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

Substrate reduction therapy with miglustat in chronic GM2 gangliosidosis type Sandhoff: results of a 3-year follow-up

GM2 gangliosidosis type Sandhoff is caused by a defect of beta-hexosaminidase, an enzyme involved in the catabolism of gangliosides. It has been proposed that substrate reduction therapy using N-butyl-deoxynojirimycin (miglustat) may delay neurological progression, at least in late-onset forms of GM2 gangliosidosis. We report the results of a 3-year treatment with miglustat (100 mg t.i.d) in a patient with chronic Sandhoff disease manifesting with an atypical, spinal muscular atrophy phenotype. The follow-up included serial neurological examinations, blood tests, abdominal ultrasound, and neurophysiologic, cognitive, brain, and muscle MRI studies. We document some minor effects on neurological progression in chronic Sandhoff disease by miglustat treatment, confirming the necessity of phase II therapeutic trials including early-stage patients in order to assess its putative efficacy in chronic Sandhoff disease.

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.

Quantitative magnetization transfer in in vivo healthy human skeletal muscle at 3 T

The value of quantitative MR methods as potential biomarkers in neuromuscular disease is being increasingly recognized. Previous studies of the magnetization transfer ratio have demonstrated sensitivity to muscle disease. The aim of this work was to investigate quantitative magnetization transfer imaging of skeletal muscle in healthy subjects at 3 T to evaluate its potential use in pathological muscle. The lower limb of 10 subjects was imaged using a 3D fast low-angle shot acquisition with variable magnetization transfer saturation pulse frequencies and amplitudes. The data were analyzed with an established quantitative two-pool model of magnetization transfer. T₁ and B₁ amplitude of excitation radiofrequency field maps were acquired and used as inputs to the quantitative magnetization transfer model, allowing properties of the free and restricted proton pools in muscle to be evaluated in seven different muscles in a region of interest analysis. The average restricted pool T₂ relaxation time was found to be 5.9 ± 0.2μs in the soleus muscle and the restricted proton pool fraction was 8 ± 1%. Quantitative magnetization transfer imaging of muscle offers potential new biomarkers in muscle disease within a clinically feasible scan time. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.

T2 mapping in Duchenne muscular dystrophy: distribution of disease activity and correlation with clinical assessments

PURPOSE

To analyze T2 maps of pelvic and thigh muscles in Duchenne muscular dystrophy (DMD), to identify the most severely affected muscle, and to correlate the T2 of muscle with the grade of fatty infiltration at nonquantitative magnetic resonance (MR) imaging and results of clinical assessment.

MATERIALS AND METHODS

This prospective study was HIPAA compliant and was approved by the institutional review board; written consent was obtained from all participants' parents or guardians. Thirty-four boys with DMD (mean age, 8.4 years) were evaluated clinically (age, clinical function score, timed Gower score, time to run 30 feet, and serum creatine kinase [CK] level) and with nonquantitative MR imaging and axial T2 mapping from the iliac crest to the mid thigh. The T2 maps and mean T2 of 18 muscles in the pelvis and thighs were analyzed to identify the most severely involved muscle. The amount of fatty infiltration was assigned a grade of zero to four for all pelvic and thigh muscles by using T1-weighted nonquantitative MR images. The Spearman correlation coefficients model was used to correlate the mean T2, nonquantitative MR imaging score and clinical assessments.

RESULTS

The gluteus maximus muscle had the highest T2. The mean T2 for this muscle showed a significant correlation with the nonquantitative MR imaging score for fatty infiltration (P < .001) and with all clinical assessments except CK level.

CONCLUSION

Gluteus maximus muscles are most severely affected in patients with DMD. The T2 of the gluteus maximus muscle can be used as a quantitative and objective measure of disease severity.

Only fat infiltrated muscles in resting lower leg of FSHD patients show disturbed energy metabolism

