HIV-associated nemaline myopathy manifesting as bent spine syndrome.

HIV-associated myopathies include HIV-associated polymyositis, inclusion body myositis, diffuse infiltrative lymphocytosis syndrome and sporadic late-onset nemaline myopathy (HIV-NM). HIV-NM typically manifests as a painless, progressive proximal and axial muscle weakness with characteristic histological findings of intracytoplasmic rods, or nemaline bodies, seen in atrophic muscle fibres. HIV-NM presents prior to or shortly after initiation of antiretroviral therapy (ART) and is treated with intravenous immunoglobulin, glucocorticoids or immunosuppression. We present a case of HIV-NM in a patient with well-controlled HIV on decades-long ART with progressive bent spine syndrome, or camptocormia. This case highlights the importance of considering HIV-associated myopathies such as HIV-NM in patients with HIV who present with musculoskeletal complaints.

Sporadic Late-Onset Nemaline Myopathy: Current Landscape.

PURPOSE OF REVIEW: Sporadic late-onset nemaline myopathy (SLONM) is a rare adult-onset, acquired, muscle disease that can be associated with monoclonal gammopathy or HIV infection. The pathological hallmark of SLONM is the accumulation of nemaline rods in muscle fibers. We review here current knowledge about its presentation, pathophysiology, and management. RECENT FINDINGS: SLONM usually manifests with subacutely progressive proximal and axial weakness, but it can also present with chronic progressive weakness mimicking muscular dystrophy. The pathophysiology of the disease remains poorly understood, with evidence pointing to both autoimmune mechanisms and hematological neoplasia. Recent studies have identified histological, proteomic, and transcriptomic alterations that shed light on disease mechanisms and distinguish SLONM from inherited nemaline myopathies. A majority of SLONM patients respond to intravenous immunoglobulins, chemotherapy, or hematopoietic stem cell transplant. SLONM is a treatable myopathy, although its underlying etiology and pathomechanisms remain unclear. A high degree of suspicion should be maintained for this disease to reduce diagnostic delay and treatment in SLONM and facilitate its distinction from inherited nemaline myopathies.

Early clinical and pre-clinical therapy development in Nemaline myopathy.

INTRODUCTION: Nemaline myopathies (NM) represent a group of clinically and genetically heterogeneous congenital muscle disorders with the common denominator of nemaline rods on muscle biopsy. NEB and ACTA1 are the most common causative genes. Currently, available treatments are supportive. AREAS COVERED: We explored experimental treatments for NM, identifying at least eleven mainly pre-clinical approaches utilizing murine and/or human muscle cells. These approaches target either i) the causative gene or associated genes implicated in the same pathway; ii) pathophysiologically relevant biochemical mechanisms such as calcium/myosin regulation of muscle contraction; iii) myogenesis; iv) other therapies that improve or optimize muscle function more generally; v) and/or combinations of the above. The scope and efficiency of these attempts is diverse, ranging from gene-specific effects to those widely applicable to all NM-associated genes. EXPERT OPINION: The wide range of experimental therapies currently under consideration for NM is promising. Potential translation into clinical use requires consideration of additional factors such as the potential muscle type specificity as well as the possibility of gene expression remodeling. Challenges in clinical translation include the rarity and heterogeneity of genotypes, phenotypes, and disease trajectories, as well as the lack of longitudinal natural history data and validated outcomes and biomarkers.

Clinicopathologic Profiles of Sporadic Late-Onset Nemaline Myopathy: Practical Importance of Anti-α-Actinin Immunostaining.

