MR biomarkers predict clinical function in Duchenne muscular dystrophy

Reductions in functional muscle mass and ability to ambulate in Duchenne muscular dystrophy from ages 4 to 24 years

Duchenne muscular dystrophy (DMD) results in a progressive loss of functional skeletal muscle mass (MM) and replacement with fibrofatty tissue. Accurate evaluation of MM in DMD patients has not previously been available. Our objective was to measure MM using the D3creatine (D3Cr) dilution method and determine its relationship with strength and functional capacity in patients with DMD over a wide range of ages. Subjects were recruited for participation in a 12 month, longitudinal, observational study. Here, we report the baseline data. A 20 mg dose of D3Cr dissolved in water was ingested by 92 patients with DMD (ages 4-25 years) followed later with a fasting urine sample. Enrichment of D3creatinine was determined by liquid chromatography-mass spectrometry analysis. The North Star Ambulatory Assessment (NSAA) total score was determined for ambulatory participants, and the Performance of Upper Limb (PUL 2.0) total score and grip strength for all participants. We observed a significant age-associated increase in body weight along with a substantial decrease in MM/body weight (%MM). MM and %MM were associated with PUL score (r = 0.517, P < 0.0001 and r = 0.764, P < 0.0001 respectively). The age-associated decrease in MM and %MM was strongly associated with ambulatory status. We observed very little overlap in %MM between ambulant and non-ambulant subjects, suggesting a threshold of 18-22% associated with loss of ambulation. MM is substantially diminished with advancing age and is highly related to clinically meaningful functional status. The D3Cr dilution method may provide a biomarker of disease progression and therapeutic efficacy in patients with DMD or other neuromuscular disorders. KEY POINTS: The non-invasive D3creatine dilution method provides novel data on whole body functional muscle mass (MM) in a wide range of ages in patients with DMD and reveals profoundly low functional MM in older non-ambulant patients. The difference in %MM between ambulant and non-ambulant subjects suggests a threshold for loss of ambulatory ability between 18 and 22% MM. The data suggest that as functional MM declines with age, maintaining a lower body weight may help to conserve ambulatory ability.

Volumetric muscle composition analysis in sporadic inclusion body myositis using fat-referenced magnetic resonance imaging: Disease pattern, repeatability, and natural progression

INTRODUCTION/AIMS

Fat-referenced magnetic resonance imaging (MRI) has emerged as a promising volumetric technique for measuring muscular volume and fat in neuromuscular disorders, but the experience in inflammatory myopathies remains limited. Therefore, this work aimed at describing how sporadic inclusion body myositis (sIBM) manifests on standardized volumetric fat-referenced MRI muscle measurements, including within-scanner repeatability, natural progression rate, and relationship to clinical parameters.

METHODS

Ten sIBM patients underwent whole-leg Dixon MRI at baseline (test-retest) and after 12 months. The lean muscle volume (LMV), muscle fat fraction (MFF), and muscle fat infiltration (MFI) of the quadriceps, hamstrings, adductors, medial gastrocnemius, and tibialis anterior were computed. Clinical assessments of IBM Functional Rating Scale (IBMFRS) and knee extension strength were also performed. The baseline test-retest MRI measurements were used to estimate the within-subject standard deviation (sw). 12-month changes were derived for all parameters.

RESULTS

The MRI measurements showed high repeatability in all muscles; sw ranged from 2.7 to 18.0 mL for LMV, 0.7-1.3 percentage points (pp) for MFF, and 0.2-0.7 pp for MFI. Over 12 months, average LMV decreased by 7.4% while MFF and MFI increased by 3.8 pp and 1.8 pp, respectively. Mean IBMFRS decreased by 2.4 and mean knee extension strength decreased by 32.8 N.

DISCUSSION

The MRI measurements showed high repeatability and 12-month changes consistent with muscle atrophy and fat replacement as well as a decrease in both muscle strength and IBMFRS. Our findings suggest that fat-referenced MRI measurements are suitable for assessing disease progression and treatment response in inflammatory myopathies.

High mobility group box 1 (HMGB1) is a potential disease biomarker in cell and mouse models of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disorder affecting 1:3500 male births and is associated with myofiber degeneration, regeneration, and inflammation. Glucocorticoid treatments have been the standard of care due to immunomodulatory/immunosuppressive properties but novel genetic approaches, including exon skipping and gene replacement therapy, are currently being developed. The identification of additional biomarkers to assess DMD-related inflammatory responses and the potential efficacy of these therapeutic approaches are thus of critical importance. The current study uses RNA sequencing of skeletal muscle from two mdx mouse models to identify high mobility group box 1 (HMGB1) as a candidate biomarker potentially contributing to DMD-related inflammation. HMGB1 protein content was increased in a human iPSC-derived skeletal myocyte model of DMD and microdystrophin treatment decreased HMGB1 back to control levels. In vivo, HMGB1 protein levels were increased in vehicle treated B10-mdx skeletal muscle compared to B10-WT and significantly decreased in B10-mdx animals treated with adeno-associated virus (AAV)-microdystrophin. However, HMGB1 protein levels were not increased in D2-mdx skeletal muscle compared to D2-WT, demonstrating a strain-specific difference in DMD-related immunopathology.

Assessment of lumbar paraspinal muscle morphology using mDixon Quant magnetic resonance imaging (MRI): a cross-sectional study in healthy subjects

Background

Lumbar paraspinal muscles (LPM) are a part of the deep spinal stabilisation system and play an important role in stabilising the lumbar spine and trunk. Inadequate function of these muscles is thought to be an essential aetiological factor in low back pain, and several neuromuscular diseases are characterised by dysfunction of LPM. The main aims of our study were to develop a methodology for LPM assessment using advanced magnetic resonance imaging (MRI) methods, including a manual segmentation process, to confirm the measurement reliability, to evaluate the LPM morphological parameters [fat fraction (FF), total muscle volume (TMV) and functional muscle volume (FMV)] in a healthy population, to study the influence of physiological factors on muscle morphology, and to build equations to predict LPM morphological parameters in a healthy population.

Methods

This prospective cross-sectional observational comparative single-centre study was conducted at the University Hospital in Brno, enrolling healthy volunteers from April 2021 to March 2023. MRI of the lumbar spine and LPM (erector spinae muscle and multifidus muscle) were performed using a 6-point Dixon gradient echo sequence. The segmentation of the LPM and the control muscle (psoas muscle) was done manually to obtain FF and TMV in a range from Th12/L1 to L5/S1. Intra-rater and inter-rater reliability were evaluated. Linear regression models were constructed to assess the effect of physiological factors on muscle FF, TMV and FMV.

Results

We enrolled 90 healthy volunteers (median age 38 years, 45 men). The creation of segmentation masks and the assessment of FF and TMV proved reliable (Dice coefficient 84% to 99%, intraclass correlation coefficient ≥0.97). The univariable models showed that FF of LPM was influenced the most by age (39.6% to 44.8% of variability, P<0.001); TMV and FMV by subject weight (34.9% to 67.6% of variability, P<0.001) and sex (24.7% to 64.1% of variability, P<0.001). Multivariable linear regression models for FF of LPM included age, body mass index and sex, with R-squared values ranging from 45.4% to 51.1%. Models for volumes of LPM included weight, age and sex, with R-squared values ranged from 37.4% to 76.8%. Equations were developed to calculate predicted FF, TMV and FMV for each muscle.

Conclusions

A reliable methodology has been developed to assess the morphological parameters (biomarkers) of the LPM. The morphological parameters of the LPM are significantly influenced by physiological factors. Equations were constructed to calculate the predicted FF, TMV and FMV of individual muscles in relation to anthropometric parameters, age, and sex. This study, which presented LPM assessment methodology and predicted values of LPM morphological parameters in a healthy population, could improve our understanding of diseases involving LPM (low back pain and some neuromuscular diseases).

"If you cannot measure it, you cannot improve it". Outcome measures in Duchenne Muscular Dystrophy: current and future perspectives

Duchenne Muscular Dystrophy (DMD) is an X-linked recessive neuromuscular disorder primarily affecting males, caused by mutations in the dystrophin gene. The absence of dystrophin protein leads to progressive skeletal muscle degeneration. Recent advances in the therapeutic landscape underscore the need to identify appropriate outcome measures to assess treatment efficacy in ambulant and non-ambulant DMD patients, across clinical and research settings. This is essential for accurately evaluating new treatments and attributing therapeutic benefits.It is crucial to establish a robust correlation between outcome scores and disease progression patterns. This task is challenging since functional test performance may be influenced by different patient's characteristics, including the physiological evolution of the neurodevelopment together with the disease progression. While widely used DMD outcomes such as the North Star Ambulatory Assessment, the 6-Minute Walking Test, the 4 stairs climbed, and the Performance of the Upper Limb exhibit reliability and validity, their clinical significance is influenced by the wide phenotype and progression variability of the disease.We present and discuss the features (relevance, quantifiability, validity, objectivity, reliability, sensitivity, specificity, precision) of available DMD outcome measures, including new potential measures that may be provided by digital tools and artificial intelligence.

Current Concepts in the Orthopaedic Management of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD), a genetic condition marked by progressive muscle degeneration, presents notable orthopaedic challenges, especially scoliosis, which deteriorates patients' quality of life by affecting sitting balance and complicating cardiac and respiratory functions. Current orthopaedic management strategies emphasize early intervention with corticosteroids to delay disease progression and the use of surgical spinal fusion to address severe scoliosis, aiming to enhance sitting balance, alleviate discomfort, and potentially extend patient lifespan. Despite advancements, optimal management requires ongoing research to refine therapeutic approaches, ensuring improved outcomes for patients with DMD. This review synthesizes recent findings on surgical and nonsurgical interventions, underscoring the importance of a multidisciplinary approach tailored to the dynamic needs of patients with DMD.

