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ObjectivesInflammatory myopathy or myositis is a heterogeneous family of immune-mediated diseases including dermatomyositis (DM), antisynthetase syndrome (AS), immune-mediated necrotising myopathy (IMNM) and inclusion body myositis (IBM). Immune checkpoint inhibitors (ICIs) can also cause myositis (ICI-myositis). This study was designed to define gene expression patterns in muscle biopsies from patients with ICI-myositis.MethodsBulk RNA sequencing was performed on 200 muscle biopsies (35 ICI-myositis, 44 DM, 18 AS, 54 IMNM, 16 IBM and 33 normal muscle biopsies) and single nuclei RNA sequencing was performed on 22 muscle biopsies (seven ICI-myositis, four DM, three AS, six IMNM and two IBM).ResultsUnsupervised clustering defined three distinct transcriptomic subsets of ICI-myositis: ICI-DM, ICI-MYO1 and ICI-MYO2. ICI-DM included patients with DM and anti-TIF1γ autoantibodies who, like DM patients, overexpressed type 1 interferon-inducible genes. ICI-MYO1 patients had highly inflammatory muscle biopsies and included all patients that developed coexisting myocarditis. ICI-MYO2 was composed of patients with predominant necrotising pathology and low levels of muscle inflammation. The type 2 interferon pathway was activated both in ICI-DM and ICI-MYO1. Unlike the other types of myositis, all three subsets of ICI-myositis patients overexpressed genes involved in the IL6 pathway.ConclusionsWe identified three distinct types of ICI-myositis based on transcriptomic analyses. The IL6 pathway was overexpressed in all groups, the type I interferon pathway activation was specific for ICI-DM, the type 2 IFN pathway was overexpressed in both ICI-DM and ICI-MYO1 and only ICI-MYO1 patients developed myocarditis.

Non-necrotizing granulomatous inflammation is a rare but easily recognized histopathological finding in skeletal muscle biopsy. A limited number of diseases are known to be associated with non-necrotizing granulomatous myopathy. Once identified, a careful evaluation for evidence of extramuscular granulomatosis and other signs suggestive of sarcoidosis is warranted as about half of the patients have sarcoid myopathy. In addition, the presence of granulomatous myopathy should trigger a search for clinical and pathological clues of inclusion body myositis (IBM), which accounts for most of the remaining patients and can coexist with sarcoidosis. Recognizing the features of IBM in patients with granulomatous myopathy can potentially spare the patients from unnecessary exposure to immunosuppressive therapies. In patients whose granulomatous myopathy remain unexplained, further investigations should aim at identifying myasthenia gravis and other autoimmune disorders, especially those known to cause granulomatous inflammation in other organs. Laboratory investigations should include acetylcholine receptor, antimitochondrial, antineutrophil cytoplasmic, thyroglobulin, and thyroid peroxidase autoantibodies. In the appropriate clinical context, exposure to immune checkpoint inhibitors and chronic graft-vs-host disease can be causes of granulomatous myopathy. In cases of unexplained granulomatous myopathy, natural killer/T-cell lymphoma should be considered and careful histopathological examination for atypical cells and appropriate immunostaining is crucial. Identifying the etiology of granulomatous myopathy in each patient can guide appropriate treatment.

ObjectivesInflammatory myopathy or myositis is a heterogeneous family of immune-mediated diseases including dermatomyositis (DM), antisynthetase syndrome (AS), immune-mediated necrotizing myopathy (IMNM), and inclusion body myositis (IBM). Immune checkpoint inhibitors (ICI) can also cause myositis (ICI-myositis). This study was designed to define gene expression patterns in muscle biopsies from patients with ICI-myositis.MethodsBulk RNA sequencing was performed on 200 muscle biopsies (35 ICI-myositis, 44 DM, 18 AS, 54 IMNM, 16 IBM, and 33 normal muscle biopsies) and single nuclei RNA sequencing was performed on 22 muscle biopsies (7 ICI-myositis, 4 DM, 3 AS, 6 IMNM, and 2 IBM).ResultsUnsupervised clustering defined three distinct transcriptomic subsets of ICI-myositis: ICI-DM, ICI-MYO1, and ICI-MYO2. ICI-DM included patients with DM and anti-TIF1γ autoantibodies who, like DM patients, overexpressed type 1 interferon-inducible genes. ICI-MYO1 patients had highly inflammatory muscle biopsies and included all patients that developed co-existing myocarditis. ICI-MYO2 was composed of patients with predominant necrotizing pathology and low levels of muscle inflammation. The type 2 interferon pathway was activated both in ICI-DM and ICI-MYO1. Unlike the other types of myositis, all three subsets of ICI-myositis patients overexpressed genes involved in the IL6 pathway.ConclusionsWe identified three distinct types of ICI-myositis based on transcriptomic analyses. The IL6 pathway was overexpressed in all groups, the type I interferon pathway activation was specific for ICI-DM, the type 2 IFN pathway was overexpressed in both ICIDM and ICI-MYO1, and only ICI-MYO1 patients developed myocarditis.

