European muscle MRI study in limb girdle muscular dystrophy type R1/2A (LGMDR1/LGMD2A)

French National Protocol for diagnosis and care of facioscapulohumeral muscular dystrophy (FSHD)

Facioscapulohumeral muscular dystrophy (FSHD) is one of the most common genetically inherited myopathies in adults. It is characterized by incomplete penetrance and variable expressivity. Typically, FSHD patients display asymmetric weakness of facial, scapular, and humeral muscles that may progress to other muscle groups, particularly the abdominal and lower limb muscles. Early-onset patients display more severe muscle weakness and atrophy, resulting in a higher frequency of associated skeletal abnormalities. In these patients, multisystem involvement, including respiratory, ocular, and auditory, is more frequent and severe and may include the central nervous system. Adult-onset FSHD patients may also display some degree of multisystem involvement which mainly remains subclinical. In 95% of cases, FSHD patients carry a pathogenic contraction of the D4Z4 repeat units (RUs) in the subtelomeric region of chromosome 4 (4q35), which leads to the expression of DUX4 retrogene, toxic for muscles (FSHD1). Five percent of patients display the same clinical phenotype in association with a mutation in the SMCHD1 gene located in chromosome 18, inducing epigenetic modifications of the 4q D4Z4 repeated region and expression of DUX4 retrogene. This review highlights the complexities and challenges of diagnosing and managing FSHD, underscoring the importance of standardized approaches for optimal patient outcomes. It emphasizes the critical role of multidisciplinary care in addressing the diverse manifestations of FSHD across different age groups, from skeletal abnormalities in early-onset cases to the often-subclinical multisystem involvement in adults. With no current cure, the focus on alleviating symptoms and slowing disease progression through coordinated care is paramount.

Effect of sirolimus on muscle in inclusion body myositis observed with magnetic resonance imaging and spectroscopy

BACKGROUND

Finding sensitive clinical outcome measures has become crucial in natural history studies and therapeutic trials of neuromuscular disorders. Here, we focus on 1-year longitudinal data from quantitative magnetic resonance imaging (MRI) and phosphorus magnetic resonance spectroscopy (31P MRS) in a placebo-controlled study of sirolimus for inclusion body myositis (IBM), also examining their links to functional, strength, and clinical parameters in lower limb muscles.

METHODS

Quantitative MRI and 31P MRS data were collected at 3 T from a single site, involving 44 patients (22 on placebo, 22 on sirolimus) at baseline and year-1, and 21 healthy controls. Assessments included fat fraction (FF), contractile cross-sectional area (cCSA), and water T2 in global leg and thigh segments, muscle groups, individual muscles, as well as 31P MRS indices in quadriceps or triceps surae. Analyses covered patient-control comparisons, annual change assessments via standard t-tests and linear mixed models, calculation of standardized response means (SRM), and exploration of correlations between MRI, 31P MRS, functional, strength, and clinical parameters.

RESULTS

The quadriceps and gastrocnemius medialis muscles had the highest FF values, displaying notable heterogeneity and asymmetry, particularly in the quadriceps. In the placebo group, the median 1-year FF increase in the quadriceps was 3.2% (P < 0.001), whereas in the sirolimus group, it was 0.7% (P = 0.033). Both groups experienced a significant decrease in cCSA in the quadriceps after 1 year (P < 0.001), with median changes of 12.6% for the placebo group and 5.5% for the sirolimus group. Differences in FF and cCSA changes between the two groups were significant (P < 0.001). SRM values for FF and cCSA were 1.3 and 1.4 in the placebo group and 0.5 and 0.8 in the sirolimus group, respectively. Water T2 values were highest in the quadriceps muscles of both groups, significantly exceeding control values in both groups (P < 0.001) and were higher in the placebo group than in the sirolimus group. After treatment, water T2 increased significantly only in the sirolimus group's quadriceps (P < 0.01). Multiple 31P MRS indices were abnormal in patients compared to controls and remained unchanged after treatment. Significant correlations were identified between baseline water T2 and FF at baseline and the change in FF (P < 0.001). Additionally, significant correlations were observed between FF, cCSA, water T2, and functional and strength outcome measures.

CONCLUSIONS

This study has demonstrated that quantitative MRI/31P MRS can discern measurable differences between placebo and sirolimus-treated IBM patients, offering promise for future therapeutic trials in idiopathic inflammatory myopathies such as IBM.

Evaluation of Neuromuscular Diseases and Complaints by Quantitative Muscle MRI

Background: Quantitative muscle MRI (qMRI) is a promising tool for evaluating and monitoring neuromuscular disorders (NMD). However, the application of different imaging protocols and processing pipelines restricts comparison between patient cohorts and disorders. In this qMRI study, we aim to compare dystrophic (limb-girdle muscular dystrophy), inflammatory (inclusion body myositis), and metabolic myopathy (Pompe disease) as well as patients with post-COVID-19 conditions suffering from myalgia to healthy controls. Methods: Ten subjects of each group underwent a 3T lower extremity muscle MRI, including a multi-echo, gradient-echo, Dixon-based sequence, a multi-echo, spin-echo (MESE) T2 mapping sequence, and a spin-echo EPI diffusion-weighted sequence. Furthermore, the following clinical assessments were performed: Quick Motor Function Measure, patient questionnaires for daily life activities, and 6-min walking distance. Results: Different involvement patterns of conspicuous qMRI parameters for different NMDs were observed. qMRI metrics correlated significantly with clinical assessments. Conclusions: qMRI metrics are suitable for evaluating patients with NMD since they show differences in muscular involvement in different NMDs and correlate with clinical assessments. Still, standardisation of acquisition and processing is needed for broad clinical use.

