Immune-Mediated Necrotizing Myopathies: Current Landscape

PURPOSE OF REVIEW

Immune-mediated necrotizing myopathy (IMNM), characterized by acute or subacute onset, severe weakness, and elevated creatine kinase levels, poses diagnostic and therapeutic challenges. This article provides a succinct overview of IMNM, including clinical features, diagnostic strategies, and treatment approaches.

RECENT FINDINGS

Recent insights highlight the different clinical presentations and therapeutic options of IMNM stratified by autoantibody positivity and type. Additionally, recent findings call into question the reported link between statin use and IMNM. This review synthesizes current knowledge on IMNM, emphasizing its distinct clinical features and challenging management. The evolving understanding of IMNM underscores the need for a comprehensive diagnostic approach that utilizes a growing range of modalities. Early and aggressive immunomodulatory therapy remains pivotal. Ongoing research aims to refine diagnostic tools and therapeutic interventions for this challenging muscle disorder, underscoring the importance of advancing our understanding to enhance patient outcomes.

Paraneoplastic myopathies

This chapter reviews the association between cancer and the idiopathic inflammatory myopathies (IIM), which includes dermatomyositis (DM), antisynthetase syndrome (ASyS), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). Accumulating evidence shows that the risk of a coexisting malignancy is high in patients with DM, especially among those with anti-Tif1γ autoantibodies. Patients with IMNM and no defined autoantibodies also have an increased risk of malignancy. Recent evidence demonstrates that many IBM patients have increased numbers of circulating CD57+ CD8+ T cells, consistent with a diagnosis of large granular lymphocytic leukemia. In contrast, IMNM patients with anti-SRP or anti-HMGCR autoantibodies as well as patients with ASyS syndrome do not have a definitively increased risk of cancer. Patients who have a cancer treated with one of the immune checkpoint inhibitors can develop myositis (ICI-myositis), sometimes along with myasthenia gravis and/or myocarditis.

Granulomatous myopathy co-existent immune-mediated necrotizing myopathy: A case report

Granulomatous myopathy (GM) is a rare disease characterized by non-caseating inflammation of the skeletal muscle, with sarcoidosis as a common cause. Here, we report a case of GM co-existent immune-mediated necrotizing myopathy (IMNM) in which an anti-signal recognition particle (SRP) antibody was positive and a muscle biopsy showed a non-caseating granulomatous structure, along with myofiber necrosis and inflammatory cell infiltration.

Immune-mediated necrotizing myopathy: Report of two cases

BACKGROUND

Immune-mediated necrotizing myopathy is a rare autoimmune myopathy characterized by muscle weakness and elevated serum creatine kinase, with unique skeletal muscle pathology and magnetic resonance imaging features.

CASE SUMMARY

In this paper, two patients are reported: One was positive for anti-signal recognition particle antibody, and the other was positive for anti-3-hydroxy-3-methylglutaryl coenzyme A reductase antibody.

CONCLUSION

The clinical characteristics and treatment of the two patients were analysed, and the literature was reviewed to improve the recognition, diagnosis, and treatment of this disease.

Statin-Induced Immune-Mediated Necrotizing Myopathy Resulting in Proximal Muscle Weakness

Statin-induced immune-mediated necrotizing myopathy (IMNM) is a subtype of IMNM linked to exposure to statins and is characterized by positive anti-hydroxymethylglutaryl (HMG) coenzyme A reductase (HMGCR) antibodies. Although rare, this entity has become increasingly recognized as a cause of proximal muscle weakness, especially with the widespread use of statin therapy. Unlike typical statin-associated muscle symptoms, IMNM myopathy often causes severe muscle injury, and muscle weakness persists or sometimes worsens following the withdrawal of statin therapy. Medical practitioners need to keep a high index of clinical suspicion for statin-induced IMNM in patients taking statins who present with muscle weakness. The disease can be debilitating, and treatment strategies are not well established despite the advances that have been made in the diagnosis. Here we present the clinical characteristics and disease course of two cases of statin-induced IMNM. Both patients presented with progressive proximal muscle weakness and myalgias while on long-term statin therapy without significant improvement in their symptoms following the withdrawal of statin therapy. IMNM was suspected, and both patients were found to have high titers of anti-HMG coenzyme A reductase antibodies and demonstrated microscopic features consistent with a diagnosis of IMNM on muscle biopsy. The patients experienced significant disability due to muscle weakness and required a protracted course of escalated immunosuppressive therapy. Although rare, IMNM should be suspected in patients taking statins who present with muscle weakness that fails to improve or worsens when statins were stopped. Early diagnosis and institution of immunosuppressive therapy are important to prevent the progression of the disease.

