were infrequent. Creatine kinase levels were mostly more than 1000 IU/L. Histological diagnosis showed 84 patients had necrotizing myopathy, and apparent cell infiltration was observed in 16 patients. Anti-SRP54 antibodies were undetectable in 18 serum samples with autoantibodies to 7S RNA. Anti-HMGCR antibodies were positive in 3 patients without the statin treatment, however, were negative in 5 patients with statin-exposure at disease onset. All but 3 patients were treated by corticosteroids and 62 (77 %) of these 81 patients required additional immunotherapy. After 2-years treatment, 22 (27 %) of these 81 patients had poor neurological outcomes with modified Rankin scale scores of 3–5. Multivariate analysis revealed that pediatric disease onset was associated with the poor outcomes.

Conclusion

Anti-SRP antibodies are associated with different clinical courses and histological presentations.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-015-0277-y) contains supplementary material, which is available to authorized users.