Introduction/aims Immune-mediated necrotizing myopathy (IMNM) is an immune-mediated myopathy typically presenting with progressive subacute weakness and characteristic, but nonspecific, myopathological findings. Atypical cases however can mimic other inherited or acquired myopathies, depriving patients of treatment. We describe a cohort of such patients. Methods We retrospectively identified IMNM patients who either previously carried a diagnosis of an inherited myopathy established on clinicopathological grounds or whose muscle biopsies displayed atypical features suggestive of a different myopathy. Results Among 131 IMNM patients, seven previously unreported patients (5%) met one of the above criteria. Three patients were diagnosed with limb-girdle muscular dystrophy on the basis of a chronic progressive course of weakness and family history of myopathy or cardiomyopathy. The other four patients displayed atypical histological features (two prominent mitochondrial abnormalities, one myofibrillar pathology, and one granulomatous inflammation). Immunostaining of biopsies from 12 additional IMNM patients did not identify myofibrillar pathology. The patient with granulomatous inflammation was known to have pulmonary sarcoidosis. Genetic testing for inherited myopathies was unrevealing. Antibodies against 3-hydroxy-3-methylglutaryl-CoA reductase or signal recognition particle were identified in 5 and 1 patients, respectively. Four patients presented with slowly progressive weakness over 3-13 y, while weakness was subacute over ≤6 mo in three patients. All patients responded to immunomodulatory therapy. Discussion Atypical clinical and histological features can occur in IMNM patients, causing delays in diagnosis and treatment. Clinicians should, therefore, consider IMNM in the differential diagnosis of unexplained proximal myopathies in spite of atypical clinical and myopathological findings.

Objective To evaluate survival and associated comorbidities in inclusion body myositis (IBM) in a population-based, case-control study. Methods We utilized the expanded Rochester Epidemiology Project medical records-linkage system, including 27 counties in Minnesota and Wisconsin, to identify patients with IBM, other inflammatory myopathies (IIM), and age/sex-matched population-controls. We compared the frequency of various comorbidities and survival among groups. Results We identified 50 IBM patients, 65 IIM controls and 294 population controls. Dysphagia was most common in IBM (64%) patients. The frequency of neurodegenerative disorders (dementia/parkinsonism) and solid cancers was not different between groups. Rheumatoid arthritis was the most common rheumatic disease in all groups. A total of 36% of IBM patients had a peripheral neuropathy, 6% had Sjögren’s syndrome and 10% had a haematologic malignancy. T-cell large granular lymphocytic leukaemia was only observed in the IBM group. None of the IBM patients had hepatitis B or C, or HIV. IBM patients were 2.7 times more likely to have peripheral neuropathy, 6.2 times more likely to have Sjögren’s syndrome and 3.9 times more likely to have a haematologic malignancy than population controls. IBM was associated with increased mortality, with a 10-year survival of 36% from index, compared with 67% in IIM and 59% in population controls. Respiratory failure or pneumonia (44%) was the most common cause of death. Conclusions IBM is associated with lower survival, and higher frequency of peripheral neuropathy, Sjögren’s syndrome and haematologic malignancies than the general population. Close monitoring of IBM-related complications is warranted.

Objectives Symptomatic myopathy in sarcoidosis patients is not always due to sarcoid myopathy (ScM). We investigated the clinical and pathological spectrum including myxovirus resistance protein A (MxA) expression among sarcoidosis patients. Methods We reviewed the Mayo Clinic database (May 1980–December 2020) to identify sarcoidosis patients with myopathic symptoms and pathological evidence of myopathy. Results Among 5885 sarcoidosis patients, 21 had symptomatic myopathy. Eight carried a diagnosis of sarcoidosis 5.5 years (median) prior to myopathy onset. Eleven patients had ScM. The remaining had non-sarcoid myopathies (five IBM, one immune-mediated necrotizing myopathy, one non-specific myositis, two non-specific myopathy and one steroid myopathy). Estimated frequency of IBM is 85 per 100 000 sarcoidosis patients. The following features were associated with non-sarcoid myopathies (P 2 at time of diagnosis, (iii) creatine kinase >500 U/l, and (iv) absence of intramuscular granulomas. Sarcoplasmic MxA expression was observed in scattered myofibres in three patients, two of whom were tested for DM-specific autoantibodies and were negative. Immunosuppressive therapy led to improvement in mRS ≥1 in 5/10 ScM, none of the five IBM, and 3/3 remaining patients with non-sarcoid myopathies. Discussion Symptomatic myopathy occurred in 0.36% of sarcoidosis. IBM was the second most common cause of myopathies after ScM. Frequency of IBM in sarcoidosis is higher than in the general population. Recognition of features suggestive of alternative aetiologies can guide proper treatment. Our findings of abnormal MxA expression warrant a larger study.

Introduction/aims Intracellular congophilic inclusions within muscle fibers, although nonspecific, are one of the pathological hallmarks of sporadic inclusion body myositis (sIBM). Extracellular amyloid deposits in muscle, on the other hand, are the canonical findings of amyloid myopathies, which occur with or without systemic amyloidosis. Methods We reviewed the muscle biopsy database (1998-2020) to identify sIBM patients with extracellular amyloid deposits. Clinical and laboratory data were reviewed. Results We identified five sIBM patients (three clinicopathologically defined and two clinically defined) with extracellular amyloid deposits in muscle. Mean age at diagnosis was 74.8 y (range, 68-84 y). All patients had a typical sIBM pattern of weakness without associated sensory or autonomic symptoms. None had electrophysiological evidence of peripheral neuropathy. Only one patient had a monoclonal gammopathy (immunoglobulin M-lambda, IgM-λ) with normal bone marrow biopsy. This patient with monoclonal gammopathy and three other patients underwent abdominal fat pad aspirate and were negative for amyloid. Cardiac evaluation was unrevealing in the four patients tested. Three patients without monoclonal gammopathy had normal transthyretin gene sequencing and inconclusive mass spectrometry-based analysis. The patient with monoclonal gammopathy died of pneumosepsis 5 y after diagnosis and autopsy revealed multi-organ transthyretin amyloidosis. Discussion Detection of extracellular amyloid deposition in muscle should trigger an aggressive search for systemic amyloidosis independently from other associated myopathological abnormalities. Amyloid subtyping is crucial for early therapy and mortality prevention. An isolated monoclonal gammopathy should not halt a search for non-hematological causes of systemic amyloidosis.