The Management of Hypercholesterolemia in Patients with Neuromuscular Disorder

PURPOSE OF REVIEW

We describe and discuss the safety of statins and non-statin drugs in neuromuscular disorders (NMDs). We also propose a pragmatic model of care for the management of such cases.

RECENT FINDINGS

Patients with both NMD and hypercholesterolemia may be particularly disadvantaged owing to the toxic effects of cholesterol-lowering therapy and the inability to take medication. Specifically, the management of hypercholesterolemia in patients with NMD is complicated by the increased risk of statin-related myotoxicity and concerns that statins may aggravate or possibly induce the onset of a specific NMD. The most severe form of statin-related myotoxicity is immune-mediated necrotizing myopathy. Management of hypercholesterolemia in patients with NMDs include treating modifiable factors, consideration of toxicity risk of statin, use of non-statin lipid lowering agents, noting possible drug interactions, and careful monitoring.

Is it really myositis? Mimics and pitfalls

Idiopathic inflammatory myopathies are a heterogeneous set of systemic inflammatory disorders primarily affecting muscle. Signs and symptoms vary greatly between and within subtypes, requiring supportive laboratory and pathologic evidence to confirm the diagnosis. Several studies are typical assessments for patients with suspected inflammatory myopathy, including muscle enzymes, autoimmune markers, imaging, and muscle biopsy. Misdiagnoses of myositis are not only related to the overlap of clinical phenotype with non-inflammatory myopathies, but also due to the limitations of diagnostic tests employed. Since many of the investigative tests are non-specific, they share features with other disorders, including muscular dystrophies, endocrine, toxic, and metabolic myopathies, and other neuromuscular or rheumatologic conditions. Recognizing the limitations of tests and understanding the shared features between inflammatory and non-inflammatory myopathies can help prevent misdiagnosing myositis with one of its several mimics.

Dengue infection triggered immune mediated necrotizing myopathy in children: a case report and literature review

BACKGROUND

Immune-mediated necrotizing myopathy (IMNM) is a subgroup of idiopathic inflammatory myopathies manifesting with progressive weakness, elevated serum creatine kinase (CK) levels, and necrotizing myopathic features on muscle biopsy. There is a paucity of data on the clinical presentation of IMNM in children. We report a paediatric patient who developed anti-3-hydroxy-3-methylglutaryl-CoA reductase (anti-HMGCR)-positive necrotizing myopathy after recent dengue infection.

CASE PRESENTATION

A previously healthy 9-year-old boy presented with acute proximal muscle weakness after recovery from dengue infection. Five days after the fever subsided, he could not stand from a squatting position. He denied having skin rash, arthritis, or other systemic features. He had marked elevation of CK level of 30,833 mg/dL and was put on steroid therapy. The patient initially responded to oral prednisolone, however the weakness persisted and muscle enzymes increased as steroids were decreased. He was then referred to our hospital for further assessment. Subsequent investigation revealed anti-HMGCR positivity along with specific histopathological findings consistent with IMNM. The patient was treated with six cycles of intravenous immunoglobulin (IVIG) monthly, then followed by a gradual taper of prednisolone and oral methotrexate weekly with complete recovery in motor power.

CONCLUSIONS

Our report presents a child with clinical manifestations of IMNM which can be categorized as acute onset of muscle weakness following dengue infection. Two key points supporting a diagnosis in this case are clinical response after immunosuppressive therapy and absence of rashes found in juvenile dermatomyositis.