BACKGROUND AND OBJECTIVES: Sporadic late-onset nemaline myopathy (SLONM) is a treatable or otherwise fatal myopathy. Diagnosis of SLONM is still challenging, and no therapeutic consensus has been achieved. Here, we reported the clinicopathologic features and long-term follow-up data of SLONM in a Chinese cohort. METHODS: We performed a retrospective evaluation of clinical, pathologic, and treatment outcomes of 17 patients with SLONM diagnosed between March 1986 and April 2021 at our neuromuscular center. Immunohistochemistry (IHC) with antibodies against 5 Z-disc-associated proteins was performed in the muscle biopsies of SLONM to identify a potential pathologic marker in aid of diagnosis. In comparison, we also performed muscle IHC in patients with selective type II fiber atrophy (n = 22), neurogenic atrophy (n = 22), mitochondrial myopathy (n = 5), immune-mediated necrotizing myopathy (n = 5), and normal controls (n = 5). RESULTS: Most of the patients exhibited asymmetric limb muscles weakness (71%, 12/17) and neck extensor weakness (53%, 9/17). Immunofixation electrophoresis was performed in 11 patients, and 4 of them were identified with monoclonal gammopathy of undetermined significance (MGUS). EMG from 16 patients demonstrated a myopathic pattern with spontaneous activities in 69% (11/16) of them. Muscle MRI showed preferential involvement of paraspinal, gluteus minimus and medius, semimembranosus, and soleus muscles. Suspected nemaline bodies on modified Gomori trichrome were confirmed by IHC using anti-α-actinin antibody (100%, 17/17), anti-myotilin antibody (94%, 16/17), anti-desmin antibody (94%, 16/17), anti-α-B crystallin antibody (65%, 11/17), and anti-telethonin antibody (18%, 3/17) with various positive rates. Notably, anti-α-actinin IHC showed the highest percentage of strongly positive staining (77%, 13/17), being the only one without negative results. Moderate improvement following autologous stem cell transplantation (ASCT) was noted in 3/4 patients with MGUS; favorable outcomes were also achieved in 6/7 patients without MGUS, including 3 patients with complete recovery who were given a combined treatment of prednisone and another immunosuppressant. DISCUSSION: SLONM is a treatable myopathy with ASCT or traditional immunotherapy, especially when combined with steroids and immunosuppressants. Anti-α-actinin immunostaining is the most reliable pathologic marker to identify rod-bearing fibers, and it should be performed routinely in adult patients with undiagnosed nonnecrotic myopathies.

Pediatric Nemaline Myopathy: A Systematic Review Using Individual Patient Data.

Nemaline myopathy is a skeletal muscle disease that affects 1 in 50 000 live births. The objective of this study was to develop a narrative synthesis of the findings of a systematic review of the latest case descriptions of patients with NM. A systematic search of MEDLINE, Embase, CINAHL, Web of Science, and Scopus was performed using Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) guidelines using the keywords pediatric, child, NM, nemaline rod, and rod myopathy. Case studies focused on pediatric NM and published in English between January 1, 2010, and December 31, 2020, in order to represent the most recent findings. Information was collected about the age of first signs, earliest presenting neuromuscular signs and symptoms, systems affected, progression, death, pathologic description, and genetic changes. Of a total of 385 records, 55 case reports or series were reviewed, covering 101 pediatric patients from 23 countries. We review varying presentations in children ranging in severity despite being caused by the same mutation, in addition to current and future clinical considerations relevant to the care of patients with NM. This review synthesizes genetic, histopathologic, and disease presentation findings from pediatric NM case reports. These data strengthen our understanding of the wide spectrum of disease seen in NM. Future studies are needed to identify the underlying molecular mechanism of pathology, to improve diagnostics, and to develop better methods to improve the quality of life for these patients.

Inflammatory features in sporadic late-onset nemaline myopathy are independent from monoclonal gammopathy.

Sporadic late-onset nemaline myopathy (SLONM) is a rare adult-onset non-hereditary disease with subacute proximal muscle and often axial muscle weakness, characterized by the presence of nemaline bodies in skeletal muscle biopsies. Considering its association with concurrent monoclonal gammopathy of undetermined significance (MGUS), the disease is classified into two major subtypes (1) SLONM without MGUS (SLONM-noMGUS) and (2) with MGUS (SLONM-MGUS) association. SLONM associated with HIV infection (SLONM-HIV) is also reported. SLONM-MGUS has been shown to be associated with poorer prognosis and required aggressive treatment including high-dose melphalan and autologous stem cell transplantation. The approach is currently debatable as recent reports suggested effectiveness of intravenous immunoglobulin as initial treatment with indifference of overall survival despite the presence of MGUS. Our study aimed to find an underlying basis by review of pathological features in 49 muscle biopsy proven-SLONM from two large tertiary centers in Japan and Germany (n = 49: SLONM-noMGUS = 34, SLONM-MGUS = 13, SLONM-HIV = 2). We compared pathological findings in SLONM-noMGUS and SLONM-MGUS and focused on the presence of any detectable inflammatory features by immunohistochemistry. The clinical and histological features in SLONM-noMGUS and SLONM-MGUS were not distinctively different except for more common regenerating fibers (>5% of myofibers) present in SLONM-MGUS (p < 0.01). HLA-ABC expression and fine granular p62 were observed in 66.7% and 78.3% of SLONM, respectively. The predominant inflammatory cells were CD68+ cells. The inflammatory cells showed positive correlations with the percentage of nemaline-containing fibers (p < 0.001). In conclusion, inflammatory features are present although rather mild in SLONM. This finding contributes to the hypothesis of an acquired inflammatory disease pathogenesis and opens the possibility to offer immunotherapy in SLONM with inflammatory features regardless of the monoclonal gammopathy status.

