MR quantification of muscle fatty replacement in McArdle's disease

Muscle MRI in McArdle Disease: A European Multicenter Observational Study

BACKGROUND AND OBJECTIVES

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

METHODS

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

RESULTS

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

DISCUSSION

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

Quantification of intermuscular and intramuscular adipose tissue using magnetic resonance imaging after neurodegenerative disorders

Ectopic adiposity has gained considerable attention because of its tight association with metabolic and cardiovascular health in persons with spinal cord injury (SCI). Ectopic adiposity is characterized by the storage of adipose tissue in non-subcutaneous sites. Magnetic resonance imaging (MRI) has proven to be an effective tool in quantifying ectopic adiposity and provides the opportunity to measure different adipose depots including intermuscular adipose tissue (IMAT) and intramuscular adipose tissue (IntraMAT) or intramuscular fat (IMF). It is highly important to distinguish and clearly define these compartments, because controversy still exists on how to accurately quantify these adipose depots. Investigators have relied on separating muscle from fat pixels based on their characteristic signal intensities. A common technique is plotting a threshold histogram that clearly separates between muscle and fat peaks. The cut-offs to separate between muscle and fat peaks are still not clearly defined and different cut-offs have been identified. This review will outline and compare the Midpoint and Otsu techniques, two methods used to determine the threshold between muscle and fat pixels on T1 weighted MRI. The process of water/fat segmentation using the Dixon method will also be outlined. We are hopeful that this review will trigger more research towards accurately quantifying ectopic adiposity due to its high relevance to cardiometabolic health after SCI.

Magnetic resonance imaging of skeletal muscle disease

Neuromuscular diseases often exhibit a temporally varying, spatially heterogeneous, and multifaceted pathology. The goals of this chapter are to describe and evaluate the use of quantitative magnetic resonance imaging (MRI) methods to characterize muscle pathology. The following criteria are used for this evaluation: objective measurement of continuously distributed variables; clear and well-understood relationship to the pathology of interest; sensitivity to improvement or worsening of clinical status; and the measurement properties of accuracy and precision. Two major classes of MRI methods meet all of these criteria: (1) MRI methods for measuring muscle contractile volume or cross-sectional area by combining structural MRI and quantitative fat-water MRI; and (2) an MRI method for characterizing the edema caused by inflammation, the measurement of the transverse relaxation time constant (T2). These methods are evaluated with respect to the four criteria listed above and examples from neuromuscular disorders are provided. Finally, these methods are summarized and synthesized and recommendations for additional quantitative MRI developments are made.

Quantification of early fatty infiltration of the rotator cuff muscles: comparison of multi-echo Dixon with single-voxel MR spectroscopy

OBJECTIVES

To evaluate quantification of early fatty infiltration in supraspinatus muscles with magnetic resonance (MR) imaging using a T2*-corrected multi-echo 3D-gradient-echo Dixon-based sequence (multi-echo Dixon) and compare it to proton-MR-spectroscopy.

METHODS

Sixty subjects (mean age 46 years, 41 men) with good supraspinatus muscle quality on 1.5 T MR imaging were included. Fat percentage (FP) in the supraspinatus muscle was quantified using a multi-echo Dixon compared to single-voxel MR spectroscopy as reference standard. In 18 subjects the multi-echo Dixon was repeated to assess test-retest reliability. Measurements based on multi-echo Dixon were performed by two independent readers by placing regions-of-interest (ROIs) in the supraspinatus muscle corresponding to the MR-spectroscopy voxel. Intraclass and concordance correlation coefficients (ICC/CCC) were used for statistical analysis.

RESULTS

Test-retest reliability was substantial for reader 1 (ICC = 0.757) and almost perfect for reader 2 (ICC = 0.873). Inter-reader reliability for multi-echo Dixon was almost perfect (ICC = 0.893, P < .0005). Mean FP in all 60 subjects with multi-echo Dixon was 3.5 ± 1.6 for reader 1, 3.7 ± 1.8 for reader 2, and 2.8 ± 1.4 with MR spectroscopy. Correlation between multi-echo Dixon and MR spectroscopy was moderate (CCC = 0.641).

CONCLUSION

The multi-echo Dixon sequence is a reliable method and comparable to MR-spectroscopy for quantification of low levels of fatty infiltration in the supraspinatus muscle.

