Near-Infrared Optical Imaging Noninvasively Detects Acutely Damaged Muscle

Muscle damage is currently assessed through methods such as muscle biopsy, serum biomarkers, functional testing, and imaging procedures, each with its own inherent limitations, and a pressing need for a safe, repeatable, inexpensive, and noninvasive modality to assess the state of muscle health remains. Our aim was to develop and assess near-infrared (NIR) optical imaging as a novel noninvasive method of detecting and quantifying muscle damage. An immobilization-reambulation model was used for inducing muscle damage and recovery in the lower hindlimbs in mice. Confirmation of muscle damage was obtained using in vivo indocyanine green-enhanced NIR optical imaging, magnetic resonance imaging, and ex vivo tissue analysis. The soleus of the immobilized-reambulated hindlimb was found to have a greater amount of muscle damage compared to that in the contralateral nonimmobilized limb, confirmed by in vivo indocyanine green-enhanced NIR optical imaging (3.86-fold increase in radiant efficiency), magnetic resonance imaging (1.41-fold increase in T2), and an ex vivo spectrophotometric assay of indocyanine green uptake (1.87-fold increase in normalized absorbance). Contrast-enhanced NIR optical imaging provides a sensitive, rapid, and noninvasive screening method that can be used for imaging and quantifying muscle damage and recovery in vivo.

Resistance training improves strength and functional capacity in persons with multiple sclerosis

The purpose of this study was to evaluate the effect of an eight-week progressive resistance training programme on lower extremity strength, ambulatory function, fatigue and self-reported disability in multiple sclerosis (MS) patients (mean disability score 3.79-0.8). Eight MS subjects volunteered for twice weekly training sessions. During the first two weeks, subjects completed one set of 8 -10 reps at 50% of maximal voluntary contraction (MVC) of knee flexion, knee extension and plantarflexion exercises. In subsequent sessions, the subjects completed one set of 10 -15 repetitions at 70% of MVC. The resistance was increased by 2 -5% when subjects completed 15 repetitions in consecutive sessions. Isometric strength of the quadriceps, hamstring, plantarflexor and dorsiflexor muscle groups was assessed before and after the training programme using an isokinetic dynamometer. Magnetic resonance images of the thigh were acquired before and after the exercise programme as were walking speed (25-ft), number of steps in 3 min, and self-reported fatigue and disability. Knee extension (7.4%), plantarflexion (52%) and stepping performance (8.7%) increased significantly (PB-0.05). Self-reported fatigue decreased (PB-0.05) and disability tended to decrease (P -0.07) following the training programme. MS patients are capable of making positive adaptations to resistance training that are associated with improved ambulation and decreased fatigue.

Multicenter prospective longitudinal study of magnetic resonance biomarkers in a large duchenne muscular dystrophy cohort

OBJECTIVE

The aim of this study was to describe Duchenne muscular dystrophy (DMD) disease progression in the lower extremity muscles over 12 months using quantitative magnetic resonance (MR) biomarkers, collected across three sites in a large cohort.

METHODS

A total of 109 ambulatory boys with DMD (8.7 ± 2.0 years; range, 5.0-12.9) completed baseline and 1-year follow-up quantitative MR imaging (transverse relaxation time constant; MRI-T2 ), MR spectroscopy (fat fraction and (1) H2 O T2 ), and 6-minute walk test (6MWT) measurements. A subset of boys completed additional measurements after 3 or 6 months.

RESULTS

MRI-T2 and fat fraction increased significantly over 12 months in all age groups, including in 5- to 6.9-year-old boys. Significant increases in vastus lateralis (VL) fat fraction were observed in 3 and 6 months. Even in boys whose 6MWT performance improved or remained stable over 1 year, significant increases in MRI-T2 and fat fraction were found. Of all the muscles examined, the VL and biceps femoris long head were the most responsive to disease progression in boys with DMD.

INTERPRETATION

MR biomarkers are responsive to disease progression in 5- to 12.9-year-old boys with DMD and able to detect subclinical disease progression in DMD, even within short (3-6 months) time periods. The measured sensitivity of MR biomarkers in this multicenter study may be critically important to future clinical trials, allowing for smaller sample sizes and/or shorter study windows in this fatal rare disease.