Analysis of muscle magnetic resonance imaging of a large cohort of patient with VCP-mediated disease reveals characteristic features useful for diagnosis

BACKGROUND

The diagnosis of patients with mutations in the VCP gene can be complicated due to their broad phenotypic spectrum including myopathy, motor neuron disease and peripheral neuropathy. Muscle MRI guides the diagnosis in neuromuscular diseases (NMDs); however, comprehensive muscle MRI features for VCP patients have not been reported so far.

METHODS

We collected muscle MRIs of 80 of the 255 patients who participated in the "VCP International Study" and reviewed the T1-weighted (T1w) and short tau inversion recovery (STIR) sequences. We identified a series of potential diagnostic MRI based characteristics useful for the diagnosis of VCP disease and validated them in 1089 MRIs from patients with other genetically confirmed NMDs.

RESULTS

Fat replacement of at least one muscle was identified in all symptomatic patients. The most common finding was the existence of patchy areas of fat replacement. Although there was a wide variability of muscles affected, we observed a common pattern characterized by the involvement of periscapular, paraspinal, gluteal and quadriceps muscles. STIR signal was enhanced in 67% of the patients, either in the muscle itself or in the surrounding fascia. We identified 10 diagnostic characteristics based on the pattern identified that allowed us to distinguish VCP disease from other neuromuscular diseases with high accuracy.

CONCLUSIONS

Patients with mutations in the VCP gene had common features on muscle MRI that are helpful for diagnosis purposes, including the presence of patchy fat replacement and a prominent involvement of the periscapular, paraspinal, abdominal and thigh muscles.

Altered expression of proteins involved in metabolism in LGMDR1 muscle is lost in cell culture conditions

BACKGROUND

Limb-girdle muscular dystrophy R1 calpain 3-related (LGMDR1) is an autosomal recessive muscular dystrophy due to mutations in the CAPN3 gene. While the pathophysiology of this disease has not been clearly established yet, Wnt and mTOR signaling pathways impairment in LGMDR1 muscles has been reported.

RESULTS

A reduction in Akt phosphorylation ratio and upregulated expression of proteins implicated in glycolysis (HK-II) and in fructose and lactate transport (GLUT5 and MCT1) in LGMDR1 muscle was observed. In vitro analysis to establish mitochondrial and glycolytic functions of primary cultures were performed, however, no differences between control and patients were observed. Additionally, gene expression analysis showed a lack of correlation between primary myoblasts/myotubes and LGMDR1 muscle while skin fibroblasts and CD56- cells showed a slightly better correlation with muscle. FRZB gene was upregulated in all the analyzed cell types (except in myoblasts).

CONCLUSIONS

Proteins implicated in metabolism are deregulated in LGMDR1 patients' muscle. Obtained results evidence the limited usefulness of primary myoblasts/myotubes for LGMDR1 gene expression and metabolic studies. However, since FRZB is the only gene that showed upregulation in all the analyzed cell types it is suggested its role as a key regulator of the pathophysiology of the LGMDR1 muscle fiber. The Wnt signaling pathway inactivation, secondary to FRZB upregulation, and GLUT5 overexpression may participate in the impaired adipogenesis in LGMD1R patients.

Muscle MRI patterns for limb girdle muscle dystrophies: systematic review

Limb girdle muscle dystrophies (LGMDs) are a group of inherited neuromuscular disorders comprising more than 20 genes. There have been increasing efforts to characterize this group with Muscle MRI. However, due to the complexity and similarities, the interpretation of the MRI patterns is usually done by experts in the field. Here, we proposed a step-by-step image interpretation of Muscle MRI in LGDM by evaluating the variability of muscle pattern involvement reported in the literature. A systematic review with an open start date to November 2022 was conducted to describe all LGMDs' muscle MRI patterns. Eighty-eight studies were included in the final review. Data were found to describe muscle MRI patterns for 15 out of 17 LGMDs types. Although the diagnosis of LGMDs is challenging despite the advanced genetic testing and other diagnostic modalities, muscle MRI is shown to help in the diagnosis of LGMDs. To further increase the yield for muscle MRI in the neuromuscular field, larger cohorts of patients need to be conducted.

Long-term clinical and MRI follow-up in two POMT2-related limb girdle muscular dystrophy (LGMDR14) patients

INTRODUCTION

POMT2-related limb girdle muscular dystrophy (LGMDR14) is a rare muscular dystrophy caused by mutations in the POMT2 gene. Thus far only 26 LGMDR14 subjects have been reported and no longitudinal natural history data are available.

CASE REPORT

We describe two LGMDR14 patients followed for 20 years since infancy. Both patients presented a childhood-onset, slowly progressive pelvic girdle muscular weakness leading to loss of ambulation in the second decade in one patient, and cognitive impairment without detectable brain structural abnormalities. Glutei, paraspinal, and adductor muscles were the primarily involved muscles at MRI.

DISCUSSION

This report provides natural history data on LGMDR14 subjects, with a focus on longitudinal muscle MRI. We also reviewed the LGMDR14 literature data, providing information on the LGMDR14 disease progression. Considering the high prevalence of cognitive impairment in LGMDR14 patients, a reliable application of functional outcome measures can be challenging, therefore a muscle MRI follow-up to assess disease evolution is recommended.

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.