Ranolazine is an anti-ischemic drug often used along with statins in patients with ischemic heart disease. Ranolazine-induced proximal myopathy or rhabdomyolysis have been rarely reported, but toxic effects of statins could not be completely ruled out in those cases. We report a 68-year-old man with ranolazine-induced myopathy who presented with respiratory insufficiency and head drop. Creatine kinase level was normal. The Patient continued to worsen despite statin cessation but markedly improved after stopping ranolazine. Muscle biopsy showed excessive lipid accumulation predominantly in type 1 myofibers. The precise mechanism of toxicity is not clear. Treating physicians should be aware of this rare but potentially debilitating adverse effect of ranolazine. Prognosis is good upon discontinuation of the offending drug.

Anoctaminopathy-5 refers to a group of hereditary skeletal muscle or bone disorders due to mutations in the anoctamin 5 (ANO5)-encoding gene, ANO5. ANO5 is a 913-amino acid protein of the anoctamin family that functions predominantly in phospholipid scrambling and plays a key role in the sarcolemmal repairing process. Monoallelic mutations in ANO5 give rise to an autosomal dominant skeletal dysplastic syndrome (gnathodiaphyseal dysplasia or GDD), while its biallelic mutations underlie a continuum of four autosomal recessive muscle phenotypes: (1). limb–girdle muscular dystrophy type R12 (LGMDR12); (2). Miyoshi distal myopathy type 3 (MMD3); (3). metabolic myopathy-like (pseudometabolic) phenotype; (4). asymptomatic hyperCKemia. ANO5 muscle disorders are rare, but their prevalence is relatively high in northern European populations because of the founder mutation c.191dupA. Weakness is generally asymmetric and begins in proximal muscles in LGMDR12 and in distal muscles in MMD3. Patients with the pseudometabolic or asymptomatic hyperCKemia phenotype have no weakness, but conversion to the LGMDR12 or MMD3 phenotype may occur as the disease progresses. There is no clear genotype–phenotype correlation. Muscle biopsy displays a broad spectrum of pathology, ranging from normal to severe dystrophic changes. Intramuscular interstitial amyloid deposits are observed in approximately half of the patients. Symptomatic and supportive strategies remain the mainstay of treatment. The recent development of animal models of ANO5 muscle diseases could help achieve a better understanding of their underlying pathomechanisms and provide an invaluable resource for therapeutic discovery.

Immune-mediated rippling muscle disease (iRMD) is a rare myopathy characterized by wavelike muscle contractions (rippling) and percussion- or stretch-induced muscle mounding. A serological biomarker of this disease is lacking.To describe a novel autoantibody biomarker of iRMD and report associated clinicopathological characteristics.This retrospective cohort study evaluated archived sera from 10 adult patients at tertiary care centers at the Mayo Clinic, Rochester, Minnesota, and BrighamWomen's Hospital, Boston, Massachusetts, who were diagnosed with iRMD by neuromuscular specialists in 2000 and 2021, based on the presence of electrically silent percussion- or stretch-induced muscle rippling and percussion-induced rapid muscle contraction with or without muscle mounding and an autoimmune basis. Sera were evaluated for a common biomarker using phage immunoprecipitation sequencing. Myopathology consistent with iRMD was documented in most patients. The median (range) follow-up was 18 (1-30) months.Diagnosis of iRMD.Detection of a common autoantibody in serum of patients sharing similar clinical and myopathological features.Seven male individuals and 3 female individuals with iRMD were identified (median [range] age at onset, 60 [18-76] years). An IgG autoantibody specific for caveolae-associated protein 4 (cavin-4) was identified in serum of patients with iRMD using human proteome phage immunoprecipitation sequencing. Immunoassays using recombinant cavin-4 confirmed cavin-4 IgG seropositivity in 8 of 10 patients with iRMD. Results for healthy and disease-control individuals (n = 241, including myasthenia gravis and immune-mediated myopathies) were cavin-4 IgG seronegative. Six of the 8 individuals with cavin-4 IgG were male, and the median (range) age was 60 (18-76) years. Initial symptoms included rippling of lower limb muscles in 5 of 8 individuals or all limb muscles in 2 of 8 sparing bulbar muscles, fatigue in 9 of 10, mild proximal weakness in 3 of 8, and isolated myalgia in 1 of 8, followed by development of diffuse rippling. All patients had percussion-induced muscle rippling and half had percussion- or stretch-induced muscle mounding. Four of the 10 patients had proximal weakness. Plasma creatine kinase was elevated in all but 1 patient. Six of the 10 patients underwent malignancy screening; cancer was detected prospectively in only 1. Muscle biopsy was performed in 7 of the 8 patients with cavin-4 IgG; 6 of 6 specimens analyzed immunohistochemically revealed a mosaic pattern of sarcolemmal cavin-4 immunoreactivity. Three of 6 patients whose results were seropositive and who received immunotherapy had complete resolution of symptoms, 1 had mild improvement, and 2 had no change.The findings indicate that cavin-4 IgG may be the first specific serological autoantibody biomarker identified in iRMD. Depletion of cavin-4 expression in muscle biopsies of patients with iRMD suggests the potential role of this autoantigen in disease pathogenesis.