Immune-mediated necrotizing myopathy which showed deposition of C5b-9 in the necrotic muscle fibers and was successfully treated with intensive combined therapy with high-dose glucocorticoids, tacrolimus, and intravenous immunoglobulins

Currently, no standard treatment strategy has been established for immune-mediated necrotizing myopathy (IMNM). Here we present a case of IMNM which was successfully treated with intensive combined therapy with high-dose glucocorticoids, tacrolimus, and intravenous immunoglobulins. Her muscle weakness was rapidly progressive and severe so that she became bedridden one week after admission. She was complicated with dysphagia and had serum myogenic enzymes elevation, ventricular diastolic dysfunction, and interstitial lung disease. Serum anti-SRP antibody was positive and her muscle biopsy revealed many necrotic fibers with minimal inflammation. Further histological analysis demonstrated infiltration of phagocytic macrophages with deposition of membrane attack complex (C5b-9) in the necrotic muscle fibers, suggesting activation of complement pathway and macrophages as a pathomechanism of this disease. She was diagnosed as IMNM and was immediately initiated a combination therapy described above, which led to dramatic clinical improvements. Recent studies suggest that intravenous immunoglobulins and tacrolimus can inhibit the activation of complement pathway and macrophages. Our present case suggests that early initiation of intensive combined therapy including intravenous immunoglobulins and tacrolimus might be effective for preventing irreversible muscle damages by disrupting a pathogenic activation of complement and macrophages in IMNM.

Interstitial lung disease is not rare in immune-mediated necrotizing myopathy with anti-signal recognition particle antibodies

Objectives

The purpose was to clarify the characteristics of interstitial lung disease (ILD) in immune-mediated necrotizing myopathy (IMNM) patients with anti-signal recognition particle (SRP) antibodies.

Methods

Medical records of IMNM patients with anti-SRP antibodies were reviewed retrospectively.

Results

A total of 60 patients were identified. Twenty-seven (45.0%) patients were diagnosed with ILD based on lung imaging: nonspecific interstitial pneumonia (NSIP) in 17 patients (63.0%) and organizing pneumonia in 9 patients (33.3%). Reticulation pattern was identified in 17 patients (63.0%) whereas 10 cases (37.0%) showed ground glass opacity and patchy shadows by high-resolution computed tomography (HRCT). Pulmonary function tests (PFTs) were available in 18 patients, 6 (33.3%) and 10 (55.6%) patients were included in the mild and moderate group, respectively. The average age at the time of ILD onset was significantly older than those without ILD (48.6 ± 14.4 years vs. 41.2 ± 15.4 years, p < 0.05), and the frequency of dysphagia in the ILD group was higher than the group without ILD (p < 0.05). Long-term follow-up was available on 9 patients. PFTs were stable in 8 (88.9%), and the HRCT remained stable in 6 (66.7%) patients.

Conclusions

ILD is not rare in IMNM patients with anti-SRP antibodies, most being characterized as mild to moderate in severity. NSIP is the principal radiologic pattern, and ILD typically remains stable following treatment.

Deep venous thrombosis in an individual with statin-exposed anti-SRP myopathy: case report and review of literature

Background

Immune-mediated necrotizing myopathy (IMNM) is characterized by proximal muscle weakness, elvated serum muscle enzyme levels, myopathic electromyography findings, and necrotic muscle fiber with few inflammatory cell infiltration in muscle biopsies. Statins, the first line drug to lower triglyceride and cholesterol level in blood, have been reported to be associated with statins-induced necrotizing autoimmune myopathy (SINAM). Although anti-3-hydroxy-3-methylglutarylcoenzyme-A reductase (anti-HMGCR) myopathy is considered as the leading myopathy related to the statins medication, anti-signal recognition particle (SRP) myopathy were also identified in several cases with statin exposure. The risk of deep venous thrombosis (DVT) is substantially high in individuals with autoimmune inflammatory diseases. But few studies have reported the occurrence and recommendation for treatment of DVT in patients with anti-SRP myopathy. Here, we reported a statin-exposed anti-SRP myopathy individual developed DVT who was successfully treated with catheter-directed thrombolysis (CDT) and systemic anticoagulants therapy.

