Impact of muscle biopsy on the clinical decision-making process in patients with suspected idiopathic inflammatory myopathy.

BACKGROUND: The significance of muscle biopsy as a diagnostic tool in idiopathic inflammatory myopathies (IIM) remains elusive. We aimed to determine the diagnostic weight that has been given to muscle biopsy in patients with suspected IIM, particularly in terms of clinical diagnosis and therapeutic decisions. MATERIAL AND METHODS: In this retrospective multicentric study, we analyzed muscle biopsy results of adult patients with suspected IIM referred to a tertiary center between January 1, 2007, and October 31, 2021. Information regarding referral department, suspected diagnosis, biopsy site, demographic, clinical, laboratory data, and imaging results were extracted. Statistical analyses included the level of agreement between suspected and histological diagnosis and calculation of diagnostic performance (positive and negative predictive values, positive and negative likelihood ratios, sensitivity, and specificity of muscle biopsy in relation to clinical diagnosis and/or treatment initiation). Performance was tested in different strata based on clinical pre-test probability. RESULTS: Among 758 muscle biopsies, IIM was histologically compatible in 357/758 (47.1%) cases. Proportion of IIM was higher if there was a solid clinical pre-test probability (64.3% vs. 42.4% vs. 48% for high, medium and low pre-test probability). Sensitivity and specificity of muscle biopsy were highest (82%) when the diagnosis by the clinician was used as outcome scenario. Negative predictive value was only moderate (between 63% and 80%) and lowest if autoantibodies were positive (35%). CONCLUSION: In patients with clinically suspected IIM, approximately 50% of biopsies revealed features indicative of IIM. Diagnostic performance of muscle biopsy was moderate to high depending on clinical pre-test probability.

Magnetic resonance imaging patterns revealing muscle pathology and clinical features in idiopathic inflammatory myopathies.

OBJECTIVE: Idiopathic inflammatory myopathies (IIMs) are autoimmune disorders significantly impacting skeletal muscles; however, the precise correlation between muscle magnetic resonance imaging (MRI) findings, muscle pathology, disease subtypes and clinical characteristics remains uncertain. Thus, we investigated the association of muscle MRI findings in IIMs with muscle pathology and clinical features. METHODS: New-onset IIM patients underwent proximal upper and/or lower limb muscle MRI. Patterns of muscle oedema on MRI were categorised into fascial, honeycomb, peripheral, foggy, dense, or coarse dot patterns and compared with inflammatory cell infiltration sites in corresponding muscle biopsies. The incidence of MRI patterns was examined in patient subgroups using myositis-specific antibodies (MSAs) and 2017 EULAR/ACR classification criteria. Univariate and multivariate analyses were conducted to determine the odds ratios (ORs) of MRI findings for clinical characteristics. RESULTS: Fifty-six of 85 patients underwent muscle biopsy. Foggy, honeycomb and fascial patterns at biopsy sites correlated with inflammatory cell infiltration in the endomysium (OR 11.9, P = 0.005), perimysium (OR 6.0, P = 0.014) and fascia (OR 16.9, P < 0.001), respectively. Honeycomb and foggy patterns were characteristic of patients with anti-TIF1γ or anti-Mi2 antibodies and MSA-negative dermatomyositis, and those with anti-SRP or anti-HMGCR antibodies and MSA-negative polymyositis (PM), respectively. The honeycomb pattern positively correlated with malignancy (OR 6.87, P < 0.001) and Gottron sign (OR 8.05, P = 0.002); the foggy pattern correlated with muscle weakness (OR 11.24, P = 0.005). The dense dot pattern was associated with dysphagia (OR 6.27, P = 0.006) and malignancy (OR 8.49, P = 0.002). CONCLUSION: Muscle MRI holds promise in predicting muscle pathology, disease subtypes and clinical manifestations of IIMs.

Muscle involvement in systemic sclerosis: high mortality not associated with nature of histological lesions.

