Bulky malignant peripheral nerve sheath tumour of the left thigh in a pregnant woman presenting with a pathological fracture of the proximal femur.

Malignant peripheral nerve sheath tumour (MPNST) is an aggressive soft tissue sarcoma with a poor prognosis, affecting most commonly the extremities. The lungs constitute the most frequent location for distant metastases. Half of all MPNSTs arise in patients with neurofibromatosis type 1, while approximately 10% are radiation induced and the rest are sporadic.The authors present a pregnant woman in her 40s with a sporadic MPNST of the lower limb and with lung metastases at diagnosis. Treatment consisted of interilioabdominal amputation, followed by adjuvant chemotherapy. Partial response and disease stabilisation were achieved with chemotherapy.Surgical resection with negative margins is the only potentially curative therapy, while radiation therapy and chemotherapy might be useful in the neoadjuvant or adjuvant setting, but their advantage in survival is not demonstrated. In the reported case, chemotherapy permitted the achievement of partial response and stabilisation of the disease.

Thigh muscle and fat volumes are associated with knee cartilage abnormalities and bone marrow edema-like lesions: data from the osteoarthritis initiative.

OBJECTIVE: To investigate the associations of thigh muscle and fat volumes with structural abnormalities on MRI related to knee osteoarthritis. MATERIALS AND METHODS: MRI studies of the thighs and knees from 100 individuals were randomly selected from the Osteoarthritis Initiative Cohort. Whole Organ MR Scoring (WORMS) and effusion-synovitis scoring were performed in all knee MRI. Thigh muscles, intermuscular fat, and subcutaneous fat were manually segmented in 15 consecutive MR thigh images. Radiographic Kellgren-Lawrence grades (KLG) were also obtained in all knee radiographs. Independent t-tests were used to investigate the associations between thigh muscle and fat volumes, and sex. Mixed-effects analyses were obtained to investigate the associations between thigh muscle and fat volumes, KLG, WOMAC pain score, cartilage and bone marrow WORMS, as well as effusion-synovitis scores. RESULTS: Women had higher subcutaneous fat volume than men (616.82 vs. 229.13 cm3, p < 0.01) and men had higher muscle volumes than women (p < 0.01). Quadriceps (coef = -2.15, p = 0.01) and vastus medialis (coef = -1.84, p = 0.03) volumes were negatively associated with the WORMS cartilage scores. Intermuscular fat volume (coef = 0.48, p = 0.01) was positively associated with WORMS bone marrow edema-like lesion (BMEL) scores. The quadriceps (coef = -0.99, p < 0.01) and hamstring (coef = -0.59, p = 0.01) volumes were negatively associated with WORMS BMEL scores. No evidence of an association was found between thigh muscle and fat volumes with KLG and effusion-synovitis grading (p > 0.05). CONCLUSION: Increased quadriceps and hamstring volumes were negatively associated with cartilage lesion and BMEL scores while no evidence of an association was found between thigh muscle and fat volumes, and radiographic knee osteoarthritis or effusion-synovitis grading.

Semi-quantitative thigh magnetic resonance imaging scores in assessing disease activity and determining long-term clinical outcome in idiopathic inflammatory myopathies: a causal mediation analysis.

