Imaging techniques in myotonic dystrophy. A comparative study of ultrasound, computed tomography and magnetic resonance imaging of skeletal muscles

Multimodal Diagnostic Approaches to Advance Precision Medicine in Sarcopenia and Frailty

Sarcopenia, defined as the loss of muscle mass, strength, and function with aging, is a geriatric syndrome with important implications for patients and healthcare systems. Sarcopenia increases the risk of clinical decompensation when faced with physiological stressors and increases vulnerability, termed frailty. Sarcopenia develops due to inflammatory, hormonal, and myocellular changes in response to physiological and pathological aging, which promote progressive gains in fat mass and loss of lean mass and muscle strength. Progression of these pathophysiological changes can lead to sarcopenic obesity and physical frailty. These syndromes independently increase the risk of adverse patient outcomes including hospitalizations, long-term care placement, mortality, and decreased quality of life. This risk increases substantially when these syndromes co-exist. While there is evidence suggesting that the progression of sarcopenia, sarcopenic obesity, and frailty can be slowed or reversed, the adoption of broad-based screening or interventions has been slow to implement. Factors contributing to slow implementation include the lack of cost-effective, timely bedside diagnostics and interventions that target fundamental biological processes. This paper describes how clinical, radiographic, and biological data can be used to evaluate older adults with sarcopenia and sarcopenic obesity and to further the understanding of the mechanisms leading to declines in physical function and frailty.

Quantitative Muscle MRI in Patients with Neuromuscular Diseases-Association of Muscle Proton Density Fat Fraction with Semi-Quantitative Grading of Fatty Infiltration and Muscle Strength at the Thigh Region

(1) Background and Purpose: The skeletal muscles of patients suffering from neuromuscular diseases (NMD) are affected by atrophy, hypertrophy, fatty infiltration, and edematous changes. Magnetic resonance imaging (MRI) is an important tool for diagnosis and monitoring. Concerning fatty infiltration, T₁-weighted or T₂-weighted DIXON turbo spin echo (TSE) sequences enable a qualitative assessment of muscle involvement. To achieve higher comparability, semi-quantitative grading scales, such as the four-point Mercuri scale, are commonly applied. However, the evaluation remains investigator-dependent. Therefore, effort is being invested to develop quantitative MRI techniques for determination of imaging markers such as the proton density fat fraction (PDFF). The present work aims to assess the diagnostic value of PDFF in correlation to Mercuri grading and clinically determined muscle strength in patients with myotonic dystrophy type 2 (DM2), limb girdle muscular dystrophy type 2A (LGMD2A), and adult Pompe disease. (2) Methods: T₂-weighted two-dimensional (2D) DIXON TSE and chemical shift encoding-based water-fat MRI were acquired in 13 patients (DM2: n = 5; LGMD2A: n = 5; Pompe disease: n = 3). Nine different thigh muscles were rated in all patients according to the Mercuri grading and segmented to extract PDFF values. Muscle strength was assessed according to the British Medical Research Council (BMRC) scale. For correlation analyses between Mercuri grading, muscle strength, and PDFF, the Spearman correlation coefficient (r_s) was computed. (3) Results: Mean PDFF values ranged from 7% to 37% in adults with Pompe disease and DM2 and up to 79% in LGMD2A patients. In all three groups, a strong correlation of the Mercuri grading and PDFF values was observed for almost all muscles (r_s > 0.70, p < 0.05). PDFF values correlated significantly to muscle strength for muscle groups responsible for knee flexion (r_s = -0.80, p < 0.01). (4) Conclusion: In the small, investigated patient cohort, PDFF offers similar diagnostic precision as the clinically established Mercuri grading. Based on these preliminary data, PDFF could be further considered as an MRI-based biomarker in the assessment of fatty infiltration of muscle tissue in NMD. Further studies with larger patient cohorts are needed to advance PDFF as an MRI-based biomarker in NMD, with advantages such as its greater dynamic range, enabling the assessment of subtler changes, the amplified objectivity, and the potential of direct correlation to muscle function for selected muscles.

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

Background

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

Methods

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

Results

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

Conclusions

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

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

PURPOSE OF REVIEW

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

CONCLUSION

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

KEY POINTS

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

Exercise induced changes in echo intensity within the muscle: a brief review

Echo intensity is the mean pixel intensity of a specific region of interest from an ultrasound image. This variable has been increasingly used in the literature as a physiological marker. Although there has been an increased interest in reporting changes in echo intensity in response to exercise, little consensus exists as to what a change in echo intensity represents physiologically. The purpose of this paper is to review some of the earliest, as well as the most up to date literature regarding the changes in echo intensity in response to exercise. Echo intensity has been used to measure muscle quality, muscle damage, acute swelling, and intramuscular glycogen. The changes in echo intensity, however, are not consistent throughout the literature and often times lead to conclusions that seem contrary to the physiologic effects of exercise. For example, echo intensity increases in conjunction with increases in strength, contrary to what would be expected if echo intensity was a marker of muscle quality/muscle damage. It is conceivable that a change in echo intensity represents a range of physiologic effects at different time points. We recommend that these effects should be determined experimentally in order to rule out what echo intensity might and might not represent. Until this is done, caution should be employed when interpreting changes in echo intensity with acute and chronic exercise.

Ultrasonography-Based Qualitative and Quantitative Evaluation Approaches for Pompe Disease

Purpose

The aim of this study was to propose the qualitative and quantitative approaches to evaluate the skeletal muscle ultrasound images of 23 Pompe disease (i.e., acid maltase deficiency, AMD) patients and 14 normal subjects.

Methods

A cohort of 23 AMD patients and 14 normal subjects has been investigated. We compared the B-mode echo intensity of the rectus femoris muscle with that of its surrounding fat (subcutaneous fat) and proposed a qualitative grading method. Quantitative analysis of the region of interest (ROI) with the echo intensity and the segmented area was also performed.