ObjectivesTo determine the prevalence and natural history of sporadic inclusion body myositis (sIBM) and to test the hypothesis that patients with sIBM have higher cancer or mortality rates than the general population.MethodsWe sought patients with sIBM defined by the 2011 European Neuromuscular Centre (ENMC) diagnostic criteria among Olmsted County, Minnesota, residents in 40-year time period.ResultsWe identified 20 patients (10 clinicopathologically defined, 9 clinically defined, and 1 probable) according to the ENMC criteria and 1 patient with all features of clinicopathologically defined sIBM except for symptom onset at p = 0.24). Two-thirds of patients developed dysphagia, and half required a feeding tube. Nine patients required a wheelchair. The median time from symptom onset to wheelchair dependence was 10.5 (range 1–29) years. Overall life expectancy was shorter in the sIBM group compared to the general population (84.1 [95% CI 78–88.4] vs 87.5 [95% CI 85.2–89.5] years, p = 0.03). Thirteen patients died; 9 deaths were sIBM related (7 respiratory and 2 unspecified sIBM complications). Female sex (p = 0.03) and dysphagia (p = 0.05) were independent predictors of death.ConclusionOlmsted County has the highest prevalence of sIBM reported to date. Patients with sIBM have similar risk of cancer, but slightly shorter life expectancy compared to matched patients without sIBM.Classification of EvidenceThis study provides Class II evidence that patients with sIBM have similar risks of cancers and slightly shorter life expectancy compared to controls.

ObjectiveTo improve myasthenia gravis (MG) autoantibody testing.MethodsMG serologic tests with confirmatory or refuting clinical–electrodiagnostic (EDX) testing and cancer evaluations were reviewed over 4 years (2012–2015). All patients had acetylcholine receptor–binding (AChR-Bi), modulating (AChR-Mo), and striational (STR) autoantibody testing, and negatives reflexed to muscle-specific kinase (MuSK). Thymoma and cancer occurrences were correlated with STR and reflexed glutamic acid decarboxylase 65 (GAD65), ganglionic acetylcholine receptor (α3), collapsin response mediating protein-5, and voltage-gated potassium channel complex autoantibodies.ResultsOf 433 samples tested, 133 (31%) met clinical–EDX criteria for MG. Best sensitivity (90%) occurred at AChR-Bi >0.02 nmol/L, leaving 14 negative (6 ocular MG, 7 generalized MG, 1 MuSK MG) with specificity 90% (31 false-positives). Using AChR-Mo antibodies (>20% loss), specificity was better (92%, 24 false-positives), but sensitivity dropped (85%). Specificity improved (95%) by testing AChR-Mo when AChR-Bi are positive, resulting in 45% reduction of false-positives (31–17), maintaining AChR-Bi 90% sensitivity. Cutoff values recommended by area under the curve analysis did not outperform this approach. AChR-Bi and AChR-Mo values were significantly higher in true-positives. CT evaluations in 121 MG samples revealed 16 thymomas. Historical or subsequent cancers occurred in 22. STR and reflexed autoantibodies were not more common in MG with thymoma or other cancers. Full-body CT (n = 34) was performed in those with STR and reflex autoantibody positivity, but without additional cancers found.ConclusionAccuracy of MG serologic testing is improved by reflexing AChR-Bi–positive cases to AChR-Mo. STR and other reflexed cancer evaluation autoantibodies did not provide value beyond standard CT chest imaging at the time of MG diagnosis. Diagnostic certainty is informed by AChR-Bi and AChR-Mo with higher values increasing specificity.

Background Limited data exist regarding myopathies with early or prominent dysphagia. Methods A retrospective study was performed (January 2003 to August 2019) to identify myopathy patients in whom dysphagia was the initial symptom or was disproportionately severe compared with limb weakness. Results Thirty-two patients were identified. The median age at diagnosis was 65 y (range, 36-80 y). Inclusion body myositis (IBM) (n = 15), immune-mediated necrotizing myopathy (IMNM) (n = 5), and oculopharyngeal muscular dystrophy (n = 4), were the most common diagnoses. In 4 patients (3 IMNM and 1 nonspecific myositis) dysphagia evolved rapidly. At evaluation, 21 patients required diet alterations, 5 required feeding tubes, and 8 had aspiration pneumonia. Follow-up data were available for 20 patients (median, 24 mo). Eight patients received immunosuppressive therapies with improvement in 7, including 3 of 4 with rapidly progressive dysphagia. Conclusions IBM and IMNM accounted for approximately two-thirds of patients with early or prominent dysphagia at our institution. Rapidly progressive dysphagia may predict immunotherapy responsiveness.

Mutations in heat shock protein B8 were initially identified in inherited neuropathies and were more recently found to cause a predominantly distal myopathy with myofibrillar pathology and rimmed vacuoles. Rare patients also had proximal weakness. Only very few pathogenic variants have been identified in HSPB8. Disruption of the chaperone activity of heat shock protein B8 impairs chaperone-assisted selective autophagy and results in protein aggregation. We report a 23-year-old patient who presented with a 4-year history of predominantly proximal lower limb weakness due to a novel variant in HSPB8. The creatine kinase level was mildly elevated. Electrodiagnostic studies demonstrated a proximal-predominant myopathy without evidence of neuropathy, and muscle histopathology revealed rimmed vacuoles and myofibrillar protein aggregates. Whole exome sequencing identified a de novo frameshift variant in the C-terminal region of HSPB8 (c.577_580dupGTCA, p.Thr194Serfs*23). This case demonstrates that HSPB8-related disorders can present with early onset limb-girdle myopathy without associated neuropathy.