Contribution of muscle MRI for diagnosis of myopathy

Inherited myopathies are a group of disease, which, although distinct from a genetic and prognostic point of view, can lead to non-specific clinical pictures due to phenotypic overlap. Acquired immuno-mediated myopathies may also pose the problem of clinically accurate etiological orientation. The assessment of fatty infiltration and pathological increase in water volume of the muscle contingent on whole-body muscle MRI is becoming increasingly important in aiding the initial diagnosis of inherited and acquired myopathies. MRI helps orientating the clinical diagnostic hypotheses thanks to the patterns of muscle involved (more or less specific according to the entities), which led to the development of decision-making algorithms proposed in the literature. The aim of this article is to specify the proper MRI protocol for the evaluation of myopathies and the basis of the interpretation and to provide a summary of the most frequently inherited and acquired myopathies described in the literature.

The Limb-Girdle Muscular Dystrophies

PURPOSE OF REVIEW

The limb-girdle muscular dystrophies (LGMDs) are a group of inherited muscle disorders with a common feature of limb-girdle pattern of weakness, caused by over 29 individual genes. This article describes the classification scheme, common subtypes, and the management of individuals with LGMD.

RECENT FINDINGS

Advances in genetic testing and next-generation sequencing panels containing all of the LGMD genes have led to earlier genetic confirmation, but also to more individuals with variants of uncertain significance. The LGMDs include disorders with autosomal recessive inheritance, which are often due to loss-of-function mutations in muscle structural or repair proteins and typically have younger ages of onset and more rapidly progressive presentations, and those with autosomal dominant inheritance, which can have older ages of presentation and chronic progressive disease courses. All cause progressive disability and potential loss of ability to walk or maintain a job due to progressive muscle wasting. Certain mutations are associated with cardiac or respiratory involvement. No disease-altering therapies have been approved by the US Food and Drug Administration (FDA) for LGMDs and standard treatment uses a multidisciplinary clinic model, but recessive LGMDs are potentially amenable to systemic gene replacement therapies, which are already being tested in clinical trials for sarcoglycan and FKRP mutations. The dominant LGMDs may be amenable to RNA-based therapeutic approaches.

SUMMARY

International efforts are underway to better characterize LGMDs, help resolve variants of uncertain significance, provide consistent and improved standards of care, and prepare for future clinical trials.

Quantitative muscle MRI captures early muscle degeneration in calpainopathy

To evaluate differences in qMRI parameters of muscle diffusion tensor imaging (mDTI), fat-fraction (FF) and water T2 time in leg muscles of calpainopathy patients (LGMD R1/D4) compared to healthy controls, to correlate those findings to clinical parameters and to evaluate if qMRI parameters show muscle degeneration in not-yet fatty infiltrated muscles. We evaluated eight thigh and seven calf muscles of 19 calpainopathy patients and 19 healthy matched controls. MRI scans were performed on a 3T MRI including a mDTI, T2 mapping and mDixonquant sequence. Clinical assessment was done with manual muscle testing, patient questionnaires (ACTIVLIM, NSS) as well as gait analysis. Average FF was significantly different in all muscles compared to controls (p < 0.001). In muscles with less than 8% FF a significant increase of FA (p < 0.005) and decrease of RD (p < 0.004) was found in high-risk muscles of calpainopathy patients. Water T2 times were increased within the low- and intermediate-risk muscles (p ≤ 0.045) but not in high-risk muscles (p = 0.062). Clinical assessments correlated significantly with qMRI values: QMFM vs. FF: r = - 0.881, p < 0.001; QMFM versus FA: r = - 0.747, p < 0.001; QMFM versus MD: r = 0.942, p < 0.001. A good correlation of FF and diffusion metrics to clinical assessments was found. Diffusion metrics and T2 values are promising candidates to serve as sensitive early and non-invasive methods to capture early muscle degeneration in non-fat-infiltrated muscles in calpainopathies.

The Clinicopathological Distinction between Immune-Mediated Necrotizing Myopathy and Limb-Girdle Muscular Dystrophy R2: Key Points to Prevent Misdiagnosis

Background: Limb−girdle muscular dystrophy R2 (LGMD R2) is most frequently misdiagnosed as immune-mediated necrotizing myopathy (IMNM). This study aimed to compare the clinicopathological data of IMNM and LGMD R2 to find distinguishing features. Methods: We retrospectively reassessed the medical data of patients with IMNM (n = 41) and LGMD R2 (n = 8) treated at Tongji Hospital from January 2017 to December 2021. Results: In our cohort, patients with LGMD R2 had a longer interval of onset to first visit, mild muscle weakness with late upper limb involvement, less myalgia, no cervical muscle weakness or dysphagia, no extramuscular organs affected except cardiac involvement, and lack of various autoantibodies, such as antinuclear antibodies. These features were completely reversed in IMNM. Moreover, thigh MRIs showed that muscle edema prominently affecting the adductor magnus was a characteristic of IMNM, while extensive fatty replacement was more common in LGMD R2 (p = 0.0086). Necrotic myofibers presented in both entities (p = 0.1693), while features such as ring/whorled and splitting myofibers were more often found in LGMD R2 (p = 0.0112 and p < 0.0001, respectively). Conversely, sarcoplasmic p62 expression was more pronounced in IMNM (p < 0.05). There were 4 of 8 (50%) patients with LGMD R2 initially considered as seronegative IMNM, and therefore unnecessarily treated with immunosuppressive drugs. Insufficient recognition of the early clinical, imaging, and histopathological features of LGMD R2 is the main reason for misdiagnosis. Conclusions: These findings may help clinicians differentiate seronegative IMNM and LGMD R2, reducing early misdiagnosis and mismanagement. Particularly, prominent adductor magnus edema on MRI and abundant p62 staining seem to be good markers for IMNM, while the presence of splitting myofibers is a crucial clue to early hereditary myopathy, including LGMD R2.