Five multivariate Duchenne muscular dystrophy progression models bridging six-minute walk distance and MRI relaxometry of leg muscles

The study aimed to provide quantitative information on the utilization of MRI transverse relaxation time constant (MRI-T2) of leg muscles in DMD clinical trials by developing multivariate disease progression models of Duchenne muscular dystrophy (DMD) using 6-min walk distance (6MWD) and MRI-T2. Clinical data were collected from the prospective and longitudinal ImagingNMD study. Disease progression models were developed by a nonlinear mixed-effect modeling approach. Univariate models of 6MWD and MRI-T2 of five muscles were developed separately. Age at assessment was the time metric. Multivariate models were developed by estimating the correlation of 6MWD and MRI-T2 model variables. Full model estimation approach for covariate analysis and five-fold cross validation were conducted. Simulations were performed to compare the models and predict the covariate effects on the trajectories of 6MWD and MRI-T2. Sigmoid Imax and Emax models best captured the profiles of 6MWD and MRI-T2 over age. Steroid use, baseline 6MWD, and baseline MRI-T2 were significant covariates. The median age at which 6MWD is half of its maximum decrease in the five models was similar, while the median age at which MRI-T2 is half of its maximum increase varied depending on the type of muscle. The models connecting 6MWD and MRI-T2 successfully quantified how individual characteristics alter disease trajectories. The models demonstrate a plausible correlation between 6MWD and MRI-T2, supporting the use of MRI-T2. The developed models will guide drug developers in using the MRI-T2 to most efficient use in DMD clinical trials.

Safety and efficacy of givinostat in boys with Duchenne muscular dystrophy (EPIDYS): a multicentre, randomised, double-blind, placebo-controlled, phase 3 trial

BACKGROUND

Duchenne muscular dystrophy, the most common childhood muscular dystrophy, is caused by dystrophin deficiency. Preclinical and phase 2 study data have suggested that givinostat, a histone deacetylase inhibitor, might help to counteract the effects of this deficiency. We aimed to evaluate the safety and efficacy of givinostat in the treatment of Duchenne muscular dystrophy.

METHODS

This multicentre, randomised, double-blind, placebo-controlled, phase 3 trial was done at 41 tertiary care sites in 11 countries. Eligible participants were ambulant, male, and aged at least 6 years, had a genetically confirmed diagnosis of Duchenne muscular dystrophy, completed two four-stair climb assessments with a mean of 8 s or less (≤1 s variance), had a time-to-rise of at least 3 s but less than 10 s, and had received systemic corticosteroids for at least 6 months. Participating boys were randomly assigned (2:1, allocated according to a list generated by the interactive response technology provider) to receive either oral givinostat or matching placebo twice a day for 72 weeks, stratified by concomitant steroid use. Boys, investigators, and site and sponsor staff were masked to treatment assignment. The dose was flexible, based on weight, and was reduced if not tolerated. Boys were divided into two groups on the basis of their baseline vastus lateralis fat fraction (VLFF; measured by magnetic resonance spectroscopy): group A comprised boys with a VLFF of more than 5% but no more than 30%, whereas group B comprised boys with a VLFF of 5% or less, or more than 30%. The primary endpoint compared the effects of givinostat and placebo on the change in results of the four-stair climb assessment between baseline and 72 weeks, in the intention-to-treat, group A population. Safety was assessed in all randomly assigned boys who received at least one dose of study drug. When the first 50 boys in group A completed 12 months of treatment, an interim futility assessment was conducted, after which the sample size was adapted using masked data from the four-stair climb assessments. Furthermore, the starting dose of givinostat was reduced following a protocol amendment. This trial is registered with ClinicalTrials.gov, NCT02851797, and is complete.

FINDINGS

Between June 6, 2017, and Feb 22, 2022, 359 boys were assessed for eligibility. Of these, 179 were enrolled into the study (median age 9·8 years [IQR 8·1-11·0]), all of whom were randomly assigned (118 to receive givinostat and 61 to receive placebo); 170 (95%) boys completed the study. Of the 179 boys enrolled, 120 (67%) were in group A (81 givinostat and 39 placebo); of these, 114 (95%) completed the study. For participants in group A, comparing the results of the four-stair climb assessment at 72 weeks and baseline, the geometric least squares mean ratio was 1·27 (95% CI 1·17-1·37) for boys receiving givinostat and 1·48 (1·32-1·66) for those receiving placebo (ratio 0·86, 95% CI 0·745-0·989; p=0·035). The most common adverse events in the givinostat group were diarrhoea (43 [36%] of 118 boys vs 11 [18%] of 61 receiving placebo) and vomiting (34 [29%] vs 8 [13%]); no treatment-related deaths occurred.

INTERPRETATION

Among ambulant boys with Duchenne muscular dystrophy, results of the four-stair climb assessment worsened in both groups over the study period; however, the decline was significantly smaller with givinostat than with placebo. The dose of givinostat was reduced after an interim safety analysis, but no new safety signals were reported. An ongoing extension study is evaluating the long-term safety and efficacy of givinostat in patients with Duchenne muscular dystrophy.

FUNDING

Italfarmaco.

Clinical importance of changes in magnetic resonance biomarkers for Duchenne muscular dystrophy

OBJECTIVE

Magnetic resonance (MR) measures of muscle quality are highly sensitive to disease progression and predictive of meaningful functional milestones in Duchenne muscular dystrophy (DMD). This investigation aimed to establish the reproducibility, responsiveness to disease progression, and minimum clinically important difference (MCID) for multiple MR biomarkers at different disease stages in DMD using a large natural history dataset.

METHODS

Longitudinal MR imaging and spectroscopy outcomes and ambulatory function were measured in 180 individuals with DMD at three sites, including repeated measurements on two separate days (within 1 week) in 111 participants. These data were used to calculate day-to-day reproducibility, responsiveness (standardized response mean, SRM), minimum detectable change, and MCID. A survey of experts was also performed.

RESULTS

MR spectroscopy fat fraction (FF), as well as MR imaging transverse relaxation time (MRI-T2 ), measures performed in multiple leg muscles, and had high reproducibility (Pearson's R > 0.95). Responsiveness to disease progression varied by disease stage across muscles. The average FF from upper and lower leg muscles was highly responsive (SRM > 0.9) in both ambulatory and nonambulatory individuals. MCID estimated from the distribution of scores, by anchoring to function, and via expert opinion was between 0.01 and 0.05 for FF and between 0.8 and 3.7 ms for MRI-T2 .

INTERPRETATION

MR measures of FF and MRI T2 are reliable and highly responsive to disease progression. The MCID for MR measures is less than or equal to the typical annualized change. These results confirm the suitability of these measures for use in DMD and potentially other muscular dystrophies.

Draft Guidance for Industry Duchenne Muscular Dystrophy, Becker Muscular Dystrophy, and Related Dystrophinopathies - Developing Potential Treatments for the Entire Spectrum of Disease

Background

Duchenne muscular dystrophy (DMD) and related dystrophinopathies are neuromuscular conditions with great unmet medical needs that require the development of effective medical treatments.

Objective

To aid sponsors in clinical development of drugs and therapeutic biological products for treating DMD across the disease spectrum by integrating advancements, patient registries, natural history studies, and more into a comprehensive guidance.

Methods

This guidance emerged from collaboration between the FDA, the Duchenne community, and industry stakeholders. It entailed a structured approach, involving multiple committees and boards. From its inception in 2014, the guidance underwent revisions incorporating insights from gene therapy studies, cardiac function research, and innovative clinical trial designs.

Results

The guidance provides a deeper understanding of DMD and its variants, focusing on patient engagement, diagnostic criteria, natural history, biomarkers, and clinical trials. It underscores patient-focused drug development, the significance of dystrophin as a biomarker, and the pivotal role of magnetic resonance imaging in assessing disease progression. Additionally, the guidance addresses cardiomyopathy's prominence in DMD and the burgeoning field of gene therapy.

Conclusions

The updated guidance offers a comprehensive understanding of DMD, emphasizing patient-centric approaches, innovative trial designs, and the importance of biomarkers. The focus on cardiomyopathy and gene therapy signifies the evolving realm of DMD research. It acts as a crucial roadmap for sponsors, potentially leading to improved treatments for DMD.

Predictors of Loss of Ambulation in Duchenne Muscular Dystrophy: A Systematic Review and Meta-Analysis

Objective

The objective of this study was to describe predictors of loss of ambulation in Duchenne muscular dystrophy (DMD).

Methods

This systematic review and meta-analysis included searches of MEDLINE ALL, Embase, and the Cochrane Database of Systematic Reviews from January 1, 2000, to December 31, 2022, for predictors of loss of ambulation in DMD. Search terms included "Duchenne muscular dystrophy" as a Medical Subject Heading or free text term, in combination with variations of the term "predictor". Risk of bias was assessed using the Newcastle-Ottawa Scale. We performed meta-analysis pooling of hazard ratios of the effects of glucocorticoids (vs. no glucocorticoid therapy) by fitting a common-effect inverse-variance model.

