Muscle MRI in inherited neuromuscular disorders: past, present, and future

Clinical and genetic characteristics of myotonia congenita in Chinese population

Myotonia congenita (MC) is a rare hereditary muscle disease caused by variants in the CLCN1 gene. Currently, the correlation of phenotype-genotype is still uncertain between dominant-type Thomsen (TMC) and recessive-type Becker (BMC). The clinical data and auxiliary examinations of MC patients in our clinic were retrospectively collected. Electromyography was performed in 11 patients and available family members. Whole exome sequencing was conducted in all patients. The clinical and laboratory data of Chinese MC patients reported from June 2004 to December 2022 were reviewed. A total of 11 MC patients were included in the study, with a mean onset age of 12.64 ± 2.73 years. The main symptom was muscle stiffness of limbs. Warm-up phenomenon and percussion myotonia were found in all patients. Electromyogram revealed significant myotonic charges in all patients and two asymptomatic carriers, while muscle MRI and biopsy showed normal or nonspecific changes. Fourteen genetic variants including 6 novel variants were found in CLCN1. Ninety-eight Chinese patients were re-analyzed and re-summarized in this study. There were no significant differences in the demographic data, clinical characteristics, and laboratory findings between 52 TMC and 46 BMC patients. Among the 145 variants in CLCN1, some variants, including the most common variant c.892 G>A, could cause TMC in some families and BMC in others. This study expanded the clinical and genetic spectrum of Chinese patients with MC. It was difficult to distinguish between TMC and BMC only based on the clinical, laboratory, and genetic characteristics.

Muscular MRI and magnetic resonance neurography in spinal muscular atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disease caused by the degeneration of the α-motor neurons in the anterior horn of the spinal cord. SMA is clinically characterized by progressive and symmetrical muscle weakness and muscle atrophy and ends up with systemic multisystem abnormalities. Quantitative MRI (qMRI) has the advantages of non-invasiveness, objective sensitivity, and high reproducibility, and has important clinical value in evaluating the severity of neuromuscular diseases and monitoring the efficacy of treatment. This article summarizes the clinical use of muscular MRI and magnetic resonance neurography in assessing the progress of SMA.

Risk Factors and Electromyographic Characteristics of Acquired Weakness in Critically Ill Patients: A Retrospective Study

Objective

This retrospective study examines risk factors and electromyographic (EMG) characteristics associated with acquired weakness in critically ill patients and assesses their impact on patient prognosis.

Methods

Ninety-seven critically ill patients, ventilated for over 48 hours, were included. Patient data, encompassing general condition, medical history, Medical Research Council (MRC) scores, serum markers (c-reactive protein, calcitonin gene, albumin, brain natriuretic peptide, urea nitrogen, creatinine), EMG characteristics, respiratory treatment modalities, and parameters, were recorded. Mechanical ventilation duration, ICU stay duration, hospitalization duration, and patient prognosis were documented. Based on MRC scores, patients were categorized into the ICU-acquired weakness (ICU-AW) group (MRC <48 points) and the non-ICU-AW group (MRC ≥48 points).

Results

The study comprised 47 ICU-AW and 50 non-ICU-AW patients. Significant differences (p <0.05) were observed in age, MRC scores, albumin levels, c-reactive protein, calcitonin gene, brain natriuretic peptide, urea nitrogen, creatinine, mechanical ventilation duration, ICU stay duration, and hospitalization duration between groups. In the ICU-AW group, nerve conduction examinations revealed slow conduction velocity, reduced wave amplitude, and in severe cases, a complete loss of motor and sensory potentials. Multivariate logistic analysis identified low serum albumin levels and MRC scores as potential ICU-AW risk factors.

Conclusion

This study suggests that low serum albumin levels and MRC scores may contribute to ICU-AW risk. The ICU-AW group exhibited varied peripheral nerve damage and slow conduction velocities on EMG. Additionally, severe systemic inflammatory responses, renal function, brain natriuretic peptide levels, prolonged mechanical ventilation, and peripheral nerve damage may be associated with ICU-AW. Follow-up studies are essential for further understanding these complex interactions.

[Expert recommendations for magnetic resonance imaging of muscle disorders]

BACKGROUND

Magnetic resonance (MRI) imaging of the skeletal muscles (muscle MRI for short) is increasingly being used in clinical routine for diagnosis and longitudinal assessment of muscle disorders. However, cross-centre standards for measurement protocol and radiological assessment are still lacking.

OBJECTIVES

The aim of this expert recommendation is to present standards for the application and interpretation of muscle MRI in hereditary and inflammatory muscle disorders.

METHODS

This work was developed in collaboration between neurologists, neuroradiologists, radiologists, neuropaediatricians, neuroscientists and MR physicists from different university hospitals in Germany. The recommendations are based on expert knowledge and a focused literature search.

RESULTS

The indications for muscle MRI are explained, including the detection and monitoring of structural tissue changes and oedema in the muscle, as well as the identification of a suitable biopsy site. Recommendations for the examination procedure and selection of appropriate MRI sequences are given. Finally, steps for a structured radiological assessment are presented.

CONCLUSIONS

The present work provides concrete recommendations for the indication, implementation and interpretation of muscle MRI in muscle disorders. Furthermore, it provides a possible basis for the standardisation of the measurement protocols at all clinical centres in Germany.

[Expert recommendations for magnetic resonance imaging of muscle disorders]

BACKGROUND

Magnetic resonance (MRI) imaging of the skeletal muscles (muscle MRI for short) is increasingly being used in clinical routine for diagnosis and longitudinal assessment of muscle disorders. However, cross-centre standards for measurement protocol and radiological assessment are still lacking.

OBJECTIVES

The aim of this expert recommendation is to present standards for the application and interpretation of muscle MRI in hereditary and inflammatory muscle disorders.

METHODS

This work was developed in collaboration between neurologists, neuroradiologists, radiologists, neuropaediatricians, neuroscientists and MR physicists from different university hospitals in Germany. The recommendations are based on expert knowledge and a focused literature search.

RESULTS

The indications for muscle MRI are explained, including the detection and monitoring of structural tissue changes and oedema in the muscle, as well as the identification of a suitable biopsy site. Recommendations for the examination procedure and selection of appropriate MRI sequences are given. Finally, steps for a structured radiological assessment are presented.

CONCLUSIONS

The present work provides concrete recommendations for the indication, implementation and interpretation of muscle MRI in muscle disorders. Furthermore, it provides a possible basis for the standardisation of the measurement protocols at all clinical centres in Germany.

Exome sequencing in undiagnosed congenital myopathy reveals new genes and refines genes-phenotypes correlations

BACKGROUND

Congenital myopathies are severe genetic diseases with a strong impact on patient autonomy and often on survival. A large number of patients do not have a genetic diagnosis, precluding genetic counseling and appropriate clinical management. Our objective was to find novel pathogenic variants and genes associated with congenital myopathies and to decrease diagnostic odysseys and dead-end.

METHODS

To identify pathogenic variants and genes implicated in congenital myopathies, we established and conducted the MYOCAPTURE project from 2009 to 2018 to perform exome sequencing in a large cohort of 310 families partially excluded for the main known genes.

RESULTS

Pathogenic variants were identified in 156 families (50%), among which 123 families (40%) had a conclusive diagnosis. Only 44 (36%) of the resolved cases were linked to a known myopathy gene with the corresponding phenotype, while 55 (44%) were linked to pathogenic variants in a known myopathy gene with atypical signs, highlighting that most genetic diagnosis could not be anticipated based on clinical-histological assessments in this cohort. An important phenotypic and genetic heterogeneity was observed for the different genes and for the different congenital myopathy subtypes, respectively. In addition, we identified 14 new myopathy genes not previously associated with muscle diseases (20% of all diagnosed cases) that we previously reported in the literature, revealing novel pathomechanisms and potential therapeutic targets.

CONCLUSIONS

Overall, this approach illustrates the importance of massive parallel gene sequencing as a comprehensive tool for establishing a molecular diagnosis for families with congenital myopathies. It also emphasizes the contribution of clinical data, histological findings on muscle biopsies, and the availability of DNA samples from additional family members to the diagnostic success rate. This study facilitated and accelerated the genetic diagnosis of congenital myopathies, improved health care for several patients, and opened novel perspectives for either repurposing of existing molecules or the development of novel treatments.