Chemotherapy-based approach is the preferred treatment for sporadic late-onset nemaline myopathy with a monoclonal protein.

Sporadic late-onset nemaline myopathy (SLONM) associated with monoclonal protein (MP) is a rare disease with an aggressive, and often fatal course. Whether SLONM + MP represents a malignancy or dysimmune disease remains unclear. Currently, two main approaches are used to treat SLONM + MP: nonchemotherapy-based treatment (immunosuppression, intravenous immunoglobulins, plasmapheresis and plasma exchange) or chemotherapy with or without autologous stem cell transplantation. Due to the rare occurrence of the disease, the best treatment modality is unknown. We analyzed treatment and outcomes in a large cohort of 53 patients with SLONM + MP: four our own patients and 49 cases from published literature. Neurological improvement in the nonchemotherapy group (N = 25) was observed in 52% of patients: 8% reached marked improvement, 8% moderate response, 36% mild response; none reached complete remission (CR). In the chemotherapy group (N = 28), neurological improvement was seen in 86% of patients: 46% reached CR, 25% marked response, 11% moderate response and 4% mild response. The best neurological improvement correlated with deep hematological remission. Mean time to best response in the chemotherapy group was 8 months versus 21 months in the nonchemotherapy group (P < .001). Overall survival was higher in patients in the chemotherapy group. A chemotherapy approach should be the preferred treatment for patients with SLOMN + MP with the goal to reach complete hematologic remission. Based on the clinical, morphological peculiarities, aggressive disease course and superior clinical benefits of chemotherapy over nonchemotherapy, SLONM + MP should be considered as a hematological malignancy with the presence of MP of clinical rather than undetermined significance.

Expressing a Z-disk nebulin fragment in nebulin-deficient mouse muscle: effects on muscle structure and function.

BACKGROUND: Nebulin is a critical thin filament-binding protein that spans from the Z-disk of the skeletal muscle sarcomere to near the pointed end of the thin filament. Its massive size and actin-binding property allows it to provide the thin filaments with structural and regulatory support. When this protein is lost, nemaline myopathy occurs. Nemaline myopathy causes severe muscle weakness as well as structural defects on a sarcomeric level. There is no known cure for this disease. METHODS: We studied whether sarcomeric structure and function can be improved by introducing nebulin's Z-disk region into a nebulin-deficient mouse model (Neb cKO) through adeno-associated viral (AAV) vector therapy. Following this treatment, the structural and functional characteristics of both vehicle-treated and AAV-treated Neb cKO and control muscles were studied. RESULTS: Intramuscular injection of this AAV construct resulted in a successful expression of the Z-disk fragment within the target muscles. This expression was significantly higher in Neb cKO mice than control mice. Analysis of protein expression revealed that the nebulin fragment was localized exclusively to the Z-disks and that Neb cKO expressed the nebulin fragment at levels comparable to the level of full-length nebulin in control mice. Additionally, the Z-disk fragment displaced full-length nebulin in control mice, resulting in nemaline rod body formation and a worsening of muscle function. Neb cKO mice experienced a slight functional benefit from the AAV treatment, with a small increase in force and fatigue resistance. Disease progression was also slowed as indicated by improved muscle structure and myosin isoform expression. CONCLUSIONS: This study reveals that nebulin fragments are well-received by nebulin-deficient mouse muscles and that limited functional benefits are achievable.