Results

The bibliographic searches resulted in the inclusion of 45 studies of children and adults with DMD from 17 countries across Europe, Asia, and North America. Glucocorticoid therapy was associated with delayed loss of ambulation (overall meta-analysis HR deflazacort/prednisone/prednisolone: 0.44 [95% CI: 0.40-0.48]) (n = 25 studies). Earlier onset of first signs or symptoms, earlier loss of developmental milestones, lower baseline 6MWT (i.e.,<350 vs. ≥350 metres and <330 vs. ≥330 metres), and lower baseline NSAA were associated with earlier loss of ambulation (n = 5 studies). Deletion of exons 3-7, proximal mutations (upstream intron 44), single exon 45 deletions, and mutations amenable of skipping exon 8, exon 44, and exon 53, were associated with prolonged ambulation; distal mutations (intron 44 and downstream), deletion of exons 49-50, and mutations amenable of skipping exon 45, and exon 51 were associated with earlier loss of ambulation (n = 13 studies). Specific single-nucleotide polymorphisms in CD40 gene rs1883832, LTBP4 gene rs10880, SPP1 gene rs2835709 and rs11730582, and TCTEX1D1 gene rs1060575 (n = 7 studies), as well as race/ethnicity and level of family/patient deprivation (n = 3 studies), were associated with loss of ambulation. Treatment with ataluren (n = 2 studies) and eteplirsen (n = 3 studies) were associated with prolonged ambulation. Magnetic resonance biomarkers (MRI and MRS) were identified as significant predictors of loss of ambulation (n = 6 studies). In total, 33% of studies exhibited some risk of bias.

Conclusion

Our synthesis of predictors of loss of ambulation in DMD contributes to the understanding the natural history of disease and informs the design of new trials of novel therapies targeting this heavily burdened patient population.

Longitudinal changes in magnetic resonance imaging biomarkers of the gluteal muscle groups and functional ability in Duchenne muscular dystrophy: a 12-month cohort study

BACKGROUND

Quantitative magnetic resonance imaging (MRI) is considered an objective biomarker of Duchenne muscular dystrophy (DMD), but the longitudinal progression of MRI biomarkers in gluteal muscle groups and their predictive value for future motor function have not been described.

OBJECTIVE

To explore MRI biomarkers of the gluteal muscle groups as predictors of motor function decline in DMD by characterizing the progression over 12 months.

MATERIALS AND METHODS

A total of 112 participants with DMD were enrolled and underwent MRI examination of the gluteal muscles to determine fat fraction and longitudinal relaxation time (T1). Investigations were based on gluteal muscle groups including flexors, extensors, adductors, and abductors. The North Star Ambulatory Assessment and timed functional tests were performed. All participants returned for follow-up at an average of 12 months and were divided into two subgroups (functional stability/decline groups) based on changes in timed functional tests. Univariable and multivariable logistic regression methods were used to explore the risk factors associated with future motor function decline.

RESULTS

For the functional decline group, all T1 values decreased, while fat fraction values increased significantly over 12 months (P<0.05). For the functional stability group, only the fat fraction of the flexors and abductors increased significantly over 12 months (P<0.05). The baseline T1 value was positively correlated with North Star Ambulatory Assessment and negatively correlated with timed functional tests at the 12-month follow-up (P<0.001), while the baseline fat fraction value was negatively correlated with North Star Ambulatory Assessment and positively correlated with timed functional tests at the 12-month follow-up (P<0.001). Multivariate regression showed that increased fat fraction of the abductors was associated with future motor function decline (model 1: odds ratio [OR]=1.104, 95% confidence interval [CI]: 1.026~1.187, P=0.008; model 2: OR=1.085, 95% CI: 1.013~1.161, P=0.019), with an area under the curve of 0.874.

CONCLUSION

Fat fraction of the abductors is a powerful predictor of future motor functional decline in DMD patients at 12 months, underscoring the importance of focusing early on this parameter in patients with DMD.

Left Atrial Phasic Function via Cardiac Magnetic Resonance Imaging in Patients with Duchenne Muscular Dystrophy

Cardiac dysfunction is a leading cause of morbidity and mortality in Duchenne muscular dystrophy (DMD). Left atrial (LA) function is a poorly understood concept in this patient population, and research suggests underlying structural changes that could affect atrial function. Cardiac magnetic resonance (CMR) imaging may provide an important non-invasive approach to evaluating LA function. This study was a single center retrospective review of consecutive CMR studies over a 1 year period comparing LA phasic function within a cohort of DMD patients, and to those with structurally and functionally normal hearts. LA strain measurements including global reservoir, conduit, boost-pump strain, and LA volumes were obtained retrospectively. Spearman correlation analyses were performed on atrial strain measurements. 107 DMD and 79 normal CMR studies were included. The DMD cohort had worse systolic function (p < 0.001), smaller indexed max LA and left ventricular (LV) volumes (p < 0.001), and greater LA emptying fraction (p < 0.001). In the DMD cohort, emptying fraction decreased with advanced patient age (p < 0.001) and diminishing systolic function (p < 0.001). DMD patients with moderate or severe LV dysfunction demonstrated lower LA emptying fraction (p = 0.002), more impaired 2-chamber LA reservoir (p = 0.003), and LA pump (p = 0.006) and conduit strain (p = 0.018). DMD patients with preserved function have lower indexed LA volumes with higher LA emptying fractions than controls. Progression of disease and age is associated with decreased LA emptying fraction with early manifestations in reservoir and conduit strain. These findings suggest that strain markers of LA compliance and early left ventricular relaxation are associated with worsening cardiomyopathy in the DMD population.

Multivariate modeling of magnetic resonance biomarkers and clinical outcome measures for Duchenne muscular dystrophy clinical trials

Although regulatory agencies encourage inclusion of imaging biomarkers in clinical trials for Duchenne muscular dystrophy (DMD), industry receives minimal guidance on how to use these biomarkers most beneficially in trials. This study aims to identify the optimal use of muscle fat fraction biomarkers in DMD clinical trials through a quantitative disease-drug-trial modeling and simulation approach. We simultaneously developed two multivariate models quantifying the longitudinal associations between 6-minute walk distance (6MWD) and fat fraction measures from vastus lateralis and soleus muscles. We leveraged the longitudinal individual-level data collected for 10 years through the ImagingDMD study. Age of the individuals at assessment was chosen as the time metric. After the longitudinal dynamic of each measure was modeled separately, the selected univariate models were combined using correlation parameters. Covariates, including baseline scores of the measures and steroid use, were assessed using the full model approach. The nonlinear mixed-effects modeling was performed in Monolix. The final models showed reasonable precision of the parameter estimates. Simulation-based diagnostics and fivefold cross-validation further showed the model's adequacy. The multivariate models will guide drug developers on using fat fraction assessment most efficiently using available data, including the widely used 6MWD. The models will provide valuable information about how individual characteristics alter disease trajectories. We will extend the multivariate models to incorporate trial design parameters and hypothetical drug effects to inform better clinical trial designs through simulation, which will facilitate the design of clinical trials that are both more inclusive and more conclusive using fat fraction biomarkers.

High-Speed T2 -Corrected Multiecho Magnetic Resonance Spectroscopy for Quantitatively Detecting Skeletal Muscle Fatty Infiltration and Predicting the Loss of Ambulation in Patients With Duchenne Muscular Dystrophy

BACKGROUND

High-speed T2 -corrected multiecho MRS (HISTO-MRS) is emerging as a quantitative modality for detecting muscle fat infiltration (MFF). However, the predictive value of HISTO-MRS for the loss of ambulation (LoA) in Duchenne muscular dystrophy (DMD) is unknown.

PURPOSE

To determine the feasibility of HISTO-MRS for assessing MFF in DMD and further identify the predictive value of HISTO-MRS for the LoA.

STUDY TYPE

Prospective.

SUBJECTS

A total of 134 DMD boys (9.20 ± 2.43 years old) and 21 healthy boys (9.25 ± 2.10 years old).

FIELD STRENGTH/SEQUENCE

A 3 T, fast spin echo T1 -weighted imaging (T1 WI), two-point-Dixon gradient echo sequence (2-pt-Dixon) and HISTO-MRS.

ASSESSMENT

Subjective T1 WI fat grades by three radiologists, ROI analysis for MFF on 2 pt-Dixon (Dixon MFF) and MFF on HISTO-MRS (HISTO MFF) by two radiologists. Clinical motor function: North Star Ambulatory Assessment, 10-m run/walk time, Gowers maneuver, and time to four-stairs climb and descend.

STATISTICAL TESTS

Spearman rank correlation was used to assess the relation of fat filtration assessments and motor ability. Bland-Altman plots was performed to determine the agreement of HISTO MFF and Dixon MFF. Receiver operating characteristic (ROC) curves were analyzed to determine the discriminating ability of above MRI modalities for ambulatory and nonambulatory DMD. Logistic regression was used to identify the predictor of LoA. Variables with P < 0.05 in univariate logistic regression analysis were entered into the multivariate logistic regression model.

RESULTS

HISTO MFF was significantly correlated with Dixon MFF. Bland-Altman plots show good agreement of HISTO MFF and Dixon MFF. ROC curves indicated that HISTO MFF show similar discrimination of LoA for DMD with Dixon MFF but better value than T1WI fat grades. Logistic regression showed that HISTO MFF was an independent predictor for LoA.

DATA CONCLUSION

HISTO-MRS is a potential quantitative method for assessing fat infiltration and shows predictive value for LoA in DMD patients.

LEVEL OF EVIDENCE: 1

TECHNICAL EFFICACY

Stage 5.

