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

Low serum complements in idiopathic inflammatory myositis: clinical features and impact on the prognosis

This study investigated the clinical features and prognostic relevance of decreased serum complement levels in patients with idiopathic inflammatory myositis (IIM). The clinical information of IIM patients with less than normal serum complement levels (L-Com) and that of those with normal serum complement levels (N-Com) was compared. In patients with interstitial lung disease (ILD), regression analyses were used to investigate the implication of L-Com in their PaO2/FiO2 (P/F) ratio. Prognostic outcomes of ILD were evaluated using the log-rank test. Of 94 IIM patients, 26 with L-Com (median age, 56.0 years) and 68 with N-Com (56.5 years) were included. The prevalence of women was significantly higher in patients with L-Com (92.3%) than in those with N-Com (67.6%). ILD was observed in 17 (65.4%) patients with L-Com and in 46 (67.6%) with N-Com. Among patients with ILD, the P/F ratio was significantly lower in those with L-Com than in those with N-Com. Serum C3 levels were correlated with decreased P/F ratio. Inferior prognosis of ILD was significantly demonstrated in patients with L-Com, especially in those positive for anti-melanoma differentiation-associated protein 5 antibody. L-Com may be implicated in reduced arterial oxygen levels and a poorer prognosis in patients with IIM-related ILD.

Immune-Mediated Necrotizing Myopathy Associated With Anti-signal Recognition Particle Antibody Complicated With Acute Respiratory Distress Syndrome: A Report of Two Cases

Immune-mediated necrotizing myopathy (IMNM) represents a rare category of inflammatory myopathies characterized by more severe and rapid progression of symmetrical proximal muscle weakness. It is also marked by notably elevated serum muscle enzyme levels and distinct histological features, setting it apart from other types of myositis. Moreover, acute chronic lung respiratory dysfunction is a major comorbidity of great concern. We herein present two cases of IMNM associated with anti-signal recognition particle antibodies complicated by acute respiratory distress syndrome.

Cancer Risk and Mortality in Hospitalized Patients With Idiopathic Inflammatory Myopathies in Western Australia

OBJECTIVE

To compare cancer incidence, type, and survival between patients with idiopathic inflammatory myopathies (IIMs) in Western Australia (WA) and the general population.

METHODS

Administrative health data for hospitalized patients with incident IIM (n = 803, 56.5% female, median age 62.0 yrs), classified by a validated algorithm as polymyositis (PM; 36.2%), dermatomyositis (DM; 27.4%), inclusion body myositis (IBM; 17.1%), overlap myositis (OM; 10.7%), and other IIM (8.6%), were linked to WA cancer and death registries for the period of 1980 to 2014. Cancer incidence rates (CIRs) before and after IIM diagnosis as well as cancer mortality were compared with age-, sex-, and calendar year-matched controls (n = 3225, 54.9% female, median age 64 yrs) by rate ratios (RRs) and Kaplan-Meier survival estimates.

RESULTS

The prediagnosis CIR was similar for patients with IIM and controls (6.57 vs 5.95; RR 1.11, 95% CI 0.88-1.39) and for patients evolving to DM (n = 220) or other IIM subtypes (6.59 vs 6.56; RR 1.01, 95% CI 0.38-3.69). During follow-up, CIR was higher for all DM (4.05, 95% CI 3.04-5.29), with increased CIR for lung cancer vs controls (1.05 vs 0.33; RR 3.18, 95% CI 1.71-5.47). Cancer post diagnosis shortened life span by 59 months for patients with IIM (103 vs 162 months, P < 0.01), but reduced survival rates were observed only in patients with DM and IBM.

CONCLUSION

Cancer risk was not increased prior to IIM, but CIR for lung cancer was increased following DM diagnosis. As cancer reduced survival only in patients with DM and IBM, these data support a strategy of limited cancer screening in IIM.

Evaluation of the effectiveness of using prednisolone, tacrolimus, and intravenous immunoglobulin combination therapy on immune-mediated necrotizing myopathy-A non-randomized, observational research

OBJECTIVE

To recruit immune-mediated necrotizing myopathy (IMNM) patients with extramuscular manifestations who were refractory to initial therapy with either monotherapy with prednisolone or dual therapy with prednisolone and immunosuppressants. These patients subsequently received a combination of prednisolone, tacrolimus, and intravenous immunoglobulin (IVIG), and the efficacy of this treatment regimen was assessed in patients with IMNM.

METHOD

①Clinical data and treatment measures are as follows: This study enrolled IMNM patients who were treated at the Neurology Department of the First Medical Center of PLA General Hospital from April 2020 to May 2023. These patients received a combination therapy of prednisolone, tacrolimus, and IVIG. ②Observational indicators included manual muscle test for 8 groups of muscles (MMT-8), muscle enzyme levels (creatine kinase (CK), lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotransferase (AST)), and myositis disease activity assessment tool (MDAAT).

RESULTS

This study enrolled eight patients. All observational indicators declined after treatment compared to before treatment, and these changes were statistically significant. Moreover, extramuscular manifestations also ameliorated compared to before treatment.

CONCLUSION

The combination therapy of prednisolone, tacrolimus, and IVIG has demonstrated favorable efficacy in IMNM and broadened the treatment options for this disease. However, the results still require further validation by large-scale and randomized controlled studies.

Interpreting a Delayed Workup of Idiopathic Inflammatory Myopathy

Idiopathic inflammatory myopathies are a widely heterogeneous group of muscle diseases and encompass multiple clinicopathologic entities. Our case presentation describes a 70-year-old male who presented with progressively worsening dyspnea, along with worsening proximal muscle weakness in the bilateral lower extremities. Extensive clinical evaluation revealed a creatine kinase level of 105 IU/L, severe and chronic widespread myopathy seen on electromyography (EMG), and asymmetric but widespread muscle atrophy with fibro-fatty replacement seen on ultrasonography. Muscle biopsy specimen from the left deltoid was suboptimal but demonstrated characteristics that could be consistent with several clinicopathologic diagnoses, including sporadic inclusion body myositis (sIBM), immune-mediated necrotizing myositis (IMNM), antisynthetase syndrome (AS), and direct toxin-induced myopathy. Electron microscopy revealed tubulofilamentous inclusion associated with autophagic debris, finally rendering an accurate diagnosis. This case summary highlights the testing workflow required to diagnose a patient with an inflammatory myopathy and outlines the difficulty in establishing a diagnosis when the workup for an inflammatory myopathy is delayed and the muscle biopsy is suboptimal.