Miopatía nemalínica tratada con L-tirosina para aliviar los síntomas en un recién nacido / Nemaline rod myopathy treated with L-tyrosine to relieve symptoms in a neonate

La miopatía nemalínica es un trastorno heterogéneo definido por la presencia de estructuras con forma de bastones, conocidas como cuerpos nemalínicos (o bastones de nemalina). El diagnóstico se funda en la debilidad muscular, además de la visualización de cuerpos nemalínicos en la biopsia muscular. La miopatía nemalínica no tiene cura. Las estrategias terapéuticas para este trastorno son sintomáticas y empíricas. En este artículo, presentamos el caso de una recién nacida con insuficiencia respiratoria grave y debilidad muscular generalizada, a la que se le diagnosticó miopatía nemalínica a través de la biopsia muscular. La paciente tuvo una notable disminución de la sialorrea y una mejora de los movimientos espontáneos después del tratamiento con L-tirosina. Este caso se presenta para destacar la importancia de la biopsia muscular en el diagnóstico diferencial de la hipotonía grave durante el período neonatal y el posible beneficio del aporte suplementario de L-tirosina para disminuir la sialorrea y restaurar la fuerza muscular.

Nemaline myopathy (NM) is a heterogeneous disorder defined by the presence of rod-shaped structures known as nemaline bodies or rods. The diagnosis is based on muscle weakness, combined with visualization of nemaline bodies on muscle biopsy. There is no curative treatment for nemaline myopathy. Therapeutic strategies for this condition are symptomatic and empirical. Herein, we present a newborn with severe respiratory failure and generalized muscle weakness, who was diagnosed as NM by muscle biopsy. The patient experienced remarkable decrease in sialorrhea and improvement of spontaneous movements after L-tyrosine treatment. This case is presented to emphasize the importance of muscle biopsy in the differential diagnosis of severe hypotonia during neonatal period and a possible benefit of L-tyrosine supplementation for decreasing sialorrhea and restoring muscle strength.

Sporadic late-onset nemaline myopathy: Clinical spectrum, survival, and treatment outcomes.

OBJECTIVE: To describe the clinical phenotype, long-term treatment outcome, and overall survival of sporadic late-onset nemaline myopathy (SLONM) with or without a monoclonal protein (MP). METHODS: We conducted a retrospective chart review of patients seen between September 2000 and June 2017 and collected clinical, laboratory, and survival data. Treatment response was classified as mild, moderate, or marked as adjudged by predefined criteria. RESULTS: We identified 28 patients with SLONM; 17 (61%) had an associated MP. Median age at symptom onset was 62 years. Diagnosis was often delayed by a median of 35 months from symptom onset. There was no difference in clinical or laboratory features between patients with or without MP. Although the majority of patients had proximal or axial weakness at onset, about 18% of patients had atypical presentations. A total of 7/9 (78%) patients receiving IV immunoglobulin (IVIg), 6/8 (75%) receiving hematologic therapy as either autologous stem cell transplant (ASCT) or chemotherapy, and 1/8 (13%) receiving immunosuppressive therapies responded to treatment (p = 0.001). All 3 patients with marked response were treated with IVIg; 2 of them had an MP. The 5-year and 10-year overall survival from symptom onset was 92% and 68%, respectively, with no difference between patients with or without MP. CONCLUSION: SLONM has a wide spectrum of clinical presentations. In this contemporary case series, overall survival of patients did not seem to be affected by the presence of an MP. Initial treatment with IVIg is reasonable in all patients, followed by ASCT or chemotherapy as second-line therapy in patients with an associated MP.

Testing of therapies in a novel nebulin nemaline myopathy model demonstrate a lack of efficacy.

Nemaline myopathies are heterogeneous congenital muscle disorders causing skeletal muscle weakness and, in some cases, death soon after birth. Mutations in nebulin, encoding a large sarcomeric protein required for thin filament function, are responsible for approximately 50% of nemaline myopathy cases. Despite the severity of the disease there is no effective treatment for nemaline myopathy with limited research to develop potential therapies. Several supplements, including L-tyrosine, have been suggested to be beneficial and consequently self-administered by nemaline myopathy patients without any knowledge of their efficacy. We have characterized a zebrafish model for nemaline myopathy caused by a mutation in nebulin. These fish form electron-dense nemaline bodies and display reduced muscle function akin to the phenotypes observed in nemaline myopathy patients. We have utilized our zebrafish model to test and evaluate four treatments currently self-administered by nemaline myopathy patients to determine their ability to increase skeletal muscle function. Analysis of muscle pathology and locomotion following treatment with L-tyrosine, L-carnitine, taurine, or creatine revealed no significant improvement in skeletal muscle function emphasizing the urgency to develop effective therapies for nemaline myopathy.