Results

Qualitative results showed that AMD patients without clinical symptoms (without undergoing ERT) had the highest distribution of Grade 1, and AMD patients undergoing ERT had the widest distribution of Grade 2, and control group (n = 14) with the highest distribution of Grade 1. Using the segmented area approach, quantitative results showed that AMD patients undergoing ERT had the largest and widest distribution. Meanwhile the control subjects (normal subjects) had the lowest and the narrowest areas. The echo intensity of the segmented ROI of AMD patients undergoing ERT displayed the highest and widest (inhomogeneous) distributions. By contrast, the echo intensity of AMD patients without clinical symptoms was slightly increased and with low inhomogeneity.

Conclusion

The proposed ultrasonography-based qualitative and quantitative approach may be used to evaluate the severity of muscle destruction for AMD patients. Besides, the quantitative segmented area with regression analysis could help predict the incidence of onset of Pompe disease patients.

Clinical review: peripheral muscular ultrasound in the ICU

Muscular weakness developing from critical illness neuropathy, myopathy and muscle atrophy has been characterized as intensive care unit-acquired weakness (ICUAW). This entity occurs commonly during and after critical care stay. Various causal factors for functional incapacity have been proposed. Among these, individual patient characteristics (such as age, comorbidities and nutritional status), acting in association with sustained bed rest and pharmacological interventions (included the metabolic support approach), seem influential in reducing muscular mass. Long-term outcomes in heterogeneous ICUAW populations include transient disability in 30% of patients and persistent disabilities that may occur even in patients with nearly complete functional recovery. Currently available tools for the assessment of skeletal muscle mass are imprecise and difficult to perform in the ICU setting. A valid alternative to these imaging modalities is muscular ultrasonography, which allows visualization and classification of muscle characteristics by cross-sectional area, muscle layer thickness, echointensity by grayscale and the pennation angle). The aim of this narrative review is to describe the current literature addressing muscular ultrasound for the detection of muscle weakness and its potential impact on treatment and prognosis of critically ill patients when combined with biomarkers of muscle catabolism/anabolism and bioenergetic state. In addition, we suggest a practical flowchart for establishing an early diagnosis.

Myoimaging in Congenital Myopathies

There is a great clinical and genetic heterogeneity in congenital myopathies. Myo-MRI with pattern recognition has become a first-line complementary tool in clinical practice for this group of diseases. For diagnostic purposes, whole-body imaging techniques are preferred when involvement is axial or diffuse, as in most congenital myopathies, because of involvement of the tongue, masticator, neck or trunk muscles. Myo-MRI is widely used to identify abnormalities in muscle signal, volume or texture. Recognizable profiles or patterns have been identified in many of these genetic myopathies. The role of the radiologist is crucial in order to adapt the Myo-MRI protocols to the age of the patient and several clinical situations. Myo-MRI in children with congenital myopathies is a very demanding technique with a balance between acceptable time of examination and sufficient spatial resolution in order to detect subtle changes. Technical evolutions combining qualitative and quantitative analysis are useful to follow disease progression overtime. Outcome measures are expected to play a role in natural history description as well as in future therapeutic trials. Genetic diagnosis and interpretation of next generation sequencing results could be greatly influenced by statistical analysis with tools such as algorithms as well as graphical representations using heatmaps.

Myopathology in times of modern imaging

Over the last two decades, muscle (magnetic resonance) imaging has become an important complementary tool in the diagnosis and differential diagnosis of inherited neuromuscular disorders, particularly in conditions where the pattern of selective muscle involvement is often more predictive of the underlying genetic background than associated clinical and histopathological features. Following an overview of different imaging modalities, the present review will give a concise introduction to systematic image analysis and interpretation in genetic neuromuscular disorders. The pattern of selective muscle involvement will be presented in detail in conditions such as the congenital or myofibrillar myopathies where muscle imaging is particularly useful to inform the (differential) diagnosis, and in disorders such as Duchenne or fascioscapulohumeral muscular dystrophy where the diagnosis is usually made on clinical grounds but where detailed knowledge of disease progression on the muscle imaging level may inform better understanding of the natural history. Utilizing the group of the congenital myopathies as an example, selected case studies will illustrate how muscle MRI can be used to inform the diagnostic process in the clinico-pathological context. Future developments, in particular, concerning the increasing use of whole-body MRI protocols and novel quantitative fat assessments techniques potentially relevant as an outcome measure, will be briefly outlined.

Differential Relationship between Intermuscular Adipose Depots with Indices of Cardiometabolic Health

BACKGROUND

Globally, accumulation of intermuscular adipose tissue (IMAT) is positively associated with insulin resistance. Whether this association is observed consistently in different skeletal muscles and encompasses other markers of cardiometabolic health is not well known.

OBJECTIVES

The purpose of this secondary analysis study was to investigate associations among thigh or calf IMAT stores and indices of cardiometabolic health in adults who are overweight and obese participating in dietary interventions. A subset of calf data was analyzed to assess relations between IMAT in the gastrocnemius (type II fiber predominance) and soleus (type I fiber predominance) with markers of cardiometabolic health.

MATERIALS AND METHODS

Thigh and calf compositions were assessed via magnetic resonance imaging in 113 subjects (mean ± SD, age: 50 ± 16 y (range: 21-77 y), BMI: 31 ± 3 kg/m²), 103 of which completed dietary interventions with or without energy restriction-induced weight loss. A subset of data (n = 37) was analyzed for relations between muscle compartments (gastrocnemius and soleus) and cardiometabolic health. IMAT was regressed separately against fasting serum glucose concentrations, insulin, homeostatic model assessment-insulin resistance (HOMA-IR), and lipids and lipoproteins.

RESULTS

In general, total thigh IMAT was predictive of markers of glucose control, while total calf IMAT was not. Specifically, baseline thigh IMAT was positively associated with fasting glucose, insulin, and HOMA-IR. IMAT content changes in any depot did not predict improvement in cardiometabolic health.