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by asymmetric dysfunctioning of individual muscles. Currently, it is unknown why specific muscles are affected before others and more particularly what pathophysiology is causing this differential progression. The aim of our study was to use a combination of (31)P magnetic resonance spectroscopic imaging (MRSI) and T1-weighted MRI to uncover metabolic differences in fat infiltrated and not fat infiltrated muscles in patients with FSHD. T1-weighted images and 3D (31)P MRSI were obtained from the calf muscles of nine patients with diagnosed FSHD and nine healthy age and sex matched volunteers. Muscles of patients were classified as fat infiltrated (PFM) and non fat-infiltrated (PNM) based on visual assessment of the MR images. Ratios of phosphocreatine (PCr), phosphodiesters (PDE) and inorganic phosphate (Pi) over ATP and tissue pH were compared between PFM and PNM and the same muscles in healthy volunteers. Of all patients, seven showed moderate to severe fatty infiltration in one or more muscles. In these muscles, decreases in PCr/ATP and increases in tissue pH were observed compared to the same muscles in healthy volunteers. Interestingly, these differences were absent in the PNM group. Our data show that differences in metabolite ratios and tissue pH in skeletal muscle between healthy volunteers and patients with FSHD appear to be specific for fat infiltrated muscles. Normal appearing muscles on T1 weighted images of patients showed normal phosphoryl metabolism, which suggests that in FSHD disease progression is truly muscle specific.

Differentiating Emery-Dreifuss muscular dystrophy and collagen VI-related myopathies using a specific CT scanner pattern

Bethlem myopathy and Ullrich congenital muscular dystrophy are part of the heterogeneous group of collagen VI-related muscle disorders. They are caused by mutations in collagen VI (ColVI) genes (COL6A1, COL6A2, and COL6A3) while LMNA mutations cause autosomal dominant Emery-Dreifuss muscular dystrophy. A muscular dystrophy pattern and contractures are found in all three conditions, making differential diagnosis difficult especially in young patients when cardiomyopathy is absent. We retrospectively assessed upper and lower limb muscle CT scans in 14 Bethlem/Ullrich patients and 13 Emery-Dreifuss patients with identified mutations. CT was able to differentiate Emery-Dreifuss muscular dystrophy from ColVI-related myopathies in selected thigh muscles and to a lesser extent calves muscles: rectus femoris fatty infiltration was selectively present in Bethlem/Ullrich patients while posterior thigh muscles infiltration was more prominently found in Emery-Dreifuss patients. A more severe fatty infiltration particularly in the leg posterior compartment was found in the Emery-Dreifuss group.

Infantile spinal muscular atrophy with respiratory distress type 1: a case report

The condition, currently known as spinal muscular atrophy with respiratory distress type 1, is an unusual variant of spinal muscular atrophy type 1 that is characterized by early respiratory failure due to diaphragmatic paralysis. The defective gene, the immunoglobulin mu-binding protein 2 (IGHMBP2 gene), of this autosomal recessive disorder is located on chromosome 11q13 and encodes immunoglobulin mu-binding protein 2. The natural history and phenotypic spectrum of the disease are still not clear. The authors present the first genetically proven case of spinal muscular atrophy with respiratory distress type 1 to be reported from Saudi Arabia. The parents are first cousins and the causative gene sequencing revealed mutation in exon 7 reported for the first time in a homozygous form. The clinical scenario of the case is discussed. The findings in the muscle magnetic resonance imaging (MRI) are presented.

Quantitative assessment of the T2 relaxation time of the gluteus muscles in children with Duchenne muscular dystrophy: a comparative study before and after steroid treatment

OBJECTIVE

To determine the feasibility of using T2 mapping as a quantitative method to longitudinally follow the disease activity in children with Duchenne muscular dystrophy (DMD) who are treated with steroids.

MATERIALS AND METHODS

ELEVEN BOYS WITH DMD (AGE RANGE: 5-14 years) underwent evaluation with the clinical functional score (CFS), and conventional pelvic MRI and T2 mapping before and during steroid therapy. The gluteus muscle inflammation and fatty infiltration were evaluated on conventional MRI. The histograms and mean T2 relaxation times were obtained from the T2 maps. The CFS, the conventional MRI findings and the T2 values were compared before and during steroid therapy.

RESULTS

None of the patients showed interval change of their CFSs. On conventional MRI, none of the images showed muscle inflammation. During steroid treatment, two boys showed increased fatty infiltration on conventional MRI, and both had an increase of the mean T2 relaxation time (p < 0.05). The remaining nine boys had no increase in fatty infiltration. Of these, three showed an increased mean T2 relaxation time (p < 0.05), two showed no change and four showed a decreased mean T2 relaxation time (p < 0.05).

CONCLUSION

T2 mapping is a feasible technique to evaluate the longitudinal muscle changes in those children who receive steroid therapy for DMD. The differences of the mean T2 relaxation time may reflect alterations in disease activity, and even when the conventional MRI and CFS remain stable.