Immune-mediated necrotizing myopathy (IMNM) is considered a rare subtype of the immune-mediated myopathies, but its incidence and prevalence are unknown. In this study we aimed to determine the incidence and prevalence of IMNM among adults in Olmsted County, Minnesota.We identified adult patients with IMNM, as defined by the 2016 European Neuromuscular Centre diagnostic criteria, among residents of Olmsted County, Minnesota over a 20-year period.Seven patients fulfilled the inclusion criteria. Six patients were tested for IMNM antibodies: four were anti-3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) positive, one was anti-signal recognition particle positive, and one was seronegative. The incidence of IMNM during 2010-2019 was 8.3 per million person-years. The prevalence of IMNM in 2010 was 1.85 per 100 000 people at least 50 years of age. Median age at symptom onset was 64 (range, 52-86) years and median time from symptom onset to diagnosis was 3 (range,1 to 156) months. Statin use among anti-HMGCR IMNM patients, but not the entire IMNM cohort, was higher than in controls (P = .024). Two IMNM patients developed cancers. The incidence of malignancy in IMNM was not higher than that of the general population. Treatment outcome was favorable in all patients except for one patient with delayed treatment and another with insufficient therapy. Among three deceased patients, one died of cancer and another died of IMNM-related cardiorespiratory complications.IMNM is a rare disease. Its prevalence is one tenth that of inclusion-body myositis in Olmsted County, Minnesota. IMNM patients in our cohort were not at higher risk for developing cancer.

To describe a Filipino patient with adult-onset Sandhoff disease manifesting with an atypical asymmetric lower motor neuron syndrome due to a novel wholeWe performed clinical, laboratory, myopathologic, and genetic evaluation with next-generation sequencing in the proband and targeted mutational analysis in an asymptomatic sibling.A 59-year-old Filipino woman presented with 15 years of slowly progressive, asymmetric, proximal-predominant, lower greater than upper extremity weakness, mildly elevated creatine kinase, and generalized cerebellar atrophy. Serum total β-hexosaminidase was significantly reduced, and hexosaminidase A percentage was increased. We identified a novelThis patient expands the genotypic, phenotypic, and ethnic spectrum of Sandhoff disease and highlights challenges generated by low-penetrant pathogenic variants, especially when considering a potentially polygenic phenotype.

The diagnostic evaluation of a patient with suspected hereditary muscle disease can be challenging. Clinicians rely largely on clinical history and examination features, with additional serological, electrodiagnostic, radiologic, histopathologic, and genetic investigations assisting in definitive diagnosis. Hematological testing is inexpensive and widely available, but frequently overlooked in the hereditary myopathy evaluation. Hematological abnormalities are infrequently encountered in this setting; however, their presence provides a valuable clue, helps refine the differential diagnosis, tailors further investigation, and assists interpretation of variants of uncertain significance. A diverse spectrum of hematological abnormalities is associated with hereditary myopathies, including anemias, leukocyte abnormalities, and thrombocytopenia. Recurrent rhabdomyolysis in certain glycolytic enzymopathies co-occurs with hemolytic anemia, often chronic and mild in phosphofructokinase and phosphoglycerate kinase deficiencies, or acute and fever-associated in aldolase-A and triosephosphate isomerase deficiency. Sideroblastic anemia, commonly severe, accompanies congenital-to-childhood onset mitochondrial myopathies including Pearson marrow-pancreas syndrome and mitochondrial myopathy, lactic acidosis, and sideroblastic anemia phenotypes. Congenital megaloblastic macrocytic anemia and mitochondrial dysfunction characterize SFXN4-related myopathy. Neutropenia, chronic or cyclical, with recurrent infections, infantile-to-childhood onset skeletal myopathy and cardiomyopathy are typical of Barth syndrome, while chronic neutropenia without infection occurs rarely in DNM2-centronuclear myopathy. Peripheral eosinophilia may accompany eosinophilic inflammation in recessive calpainopathy. Lipid accumulation in leukocytes on peripheral blood smear (Jordans' anomaly) is pathognomonic for neutral lipid storage diseases. Mild thrombocytopenia occurs in autosomal dominant, childhood-onset STIM1 tubular aggregate myopathy, STIM1 and ORAI1 deficiency syndromes, and GNE myopathy. Herein, we review these hereditary myopathies in which hematological features play a prominent role.

ObjectiveTo describe a novel autoantibody biomarker of Immune mediated rippling muscle disease (iRMD).BackgroundiRMD is a rare immunotherapy-responsive myopathy characterized by wave-like muscle contractions (rippling) and percussion/stretch-induced muscle mounding. However, serological biomarker of this disease is lacking.Design/MethodsA Retrospective review was done to identify iRMD patients with stored sera in Mayo Neuroimmunology laboratory. Archived sera from IRMD patients were evaluated for a common biomarker of IRMD using phage immunoprecipitation sequencing (PhIP-Seq).ResultsArchival sera from 10 patients with clinical diagnosis of iRMD were retrieved. Whole human proteome PhIP-Seq identified peptides corresponding to different regions of the cavin-4 in sera of iRMD patients. Eight of the ten iRMD cases were positive for cavin-4 IgG by immunofluorescent cell-based-assay (CBA) using cavin-4-transfected COS7 cells. The cavin-4-reactive IgG in all 8 positive sera was of IgG1 subclass. None of the disease control sera (98 immune-mediated myopathy/neuromuscular junction disorders, 20 autoimmune CNS diseases and 123 healthy subjects) contained cavin-4-reactive IgG. Furthermore, none of the iRMD patients' sera were positive for caveolin-3 IgG. The majority of seropositive cases were males (6/8, 75%) with median age of 51 years (range 18-76). Three seropositive patients had co-existing myasthenia gravis (38%). Creatine Kinase was elevated in 6/7 tested patients (median 771 U/L, range: 132-2625 U/L). Muscle biopsy was performed in 7 of the 8 cavin-4 IgG seropositive patients; 6/6 specimens analyzed immunohistochemically revealed a mosaic pattern of sarcolemmal cavin-4 immunoreactivity. Three of 6 seropositive patients who received immunotherapy had complete resolution of symptoms; one had mild improvement and two had no change.ConclusionsCavin-4 IgG is a novel and specific serological autoantibody biomarker identified in iRMD. Depletion of cavin-4 expression in iRMD patient muscle biopsies suggests the potential role of this autoantigen in disease pathogenesis.