AI driven analysis of MRI to measure health and disease progression in FSHD

Facioscapulohumeral muscular dystrophy (FSHD) affects roughly 1 in 7500 individuals. While at the population level there is a general pattern of affected muscles, there is substantial heterogeneity in muscle expression across- and within-patients. There can also be substantial variation in the pattern of fat and water signal intensity within a single muscle. While quantifying individual muscles across their full length using magnetic resonance imaging (MRI) represents the optimal approach to follow disease progression and evaluate therapeutic response, the ability to automate this process has been limited. The goal of this work was to develop and optimize an artificial intelligence-based image segmentation approach to comprehensively measure muscle volume, fat fraction, fat fraction distribution, and elevated short-tau inversion recovery signal in the musculature of patients with FSHD. Intra-rater, inter-rater, and scan-rescan analyses demonstrated that the developed methods are robust and precise. Representative cases and derived metrics of volume, cross-sectional area, and 3D pixel-maps demonstrate unique intramuscular patterns of disease. Future work focuses on leveraging these AI methods to include upper body output and aggregating individual muscle data across studies to determine best-fit models for characterizing progression and monitoring therapeutic modulation of MRI biomarkers.

Phenotype variability and natural history of X-linked myopathy with excessive autophagy

OBJECTIVE

X-linked myopathy with excessive autophagy (XMEA) linked to the VMA21 gene leads to autophagy failure with progressive vacuolation and atrophy of skeletal muscles. Current knowledge of this rare disease is limited. Our objective was to define the clinical, radiological, and natural history of XMEA.

METHODS

We conducted a retrospective study collecting clinical, genetic, muscle imaging, and biopsy data of XMEA patients followed in France and reviewed the literature for additional cases.

RESULTS

Eighteen males had genetically confirmed XMEA in France, carrying four different VMA21 variants. Mean age at disease onset was 9.4 ± 9.9 (range 1-40) years. In 14/18 patients (77.8%), onset occurred during childhood (< 15 years); however in four patients, the disease started in adulthood. Patients had anterior and medial compartment thigh muscle weakness, distal contractures (56.3%), elevated CK levels (1287.9 ± 757.8 U/l) and autophagic vacuoles with sarcolemmal features on muscle histopathology. Muscle MRI (n = 10) showed a characteristic pattern of lower limb muscle involvement. In 11 patients, outcome measures were available for an average follow-up period of 10.6 ± 9.8 years and six of them show disease progression. Mean change of functional outcomes was 0.5 ± 1.2 points for Brooke and 2.2 ± 2.5 points for Vignos score, 7/16 patients (43.8%) needed a walking aid and 3/16 (18.8%) were wheelchair-bound (median age of 40 years old, range 39-48). The variant c.164-7 T > G was associated with a later onset of symptoms. Respiratory insufficiency was common (57.1%) but cardiac involvement rare (12.5%).

INTERPRETATION

XMEA has variable age of onset, but a characteristic clinical, histopathological, and muscle imaging presentation, guiding the diagnosis. Although slowly, motor disability progresses with time, and relevant genotype-phenotype correlations will help design future clinical trials.

Recognizing Myopathy in Patients with Muscle Weakness or Pain

Muscle weakness and pain can be seen in orthopedic, rheumatologic, cardiac, and musculoskeletal conditions in addition to neurologic disorders. Myopathy, which describes a heterogenous group of hereditary and acquired disorders that affect muscle channels, structure, and metabolism, is one possible cause. This review focuses on essential information to support primary care providers as they assess patients with muscle weakness and pain for myopathy. As with most neurologic disorders, a thorough clinical history and physical examination are essential first steps. These findings will then guide diagnostic testing and facilitate appropriate management or referral for further neuromuscular care.

Studying intramuscular fat deposition and muscle regeneration: insights from a comparative analysis of mouse strains, injury models, and sex differences

Intramuscular fat (IMAT) infiltration, pathological adipose tissue that accumulates between muscle fibers, is a shared hallmark in a diverse set of diseases including muscular dystrophies and diabetes, spinal cord and rotator cuff injuries, as well as sarcopenia. While the mouse has been an invaluable preclinical model to study skeletal muscle diseases, they are also resistant to IMAT formation. To better understand this pathological feature, an adequate pre-clinical model that recapitulates human disease is necessary. To address this gap, we conducted a comprehensive in-depth comparison between three widely used mouse strains: C57BL/6J, 129S1/SvlmJ and CD1. We evaluated the impact of strain, sex and injury type on IMAT formation, myofiber regeneration and fibrosis. We confirm and extend previous findings that a Glycerol (GLY) injury causes significantly more IMAT and fibrosis compared to Cardiotoxin (CTX). Additionally, females form more IMAT than males after a GLY injury, independent of strain. Of all strains, C57BL/6J mice, both females and males, are the most resistant to IMAT formation. In regard to injury-induced fibrosis, we found that the 129S strain formed the least amount of scar tissue. Surprisingly, C57BL/6J of both sexes demonstrated complete myofiber regeneration, while both CD1 and 129S1/SvlmJ strains still displayed smaller myofibers 21 days post injury. In addition, our data indicate that myofiber regeneration is negatively correlated with IMAT and fibrosis. Combined, our results demonstrate that careful consideration and exploration are needed to determine which injury type, mouse model/strain and sex to utilize as preclinical model especially for modeling IMAT formation.

Assessment of Calcaneal Spongy Bone Magnetic Resonance Characteristics in Women: A Comparison between Measures Obtained at 0.3 T, 1.5 T, and 3.0 T

BACKGROUND

There is a growing interest in bone tissue MRI and an even greater interest in using low-cost MR scanners. However, the characteristics of bone MRI remain to be fully defined, especially at low field strength. This study aimed to characterize the signal-to-noise ratio (SNR), T2, and T2* in spongy bone at 0.3 T, 1.5 T, and 3.0 T. Furthermore, relaxation times were characterized as a function of bone-marrow lipid/water ratio content and trabecular bone density.

METHODS

Thirty-two women in total underwent an MR-imaging investigation of the calcaneus at 0.3 T, 1.5 T, and 3.0 T. MR-spectroscopy was performed at 3.0 T to assess the fat/water ratio. SNR, T2, and T2* were quantified in distinct calcaneal regions (ST, TC, and CC). ANOVA and Pearson correlation statistics were used.

RESULTS

SNR increase depends on the magnetic field strength, acquisition sequence, and calcaneal location. T2* was different at 3.0 T and 1.5 T in ST, TC, and CC. Relaxation times decrease as much as the magnetic field strength increases. The significant linear correlation between relaxation times and fat/water found in healthy young is lost in osteoporotic subjects.

CONCLUSION

The results have implications for the possible use of relaxation vs. lipid/water marrow content for bone quality assessment and the development of quantitative MRI diagnostics at low field strength.

Diffusion tensor imaging reveals subclinical alterations in muscles of patients with Becker muscular dystrophy

OBJECTIVES

Becker muscular dystrophy (BMD) is a relatively less investigated neuromuscular disease, partially overlapping the phenotype of Duchenne dystrophy (DMD). Physiopathological and anatomical patterns are still not comprehensively known, despite recent effort in the search of early biomarkers. Aim of this study was to selectively compare normal appearing muscles of BMD with healthy controls.

METHODS

Among a pool of 40 BMD patients and 20 healthy controls, Sartorius and gracilis muscles were selected on the basis of a blinded clinical quantitative/qualitative evaluation, if classified as normal (0 or 1 on Mercuri scale) and subsequently segmented on diffusion tensor MRI scans with a tractographic approach. Diffusion derived parameters were extracted.

RESULTS

Non-parametric testing revealed significant differences between normal and normal appearing BMD derived parameters in both muscles, the difference being more evident in sartorius. Bonferroni-corrected P-values (<.05) of Mann-Whitney test could discriminate between BMD and controls for standard deviation of all diffusion parameters (mean diffusivity, fractional anisotropy, axial and radial diffusivity) in both sartorius and gracilis, while in sartorius the significant difference was found also in the average values of the same parameters (with exception of RD).

CONCLUSIONS

This method could identify microstructural alterations in BMD normal appearing sartorius and gracilis.

ADVANCES IN KNOWLEDGE

Diffusion based MRI could be able to identify possible early or subclinical microstructural alterations in dystrophic patients with BMD.

The complementary use of muscle ultrasound and MRI in FSHD: Early versus later disease stage follow-up

OBJECTIVES

Muscle MRI and ultrasound provide complementary techniques for characterizing muscle changes and tracking disease progression in facioscapulohumeral muscular dystrophy (FSHD). In this cohort study, we provide longitudinal data that compares both imaging modalities head-to-head.

METHODS

FSHD patients were assessed at baseline and after five years. Standardized muscle MRI and ultrasound images of five leg muscles were assessed bilaterally. Fat replacement was quantified using MRI fat-fraction (FF) and ultrasound Heckmatt and echogenicity z-scores (EZ-score). Muscle edema was evaluated using T2-weighted turbo inversion recovery magnitude (TIRM) MRI.