KEY POINTS

• Multi-echo Dixon for low fat quantification in muscles is reliable. • Multi-echo Dixon low fat quantification is comparable to single-voxel MR spectroscopy • Multi-echo Dixon detects substantial differences in fatty infiltration within Goutallier 0-1.

McArdle disease: 2 case reports

A high serum level of creatine kinase (CK) is a common reason for referring to medical specialities. Myopathies are one of the causes of elevated levels of CK. McArdle disease is the most common disorder of skeletal muscle carbohydrate metabolism. The cases are presented on 2 patients who were referred to our medical consultation to study the cause of their increased CK levels: a 72 year old asymptomatic man with high levels of CK detected by chance in a routine analysis, and a 30 year old woman with very few symptoms, apart from slight muscle pain and tiredness. Electromyography was normal in both patients. There was null activity of myophosphorylase in muscle biopsy of both cases, so a diagnosis of McArdle disease was made.

Exercise might bias skeletal-muscle fat fraction calculation from Dixon images

We examined the influence of a single exercise session on quantitative muscle fat fraction MRI measurements. Ten healthy volunteers were scanned on a 3T body scanner before and after a session of bilateral squats until muscular fatigue. Axial in- and opposed phase images were acquired at a fixed distance from the knee joint and fat fractions were calculated using a 2-point Dixon technique as well as muscle cross sectional area at the same position. After the squat session, calculated fat fraction in the quadriceps bilaterally appeared to be significantly decreased, while all but one non-exercised muscles showed no change. In conclusion exercise might modify the measured apparent fat fraction. Trials using quantitative MRI should consider the timing of scanning sessions and physical examinations to avoid bias caused by the influence of exercise on measurements.

Obesity in the elderly: is faulty metabolism to blame?

The fastest growing segment of the US population, and that of other developed countries, is the oldest-old (aged >85 years). Many children born after the year 2000 in countries with the longest lived residents may live to see their 100th birthday. The combination of reduced mortality along with reduced fertility in developed countries is producing 'population aging', and the comorbidities associated with aging are becoming important public health issues. Age-associated obesity is one such important public health issue. Aging is associated with significant changes in body composition, including loss of skeletal muscle mass and increased visceral fat accumulation. The loss of muscle mass is accompanied by a disproportionate decline in muscle strength (up to three-times greater than the loss of mass), indicative of reduced muscle 'quality' or muscle dysfunctionality. Aging is characterized by markedly reduced physical activity and a drop in resting metabolic rate that is disproportionate to the loss of muscle mass, with a shift towards preferentially oxidizing carbohydrate at the expense of fat. A combination of these factors may act to increase muscular lipid infiltration and decrease insulin sensitivity; however, the cause and effect relationship remains undetermined. Changes in cellular energy (i.e., ATP) requirement owing to decreased ion channel activity, decreased protein synthesis or increased mitochondrial energy efficiency may underlie the decreased resting metabolic rate. Increasing energy demand through physical activity may alleviate some of the adverse metabolic changes that are associated with aging.

Longitudinal study of muscle strength, quality, and adipose tissue infiltration

BACKGROUND

Sarcopenia is thought to be accompanied by increased muscle fat infiltration. However, no longitudinal studies have examined concomitant changes in muscle mass, strength, or fat infiltration in older adults.

OBJECTIVE

We present longitudinal data on age-related changes in leg composition, strength, and muscle quality (MQ) in ambulatory, well-functioning men and women. We hypothesized that muscle cross-sectional area (CSA) and strength would decrease and muscular fat infiltration would increase over 5 y.

DESIGN

Midthigh muscle, subcutaneous fat (SF), and intermuscular fat (IMF) CSAs and isokinetic leg muscle torque (MT) and MQ (MT/quadriceps CSA) were examined over 5 y in the Health, Aging, and Body Composition study cohort (n = 1678).

RESULTS

Men experienced a 16.1% loss of MT, whereas women experienced a 13.4% loss. Adjusted annualized decreases in MT were 2-5 times greater than the loss of muscle CSA in those who lost weight and in those who remained weight-stable. Weight gain did not prevent the loss of MT, despite a small increase in muscle CSA. Only those who gained weight had an increase in SF (P < 0.001), whereas those who lost weight also lost SF (P < 0.001). There was an age-related increase in IMF in men and women (P < 0.001), and IMF increased in those who lost weight, gained weight, or remained weight-stable (all P < 0.001).