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.

Three-year quantitative magnetic resonance imaging and phosphorus magnetic resonance spectroscopy study in lower limb muscle in dysferlinopathy

BACKGROUND

Natural history studies in neuromuscular disorders are vital to understand the disease evolution and to find sensitive outcome measures. We performed a longitudinal assessment of quantitative magnetic resonance imaging (MRI) and phosphorus magnetic resonance spectroscopy (³¹ P MRS) outcome measures and evaluated their relationship with function in lower limb skeletal muscle of dysferlinopathy patients.

METHODS

Quantitative MRI/³¹ P MRS data were obtained at 3 T in two different sites in 54 patients and 12 controls, at baseline, and three annual follow-up visits. Fat fraction (FF), contractile cross-sectional area (cCSA), and muscle water T₂ in both global leg and thigh segments and individual muscles and ³¹ P MRS indices in the anterior leg compartment were assessed. Analysis included comparisons between patients and controls, assessments of annual changes using a linear mixed model, standardized response means (SRM), and correlations between MRI and ³¹ P MRS markers and functional markers.

RESULTS

Posterior muscles in thigh and leg showed the highest FF values. FF at baseline was highly heterogeneous across patients. In ambulant patients, median annual increases in global thigh and leg segment FF values were 4.1% and 3.0%, respectively (P < 0.001). After 3 years, global thigh and leg FF increases were 9.6% and 8.4%, respectively (P < 0.001). SRM values for global thigh FF were over 0.8 for all years. Vastus lateralis muscle showed the highest SRM values across all time points. cCSA decreased significantly after 3 years with median values of 11.0% and 12.8% in global thigh and global leg, respectively (P < 0.001). Water T₂ values in ambulant patients were significantly increased, as compared with control values (P < 0.001). The highest water T₂ values were found in the anterior part of thigh and leg. Almost all ³¹ P MRS indices were significantly different in patients as compared with controls (P < 0.006), except for pH_w , and remained, similar as to water T₂ , abnormal for the whole study duration. Global thigh water T₂ at baseline was significantly correlated to the change in FF after 3 years (ρ = 0.52, P < 0.001). There was also a significant relationship between the change in functional score and change in FF after 3 years in ambulant patients (ρ = -0.55, P = 0.010).

CONCLUSIONS

This multi-centre study has shown that quantitative MRI/³¹ P MRS measurements in a heterogeneous group of dysferlinopathy patients can measure significant changes over the course of 3 years. These data can be used as reference values in view of future clinical trials in dysferlinopathy or comparisons with quantitative MRI/S data obtained in other limb-girdle muscular dystrophy subtypes.

Magnetic resonance imaging pattern variability in dysferlinopathy

The widespread use of magnetic resonance imaging (MRI) in the diagnosis of myopathies has made it possible to clarify the typical MRI pattern of dysferlinopathy. However, sufficient attention has not been given to the variability of MRI patterns in dysferlinopathy.

MATERIALS AND METHODS

Twenty-five patients with the clinical manifestations of dysferlinopathy were examined. For all patients, creatine phosphokinase levels were measured and molecular genetics were examined. In two patients, immunohistochemical examinations of muscle biopsies were performed. MRI scanning was included T2 multi-slice multi-echo, T1 weighted, T2 weighted and Short Tau Inversion Recovery T2 weighted sequences. Quantitative and semi-quantitative evaluations of fatty replacement and swelling of the muscles were undertaken.

RESULTS

Variability in the MRI patterns was lowest in the pelvis and leg muscles and highest in the thigh muscles. Three main types of MRI patterns were distinguished: posterior-dominant (80%), anterior-dominant (16%), and diffuse (4%). Among patients with the anterior-dominant pattern, the collagen-like variant (4%), proximal variant (4%) and pseudo-myositis (8%) were separately distinguished.

CONCLUSIONS

Awareness of atypical MRI patterns in dysferlinopathy is important for increasing the efficiency of routine diagnostics and optimizing the search for causative gene mutations.

A Muscle Biosignature Differentiating Between Limb-Girdle Muscular Dystrophy and Idiopathic Inflammatory Myopathy on Magnetic Resonance Imaging

Background: The overlapping clinical presentations of limb-girdle muscular dystrophy (LGMD) and idiopathic inflammatory myopathy (IIM) make clinical diagnosis challenging. This study provides a comprehensive evaluation of the distributions and characteristics of muscle fat substitution and edema and aims to differentiate those two diseases.

Methods: This retrospective study reviewed magnetic resonance imaging (MRI) of seventeen patients with pathologically proved diagnosis, comprising 11 with LGMD and 6 with IIM. The fat-only and water-only images from a Dixon sequence were used to evaluate muscle fat substitution and edema, respectively. The degrees of muscle fat substitution and edema were graded and compared using the appropriate statistical methods.

Results: In LGMD, more than 50% of patients had high-grade fat substitution in the majority of muscle groups in the thigh and calf. However, <50% of IIM patients had high-grade fat substitution in all muscle groups. Moreover, LGMD patients had significantly higher grade fat substitution than IIM patients in all large muscle groups (p < 0.05). However, there was no significant difference in edema in the majority of muscle groups, except the adductor magnus (p = 0.012) and soleus (p = 0.009) with higher grade edema in IIM. Additionally, all the adductor magnus muscles in LGMD (100%) showed high-grade fat substitution, but none of them showed high-grade edema.