RESULTS

Twenty FSHD patients were included. Muscles with normal baseline imaging showed increases in ultrasound EZ-scores (≥1; in 17%) more often than MRI FF increases (≥10%; in 7%) over time. Muscles with only baseline ultrasound abnormalities often showed considerable FF increases (in 22%), and TIRM positivity at follow-up (44%). Muscles with increased FF at baseline showed stable (80%) or increasing FF (20%) over time. EZ-scores of those muscles either increased (23%), decreased (33%) or remained stable (44%).

CONCLUSIONS

Muscle ultrasound may capture accelerated pathological muscle changes in FSHD in early disease, while muscle MRI appears better-suited to detecting and monitoring pathology in later stages.

SIGNIFICANCE

Our results help establish each techniques' optimal use as imaging biomarker.

Neuromuscular imaging in clinical practice: an ESNR survey of 30 centers

PURPOSE

We assessed the current clinical imaging practice in the primary evaluation of neuromuscular disorders (NMD), with respect to standardized imaging, evaluation and reporting through a European and extra-European-wide survey.

METHODS

An online questionnaire was emailed to all European Society of Neuroradiology (ESNR) members (n = 1662) who had expressed their interest in NMD. The questionnaire featured 40 individual items. Information was gathered on the context of the practices, available and preferred imaging modalities, applied imaging protocols and standards for interpretation, reporting and communication.

RESULTS

A total of 30 unique entries from European and extra-European academic and non-academic institutions were received. Of these, 70% were neuroradiologists, 23% general radiologists and 7% musculoskeletal radiologists. Of the 30 responding institutes, 40% performed from 20 to 50 neuromuscular scans per year for suspected NMD. The principal modality used for a suspected myopathy was magnetic resonance imaging (MRI) (50%) or "mainly MRI" (47%). The primary imaging modality used for the evaluation of patients suspected of a neuropathy was MRI in 63% of all institutions and "mainly MRI" in 37%. For both muscle and nerve pathology, pelvic girdle and inferior limbs are the most scanned parts of the body (28%), followed by the thigh and leg (24%), whole body MR (24%), scapular girdle (16%), and the thigh in just 8% of institutions. Multiplanar acquisitions were performed in 50% of institutions. Convectional sequences used for muscle MRI included T2-STIR (88%), 2D T1weighted (w) (68%), T1 Dixon or equivalent (52%), T2 Dixon (40%), DWI (36%), 2D T2w (28%), T1 3D and T2 3D (20% respectively). For nerve MRI conventional sequences included T2-STIR (80%), DWI (56%), T2 3D (48%), 2D T2w (48%), T1 3D (44%), T1 Dixon or equivalent (44%), 2D T1 (36%), T2 Dixon (28%). Quantitative sequences were used regularly by 40% respondents. While only 28% of institutions utilized structured reports, a notable 88% of respondents expressed a desire for a standardized consensus structured report. Most of the respondents (93%) would be interested in a common MRI neuromuscular protocol and would like to be trained (87%) by the ESNR society with specific neuromuscular sessions in European annual meetings.

CONCLUSIONS

Based on the survey findings, we can conclude that the current approach to neuromuscular imaging varies considerably among European and extra-European countries, both in terms of image acquisition and post-processing. Some of the challenges identified include the translation of research achievements (related to advanced imaging) into practical applications in a clinical setting, implementation of quantitative imaging post-processing techniques, adoption of structured reporting methods, and communication with referring physicians.

A phase 2 open-label study of the safety and efficacy of weekly dosing of ATL1102 in patients with non-ambulatory Duchenne muscular dystrophy and pharmacology in mdx mice

BACKGROUND

ATL1102 is a 2'MOE gapmer antisense oligonucleotide to the CD49d alpha subunit of VLA-4, inhibiting expression of CD49d on lymphocytes, reducing survival, activation and migration to sites of inflammation. Children with DMD have dystrophin deficient muscles susceptible to contraction induced injury, which triggers the immune system, exacerbating muscle damage. CD49d is a biomarker of disease severity in DMD, with increased numbers of high CD49d expressing T cells correlating with more severe and progressive weakess, despite corticosteroid treatment.

METHODS

This Phase 2 open label study assessed the safety, efficacy and pharmacokinetic profile of ATL1102 administered as 25 mg weekly by subcutaneous injection for 24 weeks in 9 non-ambulatory boys with DMD aged 10-18 years. The main objective was to assess safety and tolerability of ATL1102. Secondary objectives included the effect of ATL1102 on lymphocyte numbers in the blood, functional changes in upper limb function as assessed by Performance of Upper Limb test (PUL 2.0) and upper limb strength using MyoGrip and MyoPinch compared to baseline.

RESULTS

Eight out of nine participants were on a stable dose of corticosteroids. ATL1102 was generally safe and well tolerated. No serious adverse events were reported. There were no participant withdrawals from the study. The most commonly reported adverse events were injection site erythema and skin discoloration. There was no statistically significant change in lymphocyte count from baseline to week 8, 12 or 24 of dosing however, the CD3+CD49d+ T lymphocytes were statistically significantly higher at week 28 compared to week 24, four weeks past the last dose (mean change 0.40x109/L 95%CI 0.05, 0.74; p = 0.030). Functional muscle strength, as measured by the PUL2.0, EK2 and Myoset grip and pinch measures, and MRI fat fraction of the forearm muscles were stable throughout the trial period.

CONCLUSION

ATL1102, a novel antisense drug being developed for the treatment of inflammation that exacerbates muscle fibre damage in DMD, appears to be safe and well tolerated in non-ambulant boys with DMD. The apparent stabilisation observed on multiple muscle disease progression parameters assessed over the study duration support the continued development of ATL1102 for the treatment of DMD.

TRIAL REGISTRATION

Clinical Trial Registration. Australian New Zealand Clinical Trials Registry Number: ACTRN12618000970246.

The Impact of Fatty Infiltration on MRI Segmentation of Lower Limb Muscles in Neuromuscular Diseases: A Comparative Study of Deep Learning Approaches

BACKGROUND

Deep learning methods have been shown to be useful for segmentation of lower limb muscle MRIs of healthy subjects but, have not been sufficiently evaluated on neuromuscular disease (NDM) patients.

PURPOSE

Evaluate the influence of fat infiltration on convolutional neural network (CNN) segmentation of MRIs from NMD patients.

STUDY TYPE

Retrospective study.

SUBJECTS

Data were collected from a hospital database of 67 patients with NMDs and 14 controls (age: 53 ± 17 years, sex: 48 M, 33 F). Ten individual muscles were segmented from the thigh and six from the calf (20 slices, 200 cm section).

FIELD STRENGTH/SEQUENCE

A 1.5 T. Sequences: 2D T1 -weighted fast spin echo. Fat fraction (FF): three-point Dixon 3D GRE, magnetization transfer ratio (MTR): 3D MT-prepared GRE, T2: 2D multispin-echo sequence.

ASSESSMENT

U-Net 2D, U-Net 3D, TransUNet, and HRNet were trained to segment thigh and leg muscles (101/11 and 95/11 training/validation images, 10-fold cross-validation). Automatic and manual segmentations were compared based on geometric criteria (Dice coefficient [DSC], outlier rate, absence rate) and reliability of measured MRI quantities (FF, MTR, T2, volume).

STATISTICAL TESTS

Bland-Altman plots were chosen to describe agreement between manual vs. automatic estimated FF, MTR, T2 and volume. Comparisons were made between muscle populations with an FF greater than 20% (G20+) and lower than 20% (G20-).

RESULTS

The CNNs achieved equivalent results, yet only HRNet recognized every muscle in the database, with a DSC of 0.91 ± 0.08, and measurement biases reaching -0.32% ± 0.92% for FF, 0.19 ± 0.77 for MTR, -0.55 ± 1.95 msec for T2, and - 0.38 ± 3.67 cm3 for volume. The performances of HRNet, between G20- and G20+ decreased significantly.

DATA CONCLUSION

HRNet was the most appropriate network, as it did not omit any muscle. The accuracy obtained shows that CNNs could provide fully automated methods for studying NMDs. However, the accuracy of the methods may be degraded on the most infiltrated muscles (>20%).

EVIDENCE LEVEL

4.

TECHNICAL EFFICACY

Stage 1.

Hypokalemic periodic paralysis: a 3-year follow-up study

BACKGROUND AND OBJECTIVES

Primary hypokalemic periodic paralysis (HypoPP) is an inherited channelopathy most commonly caused by mutations in CACNA1S. HypoPP can present with different phenotypes: periodic paralysis (PP), permanent muscle weakness (PW), and mixed weakness (MW) with both periodic and permanent weakness. Little is known about the natural history of HypoPP.

METHODS

In this 3-year follow-up study, we used the MRC scale for manual muscle strength testing and whole-body muscle MRI (Mercuri score) to assess disease progression in individuals with HypoPP-causing mutations in CACNA1S.