Case presentation

A 56-year-old Chinese female came to the outpatient room with gradually progressive bilateral lower-extremity weakness. Magnetic resonance imaging revealed myopathy in bilateral thighs. Serum anti-SRP antibody was positive. She was diagnosed with anti-SRP myopathy. When treated with corticosteroids and immunosuppressants, the patient developed mild edema and pain of left lower extremity. Angiography and ultrasound revealed diffuse venous thrombosis of left lower extremity. Therapy was initiated with CDT and lower molecular weight heparin, then switched to once daily oral rivaroxaban. Meanwhile, steroids combined with tacrolimus were also carried on while simvastatin was discontinued. One month later, patient’s symptoms were resolved and only partial thrombosis in left femoral vein was remained.

Conclusion

The prevalence of DVT in patient with anti-SRP myopathy was rare. No well-established treatment strategy is available to manage the IMNM and DVT at the same time. The systemic anticoagulants therapy combined CDT can be an effective therapeutic approach to address extensive DVT in patient with anti-SRP myopathy.

Alanine transaminase is predominantly increased in the active phase of anti-HMGCR myopathy

Autoantibodies against 3‑hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and the signal recognition particle (SRP) are representative antibodies causing immune-mediated necrotizing myopathies (IMNM), called as anti-HMGCR and anti-SRP myopathies, respectively. Here, we analyzed the differences in routine blood test results between 56 anti-HMGCR and 77 anti-SRP myopathy patients. A higher alanine transaminase (ALT) level and a lower aspartate transaminase (AST)/ALT ratio were observed in anti-HMGCR myopathy patients [ALT, 265.7 ± 213.3 U/L (mean ± standard deviation); AST/ALT ratio, 0.88 ± 0.32] than in anti-SRP-myopathy patients (ALT, 179.3 ± 111.2 U/L, p < 0.05; AST/ALT ratio, 1.28 ± 0.40, p < 0.01). In the active phase, anti-HMGCR myopathy often showed ALT predominance, whereas anti-SRP myopathy often showed AST predominance. In addition, there were differences in erythrocyte sedimentation rate (ESR), total cholesterol (TChol) level, and high-density lipoprotein (HDL) level between anti-HMGCR and anti-SRP myopathies (ESR: HMGCR, 24.4 ± 20.8 mm/1 h; SRP, 35.7 ± 26.7 mm/1 h, p = 0.0334; TChol: HMGCR, 226.7 ± 36.6 mg/dL; SRP, 207.6 ± 40.8 mg/dL, p = 0.0163; HDL: HMGCR, 58.4 ± 13.9 mg/dL; SRP, 46.2 ± 17.3 mg/dL, p < 0.01). Additional studies on the differences in routine blood test results may further reveal the pathomechanisms of IMNM.

Muscle pathological features and extra-muscle involvement in idiopathic inflammatory myopathies with anti-mitochondrial antibody

OBJECTIVE

Anti-mitochondrial antibodies (AMAs) can be detected in some idiopathic inflammatory myopathy (IIM) patients. We aimed to investigate the clinical features of IIM patients with AMAs.

METHODS

We retrospectively analysed 1,167 consecutive patients with IIM for AMA-associated myositis and compared them to age- and gender-matched AMA-negative IIM patients.