Objectives To investigate immune-mediated necrotizing myopathy (IMNM) association with cancer and its clinical implications. Methods IMNM cases were identified 1 January 2000 to 31 December 2020 matching sex and age controls (4:1). Results A total of 152 patients with IMNM were identified and among serologically tested, 60% (83/140) were HMGCR-IgG+, 14% (20/140) were SRP-IgG+ and 26% (37/140) were seronegative. Cancer rates were not significantly different between serological subgroups; 18.1% (15/83) HMGCR-IgG+, 25% (5/20) SRP-IgG+ and 30% (11/37) seronegative (P = 0.34). Cancer screening was performed within 12 months from IMNM diagnosis in 88% (134/152) (whole-body CT plus FDG-PET CT in 53, CT alone in 72 and FDG-PET alone in 9). FDG-PET/CT was positive in 73% (25/34) of cancers. Increasing age was the only risk associated with cancer (P = 0.02). The odds of developing cancer at ±3 or ±5 years from IMNM diagnosis was not higher than controls (OR = 0.49; CI: 0.325–0.76). Lifetime IMNM diagnosis of cancer was less compared with controls (OR = 0.5 CI: 0.33–0.78, P = 0.002). Most patients responded to treatment (137/147, P Conclusions Greater cancer risk is not observed in IMNM vs controls. Cancer screening in IMNM should be individualized based on age-personal and family history, including consideration of FDG-PET/CT. Immune-treatment response did not differ with cancer.

A 47-year-old man with hypercholesterolemia sought care for a 4-month history of progressive, proximal upper limb weakness and myalgia, followed by dysphagia, difficulty climbing stairs, and facial rash. Discontinuation of atorvastatin was of no benefit. Neurologic examination showed moderate weakness of the neck flexor muscles, shoulder girdle muscles, and finger extensors, and mild weakness of hip flexor and ankle dorsiflexor muscles. He had a heliotrope rash and Gottron sign. Serum testing showed an increased creatine kinase level. Needle electromyography showed myopathic changes with fibrillation potentials in proximal and axial muscles. Biopsy of the deltoid demonstrated a perifascicular pathologic process, including muscle fiber atrophy, and perivascular inflammatory exudate in the perimysium. Immunocytochemical studies showed patchy loss of intramuscular capillaries, some of which had complement (C5b9) deposition, and sarcoplasmic expression of myxovirus resistance protein A, mainly in the perifascicular regions. Immunologic testing was positive for autoantibodies to nuclear matrix protein 2 and negative for 3-hydroxy-3-methylglutaryl–coenzyme A reductase antibodies. Video swallow studies showed oropharyngeal dysphagia. Pulmonary function tests indicated mildly decreased maximal respiratory pressures but normal diffusing lung capacity for carbon monoxide. The findings were consistent with a diagnosis of dermatomyositis. The patient was started on oral prednisone and azathioprine, after checking for adequate thiopurine methyltransferase activity. Liver function tests and complete blood cell count with differential were assessed to monitor for potential azathioprine toxicity. Intravenous immunoglobulin was given. Follow-up examination revealed mild weakness of the shoulder girdle muscles after immunotherapy, and normal strength and creatine kinase value while on azathioprine monotherapy. Dermatomyositis is an idiopathic inflammatory myopathy. Idiopathic inflammatory myopathy is a group of autoimmune muscle diseases that includes dermatomyositis, polymyositis, inclusion body myositis, immune-mediated necrotizing myopathy, and overlap myositis, including antisynthetase syndrome.

Muscle diseases consist of various disorders that primarily affect skeletal muscle, but they can also affect cardiac or smooth muscle. The disorders may be inherited or acquired. The pathophysiology, clinical manifestations, diagnostic pathways, and treatment options will vary for each disorder. This chapter reviews common acquired muscle disorders. Inflammatory myopathies are characterized by muscle weakness and inflammatory reaction in muscle, and often, but not always, are accompanied by elevated creatine kinase values. They can occur with infections, systemic inflammatory diseases, or they may be idiopathic. On the basis of clinical, histologic, and immunopathologic criteria, idiopathic inflammatory myopathies can be distinguished as dermatomyositis, polymyositis, or inclusion body myositis. When dermatomyositis or polymyositis occurs in association with a connective tissue disease, the disorder is called overlap syndrome.