Single-cell analysis of refractory anti-SRP necrotizing myopathy treated with anti-BCMA CAR-T cell therapy

Immune-mediated necrotizing myopathy (IMNM) is an autoimmune disorder associated with the presence of autoantibodies, characterized by severe clinical presentation with rapidly progressive muscular weakness and elevated levels of creatine kinase, while traditional pharmacological approaches possess varying and often limited effects. Considering the pathogenic role of autoantibodies, chimeric antigen receptor (CAR)-T cells targeting B cell maturation antigen (BCMA) have emerged as a promising therapeutic strategy. We reported here a patient with anti-signal recognition particle IMNM refractory to multiple available therapies, who was treated with BCMA-targeting CAR-T cells, exhibited favorable safety profiles, sustained reduction in pathogenic autoantibodies, and persistent clinical improvements over 18 mo. Longitudinal single-cell RNA, B cell receptor, T cell receptor sequencing analysis presented the normalization of immune microenvironment after CAR-T cell infusion, including reconstitution of B cell lineages, replacement of T cell subclusters, and suppression of overactivated immune cells. Analysis on characteristics of CAR-T cells in IMNM demonstrated a more active expansion of CD8+ CAR-T cells, with a dynamic phenotype shifting pattern similar in CD4+ and CD8+ CAR-T cells. A comparison of CD8+ CAR-T cells in patients with IMNM and those with malignancies collected at different timepoints revealed a more NK-like phenotype with enhanced tendency of cell death and neuroinflammation and inhibited proliferating ability of CD8+ CAR-T cells in IMNM while neuroinflammation might be the distinct characteristics. Further studies are warranted to define the molecular features of CAR-T cells in autoimmunity and to seek higher efficiency and longer persistence of CAR-T cells in treating autoimmune disorders.

The spectrum of idiopathic inflammatory myopathies in Western Australia: epidemiological characteristics and mortality over time

To determine long term overall and subgroup specific incidence rates and associated mortality for idiopathic inflammatory myopathies (IIM) in a population wide study. We included patients hospitalised between 1980 and 2015 with incident IIM as defined by relevant diagnostic codes for dermatomyositis (DM) polymyositis (PM), inclusion body myositis (IBM), other IIM and overlap myositis (OM) in the Western Australia Health Hospital Morbidity Data Collection (n = 846). Trends over time for annual incidence rate per million population (AIR) were analysed by least square regression and Kaplan-Meier survival and mortality rates (MR)/100 person years compared with a matched control group (n = 3681). The averaged AIR for all IIM was 19 (CI 10.4-27.5) and stable over time with point prevalence reaching 205.3 (CI 185.6-226.6) per million in 2015. Over time, the AIR for DM 5.0 (CI 0.6-9.4) and IBM 3.3 (CI 0.7-9.6) was stable, while AIR decreased for PM (p < 0.01) and increased for other IIM (p < 0.01) and OM (p < 0.01). IBM patients were eldest at diagnosis (68 years, CI 59-77) with male preponderance in IBM (53.4%) and other IIM (55.8%) groups. Crude mortality (54.5 vs 41.3%), MR ratio (6.65 vs 5.91) and 5 (65.8% vs 71.6%) and 10-year (52.5% vs 58.7%) survival were all worse for IIM patients (all p < 0.05). IBM patients had highest MR (10.1; CI 8.38-12.14) and lowest 10-year survival (39.2%). While cardiovascular disease and cancer were predominant causes of death, they were proportionally lower in IIM patients, where respiratory and rheumatic disease were more frequent causes of death. While the overall incidence of IIM in WA was stable over 35 years, the spectrum of IIM has changed significantly with increases especially in other IIM and OM. The overall prognosis with IIM remains guarded with 10-year survival just over 50%.

Rheumatoid Arthritis Associated With Anti-Signal Recognition Particle Immune-Mediated Necrotizing Myopathy: A Case Report

Immune-mediated necrotizing myopathy (IMNM) is a rare subtype of idiopathic inflammatory myopathy that is characterized by severe subacute proximal weakness, myofiber necrosis, and significantly elevated serum creatine kinase. Anti-signal recognition particle (SRP) and anti-3-hydroxy-3-methylglutaryl-coenzyme-A reductase autoantibodies have been found in about two-thirds of patients with IMNM. This myopathy is usually idiopathic and there is a scarce literature concerning its association with connective tissue diseases. Herein, we report an unusual case of a young woman who presented with both rheumatoid arthritis and severe anti-SRP IMNM. Thankfully to a therapeutic protocol combining rituximab and cyclophosphamide, an important improvement was achieved, and notably no serious side effect was observed.

Immune-mediated necrotizing myopathy with concomitant development of Kikuchi-Fujimoto disease

Immune-mediated necrotizing myopathy (IMNM) is a distinct type of idiopathic inflammatory myositis, pathologically characterized by myofiber necrosis and degeneration in the absence of lymphocyte infiltration. Herein, we present a case of IMNM with concomitant development of Kikuchi-Fujimoto disease (KFD), characterized by histiocytic necrotizing lymphadenitis, in a 36-year-old woman who had a treatment history for rheumatoid arthritis (RA). Treatment with oral prednisolone and tacrolimus as immunosuppressants resulted in the remission of the skeletomuscular involvement and lymphadenopathy. To the best of our knowledge, this is the first report of IMNM and KFD developing concomitantly during the clinical course of RA.

TWEAK and Fn14 are overexpressed in immune-mediated necrotizing myopathy: implications for muscle damage and repair

OBJECTIVES

TNF-like weak inducer of apoptosis (TWEAK) and its sole receptor fibroblast growth factor-inducible 14 (Fn14) are involved in various inflammatory conditions. This study was performed to investigate the potential role of TWEAK/Fn14 in immune-mediated necrotizing myopathy (IMNM).

METHODS

Muscle biopsies from patients with IMNM (n = 37) and controls (n = 11) were collected. Human muscle cells were treated with TWEAK in vitro. Muscle biopsies and cultured muscle cells were analysed by immunostaining and quantitative PCR. Serum levels of TWEAK and Fn14 were detected by ELISA.