Clinical utilisation of multimodal quantitative magnetic resonance imaging in investigating muscular damage in Duchenne muscular dystrophy: a study on the association between gluteal muscle groups and motor function

BACKGROUND

Duchenne muscular dystrophy (DMD) is a neuromuscular disease characterised by progressive muscular weakness and atrophy. Currently, studies on DMD muscle function mostly focus on individual muscles; little is known regarding the effect of gluteal muscle group damage on motor function.

OBJECTIVE

To explore potential imaging biomarkers of hip and pelvic muscle groups for measuring muscular fat replacement and inflammatory oedema in DMD with multimodal quantitative magnetic resonance imaging (MRI).

MATERIALS AND METHODS

One hundred fifty-nine DMD boys and 32 healthy male controls were prospectively included. All subjects underwent MRI examination of the hip and pelvic muscles with T1 mapping, T2 mapping and Dixon sequences. Quantitatively measured parameters included longitudinal relaxation time (T1), transverse relaxation time (T2) and fat fraction. Investigations were all based on hip and pelvic muscle groups covering flexors, extensors, adductors and abductors. The North Star Ambulatory Assessment and stair climbing tests were used to measure motor function in DMD.

RESULTS

T1 of the extensors (r = 0.720, P < 0.01), flexors (r = 0.558, P < 0.01) and abductors (r = 0.697, P < 0.001) were positively correlated with the North Star Ambulatory Assessment score. In contrast, T2 of the adductors (r = -0.711, P < 0.01) and fat fraction of the extensors (r = -0.753, P < 0.01) were negatively correlated with the North Star Ambulatory Assessment score. Among them, T1 of the abductors (b = 0.013, t = 2.052, P = 0.042), T2 of the adductors (b = -0.234, t = -2.554, P = 0.012) and fat fraction of the extensors (b = -0.637, t =  - 4.096, P < 0.001) significantly affected the North Star Ambulatory Assessment score. Moreover, T1 of the abductors was highly predictive for identifying motor dysfunction in DMD, with an area under the curve of 0.925.

CONCLUSION

Magnetic resonance biomarkers of hip and pelvic muscle groups (particularly T1 values of the abductor muscles) have the potential to be used as independent risk factors for motor dysfunction in DMD.

Is it time for genetic modifiers to predict prognosis in Duchenne muscular dystrophy?

Patients with Duchenne muscular dystrophy (DMD) show clinically relevant phenotypic variability, despite sharing the same primary biochemical defect (dystrophin deficiency). Factors contributing to this clinical variability include allelic heterogeneity (specific DMD mutations), genetic modifiers (trans-acting genetic polymorphisms) and variations in clinical care. Recently, a series of genetic modifiers have been identified, mostly involving genes and/or proteins that regulate inflammation and fibrosis - processes increasingly recognized as being causally linked with physical disability. This article reviews genetic modifier studies in DMD to date and discusses the effect of genetic modifiers on predicting disease trajectories (prognosis), clinical trial design and interpretation (inclusion of genotype-stratified subgroup analyses) and therapeutic approaches. The genetic modifiers identified to date underscore the importance of progressive fibrosis, downstream of dystrophin deficiency, in driving the disease process. As such, genetic modifiers have shown the importance of therapies aimed at slowing this fibrotic process and might point to key drug targets.

Orthogonal proteomics methods warrant the development of Duchenne muscular dystrophy biomarkers

BACKGROUND

Molecular components in blood, such as proteins, are used as biomarkers to detect or predict disease states, guide clinical interventions and aid in the development of therapies. While multiplexing proteomics methods promote discovery of such biomarkers, their translation to clinical use is difficult due to the lack of substantial evidence regarding their reliability as quantifiable indicators of disease state or outcome. To overcome this challenge, a novel orthogonal strategy was developed and used to assess the reliability of biomarkers and analytically corroborate already identified serum biomarkers for Duchenne muscular dystrophy (DMD). DMD is a monogenic incurable disease characterized by progressive muscle damage that currently lacks reliable and specific disease monitoring tools.

METHODS

Two technological platforms are used to detect and quantify the biomarkers in 72 longitudinally collected serum samples from DMD patients at 3 to 5 timepoints. Quantification of the biomarkers is achieved by detection of the same biomarker fragment either through interaction with validated antibodies in immuno-assays or through quantification of peptides by Parallel Reaction Monitoring Mass Spectrometry assay (PRM-MS).

RESULTS

Five, out of ten biomarkers previously identified by affinity-based proteomics methods, were confirmed to be associated with DMD using the mass spectrometry-based method. Two biomarkers, carbonic anhydrase III and lactate dehydrogenase B, were quantified with two independent methods, sandwich immunoassays and PRM-MS, with Pearson correlations of 0.92 and 0.946 respectively. The median concentrations of CA3 and LDHB in DMD patients was elevated in comparison to those in healthy individuals by 35- and 3-fold, respectively. Levels of CA3 vary between 10.26 and 0.36 ng/ml in DMD patients whereas those of LDHB vary between 15.1 and 0.8 ng/ml.

CONCLUSIONS

These results demonstrate that orthogonal assays can be used to assess the analytical reliability of biomarker quantification assays, providing a means to facilitate the translation of biomarkers to clinical practice. This strategy also warrants the development of the most relevant biomarkers, markers that can be reliably quantified with different proteomics methods.

Associations between lower extremity muscle fat fraction and motor performance in myotonic dystrophy type 2: A pilot study

INTRODUCTION/AIMS

Although muscle structure measures from magnetic resonance imaging (MRI) have been used to assess disease severity in muscular dystrophies, little is known about how these measures are affected in myotonic dystrophy type 2 (DM2). We aim to characterize lower extremity muscle fat fraction (MFF) as a potential biomarker of disease severity, and evaluate its relationship with motor performance in DM2.

METHODS

3-Tesla MRIs were obtained from nine patients with DM2 and six controls using a T1W-Dixon protocol. To calculate MFF, muscle volumes were segmented from proximal, middle, and distal regions of the thigh and calf. Associations between MFF and motor performance were calculated using Spearman's correlations (ρ).

RESULTS

Mean age of DM2 participants was 62 ± 11 y (89% female), and mean symptom duration was 20 ± 12 y. Compared to controls, the DM2 group had significantly higher MFF in the thigh and the calf segments (p-value = .002). The highest MFF at the thigh in DM2 was located in the posterior compartment (39.7 ± 12.9%) and at the calf was the lateral compartment (31.5 ± 8.7%). In the DM2 group, we found a strong correlation between the posterior thigh MFF and the 6-min walk test (ρ = -.90, p-value = .001). The lateral calf MFF was also strongly correlated with the step test (ρ = -0.82, p-value = .006).

DISCUSSION

Our pilot data suggest a potential correlation between lower extremity MFF and some motor performance tests in DM2. Longitudinal studies with larger sample sizes are required to validate MFF as a marker of disease severity in DM2.

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.

Givinostat for Becker muscular dystrophy: A randomized, placebo-controlled, double-blind study

Objective

No treatments are approved for Becker muscular dystrophy (BMD). This study investigated the efficacy and safety of givinostat, a histone deacetylase pan-inhibitor, in adults with BMD.

Methods

Males aged 18-65 years with a diagnosis of BMD confirmed by genetic testing were randomized 2:1 to 12 months treatment with givinostat or placebo. The primary objective was to demonstrate statistical superiority of givinostat over placebo for mean change from baseline in total fibrosis after 12 months. Secondary efficacy endpoints included other histological parameters, magnetic resonance imaging and spectroscopy (MRI and MRS) measures, and functional evaluations.

Results

Of 51 patients enrolled, 44 completed treatment. At baseline, there was greater disease involvement in the placebo group than givinostat, based on total fibrosis (mean 30.8 vs. 22.8%) and functional endpoints. Mean total fibrosis did not change from baseline in either group, and the two groups did not differ at Month 12 (least squares mean [LSM] difference 1.04%; p = 0.8282). Secondary histology parameters, MRS, and functional evaluations were consistent with the primary. MRI fat fraction in whole thigh and quadriceps did not change from baseline in the givinostat group, but values increased with placebo, with LSM givinostat-placebo differences at Month 12 of -1.35% (p = 0.0149) and -1.96% (p = 0.0022), respectively. Adverse events, most mild or moderate, were reported by 88.2% and 52.9% patients receiving givinostat and placebo.

Conclusion

The study failed to achieve the primary endpoint. However, there was a potential signal from the MRI assessments suggesting givinostat could prevent (or slow down) BMD disease progression.

The Dystrophinopathies

PURPOSE OF REVIEW

This article reviews the history, epidemiology, genetics, clinical presentation, multidisciplinary management, and established and emerging therapies for the dystrophinopathies.

RECENT FINDINGS

The multidisciplinary care of individuals with dystrophinopathies continues to improve in many ways, including early surveillance and implementation of respiratory, cardiac, and orthopedic health management. The era of genetic therapeutics has altered the treatment landscape in neuromuscular disorders, including the dystrophinopathies.

SUMMARY

The dystrophinopathies are a spectrum of X-linked genetic disorders characterized by childhood-onset progressive weakness and variable cardiac and cognitive involvement. Corticosteroids are the mainstay of therapy to slow disease progression. Additional strategies for disease amelioration and dystrophin restoration, including gene replacement therapy, are under investigation.