Muscle imaging analogies in a cohort of patients with different clinical phenotypes caused by LMNA gene mutations

Laminopathies are a heterogeneous group of LMNA-gene-mutation-related clinical disorders associated with alterations of cardiac and skeletal muscle and peripheral nerves, metabolic defects, and premature aging. Leg muscle imaging investigations were performed in a cohort of patients with LMNA gene alterations who were suffering from Emery-Dreifuss muscular dystrophy, limb-girdle muscular dystrophy type 1B, isolated cardiac disorders or a phenotype of cardiac disorders, and lipodystrophy, including one individual with peripheral neuropathy. Leg muscle imaging revealed varying degrees of alteration in the soleus and medial head of gastrocnemius in each subject. This study demonstrates that LMNA-gene-mutated patients devoid of any clinically detectable skeletal muscle involvement have the same pattern of leg muscle involvement as patients with overt skeletal muscle compromise. This finding suggests the presence of a continuum of skeletal muscle involvement among phenotypes of LMNA-gene-mutation-related skeletalmyopathy and cardiomyopathy.

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.

Interventions for increasing ankle range of motion in patients with neuromuscular disease

BACKGROUND

Reduced ankle dorsiflexion range of motion, or ankle equinus, is a common and disabling problem for patients with neuromuscular disease. Clinicians devote considerable time and resources implementing interventions to correct this problem although few of these interventions have been subject to rigorous empirical investigation.

OBJECTIVES

To assess the effect of interventions to reduce or resolve ankle equinus in people with neuromuscular disease.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group Trials Specialized Register (August 2009), Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2009), MEDLINE (1966 to August 2009), EMBASE (1980 to August 2009), CINAHL 1982 to August 2009), AMED (1985 to August 2009) and The Physiotherapy Evidence Database (PEDro) (1929 to August 2009). We searched the reference lists of identified articles and also contacted known experts in the field to identify additional or unpublished data.

SELECTION CRITERIA

Randomised controlled trials evaluating interventions for increasing ankle dorsiflexion range of motion in neuromuscular disease. Outcomes included ankle dorsiflexion range of motion, functional improvement, foot alignment, foot and ankle muscle strength, health-related quality of life, satisfaction with the intervention and adverse events.

DATA COLLECTION AND ANALYSIS

Two authors independently selected papers, assessed trial quality and extracted data.

MAIN RESULTS

Four studies involving 149 participants met inclusion criteria for this review. Two studies assessed the effect of night splinting in a total of 26 children and adults with Charcot-Marie-Tooth disease type 1A. There were no statistically or clinically significant differences between wearing a night splint and not wearing a night splint. One study assessed the efficacy of prednisone treatment in 103 boys with Duchenne muscular dystrophy. While a daily dose of prednisone at 0.75 mg/kg/day resulted in significant improvements in some strength and function parameters compared with placebo, there was no significant difference in ankle range of motion between groups. Increasing the prednisone dose to 1.5 mg/kg/day had no significant effect on ankle range of motion. One study evaluated early surgery in 20 young boys with Duchenne muscular dystrophy. Surgery resulted in increased ankle dorsiflexion range at 12 months but functional outcomes favoured the control group. By 24 months, many boys in the surgical group experienced a relapse of achilles tendon contractures.

AUTHORS' CONCLUSIONS

There is no evidence of significant benefit from any intervention for increasing ankle range of motion in Charcot-Marie-Tooth disease type 1A or Duchenne muscular dystrophy. Further research is required.

Whole-body high-field MRI shows no skeletal muscle degeneration in young patients with recessive myotonia congenita

BACKGROUND

Muscle magnetic resonance imaging (MRI) is the most sensitive method in the detection of dystrophic and non-dystrophic abnormalities within striated muscles. We hypothesized that in severe myotonia congenita type Becker muscle stiffness, prolonged transient weakness and muscle hypertrophy might finally result in morphologic skeletal muscle alterations reflected by MRI signal changes.

AIM OF THE STUDY

To assess dystrophic and/or non-dystrophic alterations such as fatty or connective tissue replacement and muscle edema in patients with severe recessive myotonia congenita.

METHODS

We studied three seriously affected patients with myotonia congenita type Becker using multisequence whole-body high-field MRI. All patients had molecular genetic testing of the muscle chloride channel gene (CLCN1).

RESULTS

Molecular genetic analyses demonstrated recessive CLCN1 mutations in all patients. Two related patients were compound heterozygous for two novel CLCN1 mutations, Q160H and L657P. None of the patients showed skeletal muscle signal changes indicative of fatty muscle degeneration or edema. Two patients showed muscle bulk hypertrophy of thighs and calves in line with the clinical appearance.