OBJECTIVES: To evaluate the relationship of thigh MRI (t-MRI) with manual muscle testing-8 (MMT-8), muscle enzymes and autoantibodies. To determine the causal and mediating factors resulting in poor recovery of MMT-8 in inflammatory myositis (IIM). METHODS: This was a single-centre retrospective study in IIM patients. t-MRI was semi-quantitatively scored for muscle oedema, fascial oedema, muscle atrophy and fatty infiltration. Spearman correlation of t-MRI scores was done with muscle enzymes at baseline, and MMT-8 at baseline and on follow-up. Causal mediation analysis was performed with age, sex, symptom duration, autoantibodies, diabetes and BMI as independent variables, follow-up MMT-8 as dependent and t-MRI scores as mediating variables. RESULTS: Baseline evaluation was done on 59 and follow-up on 38 patients. Median follow-up of the cohort was 31 (10-57) months. Baseline MMT-8 negatively correlated with muscle oedema (r = -0755), fascial oedema (r = -0.443) and muscle atrophy (r = -0.343). Creatinine kinase (r = 0.422) and aspartate transaminase (r = 0.480) positively correlated with muscle oedema. Follow-up MMT-8 correlated negatively with baseline atrophy (r = -0.497) and fatty infiltration (r = -0.531). On follow-up, MMT-8 males had positive total effect (estimate (95%CI)) via atrophy [2.93 (0.44, 4.89)] and fatty infiltration [2.08 (0.54, 3.71)]. Antisynthetase antibody had a positive total effect via fatty infiltration [4.50 (0.37, 7.59)]. Age had a negative total effect via atrophy [-0.09 (0.19, -0.01)] and fatty infiltration [-0.07 (-0.15, -0.01)]. Disease duration had a negative total effect via fatty infiltration [-0.18 (-0.27, -0.02)]. CONCLUSION: Baseline fatty infiltration and muscle atrophy resulting from older age, female sex, longer disease duration and absent anti-synthetase antibodies, partly mediate muscle recovery in IIM.

Evaluation of the factors affecting survival and local recurrence in thigh soft tissue sarcomas.

OBJECTIVES: The aim of this study was to evaluate the factors affecting local recurrence and survival in patients with soft-tissue sarcomas located in the thigh. PATIENTS AND METHODS: This retrospective cross-sectional study evaluated 41 soft tissue sarcoma patients (21 males, 20 females; mean age: 57.9±13.7 years; range, 18 to 90 years) with thigh involvement between January 2010 and December 2020. All surgical intervention was performed by one surgeon with an experience of 15 years in orthopedic oncologic surgery. Epidemiological, radiological, histopathological, and metabolic features, as well as surgical and oncological treatments and prognoses, were assessed. The data was statistically analyzed to determine factors affecting local recurrence and survival in these cases, staged using Enneking and the American Joint Committee on Cancer classifications. RESULTS: Liposarcomas were the most common type of tumor (39%), followed by undifferentiated pleomorphic sarcomas (32%). Tumors >10 cm were associated with decreased survival rates. High-grade tumors, tumor necrosis, Ki-67 index >20%, and positive surgical margins were also associated with lower survival rates. Metastatic patients had significantly lower survival rates. Local recurrence was significantly more frequent in patients with positive surgical margins. Survival rates were significantly lower in metastatic patients. CONCLUSION: There are many factors that affect local recurrence and survival of soft tissue sarcomas. The size of the mass, the presence of necrosis, a high Ki-67 index, positive surgical margins, and the presence of metastasis are the main factors that should be taken into consideration.

Cervico-thoracic Morel-Lavallée lesion.

Morel-Lavallée lesions (MLLs) result from high-energy trauma causing separation of subcutaneous tissue from the underlying tissue, most commonly in the gluteal region or thigh.We report the case of a woman in her 40s with a fluctuant collection of the cervico-thoracic region following trauma. Further imaging identified an MLL. An orthoplastic approach resulted in non-operative management with a spinal brace. Three months from initial injury, the lesion completely resolved. She was symptom free at final follow-up and discharged.We present the only recorded case of MLL developing in the cervico-thoracic region. Management posed difficultly as no literature currently exists. We demonstrated conservative management for cervico-thoracic MLL can be effective.We have described the first documented case of cervico-thoracic MLL. MLL is not exclusive to pelvic injuries and can develop in the cervico-thoracic region. We have shown conservative management is a viable treatment of atypical MLL.

Muscle strength and psychometric properties of the health-related quality of life in patients with soft tissue sarcoma resection in the thigh.