CONCLUSIONS

The strength of the relationship between IMAT and glucose control-related indices of cardiometabolic health is dependent on IMAT location. Specifically, greater IMAT in the thigh is a better predictor of cardiometabolic risk than greater IMAT in the calf in adults who are overweight and obese.

Magnetic resonance imaging to detect local tissue reactions after vaccination in sheep in vivo

OBJECTIVES

Vaccination is one of the most effective methods to keep up the health status in humans and in livestock. Therefore, farm animals are vaccinated several times during their lifetime. Although vaccines are being checked regarding their local reactogenicity, side effects occur frequently-especially in the case of the application of adjuvanted products. Many reports exist about local reactions in sheep. The present study aimed at testing MRI as a method to document injection site reactions three-dimensionally.

DESIGN

Two groups of Merino lambs (n=16 each) were vaccinated subcutaneously into the left neck side. Two different, licensed inactivated vaccines were used. Both groups of lambs were anaesthetised and scanned using MRI at days 1, 3, 8, 15, 22 and 29 after vaccination.

SETTING

The study was performed on a commercial-like farm.

PARTICIPANTS

Thirty-two Merino lambs entered the experiment, 16 male and 16 female ones (one animal died at day 22 after vaccination). At first examination day they were approximately three months old.

PRIMARY AND SECONDARY OUTCOME MEASURES

Volume differences were measured between vaccination and control neck side to evaluate the time pattern of local tissue reactions.

RESULTS

Local tissue reactions were visible on the skin surface and also appeared in deeper tissue layers on MRI. These deeper reactions would not have been found without MRI or, alternatively, without sacrificing the animals. Some of these extensive local reactions lasted for more than 29 days.

CONCLUSIONS

The in vivo MRI results proved suitable to record local tissue reactions in terms of three-dimensional extent over a longer period of time in large farm animals without the need to sacrifice test animals. A three-dimensional MRI examination of the injection site during regulatory licensing studies offers an objective evaluation that could be used in a benefit-risk assessment of veterinary vaccines.

TRIAL REGISTRATION NUMBER

District Government of Upper Bavaria:55.2-1-54-2532-2-13.

Magnetic resonance imaging of leg muscles in patients with myotonic dystrophies

Magnetic resonance imaging (MRI) of muscles has recently become a significant diagnostic procedure in neuromuscular disorders. There is a lack of muscle MRI studies in patients with myotonic dystrophy type 1 (DM1), especially type 2 (DM2). To analyze fatty infiltration of leg muscles, using 3.0 T MRI in patients with genetically confirmed DM1 and DM2 with different disease durations. The study comprised 21 DM1 and 10 DM2 adult patients. Muscle MRI was performed in axial plane of the lower limbs using T1-weighted (T1w) sequence. Six-point scale by Mercuri et al. was used. Fatty infiltration registered in at least one muscle of lower extremities was found in 71% of DM1 and 40% of DM2 patients. In DM1 patients, early involvement of the medial head of gastrocnemius and tibialis anterior muscles was observed with later involvement of other lower leg muscles and of anterior and posterior thigh compartments with relative sparing of the rectus femoris. In DM2, majority of patients had normal MRI findings. Early involvement of lower legs and posterior thighs was found in some patients. Less severe involvement of the medial head of the gastrocnemius compared to other lower leg muscles was also observed, while involvement of proximal muscles was rather diffuse than selective. It seems that both in DM1 and DM2 some muscles may be affected before weakness is clinically noted and vice versa. We described characteristic pattern and way of progression of muscle involvement in DM1 and DM2.

Application of ultrasonography in the assessment of skeletal muscles in children with and without neuromuscular disorders: a systematic review

The purpose of this study was to systematically review published studies (2000-2014) carried out on the application of ultrasonography (US) to evaluation of skeletal muscle size in children with and without neuromuscular disorders. Different databases including PubMed, Science Direct, OVID, MEDLINE, CINAHL, EMBASE, ProQuest and Google Scholar were searched. The key words used were: "children," "ultrasound," "skeletal muscles," "neuromuscular disease," "neurogenic disorders," "spina bifida," "myelomeningocele" and "reliability." Eighteen articles were found to be relevant. Eight studies applied US in combination with additional methods of assessment. Four of the 18 studies did not have a control group. Ten studies applied only US in the assessment of skeletal muscles in children with and without neuromuscular diseases. In 9 studies, there were children ranging widely in age, and in 3 studies US was used to determine normal values for skeletal muscles. According to the results of these 18 reviewed articles, US is an appropriate, reliable and highly predictive method for assessment of skeletal muscles in children.

Selective disappearance of medial back muscles in a case of myotonic dystrophy type 1

Here, we report a unique case of late-onset myotonic dystrophy type 1 in a 64-year-old woman, with selective disappearance of the medial lower back muscles. We compared the clinical features of this patient with those of a cohort of 29 patients with myotonic dystrophy type 1 to clarify the correlation between clinical features and lower back muscle atrophy. After classification into three subgroups according to muscle atrophy pattern, medial muscle atrophy was present in 17.2% of the patients. Affected patients were older at onset than non-affected patients, and limb muscle power and respiratory function decreased with atrophy progression.

Role of Radiologic Imaging in Genetic and Acquired Neuromuscular Disorders

Great technologic and clinical progress have been made in the last two decades in identifying genetic defects of several neuromuscular diseases, as Spinal Muscular Atrophy, genetic muscular dystrophies and other genetic myopathies. The diagnosis is usually challenging, due to great variability in genetic abnormalities and clinical phenotypes and the poor specificity of complementary analyses, i.e., serum creatine kinase (CK) and electrophysiology. Muscle biopsy represents the gold standard for the diagnosis of genetic neuromuscular diseases, but clinical imaging of muscle tissue is an important diagnostic tool to identify and quantifyies muscle damage. Radiologic imaging is, indeed, increasingly used as a diagnostic tool to describe patterns and the extent of muscle involvement, thanks to modern techniques that enable to definethe definition of degrees of muscle atrophy and changes in connective tissue. They usually grade the severity of the disease process with greater accuracy than clinical scores. Clinical imaging is more than complementary to perform muscle biopsy, especially as ultrasound scans are often mandatory to identify the muscle to be biopsied. We will here detail and provideWe will herein provide detailed examples of the radiologic methods that can be used in genetic and acquired neuromuscular disorders, stressing pros and cons.