RESULTS

We included 25 men (mean age 43 years, range 18-76 years) and 12 women (mean age 42 years, range 18-76 years). Two participants were asymptomatic, 21 had PP, 12 MW, and two PW. The median number of months between baseline and follow-up was 42 (range 26-52). Muscle strength declined in 11 patients during follow-up. Four of the patients with a decline in muscle strength had no attacks of paralysis during follow-up, and two of these patients had never had attacks of paralysis. Fat replacement of muscles increased in 27 patients during follow-up. Eight of the patients with increased fat replacement had no attacks of paralysis during follow-up, and two of these patients had never had attacks of paralysis.

DISCUSSION

The study demonstrates that HypoPP can be a progressive myopathy in both patients with and without attacks of paralysis.

Usefulness and Clinical Impact of Whole-Body MRI in Detecting Autoimmune Neuromuscular Disorders

Autoimmune neuromuscular diseases are a group of heterogenous pathologies secondary to the activation of the immune system that damage the structures of the peripheric nerve, the neuromuscular junction, or the skeleton muscle. The diagnosis of autoimmune neuromuscular disorders comprises a combination of data from clinical, laboratory, electromyography, imaging exam, and biopsy. Particularly, the whole-body MRI examination in the last two decades has been of great use in the assessment of neuromuscular disorders. MRI provides information about the structures involved and the status of activity of the disease. It can also be used as a biomarker, detect the pattern of specific muscle involvement, and is a useful tool for targeting the optimal muscle site for biopsy. In this work, we summarized the most used technical protocol of whole-body MRI and the role of this imaging technique in autoimmune neuromuscular disorders.

Sex influences clinical phenotype in valosin-containing protein mutations: A case family report and systematic literature review

OBJECTIVE

Mutations in the valosin-containing protein (VCP) gene cause autosomal dominant multisystem proteinopathy 1 (MSP1), characterized by a variable combination of inclusion body myopathy (IBM), Paget's disease of bone (PDB), and frontotemporal dementia (FTD). Here we report a novel VCP missense mutations in an Italian family with FTD as the prevalent manifestation and compare our results with those described in the literature.

METHODS

We described the clinical, molecular, and imaging data of the studied family. We also conducted a systematic literature search with the aim of comparing our findings with previously reported VCP-related phenotypes.

RESULTS

A novel heterozygous VCP missense mutation (c 0.473 T > C/p.Met158Thr) was found in all the affected family members. The proband is a 69-year-old man affected by progressive muscle weakness since the age of 49. Muscle MRI showed patchy fatty infiltration in most muscles, and STIR sequences revealed an unusual signal increase in distal leg muscles. At age 65, he presented a cognitive disorder suggestive of behavioral variant FTD. A bone scintigraphy also revealed PDB. The patient's mother, his maternal aunt and her daughter had died following a history of cognitive deterioration consistent with FTD; the mother also had PDB. No relatives had any muscular impairments. Reviewing the literature data, we observed a different sex distribution of VCP-related phenotypes, being FTD prevalence higher among women as compared to men (51.2 % vs 31.2 %) and IBM prevalence higher among men as compared to women (92.1 % vs 72.8 %).

DISCUSSION

This study broadened our clinical, genetic, and imaging knowledge of VCP-related disorders.

Novel Muscle Sensing by Radiomyography (RMG) and Its Application to Hand Gesture Recognition

Conventional electromyography (EMG) measures the continuous neural activity during muscle contraction, but lacks explicit quantification of the actual contraction. Mechanomyography (MMG) and accelerometers only measure body surface motion, while ultrasound, CT-scan and MRI are restricted to in-clinic snapshots. Here we propose a novel radiomyography (RMG) for continuous muscle actuation sensing that can be wearable or touchless, capturing both superficial and deep muscle groups. We verified RMG experimentally by a wearable forearm sensor for hand gesture recognition (HGR). We first converted the sensor outputs to the time-frequency spectrogram, and then employed the vision transformer (ViT) deep learning network as the classification model, which can recognize 23 gestures with an average accuracy up to 99% on 8 subjects. By transfer learning, high adaptivity to user difference and sensor variation were achieved at an average accuracy up to 97%. We further extended RMG to monitor eye and leg muscles and achieved high accuracy for eye movement and body posture tracking. RMG can be used with synchronous EMG to derive stimulation-actuation waveforms for many potential applications in kinesiology, physiotherapy, rehabilitation, and human-machine interface.

Imaging biomarkers in the idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are a group of acquired muscle diseases with muscle inflammation, weakness, and other extra-muscular manifestations. IIMs can significantly impact the quality of life, and management of IIMs often requires a multi-disciplinary approach. Imaging biomarkers have become an integral part of the management of IIMs. Magnetic resonance imaging (MRI), muscle ultrasound, electrical impedance myography (EIM), and positron emission tomography (PET) are the most widely used imaging technologies in IIMs. They can help make the diagnosis and assess the burden of muscle damage and treatment response. MRI is the most widely used imaging biomarker of IIMs and can assess a large volume of muscle tissue but is limited by availability and cost. Muscle ultrasound and EIM are easy to administer and can even be performed in the clinical setting, but they need further validation. These technologies may complement muscle strength testing and laboratory studies and provide an objective assessment of muscle health in IIMs. Furthermore, this is a rapidly progressing field, and new advances are going to equip care providers with a better objective assessment of IIMS and eventually improve patient management. This review discusses the current state and future direction of imaging biomarkers in IIMs.

A homozygous loss of function variant in POPDC3: From invalidating exercise intolerance to a limb-girdle muscular dystrophy phenotype

Recessive pathogenic variants in POPDC3 have recently been associated with the rare limb-girdle muscular dystrophy (LGMD) subtype LGMDR26. We studied three siblings and a distantly related individual with a skeletal muscle disorder, harboring the c.486-6T>A splice site variant in POPDC3 in homozygosity. Immunohistochemistry, western blot, and mRNA experiments on patients' skeletal muscle tissue as well as on patients' myoblasts were performed to study the pathogenicity of the predicted loss of function mechanism of the variant. Patients mainly presented with invalidating myalgia and exercise intolerance and limited to no segmentary muscle weakness. CK levels were markedly elevated in all patients. A loss of function mechanism at the RNA level was shown (r.485_486insauag, p.Ile163*). Muscle biopsies performed in three out of four patients showed non-specific myopathic features with a marked type 2 fiber predominance and the presence of a large number of severely atrophic fibers with pyknotic nuclear clumps. We show that skeletal muscle symptoms in LGMDR26 may range from an overt late juvenile to young adult-onset limb-girdle muscular dystrophy phenotype to severe exercise intolerance and myalgia, with consistently highly elevated CK levels. We further prove a clear LOF mechanism of POPDC3 in this rare disorder.

Estimation of subvoxel fat infiltration in neurodegenerative muscle disorders using quantitative multi-T2 analysis

MRI's T₂ relaxation time is a valuable biomarker for neuromuscular disorders and muscle dystrophies. One of the hallmarks of these pathologies is the infiltration of adipose tissue and a loss of muscle volume. This leads to a mixture of two signal components, from fat and from water, to appear in each imaged voxel, each having a specific T₂ relaxation time. In this proof-of-concept work, we present a technique that can separate the signals from water and from fat within each voxel, measure their separate T₂ values, and calculate their relative fractions. The echo modulation curve (EMC) algorithm is a dictionary-based technique that offers accurate and reproducible mapping of T₂ relaxation times. We present an extension of the EMC algorithm for estimating subvoxel fat and water fractions, alongside the T₂ and proton-density values of each component. To facilitate data processing, calf and thigh anatomy were automatically segmented using a fully convolutional neural network and FSLeyes software. The preprocessing included creating two signal dictionaries, for water and for fat, using Bloch simulations of the prospective protocol. Postprocessing included voxelwise fitting for two components, by matching the experimental decay curve to a linear combination of the two simulated dictionaries. Subvoxel fat and water fractions and relaxation times were generated and used to calculate a new quantitative biomarker, termed viable muscle index, and reflecting disease severity. This biomarker indicates the fraction of remaining muscle out of the entire muscle region. The results were compared with those using the conventional Dixon technique, showing high agreement (R = 0.98, p < 0.001). It was concluded that the new extension of the EMC algorithm can be used to quantify abnormal fat infiltration as well as identify early inflammatory processes corresponding to elevation in the T₂ value of the water (muscle) component. This new ability may improve the diagnostic accuracy of neuromuscular diseases, help stratification of patients according to disease severity, and offer an efficient tool for tracking disease progression.

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

OBJECTIVE

To describe the disease progression of Duchenne muscular dystrophy (DMD) in the pelvic and thigh muscles over 1-year using multiple-parameter quantitative magnetic resonance imaging (qMRI), and to determine the most responsive muscle and predict subclinical disease progression in functionally stable patients.