OBJECTIVES: The aim of this study was to determine the association between different histological patterns and prognosis in patients with SSc and histologically proven muscle involvement. METHODS: A multicentre retrospective study was conducted of a cohort of scleroderma patients who had undergone muscle biopsy. The biopsies were reviewed in a coordinated manner to classify patients based on histological findings. Three different patterns were observed: fibrosing myopathy (FM), inflammatory myopathy (IM) and necrotizing myopathy (NM). Rates of survival, muscle relapse, and cardiac and pulmonary events were compared between these three groups. RESULTS: Among 71 scleroderma patients with muscle biopsy specimens available for review, 33 (46.5%) were classified in the FM group, 18 (25.5%) in the IM group, and 20 (28%) in the NM group. The median follow-up time was 6.4 years (interquartile range, 2.2-10.9 years) and 21 patients died during follow-up, primarily from heart disease and infections. The 10-year survival rate after the first non-Raynaud's disease symptom was 80% and the cumulative incidence of muscle relapse was 25%. Neither factor differed significantly between the three groups. The risk of pulmonary events was lowest in the OM group, significantly lower than in the FM group (hazard ratio, 0.17; 95% CI, 0.04-0.67) and non-significantly lower than in the IMNM group (hazard ratio, 0.28; 95% CI, 0.06-1.24). The risk of cardiac events did not differ significantly between the three groups. CONCLUSION: The mortality rate of scleroderma patients with muscle involvement was not associated with their histological patterns.

Diffusion tensor imaging of vastus lateralis in patients with inflammatory myopathies.

OBJECTIVE: Inflammation in patients with myositis would increase diffusion of water molecules across sarcolemma that could be detected with the help of diffusion tensor imaging (DTI). We aimed to determine an association between DTI of vastus lateralis (VL) and histopathological findings in cases of myositis and to estimate diagnostic performance of different MRI variables in predicting histopathological outcomes. METHODS: This prospective cross-sectional observational study included 43 patients with myositis. MRI of bilateral thighs with DWI/DTI protocol was performed in all the patients. Thirty-three patients further underwent biopsy of right VL muscle. Imaging analysis included grading of "Muscle oedema" based on signal intensity (SI) and extent and "fatty infiltration" based on extent on conventional sequences and, acquiring DWI and DTI parameters. Gold standard method to determine inflammation in muscles was histopathological examination. Comparison of DTI/DWI variables with clinical and histopathological variables was done. RESULTS: The average DWI apparent diffusion coefficient (ADC) and DTI ADC values in the patients were 1.77 ± 0.35 and 2.06 ± 0.35 respectively. The average functional anisotropy (FA) was 0.39 ± 0.17 and, the 3 eigenvalues in the patients were 2.96 ± 0.63, 2.05 ± 0.32, and 1.20 ± 0.39 respectively. VL oedema SI weighted score was the best parameter for predicting effaced fascicular architecture and marked lymphocytic inflammation in endomysium on histopathology. VL fatty infiltration weighted score was the best parameter in predicting perifascicular atrophy. CONCLUSION: Addition of DWI or DTI didn't add significantly in determining active inflammation in cases of myositis.

Myxovirus resistance protein A (MxA) expression in myositides: Sarcoplasmic expression is common in both dermatomyositis and lupus myositis.