Conclusions: MRI could be a valuable tool to differentiate LGMD from IIM based on the discrepancy in muscle fat substitution, and the adductor magnus muscle could provide a biosignature to categorizing LGMD.

Muscle MRI as a Useful Biomarker in Hereditary Transthyretin Amyloidosis: A Pilot Study

Hereditary transthyretin amyloidosis (ATTRv, v for variant) is a severe and heterogeneous multisystem condition with a prevalent peripheral nervous system impairment, due to mutations in the transthyretin gene. Considering the introduction of different disease-modifying therapies in the last few years, a need of reliable biomarkers is emerging. In this study, we evaluated muscle MRI in a cohort of ATTRv patients in order to establish if the severity of muscle involvement correlated with disease severity. Linear regression analysis showed a significant positive correlation between the total fatty infiltration score and NIS, NIS-LL, and Norfolk, and an inverse correlation with Sudoscan registered from feet. In conclusion, we demonstrated the role of muscle MRI in ATTRv as possible disease biomarker, both for diagnostic purposes and for assessing the severity of the disease.

Muscle MRI in Myotonic Dystrophy type 1 (DM1): refining muscle involvement and implications for clinical trials

BACKGROUND

Only few studies reported muscle imaging data on small cohorts of patients with Myotonic dystrophy type 1 (DM1). We aimed to investigate the muscle involvement in a large cohort of patients, to refine the pattern of muscle involvement, to better understand the pathophysiological mechanisms of muscle weakness and to identify potential imaging biomarkers for disease activity and severity.

METHODS

134 DM1 patients underwent a cross-sectional muscle MRI study. STIR and T1- sequences in lower and upper body were analysed. Fat replacement, muscle atrophy and STIR positivity were evaluated using three different scales. Correlations between MRI scores, clinical features and genetic background were investigated.

RESULTS

The most frequent pattern of muscle involvement in T1 consisted of fat replacement of the tongue, sternocleidomastoideus, paraspinalis, gluteus minimus, distal quadriceps and gastrocnemius medialis. Degree of fat replacement at MRI correlated with clinical severity and disease duration, but not with CTG expansion. Fat replacement was also detected in milder/asymptomatic patients. More than 80% of patients had STIR positive signal in muscles. Most DM1 patients also showed a variable degree of muscle atrophy regardless MRI signs of fat replacement. A subset of patients (20%) showed a "marbled" muscle appearance.

CONCLUSIONS

muscle MRI is a sensitive biomarker of disease severity also for the milder spectrum of disease. STIR hyperintensty seems to precede fat replacement in T1. Beyond fat replacement, STIR positivity, muscle atrophy and "marbled" appearance suggest further mechanisms of muscle wasting and weakness in DM1, representing additional outcome measures and therapeutical targets for forthcoming clinical trials.

Two decades of advances in muscle imaging in children: from pattern recognition of muscle diseases to quantification and machine learning approaches

Muscle imaging has progressively gained popularity in the neuromuscular field. Together with detailed clinical examination and muscle biopsy, it has become one of the main tools for deep phenotyping and orientation of etiological diagnosis. Even in the current era of powerful new generation sequencing, muscle MRI has arisen as a tool for prioritization of certain genetic entities, supporting the pathogenicity of variants of unknown significance and facilitating diagnosis in cases with an initially inconclusive genetic study. Although the utility of muscle imaging is increasingly clear, it has not reached its full potential in clinical practice. Pattern recognition is known for a number of diseases and will certainly be enhanced by the use of machine learning approaches. For instance, MRI heatmap representations might be confronted with molecular results by obtaining a probabilistic diagnosis based in each disease "MRI fingerprints". Muscle ultrasound as a screening tool and quantified techniques such as Dixon MRI seem still underdeveloped. In this paper, we aim to appraise the advances in recent years in pediatric muscle imaging and try to define areas of uncertainty and potential advances that might become standardized to be widely used in the future.

Muscle magnetic resonance imaging in patients with LAMA2-related muscular dystrophy

LAMA2-related muscular dystrophy (LAMA2-MD) is classified into congenital muscular dystrophy type 1A (MDC1A) and autosomal recessive limb-girdle muscular dystrophy-23 (LGMDR23). The purpose of this study was to identify the involvement pattern of thigh muscles of LAMA2-MD patients on magnetic resonance imaging. Fourteen MDC1A and 3 LGMDR23 patients were included, with 21 known and 8 novel LAMA2 disease-causing variants. In LAMA2-MD, the gluteus maximus, anterior (quadriceps femoris) and posterior (adductor magnus and biceps femoris) thigh muscles were extensively and severely affected with fatty infiltration, with relatively sparing of the adductor longus. The pattern of muscle involvement was similar between MDC1A and LGMDR23, but more severe in MDC1A, as well as in LAMA2-MD patients without ambulation. The rather peculiar pattern of the adductor magnus and long head of the biceps femoris first and severely affected in the mid-thigh level was found in LGMDR23. Strong correlation between fatty infiltration and age as well as disease duration was observed for the adductor longus in MDC1A. Edema and atrophy selectively involved in some muscles. The pattern of fatty infiltration on thigh muscle MRI of LAMA2-MD could provide important information for the diagnosis, differential diagnosis and assessment of clinical severity.

Diagnostic interest of whole-body MRI in early- and late-onset LAMA2 muscular dystrophies: a large international cohort

BACKGROUND

LAMA2-related muscular dystrophy (LAMA2-RD) encompasses a group of recessive muscular dystrophies caused by mutations in the LAMA2 gene, which codes for the alpha-2 chain of laminin-211 (merosin). Diagnosis is straightforward in the classic congenital presentation with no ambulation and complete merosin deficiency in muscle biopsy, but is far more difficult in milder ambulant individuals with partial merosin deficiency.