METHODS

Fifty-four DMD patients (mean age 8.9 ± 2.5, range 5-15 years) completed baseline and 1-year follow-up qMRI examinations/biomarkers [3-point Dixon/fat fraction (FF); T1 mapping/T1; T2 mapping/T2]. Meanwhile, clinical assessments [NorthStar ambulatory assessment (NSAA) score] and timed function tests were performed in DMD patients. Twenty-four healthy male controls (range 5-15 years) accomplished baseline qMRI examinations. Group differences were compared using the Wilcoxon test. The standardized response mean (SRM) was taken as the responsiveness to the disease progression index.

RESULTS

FF, T1, and T2 in all DMD age subgroups changed significantly over 1-year (P < 0.05). Even in functionally stable patients (NSAA score increased, unchanged, or decreased by 1-point) over 1-year, significant increases in FF and T2 and decreases in T1 were observed in gluteus maximus (GMa), gluteus medius, vastus lateralis, and adductor magnus (P < 0.05). Overall, the SRM of FF, T1, and T2 was all the highest in GMa, which were 1.25, - 0.92, and 0.93, respectively.

CONCLUSIONS

qMRI biomarkers are responsive to disease progression and can also detect subclinical disease progression in functionally stable DMD patients over 1-year. GMa is the most responsive to disease progression of all the muscles analyzed.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ( http://www.chictr.org.cn/index.aspx ) ChiCTR1800018340, 09/12/2018, prospectively registered.

Shear Wave Elastography in Patients with Spinal Muscular Atrophy Types 2 and 3

INTRODUCTION

 This study aimed to investigate selective muscle involvement by shear wave elastography (SWE) in patients with spinal muscular atrophy (SMA) types 2 and 3 and to compare SWE values with magnetic resonance imaging (MRI) in demonstrating muscle involvement.

METHODS

 Seventeen patients with SMA types 2 and3 were included in the study. SWE was used to evaluate stiffness of the upper and lower extremities and paraspinal muscles. Involvement of the paraspinal muscles was evaluated using 1.5-T MRI.

RESULTS

 Among the upper extremity muscles, SWE values were the highest for the triceps brachii; however, no significant difference was noted (p = 0.23). In post hoc analysis, a significant difference was observed between triceps brachii and biceps brachii (p = 0.003). Patients with a longer disease duration have the highest SWE values for the triceps brachii (r = 0.67, p = 0.003). Among the lower extremity muscles, SWE values for the iliopsoas were significantly higher than the gluteus maximus (p < 0.001). A positive correlation was found between SWE values and MRI scores of paraspinal muscles (r = 0.49, p = 0.045; r = 0.67, p = 0.003).

CONCLUSION

 This is the first study to report muscle involvement assessed by SWE in patients with SMA types 2 and 3. Our findings are similar to the presence of selective muscle involvement demonstrated in previous studies, and also SWE and MRI values were similar. SWE is an alternative noninvasive practical method that can be used to demonstrate muscle involvement in patients with SMA, to understand the pathogenesis of segmental involvement, and to guide future treatments or to monitor the effectiveness of existing new treatment options.

Muscle fat replacement and contractility in patients with skeletal muscle sodium channel disorders

Skeletal muscle sodium channel disorders give rise to episodic symptoms such as myotonia and/or periodic paralysis. Chronic symptoms with permanent weakness are not considered characteristic of the phenotypes. Muscle fat replacement represents irreversible damage that inevitably will impact on muscle strength. This study investigates muscle fat replacement and contractility in patients with pathogenic SCN4A variants compared to healthy controls. T1-weighted and 2-point Dixon MRI of the legs were conducted to assess fat replacement. Stationary dynamometry was used to assess muscle strength. Contractility was determined by maximal muscle contraction divided by cross-sectional muscle area. The average cross-sectional intramuscular fat fraction was greater in patients compared with controls by 2.5% in the calves (95% CI 0.74-4.29%, p = 0.007) and by 2.0% in the thighs (95% CI 0.75-3.2%, p = 0.003). Muscle contractility was less in patients vs. controls by 14-27% (p < 0.05). Despite greater fat fraction and less contractility, absolute strength was not significantly less. This study quantitatively documents greater fat fraction and additionally describes difference in muscle contractility in a large cohort of patients with skeletal muscle sodium channel disorders. The clinical impact of these abnormal findings is likely limited as muscle hypertrophy in the patients served to preserve absolute muscle strength. Subgroup analysis indicated significant difference in phenotype by genotype, however these findings lack statistical significance and serve as inspiration for future researchers to probe into the geno- phenotype relationship in these disorders.Trial registration: The study was registered at http://clinicaltrials.gov (identifier: NCT04808388).

Muscle MRI in immune-mediated necrotizing myopathy (IMNM): implications for clinical management and treatment strategies

OBJECTIVES

Immune-mediated necrotizing myopathy (IMNM) is the most severe idiopathic inflammatory myopathy (IIM) and early aggressive poly-immunotherapy is often required to reduce long-term disability. The aim of this study is to investigate muscle MRI in IMNM as outcome measure for disease activity, severity, progression, response to treatment, and to better characterize the pattern of muscle involvement.

METHODS

This is a retrospective, observational, cross-sectional, and longitudinal study including 22 IMNM patients, divided into three groups based on timing of first MRI and if performed before or under treatment. T1 score and percentage of STIR positive muscles (STIR%) were considered and analyzed also in relation to demographic, clinical and laboratory characteristics.

RESULTS

STIR% was higher in untreated patients and in those who performed MRI earlier (p = 0.001). Pelvic girdle and thighs were in general more affected than legs. T1 score was higher in patients with MRI performed later in disease course (p = 0.004) with a prevalent involvement of the lumbar paraspinal muscles, gluteus medius and minimus, adductor magnus and hamstrings. 22% of STIR positive muscles showed fat replacement progression at second MRI. Higher STIR% at baseline correlated with higher risk of fat replacement at follow-up (p = 0.003); higher T1 score correlated with clinical disability at follow-up, with late treatment start and delayed treatment with IVIG (p = 0.03).

INTERPRETATION

Muscle MRI is a sensitive biomarker for monitoring disease activity and therapy response, especially when performed early in disease course and before treatment start, and could represent a supportive outcome measure and early prognostic index in IMNM.

Distinctive chaperonopathy in skeletal muscle associated with the dominant variant in DNAJB4

DnaJ homolog, subfamily B, member 4, a member of the heat shock protein 40 chaperones encoded by DNAJB4, is highly expressed in myofibers. We identified a heterozygous c.270 T > A (p.F90L) variant in DNAJB4 in a family with a dominantly inherited distal myopathy, in which affected members have specific features on muscle pathology represented by the presence of cytoplasmic inclusions and the accumulation of desmin, p62, HSP70, and DNAJB4 predominantly in type 1 fibers. Both Dnajb4F90L knockin and knockout mice developed muscle weakness and recapitulated the patient muscle pathology in the soleus muscle, where DNAJB4 has the highest expression. These data indicate that the identified variant is causative, resulting in defective chaperone function and selective muscle degeneration in specific muscle fibers. This study demonstrates the importance of DNAJB4 in skeletal muscle proteostasis by identifying the associated chaperonopathy.

Deformable image registration based on single or multi-atlas methods for automatic muscle segmentation and the generation of augmented imaging datasets

Muscle segmentation is a process relied upon to gather medical image-based muscle characterisation, useful in directly assessing muscle volume and geometry, that can be used as inputs to musculoskeletal modelling pipelines. Manual or semi-automatic techniques are typically employed to segment the muscles and quantify their properties, but they require significant manual labour and incur operator repeatability issues. In this study an automatic process is presented, aiming to segment all lower limb muscles from Magnetic Resonance (MR) imaging data simultaneously using three-dimensional (3D) deformable image registration (single inputs or multi-atlas). Twenty-three of the major lower limb skeletal muscles were segmented from five subjects, with an average Dice similarity coefficient of 0.72, and average absolute relative volume error (RVE) of 12.7% (average relative volume error of -2.2%) considering the optimal subject combinations. The multi-atlas approach showed slightly better accuracy (average DSC: 0.73; average RVE: 1.67%). Segmented MR imaging datasets of the lower limb are not widely available in the literature, limiting the potential of new, probabilistic methods such as deep learning to be used in the context of muscle segmentation. In this work, Non-linear deformable image registration is used to generate 69 manually checked, segmented, 3D, artificial datasets, allowing access for future studies to use these new methods, with a large amount of reliable reference data.