Sporadic late-onset nemaline myopathy with monoclonal gammopathy of undetermined significance.

PURPOSE OF REVIEW: Sporadic late-onset nemaline myopathy (SLONM) with monoclonal gammopathy of undetermined significance (MGUS) is a rare subacute progressive muscle disease. The prognosis is poor due to severe respiratory insufficiency. Recently, however, autologous stem-cell transplantation following high-dose melphalan has been shown to be effective unless there is delay before the treatment. Therefore, early recognition of the disease is important. This review gives an overview of recent advances in SLONM-MGUS, which could help to understand clinical and pathological features and treatment. RECENT FINDINGS: Efficacy of autologous stem-cell transplantation following high-dose melphalan has been demonstrated in a long-term observation study. Subsequently, reports from other groups also have supported it. Furthermore, efficacy of chemotherapy toward plasma cell dyscrasia without stem-cell transplantation have been reported as well. A few case reports have suggested the presence of cardiac involvement related to SLONM-MGUS. SUMMARY: SLONM-MGUS is now considered as a treatable disease. Antiplasma cell dyscrasia therapy is a promising therapeutic option. Meanwhile, the pathomechanic link between muscle degeneration and monoclonal gammopathy remains unclear and further investigations are warranted.

Sporadic late-onset nemaline myopathy: clinico-pathological characteristics and review of 76 cases.

BACKGROUND: Sporadic late-onset nemaline myopathy (SLONM) is a rare, late-onset muscle disorder, characterized by the presence of nemaline rods in muscle fibers. Phenotypic characterization in a large cohort and a comprehensive overview of SLONM are lacking. METHODS: We studied the clinico-pathological features, treatment and outcome in a large cohort of 76 patients with SLONM, comprising 10 new patients and 66 cases derived from a literature meta-analysis (PubMed, 1966-2016), and compared these with 15 reported HIV-associated nemaline myopathy (HIV-NM) cases. In 6 SLONM patients, we performed a targeted next-generation sequencing (NGS) panel comprising 283 myopathy genes. RESULTS: SLONM patients had a mean age at onset of 52 years. The predominant phenotype consisted of weakness and atrophy of proximal upper limbs in 84%, of proximal lower limbs in 80% and both in 67%. Other common symptoms included axial weakness in 68%, as well as dyspnea in 55% and dysphagia in 47% of the patients. In 53% a monoclonal gammopathy of unknown significance (MGUS) was detected in serum. The mean percentage of muscle fibers containing rods was 28% (range 1-63%). In 2 cases ultrastructural analysis was necessary to detect the rods. The most successful treatment in SLONM patients (all with MGUS) was autologous peripheral blood stem cell therapy. A targeted NGS gene panel in 6 SLONM patients (without MGUS) did not reveal causative pathogenic variants. In a comparison of SLONM patients with and without MGUS, the former comprised significantly more males, had more rapid disease progression, and more vacuolar changes in muscle fibers. Interestingly, the muscle biopsy of 2 SLONM patients with MGUS revealed intranuclear rods, whereas this feature was not seen in any of the biopsies from patients without paraproteinemia. Compared to the overall SLONM cohort, significantly more HIV-NM patients were male, with a lower age at onset (mean 34 years). In addition, immunosuppression was more frequently applied with more favorable outcome, and muscle biopsies revealed a significantly higher degree of inflammation and necrosis in this cohort. Similar to SLONM, MGUS was present in half of the HIV-NM patients. CONCLUSIONS: SLONM presents a challenging, but important differential diagnosis to other neuromuscular diseases of adult onset. Investigations for MGUS and HIV should be performed, as they require distinct but often effective therapeutic approaches. Even though SLONM and HIV-NM show some differences, there exists a large clinico-pathological overlap between the 2 entities.

An Overview of Congenital Myopathies.