KEY WORDS

Muscle Imaging, MRI, CT, genetic muscle disorders, myopathies, dystrophies.

Muscle MR imaging in tubular aggregate myopathy

Purpose

To evaluate with Magnetic Resonance (MR) the degree of fatty replacement and edematous involvement in skeletal muscles in patients with Tubular Aggregate Myopathy (TAM). To asses the inter-observer agreement in evaluating muscle involvement and the symmetry index of fatty replacement.

Materials and Methods

13 patients were evaluated by MR to ascertain the degree of fatty replacement (T1W sequences) according to Mercuri's scale, and edema score (STIR sequences) according to extent and site.

Results

Fatty replacement mainly affects the posterior superficial compartment of the leg; the anterior compartment is generally spared. Edema was generally poor and almost only in the superficial compartment of the leg. The inter-observer agreement is very good with a Krippendorff's coefficient >0.9. Data show a total symmetry in the muscular replacement (McNemar-Bowker test with p = 1).

Conclusions

MR reveals characteristic muscular involvement, and is a reproducible technique for evaluation of TAM. There may also be a characteristic involvement of the long and short heads of the biceps femoris. It is useful for aimed biopsies, diagnostic hypotheses and evaluation of disease progression.

Selective pattern of muscle involvement seen in distal muscular dystrophy associated with anoctamin 5 mutations: a follow-up muscle MRI study

Anoctaminopathy is a new muscular dystrophy caused by mutations in the ANO5 gene. ANO5 mutations cause distal and proximal phenotypes. We report here a follow-up muscle MRI study on five patients affected by distal form of anoctaminopathy. T1 weighted scans showed subsequent involvement of gastrocnemius medialis and soleus, hip adductors, hamstrings, gastrocnemius lateralis and quadriceps muscles, and later on tensor fascia lata, gluteus minimus and biceps brachii muscles, respectively. The STIR weighted images showed in the early stages widely distributed hyperintense signals, myoedema, in the adductors, hamstrings, and quadriceps muscles, which at that time have normal T1 signals. All patients showed asymmetry of muscle involvement both clinically and on muscle imaging. The progression of muscle involvement was relatively slow. We conclude that the pattern of muscle involvement seen in patients with distal myopathy with anoctamin 5 mutations (MMD3) is typical and can thus be useful during the differential diagnosis process allowing for a more targeted molecular approach.

Importance and challenges of measuring intrinsic foot muscle strength

BACKGROUND

Intrinsic foot muscle weakness has been implicated in a range of foot deformities and disorders. However, to establish a relationship between intrinsic muscle weakness and foot pathology, an objective measure of intrinsic muscle strength is needed. The aim of this review was to provide an overview of the anatomy and role of intrinsic foot muscles, implications of intrinsic weakness and evaluate the different methods used to measure intrinsic foot muscle strength.

METHOD

Literature was sourced from database searches of MEDLINE, PubMed, SCOPUS, Cochrane Library, PEDro and CINAHL up to June 2012.

RESULTS

There is no widely accepted method of measuring intrinsic foot muscle strength. Methods to estimate toe flexor muscle strength include the paper grip test, plantar pressure, toe dynamometry, and the intrinsic positive test. Hand-held dynamometry has excellent interrater and intrarater reliability and limits toe curling, which is an action hypothesised to activate extrinsic toe flexor muscles. However, it is unclear whether any method can actually isolate intrinsic muscle strength. Also most methods measure only toe flexor strength and other actions such as toe extension and abduction have not been adequately assessed. Indirect methods to investigate intrinsic muscle structure and performance include CT, ultrasonography, MRI, EMG, and muscle biopsy. Indirect methods often discriminate between intrinsic and extrinsic muscles, but lack the ability to measure muscle force.

CONCLUSIONS

There are many challenges to accurately measure intrinsic muscle strength in isolation. Most studies have measured toe flexor strength as a surrogate measure of intrinsic muscle strength. Hand-held dynamometry appears to be a promising method of estimating intrinsic muscle strength. However, the contribution of extrinsic muscles cannot be excluded from toe flexor strength measurement. Future research should clarify the relative contribution of intrinsic and extrinsic muscles during intrinsic foot muscle strength testing.

Neuromuscular ultrasonography: quantifying muscle and nerve measurements

Neuromuscular ultrasonography can be used both descriptively and quantitatively in the evaluation of patients with neuromuscular disorders. This article reviews the quantitative use of this technology, particularly measurements of the size and echogenicity of nerve and muscle, as a tool for assessing the severity, progression, and response of these tissues to therapeutic interventions. Neuromuscular ultrasonography has several features, including portability and noninvasiveness, that make it an attractive research tool for advancing the diagnosis and treatment of neuromuscular disorders.

Neuromuscular imaging in inherited muscle diseases

Driven by increasing numbers of newly identified genetic defects and new insights into the field of inherited muscle diseases, neuromuscular imaging in general and magnetic resonance imaging (MRI) in particular are increasingly being used to characterise the severity and pattern of muscle involvement. Although muscle biopsy is still the gold standard for the establishment of the definitive diagnosis, muscular imaging is an important diagnostic tool for the detection and quantification of dystrophic changes during the clinical workup of patients with hereditary muscle diseases. MRI is frequently used to describe muscle involvement patterns, which aids in narrowing of the differential diagnosis and distinguishing between dystrophic and non-dystrophic diseases. Recent work has demonstrated the usefulness of muscle imaging for the detection of specific congenital myopathies, mainly for the identification of the underlying genetic defect in core and centronuclear myopathies. Muscle imaging demonstrates characteristic patterns, which can be helpful for the differentiation of individual limb girdle muscular dystrophies. The aim of this review is to give a comprehensive overview of current methods and applications as well as future perspectives in the field of neuromuscular imaging in inherited muscle diseases. We also provide diagnostic algorithms that might guide us through the differential diagnosis in hereditary myopathies.