A 53-year-old woman had development of subacute-onset muscle weakness resulting in difficulty climbing stairs, rising from a chair, and reaching over her shoulders. She reported no dysphagia, dysarthria, dyspnea, or diplopia. She also disclosed no rash, joint pain, or urine discoloration. She had no history of statin exposure. There was no family history of neuromuscular disorders, early cataracts, cardiac arrhythmia, or cardiomyopathy. Two months of treatment with prednisone had resulted in no clinical improvement. Neurologic examination indicated moderate neck flexor, shoulder, and hip girdle muscle weakness, with sparing of cranial muscles. There was no action- or percussion-induced myotonia. Needle electromyography showed short-duration, low-amplitude, and complex motor unit potentials, predominantly affecting proximal muscles, associated with fibrillation potentials and myotonic discharges in proximal and axial muscles. Her creatine kinase level was increased. Biopsy of the left quadriceps showed variation in muscle fiber size, a moderate increase in internalized nuclei, fiber splitting, and scattered necrotic and regenerating fibers. There was a mild increase in perimysial fibrous and fatty connective tissue. 3-Hydroxy-3-methylglutaryl–coenzyme A reductase antibodies were strongly positive. The patient was diagnosed with hydroxy-3-methylglutaryl–coenzyme A reductase antibody–positive necrotizing autoimmune myopathy. The patient received intravenous immunoglobulin and mycophenolate mofetil while continuing prednisone. At 1-year follow-up, she had no weakness, and her creatine kinase value was normal while she continued taking prednisone, mycophenolate mofetil, and intravenous immunoglobulin. Necrotizing autoimmune myopathy, or immune-mediated necrotizing myopathy, is a subtype of immune-mediated myopathy, clinically characterized by subacute, progressive, proximal limb weakness and persistently increased creatine kinase level. Pathologically, it is characterized by myonecrosis with minimal or no inflammation. One-third of patients with necrotizing autoimmune myopathy have myalgia.

Hereditary muscle diseases are disabling disorders lacking effective treatments. UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase (GNE) myopathy is an autosomal recessive distal myopathy with rimmed vacuoles that typically manifests in late adolescence/early adulthood. GNE encodes an enzyme that is the rate-limiting step in sialic acid biosynthesis which is necessary for proper function of numerous biological processes. Outside of the causative gene, very little is known about the mechanisms contributing to the development of GNE myopathy. In the present study we aimed to address this knowledge gap by querying underlying mechanisms of GNE myopathy using a patient-derived induced pluripotent stem cell (iPSC) model. Muscle and skin biopsies were acquired from two patients with GNE myopathy that presented with distinct histopathological features. Control and patient-specific iPSCs were derived from skin fibroblasts and differentiated down a skeletal muscle lineage in a three-stage process analogous to muscle development and muscle regeneration. Initial studies revealed: 1) the ability of patient-derived GNE iPSC clones to recapitulate key characteristics of the human pathology including TDP-43 accumulation and evidence of dysregulated autophagy, and 2) a striking defect in myogenic progression of the more severe GNE iPSC clone. Single-cell RNA sequencing time course studies were then performed to more rigorously explore myogenesis defects. Cluster-based bioinformatics analyses revealed clear differences between control and GNE iPSC-derived muscle precursor cells (iMPCs). On a transcriptional level, late stage GNE iMPCs resembled that of early stage control iMPCs, confirming stalled myogenic progression on a molecular level. Comparative expression and pathway studies revealed EIF2 signaling as a top signaling pathway altered in GNE iMPCs. In summary, we report a novel in vitro, iPSC-based model of GNE myopathy and implicate defective myogenesis as a likely novel contributing mechanism to the etiology of GNE myopathy.SUMMARY STATEMENTDevelopment of a novel cell-based model of GNE myopathy, utilizing GNE patient-derived samples, which recapitulates human disease characteristics, uncovered myogenic differentiation defects, and can elucidate possible mechanistic contributors to the disease.

Myopathies include a group of acquired and inherited disorders of skeletal muscle with marked clinical and pathological heterogeneity. Electrodiagnostic studies can be used as an extension of neurologic examination, in conjunction with serologic tests, to help confirm the presence of myopathy and exclude its mimickers. The pattern of findings, including the presence of fibrillation potentials, myotonic discharges, an underlying peripheral neuropathy, or a concomitant defect of neuromuscular transmission can help narrow the differential diagnosis of myopathy subtypes. Although none of the electrodiagnostic abnormalities are specific for any given types of myopathies and the final diagnosis frequently relies on histopathologic, antibody, or genetic confirmation, electrodiagnostic studies can assist in selecting the suitable muscle for biopsy or guiding the appropriate molecular study. In cases of immune-mediated myopathies, needle electromyography can be used to assess the treatment response.

Objective To characterize the natural history and clinical features of myopathies caused by mono‐allelic, dominantly acting pathogenic variants in COL12A1. Methods Patients with dominant COL12A1‐related myopathies were characterized by history and clinical examination, muscle imaging, and genetic analysis. Pathogenicity of the variants was assessed by immunostaining patient‐derived dermal fibroblast cultures for collagen XII. Results Four independent families with childhood‐onset weakness due to novel, dominantly acting pathogenic variants in COL12A1 were identified. Adult patients exhibited distal‐predominant weakness. Three families carried dominantly acting glycine missense variants, and one family had a heterozygous, intragenic, in‐frame deletion of exon 52 of COL12A1. All pathogenic variants resulted in increased intracellular retention of collagen XII in patient‐derived fibroblasts as well as loss of extracellular, fibrillar collagen XII deposition. Since haploinsufficiency for COL12A1 is largely clinically asymptomatic, we designed and evaluated small interfering RNAs (siRNAs) that specifically target the mutant allele containing the exon 52 deletion. Immunostaining of the patient fibroblasts treated with the siRNA showed a near complete correction of collagen XII staining patterns. Interpretation This study characterizes a distal myopathy phenotype in adults with dominant COL12A1 pathogenic variants, further defining the phenotypic spectrum and natural history of COL12A1‐related myopathies. This work also provides proof of concept of a precision medicine treatment approach by proposing and validating allele‐specific knockdown using siRNAs specifically designed to target a patient’s dominant COL12A1 disease allele.