INTRODUCTION/AIMS: Myxovirus resistance protein A (MxA) is a type I interferon (IFN1) pathway activation marker and MxA sarcoplasmic expression is currently recognized as a highly specific marker for dermatomyositis (DM). However, we have frequently observed endothelial tubuloreticular inclusions (TRI), another surrogate IFN1 activation marker, in a variety of overlap myositides. The aim of this study was to examine MxA expression in those myositides. METHODS: We retrospectively performed MxA immunostaining on a wide range of myositides. RESULTS: MxA sarcoplasmic expression was present in DM (94.4%, 17/18), active lupus myositis (LM, 80%,16/20), inactive LM (36%, 4/11), antisynthetase syndrome (ASyS, 20%, 2/10), systemic sclerosis (13%, 2/15), Sjogren's syndrome (7.7%, 1/13), and human immunodeficiency virus (HIV) myositis (5.6%, 1/18) and was absent in immune-mediated necrotizing myopathy (IMNM, 0/16) and hydroxychloroquine myopathy (0/5). The sensitivity and specificity of MxA sarcoplasmic expression for LM and DM combined compared with all other myositides were 84.6% (95% CI: 69.5-94.1) and 92.1 (95% CI: 83.6-97.0), respectively, and superior to TRIs. MxA capillary expression was nonspecific. Histologically, 35% of LM cases demonstrated a unique panfascicular necrotizing myopathy pattern. The remainder of the LM cases had significant morphological overlap with DM/ASyS (20%), IMNM (20%), or polymyositis (15%). DISCUSSION: MxA sarcoplasmic expression is highly prevalent in LM and DM and is a useful marker in differentiating DM and LM from other myositides. LM can manifest in various pathology patterns that need to be differentiated from DM, IMNM, ASyS, and polymyositis.

Can non-invasive motor unit analysis reveal distinct neural strategies of force production in young with uncomplicated type 1 diabetes?

PURPOSE: to investigate the early consequences of type 1 diabetes (T1D) on the neural strategies of muscle force production. METHODS: motor unit (MU) activity was recorded from the vastus lateralis muscle with High-Density surface Electromyography during isometric knee extension at 20 and 40% of maximum voluntary contraction (MVC) in 8 T1D (4 males, 4 females, 30.5 ± 3.6 years) and 8 matched control (4 males, 4 females, 27.3 ± 5.9 years) participants. Muscle biopsies were also collected from vastus lateralis for fiber type analysis, including myosin heavy chain (MyHC) isoform content via protein and mRNA expression. RESULTS: MVC was comparable between groups as well as MU conduction velocity, action potentials' amplitude and proportions of MyHC protein isoforms. Nonetheless, MU discharge rate, relative derecruitment thresholds and mRNA expression of MyHC isoform I were lower in T1D. CONCLUSIONS: young people with uncomplicated T1D present a different neural control of muscle force production. Furthermore, differences are detectable non-invasively in absence of any functional manifestation (i.e., force production and fiber type distribution). These novel findings suggest that T1D has early consequences on the neuromuscular system and highlights the necessity of a better characterization of neural control in this population.

Contrast of muscle magnetic resonance imaging and pathological findings of muscle tissue in patients with anti-aminoacyl transfer RNA synthetase antibodies.

OBJECTIVES: TO DETERMINE WHETHER MAGNETIC RESONANCE IMAGING (MRI) FINDINGS REFLECT THE PATHOLOGICAL FEATURES OF INFLAMMATORY MYOPATHIES: Methods: Patients with idiopathic inflammatory myopathies (IIMs) diagnosed using the 2017 EULAR/ACR classification criteria in our university between 2005 and 2020 were retrospectively reviewed. IIMs were subclassified into the anti-ARS syndrome (ASSD), immune-mediated necrotizing myositis (IMNM), Dermatomyositis DM and others. Fat-suppressed T2-weighted MRI and muscle biopsy specimens were assessed in IIMs followed by the comparison among the four subgroups. RESULTS: MRI findings were available for 62 patients and histopathological findings were available for 27 patients. Perifascicular atrophy or necrosis in the muscle tissues from the patients with IIM was more frequently observed in patients with subcutaneous and fascial high signal intensity (HSI) on MRI than those without. Four-group comparison among ASSD, IMNM, DM and others revealed HSI in fasciae on MRI was more frequently observed in patients with ASSD and DM than others. Perifascicular atrophy or necrosis in muscle tissues was more frequently observed in patients with ASSD than in others. CONCLUSION: Patients with ASSD had distinct MRI features compared with anti-ARS negative patients. The fascial high signal intensity on MRI may reflect distinctive pathological features of muscles.

Muscle biopsy practices in the evaluation of neuromuscular disease: A systematic literature review.