RESULTS

Twenty-nine patients (2.5%) were identified with AMA-positive myositis; eight of them had primary biliary cholangitis (PBC). There were no significant differences in skin rash, dysphagia, interstitial lung disease, and muscle strength between AMA-positive patients and AMA-negative patients. Of 23 cases, 12 (52.2%) showed immune-mediated necrotizing myopathy (IMNM)-like pathological features. amongst AMA-positive patients, 11 of 16 patients with isolated anti-AMAs were classified as IMNM which was significantly higher than that of patients with coexistent anti-AMAs and myositis-specific antibodies (p = 0.026). Moreover, subclinical cardiac involvement was significantly more common in AMA-positive patients than in AMA-negative patients (21/29 VS 33/116, p<0.001). In addition, patients without PBC had a significantly higher incidence of abnormal echocardiography findings than that of patients with PBC (p = 0.009). Patients without heart abnormalities took significantly less time to achieve disease remission and prednisone tapering to <10 mg than patients with heart abnormalities (p = 0.000 and p = 0.001, respectively).

CONCLUSIONS

IMNM was a major histopathological finding in IIM patients with isolated AMAs. AMAs were significantly associated with subclinical cardiac involvement in IIM. PBC seemed to be a protective factor for abnormal echocardiography findings in AMA-positive patients. Patients without heart involvement took less time to achieve disease remission and prednisone tapering off.

Anti-HMGCR Antibody-Positive Myopathy Shows Bcl-2-Positive Inflammation and Lymphocytic Accumulations

Anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) and antisignal recognition particle (SRP) antibodies are frequently associated with immune-mediated necrotizing myopathy (IMNM). However, the difference in clinical manifestations between anti-HMGCR and anti-SRP antibodies is unclear. HMGCR is an essential enzyme for cholesterol biosynthesis and is inhibited by statins that regulate apoptosis of Bcl-2-positive and beta chemokine receptor 4 (CCR4)-positive lymphoma cells. In this study, we aimed to clarify Bcl-2 and CCR4 expressions of lymphocytes in anti-HMGCR antibody-positive IMNM and explore the difference between anti-HMGCR antibody-positive myopathy and other inflammatory myopathies. We retrospectively examined Bcl-2- and CCR4-positive lymphocyte infiltrations in muscle and skin biopsy specimens from 19 anti-HMGCR antibody-positive patients and 75 other idiopathic inflammatory myopathies (IIMs) patients. A higher incidence of Bcl-2- and CCR4-positive lymphocytes was detected in the muscle and skin of anti-HMGCR antibody-positive IMNM patients (p < 0.001). In 5 patients with anti-HMGCR antibodies, Bcl-2-positive lymphocytes formed lymphocytic accumulations, which were not observed in other IIMs. Low-density lipoprotein cholesterol levels were not increased except for patients with Bcl-2-positive lymphocytic accumulations (p = 0.010). Bcl-2 and CCR4 lymphocyte infiltrations could be a pathological characteristic of anti-HMGCR antibody-positive IMNM.

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.

Promising and Upcoming Treatments in Myositis

PURPOSE OF REVIEW

To highlight new and emerging treatment targets in myositis.

RECENT FINDINGS

The landscape of novel therapeutics in myositis has vastly changed in the past 5 years. This is largely due to a greater understanding of the pathogenesis of myositis and validation of more robust outcome measures that standardize the ability to assess treatment response. Clinical trials in dermatomyositis are leading the way with ongoing multicenter, international phase 3 clinical trials. Proof-of-concept studies targeting the JAK/STAT pathway have also showed early promise in treating refractory dermatomyositis in adults and children. This review highlights that the future armamentarium of therapeutic drugs will likely be larger and more selective in treating different subgroups of myositis.

Initial seronegative immune-mediated necrotising myopathy with subsequent anti-HMGCR antibody development and response to rituximab: case report

Background

Immune-mediated necrotising myopathy (IMNM) is characterised by severe muscle weakness and necrosis with a paucity of inflammation on muscle biopsy. Around 60% of cases are associated with antibodies to the signal recognition particle (SRP) or 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR); the remainder are seronegative. IMNM is more treatment resistant than inflammatory myopathies.