MRI in the assessment of muscular pathology: a comparison between limb-girdle muscular dystrophies, hyaline body myopathies and myotonic dystrophies

PURPOSE

The continuous discovery of new subtypes of neuromuscular disorders demands more accurate imaging analyses. We set out to establish the specific patterns of muscular involution using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

A systematic clinical evaluation based on the Medical Research Council scale and MRI was completed in ten patients with calpainopathy [limb-girdle muscular dystrophy (LGMD)-2A], 16 with dysferlinopathy (LGMD-2B), ten with hyaline body myopathy (HBM), six with myotonic dystrophy (MD) types 1 and 5 with MD type 2. Severity of fibroadipose degeneration was specifically staged using T1-weighted sequences. Turbo inversion recovery magnitude (TIRM) sequences were used to assess oedema-like changes.

RESULTS

T1 scans showed recurrent patterns of fibroadipose replacement, whereas TIRM images revealed differences in oedema-like changes between the various diseases. In LGMD, the posterior compartments are more vulnerable to degeneration. In HBM, fatty muscle degeneration and oedema are allocated to muscles of the posterior compartments of the leg. In MD, fatty muscle degeneration and oedematous changes are allocated to muscles of the anterior thigh and posterior lower leg.

CONCLUSIONS

Imaging examination suggests a characteristic pattern of muscle involvement. MRI represents an important diagnostic technique useful in differential diagnosis, thanks to the distinctive patterns observed in the distribution of muscular changes between the different muscular diseases.

Atrophy of foot muscles in diabetic patients can be detected with ultrasonography

OBJECTIVE

To establish a bedside test with ultrasonography for evaluation of foot muscle atrophy in diabetic patients.

RESEARCH DESIGN AND METHODS

Thickness and cross-sectional area (CSA) of the extensor digitorum brevis muscle (EDB) and of the muscles of the first interstitium (MILs) were determined in 26 diabetic patients and in 26 matched control subjects using ultrasonography. To estimate the validity, findings were related to the total volume of all foot muscles determined at magnetic resonance imaging (MRI-FM(vol)). Furthermore, the relations of ultrasonographic estimates to nerve conduction, sensory perception thresholds, and clinical condition were established.

RESULTS

In diabetic patients, the ultrasonographic thickness of EDB (U-EDB(t)) was (means +/- SD) 6.4 +/- 2.1 vs. 9.0 +/- 1.0 mm in control subjects (P < 0.001), the thickness of MIL (U-MIL(t)) was 29.6 +/- 8.3 vs. 40.2 +/- 3.6 mm in control subjects (P < 0.001), and the CSA of EDB (U-EDB(CSA)) was 116 +/- 65 vs. 214 +/- 38 mm(2) in control subjects (P < 0.001). The MRI-FM(vol) was directly related to U-EDB(t) (r = 0.77), U-MIL(t) (r = 0.71), and U-EDB(CSA) (r = 0.74). U-EDB(t) and U-MIL(t) were thinner in neuropathic than in nonneuropathic diabetic patients (5.8 +/- 2.1 vs. 7.5 +/- 1.7 mm [P < 0.05] and 28.3 +/- 8.8 vs. 35.6 +/- 4.3 mm [P < 0.03], respectively).

CONCLUSIONS

Atrophy of intrinsic foot muscles determined at ultrasonography is directly related to foot muscle volume determined by MRI and to various measures of diabetic neuropathy. Ultrasonography seems to be useful for detection of foot muscle atrophy in diabetes.

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

Interest in muscle MRI has been largely stimulated in the last few years by the recognition of an increasing number of genetic defects in the field of inherited neuromuscular disorders. Muscle ultrasound (US) and computed tomography (CT) have been used to detect the presence of muscle involvement in patients affected by these disorders, but until recently the use of muscle MRI has been, with a few exceptions, limited to detecting inflammatory forms. The aim of this review is to illustrate how muscle MRI, in combination with clinical evaluation, can contribute to the selection of appropriate genetic tests and more generally in the differential diagnosis of genetically distinct forms of neuromuscular disorders. Possible future applications of muscle MRI are also discussed.

MRI for the demonstration of subclinical muscle involvement in muscular dystrophy

AIM

To compare magnetic resonance imaging (MRI) with clinical examination for the detection of muscle abnormality in patients with muscular dystrophy.

METHODS

Muscle power in 20 patients with a variety of forms of muscular dystrophy was examined clinically using the Medical Research Council (MRC) grading scale, and patients were subsequently imaged with MRI. MRI and clinical examination for the detection of muscle normality and abnormality were compared using a McNemar chi-squared test to examine differences between the two methods.

RESULTS

MRI demonstrated radiological evidence of muscle abnormality more often than clinical examination; 50% of movements assessed as normal on clinical examination were associated with muscle abnormalities on MRI, including a significant proportion where there was severe radiological abnormality, indicating that focally advanced disease may be undetectable clinically.

CONCLUSION

The combination of clinical examination and MRI could improve the accuracy of phenotypic characterization of patients with muscular dystrophy, and this in turn could allow a more focussed molecular analysis through muscle biopsy or genetic investigation. This may also be very helpful in the assessment of the degree of muscle compromise not only in the early phases of the disease but especially during follow-up and can be used in therapeutic trials.