AIMS: Muscle biopsy techniques range from needle muscle biopsy (NMB) and conchotome biopsy to open surgical biopsy. It is unknown whether specific biopsy techniques offer superior diagnostic yield or differ in procedural complication rates. Therefore, we aimed to compare the diagnostic utility of NMB, conchotome and open muscle biopsies in the assessment of neuromuscular disorders. METHODS: A systematic literature review of the EMBASE and Medline (Ovid) databases was performed to identify original, full-length research articles that described the muscle biopsy technique used to diagnose neuromuscular disease in both adult and paediatric patient populations. Studies of any design, excluding case reports, were eligible for inclusion. Data pertaining to biopsy technique, biopsy yield and procedural complications were extracted. RESULTS: Sixty-four studies reporting the yield of a specific muscle biopsy technique and, or procedural complications were identified. Open surgical biopsies provided a larger tissue sample than any type of percutaneous muscle biopsy. Where anaesthetic details were reported, general anaesthesia was required in 60% of studies that reported open surgical biopsies. Percutaneous biopsies were most commonly performed under local anaesthesia and despite the smaller tissue yield, moderate- to large-gauge needle and conchotome muscle biopsies had an equivalent diagnostic utility to that of open surgical muscle biopsy. All types of muscle biopsy procedures were well tolerated with few adverse events and no scarring complications were reported with percutaneous sampling. CONCLUSIONS: When a histological diagnosis of myopathy is required, moderate- to large-gauge NMB and the conchotome technique appear to have an equivalent diagnostic yield to that of an open surgical biopsy.

Revisiting idiopathic eosinophilic myositis: towards a clinical-pathological continuum from the muscle to the fascia and skin.

OBJECTIVES: Idiopathic inflammatory myopathies are mainly defined by inflammatory infiltrates within the muscle (lymphocytes and macrophages). Eosinophil muscle infiltration has been described in idiopathic eosinophilic myositis (IEM) and rarely in EF. This study aimed to further delineate the nosological frame of idiopathic eosinophil muscle infiltration through the exhaustive analysis of IEM and EF patients. METHODS: This multicentre retrospective case series included IEM patients diagnosed between 2000 and 2022. IEM inclusion criteria were eosinophilic muscle infiltration with myositis pathological features, after the exclusion of differential diagnoses. An additional group of EF patients diagnosed between 2016 and 2022 was constituted. Inclusion criteria were an EF diagnosis and fascia thickening with inflammatory infiltrate. RESULTS: A total of 20 IEM cases and 10 EF cases were included. The median (interquartile range) age at diagnosis was 65 (49-70) years; there were 18 males. Data analysis delineated four subgroups: focal EM (FEM, n = 3), diffuse EM (DEM, n = 6), eosinophilic myofasciitis (EMF, n = 11) and EF (n = 10). FEM represented a limited and benign form of myositis. DEM cases presented objective muscle impairment with eosinophilic muscle infiltration. EMF patients presented subjective muscle impairment (myalgia, 55%), fasciitis (on histology and/or imaging), eosinophilic muscle infiltration and frequent hypereosinophilia (55%). EF patients presented myalgia (50%), muscle lesions on histology with fascia-restricted inflammatory infiltrates with (60%) or without (40%) eosinophils. CONCLUSIONS: The analysis of IEM and EF patient characteristics delineates four subgroups (FEM, DEM, EMF and EF) in terms of clinical, laboratory, imaging, pathological and outcome specificities, and proposes an adapted diagnostic and care management approach.

The pattern of MHC class I expression in muscle biopsies from patients with myositis and other neuromuscular disorders.