Correlation between whole body muscle MRI and functional measures in paediatric patients with facioscapulohumeral muscular dystrophy

Symptoms and severity of facioscapulohumeral muscular dystrophy (FSHD) can vary greatly, even within the same family. Clinical trial readiness requires accurate and reliable methods of assessing disease stage and progression. MRI has not previously been assessed as a disease biomarker in paediatric FSHD. Eleven patients with FSHD1 underwent whole body muscle MRI. Pre-selected muscles were analysed by a paediatric radiologist using the semi-quantitative Mercuri/Kim method. Within each domain (oedema, fat replacement, atrophy) scores for each muscle were then summated to give each participant three cumulative domain scores. The same participants had functional measures scored: FSHD-CSS (Ricci), FSHD-CS (Lamperti), FSHD-COM, PUL2.0, MFM-32, 6MWT, myometry and manual muscle testing. Pearson coefficient was calculated to determine strength of correlation. The scores for atrophy and fat replacement showed strong correlation with functional outcome measures, particularly FSHD-CSS, FSHD-CS and FSHD-COM. In contrast, muscle oedema correlated poorly with all functional outcome measures, with no relationship seen to the 6MWT. This study of eleven children suggests that semi-quantitative visual Mercuri score utilising fat replacement or atrophy on whole body muscle MRI correlates strongly with disease-specific functional measures and may be a useful measure of disease severity in paediatric FSHD.

MRI Evaluation of Gene Therapy in the Canine Model of Duchenne Muscular Dystrophy

Magnetic resonance imaging (MRI) is a well-established and widely used technique to characterize and quantify skeletal and cardiac muscle changes in Duchenne muscular dystrophy (DMD). Recently, MRI has been explored to study disease progression and response to gene therapy in the canine DMD model. Using traditional sequences, delayed gadolinium enhancement, novel sequences, and spectroscopy, investigators have begun to (i) establish the baseline MRI characteristics of the muscles in normal and affected dogs and (ii) evaluate gene therapy outcomes in treated dogs. As a noninvasive assay, MRI offers an excellent opportunity to study longitudinal muscle changes in long-term gene therapy studies in the canine model. In this chapter, we outline the MRI method used to study DMD in the canine model.

Radiomics and machine learning applied to STIR sequence for prediction of quantitative parameters in facioscapulohumeral disease

Purpose

Quantitative Muscle MRI (qMRI) is a valuable and non-invasive tool to assess disease involvement and progression in neuromuscular disorders being able to detect even subtle changes in muscle pathology. The aim of this study is to evaluate the feasibility of using a conventional short-tau inversion recovery (STIR) sequence to predict fat fraction (FF) and water T2 (wT2) in skeletal muscle introducing a radiomic workflow with standardized feature extraction combined with machine learning algorithms.

Methods

Twenty-five patients with facioscapulohumeral muscular dystrophy (FSHD) were scanned at calf level using conventional STIR sequence and qMRI techniques. We applied and compared three different radiomics workflows (WF1, WF2, WF3), combined with seven Machine Learning regression algorithms (linear, ridge and lasso regression, tree, random forest, k-nearest neighbor and support vector machine), on conventional STIR images to predict FF and wT2 for six calf muscles.

Results

The combination of WF3 and K-nearest neighbor resulted to be the best predictor model of qMRI parameters with a mean absolute error about ± 5 pp for FF and ± 1.8 ms for wT2.

Conclusion

This pilot study demonstrated the possibility to predict qMRI parameters in a cohort of FSHD subjects starting from conventional STIR sequence.

Muscle ultrasound in hereditary muscle disease

In this review we summarise the key techniques of muscle ultrasound as they apply to hereditary muscle disease. We review the diagnostic utility of muscle ultrasound including its role in guiding electromyography and muscle biopsy sampling. We summarize the different patterns of sonographic muscle involvement in the major categories of genetic muscle disorders and discuss the limitations of the technique. We hope to encourage others to adopt ultrasound in their care for patients with hereditary muscle diseases.

Beyond mean value analysis - a voxel-based analysis of the quantitative MR biomarker water T2 in the presence of fatty infiltration in skeletal muscle tissue of patients with neuromuscular diseases

The main pathologies in the muscles of patients with neuromuscular diseases (NMD) are fatty infiltration and edema. Recently, quantitative magnetic resonance (MR) imaging for determination of the MR biomarkers proton density fat fraction (PDFF) and water T₂ (T_2w ) has been advanced. Biophysical effects or pathology can have different effects on MR biomarkers. Thus, for heterogeneously affected muscles, the routinely performed mean or median value analyses of MR biomarkers are questionable. Our work presents a voxel-based histogram analysis of PDFF and T_2w images to point out potential quantification errors. In 12 patients with NMD, chemical-shift encoding-based water-fat imaging for PDFF and T₂ mapping with spectral adiabatic inversion recovery (SPAIR) for T_2w determination was performed. Segmentation of nine thigh muscles was performed bilaterally (n = 216). PDFF and T₂ maps were coregistered. A voxel-based comparison of PDFF and T_2w showed a decreased T_2w with increasing PDFF. Mean T_2w and mean T_2w ^{without fatty voxels} (PDFF < 10%) show good agreement, whereas standard deviation (σ) T_2w and σ T_2w ^{without fatty voxels} show increasing difference with increasing values of σ. Thereby two subgroups can be observed, referring to muscles in which the exclusion of fatty voxels has a negligible influence versus muscles in which a strong dependency of the T_2w value distribution on the exclusion of fatty voxels is present. Because of the two opposite effects that influence T_2w in a voxel, namely, (i) a pathophysiologically increased water mobility leading to T_2w elevation, and (ii) a dependency of T_2w on the PDFF leading to decreased T_2w , the T_2w distribution within a muscle might be heterogenous and the routine mean or median analysis can lead to a misinterpretation of the muscle health. It was concluded that muscle T_2w mean values can wrongly suggest healthy muscle tissue. A deeper analysis of the underlying value distribution is necessary. Therefore, a quantitative analysis of T_2w histograms is a potential alternative.

Whole-muscle fat analysis identifies distal muscle end as disease initiation site in facioscapulohumeral muscular dystrophy

BACKGROUND

Facioscapulohumeral dystrophy (FSHD) is a major muscular dystrophy characterized by asymmetric fatty replacement of muscles. We aimed to determine the initiation site and progression profile of the disease in lower extremity muscles of FSHD patients by assessing fat infiltration along their full proximo-distal axis using quantitative MRI.

METHODS

Nine patients underwent MRI of lower extremities to assess end-to-end muscle fat fractions (FFs) and inflammatory lesions. Seven patients underwent the same MRI ~3.5 years later. Individual muscles (n = 396) were semi-automatically segmented to calculate average FFs over all slices covering whole muscles. To assess disease progression we determined FF changes in 5 adjacent muscle segments.

RESULTS

We provide evidence that fat replacement commonly starts at the distal end of affected muscles where the highest FFs occur (p < 0.001). It progresses in a wave-like manner in the proximal direction at an increasing rate with the highest value (4.9 ± 2.7%/year) for muscles with baseline FFs of 30-40%. Thereafter it proceeds at a slower pace towards the proximal muscle end. In early phases of disease, inflammatory lesions preferentially occur at the distal muscle end. Compared with whole-muscle analysis, the common FF assessments using only few MR slices centrally placed in muscles are significantly biased (~50% in progression rate).

CONCLUSIONS

These findings identify the distal end of leg muscles as a prime location for disease initiation in FSHD and demonstrate a wave-like progression towards the proximal end, consistent with proposed disease mechanisms. End-to-end whole-muscle fat assessment is essential to properly diagnose FSHD and its progression.

Identification of immune-related features involved in Duchenne muscular dystrophy: A bidirectional transcriptome and proteome-driven analysis

Background

We aimed to investigate the biological mechanism and feature genes of Duchenne muscular dystrophy (DMD) by multi-omics and experimental verification strategy.

Methods

We integrated the transcriptomic and proteomic methods to find the differentially expressed mRNAs (DEMs) and proteins (DEPs) between DMD and Control groups. Weighted gene co-expression network analysis (WGCNA) was then used to identify modules of highly correlated genes and hub genes. In the following steps, the immune and stromal cells infiltrations were accomplished by xCELL algorithm. Furthermore, TF and miRNA prediction were performed with Networkanalyst. ELISA, western blot and external datasets were performed to verify the key proteins/mRNAs in DMD patient and mouse. Finally, a nomogram model was established based on the potential biomarkers.

Results

4515 DEMs and 56 DEPs were obtained from the transcriptomic and proteomic study respectively. 14 common genes were identified, which is enriched in muscle contraction and inflammation-related pathways. Meanwhile, we observed 33 significant differences in the infiltration of cells in DMD. Afterwards, a total of 22 miRNAs and 23 TF genes interacted with the common genes, including TFAP2C, MAX, MYC, NFKB1, RELA, hsa-miR-1255a, hsa-miR-130a, hsa-miR-130b, hsa-miR-152, and hsa-miR-17. In addition, three genes (ATP6AP2, CTSS, and VIM) showed excellent diagnostic performance on discriminating DMD in GSE1004, GSE3307, GSE6011 and GSE38417 datasets (all AUC > 0.8), which is validated in patients (10 DMD vs. 10 controls), DMD with exon 55 mutations, mdx mouse, and nomogram model.