[Non-invasive investigation of muscle function using 31P magnetic resonance spectroscopy and 1H MR imaging]

31P MRS and 1H MRI of skeletal muscle have become major new tools allowing a complete non invasive investigation of muscle function both in the clinical setting and in basic research. The comparative analysis of normal and diseased muscle remains a major requirement to further define metabolic events surrounding muscle contraction and the metabolic anomalies underlying pathologies. Also, standardized rest-exercise-recovery protocols for the exploration of muscle metabolism by P-31 MRS in healthy volunteers as well as in patients with intolerance to exercise have been developed. The CRMBM protocol is based on a short-term intense exercise, which is very informative and well accepted by volunteers and patients. Invariant metabolic parameters have been defined to characterize the normal metabolic response to the protocol. Deviations from normality can be directly interpreted in terms of specific pathologies in some favorable cases. This protocol has been applied to more than 4,000 patients and healthy volunteers over a period of 15 years. On the other hand, MRI investigations provide anatomical and functional information from resting and exercising muscle. From a diagnostic point of view, dedicated pulse sequences can be used in order to detect and quantify muscle inflammation, fatty replacement, muscle hyper and hypotrophy. In most cases, MR techniques provide valuable information which has to be processed in conjunction with traditional invasive biochemical, electrophysiological and histoenzymological tests. P-31 MRS has proved particularly useful in the therapeutic follow-up of palliative therapies (coenzyme Q treatment of mitochondriopathies) and in family investigations. It is now an accepted diagnostic tool in the array of tests which are used to characterize muscle disorders in clinical routine. As a research tool, it will keep bringing new information on the physiopathology of muscle diseases in animal models and in humans and should play a role in the metabolic characterization of gene and cell therapy.

Distinct neuromuscular phenotypes in myotonic dystrophy types 1 and 2 : a whole body highfield MRI study

Myotonic Dystrophy Type 1 (DM1) and 2 (DM2) present with distinct though overlapping clinical phenotypes. Comparative imaging data on skeletal muscle involvement are not at present available. We used the novel technique of whole body 3.0 Tesla (T) Magnetic Resonance Imaging (MRI) to further characterize musculoskeletal features in DM2 and compared the results with DM1.MRI findings of 15 DM1 and 14 DM2 patients were evaluated with respect to patterns of skeletal muscle affection and clinical data using the Muscular Impairment Rating Scale (MIRS) and Medical Research Council scale (MRC). All DM1 patients had pathological MRI compared with only 5 DM2 patients. In contrast to DM2, DM1 patients showed a characteristic distribution of muscle involvement with frequent and early degeneration of the medial heads of gastrocnemius muscles, and a perifemoral semilunar pattern of quadriceps muscle affection sparing the rectus femoris. The most frequently affected muscles in DM1 were the medial heads of gastrocnemius, soleus, and vastus medialis muscles. In DM2, however, the erector spinae and gluteus maximus muscles were most vulnerable to degeneration. MRI data were in line with the clinical grading in 12 DM1 and 3 DM2 patients. In 3 DM1 and 5 DM2 patients, MRI detected subclinical muscle involvement. 9 DM2 patients with mild to moderate proximal muscle weakness and/or myalgias had normal MRI. Pathological MRI changes in DM2 emerged with increasing age and were restricted to women. Whole body 3.0T MRI is a sensitive imaging technique that demonstrated a characteristic skeletal muscle affection in DM1. In contrast, MRI was no reliable indicator for skeletal muscle involvement in mildly affected DM2 patients since myalgia and mild paresis were usually not reflected by MRI signal alterations.

Quantitative ultrasound tissue characterization in shoulder and thigh muscles--a new approach

BACKGROUND

The echogenicity patterns of ultrasound scans contain information of tissue composition in muscles. The aim was: (1) to develop a quantitative ultrasound image analysis to characterize tissue composition in terms of intensity and structure of the ultrasound images, and (2) to use the method for characterization of ultrasound images of the supraspinatus muscle, and the vastus lateralis muscle.

METHODS

Computerized texture analyses employing first-order and higher-order grey-scale statistics were developed to objectively characterize ultrasound images of m. supraspinatus and m. vastus lateralis from 9 healthy participants.

RESULTS

The mean grey-scale intensity was higher in the vastus lateralis muscle (p < 0.05) than in the supraspinatus muscle (average value of middle measuring site 51.4 compared to 35.0). Furthermore, the number of spatially connected and homogeneous regions (blobs) was higher in the vastus lateralis (p < 0.05) than in the supraspinatus (average for m. vastus lateralis: 0.092 mm(-2) and for m. supraspinatus: 0.016 mm(-2)).

CONCLUSION

The higher intensity and the higher number of blobs in the vastus lateralis muscle indicates that the thigh muscle contained more non-contractile components than the supraspinatus muscle, and that the muscle was coarser. The image analyses supplemented each other and gave a more complete description of the tissue composition in the muscle than the mean grey-scale value alone.

Muscle magnetic resonance imaging shows distinct diagnostic patterns in Welander and tibial muscular dystrophy

OBJECTIVES

This is a report on a retrospective muscle magnetic resonance imaging (MRI) study on 11 patients affected by Welander distal myopathy (WDM) and 22 patients with tibial muscular dystrophy (TMD) carried out in order to define the pattern and characteristics of muscle involvement.

RESULTS

WDM patients showed involvement of gastrocnemius, soleus, tibial anterior (TA) and extensor digitorum longus (EDL), as well as hamstrings and hip adductor muscles. TMD patients showed involvement of the TA and EDL muscles, and in some patients also hamstring and posterior compartment muscles of the legs. Some patients showed asymmetry of muscle involvement.

CONCLUSION

We conclude that muscle MRI examination proved to be very useful in the determination of the exact pattern of muscle involvement in WDM and TMD. Clinical testing using the Medical Research Council scale is not sensitive enough to establish the pattern of muscle involvement in focal muscle diseases.