OBJECTIVE: Diagnostic muscle biopsies are routinely immunostained for major histocompatibility complex class I (MHC-I) protein. In this study we analysed the prevalence and patterns of MHC-I immunostaining in biopsies from patients with different types of myopathies and neurogenic disorders. METHODS: All 357 diagnostic muscle biopsies processed at the Johns Hopkins Neuromuscular Pathology Laboratory from August 2013 to January 2017 were immunostained for MHC-I. The prevalence and patterns of MHC-I immunostaining were compared between patients with histologically normal muscle biopsies (n = 31), idiopathic inflammatory myopathies (IIMs; n = 170), non-inflammatory myopathies (n = 60) and neurogenic disorders (n = 96). RESULTS: MHC-I immunostaining was abnormal in most patients with DM (98%), sporadic IBM (sIBM; 100%), immune-mediated necrotizing myopathy (IMNM; 100%) and polymyositis (77%). In contrast, MHC-I immunostaining was less frequently present in non-inflammatory myopathies (32%) or neurogenic disorders (30%). Overall, abnormal MHC-I immunostaining had a sensitivity of 0.95 and a specificity of 0.82 for diagnosing IIMs. A focal MHC-I staining pattern was associated with IMNM, whereas a global pattern was more prevalent in sIBM and a perifascicular pattern was significantly more common in dermatomyositis. Among 18 DM biopsies without perifascicular atrophy, 50% had a perifascicular MHC-I staining pattern. Sarcoplasmic upregulation staining was more common than sarcolemmal staining across all groups. CONCLUSION: MHC-I immunostaining was useful to distinguish IIMs from non-inflammatory myopathies or neurogenic disorders. Of note, a perifascicular MHC-I staining pattern was present only in those with DM, including half of those without perifascicular atrophy; many of these biopsies may not otherwise have been diagnostic for DM.

Autophagy in non-immune-mediated rhabdomyolysis: Assessment of p62 immunohistochemistry.

INTRODUCTION/AIMS: p62 immunochemistry (IHC) has been shown to aid diagnosis with distinct patterns of muscle fiber staining observed in some inflammatory, hereditary, and degenerative myopathies, such as immune-mediated necrotizing myopathy (IMNM). The pattern of p62 staining may help narrow the pathological differential diagnosis of rhabdomyolysis. However, there is a lack of information on the pattern of p62 IHC in non-immune-mediated rhabdomyolysis. In this study we aim to describe histopathological findings in non-immune-mediated rhabdomyolysis, with particular emphasis on the pattern of p62 IHC. METHODS: We retrospectively reviewed the histopathological features of patients with a confirmed diagnoses of non-immune-mediated rhabdomyolysis referred to our center. RESULTS: Five patients were identified. Rhabdomyolysis was determined to be due to statin-associated toxicity in three patients, alcohol overuse in one patient, and intensive exercise in one patient. All patients showed increased numbers of necrotic and regenerating muscle fibers. Diffuse and finely granular sarcoplasmic positive p62 staining was present in scattered non-necrotic muscle fibers in all patients. DISCUSSION: Disturbance of autophagy appears to be a common mechanism in non-immune-mediated rhabdomyolysis. Our results show p62 IHC is sensitive but lacks specificity. Therefore, the pattern of p62 staining does not distinguish non-immune-mediated rhabdomyolysis from histopathologically similar IMNM.

Low myoglobin concentration in skeletal muscle of elite cyclists is associated with low mRNA expression levels.

Myoglobin is essential for oxygen transport to the muscle fibers. However, measurements of myoglobin (Mb) protein concentrations within individual human muscle fibers are scarce. Recent observations have revealed surprisingly low Mb concentrations in elite cyclists, however it remains unclear whether this relates to Mb translation, transcription and/or myonuclear content. The aim was to compare Mb concentration, Mb messenger RNA (mRNA) expression levels and myonuclear content within muscle fibers of these elite cyclists with those of physically-active controls. Muscle biopsies were obtained from m. vastus lateralis in 29 cyclists and 20 physically-active subjects. Mb concentration was determined by peroxidase staining for both type I and type II fibers, Mb mRNA expression level was determined by quantitative PCR and myonuclear domain size (MDS) was obtained by immunofluorescence staining. Average Mb concentrations (mean ± SD: 0.38 ± 0.04 mM vs. 0.48 ± 0.19 mM; P = 0.014) and Mb mRNA expression levels (0.067 ± 0.019 vs. 0.088 ± 0.027; P = 0.002) were lower in cyclists compared to controls. In contrast, MDS and total RNA per mg muscle were not different between groups. Interestingly, in cyclists compared to controls, Mb concentration was only lower for type I fibers (P < 0.001), but not for type II fibers (P > 0.05). In conclusion, the lower Mb concentration in muscle fibers of elite cyclists is partly explained by lower Mb mRNA expression levels per myonucleus and not by a lower myonuclear content. It remains to be determined whether cyclists may benefit from strategies that upregulate Mb mRNA expression levels, particularly in type I fibers, to enhance their oxygen supply.