CONCLUSIONS

Loss of leg MT in older adults is greater than muscle CSA loss, which suggests a decrease in MQ. Additionally, aging is associated with an increase in IMF regardless of changes in weight or SF.

Enzyme replacement therapy in adult-onset glycogenosis II: is quantitative muscle MRI helpful?

Although it has been shown that muscle magnetic resonance imaging (MRI) improves the phenotypic characterization of patients with neuromuscular disorders and allows accurate quantification of muscle and adipose tissue distribution, to date quantitative MRI has not been used to assess the therapeutic response in clinical trials of neuromuscular diseases. We discuss quantitative MRI findings after a 6-month course of enzyme replacement therapy administered to nine patients with adult-onset glycogenosis II.

Volumic patient-specific reconstruction of muscular system based on a reduced dataset of medical images

Three-dimensional mechanical modelling of muscles is essential for various biomechanical applications and clinical evaluation, but it requires a tedious manual processing of numerous images. A muscle reconstruction method is presented based on a reduced set of images to generate an approximate parametric object from basic dimensions of muscle contours. A regular volumic mesh is constructed based on this parametric object. The approximate object and the corresponding mesh are deformed to fit the exact muscles contours yielding patient-specific geometry. Evaluation was performed by comparison of geometry to that obtained by contouring all computed tomography (CT) slices, and by quantification of the mesh quality criteria. Muscle fatty infiltration was estimated using a threshold between fat and muscle. Volumic fat index (VFI) of a muscle was computed using first all the complete CT scan slices containing the muscle (VFI(ref)) and a second time only the slices used for reconstruction (VFI(recons)). Mean volume error estimation was 2.6% and hexahedron meshes fulfilled quality criteria. VFI(recons) respect the individual variation of fat content.

A new distal arthrogryposis syndrome characterized by plantar flexion contractures

The distal arthrogryposis (DA) syndromes are a distinct group of disorders characterized by contractures of two or more different body areas. More than a decade ago, we revised the classification of DAs and distinguished several new syndromes. This revision has facilitated the identification of five genes (i.e., TNNI2, TNNT3, MYH3, MYH8, and TPM2) that encode components of the contractile apparatus of fast-twitch myofibers and cause DA syndromes. We now report on the phenotypic features of a novel DA disorder characterized primarily by plantar flexion contractures in a large five-generation Utah family. Contractures of hips, elbows, wrists, and fingers were much milder though they varied in severity among affected individuals. All affected individuals had normal neurological examinations; electromyography and creatinine kinase levels were normal on selected individuals. We have tentatively labeled this condition distal arthrogryposis type 10 (DA10).

Water-saturated three-dimensional balanced steady-state free precession for fast abdominal fat quantification

PURPOSE

To compare the performance of a novel water-saturated b-SSFP sequence with that of a conventional T1-weighted turbo spin echo (T1W TSE) sequence for abdominal fat quantification.

MATERIALS AND METHODS

A water-saturated, segmented, three-dimensional balanced steady-state free precession (b-SSFP) sequence and a traditional T1W TSE sequence were both employed on phantom and human studies. For phantom studies, a dual-layered phantom with known internal/external oil volumes was imaged using the two sequences. Images obtained by the two sequences were both processed using a computer-aided semiautomatic program for oil volume quantification. For human studies, six volunteers were scanned axially, centered at L2-L3 levels. Signal-to-noise ratio (SNR)(fat), contrast-to-noise ratio (CNR)(fat-muscle), CNR(fat-large bowel), and CNR(fat-small bowel) were calculated on hand-drawn regions of interest (ROIs), and averaged over all six slices for each subject. Statistical analyses were then performed to determine the SNR and CNR differences between images obtained by the two techniques.

RESULTS

The phantom studies show that water-saturated b-SSFP offers a significantly closer estimation of true oil volumes compared with that of T1W TSE (P < 0.0001), as well as a more accurate internal/external volume ratio (P = 0.0001). In human studies, three-dimensional water-saturated b-SSFP images demonstrated higher CNR than that of T1W TSE (P < 0.0005), and very close SNR(fat) (P = 0.045).