RESULTS

TWEAK and Fn14 were overexpressed in IMNM muscle biopsies. The percentage of Fn14-positive myofibers correlated with disease severity, myonecrosis, regeneration and inflammation infiltrates. Fn14-positive myofibers tended to be surrounded or invaded by CD68+ macrophages. TWEAK treatment had a harmful effect on cultured muscle cells by inducing the production of multiple chemokines and pro-inflammatory cytokines. Serum Fn14 levels were increased in patients with IMNM and correlated with muscle weakness.

CONCLUSIONS

TWEAK/Fn14 signalling was activated in IMNM, most likely aggravating muscle damage via amplifying inflammatory response and macrophages chemotaxis. Fn14 seems to be a biomarker for assessing disease severity in IMNM. In addition, Fn14 may also contribute to muscle injury repair.

Toll-like receptors and IL-7 as potential biomarkers for immune-mediated necrotizing myopathies

We aimed to verify whether the immune system may represent a source of potential biomarkers for the stratification of immune-mediated necrotizing myopathies (IMNMs) subtypes. A group of 22 patients diagnosed with IMNM [7 with autoantibodies against signal recognition particle (SRP) and 15 against 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (HMGCR)] and 12 controls were included. A significant preponderance of M1 macrophages was observed in both SRP+ and HMGCR+ muscle samples (p < 0.0001 in SRP+ and p = 0.0316 for HMGCR+ ), with higher values for SRP+ (p = 0.01). Despite the significant increase observed in the expression of TLR4 and all endosomal Toll-like receptors (TLRs) at protein level in IMNM muscle tissue, only TLR7 has been shown considerably upregulated compared to controls at transcript level (p = 0.0026), whereas TLR9 was even decreased (p = 0.0223). Within IMNM subgroups, TLR4 (p = 0.0116) mRNA was significantly increased in SRP+ compared to HMGCR+ patients. Within IMNM group, only IL-7 was differentially expressed between SRP+ and HMGCR+ patients, with higher values in SRP+ patients (p = 0.0468). Overall, innate immunity represents a key player in pathological mechanisms of IMNM. TLR4 and the inflammatory cytokine IL-7 represent potential immune biomarkers able to differentiate between SRP+ and HMGCR+ patients.

Necrotizing Autoimmune Myopathy: A Case Report on Statin-Induced Rhabdomyolysis

Statin-induced necrotizing myopathy (SINM) is an uncommon but severe complication associated with statin medication. SINM can develop at any point after a person starts taking steroids. It is now being acknowledged as a component of the broader category of "statin-induced myopathy." Like other immune-mediated necrotizing muscle diseases, statin-induced myositis is identified by weakness in proximal muscles, increased serum creatine kinase (CK) levels, and, in some cases, dysphagia and respiratory distress. In addition, there is evidence of muscle cell damage when examined under a microscope, occurring with minimal or no infiltration of inflammatory cells. Diagnosing SINM promptly is frequently challenging due to its unpredictable development over time, with symptoms sometimes emerging many years after the initial exposure to statins. One distinctive characteristic of SINM is the continued presence of muscle inflammation and elevated CK levels even after discontinuing statin treatment. Currently, no clinical trials are available to guide how to manage statin-induced immune-mediated necrotizing myopathy (IMNM). Here, we present a case of a 42-year-old woman diagnosed with SINM and was found to have persistently elevated CPK despite discontinuation of statins. Our case also suggests that intravenous (IV) immunoglobins and steroids are an effective and well-tolerated alternative to immunosuppressants.

Characteristics of cardiac involvement in immune-mediated necrotizing myopathy

Objective

To investigate the characteristics of cardiac involvement due to Immune-mediated Necrotizing Myopathy (IMNM).

Methods

Patients diagnosed with Immune-mediated Necrotizing Myopathy (IMNM) who attended the Department of Neurology and the Department of Rheumatology and Immunology at the First Medical Center of the PLA General Hospital between February 2011 and June 2022 were collected. Clinicopathological diagnosis of IMNM was performed according to the criteria established by the European Neuromuscular Center (ENMC). All patients underwent muscle biopsy and Myositis-specific antibodies (MSAs) testing. Information included age, gender, disease duration, intramuscular and extramuscular manifestations, laboratory findings (including creatine kinase, lactate dehydrogenase levels, troponin T, myoglobin and atrial natriuretic peptide), electromyography, skeletal muscle pathology and immunohistochemical staining.

Results

A total of 57 patients were included in this study. Of the serological tests, 56.1% (32/57) were positive for SRP, 21.1% (12/57) were positive for HMGCR and 22.8% (13/57) were seronegative. Thirty patients (52.6%, 30/57) presented with varying degrees of cardiac involvement. We performed ECG in 23 patients and found 6 patients with arrhythmia (26.1%), 12 patients with myocardial ischemia (52.2%), and 7 patients with acute coronary syndrome (ST elevation and non-ST elevation myocardial infarction) (30.4%), and 4 patients with left axis deviation or left ventricular high voltage, suggesting left ventricular hypertrophy (17.4%). Cardiac ultrasound was performed in 14 patients and 3 showed pericardial effusion (21.4%); Decreased left ventricular ejection fraction and atrial enlargement were 2 each; 8 showed a decrease in left ventricular diastolic function (57.1%). In addition, one patient had myocardial edema.

Conclusion

Cardiac involvement is not uncommon in IMNM. However, besides clearly statistically significant differences in the disease course, and in the values of troponin T and myoglobin, our data did not show any statistically significant difference in other features of cardiac involvement between patients with different subtypes of IMNM.

Challenges in the diagnosis and management of immune-mediated necrotising myopathy (IMNM) in a patient on long-term statins

Immune-mediated necrotising myopathy (IMNM) is a severe and poorly understood complication of statin use. Prompt management with immunosuppressive treatment is often needed to control the condition, which differs from the management of the more commonly recognised statin-induced myopathy. We present a case report and brief review of the literature regarding the pathogenesis, diagnosis, and management of anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) positive IMNM (HMGCR IMNM). There are no randomised clinical trials, but several smaller studies and cases suggest a triple therapy of corticosteroids, IVIG, and a corticosteroid-sparing immunosuppressant appears efficacious in patients with IMNM and proximal weakness. The mechanism of statin-induced IMNM is uncertain, and this is further complicated by the reports of HMGCR IMNM in statin-naïve patients, including children. We present a case of biopsy-confirmed HMGCR IMNM in a woman taking daily statins for treatment of hypercholesterolaemia for 4 years. She presented with symptoms consistent with a urinary tract infection (UTI), including muscle weakness. She was treated as an isolated case of UTI. One month later, she presented again with worsening weakness in her shoulders and hips. Creatine kinase was elevated, and MRI showed increased signal with STIR sequences in both thighs. Anti-HMGCR was positive and leg biopsy-confirmed necrotising changes. Stopping her statin prescription and a short course of prednisolone did not improve her muscle weakness. Adding methotrexate resulted in eventual resolution of her symptoms. IMNM should be considered as a differential in any patient taking statins presenting with muscle weakness, and this case suggests that immunosuppressant therapy in addition to cessation of statins is effective at treating IMNM. Clinical trials are needed to further investigate the efficacy of different combinations of immunosuppressants.