Inclusion body myositis. Genetics, biomarkers and muscle biopsy.

Sporadic inclusion body myositis is the most common idiopathic inflammatory myopathy over the age of 50, with a male-to-female ratio of 3:1. Symptoms onset before age of 60 occurs in 18-20% of patients, with a delay in diagnosis of 5 to 8 years.The classic clinical presentation of SIBM consists of proximal leg and distal arm weakness, and most commonly patients present early slowly progressive quadriceps weakness which leads to falls and to difficulties in climbing stairs, while less common the initial complaints refer to finger flexor weakness and atrophy, foot drop, or dysphagia, and rare presentations include prominent forearm weakness, sparing the quadriceps. The aetiopathogenesis of the disease remains unclear and despite some preliminary promising results, to the day there is no effective treatment.The diagnosis of SIBM is based on the clinical presentation and the histopathological findings in muscle biopsy, however increasing evidence on genetics and paraclinical biomarkers has recently come to light giving new insights on the pathogenesis, the diagnosis and the potential treatment of the disease. In the present study we aim to review the histopathological findings, genetics and blood biomarkers, and to review the role of muscle biopsy in the diagnosis of SIBM.

Non-lethal sampling method for the analysis of white muscle fatty acid profiles in European sea bass (Dicentrarchus labrax).

This study presents a novel non-lethal sampling method for assessing fatty acid (FA) composition in juvenile European sea bass (Dicentrarchus labrax) using subcutaneous white muscle biopsies. This research aimed to evaluate the suitability of the biopsy for FA analysis using two lipid extraction protocols and comparing them to a lethal routine method. The results showed that a mass of fresh tissue as low as 1.4 mg provided good quality FA chromatograms for both reserve and membrane lipids. Although the biopsy method displayed high variability in terms of FA quantity among intra-individual replicates, it showed good FA profile repeatability in both reserve and membrane lipids. The study highlights the potential of this non-lethal approach for studying FA dynamics in fish, with its application being particularly promising for ecological and experimental studies. However, careful biopsy implementation is recommended to account for potential lipid droplet and lipid distribution variability within the tissue.

A Possible Case of Centronuclear Myopathy: A Case Report.

Congenital myopathies (CMs) are a group of diseases that primarily affect the muscle fiber, especially the contractile apparatus and the different components that condition its normal functioning. They present as muscle weakness and hypotonia at birth or during the first year of life. Centronuclear CM is characterized by a high incidence of nuclei located centrally and internally in muscle fibers. Clinical case: a 22-year-old male patient with symptoms of muscle weakness since early childhood, with difficulty in performing physical activity according to his age, with the presence of a long face, a waddling gait, and a global decrease in muscle mass. Electromyography was performed, showing a neurogenic pattern and not the expected myopathic one, neuroconduction with reduced amplitude of the motor potential of the peroneal nerve and axonal and myelin damage of the posterior tibial nerves. The microscopic study of the studied striated muscle fragments stained with hematoxylin-eosin and Masson's trichrome showed the presence of fibers with central nuclei, diagnosing CM. The patient meets most of the description for CM, with involvement of all striated muscles, although it is important to note the neurogenic pattern present in this case, due to the denervation of damaged muscle fibers, which contain terminal axonal segments. Neuroconduction shows the involvement of motor nerves, but with normal sensory studies, axonal polyneuropathy is unlikely, due to normal sensory potentials. Different pathological findings have been described depending on the mutated gene in this disease, but all coincide with the presence of fibers with central nuclei for diagnosis by this means, which is so important in institutions where it is not possible to carry out genetic studies, and allowing early specific treatment, according to the stage through which the patient passes.