Case presentation

A 69-year-old woman with previous statin exposure presented aged 63 with muscle weakness and raised creatinine kinase (CK). Anti-SRP and anti-HMGCR antibodies were not detected, but muscle biopsy revealed changes consistent with necrotising myopathy. Statins were discontinued, and she was treated with prednisolone and methotrexate achieving disease remission. Clinical and biochemical parameters were largely stable until 6 years after diagnosis she experienced a rapid deterioration. This was found to be associated with new development of anti-HMGCR antibody. Rituximab was commenced, resulting rapidly in remission. She has remained in remission since, following 2 cycles of rituximab.

Conclusions

To our knowledge, this is the first reported case of serologically negative IMNM whose subsequent rapid deterioration was associated with development of anti-HMGCR antibody. The response to rituximab and subsequent sustained remission suggests a role for early use of rituximab in aggressive cases of anti-HMGCR myopathy.

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.

Clinical and histological features of immune-mediated necrotising myopathy: A multi-centre South Australian cohort study

Immune-mediated necrotising myopathy (IMNM) is a recently described entity. We describe a cohort of South Australian IMNM patients in order to define the spectrum of disease, characterise features that distinguish IMNM from other idiopathic inflammatory myopathy (IIM) subtypes and identify factors associated with clinically severe disease. Subjects were identified from the South Australian Myositis Database (SAMD), a histologically defined registry. Consecutive muscle sections from patients with IMNM (n = 62), other forms of IIM (n = 60) and histologically normal muscle (n = 17) were stained using immunohistochemistry and graded. Clinical information was collected from the SAMD and through retrospective chart review. IMNM patients displayed clinical and histological heterogeneity. While most (67%) were profoundly weak at presentation, 24% exhibited mild to moderate weakness and 9% had normal power. Histological myonecrosis ranged from minor to florid. The amount of myofibre complement deposition was closely associated with clinical severity. Patients of Aboriginal and Torres Strait Islander heritage and those with anti-SRP autoantibodies present with a severe phenotype. Despite intense immunotherapy, few IMNM patients recovered full power at one year follow up. The identification of clinical, serological and histological features which are associated with severe forms of the disease may have diagnostic and therapeutic utility.

Statin-induced anti-HMGCR myopathy: successful therapeutic strategies for corticosteroid-free remission in 55 patients

Objective

To describe successful therapeutic strategies in statin-induced anti-HMGCR myopathy.

Methods

Retrospective data from a cohort of 55 patients with statin-induced anti-HMGCR myopathy, sequentially stratified by the presence of proximal weakness, early remission, and corticosteroid and IVIG use at treatment induction, were analyzed for optimal successful induction and maintenance of remission strategies.

Results

A total of 14 patients achieved remission with a corticosteroid-free induction strategy (25%). In 41 patients treated with corticosteroids, only 4 patients (10%) failed an initial triple steroid/IVIG/steroid-sparing immunosuppressant (SSI) induction strategy. Delay in treatment initiation was independently associated with lower odds of successful maintenance with immunosuppressant monotherapy (OR 0.92, 95% CI 0.85 to 0.97, P = 0.015). While 22 patients (40%) presented with normal strength, only 9 had normal strength at initiation of treatment.

Conclusion

While corticosteroid-free treatment of anti-HMGCR myopathy is now a safe option in selected cases, initial triple steroid/IVIG/SSI was very efficacious in induction. Delays in treatment initiation and, as a corollary, delays in achieving remission decrease the odds of achieving successful maintenance with an SSI alone. Avoiding such delays, most notably in patients with normal strength, may reset the natural history of anti-HMGCR myopathy from a refractory entity to a treatable disease.

Muscle aches and pains: do I have leukemia?

We describe a 65-year-old man who presented with 'aches and pains' localized to the lower extremities, and was diagnosed with acute myeloid leukemia (AML). We hypothesize that this case represents an atypical presentation of AML with an immune-mediated necrotizing-like myopathy as a possible paraneoplastic manifestation of the disease, which improved after initiating chemotherapy. Our patient received a full course of 7 + 3 chemotherapy with cytarabine and daunorubicin. Proximal leg weakness and pain improved markedly following this treatment, establishing a temporal relationship between the possible paraneoplastic manifestation and treatment of underlying disease. Associations between malignancy and myopathies such as polymyositis and dermatomyositis have been well established in the literature. However, paraneoplastic IMNM is still a rare clinical phenomenon and has infrequently been associated with AML. This case may suggest myopathy and associated muscle 'aches and pains' as possible presenting symptoms of underlying AML, highlighting the heterogeneity of the clinical manifestations of this disease.