A Case of Statin-Associated Autoimmune Myopathy: Management and Treatment

Elevated lipid panels are associated with an increased risk of cardiovascular disease. Management of heart disease with lipid lowering agents play a vital role in medicine. Statins are one group of medications that are widely utilized in the medical field to decrease the risk of atherosclerotic disease. Statins work by inhibiting the hepatic enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR). Although statins are one of the most effective drugs for secondary and primary prevention of heart disease, they are not without risks and side effects such as hepatotoxicity and myopathy. We present a case of a male patient who developed progressively worsening muscle weakness and elevated muscle enzyme markers upon initiation of a statin. His symptoms persisted despite a trial of an alternative statin and subsequent discontinuation of all statin medications. A multitude of possible etiologies were considered and ranged from infectious, autoimmune, cancerous, to congenital in nature. Environmental factors, such as exposure to medications or toxins, were also considered as one of the possible precipitating factors. The association between his statin consumption and muscle weakness were not easily apparent at first. He required further workup including physical examination, electromyography, panel of myositis antibodies, and muscle biopsy. After clinical suspicion and elevated antibodies to HMGCR beyond the normal limit, he was discovered to have statin-associated autoimmune myopathy. The patient improved with the treatment of immunosuppressive agent's prednisone and methotrexate.

Leflunomide-Induced Immune-Mediated Necrotizing Myopathy in a Patient With Rheumatoid Arthritis: A Case Report

Immune-mediated necrotizing myopathy (IMNM) is a subtype of inflammatory myopathy that is characterized by proximal muscle weakness, markedly elevated serum creatine kinase, myopathic electromyographic findings, and muscle biopsies revealing necrosis or regeneration with sparse inflammatory infiltrate. IMNM tends to be idiopathic but has been associated with certain medications. This supports the possibility for other pharmacotherapies to induce IMNM-particularly leflunomide. Leflunomide is used in the treatment for rheumatoid arthritis and has been shown to induce autoimmune diseases-including autoimmune hepatitis and polymyositis. After an extensive review of history and workup of muscle weakness, we conclude that leflunomide induced an IMNM in our patient. As this is the first case of leflunomide-induced IMNM, it is important for clinicians to suspect an inflammatory myopathy in the setting of myositis while on leflunomide.

The accumulation of muscle RING finger-1 in regenerating myofibers: Implications for muscle repair in immune-mediated necrotizing myopathy

Background

Muscle RING finger-1 (MuRF-1) plays a key role in the degradation of skeletal muscle proteins. We hypothesize the involvement of MuRF-1 in immune-mediated necrotizing myopathy (IMNM).

Methods

Muscle biopsies from patients with IMNM (n = 37) were analyzed and compared to biopsies from patients with dermatomyositis (DM, n = 13), dysferlinopathy (n = 9) and controls (n = 7) using immunostaining.

Results

MuRF-1 staining could be observed in IMNM, DM and dysferlinopathy biopsies, whereas the percentage of MuRF-1 positive myofibers was significantly higher in IMNM than in dysferlinopathy (p = 0.0448), and positively correlated with muscle weakness and disease activity in IMNM and DM. Surprisingly, MuRF-1 staining predominantly presented in regenerating fibers but not in atrophic fibers. Moreover, MuRF-1-positive fibers tended to be distributed around necrotic myofibers and myofibers with sarcolemma membrane attack complex deposition. Abundant MuRF-1 expression in IMNM and DM was associated with rapid activation of myogenesis after muscle injury, whereas relatively low expression of MuRF-1 in dysferlinopathy may be attributed to damaged muscle regeneration.

Conclusions

MuRF-1 accumulated in regenerating myofibers, which may contribute to muscle injury repair in IMNM and DM. MuRF-1 staining may help clinicians differentiate IMNM and dysferlinopathy.

The Clinicopathological Distinction between Immune-Mediated Necrotizing Myopathy and Limb-Girdle Muscular Dystrophy R2: Key Points to Prevent Misdiagnosis

Background: Limb−girdle muscular dystrophy R2 (LGMD R2) is most frequently misdiagnosed as immune-mediated necrotizing myopathy (IMNM). This study aimed to compare the clinicopathological data of IMNM and LGMD R2 to find distinguishing features. Methods: We retrospectively reassessed the medical data of patients with IMNM (n = 41) and LGMD R2 (n = 8) treated at Tongji Hospital from January 2017 to December 2021. Results: In our cohort, patients with LGMD R2 had a longer interval of onset to first visit, mild muscle weakness with late upper limb involvement, less myalgia, no cervical muscle weakness or dysphagia, no extramuscular organs affected except cardiac involvement, and lack of various autoantibodies, such as antinuclear antibodies. These features were completely reversed in IMNM. Moreover, thigh MRIs showed that muscle edema prominently affecting the adductor magnus was a characteristic of IMNM, while extensive fatty replacement was more common in LGMD R2 (p = 0.0086). Necrotic myofibers presented in both entities (p = 0.1693), while features such as ring/whorled and splitting myofibers were more often found in LGMD R2 (p = 0.0112 and p < 0.0001, respectively). Conversely, sarcoplasmic p62 expression was more pronounced in IMNM (p < 0.05). There were 4 of 8 (50%) patients with LGMD R2 initially considered as seronegative IMNM, and therefore unnecessarily treated with immunosuppressive drugs. Insufficient recognition of the early clinical, imaging, and histopathological features of LGMD R2 is the main reason for misdiagnosis. Conclusions: These findings may help clinicians differentiate seronegative IMNM and LGMD R2, reducing early misdiagnosis and mismanagement. Particularly, prominent adductor magnus edema on MRI and abundant p62 staining seem to be good markers for IMNM, while the presence of splitting myofibers is a crucial clue to early hereditary myopathy, including LGMD R2.