Autosomal dominantly inherited myopathy likely caused by the TNNT1 variant p.(Asp65Ala).

Nemaline myopathies (NEMs) are genetically and clinically heterogenous. Biallelic or monoallelic variants in TNNT1, encoding slow skeletal troponin T1 (TnT1), cause NEM. We report a 2-year-old patient and his mother carrying the heterozygous TNNT1 variant c.194A>C/p.(Asp65Ala) that occurred de novo in the mother. Both had muscle hypotrophy and muscle weakness. Muscle pathology in the proband's mother revealed slow twitch type 1 fiber hypotrophy and fast twitch type 2 fiber hypertrophy that was confirmed by a reduced ratio of slow skeletal myosin to fast skeletal myosin type 2a. Reverse transcription polymerase chain reaction and immunoblotting data demonstrated increased levels of high-molecular-weight TnT1 isoforms in skeletal muscle of the proband's mother that were also observed in some controls. In an overexpression system, complex formation of TnT1-D65A with tropomyosin 3 (TPM3) was enhanced. The previously reported TnT1-E104V and TnT1-L96P mutants showed reduced or no co-immunoprecipitation with TPM3. Our studies support pathogenicity of the TNNT1 p.(Asp65Ala) variant.

Capillary pathology with prominent basement membrane reduplication is the hallmark histopathological feature of scleromyositis.

AIMS: We aim to perform ultrastructural and histopathological analysis of muscle biopsies from a large group of systemic sclerosis (SSc) patients, including some with early/mild SSc features, and examine whether capillary pathology differentiates 'scleromyositis' (SM) from other auto-immune myositis (AIM) subsets. METHODS: Muscle biopsies from a total of 60 SM patients and 43 AIM controls from two independent cohorts were examined by electron microscopy, collagen-4 immunofluorescence (Col4IF) and routine light microscopy. RESULTS: Ultrastructural examination revealed prominent capillary basement membrane (BM) reduplication (4+ layers in >50% of capillaries) in 65% of SM vs 0% of AIM controls (p < 0.001). In SM cases without prominent BM reduplication, capillary dilation was the most distinctive feature, present in 8% of capillaries in SM vs 2% in controls (p = 0.001). Accumulation of ensheathed pericyte processes was another characteristic feature of SM and closely correlated with the degree of BM reduplication (r = 0.833, p < 0.001). On light microscopy, BM marker Col4IF revealed more frequent capillary enlargement in SM than in controls (84% vs 21%, p < 0.001). SM cases were classified as non-inflammatory myopathy (36%), non-specific myositis (33%) or immune-mediated necrotizing myopathy (31%), but despite this histopathological heterogeneity, prominent BM reduplication remained a constant finding. In the 16 SM patients with early/mild SSc features, 63% showed prominent BM reduplication. CONCLUSIONS: These results show that capillary pathology, and in particular prominent capillary BM reduplication, is the hallmark histopathological feature of SM even in patients with early/mild SSc and support the concept of SM as an organ manifestation of SSc and a distinct subset of AIM.

Inclusion body myositis: correlation of clinical outcomes with histopathology, electromyography and laboratory findings.