Age-related T2 changes in hindlimb muscles of mdx mice

INTRODUCTION

Magnetic resonance imaging (MRI) was used to monitor changes in the transverse relaxation time constant (T2) in lower hindlimb muscles of mdx mice at different ages.

METHODS

Young (5 weeks), adult (44 weeks), and old mdx (96 weeks), and age-matched control mice were studied. Young mdx mice were imaged longitudinally, whereas adult and old mdx mice were imaged at a single time-point.

RESULTS

Mean muscle T2 and percent of pixels with elevated T2 were significantly different between mdx and control mice at all ages. In young mdx mice, mean muscle T2 peaked at 7-8 weeks and declined at 9-11 weeks. In old mdx mice, mean muscle T2 was decreased compared with young and adult mice, which could be attributed to fibrosis.

CONCLUSIONS

MRI captured longitudinal changes in skeletal muscle integrity of mdx mice. This information will be valuable for pre-clinical testing of potential therapeutic interventions for muscular dystrophy.

¹³C NMR metabolomics: applications at natural abundance

(13)C NMR has many advantages for a metabolomics study, including a large spectral dispersion, narrow singlets at natural abundance, and a direct measure of the backbone structures of metabolites. However, it has not had widespread use because of its relatively low sensitivity compounded by low natural abundance. Here we demonstrate the utility of high-quality (13)C NMR spectra obtained using a custom (13)C-optimized probe on metabolomic mixtures. A workflow was developed to use statistical correlations between replicate 1D (13)C and (1)H spectra, leading to composite spin systems that can be used to search publicly available databases for compound identification. This was developed using synthetic mixtures and then applied to two biological samples, Drosophila melanogaster extracts and mouse serum. Using the synthetic mixtures we were able to obtain useful (13)C-(13)C statistical correlations from metabolites with as little as 60 nmol of material. The lower limit of (13)C NMR detection under our experimental conditions is approximately 40 nmol, slightly lower than the requirement for statistical analysis. The (13)C and (1)H data together led to 15 matches in the database compared to just 7 using (1)H alone, and the (13)C correlated peak lists had far fewer false positives than the (1)H generated lists. In addition, the (13)C 1D data provided improved metabolite identification and separation of biologically distinct groups using multivariate statistical analysis in the D. melanogaster extracts and mouse serum.

Magnetic resonance imaging and spectroscopy assessment of lower extremity skeletal muscles in boys with Duchenne muscular dystrophy: a multicenter cross sectional study

Introduction

Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder that results in functional deficits. However, these functional declines are often not able to be quantified in clinical trials for DMD until after age 7. In this study, we hypothesized that ¹H₂O T₂ derived using ¹H-MRS and MRI-T₂ will be sensitive to muscle involvement at a young age (5–7 years) consistent with increased inflammation and muscle damage in a large cohort of DMD subjects compared to controls.

Methods

MR data were acquired from 123 boys with DMD (ages 5–14 years; mean 8.6 SD 2.2 years) and 31 healthy controls (age 9.7 SD 2.3 years) using 3-Tesla MRI instruments at three institutions (University of Florida, Oregon Health & Science University, and Children’s Hospital of Philadelphia). T₂-weighted multi-slice spin echo (SE) axial images and single voxel ¹H-MRS were acquired from the lower leg and thigh to measure lipid fraction and ¹H₂O T₂.

Results

MRI-T₂, ¹H₂O T₂, and lipid fraction were greater (p<0.05) in DMD compared to controls. In the youngest age group, DMD values were different (p<0.05) than controls for the soleus MRI-T₂, ¹H₂O T₂ and lipid fraction and vastus lateralis MRI-T₂ and ¹H₂O T₂. In the boys with DMD, MRI-T₂ and lipid fraction were greater (p<0.05) in the oldest age group (11–14 years) than the youngest age group (5–6.9 years), while ¹H₂O T₂ was lower in the oldest age group compared to the young age group.