OBJECTIVE

To investigate the diagnostic utility of muscle imaging in LAMA2-RD using whole-body magnetic resonance imaging (WBMRI).

RESULTS

27 patients (2-62 years, 21-80% with acquisition of walking ability and 6 never ambulant) were included in an international collaborative study. All carried two pathogenic mutations, mostly private missense changes. An intronic variant (c.909 + 7A > G) was identified in all the Chilean cases. Three patients (two ambulant) showed intellectual disability, epilepsy, and brain structural abnormalities. WBMRI T1w sequences or T2 fat-saturated images (Dixon) revealed abnormal muscle fat replacement predominantly in subscapularis, lumbar paraspinals, gluteus minimus and medius, posterior thigh (adductor magnus, biceps femoris, hamstrings) and soleus. This involvement pattern was consistent for both ambulant and non-ambulant patients. The degree of replacement was predominantly correlated to the disease duration, rather than to the onset or the clinical severity. A "COL6-like sandwich sign" was observed in several muscles in ambulant adults, but different involvement of subscapularis, gluteus minimus, and medius changes allowed distinguishing LAMA2-RD from collagenopathies. The thigh muscles seem to be the best ones to assess disease progression.

CONCLUSION

WBMRI in LAMA2-RD shows a homogeneous pattern of brain and muscle imaging, representing a supportive diagnostic tool.

Whole-body muscle MRI characteristics of LAMA2-related congenital muscular dystrophy children: An emerging pattern

Merosin-deficient or LAMA2-related congenital muscular dystrophy (CMD) belongs to a group of muscle diseases with an overlapping diagnostic spectrum. MRI plays an important role in the diagnosis and disease-tracking of muscle diseases. Whole-body MRI is ideal for describing patterns of muscle involvement. We intended to analyze the pattern of muscle involvement in merosin-deficient CMD children employing whole-body muscle MRI. Ten children with merosin-deficient CMD underwent whole-body muscle MRI. Eight of which were genetically-confirmed. We used a control group of other hereditary muscle diseases, which included 13 children (mean age was 13 SD +/- 5.5 years), (8 boys and 5 girls) for comparative analysis. Overall, 37 muscles were graded for fatty infiltration using Mercuri scale modified by Fischer et al. The results showed a fairly consistent pattern of muscle fatty infiltration in index group, which differs from that in control group. There was a statistically significant difference between the two groups in regard to the fatty infiltration of the neck, serratus anterior, intercostal, rotator cuff, deltoid, triceps, forearm, gluteus maximus, gluteus medius, gastrocnemius and soleus muscles. Additionally, the results showed relative sparing of the brachialis, biceps brachii, gracilis, sartorius, semitendinosus and extensor muscles of the ankle in index group, and specific texture abnormalities in other muscles. There is evidence to suggest that whole-body muscle MRI can become a useful contributor to the differential diagnosis of children with merosin deficient CMD. The presence of a fairly characteristic pattern of involvement was demonstrated. MRI findings should be interpreted in view of the clinical and molecular context to improve diagnostic accuracy.

Muscle involvement assessed by quantitative magnetic resonance imaging in patients with anoctamin 5 deficiency

OBJECTIVE

Using magnetic resonance imaging (MRI) and stationary dynamometry, the aim was to investigate the muscle affection in paraspinal muscles and lower extremities and compare the muscle affection in men and women with anoctamin 5 (ANO5) deficiency.

METHODS

Seventeen patients (seven women) with pathogenic ANO5-mutations were included. Quantitative muscle fat fraction of back and leg muscles were assessed by Dixon MRI. Muscle strength was assessed by stationary dynamometer. Results were compared with 11 matched, healthy controls.

RESULTS

Muscle involvement pattern in men with ANO5-deficiency is characterized by a severe fat replacement of hamstrings, adductor and gastrocnemius muscles, while paraspinal muscles are only mildly affected, while preserved gracilis and sartorius muscles were hypertrophied. Women with ANO5-myopathy, of the same age as male patients, were very mildly affected, showing muscle affection and strength resembling that found in healthy persons, with the exception of the gluteus minimus and medius and gastrocnemii muscles that were significantly replaced by fat. Although individual muscles showed clear asymmetric involvement in a few muscle groups, the overall muscle involvement was symmetric.

CONCLUSIONS

Patients with ANO5-deficiency have relatively preserved paraspinal muscles on imaging and only mild reduction of trunk extension strength in men only. Our study quantifies the large difference in muscle affection in lower extremity between women and men with ANO5-deficiency. The clinical notion is that affection may be very asymmetric in ANO5-deficiency, but the present study shows that while this may be true for a few muscles, the general impression is that muscle affection is very symmetric.

Regional variation of thigh muscle fat infiltration in patients with neuromuscular diseases compared to healthy controls

Background

Chemical shift encoding-based water-fat magnetic resonance imaging (CSE-MRI) measures a quantitative biomarker: the proton density fat fraction (PDFF). The aim was to assess regional and proximo-distal PDFF variations at the thigh in patients with myotonic dystrophy type 2 (DM2), limb-girdle muscular dystrophy type 2A (LGMD2A), and late-onset Pompe disease (LOPD) as compared to healthy controls.

Methods

Seven patients (n=2 DM2, n=2 LGMD2A, n=3 LOPD) and 20 controls were recruited. A 3D-spoiled gradient echo sequence was used to scan the thigh musculature. Muscles were manually segmented to generate mean muscle PDFF.