OBJECTIVES: The aim of this study was to evaluate the effect of STS resection in the thigh on MS and the HRQoL. METHODS: Fourteen adults patients with STS in the thigh who underwent wide resection and limb preservation were evaluated. The patients were submitted to the Mini-Mental State Examination (MMSE). A hand-held dynamometer was used to measure the MS the flexors, adductors, abductors, and extensors muscles of the operated and non-operated thighs and between the dominant and non-dominant operated sides. The Musculoskeletal Tumor Society (MSTS) and Short Form Health Survey-36 (SF-36) questionnaires were applied to quantify the psychometric properties of the HRQoL. The data were submitted to statistical analysis using the Wilcoxon test (MS), and Mann-Whitney and Spearman correlation (MSTS and SF-36) (α = 0.05). RESULTS: There was no significant difference in MS between the operated side and the non-operated side, and between the dominant and non-dominant operated side (ρ > 0.05). The MSTS presented a significant difference in the emotional acceptance for patients submitted to radiotherapy (ρ = 0.029). The SF-36 showed significant differences in the emotional aspect for patients submitted to chemotherapy (ρ = 0.027) and in the social aspect between the dominant and non-dominant operated side (ρ = 0.024). CONCLUSIONS: The HRQoL of adult patients is hampered after the treatment of STS even when MS is maintained.

Meralgia Paresthetica: Relevance, Diagnosis, and Treatment.

BACKGROUND: Pain and sensory disturbance in the distribution of the lateral femoral cutaneous nerve in the ventrolateral portion of the thigh is called meralgia paresthetica (MP). The incidence of MP has risen along with the increasing prevalence of obesity and diabetes mellitus and was recently estimated at 32 new cases per 100 000 persons per year. In this review, we provide an overview of current standards and developments in the diagnosis and treatment of MP. METHODS: This review is based on publications retrieved by a selective literature search, with special attention to meta-analyses, systematic reviews, randomized and controlled trials (RCTs), and prospective observational studies. RESULTS: The diagnosis is mainly based on typical symptoms combined with a positive response to an infiltration procedure. In atypical cases, electrophysiological testing, neurosonography, and magnetic resonance imaging can be helpful in establishing the diagnosis. The literature search did not reveal any studies of high quality. Four prospective observational studies with small case numbers and partly inconsistent results are available. In a meta-analysis of 149 cases, pain relief was described after infiltration in 85% of cases and after surgery in 80%, with 1-38 months of follow-up. In another meta-analysis of 670 cases, there was pain relief after infiltration in 22% of cases, after surgical decompression in 63%, and after neurectomy in 85%. Hardly any data are available on more recent treatment options, such as radiofrequency therapy, spinal cord stimulation, or peripheral nerve stimulation. CONCLUSION: The state of the evidence is limited in both quantity and quality, corresponding to evidence level 2a for surgical and non-surgical methods. Advances in imaging and neurophysiological testing have made the diagnosis easier to establish. When intervention is needed, good success rates have been achieved with surgery (decompression, neurectomy), and variable success rates with infiltration.

Long-term results of huge deep-seated liposarcoma in the thigh: Two case reports.

RATIONALE: Liposarcoma is an uncommon malignant tumor that develops in the fatty tissue; thus, the long-term follow-up results of extremely large liposarcomas in the submuscular layer of the thigh have rarely been reported. Here we share the course and outcome of 2 cases of a huge deep-seated liposarcoma in the thigh. PATIENT CONCERNS: Two patients visited our clinic, each with a deep-seated mass in the thigh. First, a 44-year-old man presented to the outpatient clinic with a left thigh mass. Approximately 1 year later, an 80-year-old man presented to the outpatient clinic with a right posterior thigh mass. DIAGNOSIS: Magnetic resonance imaging revealed an approximately 14 × 8 × 21 cm well-differentiated liposarcoma between the sartorius and iliopsoas muscle and an approximately 14 × 12 × 31.5 cm lipomatous mass in the posterior compartment of the right thigh involving the right adductor muscles. After complete marginal resection, an excisional biopsy was performed to confirm the diagnosis. INTERVENTIONS: Both patients underwent complete marginal resection without chemotherapy or radiotherapy. OUTCOMES: A biopsy showed a 20 × 17 × 7 cm well-differentiated, well-encapsulated liposarcoma in the 44-year-old man and a 30 × 17 × 10 cm well-differentiated liposarcoma in the 80-year-old man. These patients have achieved approximately 61 and 44 months of recurrence-free survival to date, respectively. LESSONS: Here we described the long-term outcomes of 2 patients with a huge deep-seated liposarcoma in the lower extremity. Complete marginal excision of well-differentiated liposarcoma can achieve excellent recurrence-free survival.