Discussion

Overall, MR measures of T₂ and lipid fraction revealed differences between DMD and Controls. Furthermore, MRI-T₂ was greater in the older age group compared to the young age group, which was associated with higher lipid fractions. Overall, MR measures of T₂ and lipid fraction show excellent sensitivity to DMD disease pathologies and potential therapeutic interventions in DMD, even in the younger boys.

Bone loss in a new rodent model combining spinal cord injury and cast immobilization

OBJECTIVES

Characterize bone loss in our newly developed severe contusion spinal cord injury (SCI) plus hindlimb immobilization (IMM) model and determine the influence of muscle contractility on skeletal integrity after SCI.

METHODS

Female Sprague-Dawley rats were randomized to: (a) intact controls, (b) severe contusion SCI euthanized at Day 7 (SCI-7) or (c) Day 21 (SCI-21), (d) 14 days IMM-alone, (e) SCI+IMM, or (f) SCI+IMM plus 14 days body weight supported treadmill exercise (SCI+IMM+TM).

RESULTS

SCI-7 and SCI-21 exhibited a >20% reduction in cancellous volumetric bone mineral density (vBMD) in the hindlimbs (p⋜0.01), characterized by reductions in cancellous bone volume (cBV/TV%), trabecular number (Tb.N), and trabecular thickness. IMM-alone induced no observable bone loss. SCI+IMM exacerbated cancellous vBMD deficits with values being >45% below Controls (p⋜0.01) resulting from reduced cBV/TV% and Tb.N. SCI+IMM also produced the greatest cortical bone loss with distal femoral cortical area and cortical thickness being 14-28% below Controls (p⋜0.01) and bone strength being 37% below Controls (p⋜0.01). SCI+IMM+TM partially alleviated bone deficits, but values remained below Controls.

CONCLUSIONS

Residual and/or facilitated muscle contractility ameliorate bone decrements after severe SCI. Our novel SCI+IMM model represents a clinically-relevant means of assessing strategies to prevent SCI-induced skeletal deficits.

Examination of effects of corticosteroids on skeletal muscles of boys with DMD using MRI and MRS

OBJECTIVE

To evaluate the effects of corticosteroids on the lower extremity muscles in boys with Duchenne muscular dystrophy (DMD) using MRI and magnetic resonance spectroscopy (MRS).

METHODS

Transverse relaxation time (T2) and fat fraction were measured by MRI/MRS in lower extremity muscles of 15 boys with DMD (age 5.0-6.9 years) taking corticosteroids and 15 corticosteroid-naive boys. Subsequently, fat fraction was measured in a subset of these boys at 1 year. Finally, MRI/MRS data were collected from 16 corticosteroid-naive boys with DMD (age 5-8.9 years) at baseline, 3 months, and 6 months. Five boys were treated with corticosteroids after baseline and the remaining 11 served as corticosteroid-naive controls.

RESULTS

Cross-sectional comparisons demonstrated lower muscle T2 and less intramuscular (IM) fat deposition in boys with DMD on corticosteroids, suggesting reduced inflammation/damage and fat infiltration with treatment. Boys on corticosteroids demonstrated less increase in IM fat infiltration at 1 year. Finally, T2 by MRI/MRS detected effects of corticosteroids on leg muscles as early as 3 months after drug initiation.

CONCLUSIONS

These results demonstrate the ability of MRI/MRS to detect therapeutic effects of corticosteroids in reducing inflammatory processes in skeletal muscles of boys with DMD. Our work highlights the potential of MRI/MRS as a biomarker in evaluating therapeutic interventions in DMD.