Muscle ultrasound in children: normal values and application to neuromuscular disorders

In this study, 105 healthy children (45 to 156 months old, 57 girls) were examined using ultrasound (US) imaging to obtain reference values of muscle dimensional and aspect parameters. We measured biceps and quadriceps sizes and subcutaneous tissue thickness. To quantify muscle aspect, we calculated muscle density, inhomogeneity and white-area index by digital image analysis. Age-, weight- and gender-dependencies were discussed. We demonstrated earlier that the complete set of parameters allows for differentiation between myopathies and neuropathies in adults, with high sensitivity. In this study, we investigated if these parameters have additional value in the diagnostic evaluation of 36 children with proven neuromuscular disease (20 Duchenne muscular dystrophy, 16 neuropathies). We found that density analysis provides a sensitive method for distinguishing between healthy children and children with neuromuscular disorders. We have also found that more detailed aspect analysis is necessary to further distinguish between these types of neuromuscular disorders in children. In conclusion, this set of normal muscle parameters can be used to help diagnose neuromuscular disorders in children. It will also facilitate follow-up in disease progression and therapy.

Chapter 25 Imaging nerve and muscle with ultrasound

Over the last two decades significant advances in ultrasound have made it possible for investigators to image and interpret pathologic changes in muscle and nerve. In addition to being able to assess the pathologic changes in these structures themselves, ultrasound also provides the unique ability to identify anatomic lesions responsible for nerve or muscle injury. They can be correlated with changes in neural structures or affected muscles. Like electrodiagnostic studies, ultrasound is portable and inexpensive, but it is even less invasive, and surprisingly sensitive in detecting a variety of unusual and common causes of neuromuscular dysfunction. Given recent developments in the field, ultrasound shows promise as the technique most suitable for clinical neurophysiologists and neuromuscular clinicians in the growing field of imaging. Such involvement is required to best adopt and exploit the potential of imaging for the research and clinical evaluation of neuromuscular disorders.

Muscle ultrasound analysis: normal values and differentiation between myopathies and neuropathies

In this study, 145 healthy adults (20 to 94 years old, 69 women) were examined using ultrasound (US) imaging to obtain reference values of muscle parameters that were previously not available. We measured biceps and quadriceps sizes and subcutaneous fat thickness. To quantify muscle aspect, we defined and calculated the muscle aspect parameters muscle density, inhomogeneity and white-area index by digital image analysis. All muscle aspect parameters were found to increase with age, which may be due to age-related muscle replacement by fatty tissue and collagen. Other age-, weight- and gender-dependencies are also discussed. The complete set of muscle parameters was used to differentiate between typical myopathies and neuropathies in a group of 32 patients (24 to 79 years old, 18 women). We were successful in almost completely separating the two types of disorders based on abnormality of muscle aspect parameters alone. These preliminary results show that this set of normal muscle parameters can be used to help diagnose neuromuscular disorders. It will also facilitate follow-up in disease progression and therapy.

Temporomandibular joint and masticatory muscle involvement in myotonic dystrophy: a study by magnetic resonance imaging

OBJECTIVE

The purpose of this study was to evaluate the masticatory muscles and the temporomandibular joint (TMJ) by magnetic resonance imaging (MRI) in myotonic dystrophy (MD) patients.

STUDY DESIGN

MRI of the masticatory muscles and TMJ was performed in 15 MD patients, 11 male and 4 female, aged 16 to 53 years (mean, 31 years). Many of them had dental malocclusion, especially Angle class III and anterior open bite, and 3 complained of recurrent TMJ dislocation. TMJ and masticatory muscle pain was not observed, and joint sounds were noted in only 1 patient.

RESULTS

The analysis of MRI scans showed masticatory muscle involvement in 13 patients (86.6%). In 11, the involvement was moderate to intense. The main abnormalities observed were increased intramuscular tissue signal on T1 (fatty infiltration) and volumetric reduction of muscles. Regarding the TMJ, articular disk displacement was seen in only 1 patient, but abnormalities of disk shape were common. Mild bone abnormalities were frequently observed, including changes of shape and contour of bone surface, and sclerosis of bone marrow. In 4 patients the condyle moved anterior to the eminence with the mouth opened fully (condylar hyperexcursion).

CONCLUSIONS

This study shows that masticatory muscles are frequently and intensively affected in MD patients. Bone changes are the most consistent abnormalities observed in the TMJ. It is possible that remodeling is caused by biomechanical changes in the jaw as a result of masticatory muscle involvement.

Hereditary neuromuscular diseases

This article presents the actual classification of neuromuscular diseases based on present expansion of our knowledge and understanding due to genetic developments. It summarizes the genetic and clinical presentations of each disorder together with CT findings, which we studied in a large group of patients with neuromuscular diseases. The muscular dystrophies as the largest and most common group of hereditary muscle diseases will be highlighted by giving detailed information about the role of CT and MRI in the differential diagnosis. The radiological features of neuromuscular diseases are atrophy, hypertrophy, pseudohypertrophy and fatty infiltration of muscles on a selective basis. Although the patterns and distribution of involvement are characteristic in some of the diseases, the definition of the type of disease based on CT scan only is not always possible.

Quantitative ultrasound image analysis of the supraspinatus muscle

OBJECTIVE

To develop and validate a method, based on quantitative ultrasound image analysis, to objectively analyse and characterize the ultrasound images of m. supraspinatus.

DESIGN

Quantitative ultrasonography was performed on the supraspinatus muscle of 14 healthy subjects.

METHODS

A computerized analysis using first-order grey-scale statistics to evaluate the muscle tissue composition was developed and validated.

RESULTS

Data from one scanning site were not representative for the whole muscle due to muscle inhomogenity. Using first-order grey-scale statistics the scanning direction was of no importance. By using a scanning session consisting of three different scanning sites along the muscle in two directions, longitudinally and transversely, to characterize the tissue composition of the muscle, a high day-to-day reproducibility was obtained.