Water T2 could predict functional decline in patients with dysferlinopathy

BACKGROUND

Water T2 (T2_H2O ) mapping is increasingly being used in muscular dystrophies to assess active muscle damage. It has been suggested as a surrogate outcome measure for clinical trials. Here, we investigated the prognostic utility of T2_H2O to identify changes in muscle function over time in limb girdle muscular dystrophies.

METHODS

Patients with genetically confirmed dysferlinopathy were assessed as part of the Jain Foundation Clinical Outcomes Study in dysferlinopathy. The cohort included 18 patients from two sites, both equipped with 3-tesla magnetic resonance imaging (MRI) systems from the same vendor. T2_H2O value was defined as higher or lower than the median in each muscle bilaterally. The degree of deterioration on four functional tests over 3 years was assessed in a linear model against covariates of high or low T2_H2O at baseline, age, disease duration, and baseline function.

RESULTS

A higher T2_H2O at baseline significantly correlated with a greater decline on functional tests in 21 out of 35 muscles and was never associated with slower decline. Higher baseline T2_H2O in adductor magnus, vastus intermedius, vastus lateralis, and vastus medialis were the most sensitive, being associated bilaterally with greater decline in multiple timed tests. Patients with a higher than median baseline T2_H2O (>40.6 ms) in the right vastus medialis deteriorated 11 points more on the North Star Ambulatory Assessment for Dysferlinopathy and lost an additional 86 m on the 6-min walk than those with a lower T2_H2O (<40.6 ms). Optimum sensitivity and specificity thresholds for predicting decline were 39.0 ms in adductor magnus and vastus intermedius, 40.0 ms in vastus medialis, and 40.5 ms in vastus lateralis from different sites equipped with different MRI systems.

CONCLUSIONS

In dysferlinopathy, T2_H2O did not correlate with current functional ability. However, T2_H2O at baseline was higher in patients who worsened more rapidly on functional tests. This suggests that inter-patient differences in functional decline over time may be, in part, explained by different severities of the active muscle damage, assessed by T2_H2O measure at baseline. Significant challenges remain in standardizing T2_H2O values across sites to allow determining globally applicable thresholds. The results from the present work are encouraging and suggest that T2_H2O could be used to improve prognostication, patient selection, and disease modelling for clinical trials.

Prognostic factors, disease course, and treatment efficacy in Duchenne muscular dystrophy: A systematic review and meta-analysis

INTRODUCTION/AIMS

Prognostic factors in Duchenne muscular dystrophy (DMD) predict the disease course and may help individualize patient care. The aim was to summarize the evidence on prognostic factors that may support treatment decisions.

METHODS

We searched six databases for prospective studies that each included ≥50 DMD patients with a minimum follow-up of 1 y. Primary outcomes were age at loss of ambulation (LoA), pulmonary function (forced vital capacity percent of predicted, FVC%p), and heart failure.

RESULTS

Out of 5074 references, 59 studies were analyzed. Corticosteroid use was associated with a delayed LoA (pooled effect hazard ratio [HR] 0.42, 95% confidence interval [CI] 0.23-0.75, I2 94%), better pulmonary function tests (higher peak FVC%, prolonged time with FVC%p > 50%, and reduced need for assisted ventilation) and delayed cardiomyopathy. Longer corticosteroid treatment was associated with later LoA (>1 y compared to <1 y; pooled HR: 0.50, 95% CI 0.27-0.90) and early treatment start (aged <5 y) may be associated with early cardiomyopathy and higher fracture risk. Genotype appeared to be an independent driver of LoA in some studies. Higher baseline physical function tests (e.g., 6-minute walk test) were associated with delayed LoA. Left ventricular dysfunction and FVC <1 L increased and the use of angiotensin-converting enzyme (ACE) inhibitors reduced the risk of heart failure and death. Fusion surgery in scoliosis may potentially preserve pulmonary function.

DISCUSSION

Prognostic factors that may inform clinical decisions include age at corticosteroid treatment initiation and treatment duration, ACE-inhibitor use, baseline physical function tests, pulmonary function, and cardiac dysfunction.

Quantitative magnetic resonance imaging measures as biomarkers of disease progression in boys with Duchenne muscular dystrophy: a phase 2 trial of domagrozumab

Duchenne muscular dystrophy (DMD) is a progressive, neuromuscular disorder caused by mutations in the DMD gene that results in a lack of functional dystrophin protein. Herein, we report the use of quantitative magnetic resonance imaging (MRI) measures as biomarkers in the context of a multicenter phase 2, randomized, placebo-controlled clinical trial evaluating the myostatin inhibitor domagrozumab in ambulatory boys with DMD (n = 120 aged 6 to < 16 years). MRI scans of the thigh to measure muscle volume, muscle volume index (MVI), fat fraction, and T2 relaxation time were obtained at baseline and at weeks 17, 33, 49, and 97 as per protocol. These quantitative MRI measurements appeared to be sensitive and objective biomarkers for evaluating disease progression, with significant changes observed in muscle volume, MVI, and T2 mapping measures over time. To further explore the utility of quantitative MRI measures as biomarkers to inform longer term functional changes in this cohort, a regression analysis was performed and demonstrated that muscle volume, MVI, T2 mapping measures, and fat fraction assessment were significantly correlated with longer term changes in four-stair climb times and North Star Ambulatory Assessment functional scores. Finally, less favorable baseline measures of MVI, fat fraction of the muscle bundle, and fat fraction of lean muscle were significant risk factors for loss of ambulation over a 2-year monitoring period. These analyses suggest that MRI can be a valuable tool for use in clinical trials and may help inform future functional changes in DMD.Trial registration: ClinicalTrials.gov identifier, NCT02310763; registered December 2014.

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.

Baseline fat fraction is a strong predictor of disease progression in Becker muscular dystrophy

In Becker muscular dystrophy (BMD), muscle weakness progresses relatively slowly, with a highly variable rate among patients. This complicates clinical trials, as clinically relevant changes are difficult to capture within the typical duration of a trial. Therefore, predictors for disease progression are needed. We assessed if temporal increase of fat fraction (FF) in BMD follows a sigmoidal trajectory and whether fat fraction at baseline (FFbase) could therefore predict FF increase after 2 years (ΔFF). Thereafter, for two different MR-based parameters, we tested the additional predictive value to FFbase. We used 3-T Dixon data from the upper and lower leg, and multiecho spin-echo MRI and 7-T ³¹ P MRS datasets from the lower leg, acquired in 24 BMD patients (age: 41.4 [SD 12.8] years). We assessed the pattern of increase in FF using mixed-effects modelling. Subsequently, we tested if indicators of muscle damage like standard deviation in water T₂ (stdT₂ ) and the phosphodiester (PDE) over ATP ratio at baseline had additional value to FFbase for predicting ∆FF. The association between FFbase and ΔFF was described by the derivative of a sigmoid function and resulted in a peak ΔFF around 0.45 FFbase (fourth-order polynomial term: t = 3.7, p < .001). StdT₂ and PDE/ATP were not significantly associated with ∆FF if FFbase was included in the model. The relationship between FFbase and ∆FF suggests a sigmoidal trajectory of the increase in FF over time in BMD, similar to that described for Duchenne muscular dystrophy. Our results can be used to identify muscles (or patients) that are in the fast progressing stage of the disease, thereby facilitating the conduct of clinical trials.

Quantitative Muscle Analysis in FSHD Using Whole-Body Fat-Referenced MRI: Composite Scores for Longitudinal and Cross-Sectional Analysis

BACKGROUND AND OBJECTIVES

Facioscapulohumeral muscular dystrophy (FSHD) is a rare, debilitating disease characterized by progressive muscle weakness. MRI is a sensitive assessment of disease severity and progression. We developed a quantitative whole-body (WB) musculoskeletal MRI (WB-MSK-MRI) protocol analyzing muscles in their entirety. This study aimed to assess WB-MSK-MRI as a potential imaging biomarker providing reliable measurements of muscle health that capture disease heterogeneity and clinically meaningful composite assessments correlating with severity and more responsive to change in clinical trials.

METHODS

Participants 18 to 65 years, genetically confirmed FSHD1, clinical severity 2 to 4 (Ricci's scale, range 0-5), and ≥1 short tau inversion recovery (STIR)-positive lower extremity muscle eligible for needle biopsy enrolled at 6 sites; imaged twice 4 - 12 weeks apart. Volumetric analysis of muscle fat infiltration (MFI), muscle fat fraction (MFF), and lean muscle volume (LMV) in 18 (36 total) muscles from bilateral shoulder, proximal arm, trunk, and legs was performed after automated atlas-based segmentation followed by manual verification. A WB composite score, including muscles at highest risk for progression, and functional cross-sectional composites for correlation with relevant functional outcomes including timed up and go (TUG), FSHD-TUG, and reachable workspace (RWS) were developed.

RESULTS

Seventeen participants;16 follow-up MRIs performed at 52 days (range 36 to 85). Functional cross-sectional composites (MFF and MFI) showed moderate to strong correlations: TUG (rho=0.71, rho=0.83), FSHD-TUG (rho=0.73, rho=0.73), and RWS (left arm: rho=-0.71, rho=-0.53; right arm: rho=-0.61, rho=-0.65). WB composite variability:LMV_tot, coefficient of variation (CV) 1.9% and 3.4%; MFF_tot, within-subject standard deviation (S_w) 0.5% and 1.5%; MFI_tot, (S_w), 0.3% and 0.4% for normal and intermediate muscles respectively. CV and S_w were higher in intermediate (MFI≥0.10; MFF<0.50) than in normal (MFI<0.10, MFF<0.50) muscles.