CONCLUSION

The proposed three-dimensional water-saturated b-SSFP sequence can generate high quality fat-only abdominal images with high CNR and SNR in shorter scan duration than the conventional T1W TSE approach. As images generated by this sequence suffer from no flow artifacts, and are less sensitive to bulk, respiratory, and bowel motion, three-dimensional water-saturated b-SSFP is a faster and more robust method for improving abdominal fat quantification using MRI.

Magnetic resonance imaging analysis of the upper cervical spine extensor musculature in an asymptomatic cohort: an index of fat within muscle

AIM

To establish a simple method to quantify muscle/fat constituents in cervical muscles of asymptomatic women using magnetic resonance imaging (MRI), and to determine whether there is an age effect within a defined age range.

MATERIALS AND METHODS

MRI of the upper cervical spine was performed for 42 asymptomatic women aged 18-45 years. The muscle and fat signal intensities on axial spin echo T1-weighted images were quantitatively classified by taking a ratio of the pixel intensity profiles of muscle against those of intermuscular fat for the rectus capitis posterior major and minor and inferior obliquus capitis muscles bilaterally. Inter- and intra-examiner agreement was scrutinized.

RESULTS

The average relative values of fat within the upper cervical musculature compared with intermuscular fat indicated that there were only slight variations in indices between the three sets of muscles. There was no significant correlation between age and fat indices. There were significant differences for the relative fat within the muscle compared with intermuscular fat and body mass index for the right rectus capitis posterior major and right and left inferior obliquus capitis muscles (p=0.032). Intraclass correlation coefficients for intraobserver agreement ranged from 0.94 to 0.98. Inter-rater agreement of the measurements ranged from 0.75 to 0.97.

CONCLUSION

A quantitative measure of muscle/fat constituents has been developed, and results of this study indicate that relative fatty infiltration is not a feature of age in the upper cervical extensor muscles of women aged 18-45 years.

Assessing gene and cell therapies applied in striated skeletal and cardiac muscle: is there a role for nuclear magnetic resonance?

Gene and cell therapies convey high hopes for treatment of skeletal and heart muscle diseases. In the experimental protocols under development as well as in the first clinical trials, longitudinal control by an atraumatic procedure is needed. Nuclear magnetic resonance (NMR), via its two modalities, imaging or spectroscopy, should play a major role both for in vivo animal and human studies, because of the great number of parameters that can be measured, sequentially or simultaneously, and because of its aptitude to monitor several steps of protocols, in particular to detect physiological modifications induced by therapies. We review here the many possible applications of nuclear magnetic resonance in gene/cell therapies where muscle is the target organ, with emphasis on the application of nuclear magnetic resonance to functional studies.

Segmentation of fat and muscle from MR images of the thigh by a possibilistic clustering algorithm

Physical training is proved to induce changes in physical capacity and body composition. We propose in this article a fast, unsupervised and fully three-dimensional automatic method to extract muscle and fat volumes from magnetic resonance images of thighs in order to assess these changes. The technique relies on the use of a fuzzy clustering algorithm and post-processings to accurately process the body composition of thighs. Results are compared on 11 healthy voluntary elderly people with those provided on the same data by a validated method already published, and its reliability is assessed on repeated measures on three subjects. The two methods statistically agree when computing muscle and fat volumes, and clinical implications of this fully automatic method are important for medicine, physical conditioning, weight-loss programs and predictions of optimal body weight.

Imaging of water and fat fractions in high-field MRI with multiple slice chemical shift-selective inversion recovery

Fat and water fractions were quantified at high field using a chemical shift-selective inversion recovery (CSS-IR) sequence to address the major difficulties encountered at high field by phase-sensitive techniques used for fat/water discrimination. Water- and fat-suppressed images were perfectly registered, which is a prerequisite for quantification. Immunity of the inversion pulse to B(1) field modulations and off-resonance effects was tested for two adiabatic inversion pulses, with hyperbolic secant and asymmetric hyper-pulse waveforms. Taking into account adiabaticity, immunity to off-resonance, radiofrequency power requirements, and specific absorption rate, the former was chosen. A close correlation was found between fat content measured by CSS-IR at 4.7 T (R(2)= 0.97, P < 0.001) and 9.4 T (R(2)= 0.99, P < 0.05) and that measured by Soxhlet extraction. Different sources of bias (low signal-to-noise ratio, magnetization transfer effect) are discussed. J. Magn. Reson. Imaging 2000;12:488-496.