Assessment of intramuscular lipid and metabolites of the lower leg using magnetic resonance spectroscopy in boys with Duchenne muscular dystrophy

The purpose of this study was to use proton magnetic resonance spectroscopy to assess intramuscular lipid and metabolites of lower leg muscles in boys with Duchenne muscular dystrophy (DMD) and determine its relationship with strength and functional ability. Spectroscopic measurements were obtained from four muscles of the lower leg in 25 boys with DMD (9.2±3.1 years) and 10 healthy boys (10.2±2.6 years). Lipid fractions and metabolite concentrations were also determined. Muscle strength, a timed functional test, and the Modified Brooke Lower Extremity Functional Scale were also determined. Lipid fractions were higher (p<0.01) for the DMD group than healthy subjects for all muscles, and lipid fraction was found to be greater in the older DMD boys. The peroneal muscle demonstrated a significant difference in lipid fraction in all DMD age groups. Lipid fractions in all muscles correlated with functional measures (r=0.52-0.70, p<0.001), with smaller inverse correlations with the strength measure (r=-0.36 to -0.56, p<0.05). These findings provide quantifiable information regarding intramuscular lipid and metabolite levels of different muscles across various age groups in boys with DMD and may be used in determining the effect of interventions in future clinical trials.

Gene transfer of arginine kinase to skeletal muscle using adeno-associated virus

In this study, we tested the feasibility of non-invasively measuring phosphoarginine (PArg) after gene delivery of arginine kinase (AK) using an adeno-associated virus (AAV) to murine hindlimbs. This was achieved by evaluating the time course, regional distribution and metabolic flux of PArg using (31)phosphorus magnetic resonance spectroscopy ((31)P-MRS). AK gene was injected into the gastrocnemius of the left hindlimb of C57Bl10 mice (age 5 weeks, male) using self-complementary AAV, type 2/8 with desmin promoter. Non-localized (31)P-MRS data were acquired over 9 months after injection using 11.1-T and 17.6-T Bruker Avance spectrometers. In addition, (31)P two-dimensional chemical shift imaging and saturation transfer experiments were performed to examine the spatial distribution and metabolic flux of PArg, respectively. PArg was evident in each injected mouse hindlimb after gene delivery, increased until 28 weeks, and remained elevated for at least 9 months (P<0.05). Furthermore, PArg was primarily localized to the injected posterior hindimb region and the metabolite was in exchange with ATP. Overall, the results show the viability of AAV gene transfer of AK gene to skeletal muscle, and provide support of PArg as a reporter that can be used to non-invasively monitor the transduction of genes for therapeutic interventions.

Participation in daily life activities and its relationship to strength and functional measures in boys with Duchenne muscular dystrophy

PURPOSE

While most studies of Duchenne muscular dystrophy (DMD) have focused on physical impairment, there is a need to explore how impairment impacts real-life experiences in order to provide intervention strategies focused on participation. Objectives were: (1) to investigate the domains of participation in a sample of boys with DMD; (2) to compare a younger (<10 years) and older (≥10 years) group of boys with DMD with regard to participation; (3) to investigate strength and timed functional tests in a sample of boys with DMD; (4) to compare a younger (<10 years) and older (≥10 years) group of boys with DMD with regard to strength and timed functional tests; and (5) to explore associations between participation and strength and timed functional tests for our DMD cohorts.

METHODS

This cross-sectional study included 60 boys with DMD (mean 9.3 years ± 0.3). Boys completed strength testing, timed functional tests, the Children's Assessment of Participation and Enjoyment and the ACTIVLIM. Independent samples t-tests were used to test for differences in all measures between our younger and older cohorts; Spearman's (rank) correlation was used to assess relationships between participation and strength and time functional tests.

RESULTS

Significant differences were found between our younger and older boys with DMD in the areas of recreational (p < 0.01), social (p < 0.001), and skill-based activities (p < 0.05), as well as with whom and where the activities were performed (p < 0.05 and 0.001, respectively). Older boys with DMD report lower levels of participation in these areas, as well as less engagement in activities with individuals other than family members and less participation outside of the home. Lower levels of strength and slower rates of functional performance correlate with participation in fewer physical activities for our younger cohort and fewer physical and social activities for our older cohort.

CONCLUSIONS

Strength and function relate to the variability and type of activities in which boys with DMD participate. A key finding is the significant decline in social activities and community-based engagement as the boys with DMD age. The ultimate goal of an intervention is for our children to be as actively engaged in life as they desire. This requires addressing participation when measuring outcomes in order to more fully understand limitations and provide appropriate strategies for continued participation for boys and their families.