Results

In all three disease entities, there was an increase in muscle fat replacement compared to healthy controls. However, within each disease group, there were patients with a shorter time since symptom onset that only showed mild PDFF elevation (range, 10% to 20%) compared to controls (P≤0.05), whereas patients with a longer period since symptom onset showed a more severe grade of fat replacement with a range of 50% to 70% (P<0.01). Increased PDFF of around 5% was observed for vastus medialis, semimembranosus and gracilis muscles in advanced compared to early DM2. LGMD2A_1 showed an early disease stage with predominantly mild PDFF elevations over all muscles and levels (10.9%±7.1%) compared to controls. The quadriceps, gracilis and biceps femoris muscles showed the highest difference between LGMD2A_1 with 5 years since symptom onset (average PDFF 11.1%±6.9%) compared to LGMD2A_2 with 32 years since symptom onset (average PDFF 66.3%±6.3%). For LOPD patients, overall PDFF elevations were observed in all major hip flexors and extensors (range, 25.8% to 30.8%) compared to controls (range, 1.7% to 2.3%, P<0.05). Proximal-to-distal PDFF highly varied within and between diseases and within controls. The intra-reader reliability was high (reproducibility coefficient ≤2.19%).

Conclusions

By quantitatively measuring muscle fat infiltration at the thigh, we identified candidate muscles for disease monitoring due to their gradual PDFF elevation with longer disease duration. Regional variation between proximal, central, and distal muscle PDFF was high and is important to consider when performing longitudinal MRI follow-ups in the clinical setting or in longitudinal studies.

A form of muscular dystrophy associated with pathogenic variants in JAG2

JAG2 encodes the Notch ligand Jagged2. The conserved Notch signaling pathway contributes to the development and homeostasis of multiple tissues, including skeletal muscle. We studied an international cohort of 23 individuals with genetically unsolved muscular dystrophy from 13 unrelated families. Whole-exome sequencing identified rare homozygous or compound heterozygous JAG2 variants in all 13 families. The identified bi-allelic variants include 10 missense variants that disrupt highly conserved amino acids, a nonsense variant, two frameshift variants, an in-frame deletion, and a microdeletion encompassing JAG2. Onset of muscle weakness occurred from infancy to young adulthood. Serum creatine kinase (CK) levels were normal or mildly elevated. Muscle histology was primarily dystrophic. MRI of the lower extremities revealed a distinct, slightly asymmetric pattern of muscle involvement with cores of preserved and affected muscles in quadriceps and tibialis anterior, in some cases resembling patterns seen in POGLUT1-associated muscular dystrophy. Transcriptome analysis of muscle tissue from two participants suggested misregulation of genes involved in myogenesis, including PAX7. In complementary studies, Jag2 downregulation in murine myoblasts led to downregulation of multiple components of the Notch pathway, including Megf10. Investigations in Drosophila suggested an interaction between Serrate and Drpr, the fly orthologs of JAG1/JAG2 and MEGF10, respectively. In silico analysis predicted that many Jagged2 missense variants are associated with structural changes and protein misfolding. In summary, we describe a muscular dystrophy associated with pathogenic variants in JAG2 and evidence suggests a disease mechanism related to Notch pathway dysfunction.

MR imaging of inherited myopathies: a review and proposal of imaging algorithms

PURPOSE OF REVIEW

The aims of this review are to discuss the imaging modalities used to assess muscle changes in myopathies, to provide an overview of the inherited myopathies focusing on their patterns of muscle involvement in magnetic resonance imaging (MR), and to propose up-to-date imaging-based diagnostic algorithms that can help in the diagnostic workup.

CONCLUSION

Familiarization with the most common and specific patterns of muscular involvement in inherited myopathies is very important for radiologists and neurologists, as imaging plays a significant role in diagnosis and follow-up of these patients.

KEY POINTS

• Imaging is an increasingly important tool for diagnosis and follow-up in the setting of inherited myopathies. • Knowledge of the most common imaging patterns of muscle involvement in inherited myopathies is valuable for both radiologists and neurologists. • In this review, we present imaging-based algorithms that can help in the diagnostic workup of myopathies.

Over three decades of natural history of limb girdle muscular dystrophy type R1/2A and R2/2B: Mathematical modelling of a multifactorial study

We aimed to describe the natural history of Limb Girdle Muscular Dystrophy type 2A and 2B over more than three decades by considering muscular strength, motor, cardiac and respiratory function. 428 visits of nineteen 2A and twenty 2B patients were retrospectively analysed through a regression model to create the curves of evolution with disease duration of muscle strength (through Medical Research Council grading), motor function measure scale (D1, D2 and D3 domains) and cardio-pulmonary function tests. Clinically relevant muscular and motor function alterations occurred after the first decade of disease, while mild respiratory function alterations started after the second, with preserved cardiac function. Although type 2A showed relatively stronger distal lower limb muscles, while type 2B started with relatively stronger upper limb muscles, the corresponding motor functions were similar, becoming severely compromised after 25 years of disease. This was the longest retrospective study in types 2A and 2B. It defined curves of disease evolution not only from a neuromuscular, but also from functional, cardiac, and respiratory points of view, to be used to evaluate how the natural progression is changed by therapies. Due to slow disease progression, it was not possible to identify time sensitive endpoints.

Is Gene-Size an Issue for the Diagnosis of Skeletal Muscle Disorders?

Human genes have a variable length. Those having a coding sequence of extraordinary length and a high number of exons were almost impossible to sequence using the traditional Sanger-based gene-by-gene approach. High-throughput sequencing has partly overcome the size-related technical issues, enabling a straightforward, rapid and relatively inexpensive analysis of large genes.