Conclusion

Taken together, ATP6AP2, CTSS, and VIM play important roles in the inflammatory response in DMD, which may serve as diagnostic biomarkers and therapeutic targets.

Genetic and Clinical Spectrum of GNE Myopathy in Russia

GNE myopathy (GNEM) is a rare hereditary disease, but at the same time, it is the most common distal myopathy in several countries due to a founder effect of some pathogenic variants in the GNE gene. We collected the largest cohort of patients with GNEM from Russia and analyzed their mutational spectrum and clinical data. In our cohort, 10 novel variants were found, including 2 frameshift variants and 2 large deletions. One novel missense variant c.169_170delGCinsTT (p.(Ala57Phe)) was detected in 4 families in a homozygous state and in 3 unrelated patients in a compound heterozygous state. It was the second most frequent variant in our cohort. All families with this novel frequent variant were non-consanguineous and originated from the 3 neighboring areas in the European part of Russia. The clinical picture of the patients carrying this novel variant was typical, but the severity of clinical manifestation differed significantly. In our study, we reported two atypical cases expanding the phenotypic spectrum of GNEM. One female patient had severe quadriceps atrophy, hand joint contractures, keloid scars, and non-classical pattern on leg muscle magnetic resonance imaging, which was more similar to atypical collagenopathy rather than GNEM. Another patient initially had been observed with spinal muscular atrophy due to asymmetric atrophy of hand muscles and results of electromyography. The peculiar pattern of muscle involvement on magnetic resonance imaging consisted of pronounced changes in the posterior thigh muscle group with relatively spared muscles of the lower legs, apart from the soleus muscles. Different variants in the GNE gene were found in both atypical cases. Thus, our data expand the mutational and clinical spectrum of GNEM.

Muscle MRI in McArdle Disease: A European Multicenter Observational Study

BACKGROUND AND OBJECTIVES

Glycogen storage disease type V (GSDV) or McArdle disease is a muscle glycogenosis that classically manifests with exercise intolerance and exercise-induced muscle pain. Muscle weakness and wasting may occur, but it is typically mild and described as located around the shoulder girdle in elderly patients. Paraspinal muscle involvement has received little attention in the literature. This study aimed to quantify fat replacement of paraspinal, shoulder, and lower limb muscles by magnetic resonance imaging in a European cohort of patients with GSDV.

METHODS

This observational study included patients with verified GSDV and healthy controls (HCs). Whole-body MRIs and clinical data were collected. The degree of muscle fat replacement was evaluated on T1-weighted images with the semiquantitative visual Mercuri scale and on Dixon images where individual muscle fat fractions (FFs) were quantitatively calculated.

RESULTS

MRIs and clinical data from a total of 57 patients with GSDV (age 44.3 ± 15.2 years) from 5 European centers were assessed and compared with findings in 30 HCs (age 42.4 ± 14.8 years). Patients with GSDV had significantly more fat replacement of the paraspinal muscles compared with HCs on all levels investigated, detected by both the Mercuri and the Dixon method (Dixon, paraspinal composite FF [GSDV vs HC] at the cervical level: 31.3 ± 13.1 vs 15.4 ± 7.8; thoracic level: 34.5±19.0 vs 16.9±8.6; and lumbar level: 43.9 ± 19.6 vs 21.8 ± 10.2 [p < 0.0001]). Patients with GSDV also had significantly more fat replacement of the shoulder muscles (evaluated by the Mercuri scale), along with significantly, but numerically less, fat replacement of thigh and calf muscles compared with HC (Dixon, lower limb composite FF [GSDV vs HC] at the thigh level: 12.0 ± 5.6 vs 8.8 ± 2.7 and calf level: 13.1 ± 6.7 vs 9.1 ± 2.9 [p ≤ 0.05]).

DISCUSSION

The primary findings are that patients with GSDV exhibit severe fat replacement of the paraspinal muscles, which can have important implications for the future management of patients with GSDV, and also significant fat replacement of shoulder girdle muscles as previously described. The clinical relevance of the discrete increases in lower limb FF is uncertain. The changes were found to be age-related in both groups, but an accelerated effect was found in GSDV, probably due to continuous muscle damage.

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

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

Visceral adipose tissue is a better predictor than BMI in the alternative Fistula Risk Score in patients undergoing pancreatoduodenectomy

BACKGROUND

Muscle attenuation (MA) and visceral adipose tissue (VAT) have not yet been included in the currently used alternative Fistula Risk Score (a-FRS). The aim of this study was to examine the added value of these parameters as predictors of clinically relevant postoperative pancreatic fistula (CR-POPF) in the a-FRS after pancreatoduodenectomy compared to Body Mass Index (BMI).

METHODS

A single center retrospective cohort study was performed in patients who underwent pancreatoduodenectomy between 2009 and 2018. The a-FRS model was reproduced, MA and VAT were both combined and separately added to the model instead of BMI using logistic regression analysis. Model discrimination was assessed by ROC-curves.

RESULTS

In total, 329 patients were included of which 55 (16.7%) developed CR-POPF. The a-FRS model showed an AUC of 0.74 (95%CI: 0.68-0.80). In this model, BMI was not significantly associated with CR-POPF (p = 0.16). The MA + VAT model showed an AUC of 0.81 (95%CI: 0.75-0.86). VAT was significantly associated with CR-POPF (per cm², OR: 1.01; 95%CI: 1.00-1.01; p < 0.001). The AUC of the MA + VAT model differed significantly from the AUC of the a-FRS model (p = 0.001).

CONCLUSION

Visceral adipose tissue is of added value in the a-FRS compared to BMI in predicting CR-POPF in patients undergoing pancreatoduodenectomy.

Recognizable Pattern of Arthrogryposis and Congenital Myopathy Caused by the Recurrent TTN Metatranscript-only c.39974-11T > G Splice Variant

INTRODUCTION

Arthrogryposis is characterized by the presence of multiple contractures at birth and can be caused by pathogenic variants in TTN (Titin). Exons and variants that are not expressed in one of the three major isoforms of titin are referred to as "metatranscript-only" and have been considered to be only expressed during fetal development. Recently, the metatranscript-only variant (c.39974-11T > G) in TTN with a second truncating TTN variant has been linked to arthrogryposis multiplex congenita and myopathy.

METHODS

Via exome sequencing we identified the TTN c.39974-11T > G splice variant in trans with one of three truncating variants (p.Arg8922*, p.Lys32998Asnfs*63, p.Tyr10345*) in five individuals from three families. Clinical presentation and muscle ultrasound as well as MRI images were analyzed.

RESULTS

All five patients presented with generalized muscular hypotonia, reduced muscle bulk, and congenital contractures most prominently affecting the upper limbs and distal joints. Muscular hypotonia persisted and contractures improved over time. One individual, the recipient twin in the setting of twin-to-twin transfusion syndrome, died from severe cardiac hypertrophy 1 day after birth. Ultrasound and MRI imaging studies revealed a recognizable pattern of muscle involvement with striking fibrofatty involvement of the hamstrings and calves, and relative sparing of the femoral adductors and anterior segment of the thighs.

CONCLUSION

The recurrent TTN c.39974-11T > G variant consistently causes congenital arthrogryposis and persisting myopathy providing evidence that the metatranscript-only 213 to 217 exons impact muscle elasticity during early development and beyond. There is a recognizable pattern of muscle involvement, which is distinct from other myopathies and provides valuable clues for diagnostic work-up.

Utilization of T1-Mapping for the pelvic and thigh muscles in Duchenne Muscular Dystrophy: a quantitative biomarker for disease involvement and correlation with clinical assessments

BACKGROUND

Little is known about the disease distribution and severity detected by T1-mapping in Duchenne muscular dystrophy (DMD). Furthermore, the correlation between skeletal muscle T1-values and clinical assessments is less studied. Hence, the purposes of our study are to investigate quantitative T1-mapping in detecting the degree of disease involvement by detailed analyzing the hip and thigh muscle, future exploring the predicting value of T1-mapping for the clinical status of DMD.

METHODS

Ninety-two DMD patients were included. Grading fat infiltration and measuring the T1-values of 19 pelvic and thigh muscles (right side) in axial T1-weighted images (T1WI) and T1-maps, respectively, the disease distribution and severity were evaluated and compared. Clinical assessments included age, height, weight, BMI, wheelchair use, timed functional tests, NorthStar ambulatory assessment (NSAA) score, serum creatine kinase (CK) level. Correlation analysis were performed between the muscle T1-value and clinical assessments. Multiple linear regression analysis was conducted for the independent association of T1-value and motor function.