Unusual causes for meralgia paresthetica: systematic review of the literature and single center experience.

Meralgia paresthetica is often idiopathic, but sometimes symptoms may be caused by traumatic injury to the lateral femoral cutaneous nerve (LFCN) or compression of this nerve by a mass lesion. In this article the literature is reviewed on unusual causes for meralgia paresthetica, including different types of traumatic injury and compression of the LFCN by mass lesions. In addition, the experience from our center with the surgical treatment of unusual causes of meralgia paresthetica is presented. A PubMed search was performed on unusual causes for meralgia paresthetica. Specific attention was paid to factors that may have predisposed to LFCN injury and clues that may have pointed at a mass lesion. Moreover, our own database on all surgically treated cases of meralgia paresthetica between April 2014 and September 2022 was reviewed to identify unusual causes for meralgia paresthetica. A total of 66 articles was identified that reported results on unusual causes for meralgia paresthetica: 37 on traumatic injuries of the LFCN and 29 on compression of the LFCN by mass lesions. Most frequent cause of traumatic injury in the literature was iatrogenic, including different procedures around the anterior superior iliac spine, intra-abdominal procedures and positioning for surgery. In our own surgical database of 187 cases, there were 14 cases of traumatic LFCN injury and 4 cases in which symptoms were related to a mass lesion. It is important to consider traumatic causes or compression by a mass lesion in patients that present with meralgia paresthetica.

Muscle strength and functional recovery for soft-tissue sarcoma of the thigh: a prospective study.

BACKGROUND: This study aimed to investigate changes in muscle strength and functional outcome before and after surgery for soft-tissue sarcoma of the thigh and to examine the timing of recovery. METHODS: From 2014 to 2019, 15 patients who underwent multiple resections of the thigh muscle for soft-tissue sarcoma of the thigh were included in this study. The muscle strength was measured with an isokinetic dynamometer for the knee joint and with a hand-held dynamometer for the hip joint. The functional outcome assessment was based on the Musculoskeletal Tumor Society (MSTS) score, Toronto Extremity Salvage Score (TESS), European Quality of Life-5 Dimensions (EQ-5D), and maximum walking speed (MWS). All measurements were conducted preoperatively and at 3, 6, 12, 18, and 24 months postoperatively, and the ratio of postoperative to preoperative value was used. A repeated-measures analysis of variance was performed to compare changes over time and to investigate the recovery plateau. Correlations between changes in muscle strength and functional outcomes were also examined. RESULTS: The muscle strength of the affected limb, MSTS score, TESS, EQ-5D, and MWS were significantly decreased at 3 months postoperatively. The recovery plateau was subsequently reached at 12 months postoperatively. The changes in muscle strength of the affected limb and functional outcome showed a significant correlation. CONCLUSIONS: The estimated postoperative recovery for soft-tissue sarcoma of the thigh is 12 months after surgery.

Glomus Tumor Within the Tensor Fascia Lata: A Case Report.

BACKGROUND Glomus tumors are rare, benign, soft-tissue lesions, usually occurring in the hand, but they can occur in other regions of the body, such as the thigh. Most of the time, extradigital glomus tumors are difficult to diagnose, and symptoms can persist for a long time. The usual clinical presentations consist of pain, tenderness at the site of the tumor, and hypersensitivity to cold. CASE REPORT We report a case of a GT of the proximal thigh in a 39-year-old man with left thigh pain without palpable mass for several years, without clear diagnosis. He had pain and hyperesthesia exacerbated by running. The patient was diagnosed initially by ultrasound imaging, which revealed a round, solid, hypoechoic, homogeneous mass in the left upper thigh. Magnetic resonance imaging (MRI) with contrast showed a well-defined intramuscular lesion in the tensor fascia lata. A percutaneous biopsy was done through ultrasound guidance, followed by excisional biopsy and immediate pain relief. CONCLUSIONS Glomus tumors of the thigh are a rare neoplasm, especially in the proximal thigh; they are difficult to diagnose and are associated with morbidity. Diagnosis can be made through a systematic approach and simple investigation, such as via ultrasonography. A percutaneous biopsy can help in drawing up a management plan, and malignancy must be considered if the lesion is suspicious. Symptoms can persist in case of incomplete resection or unrecognized synchronous satellite lesions; thus, symptomatic neuroma should be considered.