Anti-SRP immune-mediated necrotizing myopathy: A critical review of current concepts

Purpose of review

This review aims to describe clinical and histological features, treatment, and prognosis in patients with anti-signal recognition particle (SRP) autoantibodies positive immune-mediated necrotizing myopathy (SRP-IMNM) based on previous findings.

Previous findings

Anti-SRP autoantibodies are specific in IMNM. Humoral autoimmune and inflammatory responses are the main autoimmune characteristics of SRP-IMNM. SRP-IMNM is clinically characterized by acute or subacute, moderately severe, symmetrical proximal weakness. Younger patients with SRP-IMNM tend to have more severe clinical symptoms. Patients with SRP-IMNM may be vulnerable to cardiac involvement, which ought to be regularly monitored and cardiac magnetic resonance imaging is the recommended detection method. The pathological features of SRP-IMNM are patchy or diffuse myonecrosis and myoregeneration accompanied by a paucity of inflammatory infiltrates. Endoplasmic reticulum stress-induced autophagy pathway and necroptosis are activated in skeletal muscle of SRP-IMNM. Treatment of refractory SRP-IMNM encounters resistance and warrants further investigation.

Summary

Anti-SRP autoantibodies define a unique population of IMNM patients. The immune and non-immune pathophysiological mechanisms are involved in SRP-IMNM.

Slowly Progressive Limb-Girdle Weakness and HyperCKemia - Limb Girdle Muscular Dystrophy or Anti-3-Hydroxy-3-Methylglutaryl-CoA-Reductase-Myopathy?

BACKGROUND

Anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR)-myopathy is a usually rapidly progressive form of immune-mediated necrotizing myopathy (IMNM). Rarer clinical courses show slow progression and resemble the phenotype of limb-girdle dystrophy (LGMD).

OBJECTIVE

We demonstrate the difficulties in differentiating LGMD versus anti-HMGCR-myopathy.

METHODS

We report on a 48-year-old patient with slowly progressive tetraparesis and hyperCKemia for more than 20 years.

RESULTS

Due to myopathic changes in initial and second muscle biopsy and typical clinical presentation, the patient was diagnosed with LGMD 20 years ago; despite comprehensive genetic testing including exome diagnostics, the genetic cause of disease could not be identified. Finally, HMG-CoA reductase antibodies were detected, confirming the diagnosis of anti-HMGCR-myopathy. By re-work-up of a second muscle biopsy specimen from year 2009, the diagnosis of a IMNM was made in retrospect. Seven cycles of high-dose immunoglobulins were administered; patient reported outcome measures have mildly improved.

CONCLUSION

Patients with clinical LGMD phenotype, degenerative changes in muscle biopsy but without genetic confirmation of the disease should be tested for HMG-CoA-myopathy, thereby allowing for an early start of treatment.

A Case Report of Statin-Induced Immune-Mediated Necrotizing Myopathy Treatment Challenges

Statin-induced necrotizing autoimmune myopathy is an immune-mediated necrotizing myopathy related to the use of statins. It is a very rare disease, which usually presents with proximal muscle weakness and frank elevation in creatine kinase levels. Stopping statin and the use of immunosuppressive therapy are considered the mainstay therapy. Use of steroids in patients with inflammatory myopathy can be complicated by steroid-induced myopathy. Herein, we present a case of a 55-year-old patient with statin-induced necrotizing autoimmune myopathy based on the presence of proximal muscle weakness, magnetic resonance findings, suggestive muscle biopsy features, and positive anti-HMGCR autoantibodies. The patient was treated with triple immunosuppressive therapy with a particularly good response to intravenous immunoglobulin. This report highlights the importance of timely diagnosis and early use of combined immunosuppressive therapy to improve patients' outcome affected by this rare disease.

[A case of anti-SRP antibody-positive immune-mediated necrotizing myopathy triggered by human parvovirus B19 infection]

We have reported a case of a 44-year-old woman with anti-signal recognition particle (SRP) antibody-positive immune-mediated necrotizing myopathy triggered by human parvovirus B19 (PVB19) infection. She was admitted to the hospital because of lower leg edema and muscle weakness after erythema infectiosum. Magnetic resonance imaging of the lower extremities revealed high signals in the proximal muscles and subcutaneous edema on STIR. Muscle biopsy showed myofiber regenerative changes and variation in fiber size. A myositis-specific autoantibody profile indicated a positive result for anti-SRP antibodies. We diagnosed the patient with immune-mediated necrotizing myopathy (IMNM). Muscle strength and subcutaneous edema improved gradually in 3 months following immunotherapy. This is the first case report of an IMNM associated with PVB19 infection.

Outcome Predictors of Immune-Mediated Necrotising Myopathy-A Retrospective, Multicentre Study

OBJECTIVES

Evidence-based treatment protocols are currently lacking for immune-mediated necrotising myopathy. In this multicentre retrospective study, we examined baseline clinical characteristics and treatment variables that may predict short-term outcome of patients with immune-mediated necrotising myopathy.

METHODS

Muscle biopsies from the John Hunter Hospital and the Royal Adelaide Hospital obtained between 2012 and 2019 were reviewed at a single laboratory at South Australia Pathology. All biopsies with histological features of IMNM were identified. Demographics of study subjects, clinical information, and myositis-specific antibody status were recorded along with muscle strength, serum CK and treatment regimens at baseline, three and six months. Primary outcome measures were muscle strength and serum creatinine kinase at 3- and 6-months. Mixed-effects regression models in a Bayesian framework were performed using Statistical Package R.

RESULTS

Female sex, older age, initial prednisone dose and intravenous methylprednisolone were associated with greater improvement in serum creatine kinase. In patients with moderate-to-severe disease at baseline, early intravenous immunoglobulin was associated with greater improvement in hip flexor strength at six months.

CONCLUSION

Early IVIg was associated with clinical improvement in short-term follow-up in IMNM. Female sex, older age, initial oral prednisone dose and initial use of IV methylprednisolone were associated with better biochemical improvement.