DISCUSSION

We developed a WB-MSK-MRI protocol and composite measures that capture disease heterogeneity and assess muscle involvement as it correlates with FSHD-relevant clinical endpoints. Functional composites robustly correlate with functional assessments. Stability of the WB composite shows it could be an assessment of change in therapeutic clinical trials.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that quantitative WB-MSK-MRI findings associate with FSHD1 severity measured using established functional assessments.

MRI Assessment of Motor Capabilities in Patients with Duchenne Muscular Dystrophy According to the Motor Function Measure Scale

The research was aimed on the study of motor capabilities on the Motor Function Measure (MFM) scale in ambulant and non-ambulant patients with Duchenne muscular dystrophy, and to conduct a correlation analysis between the results of the MFM scale and Magnetic Resonance Imaging (MRI) data. A total of 46 boys who had genetically confirmed Duchenne muscular dystrophy (age from 2.1 to 16.7 years) and were in clinical rehabilitation were investigated. An assessment was performed according to the Motor Function Measure scale (subsections D1, D2, D3, and the total score), an MRI obtaining T1-VI of the muscles of the pelvic girdle was conducted, and the thighs and lower legs were further assessed in terms of the severity of fibrous-fat degeneration according to the Mercuri scale. In ambulant patients, the ability to stand up and move (D1) was 74.4%, axial and proximal motor functions (D2)—97.6%, distal motor functions (D3)—96.2%, and total score was 87.9%. In non-ambulant patients, the ability to stand up and move (D1) was 1.7%, axial and proximal motor functions (D2)—47%, distal motor functions (D3)—67.5%, and the total score—33.1%. A high inverse correlation (r = −0.7, p < 0.05) of the MRI data of the pelvic girdle and thighs with tasks D1, as well as a noticeable inverse correlation with tasks D2 (r = −0.6, p < 0.05) of the scale MFM, were revealed in the ambulant group of patients. In the non-ambulant group of patients, the MRI data of the lower legs muscles were characterized by a high inverse correlation (r = −0.7, p < 0.05) with tasks D3 and a noticeable inverse correlation (r = −0.6, p < 0.05) with tasks D1 of the MFM scale. Conclusion: The Motor Function Measure scale allows effective assessment of the motor capabilities of patients with Duchenne muscular dystrophy at different stages of the disease, which is confirmed by visualization of fibro-fatty muscle replacement.

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.

Development of Contractures in DMD in Relation to MRI-Determined Muscle Quality and Ambulatory Function

BACKGROUND

Joint contractures are common in boys and men with Duchenne muscular dystrophy (DMD), and management of contractures is an important part of care. The optimal methods to prevent and treat contractures are controversial, and the natural history of contracture development is understudied in glucocorticoid treated individuals at joints beyond the ankle.

OBJECTIVE

To describe the development of contractures over time in a large cohort of individuals with DMD in relation to ambulatory ability, functional performance, and muscle quality measured using magnetic resonance imaging (MRI) and spectroscopy (MRS).

METHODS

In this longitudinal study, range of motion (ROM) was measured annually at the hip, knee, and ankle, and at the elbow, forearm, and wrist at a subset of visits. Ambulatory function (10 meter walk/run and 6 minute walk test) and MR-determined muscle quality (transverse relaxation time (T2) and fat fraction) were measured at each visit.

RESULTS

In 178 boys with DMD, contracture prevalence and severity increased with age. Among ambulatory participants, more severe contractures (defined as greater loss of ROM) were significantly associated with worse ambulatory function, and across all participants, more severe contractures significantly associated with higher MRI T2 or MRS FF (ρ: 0.40-0.61 in the lower extremity; 0.20-0.47 in the upper extremity). Agonist/antagonist differences in MRI T2 were not strong predictors of ROM.

CONCLUSIONS

Contracture severity increases with disease progression (increasing age and muscle involvement and decreasing functional ability), but is only moderately predicted by muscle fatty infiltration and MRI T2, suggesting that other changes in the muscle, tendon, or joint contribute meaningfully to contracture formation in DMD.

Leveraging Cardiac Magnetic Resonance Imaging to Assess Skeletal Muscle Progression in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is characterized by muscle deterioration and progressive weakness. As a result, patients with DMD have significant cardiopulmonary morbidity and mortality that worsens with age and loss of ambulation. Since most validated muscle assessments require ambulation, new functional measures of DMD progression are needed. Despite several evaluation methods available for monitoring disease progression, the relationship between these measures is unknown. We sought to assess the correlation between imaging metrics obtained from cardiac magnetic resonance imaging (CMR) and functional assessments including quantitative muscle testing (QMT), spirometry, and accelerometry. Forty-nine patients with DMD were enrolled and underwent CMR, accelerometry and QMT at baseline, 1-year and 2-year clinic visits with temporally associated pulmonary function testing obtained from the medical record. Imaging of the upper extremity musculature (triceps and biceps) demonstrated the most robust correlations with accelerometry (p<0.03), QMT (p<0.02) and spirometry (p<0.01). T₁-mapping of serratus anterior muscle showed a similar, but slightly weaker relationship with accelerometry and QMT. T₂-mapping of serratus anterior demonstrated weak indirect correlation with aspects of accelerometry. These images are either routinely obtained in standard CMR or can be added to a protocol and may allow for a more comprehensive assessment of a patient's disease progression.

Clinical and Genetic Characteristics in Young, Glucocorticoid-Naive Boys With Duchenne Muscular Dystrophy

BACKGROUND AND OBJECTIVES

Duchenne muscular dystrophy (DMD) is a pediatric neuromuscular disorder caused by mutations in the dystrophin gene. Genotype-phenotype associations have been examined in glucocorticoid-treated boys, but there are few data on the young glucocorticoid-naive DMD population. A sample of young glucocorticoid-naive DMD boys is described, and genotype-phenotype associations are investigated.

METHODS

Screening and baseline data were collected for all the participants in the Finding the Optimum Corticosteroid Regime for Duchenne Muscular Dystrophy (FOR-DMD) study, an international, multicenter, randomized, double-blind, clinical trial comparing 3 glucocorticoid regimens in glucocorticoid-naive, genetically confirmed boys with DMD between 4 and <8 years of age.

RESULTS

One hundred ninety-six boys were recruited. The mean ± SD age at randomization was 5.8 ± 1.0 years. The predominant mutation type was out-of-frame deletions (67.4%, 130 of 193), of which 68.5% (89 of 130) were amenable to exon skipping. The most frequent mutations were deletions amenable to exon 51 skipping (13.0%, 25 of 193). Stop codon mutations accounted for 10.4% (20 of 193). The mean age at first parental concerns was 29.8 ± 18.7 months; the mean age at genetic diagnosis was 53.9 ± 21.9 months; and the mean diagnostic delay was 25.9 ± 18.2 months. The mean diagnostic delay for boys diagnosed after an incidental finding of isolated hyperCKemia (n = 19) was 6.4 ± 7.4 months. The mean ages at independent walking and talking in sentences were 17.1 ± 4.2 and 29.0 ± 10.7 months, respectively. Median height percentiles were below the 25th percentile regardless of age group. No genotype-phenotype associations were identified expect for boys with exon 8 skippable deletions, who had better performance on time to walk/run 10 m (p = 0.02) compared to boys with deletions not amenable to skipping.

DISCUSSION

This study describes clinical and genetic characteristics of a sample of young glucocorticoid-naive boys with DMD. A low threshold for creatine kinase testing can lead to an earlier diagnosis. Motor and speech delays were common presenting symptoms. The effects of low pretreatment height on growth and adult height require further study. These findings may promote earlier recognition of DMD and inform study design for future clinical trials. TRIAL REGISTRATION INFORMATION: ClinicalTrials.gov Identifier: NCT01603407.

Step Activity Monitoring in Boys with Duchenne Muscular Dystrophy and its Correlation with Magnetic Resonance Measures and Functional Performance

BACKGROUND

Muscles of boys with Duchenne muscular dystrophy (DMD) are progressively replaced by fatty fibrous tissues, and weakness leads to loss of ambulation (LoA). Step activity (SA) monitoring is a quantitative measure of real-world ambulatory function. The relationship between quality of muscle health and SA is unknown in DMD.

OBJECTIVE

To determine SA in steroid treated boys with DMD across various age groups, and to evaluate the association of SA with quality of muscle health and ambulatory function.

METHODS

Quality of muscle health was measured by magnetic resonance (MR) imaging transverse magnetization relaxation time constant (MRI-T2) and MR spectroscopy fat fraction (MRS-FF). SA was assessed via accelerometry, and functional abilities were assessed through clinical walking tests. Correlations between SA, MR, and functional measures were determined. A threshold value of SA was determined to predict the future LoA.

RESULTS

The greatest reduction in SA was observed in the 9- < 11years age group. SA correlated with all functional and MR measures.10m walk/run test had the highest correlation with SA. An increase in muscle MRI-T2 and MRS-FF was associated with a decline in SA. Two years prior to LoA, SA in boys with DMD was 32% lower than age matched boys with DMD who maintained ambulation for more than two-year period. SA monitoring can predict subsequent LoA in Duchenne, as a daily step count of 3200 at baseline was associated with LoA over the next two-years.

CONCLUSION

SA monitoring is a feasible and accessible tool to measure functional capacity in the real-world environment.