IMPLICATIONS FOR REHABILITATION

Duchenne muscular dystrophy is a devastating progressive neuromuscular disorder that leads to significant strength and functional limitations, which affect physical and social participation for these boys. The ability to move beyond clinically-based outcomes and assess and monitor a child's daily activities through participation measures may provide information for therapeutic interventions. Rehabilitation specialists have a role as advocates for social and community engagement for children with physical limitations. Providing families with information on community-based opportunities, and the strategies and environmental modifications available may increase social participation for our youth growing up with a neuromuscular disorder.

Intrinsic transient tracheal occlusion training and myogenic remodeling of rodent parasternal intercostal fibers

It is recognized that diaphragm muscle plasticity occurs with mechanical overloads, yet less is known about synergistic parasternal intercostal muscle fiber remodeling. We conducted overload training with intrinsic transient tracheal occlusion (ITTO) exercises in conscious animals. We hypothesized that ITTO would yield significant fiber hypertrophy and myogenic activation that would parallel diaphragm fiber remodeling. Sprague-Dawley rats underwent placement of a tracheal cuff and were randomly assigned to receive daily 10 min sessions of conscious ITTO or observation (sham) over 2 wk. After training, fiber morphology, myosin heavy chain (MHC) isoform composition, cross-sectional area, proportion of Pax7-positive nuclei, and presence of embryonic MHC (eMHC) were quantified. Type IIx/b fibers were 20% larger after ITTO training than with sham training (ITTO: 4,431 +/– 676 μm2, sham: 3,689 +/– 400 μm2, p < 0.05), and type I fibers were more prevalent after ITTO (p < 0.01). Expression of Pax7 was increased in ITTO parasternals and diaphragm (p < 0.05). In contrast, the proportion of eMHC-positive fibers was increased only in ITTO parasternals (1.2% [3.4%–0.6%], sham: 0% [0.6%–0%], p < 0.05). Although diaphragm and parasternal type II fibers hypertrophy to a similar degree, myogenic remodeling appears to differ between the two muscles.

Chemical shift-based MRI to measure fat fractions in dystrophic skeletal muscle

PURPOSE

The relationship between fat fractions (FFs) determined based on multiple TE, unipolar gradient echo images and (1) H magnetic resonance spectroscopy (MRS) was evaluated using different models for fat-water decomposition, signal-to-noise ratios, and excitation flip angles.

METHODS

A combination of single-voxel proton spectroscopy ((1) H-MRS) and gradient echo imaging was used to determine muscle FFs in both normal and dystrophic muscles. In order to cover a large range of FFs, the soleus and vastus lateralis muscles of 22 unaffected control subjects, 16 subjects with collagen VI deficiency (COL6), and 71 subjects with Duchenne muscular dystrophy (DMD) were studied. (1) H-MRS-based FF were corrected for the increased muscle (1) H2 O T1 and T2 values observed in dystrophic muscles.

RESULTS

Excellent agreement was found between coregistered FFs derived from gradient echo images fit to a multipeak model with noise bias correction and the relaxation-corrected (1) H-MRS FFs (y = 0.93x + 0.003; R(2)  = 0.96) across the full range of FFs. Relaxation-corrected (1) H-MRS FFs and imaging-based FFs were significantly elevated (P < 0.01) in the muscles of COL6 and DMD subjects.

CONCLUSION

FFs, T2 , and T1 were all sensitive to muscle involvement in dystrophic muscle. MRI offered an additional advantage over single-voxel spectroscopy in that the tissue heterogeneity in FFs could be readily determined.

Skeletal muscles of ambulant children with Duchenne muscular dystrophy: validation of multicenter study of evaluation with MR imaging and MR spectroscopy

PURPOSE

To validate a multicenter protocol that examines lower extremity skeletal muscles of children with Duchenne muscular dystrophy (DMD) by using magnetic resonance (MR) imaging and MR spectroscopy in terms of reproducibility of these measurements within and across centers.