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.

Immune-mediated necrotising myopathy: A critical review of current concepts

Immune-mediated necrotising myopathy (IMNM) is a relatively recently described form of idiopathic inflammatory myopathy (IIM) that is characterised by progressive proximal weakness and few extra-muscular manifestations. Prominent myonecrosis, muscle fibre regeneration and a relative paucity of intramuscular lymphocytes are seen histologically. Immunological mechanisms are believed to underpin the pathogenesis, and intense immunotherapy is frequently required. Disease is often severe and neuromuscular recovery may be poor. Recently there has been an impressive international research effort to understand and characterise this emerging condition, although much remains unknown. Significant advances in the field include the discovery of specific autoantibodies, increased understanding of the risk factors, clinical characteristics and treatment options owing to a wealth of observational studies, and the development of novel classification criteria. Herein we review the current evidence regarding the pathophysiology, clinical presentation, histological features and serological profiles associated with this condition. Diagnostic approaches are discussed, including the role of muscle MRI and antibodies targeting 3‑hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and signal-recognition peptide (SRP), and a review of current treatment recommendations is provided.

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.

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.

Bench to bedside review of myositis autoantibodies

Idiopathic inflammatory myopathies represent a heterogeneous group of autoimmune diseases with systemic involvement. Even though numerous specific autoantibodies have been recognized, they have not been included, with the only exception of anti-Jo-1, into the 2017 Classification Criteria, thus perpetuating a clinical-serologic gap. The lack of homogeneous grouping based on the antibody profile deeply impacts the diagnostic approach, therapeutic choices and prognostic stratification of these patients. This review is intended to highlight the comprehensive scenario regarding myositis-related autoantibodies, from the molecular characterization and biological significance to target antigens, from the detection tools, with a special focus on immunofluorescence patterns on HEp-2 cells, to their relative prevalence and ethnic diversity, from the clinical presentation to prognosis. If, on the one hand, a notable body of literature is present, on the other data are fragmented, retrospectively based and collected from small case series, so that they do not sufficiently support the decision-making process (i.e. therapeutic approach) into the clinics.

Identification of multiple cancer-associated myositis-specific autoantibodies in idiopathic inflammatory myopathies: a large longitudinal cohort study

BACKGROUND

Cancer is a significant complication contributing to increased mortality in idiopathic inflammatory myopathies (IIMs), and the association between IIMs and cancer has been extensively reported. Myositis-specific autoantibodies (MSAs) can help to stratify patients into more homogeneous groups and may be used as a biomarker for cancer-associated myositis. In this study, we aimed to systematically define the cancer-associated MSAs in IIMs.

METHODS

Serum from 627 patients with IIMs was tested for MSAs. The cancer risk with different MSAs was estimated by standardized incidence ratio (SIR). Paraneoplastic manifestation, such as the close temporal relationship between myositis onset and cancer diagnoses in patients with different MSAs, was also evaluated.

RESULTS

Compared with the general Chinese population, patients with IIMs and anti-transcriptional intermediary factor (TIF1)-γ antibodies (SIR = 17.28, 95% CI 11.94 to 24.14), anti-nuclear matrix protein (NXP2) antibodies (SIR = 8.14, 95% CI 1.63 to 23.86), or anti-SAE1 antibodies (SIR = 12.92, 95% CI 3.23 to 32.94), or who were MSAs-negative (SIR = 3.99, 95% CI 1.96 to 7.14) faced increased risk of cancer. There was no association between specific MSAs subtypes and certain types of cancer. Paraneoplastic manifestations were observed in the patients carrying anti-TIF1-γ, as well as other MSAs. There were no prognostic differences among the patients with cancer-associated myositis (CAM) from different MSAs subgroups. However, in comparison to those with cancer unrelated to myositis, CAM had a worse prognosis, with an age-adjusted and sex-adjusted Cox hazard ratio (HR) of 10.8 (95% CI 1.38-84.5, p = 0.02) for all-cause mortality.