PURPOSE OF REVIEW: This article uses a case-based approach to highlight the clinical features as well as recent advances in molecular genetics, muscle imaging, and pathophysiology of the congenital myopathies. RECENT FINDINGS: Congenital myopathies refer to a heterogeneous group of genetic neuromuscular disorders characterized by early-onset muscle weakness, hypotonia, and developmental delay. Congenital myopathies are further classified into core myopathies, centronuclear myopathies, nemaline myopathies, and congenital fiber-type disproportion based on the key pathologic features found in muscle biopsies. Genotype and phenotype correlations are hampered by the diverse clinical variability of the genes responsible for congenital myopathies, ranging from a severe neonatal course with early death to mildly affected adults with late-onset disease. An increasing number of genes have been identified, which, in turn, are associated with overlapping morphologic changes in the myofibers. Precise genetic diagnosis has important implications for disease management, including family counseling; avoidance of anesthetic-related muscle injury for at-risk individuals; monitoring for potential cardiac, respiratory, or orthopedic complications; as well as for participation in clinical trials or potential genetic therapies. SUMMARY: Collaboration with neuromuscular experts, geneticists, neuroradiologists, neuropathologists, and other specialists is needed to ensure accurate and timely diagnosis based on clinical and pathologic features. An integrated multidisciplinary model of care based on expert-guided standards will improve quality of care and optimize outcomes for patients and families with congenital myopathies.

Nemaline myopathies: State of the art.

Nemaline myopathy (NM) is one of the most common forms of congenital myopathy. The condition is defined by the histopathological finding of nemaline bodies (rods) on muscle biopsy and is associated with hypotonia and muscle weakness. The clinical spectrum encompasses lethal forms presenting in the neonatal period with profound weakness and less severe congenital diseases of later onset. NM is significantly heterogeneous from a genetic point of view, and its inheritance can be autosomal-dominant (AD), sporadic or autosomal-recessive (AR). To date, 11 genes encoding proteins of skeletal muscle thin filaments, Kelch domain-associated proteins and an unconventional myosin have been implicated in NM. The mechanisms leading to nemaline body formation and muscle weakness are still largely unclear. This report reviews the clinical, histopathological and genetic features of NM, with a focus on some of the recently discovered forms.

Biphasic cuirass ventilation for treatment of an air leak after pneumothorax in a patient with nemaline myopathy: a case report.

We describe an 11-year-old boy with nemaline myopathy who developed tension pneumothorax while undergoing noninvasive positive-pressure ventilation (NIPPV). The patient developed a persistent air leak after pleurodesis with minocycline hydrochloride and lowering of the NIPPV inspiratory pressure. He required additional respiratory support without the high airway pressures that may aggravate pneumothorax. We provided adequate respiratory support without increasing the positive airway pressure using biphasic cuirass ventilation (BCV), which moved the patient's chest wall by negative pressure. The air leak was resolved without any additional treatment. We should provide BCV for patients in whom surgery may have a risk of both extubation failure and postoperative complications before deciding on surgery.

Two cases of sporadic late onset nemaline myopathy effectively treated with immunotherapy.

Sporadic late onset nemaline myopathy (SLONM) associated with monoclonal gammopathy of undetermined significance (MGUS) is an adult onset myopathy with poor clinical outcomes, requiring high-dose intravenous melphalan with autologous peripheral blood stem cell transplantation (HDM-SCT). Here we report two cases of SLONM associated with MGUS in which improvements were achieved only with immunotherapy. A 39-year-old woman had a two-year history of dropped head syndrome and progressive proximal weakness. On admission, she was able to walk with assistance and had lordosis with camptocormia. Combination therapy with plasmapheresis and intravenous immunoglobulin in addition to intravenous methylprednisolone pulse therapy ameliorated camptocormia and proximal weakness after one year. A 51-year-old man had difficulty in raising his arms and required walking assistance prior to visiting our hospital. He had proximal weakness and atrophy, winged scapulae, and gait disturbance. After combination immunotherapy, no progression was observed for 13 years. In both cases, patients did not desire to undergo HDM-SCT, and IgG kappa monoclonal protein was positive, of which the levels were normalized after immunotherapy. Combination immunotherapy can be a possible alternative to HDM-SCT in patients with SLONM. Both patients showed myogenic changes with abundant fibrillation, and needle EMG revealed positive sharp waves. Case 1 showed high signal intensities in MRI STIR/T2WI in muscles showing weakness. These findings are commonly observed in patients with myositis, suggesting that, without muscle biopsy, SLONM may be misdiagnosed as myositis. Muscle biopsy revealed scattered fibers with nemaline bodies without type 2B deficiency, which are important pathological findings that differentiate SLONM from congenital nemaline myopathy.