Immune-mediated necrotizing myopathy with pembrolizumab: a specific neuromuscular entity

PURPOSE

Pembrolizumab is a humanized monoclonal antibody that binds to the programmed cell-death protein-1 (PD-1) on immune T-cells, thus blocking PD-1 activity. Pembrolizumab is indicated for the treatment of advanced melanoma, metastatic non-small-cell lung cancer, and head and neck squamous cell carcinoma. However, it is associated with immune-related adverse events.

METHODS

We investigated the association between pembrolizumab and immune-mediated necrotizing myopathy (IMNM). We analyzed reports in the World Health Organization's global individual case safety report database, Vigibase, up to January 2020 with the MedDRA lower level term "IMNM." The association between exposure to pembrolizumab and occurrence of the adverse event was estimated by disproportionality analysis. The reporting odds ratio (ROR) was calculated with 95% confidence intervals (CIs). We analyzed the criteria of diagnosis of the adverse reaction.

RESULTS

Five-hundred sixty-seven notifications were identified as IMNM of which 14 with pembrolizumab. The ROR was 17.59 (95% CI: 9.4-32.9).

CONCLUSION

The diagnosis of IMNM does not always take into account recent criteria for the diagnosis of this pathology. This study highlights the existence of a signal, as well as the need for collaboration between oncologists and neurologists for these neurological pathologies.

Clinical features and diagnostic tools in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are rare autoimmune disorders affecting primarily muscles, but other organs can be involved. This review describes the clinical features, diagnosis and treatment for IIMs, namely polymyositis (PM), dermatomyositis (DM), sporadic inclusion body myositis (sIBM), immune-mediated necrotizing myopathy (IMNM), and myositis associated with antisynthetase syndrome (ASS). The diagnostic approach has been updated recently based on the discovery of circulating autoantibodies, which has enhanced the management of patients. Currently, validated classification criteria for IIMs allow clinical studies with well-defined sets of patients but diagnostic criteria to guide the care of individual patients in routine clinical practice are still missing. This review analyzes the clinical manifestations and laboratory findings of IIMs, discusses the efficiency of modern and standard methods employed in their workup, and delineates optimal practice for clinical care. Α multidisciplinary diagnostic approach that combines clinical, neurologic and rheumatologic examination, evaluation of electrophysiologic and morphologic muscle characteristics, and assessment of autoantibody immunoassays has been determined to be the preferred approach for effective management of patients with suspected IIMs.

Idiopathic inflammatory myopathies: a review

Idiopathic inflammatory myopathy (IIM) is the umbrella term including dermatomyositis (DM), polymyositis (PM), overlap myositis (OM), sporadic inclusion body myositis (IBM) and necrotising autoimmune myopathy (NAM), also known as immune-mediated necrotising myopathy. There is some debate as to whether PM exists as a discrete entity, or perhaps is an overly generalising term encompassing connective tissue disease associated myositis, or OM, and the previously poorly recognised NAM. As such, PM will not be covered in detail in this review. DM, OM and NAM all present similarly, with proximal weakness and elevated creatine kinase (CK) level. By contrast, IBM preferentially involves the long finger flexors and quadriceps, and presents with a normal or only mildly elevated CK. Developments in serological testing and imaging are shifting the diagnostic paradigm away from a reliance on histopathology. The therapeutic armamentarium for IIM continues to evolve, with intravenous immunoglobulin and rituximab proving to be successful for refractory disease. This review will provide a diagnostic algorithm for the clinician to help distinguish between IIM subtypes - with emphasis on clinical assessment, serology and imaging, as well as discussion of therapeutic options and escalation of immunotherapy.

Progressive increases in creatine kinase activity in an anorexic cat with necrotising myopathy

Case summary

A 5-year-old castrated male domestic shorthair cat with weight loss and reduced appetite was evaluated for increased and progressively rising creatine kinase (CK) activity. The cat had recently been diagnosed with hepatic lipidosis. Muscle biopsy and histopathology revealed mild myonecrosis and phagocytosis without obvious inflammatory cell infiltrates. Resolution of necrotising myopathy was observed after a short course of anti-inflammatory prednisolone and nutritional supplementation.

Relevance and novel information

This is the first report of a necrotising myopathy in a cat associated with progressively increasing CK activity and decreased appetite. Anorexia in cats has been associated with increased CK activity, but an underlying cause of this CK elevation has only been postulated. Here we document muscle necrosis and muscle stiffness in a cat with anorexia.

The Clinicopathological Distinction Between Seropositive and Seronegative Immune-Mediated Necrotizing Myopathy in China

Objectives: The present study aimed to compare the clinicopathological features of patients with seronegative immune-mediated necrotizing myopathy (IMNM) and those positive for anti-signal recognition particle (SRP) or anti-3-hydroxy-3-methylglutarylcoenzyme-a reductase (HMGCR) antibodies. Methods: We retrospectively analyzed the data of patients with IMNM treated in the Neurology Department of Tongji Hospital from January 1, 2013, to December 31, 2019. Results: Among the 117 patients with IMNM, 30.8% (36/117) were positive for anti-SRP antibodies, 6.0% (7/117) were positive for anti-HMGCR antibodies, and 13.7% (16/117) were seronegative. Myalgia at presentation (62.5 vs. 23.3%, p = 0.0114) was more commonly observed in patients with seronegative IMNM than in those with seropositive IMNM. Subclinical cardiac involvement was more frequently detected in seronegative IMNM than in seropositive IMNM (6/13 vs. 5/33, p = 0.0509, echocardiogram; 7/7 vs. 12/24, p = 0.0261, cardiac MRI). Deposition of membrane attack complex (MAC) on the sarcolemma of myofibers in biopsied muscle was less commonly observed in patients with seronegative IMNM than in patients with seropositive IMNM (16.7 vs. 68.2%, p = 0.0104). The rate of marked improvement following immunotherapy tended to be higher in patients with seronegative IMNM than in those with seropositive IMNM (87.5 vs. 61%, p = 0.0641). Conclusions: Patients with seronegative IMNM more frequently present with myalgia at onset, exhibit more subclinical cardiac involvement and uncommon MAC deposition on myofibers, and experience better outcomes than those with seropositive IMNM.

Time-Dependent Analysis of Risk of New-Onset Heart Failure Among Patients With Polymyositis and Dermatomyositis

OBJECTIVE

To determine the risk and time trends of heart failure (HF) leading to hospitalization in individuals newly diagnosed as having polymyositis/dermatomyositis (PM/DM) relative to non-PM/DM controls at the general population level.