Characterization of patients with Becker muscular dystrophy by histology, magnetic resonance imaging, function, and strength assessments

Introduction/Aims

Becker muscular dystrophy (BMD) is characterized by variable disease severity and progression, prompting the identification of biomarkers for clinical trials. We used data from an ongoing phase II study to provide a comprehensive characterization of a cohort of patients with BMD, and to assess correlations between histological and magnetic resonance imaging (MRI) markers with muscle function and strength.

Methods

Eligible patients were ambulatory males with BMD, aged 18 to 65 years (200 to 450 meters on 6‐minute walk test). The following data were obtained: function test results, strength, fat‐fraction quantification using chemical shift‐encoded MRI (whole thigh and quadriceps), and fibrosis and muscle fiber area (MFA) of the brachial biceps.

Results

Of 70 patients screened, 51 entered the study. There was substantial heterogeneity between patients in muscle morphology (histology and MRI), with high fat replacement. Total fibrosis correlated significantly and mostly moderately with all functional endpoints, including both upper arm strength assessments (left and right elbow flexion rho −.574 and −.588, respectively [both P < .0001]), as did MRI fat fraction (whole thigh and quadriceps), for example, with four‐stair‐climb velocity −.554 and −.550, respectively (both P < .0001). Total fibrosis correlated significantly and moderately with both MRI fat fraction assessments (.500 [P = .0003] and .423 [.0024], respectively).

Discussion

In this BMD cohort, micro‐ and macroscopic morphological muscle parameters correlated moderately with each other and with functional parameters, potentially supporting the use of MRI fat fraction and histology as surrogate outcome measures in patients with BMD, although additional research is required to validate this.

Longitudinal Motor Functional Outcomes and Magnetic Resonance Imaging Patterns of Muscle Involvement in Upper Limbs in Duchenne Muscular Dystrophy

Background and Objectives: The aim of this study was to evaluate longitudinal changes using both upper limb muscle Magnetic Resonance Imaging (MRI) at shoulder, arm and forearm levels and Performance of upper limb (PUL) in ambulant and non-ambulant Duchenne Muscular Dystrophy (DMD) patients. We also wished to define whether baseline muscle MRI could help to predict functional changes after one year. Materials and Methods: Twenty-seven patients had both baseline and 12month muscle MRI and PUL assessments one year later. Results: Ten were ambulant (age range 5–16 years), and 17 non ambulant (age range 10–30 years). Increased abnormalities equal or more than 1.5 point on muscle MRI at follow up were found on all domains: at shoulder level 12/27 patients (44%), at arm level 4/27 (15%) and at forearm level 6/27 (22%). Lower follow up PUL score were found in 8/27 patients (30%) at shoulder level, in 9/27 patients (33%) at mid-level whereas no functional changes were found at distal level. There was no constant association between baseline MRI scores and follow up PUL scores at arm and forearm levels but at shoulder level patients with moderate impairment on the baseline MRI scores between 16 and 34 had the highest risk of decreased function on PUL over a year. Conclusions: Our results confirmed that the integrated use of functional scales and imaging can help to monitor functional and MRI changes over time.

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.

Knee Strength and Ankle Range of Motion Impacts on Timed Function Tests in Duchenne Muscular Dystrophy: In the Era of Glucocorticoids

BACKGROUND

Duchenne Muscular Dystrophy (DMD) is a neuromuscular disorder that presents in childhood and is characterized by slowly progressive proximal weakness and lower extremity contractures that limit ambulatory ability [1, 2]. Contractures develop in the ankles, knees, and hips due to muscle imbalances, fibrotic changes, loss of strength, and static positioning [2, 5]. Currently, standards of care guidelines emphasize the importance of maintaining good musculoskeletal alignment through stretching, bracing, and glucocorticoid (GC) therapy to preserve strength and function.

METHODS

This is a retrospective analysis of prospectively collected data through the CINRG Duchenne Natural history study (DNHS). The objectives of this analysis are to understand the progression of ankle contractures for individuals with DMD and to investigate the relationship between progressive lower limb contractures, knee strength, and Timed Function Tests.A collection of TFTs including supine to stand (STS), 10 meter walk test (10MWT), and timed stair climbing (4SC) have been used to monitor disease progression and are predictive of loss of ambulation in these patients [4]. Multiple factors contribute to loss of ambulation, including progressive loss of strength and contracture development that leads to changing biomechanical demands for ambulation. A better understanding of the changes in strength and range of motion (ROM) that contribute to loss of function is important in a more individualized rehabilitation management plan. In this longitudinal study, we measured strength using quantitative muscle testing (QMT) with the CINRG Quantitative Measurement System (CQMS)), ROM was measuresed with a goniometer and TFTs were measured using a standard stopwatch and methodology.

RESULTS

We enrolled 440 participants; mean baseline age was 8.9 (2.1, 28.0) years with 1321 observations used for analysis. GC use was stratified based on duration on drug with 18.7%at <  6 months or naïve; 4.3%<1 year; 58.0%1 <  10 years; and 19.3%between 10-25 years of GC use. Ankle ROM was better for those on GC compared to GC naive but did not significantly influence long-term progression rates. QMT, ROM, age and GCs contribute to speed of TFTs. Knee extension (KE) strength and Dorsiflexion (DF) ROM are significant predictors of speed for all TFTs (p <  0.001). Of the variables used in this analysis, KE strength is the primary predictor of walking speed, estimating that every pound increase in KE results in a 0.042 m/s improvement in 10MWT, and a smaller similar increase of 0.009 m/s with every degree of ankle DF ROM.

CONCLUSION

GC use provides an improvement in strength and ROM but does not affect rate of change. Knee strength has a greater influence on speed of TFTs than DF ROM, although both are statistically significant predictors of speed. Results show that retaining knee strength [1, 2], along with joint flexibility, may be important factors in the ability to perform walking, climbing and supine to stand activities.

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.

Association of Elbow Flexor MRI Fat Fraction With Loss of Hand-to-Mouth Movement in Patients With Duchenne Muscular Dystrophy

BACKGROUND AND OBJECTIVES

To study the potential of quantitative MRI (qMRI) fat fraction (FF) as a biomarker in nonambulant patients with Duchenne muscular dystrophy (DMD), we assessed the additive predictive value of elbow flexor FF to age at loss of hand-to-mouth movement.

METHODS

Nonambulant patients with DMD (age ≥8 years) were included. Four-point Dixon MRI scans of the right upper arm were performed at baseline and at the 12-, 18-, or 24-month follow-up. Elbow flexor FFs were determined from 5 central slices. Loss of hand-to-mouth movement was determined at study visits and by phone calls every 4 months. FFs were fitted to a sigmoidal curve by use of a mixed model with random slope to predict individual trajectories. The added predictive value of elbow flexor FF to age at loss of hand-to-mouth movement was calculated from a Cox model with the predicted FF as a time-varying covariate, yielding a hazard ratio.

RESULTS

Forty-eight MRIs of 20 patients with DMD were included. The hazard ratio of a percent-point increase in elbow flexor FF for the time to loss of hand-to-mouth movement was 1.12 (95% confidence interval 1.04-1.21; p = 0.002). This corresponded to a 3.13-fold increase in the instantaneous risk of loss of hand-to-mouth movement in patients with a 10-percent points higher elbow flexor FF at any age.

DISCUSSION

In this prospective study, elbow flexor FF predicted loss of hand-to-mouth movement independently of age. qMRI-measured elbow flexor FF can be used as a surrogate endpoint or stratification tool for clinical trials in nonambulant patients with DMD.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that qMRI FF of elbow flexor muscles in patients with DMD predicts loss of hand-to-mouth movement independently of age.

Profoundly lower muscle mass and rate of contractile protein synthesis in boys with Duchenne muscular dystrophy

Boys with Duchenne muscular dystrophy (DMD) experience a progressive loss of functional muscle mass, with fibrosis and lipid accumulation. Accurate evaluation of whole-body functional muscle mass (MM) in DMD patients has not previously been possible and the rate of synthesis of muscle proteins remains unexplored. We used non-invasive, stable isotope-based methods from plasma and urine to measure the fractional rate of muscle protein synthesis (FSR) functional muscle mass (MM), and fat free mass (FFM) in 10 DMD (6-17 years) and 9 age-matched healthy subjects. An oral dose of D₃ creatine in 70% ² H₂ O was administered to determine MM and FFM followed by daily 70% ² H₂ O to measure protein FSR. Functional MM was profoundly reduced in DMD subjects compared to controls (17% vs. 41% of body weight, P < 0.0001), particularly in older, non-ambulant patients in whom functional MM was extraordinarily low (<13% body weight). We explored the urine proteome to measure FSR of skeletal muscle-derived proteins. Titin, myosin light chain and gelsolin FSRs were substantially lower in DMD subjects compared to controls (27%, 11% and 40% of control, respectively, P < 0.0001) and were strongly correlated. There were no differences in muscle-derived sarcoplasmic proteins FSRs (creatine kinase M-type and carbonic anhydrase-3) measured in plasma. These data demonstrate that both functional MM, body composition and muscle protein synthesis rates can be quantified non-invasively and are markedly different between DMD and control subjects and suggest that the rate of contractile but not sarcoplasmic protein synthesis is affected by a lack of dystrophin. KEY POINTS: Duchenne muscular dystrophy (DMD) results in a progressive loss of functional skeletal muscle but total body functional muscle mass or rates of muscle protein synthesis have not previously been assessed in these patients. D₃ -creatine dilution was used to measure total functional muscle mass and oral ² H₂ O was used to examine the rates of muscle protein synthesis non-invasively in boys with DMD and healthy controls using urine samples. Muscle mass was profoundly lower in DMD compared to control subjects, particularly in older, non-ambulant patients. The rates of contractile protein synthesis but not sarcoplasmic proteins were substantially lower in DMD. These results may provide non-invasive biomarkers for disease progression and therapeutic efficacy in DMD and other neuromuscular diseases.