MATERIALS AND METHODS

This HIPAA-compliant study was approved by the institutional review boards of all participating centers, and informed consent was obtained from each participant or a guardian. Standardized procedures with MR operator training and quality assurance assessments were implemented, and data were acquired at three centers by using different 3-T MR imaging instruments. Measures of maximal cross-sectional area (CSAmax), transverse relaxation time constant (T2), and lipid fraction were compared among centers in two-compartment coaxial phantoms and in two unaffected adult subjects who visited each center. Also, repeat MR measures were acquired twice on separate days in 30 boys with DMD (10 per center) and 10 unaffected boys. Coefficients of variation (CVs) were computed to examine the repeated-measure variabilities within and across centers.

RESULTS

CSAmax, T2 from MR imaging and MR spectroscopy, and lipid fraction were consistent across centers in the phantom (CV, <3%) and in the adult subjects who traveled to each site (CV, 2%-7%). High day-to-day reproducibility in MR measures was observed in boys with DMD (CSAmax, CV = 3.7% [25th percentile, 1.3%; 75th percentile, 5.1%]; contractile area, CV = 4.2% [25th percentile, 0.8%; 75th percentile, 4.9%]; MR imaging T2, CV = 3.1% [25th percentile, 1.2%; 75th percentile, 4.7%]; MR spectroscopy T2, CV = 3.9% [25th percentile, 1.5%; 75th percentile, 5.1%]; and lipid fraction, CV = 4.7% [25th percentile, 1.0%; 75th percentile, 5.3%]).

CONCLUSION

The MR protocol implemented in this multicenter study achieved highly reproducible measures of lower extremity muscles across centers and from day to day in ambulatory boys with DMD.

Effect of dietary restriction and exercise on lower extremity tissue compartments in obese, older women: a pilot study

BACKGROUND

Accumulating evidence suggests that both dietary restriction and exercise (DR + E) should be incorporated in weight loss interventions to treat obese, older adults. However, more information is needed on the effects to lower extremity tissue composition-an important consideration for preserving mobility in older adults.

METHODS

Twenty-seven sedentary women (body mass index: 36.3±5.4kg/m(2); age: 63.6±5.6 yrs) were randomly assigned to 6 months of DR + E or a health education control group. Thigh and calf muscle, subcutaneous adipose tissue (SAT), and intermuscular adipose tissue (IMAT) size were determined using magnetic resonance imaging. Physical function was measured using a long-distance corridor walk and knee extension strength.

RESULTS

Compared with control, DR + E significantly reduced body mass (-6.6±3.7kg vs control: -0.05±3.5kg; p < .01). Thigh and calf muscle volumes responded similarly between groups. Within the DR + E group, adipose tissue was reduced more in the thigh than in the calf (p < .04). Knee extension strength was unaltered by DR + E, but a trend toward increased walking speed was observed in the DR + E group (p = .09). Post hoc analyses showed that reductions in SAT and IMAT within the calf, but not the thigh, were associated with faster walking speed achieved with DR + E (SAT: r = -0.62; p = .01; IMAT: r = -0.62; p = .01).

CONCLUSIONS

DR + E preserved lower extremity muscle size and function and reduced regional lower extremity adipose tissue. Although the magnitude of reduction in adipose tissue was greater in the thigh than the calf region, post hoc analyses demonstrated that reductions in calf SAT and IMAT were associated with positive adaptations in physical function.

T₂ mapping provides multiple approaches for the characterization of muscle involvement in neuromuscular diseases: a cross-sectional study of lower leg muscles in 5-15-year-old boys with Duchenne muscular dystrophy