OBJECTIVE: To determine whether histopathological, electromyographic and laboratory markers correlate with clinical measures in inclusion body myositis (IBM). METHODS: We reviewed our electronic medical records to identify patients with IBM according to European Neuromuscular Center (ENMC) 2011 criteria, seen between 2015 and 2020. We only included patients who had a muscle biopsy and needle electromyography (EMG) performed on the same muscle (opposite or same side). We used a detailed grading system [0 (normal) to 4 (severe)] to score histopathological and EMG findings. Clinical severity was assessed by the modified Rankin scale (mRS), muscle strength sum score (SSS), quadriceps strength and severity of dysphagia on swallow evaluation. Serum markers of interest were creatine kinase level and cN-1A antibodies. RESULTS: We included 50 IBM patients, with a median age of 69 years; 64% were males. Median disease duration at diagnosis was 51 months. On muscle biopsy, endomysial inflammation mainly correlated with dysphagia, and inversely correlated with mRS. Vacuoles and congophilic inclusions did not correlate with any of the clinical measures. On EMG, the shortness of motor un it potential (MUP) duration correlated with all clinical measures. Myotonic discharges, and not fibrillation potentials, correlated with the severity of inflammation. Serum markers did not have a statistically significant correlation with any of the clinical measures. CONCLUSIONS: Dysphagia was the main clinical feature of IBM correlating with endomysial inflammation. Otherwise, inclusion body myositis clinical measures had limited correlation with histopathological features in this study. The shortness of MUP duration correlated with all clinical measures.

Myopathy as a cause of fatigue in long-term post-COVID-19 symptoms: Evidence of skeletal muscle histopathology.

BACKGROUND AND PURPOSE: Among post-COVID-19 symptoms, fatigue is reported as one of the most common, even after mild acute infection, and as the cause of fatigue, myopathy diagnosed by electromyography has been proposed in previous reports. This study aimed to explore the histopathological changes in patients with post-COVID-19 fatigue. METHODS: Sixteen patients (mean age = 46 years) with post-COVID-19 complaints of fatigue, myalgia, or weakness persisting for up to 14 months were included. In all patients, quantitative electromyography and muscle biopsies analyzed with light and electron microscopy were taken. RESULTS: Muscle weakness was present in 50% and myopathic electromyography in 75%, and in all patients there were histological changes. Muscle fiber atrophy was found in 38%, and 56% showed indications of fiber regeneration. Mitochondrial changes, comprising loss of cytochrome c oxidase activity, subsarcollemmal accumulation, and/or abnormal cristae, were present in 62%. Inflammation was found in 62%, seen as T lymphocytes and/or muscle fiber human leukocyte antigen ABC expression. In 75%, capillaries were affected, involving basal lamina and cells. In two patients, uncommon amounts of basal lamina were found, not only surrounding muscle fibers but also around nerves and capillaries. CONCLUSIONS: The wide variety of histological changes in this study suggests that skeletal muscles may be a major target of SARS-CoV-2, causing muscular post-COVID-19 symptoms. The mitochondrial changes, inflammation, and capillary injury in muscle biopsies can cause fatigue in part due to reduced energy supply. Because most patients had mild-moderate acute affection, the new variants that might cause less severe acute disease could still have the ability to cause long-term myopathy.

Idiopathic Orbital Myositis Revisited.

PURPOSE OF REVIEW: To review current knowledge regarding idiopathic orbital myositis. RECENT FINDINGS: Recent publications have focused on possible causes of orbital myositis and the process to reach a diagnosis of idiopathic orbital myositis. With inflamed and enlarged extraocular muscles, features to distinguish between competing diagnostic possibilities are based on imaging in the context of history and clinical signs. Idiopathic orbital myositis is characterized by the clinical triad of acute onset of orbital pain exacerbated on eye movement, double vision, and redness or swelling of the eyelids or conjunctiva, along with the radiological finding of homogeneous, fusiform enlargement of one or more extraocular muscles. In atypical or inconclusive clinico-radiological findings for a diagnosis of idiopathic orbital myositis, or where the clinical behavior changes or fails to respond to corticosteroid treatment, a systemic and oncologic work-up and muscle biopsy are warranted to exclude specific local or systemic disease as cause of the inflamed and enlarged muscle. As our understanding of idiopathic orbital myositis evolves, the diagnostic focus is shifting toward earlier identification of underlying local or systemic disease through systemic work-up and muscle biopsy.