Water-Fat Separation in MR Fingerprinting for Quantitative Monitoring of the Skeletal Muscle in Neuromuscular Disorders

Background Quantitative MRI is increasingly proposed in clinical trials related to neuromuscular disorders (NMDs). Purpose To investigate the potential of an MR fingerprinting sequence for water and fat fraction (FF) quantification (MRF T1-FF) for providing markers of fatty replacement and disease activity in patients with NMDs and to establish the sensitivity of water T1 as a marker of disease activity compared with water T2 mapping. Materials and Methods Data acquired between March 2018 and March 2020 from the legs of patients with NMDs were retrospectively analyzed. The MRI examination comprised fat-suppressed T2-weighted imaging, mapping of the FF measured with the three-point Dixon technique (FF_Dixon), water T2 mapping, and MRF T1-FF, from which the FF measured with MRF T1-FF (FF_MRF) and water T1 were derived. Data from the legs of healthy volunteers were prospectively acquired between January and July 2020 to derive abnormality thresholds for FF, water T2, and water T1 values. Kruskal-Wallis tests and receiver operating characteristic curve analysis were performed, and linear models were used. Results A total of 73 patients (mean age ± standard deviation, 47 years ± 12; 45 women) and 15 healthy volunteers (mean age, 33 years ± 8; three women) were evaluated. A linear correlation was observed between FF_MRF and FF_Dixon (R² = 0.97, P < .001). Water T1 values were higher in muscles with high signal intensity at fat-suppressed T2-weighted imaging than in muscles with low signal intensity (mean value, 1281 msec [95% CI: 1165, 1604] vs 1198 msec [95% CI: 1099, 1312], respectively; P < .001), and a correlation was found between water T1 and water T2 distribution metrics (R² = 0.66 and 0.79 for the median and 90th percentile values, respectively; P < .001). Water T1 classified the patients' muscles as abnormal based on quantitative water T2, with high sensitivity (93%; 68 of 73 patients) and specificity (80%; 53 of 73 patients) (area under the receiver operating characteristic curve, 0.92 [95% CI: 0.83, 0.97]; P < .001). Conclusion Water-fat separation in MR fingerprinting is robust for deriving quantitative imaging markers of intramuscular fatty replacement and disease activity in patients with neuromuscular disorders. © RSNA, 2021 Online supplemental material is available for this article.

Selection Approach to Identify the Optimal Biomarker Using Quantitative Muscle MRI and Functional Assessments in Becker Muscular Dystrophy

Objective

To identify the best quantitative fat–water MRI biomarker for disease progression of leg muscles in Becker muscular dystrophy (BMD) by applying a stepwise approach based on standardized response mean (SRM) over 24 months, correlations with baseline ambulatory tests, and reproducibility.

Methods

Dixon fat–water imaging was performed at baseline (n = 24) and 24 months (n = 20). Fat fractions (FF) were calculated for 3 center slices and the whole muscles for 19 muscles and 6 muscle groups. Contractile cross-sectional area (cCSA) was obtained from the center slice. Functional assessments included knee extension and flexion force and 3 ambulatory tests (North Star Ambulatory Assessment [NSAA], 10-meter run, 6-minute walking test). MRI measures were selected using SRM (≥0.8) and correlation with all ambulatory tests (ρ ≤ −0.8). Measures were evaluated based on intraclass correlation coefficient (ICC) and SD of the difference. Sample sizes were calculated assuming 50% reduction in disease progression over 24 months in a clinical trial with 1:1 randomization.

Results

Median whole muscle FF increased between 0.2% and 2.6% without consistent cCSA changes. High SRMs and strong functional correlations were found for 8 FF but no cCSA measures. All measures showed excellent ICC (≥0.999) and similar SD of the interrater difference. Whole thigh 3 center slices FF was the best biomarker (SRM 1.04, correlations ρ ≤ −0.81, ICC 1.00, SD 0.23%, sample size 59) based on low SD and acquisition and analysis time.

Conclusion

In BMD, median FF of all muscles increased over 24 months. Whole thigh 3 center slices FF reduced the sample size by approximately 40% compared to NSAA.

Plasma lipidomic analysis shows a disease progression signature in mdx mice

Duchenne muscular dystrophy (DMD) is a rare genetic disorder affecting paediatric patients. The disease course is characterized by loss of muscle mass, which is rapidly substituted by fibrotic and adipose tissue. Clinical and preclinical models have clarified the processes leading to muscle damage and myofiber degeneration. Analysis of the fat component is however emerging as more evidence shows how muscle fat fraction is associated with patient performance and prognosis. In this article we aimed to study whether alterations exist in the composition of lipids in plasma samples obtained from mouse models. Analysis of plasma samples was performed in 4 mouse models of DMD and wild-type mice by LC–MS. Longitudinal samplings of individual mice covering an observational period of 7 months were obtained to cover the different phases of the disease. We report clear elevation of glycerolipids and glycerophospholipids families in dystrophic mice compared to healthy mice. Triacylglycerols were the strongest contributors to the signatures in mice. Annotation of individual lipids confirmed the elevation of lipids belonging to these families as strongest discriminants between healthy and dystrophic mice. A few sphingolipids (such as ganglioside GM2, sphingomyelin and ceramide), sterol lipids (such as cholesteryl oleate and cholesteryl arachidonate) and a fatty acyl (stearic acid) were also found to be affected in dystrophic mice. Analysis of serum and plasma samples show how several lipids are affected in dystrophic mice affected by muscular dystrophy. This study sets the basis to further investigations to understand how the lipid signature relates to the disease biology and muscle performance.

Quantitative muscle MRI biomarkers in Duchenne muscular dystrophy: cross-sectional correlations with age and functional tests

Aim: Using baseline data from a clinical trial of domagrozumab in Duchenne muscular dystrophy, we evaluated the correlation between functional measures and quantitative MRI assessments of thigh muscle. Patients & methods: Analysis included timed functional tests, knee extension/strength and North Star Ambulatory Assessment. Patients (n = 120) underwent examinations of one thigh, with MRI sequences to enable measurements of muscle volume (MV), MV index, mean T2 relaxation time via T2-mapping and fat fraction. Results: MV was moderately correlated with strength assessments. MV index, fat fraction and T2-mapping measures had moderate correlations (r ∼ 0.5) to all functional tests, North Star Ambulatory Assessment and age. Conclusion: The moderate correlation between functional tests, age and baseline MRI measures supports MRI as a biomarker in Duchenne muscular dystrophy clinical trials. Trial registration: ClinicalTrials.gov, NCT02310763; registered 4 November 2014.

Preserved thenar muscles in non-ambulant Duchenne muscular dystrophy patients

BACKGROUND

Clinical trials in Duchenne muscular dystrophy (DMD) focus primarily on ambulant patients. Results cannot be extrapolated to later disease stages due to a decline in targeted muscle tissue. In non-ambulant DMD patients, hand function is relatively preserved and crucial for daily-life activities. We used quantitative MRI (qMRI) to establish whether the thenar muscles could be valuable to monitor treatment effects in non-ambulant DMD patients.

METHODS

Seventeen non-ambulant DMD patients (range 10.2-24.1 years) and 13 healthy controls (range 9.5-25.4 years) underwent qMRI of the right hand at 3 T at baseline. Thenar fat fraction (FF), total volume (TV), and contractile volume (CV) were determined using 4-point Dixon, and T2_water was determined using multiecho spin-echo. Clinical assessments at baseline (n = 17) and 12 months (n = 13) included pinch strength (kg), performance of the upper limb (PUL) 2.0, DMD upper limb patient reported outcome measure (PROM), and playing a video game for 10 min using a game controller. Group differences and correlations were assessed with non-parametric tests.

RESULTS

Total volume was lower in patients compared with healthy controls (6.9 cm³ , 5.3-9.0 cm³ vs. 13.0 cm³ , 7.6-15.8 cm³ , P = 0.010). CV was also lower in patients (6.3 cm³ , 4.6-8.3 cm³ vs. 11.9 cm³ , 6.9-14.6 cm³ , P = 0.010). FF was slightly elevated (9.7%, 7.3-11.4% vs. 7.7%, 6.6-8.4%, P = 0.043), while T2_water was higher (31.5 ms, 30.0-32.6 ms vs. 28.1 ms, 27.8-29.4 ms, P < 0.001). Pinch strength and PUL decreased over 12 months (2.857 kg, 2.137-4.010 to 2.243 kg, 1.930-3.339 kg, and 29 points, 20-36 to 23 points, 17-30, both P < 0.001), while PROM did not (49 points, 36-57 to 44 points, 30-54, P = 0.041). All patients were able to play for 10 min at baseline or follow-up, but some did not comply with the study procedures regarding this endpoint. Pinch strength correlated with TV and CV in patients (rho = 0.72 and rho = 0.68) and controls (both rho = 0.89). PUL correlated with TV, CV, and T2_water (rho = 0.57, rho = 0.51, and rho = -0.59).

CONCLUSIONS

Low thenar FF, increased T2_water , correlation of muscle size with strength and function, and the decrease in strength and function over 1 year indicate that the thenar muscles are a valuable and quantifiable target for therapy in later stages of DMD. Further studies are needed to relate these data to the loss of a clinically meaningful milestone.