Skeletal muscles of children with Duchenne muscular dystrophy (DMD) show enhanced susceptibility to damage and progressive lipid infiltration, which contribute to an increase in the MR proton transverse relaxation time (T₂). Therefore, the examination of T₂ changes in individual muscles may be useful for the monitoring of disease progression in DMD. In this study, we used the mean T₂, percentage of elevated pixels and T₂ heterogeneity to assess changes in the composition of dystrophic muscles. In addition, we used fat saturation to distinguish T₂ changes caused by edema and inflammation from fat infiltration in muscles. Thirty subjects with DMD and 15 age-matched controls underwent T₂ -weighted imaging of their lower leg using a 3-T MR system. T₂ maps were developed and four lower leg muscles were manually traced (soleus, medial gastrocnemius, peroneal and tibialis anterior). The mean T₂ of the traced regions of interest, width of the T₂ histograms and percentage of elevated pixels were calculated. We found that, even in young children with DMD, lower leg muscles showed elevated mean T₂, were more heterogeneous and had a greater percentage of elevated pixels than in controls. T₂ measures decreased with fat saturation, but were still higher (P < 0.05) in dystrophic muscles than in controls. Further, T₂ measures showed positive correlations with timed functional tests (r = 0.23-0.79). The elevated T₂ measures with and without fat saturation at all ages of DMD examined (5-15 years) compared with unaffected controls indicate that the dystrophic muscles have increased regions of damage, edema and fat infiltration. This study shows that T₂ mapping provides multiple approaches that can be used effectively to characterize muscle tissue in children with DMD, even in the early stages of the disease. Therefore, T₂ mapping may prove to be clinically useful in the monitoring of muscle changes caused by the disease process or by therapeutic interventions in DMD.

MRI/MRS evaluation of a female carrier of Duchenne muscular dystrophy

The purpose of this study was to evaluate skeletal muscle composition of lower extremity muscles in a manifesting female carrier of Duchenne muscular dystrophy (MFC(DMD)) using magnetic resonance imaging (MRI) and spectroscopy (MRS). MRI/MRS was performed on the lower extremities and heart of a MFC(DMD) (47 years, 51 kg) on four occasions within 21 months and in a control subject. Heterogeneity and asymmetry among muscles in the MFC(DMD) was observed in lipid fraction and mean transverse relaxation time (T(2)) of lower extremity muscles with some muscles presenting as unaffected (e.g., rectus femoris) and others showing substantial deterioration and lipid infiltration (e.g., vasti muscles). There was an association of abnormal MRI findings and strength and motor function. Over the 21 months a small decrease in CSA(max) and increase in lipid fraction and T(2) was observed in the MFC(DMD) in some muscles. In summary, this MFC(DMD) revealed significant imaging evidence of pathologic heterogeneity among muscles. Furthermore, this study shows the feasibility of combining various quantitative MRI and MRS approaches to monitor skeletal muscle involvement.

Hindlimb muscle morphology and function in a new atrophy model combining spinal cord injury and cast immobilization

Contusion spinal cord injury (SCI) animal models are used to study loss of muscle function and mass. However, parallels to the human condition typically have been confounded by spontaneous recovery observed within the first few post-injury weeks, partly because of free cage activity. We implemented a new rat model combining SCI with cast immobilization (IMM) to more closely reproduce the unloading conditions experienced by SCI patients. Magnetic resonance imaging was used to monitor hindlimb muscles' cross-sectional area (CSA) after SCI, IMM alone, SCI combined with IMM (SCI+IMM), and in controls (CTR) over a period of 21 days. Soleus muscle tetanic force was measured in situ on day 21, and hindlimb muscles were harvested for histology. IMM alone produced a decrease in triceps surae CSA to 63.9±4.9% of baseline values within 14 days. In SCI, CSA decreased to 75.0±10.5% after 7 days, and recovered to 77.9±10.7% by day 21. SCI+IMM showed the greatest amount of atrophy (56.9±9.9% on day 21). In all groups, muscle mass and soleus tetanic force decreased in parallel, such that specific force was maintained. Extensor digitorum longus (EDL) and soleus fiber size decreased in all groups, particularly in SCI+IMM. We observed a significant degree of asymmetry in muscle CSA in SCI but not IMM. This effect increased between day 7 and 21 in SCI, but also in SCI+IMM, suggesting a minor dependence on muscle activity. SCI+IMM offers a clinically relevant model of SCI to investigate the mechanistic basis for skeletal muscle adaptations after SCI and develop therapeutic approaches.