Giant thigh glomus tumor of uncertain malignant potential: Case report with pathologic-radiologic correlation.

INTRODUCTION: Glomus tumors (GT) are rare, benign tumors that arise from glomus bodies and usually develop in digital areas. Extradigital GT are exceptional and thigh location is infrequent. CASE REPORT: We report a case of a GT of the thigh in a 79-year-old male patient that measured 9.5 cm in maximum size. The GT lay above the muscular fascia without infiltrating it. Internal hypervascularity was seen by spectral Doppler ultrasound. Magnetic resonance image showed a heterogeneous mass with hyperintense and hypointense components and internal lobes with liquid-liquid levels. Histopathology revealed a monotonous round-cell proliferation with central nuclei without atypia or mitotic figures, around small-caliber vessels. These cells expressed smooth muscle actin and pericellular collagen IV. GT of uncertain malignant potential was diagnosed. The mass was completely removed. The patient did not experience local relapse nor distant metastasis. CONCLUSION: GT are rare soft tissue tumors whose diagnosis of unusual giant masses in uncommon locations may be delayed and misdiagnosed given the low suspicion.

A Size-Based Criteria for Flap Reconstruction After Thigh-Adductor, Soft-Tissue Sarcoma Resection.

BACKGROUND: Resection of soft-tissue sarcomas from the adductor compartment is associated with significant complications. Free/pedicled flaps often are used for wound closure, but their effect on healing is unclear. We compared wound complications, oncologic, and functional outcomes for patients undergoing flap reconstruction or primary closure following resection of adductor sarcomas. METHODS: A total of 177 patients underwent resection of an adductor sarcoma with primary closure (PrC) or free/pedicled flap reconstruction (FR). Patient, tumor, and treatment characteristics were compared, as well as wound complications, oncologic, and functional outcomes (TESS/MSTS87/MSTS93). To examine the relative benefit of flap reconstruction, number needed to treat (NNT) was calculated. RESULTS: In total, 143 patients underwent PrC and 34 had FR, 68% of which were pedicled. There were few differences in demographic, tumor, or treatment characteristics. No significant difference was found in the rate of wound complications. Length of stay was significantly longer in FR (18 days vs. PrC 8 days; p < 0.01). Oncologic and functional outcomes were similar over 5 years follow-up. Uncomplicated wound healing occurred more often in FR compared with PrC for tumors with ≥15 cm (NNT = 8.4) or volumes ≥ 800 ml (NNT = 8.4). Tumors ≤ 336 ml do not benefit from a flap, whereas those > 600 ml are 1.5 times more likely to heal uneventfully after flap closure. CONCLUSIONS: Although flap use prolonged hospitalization, it decreased wound healing complications for larger tumors, and in all sized tumors, it demonstrated similar functional and oncologic outcomes to primary closure. Our size-based treatment criteria can help to identify patients with large adductor sarcomas who could benefit from flap reconstruction. LEVEL OF EVIDENCE III: (Retrospective cohort study).

Longitudinal study of multi-parameter quantitative magnetic resonance imaging in Duchenne muscular dystrophy: hyperresponsiveness of gluteus maximus and detection of subclinical disease progression in functionally stable patients.