Granulomatous myopathies are etiologically heterogeneous myopathies, pathologically characterized by the presence of intramuscular granulomas. Treatment outcomes are variable. We aimed to identify prognostic factors of treatment outcomes in myopathies featuring non-caseating granulomas. Sixteen patients were identified (9 sarcoid myopathy, 6 inclusion body myositis, and 1 granulomatous myopathy of indeterminate cause) over a 21-year period. The median age at diagnosis was 67 years in sarcoid myopathy group, and 64 years in inclusion body myositis group. Three inclusion body myositis patients were initially diagnosed with sarcoid myopathy based on the presence of systemic features of sarcoidosis and findings on muscle biopsies, but subsequent biopsies performed because of treatment refractoriness, showed all canonical pathologic features of inclusion body myositis. We identified sarcoplasmic congophilic inclusions in 6 sarcoid myopathy patients without associated rimmed vacuoles or typical weakness pattern of inclusion body myositis. Four inclusion body myositis and 4 of 5 sarcoid myopathy patients with congophilic inclusions were refractory to immunotherapy. Our study portrays the overlapping clinical and pathological features of sarcoid myopathy and inclusion body myositis. The presence of sarcoplasmic congophilic inclusions in sarcoid myopathy may predict an unfavorable outcome of immunosuppressive therapy, but a larger prospective study is required to further validate this observation.

LRP4 is a post-synaptic membrane protein that promotes acetylcholine (AChR) clustering on the crest of post-synaptic neuromuscular folds. Autoantibodies against LRP4 are suggested to account for myasthenia gravis (MG) patients negative for antibodies to AChR.To report a clinical experience with service-line LRP4-IgG cell-based testing in electrodiagnostically confirmed MG patients and controls.We identified all Mayo patients undergoing MG evaluations with send out LRP4-IgG antibody testing by cell-based assay, having clinical-electrodiagnostic (EDX) testing. To be included, muscle acetylcholine receptor binding (AChR-Bi) and muscle-specific tyrosine kinase (MuSK) antibodies had to be absent prior to LRP4-IgG testing. Follow-up AChR-Bi antibody testing was reviewed. Also tested for LRP4-IgGs were 119 healthy subjects.Identified were 25 generalized MG, 24 ocular MG, and 55 patients initially considered to have MG prior to negative EDX testing. No seronegative patients with EDX confirmed MG had LRP4-IgG positivity but five non-MG patients did: Guillain-Barre syndrome with fatigue (N = 1); multiple cranial neuropathies (N = 1); functional neurologic disorders (N = 3). Of healthy subjects, 4% (5/119) were LRP4-IgG positive (N = 5) or had a borderline result (N = 1). Of MG patients with repeat AChR-Bi testing, 40% (10/25) seroconverted (5 with ocular MG and 5 with generalized MG) (median AChR IgG value: 0.34 nmol/L, range 0.2-20.9 nmol/L, median followup 26 months, range 2-72 months).Clinical review of LRP4-IgG commercial cell-based testing suggests lack of diagnostic utility in seronegative EDX-confirmed MG. The clinical utility of LRP4-IgG testing is not substantiated in service line testing. In contrast, repeat testing for AChR-Bi antibodies is shown clinically useful.

Despite recent advances in the understanding of inherited muscle and neuromuscular junction diseases, as well as the advent of a wide range of genetic tests, patients continue to face delays in diagnosis of sometimes treatable disorders. These guidelines outline an approach to genetic testing in such disorders. Initially, a patient's phenotype is evaluated to identify myopathies requiring directed testing, including myotonic dystrophies, facioscapulohumeral muscular dystrophy, oculopharyngeal muscular dystrophy, mitochondrial myopathies, dystrophinopathies, and oculopharyngodistal myopathy. Initial investigation in the remaining patients is generally a comprehensive gene panel by next-generation sequencing. Broad panels have a higher diagnostic yield and can be cost-effective. Due to extensive phenotypic overlap and treatment implications, genes responsible for congenital myasthenic syndromes should be included when evaluating myopathy patients. For patients whose initial genetic testing is negative or inconclusive, phenotypic re-evaluation is warranted, along with consideration of genes and variants not included initially, as well as their acquired mimickers.

The MYH2 gene encodes the skeletal muscle myosin heavy chain IIA (MyHC-IIA) isoform, which is expressed in the fast twitch type 2A fibers. Autosomal dominant or recessive pathogenic variants in MYH2 lead to congenital myopathy clinically featured by ophthalmoparesis and predominantly proximal weakness. MYH2-myopathy is pathologically characterized by loss and atrophy of type 2A fibers. Additional myopathological abnormalities have included rimmed vacuoles containing small p62 positive inclusions, 15–20 nm tubulofilaments, minicores and dystrophic changes. We report an adult patient with late-pediatric onset MYH2-myopathy caused by two heterozygous pathogenic variants: c.3331C>T, p.Gln1111* predicted to result in truncation of the proximal tail region of MyHC-IIA, and c.1546T>G, p.Phe516Val, affecting a highly conserved amino acid within the highly conserved catalytic motor head relay loop. This missense variant is predicted to result in a less compact loop domain and in turn could affect the protein affinity state. The patient’s genotype is accompanied by a novel myopathological phenotype characterized by centralized large myofilamentous tangles associated with clusters of nemaline rods, and ring fibers, in addition to the previously reported rimmed vacuoles, paucity and atrophy of type 2A fibers. Electron microscopy demonstrated wide areas of disorganized myofibrils which were oriented in various planes of direction and entrapped multiple nemaline rods, as corresponding to the large tangles with rods seen on light microscopy. Nemaline rods were rarely observed also in nuclei. We speculate that the mutated MyHC-IIA may influence myofibril disorganization. While nemaline rods have been described in myopathies caused by pathogenic variants in genes encoding several sarcomeric proteins, to our knowledge, nemaline rods have not been previously described in MYH2-myopathy.