CONCLUSIONS

Our study demonstrates in what is, to our knowledge, the largest population examined to date, that anti-SAE1, and previously reported anti-TIF1-γ and anti-NXP2 antibodies, are all associated with an increased risk of cancer in patients with IIMs. Moreover, our data suggest that in some cases, anti-HMGCR, anti-Jo-1 and anti-PL-12 antibody production might also be driven by malignancy. This can aid in the etiologic research of paraneoplastic myositis and clinical management.

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.

[Anti-HMG-CoA reductase necrotizing myopathy: A report of 4 cases]

INTRODUCTION

Anti-3-hydroxy-3-méthylglutaryl-coenzyme A reductase antibody-associated necrotizing autoimmune myopathy has been recently described (2011). This myopathy is distinct from statin toxic myopathy. Our objective is to report on the clinical and para-clinical characteristics of this myopathy and to show the difficulties of therapeutic care.

CASE REPORTS

We describe 4 cases of patients followed-up in Brittany, France. All data have been analyzed retrospectively. The mean age of our patients was 59.5 years, with a sex ratio of 1. The clinical presentation was homogeneous, with a subacute painful proximal and symmetrical weakness, without extra-muscular involvement. Other presentations have been described (including pseudo-dystrophic presentation). All patients had a previous statin medication (mean duration of 3.75 years) although this criteria is not a requisite. All patients had high levels of creatine kinase and abnormal electromyographic examination. The pathological pattern on muscular biopsy was a necrotizing myopathy without significant inflammatory cells infiltration. Cardio-respiratory function was normal and no associated neoplasia was found. Over the follow-up, we observed a marked corticosteroid-dependence, not improved by immunosuppressive drugs (azathioprine and methotrexate). The benefit of intravenous immunoglobulin was clear with, sometimes, prolonged responses.

CONCLUSION

An early diagnosis of this myopathy is necessary in order to introduce an immunotherapy associated with a close monitoring. The therapeutic strategy (within which the stead of intravenous immunoglobulin seems increased) remains to be defined and long-term prospective studies are thus needed.

[Therapeutic strategy in inflammatory myopathies (polymyositis, dermatomyositis, overlap myositis, and immune-mediated necrotizing myopathy)]

Inflammatory myopathies (IM) are a heterogeneous group of autoimmune muscle disorders of unknown origin that share clinical symptoms such as muscle weakness and histological features with the presence in muscle of inflammatory infiltrate. Based on clinical, histological and serological characteristics, IM can be divided into polymyositis, dermatomyositis, overlap myositis, cancer-associated myositis, immune-mediated necrotizing myopathy, and inclusion-body myositis. Because of their resistance to corticosteroids and immunosuppressive drugs, inclusion-body myositis will be treated separately in this issue. Major obstacles in conducting high quality randomized controlled trials in inflammatory myopathies include the low prevalence and the heterogeneity of these diseases as well as the lack of international consensus on the outcome measures. In the absence of adequate controlled therapeutic trials, treatment of these disorders remains largely empirical. Corticosteroids are the cornerstone therapy. Due to the chronic course of the disease, there is a frequent need to use additional immunosuppressive treatment both to improve the disease response and to reduce the side effects of corticosteroids. Intravenous immunoglobulin infusion is a costly treatment option that is reserved in the presence of refractory dermatomyositis based on a trial showing superior efficacy against control in patients with impaired swallowing or with contraindications to immunosuppressive drugs. In patients who fail second-line therapy, which usually consists of methotrexate plus corticosteroids, the diagnosis should be carefully reassessed before considering other treatment options including methotrexate plus azathioprine or biological agents such as rituximab.