OBJECTIVE: To describe the disease progression of Duchenne muscular dystrophy (DMD) in the pelvic and thigh muscles over 1-year using multiple-parameter quantitative magnetic resonance imaging (qMRI), and to determine the most responsive muscle and predict subclinical disease progression in functionally stable patients. METHODS: Fifty-four DMD patients (mean age 8.9 ± 2.5, range 5-15 years) completed baseline and 1-year follow-up qMRI examinations/biomarkers [3-point Dixon/fat fraction (FF); T1 mapping/T1; T2 mapping/T2]. Meanwhile, clinical assessments [NorthStar ambulatory assessment (NSAA) score] and timed function tests were performed in DMD patients. Twenty-four healthy male controls (range 5-15 years) accomplished baseline qMRI examinations. Group differences were compared using the Wilcoxon test. The standardized response mean (SRM) was taken as the responsiveness to the disease progression index. RESULTS: FF, T1, and T2 in all DMD age subgroups changed significantly over 1-year (P < 0.05). Even in functionally stable patients (NSAA score increased, unchanged, or decreased by 1-point) over 1-year, significant increases in FF and T2 and decreases in T1 were observed in gluteus maximus (GMa), gluteus medius, vastus lateralis, and adductor magnus (P < 0.05). Overall, the SRM of FF, T1, and T2 was all the highest in GMa, which were 1.25, - 0.92, and 0.93, respectively. CONCLUSIONS: qMRI biomarkers are responsive to disease progression and can also detect subclinical disease progression in functionally stable DMD patients over 1-year. GMa is the most responsive to disease progression of all the muscles analyzed. TRIAL REGISTRATION: Chinese Clinical Trial Registry ( http://www.chictr.org.cn/index.aspx ) ChiCTR1800018340, 09/12/2018, prospectively registered.

Extradigital glomus tumour of the thigh causing 8 years of undiagnosed debilitating pain.

A woman in her mid-50s was referred to a plastic surgeon with an 8-year history of undiagnosed, localised severe, reproducible pain of the right thigh. Treatment with oral and topical analgesics, corticosteroids, acupuncture and physiotherapy did not provide symptom relief. She was referred to multiple specialists over the preceding 8 years including chronic pain physicians, physiatry, orthopaedic surgery and plastic surgery. Investigations including sonographic and MRI eventually revealed a non-specific soft tissue abnormality in the area of tenderness, which was excised en bloc. Histopathology revealed an extradigital glomus tumour. The patient's symptoms immediately and permanently resolved postexcision.Physicians seeing patients suffering from undiagnosed focal, reproducible pain should consider extradigital glomus tumours in their differential diagnosis. Workup for extradigital glomus tumour includes focused sonographic or MRI over the area of pain. Additionally, local injection of an anaesthetic agent can be used to assist with diagnosis.

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OBJECTIVES: To summarize the skeletal muscle magnetic resonance imaging (MRI) features of the lower limbs in common subtypes of muscular dystrophy (MD) and the experience in the application of MRI in the diagnosis of MD. METHODS: A total of 48 children with MD who were diagnosed by genetic testing were enrolled as subjects. The muscle MRI features of the lower limbs were analyzed. Cumulative fatty infiltration score was calculated for each subtype, and the correlation of cumulative fatty infiltration score with clinical indices was analyzed for Duchenne muscular dystrophy (DMD). RESULTS: DMD was characterized by the involvement of the gluteus maximus and the adductor magnus. Becker muscular dystrophy was characterized by the involvement of the vastus lateralis muscle. Limb-girdle muscular dystrophy was characterized by the involvement of the adductor magnus, the vastus intermedius, the vastus medialis, and the vastus lateralis muscle. For DMD, the cumulative fatty infiltration score of the lower limb muscles was significantly correlated with age, course of the disease, muscle strength, and motor function (P<0.05), while it was not significantly correlated with the serum creatine kinase level (P>0.05). CONCLUSIONS: Different subtypes of MD have different MRI manifestations, and MRI may help with the diagnosis and assessment of MD.

Magnetic resonance imaging-based lower limb muscle evaluation in Charcot-Marie-Tooth disease type 1A patients and its correlation with clinical data.