METHODS

A retrospective cohort study was conducted using data from a nationwide insurance database in Taiwan. Patients with incident PM/DM and without a history of HF were selected between 2000 and 2013. Unmatched and propensity score-matched cohorts were established separately. A multivariable Cox proportional hazards regression model was used to estimate the adjusted hazard ratio (HR) for the risk of HF in the unmatched cohort. In the propensity score-matched cohort, general population controls were selected and matched at a 1:1 ratio to the patients with PM/DM based on propensity scores, which accounted for the confounding factors of age, sex, index date (year) of first diagnosis, comorbidities, and medication usage. The cumulative incidence of HF was estimated using the Kaplan-Meier method. A stratified Cox proportional hazards model was used to calculate the HR for the risk of HF events at different follow-up time points among patients with PM/DM compared with non-PM/DM controls in the propensity score-matched cohort.

RESULTS

In the unmatched cohort, the study assessed 2,025 patients with PM/DM and 196,109 general population controls. Results of multivariable Cox regression analysis, adjusted for age, sex, comorbidities, and medication usage, revealed a greater risk of HF leading to hospitalization in the PM/DM group than in the control group (adjusted HR 3.29, 95% confidence interval [95% CI] 2.60-4.18). After matching based on propensity score, a total of 1,997 pairs of PM/DM patients and general population controls were identified. In this propensity score-matched cohort, the cumulative incidence of HF in patients with PM/DM at 3 years, 5 years, and 10 years was 3.3%, 4.4%, and 7.4%, respectively. The absolute difference in HF risk in the PM/DM group compared with the control group was 1.8% at 3 years, 2.1% at 5 years, and 3.0% at 10 years. Compared with general population controls, patients with PM/DM exhibited an augmented risk of HF (HR 2.06, 95% CI 1.36-3.12). Analyses stratified according to follow-up time point revealed that the increased risk of HF persisted for up to 10 years after the PM/DM diagnosis.

CONCLUSION

These results indicate that the risk of HF leading to hospitalization was increased in patients with PM/DM throughout the study period, supporting the need for greater vigilance in the monitoring of patients with PM/DM for the development of this potentially lethal complication.

Myopathy associated with anti-signal recognition particle antibodies with pulmonary involvement and response to rituximab

The authors present the case of a 76-year-old female patient with progressive decrease in proximal muscle strength, fatigue, dyspnea, diffuse hand edema and painful triphasic Raynaud's phenomenon. Anti-SRP and anti-SSA antibodies were detected, muscle biopsy revealed changes consistent with necrotizing myopathy and capillaroscopy had findings compatible with systemic sclerosis. High-resolution chest computed tomography revealed interstitial lung disease with a non-specific interstitial pneumonia pattern. Lung function tests demonstrated a forced vital capacity 93% and a diffusing capacity for carbon monoxide of 65% predicted. After multidisciplinary discussion, she was diagnosed with immune-mediated necrotizing myopathy/systemic sclerosis overlap syndrome with pulmonary involvement. Initially, dual immunomodulation therapy with high-dose steroids and intravenous immunoglobulin was started, but after 4 weeks, the patient had clinical and analytical deterioration. At this time, she was started on rituximab, with an excellent and sustained response at both muscle and lung, sustained after 12 months.

Rituximab in the treatment of immune-mediated necrotizing myopathy: a review of case reports and case series

Immune-mediated necrotizing myopathy (IMNM) is a group of immune-related myopathies characterized by progressive proximal muscle weakness, extremely high serum creatine kinase (CK) levels, and necrotic muscle fibers with a relative lack of inflammation. Treatment of IMNM is challenging, with most cases refractory to high-dose steroids in combination with multiple immunotherapies. The role of rituximab (RTX) for IMNM has been explored in isolated case reports and small series. The aim of this article was to perform a literature review of patients with IMNM treated with RTX and to evaluate RTX efficacy and safety. A total of 34 patients with IMNM were reviewed: 52.9% (18/34) with anti-signal recognition particle (SRP) antibodies and 47.1% (16/34) with anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) antibodies. Patient age at onset varied from 11 years to 81 years (mean 41 years). The majority of patients presented as a severe proximal muscle weakness and the peak level of CK varied from 3900 IU/L to 56,000 IU/L (mean 18,440 IU/L). Prior to RTX administration, all patients were treated with high-dose steroids and most were treated with multiple immunotherapies. The reason for initiating RTX was that 64.7% (22/34) of patients showed no improvement after previous treatments, and 35.3% (12/34) of patients relapsed when attempting to wean steroids or other immunosuppressive agents. With regard to RTX efficacy, 61.8% (21/34) of patients presented a response to RTX. Our data may support the use of RTX as an effective treatment strategy against IMNM resistant to steroids and multiple immunotherapies. Meanwhile, RTX as a first-line therapy could be a choice in IMNM, particularly in African Americans with anti-SRP antibody-positive subsets. ANA, antinuclear antibody; CK, creatine kinase; HMGCR, 3-hydroxy-3-methylglutaryl-CoA reductase; IMNM, immune-mediated necrotizing myopathy; MAC, membrane attack complex; MHC-I, major histocompatibility complex-I; RTX, rituximab; SRP, signal recognition particle.

SRP-positive necrotising myopathy: takes more than just the muscles

Necrotising myopathy is an autoimmune disease that commonly affects muscles. Here we examine a case of a middle-aged women presenting with a chief report of shortness of breath, who subsequently developed muscle weakness. Her clinical course was complicated by respiratory failure and pulmonary hypertension likely due to the underlying pathology of signal recognition particle-positive necrotising myopathy. After further evaluation, her shortness of breath was thought to be secondary to muscle pathology rather than cardiopulmonary pathology. She was transferred to our institution for workup by rheumatology. At the time of admission, 6 months after initial presentation, her weakness progressed, so that she was unable to lift her arms and legs against gravity. Furthermore, neurological examination revealed mild facial and nuchal weakness, severe proximal weakness, more moderate distal weakness and global areflexia.