CONCLUSION

The described scanning session is a relatively sensitive and reproducible method for studying the muscle tissue composition. RelevanceQuantitative ultrasonography seems to be a potential clinical and occupational examination method to detect tissue composition of myalgic muscles compared to healthy muscles.

MRI in the study of distal primary myopathopies and of muscular alterations due to peripheral neuropathies: possible diagnostic capacities of MR equipment with low intensity field (0.2 T) dedicated to peripheral limbs

The purpose of this work was to investigate whether or not an magnetic resonance imaging (MRI) equipment with a low field intensity (0.2 T) used in the study of muscular alterations can diagnose primary or secondary myopathies, due to peripheral neuropathies. In this study the peripheral areas of all patients were examined. A total of 40 patients (23 males and 17 females) were tested. Their age ranged from 10 to 78 years age (mean age 40.8, SD +/- 19,45 years). The group includes 23 patients: 18 with Stainert Myotonic Distrophy, 5 were myositic, and the remaining 17 had peropheral neuropathies. Every patient received a clinic examination, followed by EMG and MRI. The MRI study was done with a system dedicated to the study of limbs (Artoscan, Esaote Biomedica) that used a 0.2 T permanent magnet. Spin-echo T1, T2-weighted, multiple-echo, and STIR sequences were used. A good correspondence was found between clinical and MRI data. Specifically, in the group of 23 myopathies, Sperman's index was found to be 0.80 in its correlation between the clinical examination and MRI; in the group of 17 myopathies it was found to be 0.63. A discrepancy was found among clinical examination, EMG, and MRI in patients with neuropathies who were showing a lack of myelin and mixed ones. The T2-weighted and STIR sequences had great sensitivity in showing initial changes in the muscles. The SE T1-weighted sequence was especially useful in detecting degeneration in the fibrous adipose tissue. The STIR sequence because of its high sensitivity and greater speed of response could be used instead of the SE T2 weighted particularly in the study of patients, who were noted to tolerate a prolonge period of scanning. However, because these sequences have a low signal noise ratio, they must always be associated with a SE sequence, whenever there would be need of a precise determination of the structures under study. The MRI low field intensity was also found to be a useful technique in screening familial groups having a great number of myotonic distrophies. It can have a great clinical role in revealing muscular alterations, even in asymptomatic patients.

Muscle computed tomography in adult-onset acid maltase deficiency

Nine patients with adult-onset acid maltase deficiency (Pompe's disease) were examined clinically and with computed tomography (CT). The CT scan showed early and severe involvement of the muscles of trunk and thighs, with selective sparing of the tensor fasciae latae, short head of biceps femoris, gracilis, and sartorius muscles. Shoulder and leg muscles were less affected. The disease spread over the years from trunk to extremities. Muscle strength and CT findings were positively correlated.

Objective quantification of muscle and fat in human dystrophic muscle by magnetic resonance image analysis

Information about changes in muscle composition has to date been primarily restricted to histological examination of biopsy samples or qualitative assessment of images obtained using a variety of techniques (e.g., ultrasound, CT, and MRI). We describe the development of a quantitative method for the analysis of muscle composition using MR T2 relaxation time mapping and image analysis. This approach provides an objective means of studying muscle and, when used in conjunction with force production measurements, may provide an accurate measure of response to muscle therapy.

Ultrasound imaging of the masseter muscle in myotonic dystrophy patients

Ultrasound technique was applied to measure the thickness and examine the internal structure of the masseter muscle in a group of 16 adult patients (nine women and seven men) with myotonic dystrophy (MyD) and 16 healthy individuals matched in age, sex and number of occluding teeth. The masseter thickness was measured bilaterally under both relaxed conditions and during maximal clenching. The error of measurement was found to be small, not exceeding 0.45 mm. The imaging characteristics of the masseter in most of the MyD patients was an obvious atrophy of the muscle with increased echointensity of the intramuscular tissue and loss of the internal structure concerning tendons and fasciae. The mean masseter thickness (+/- SD) in the MyD group was 10.4 (+/- 2.2) mm under relaxed conditions and 11.1 (+/- 2.4) mm during maximal clenching, compared with 13.3 (+/- 2.2) mm and 14.1 (+/- 2.4) mm, respectively, in the healthy group (P < 0.001). In conclusion, our results indicate that, in most of the myotonic dystrophy patients, the masseter muscle is atrophic with obvious signs of degeneration. Ultrasound is a useful method for both qualitative and quantitative evaluation of the condition of the masseter muscle.

Magnetic resonance imaging of skeletal muscles in idiopathic inflammatory myopathies of adults

The purpose of the study was to describe typical MRI findings in various types of idiopathic inflammatory myopathies in adulthood and to correlate the MRI with histopathological and electromyographic findings, and the serum creatine kinase (CK) activity. A third goal was to assess the diagnostic value of the use of gadolinium-DTPA (Gd-DTPA). Fifty-eight patients (35 women, 23 men), aged 21-83 years (median age 59 years), suffering from idiopathic myositides (13 with acute and 45 chronic diseases; 25 with polymyositis, 14 with dermatomyositis, 8 with granulomatous and 11 with inclusion body myositides) were examined with MRI. Seventeen of them received an intravenous infusion of Gd-DTPA. Histopathological and MRI findings of 21 muscles of 18 patients were compared. MRI of skeletal muscles showed abnormal signal intensities in 56 (96.6%) of the 58 patients. MRI abnormalities were found more often than elevated CK activity (P < 0.001). The hyperintensity of T2-weighted images was more conspicuous than on T1-weighted images in 26 (44.8%) patients, indicating oedema-like abnormalities. MRI of 50 (86.2%) patients showed fat replacement. In acute myositides, oedema-like abnormalities were more often visible and in muscle lipomatosis less often visible than in chronic diseases (P < 0.05 each). In dermatomyositis oedema-like abnormalities were more and lipomatosis less frequent than in the other types of myositis (P < 0.005) and correlated with the acuteness of the disease.(ABSTRACT TRUNCATED AT 250 WORDS)