We aimed to derive comprehensive MRI parameters that reflect intramuscular fat infiltration severity for designated lower extremity levels, based on semiquantitative analyses in Charcot-Marie-Tooth disease type 1A (CMT1A) patients. We reviewed lower extremity MRIs of 116 CMT1A patients. Intramuscular fat infiltration grading using the Mercuri scale was performed for the non-dominant lower extremity at three levels (proximal, mid, and distal) for the thigh and at two levels (proximal and distal) for the lower leg. Based on MRI results, the following parameters were calculated for each level and for entire muscles: fat infiltration proportion (FIP), significant fat infiltration proportion (SigFIP), and severe fat infiltration proportion (SevFIP). The relationships between the MRI parameters and clinical data were evaluated using Spearman's correlation analysis. FIP, SigFIP, and SevFIP measured for entire muscles significantly correlated with Charcot-Marie-Tooth Neuropathy Score (p < 0.001), functional disability scale (p < 0.001), 10-m walk test time (p = 0.0003, 0.0010, and 0.0011), and disease duration (p < 0.001). Similar correlations were demonstrated for FIP, SigFIP, and SevFIP acquired from the lower leg. Our MRI parameters obtained through semiquantitative analyses of muscles significantly correlated with clinical parameters in CMT1A patients, suggesting their potential applicability as imaging markers for clinical severity.

[Retrospective study on clinical manifestation, thigh MRI and electrophysiology characteristics of immune-mediated necrotizing myopathy].

Objective: To summarize the clinical, thigh magnetic resonance (tMRI) and electromyographic (EMG) characteristics in patients with immune-mediated necrotizing myopathy (IMNM). Methods: A total of 32 IMNM patients who were admitted to the Department of Neurology from April 2019 to April 2021 were enrolled at the First Medical Centre of Chinese PLA General Hospital. According to the type of antibody, the patients were divided into anti-SRP antibody positive (SRP+) group, anti-HMGCR antibody positive (HMGCR+) group and seronegative (SN) group. The gender, age, course of disease, myositis antibodies, extramuscular manifestations, EMG were collected and analyzed among three groups. The characteristics of skeletal muscle were assessed by tMRI inflammatory edema and fat infiltration scores. Analysis of variance, Kruskal-Wallis test and Chi-square test were used to compare the differences in different clinical characteristics and tMRI scores among the three groups. When there was a statistical difference among the three groups, the comparison between the two groups was corrected by the Bonferroni method. Result: (1) Of the 32 patients, 20 were females (62.5%).The median age of onset was 47±14 years, 25 (78.1%) patients had an acute or subacute course.There were 17 (53.1%) with SRP+, 8 (25.0%) with HMGCR+, and 7 (21.9%) with MSAs (myositis specific antibodies) negative. Anti-Ro52 antibody was the most common combined antibody (12/32, 37.5%), among which 10 were in SRP+group.(2) The CK of all patients were elevated, median was 5 948 (4 229, 7 664) U/L. There was no statistical difference of MMT scores among three groups. The proximal limb score was lower than distal limb (P<0.01). The axial muscle score was lower than the distal limb score (P<0.05).(3) Extramuscular manifestations of HMGCR+ group were lower than those of the other two groups (12.5% vs. 71.4% and 76.5%, P<0.017). Rash (60.0% vs.14.3%, P<0.05) and interstitial pulmonary diseases (70.0% vs. 14.3%, P<0.05) were more common in patients with anti-SRP coexistence with anti-Ro52 than those with isolated anti-SRP. Connective tissue disease was more common in SN group (57.1% vs. 11.8% and 0, P<0.017).(4) tMRI showed fascial edema of SN group was more obvious than that of the other two groups (P<0.017). There was no statistical difference in the degree of fat infiltration and inflammatory edema among three groups, but SRP+ group had more cases of early fat infiltration.(5) Myotonic potentials (25.0% vs. 0 and 0, P<0.017) and compound repetitive discharges (CRDs) (50.0% vs. 5.9% and 0, P<0.017) were common in HMGCR+ group. Proteomic analysis found significantly different expressed proteins in skeletal muscle of patients with myotonic potentials or CRDs were associated with cytoskeleton, cell junction and extracellular matrix. Conclusion: IMNM with pure anti-SRP antibody positive and anti-HMGCR positive were mainly affected by skeletal muscles. Those who were co-positive for anti-SRP antibody and anti-Ro52 antibody had more extramuscular manifestations, which might be a special subtype of SRP+ group. This study proposed for the first time that myofascial inflammatory edema is an early sign of SN-IMNM injury. EMG of HMGCR+group were more prone to myotonia potential and CRDs.