Immunotherapy reversed myopathy but not cardiomyopathy in a necrotizing autoimmune myopathy patient with positive anti-SRP and MDA-5 autoantibodies

Background

Necrotizing autoimmune myopathy (NAM) is pathologically characterized by myofiber necrosis and regeneration with paucity or absence of inflammatory cells in muscle biopsy. Two autoantibodies, namely anti-signal recognition particle (SRP)-antibodies and anti-3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR)-antibodies, are typically specific with NAM. Anti-SRP-positive NAM can be associated with cardiomyopathy which responds well to immunotherapy. Here we reported an anti-SRP-antibody and anti-MDA5-antibody NAM patient who developed severe cardiomyopathy after gaining significant improvement of myopathy and subsequently accepted heart transplantation.

Case presentation

A NAM case with both positive anti-SRP and MDA-5 antibodies who gained significant improvement of the skeletal muscle weakness with immunotherapy, but 3 years later he developed severe dilated cardiomyopathy and at last received heart transplantation. Myocardial biopsy showed disarranged and atrophic myofibers, remarkable interstitial fibrosis without inflammatory infiltrates. Immunohistochemistry analysis revealed increased polyubiquitin-binding protein p62/SQSTM1 protein expression and the positive staining of cleaved-caspase 3 in a few cardiomyocytes. After the transplantation, the patient was symptom-free on oral prednisone (10 mg/day) and tacrolimus (2 mg/day).

Conclusions

We described the first case of anti-SRP and anti-MAD5 positive NAM who had received heart transplantation because of cardiopathy. Though the myopathy had been clinically improved after immunotherapy, the cardiomyopathy remained progressive and lethal. The processes of dysfunctional autophagy and augmented apoptosis were putatively pathophysiological mechanisms underlying cardiac damage in anti-SRP and anti-MAD5 positive NAM.

MRI of myositis and other urgent muscle-related disorders

Myositis has many etiologies, and it can be encountered in the acute or chronic setting. Our goal is to increase the radiologist’s knowledge of myositis and other urgent muscle disorders encountered in the emergent or urgent setting. We review the clinical presentation, the MRI appearance, and the complications that can be associated with these entities. Since myositis can affect multiple muscle compartments, we review how to differentiate the compartments of the appendicular skeletal in order to generate reports that relay important anatomic information to the treating physician. Given the poor sensitivity and positive predictive value of the clinical signs and symptoms used to diagnosing acute compartment syndrome, we discuss the potential use of MRI in cases of suspected but clinically equivocal compartment syndrome in the future.

Paraneoplastic Necrotizing Myopathy Post Lumpectomy and Chemotherapy for Early Breast Cancer

Our case report describes a 60-year-old female patient with a past medical history of Stage IB breast cancer, status post lumpectomy and adjuvant chemotherapy, admitted to our hospital with the chief complaints of fever, myalgia, and muscle weakness. A physical exam revealed proximal muscle weakness and a facial rash. A full workup was done, and the muscle biopsy showed evidence of a necrotizing myopathic process, which confirmed our diagnosis. This led to a diagnosis of necrotizing myopathy, deemed to be paraneoplastic after other possible differentials were ruled out. The patient showed improvement after a five-day course of intravenous immunoglobulin (IVIG) and high-dose steroids. Necrotizing myopathy, as a paraneoplastic process, has been scarcely described. In the context of our case, we review the characteristics and relevant existing literature about paraneoplastic necrotizing myopathy as well as emphasize the need to include it as a differential in the setting of malignancy.

Update on dermatomyositis in adults

Dermatomyositis (DM) in adults has a prevalence of 6-7 per 100,000 population per year. This dedicated compact overview was prepared due to an increasing incidence as well as an often underestimated systemic involvement and new developments in myositis-specific antibodies (MSA). The spectrum of clinical dermatological and systemic symptoms is described. Related diagnostic procedures are depicted, and therapeutic regimens based on the German S2k guidelines and the current literature are presented. The urgency of an early diagnosis is emphasized as about 30 % of patients with DM manifest a tumor. Etiopathology is often associated with pulmonary fibrosis, and inflammation of myositis can cause irreversible muscle damage. Clinical signs and correct interpretation of serological markers can deliver valuable information on the extent of DM, and provide an indication for further diagnostic procedures, prognosis and choice of therapy.

Immune-Mediated Necrotizing Myopathy Initially Presenting as Erythema Nodosum

Immune-mediated necrotizing myopathy (IMNM) is a type of autoimmune myopathy characterized by severe diffuse proximal myofiber necrosis in the context of inflammatory myopathy. Autoantibodies of anti-signal recognition particle and anti-hydroxy-3-methylglutaryl-CoA reductase are two antibodies specific to IMNM. Erythema nodosum (EN) is often accompanied by various systemic diseases, such as autoimmune diseases. Herein, we report a female patient with signal recognition particle-associated IMNM, with EN as the first presentation. She showed significant clinical improvement after the initiation of glucocorticoids, intravenous immunoglobulin, rituximab, and mycophenolate mofetil. This case indicates that IMNM can initially present as EN. IMNM and EN might have overlapping pathogeneses.

Immune mediated necrotizing myopathy: A rare complication of statin therapy

Immune mediated necrotizing myopathy (IMNM) is part of the inflammatory myopathies group of diseases and presents with muscle weakness, myalgias and elevated serum creatine phosphokinase (CPK). Statin-induced IMNM is a rare complication. We present a patient with IMNM secondary to simvastatin use. The patient presented with proximal myopathy, dysphagia, and elevated creatinine kinase levels, and was subsequently found to have anti-3- hydroxy-3-methylglutaryl-CoA reductase (HMGCR) autoantibodies with a necrotizing process on muscle biopsy. This patient’s case was further complicated by sequelae of multiple disease processes, ultimately leading to deterioration of his health.

Autoantibody-Negative Immune-Mediated Necrotizing Myopathy Responds to Early and Aggressive Treatment: A Case Report

Immune-mediated necrotizing myopathy (IMNM) is a rare idiopathic disease that is further classified by the presence of serum antibodies. A modicum of patients lack serum autoantibodies. Significantly elevated creatine kinase (CK) is highly characteristic of IMNM. The pathophysiology of IMNM is partially understood, and effective treatment options are limited, particularly in patients without serum autoantibodies. In this case, we report a 76-year-old male presenting with a four-month history of proximal muscle weakness. Muscle biopsy and serology confirmed the diagnosis of autoantibody-negative IMNM. Early and aggressive treatment with high-dose steroids and a course of intravenous immunoglobulin significantly reduced the patient’s symptoms and CK within three months. This case serves as an example of an effective treatment outcome in a patient with this rare idiopathic necrotizing myopathy.