RESULTS

The gluteus maximus had the lowest T1-value, and the gracilis had the highest T1-value. T1-value decreased as the grade of fat infiltration increased scored by T1WI (P < 0.001). The decreasing of T1-values was correlated with the increase of age, height, weight, wheelchair use, and timed functional tests (P < 0.05). T1-value correlated with NSAA (r = 0.232-0.721, P < 0.05) and CK (r = 0.208-0.491, P < 0.05) positively. T1-value of gluteus maximus, tensor fascia, vastus lateralis, vastus intermedius, vastus medialis, and adductor magnus was independently associated with the clinical motor function tests (P < 0.05). Interclass correlation coefficient (ICC) analysis and Bland-Altman plots showed excellent inter-rater reliability of T1-value region of interest (ROI) measurements.

CONCLUSION

T1-mapping can be used as a quantitative biomarker for disease involvement, further assessing the disease severity and predicting motor function in DMD.

Multi-parametric quantitative magnetic resonance imaging of the upper arm muscles of patients with spinal muscular atrophy

Quantitative magnetic resonance imaging (qMRI) is frequently used to map the disease state and disease progression in the lower extremity muscles of patients with spinal muscular atrophy (SMA). This is in stark contrast to the almost complete lack of data on the upper extremity muscles, which are essential for carrying out daily activities. The aim of this study was therefore to assess the disease state in the upper arm muscles of patients with SMA in comparison with healthy controls by quantitative assessment of fat fraction, diffusion indices, and water T2 relaxation times, and to relate these measures to muscle force. We evaluated 13 patients with SMA and 15 healthy controls with a 3-T MRI protocol consisting of DIXON, diffusion tensor imaging, and T2 sequences. qMRI measures were compared between groups and related to muscle force measured with quantitative myometry. Fat fraction was significantly increased in all upper arm muscles of the patients with SMA compared with healthy controls and correlated negatively with muscle force. Additionally, fat fraction was heterogeneously distributed within the triceps brachii (TB) and brachialis muscle, but not in the biceps brachii muscle. Diffusion indices and water T2 relaxation times were similar between patients with SMA and healthy controls, but we did find a slightly reduced mean diffusivity (MD), λ1, and λ3 in the TB of patients with SMA. Furthermore, MD was positively correlated with muscle force in the TB of patients with SMA. The variation in fat fraction further substantiates the selective vulnerability of muscles. The reduced diffusion tensor imaging indices, along with the positive correlation of MD with muscle force, point to myofiber atrophy. Our results show the feasibility of qMRI to map the disease state in the upper arm muscles of patients with SMA. Longitudinal data in a larger cohort are needed to further explore qMRI to map disease progression and to capture the possible effects of therapeutic interventions.

Is it really myositis? Mimics and pitfalls

Idiopathic inflammatory myopathies are a heterogeneous set of systemic inflammatory disorders primarily affecting muscle. Signs and symptoms vary greatly between and within subtypes, requiring supportive laboratory and pathologic evidence to confirm the diagnosis. Several studies are typical assessments for patients with suspected inflammatory myopathy, including muscle enzymes, autoimmune markers, imaging, and muscle biopsy. Misdiagnoses of myositis are not only related to the overlap of clinical phenotype with non-inflammatory myopathies, but also due to the limitations of diagnostic tests employed. Since many of the investigative tests are non-specific, they share features with other disorders, including muscular dystrophies, endocrine, toxic, and metabolic myopathies, and other neuromuscular or rheumatologic conditions. Recognizing the limitations of tests and understanding the shared features between inflammatory and non-inflammatory myopathies can help prevent misdiagnosing myositis with one of its several mimics.

Unraveling the Molecular Basis of the Dystrophic Process in Limb-Girdle Muscular Dystrophy LGMD-R12 by Differential Gene Expression Profiles in Diseased and Healthy Muscles

Limb-girdle muscular dystrophy R12 (LGMD-R12) is caused by two mutations in anoctamin-5 (ANO5). Our aim was to identify genes and pathways that underlie LGMD-R12 and explain differences in the molecular predisposition and susceptibility between three thigh muscles that are severely (semimembranosus), moderately (vastus lateralis) or mildly (rectus femoris) affected in this disease. We performed transcriptomics on these three muscles in 16 male LGMD-R12 patients and 15 age-matched male controls. Our results showed that LGMD-R12 dystrophic muscle is associated with the expression of genes indicative of fibroblast and adipocyte replacement, such as fibroadipogenic progenitors and immune cell infiltration, while muscle protein synthesis and metabolism were downregulated. Muscle degeneration was associated with an increase in genes involved in muscle injury and inflammation, and muscle repair/regeneration. Baseline differences between muscles in healthy individuals indicated that muscles that are the most affected by LGMD-R12 have the lowest expression of transcription factor networks involved in muscle (re)generation and satellite stem cell activation. Instead, they show relative high levels of fetal/embryonic myosins, all together indicating that muscles differ in their baseline regenerative potential. To conclude, we profiled the gene expression landscape in LGMD-R12, identified baseline differences in expression levels between differently affected muscles and characterized disease-associated changes.

LGMD D2 TNPO3-Related: From Clinical Spectrum to Pathogenetic Mechanism

Limb-girdle muscular dystrophies (LGMDs) are clinically and genetically heterogeneous diseases presenting with a wide clinical spectrum. Autosomal dominant LGMDs represent about 10–15% of LGMDs and include disorders due to defects of DNAJB6, transportin-3 (TNPO3), HNRNPDL, Calpain-3 (CAPN3), and Bethlem myopathy. This review article aims to describe the clinical spectrum of LGMD D2 TNPO3-related, a rare disease due to heterozygous mutation in the TNPO3 gene. TNPO3 encodes for transportin-3, which belongs to the importin beta family and transports into the nucleus serine/arginine-rich (SR) proteins, such as splicing factors, and HIV-1 proteins, thus contributing to viral infection. The purpose of this review is to present and compare the clinical features and the genetic and histopathological findings described in LGMD D2, performing a comparative analytical description of all the families and sporadic cases identified. Even if the causative gene and mutations of this disease have been identified, the pathogenic mechanisms are still an open issue; therefore, we will present an overview of the hypotheses that explain the pathology of LGMD D2 TNPO3-related.

Bildgebung der Muskulatur bei Neuromuskulären Erkrankungen – von der Initialdiagnostik bis zur Verlaufsbeurteilung

Die bildgebende Diagnostik hat sich zu einem integralen Element der Betreuung von PatientInnen mit neuromuskulären Erkrankungen entwickelt. Als wesentliches Diagnostikum ist hierbei die Magnetresonanztomografie als breit verfügbares und vergleichsweise standardisiertes Untersuchungsverfahren etabliert, wobei die Sonografie der Muskulatur bei hinreichend erfahrenem Untersucher ebenfalls geeignet ist, wertvolle diagnostische Informationen zu liefern. Das CT hingegen spielt eine untergeordnete Rolle und sollte nur bei Kontraindikationen für eine MRT in Erwägung gezogen werden. Zunächst wurde die Bildgebung bei Muskelerkrankungen primär in der Initialdiagnostik unter vielfältigen Fragestellungen eingesetzt. Das Aufkommen innovativer Therapiekonzepte bei verschiedenen neuromuskulären Erkrankungen machen neben einer möglichst frühzeitigen Diagnosestellung insbesondere auch eine multimodale Verlaufsbeurteilung zur Evaluation des Therapieansprechens notwendig. Auch hier wird die Bildgebung der Muskulatur als objektiver Parameter des Therapieerfolges intensiv diskutiert und in Forschung wie Praxis zunehmend verwendet.

Multispectral optoacoustic tomography for non-invasive disease phenotyping in pediatric spinal muscular atrophy patients

Proximal spinal muscular atrophy (SMA) is a rare progressive, life limiting genetic motor neuron disease. While promising causal therapies are available, meaningful prognostic biomarkers for therapeutic monitoring are missing. We demonstrate handheld Multispectral Optoacoustic Tomography (MSOT) as a novel non-invasive imaging approach to visualize and quantify muscle wasting in pediatric SMA. While MSOT signals were distributed homogeneously in muscles of healthy volunteers (HVs), SMA patients showed moth-eaten optoacoustic signal patterns. Further signal quantification revealed greatest differences between groups at the isosbestic point for hemoglobin (SWL 800 nm). The SWL 800 nm signal intensities further correlated with clinical phenotype tested by standard motor outcome measures. Therefore, handheld MSOT could enable non-invasive assessment of disease burden in SMA patients.