Several large genes (e.g. TTN, NEB, RYR1, DMD) are recognized as disease-causing in patients with skeletal muscle diseases. However, because of their sheer size, the clinical interpretation of variants in these genes is probably the most challenging aspect of the high-throughput genetic investigation in the field of skeletal muscle diseases.

The main aim of this review is to discuss the technical and interpretative issues related to the diagnostic investigation of large genes and to reflect upon the current state of the art and the future advancements in the field.

[Calpainopathies: state of the art and therapeutic perspectives]

Calpainopathies are inherited limb-girdle muscular dystrophies, most often following an autosomal recessive (AR) transmission. Autosomal dominant (AD) forms with less severe presentation are increasingly reported. Calpainopathies with autosomal recessive (AR) mutations of the calpain3 gene (CAPN3) are associated with limb girdle muscular dystrophy type R1 (LGMD-R1, OMIM 253600) also referred to as LGMD-2A according to the old nomenclature. LGMD-R1 is the commonest form of all LGMDs, with an estimated prevalence of 10 to 70 cases per million inhabitants, that is a cohort of between 670 and 4,200 patients in France theoritically. Patients present a symmetrical proximal axial myopathy manifesting itself between the first and second decade. The clinical course is variable. The level of Creatine- Kinase (CK) is usually high and there is no cardiac involvement. From a therapeutic perspective, the autosomal recessive form of calpainopathy is quite suitable to gene replacement strategies; the viability of recombinant AAV-mediated calpain 3 transfer has been demonstrated in animal models and clinical trials are expected in the coming years. Meanwhile, natural history studies are needed to prepare for future clinical trials.

Asymmetric muscle weakness due to ACTA1 mosaic mutations

Objective

To characterize 2 unrelated patients with either asymmetric or unilateral muscle weakness at the clinical, genetic, histologic, and ultrastructural level.

Methods

The patients underwent thorough clinical examination, whole-body MRI, and exome sequencing. Muscle morphology was assessed by histology and electron microscopy.

Results

Both patients presented with early-onset hypotonia, delayed motor milestones, scoliosis, and reduced pulmonary function. Patient P1 manifested unilateral muscle weakness exclusively affecting the left side of the body; the asymmetry was less pronounced in patient P2. Muscle biopsies from both patients showed nemaline rods as the main histopathologic hallmark, and MRI revealed major fatty infiltrations in selective head, proximal, and distal muscles, correlating with the degree of muscle weakness asymmetry. Exome sequencing on blood DNA from both patients identified de novo ACTA1 missense mutations in a small number of reads, suggesting mutation mosaicism. Subsequent Sanger sequencing confirmed the presence of the mutations on muscle DNA, while they were barely detectable on blood DNA.

Conclusions

De novo mutations can occur anytime during embryonic development and may result in a mosaic pattern of affected cells and tissues and lead to the development of an asymmetric clinical picture. The present study points out that mosaic mutations might not be easily detectable on leukocyte DNA and thereby escape routine genetic analysis, and possibly account for a significant number of molecularly undiagnosed patients.

Muscle MRI in two SMA patients on nusinersen treatment: A two years follow-up

Introduction

The effects of nusinersen in adults with SMA rely on neuromotor function scales and qualitative assessments. There are limited clinical or imaging data on muscle changes over time.

Methods

Two adult SMA patients underwent clinical assessments including measures of upper and lower limb function with Revised Upper Limb Module (RULM) and Hammersmith Function Motor Scale Expanded (HFMSE); both patients were also studied with whole-body muscle MRI (T1-weighted and Diffusion Tensor Imaging/DTI sequences), at baseline and after 10 and 24 months from the beginning of treatment with nusinersen.

Results

After two years of treatment, HFMSE and RULM scores were stable in both patients. DTI sequences revealed an increased number, length and organization of muscle fiber tracks, and Fractional Anisotropy (FA) values showed a significant reduction after 10 and 24 months from baseline, in their corresponding maps.

Discussion

Muscle DTI imaging seems to play an interesting role to monitor treatment effects over time in adult SMA patients.

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Nusinersen treatment has created great expectations in older SMA patients having long-lasting muscular atrophy.

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DTI is a very sensitive technique to identify small changes in muscle architecture.

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DTI shows that nusinersen treatment may have a positive effect on size, length and organization of fiber tracts.

Splicing impact of deep exonic missense variants in CAPN3 explored systematically by minigene functional assay

Improving the accuracy of variant interpretation during diagnostic sequencing is a major goal for genomic medicine. To explore an often-overlooked splicing effect of missense variants, we developed the functional assay ("minigene") for the majority of exons of CAPN3, the gene responsible for limb girdle muscular dystrophy. By systematically screening 21 missense variants distributed along the gene, we found that eight clinically relevant missense variants located at a certain distance from the exon-intron borders (deep exonic missense variants) disrupted normal splicing of CAPN3 exons. Several recent machine learning-based computational tools failed to predict splicing impact for the majority of these deep exonic missense variants, highlighting the importance of including variants of this type in the training sets during the future algorithm development. Overall, 24 variants in CAPN3 gene were explored, leading to the change in the American College of Medical Genetics and Genomics classification of seven of them when results of the "minigene" functional assay were considered. Our findings reveal previously unknown splicing impact of several clinically important variants in CAPN3 and draw attention to the existence of deep exonic variants with a disruptive effect on gene splicing that could be overlooked by the current approaches in clinical genetics.