CONCLUSIONS

We conclude that (i) chloride channel dysfunction alone does not result in skeletal muscle morphologic changes even in advanced stages of myotonia congenita, and (ii) MRI skeletal muscle alterations in myotonic dystrophy must be clear consequences of the dystrophic disease process.

Amyloid myopathy: a diagnostic challenge

Amyloid myopathy (AM) is a rare manifestation of primary systemic amyloidosis (AL). Like inflammatory myopathies, it presents with proximal muscle weakness and an increased creatine kinase level. We describe a case of AL with severe, rapidly progressive myopathy as the initial symptom. The clinical manifestation and muscle biopsy were suggestive of inclusion body myositis. AM was not suspected until amyloidosis was seen in the gastric mucosal biopsy. The muscle biopsy was then re-examined more specifically, and Congo red staining eventually showed vascular and interstitial amyloid accumulation, which led to a diagnosis of AM. The present case illustrates the fact that the clinical picture of AM can mimic that of inclusion body myositis.

Molecular diagnosis of muscular dystrophies, focused on limb girdle muscular dystrophies

BACKGROUND

Muscular dystrophies include a spectrum of muscle disorders, some of which are phenotypically well characterized. The identification of dystrophin as the causative factor in Duchenne muscular dystrophy has led to the development of molecular genetics and has facilitated the division of muscular dystrophies into distinct groups, among which are the 'limb girdle muscular dystrophies'.

OBJECTIVES

This article reviews the methodology to be used in the diagnosis of muscular dystrophies, focused on the groups of limb girdle muscular dystrophies, and the development of new strategies to reach a final molecular diagnosis.

METHOD

A literature review (Medline) from 1985 to the present.

CONCLUSION

Immunohistochemistry and western blotting analyses of the proteins involved in the various forms of muscular dystrophies have permitted a refined pathological approach necessary to conduct genetic studies and to offer appropriate genetic counseling. The application of molecular medicine in genetic muscular dystrophies also brings great hope to the therapeutic management of these patients.

Local restoration of dystrophin expression with the morpholino oligomer AVI-4658 in Duchenne muscular dystrophy: a single-blind, placebo-controlled, dose-escalation, proof-of-concept study

BACKGROUND

Mutations that disrupt the open reading frame and prevent full translation of DMD, the gene that encodes dystrophin, underlie the fatal X-linked disease Duchenne muscular dystrophy. Oligonucleotides targeted to splicing elements (splice switching oligonucleotides) in DMD pre-mRNA can lead to exon skipping, restoration of the open reading frame, and the production of functional dystrophin in vitro and in vivo, which could benefit patients with this disorder.

METHODS

We did a single-blind, placebo-controlled, dose-escalation study in patients with DMD recruited nationally, to assess the safety and biochemical efficacy of an intramuscular morpholino splice-switching oligonucleotide (AVI-4658) that skips exon 51 in dystrophin mRNA. Seven patients with Duchenne muscular dystrophy with deletions in the open reading frame of DMD that are responsive to exon 51 skipping were selected on the basis of the preservation of their extensor digitorum brevis (EDB) muscle seen on MRI and the response of cultured fibroblasts from a skin biopsy to AVI-4658. AVI-4658 was injected into the EDB muscle; the contralateral muscle received saline. Muscles were biopsied between 3 and 4 weeks after injection. The primary endpoint was the safety of AVI-4658 and the secondary endpoint was its biochemical efficacy. This trial is registered, number NCT00159250.

FINDINGS

Two patients received 0.09 mg AVI-4658 in 900 microL (0.9%) saline and five patients received 0.9 mg AVI-4658 in 900 microL saline. No adverse events related to AVI-4658 administration were reported. Intramuscular injection of the higher-dose of AVI-4658 resulted in increased dystrophin expression in all treated EDB muscles, although the results of the immunostaining of EDB-treated muscle for dystrophin were not uniform. In the areas of the immunostained sections that were adjacent to the needle track through which AVI-4658 was given, 44-79% of myofibres had increased expression of dystrophin. In randomly chosen sections of treated EDB muscles, the mean intensity of dystrophin staining ranged from 22% to 32% of the mean intensity of dystrophin in healthy control muscles (mean 26.4%), and the mean intensity was 17% (range 11-21%) greater than the intensity in the contralateral saline-treated muscle (one-sample paired t test p=0.002). In the dystrophin-positive fibres, the intensity of dystrophin staining was up to 42% of that in healthy muscle. We showed expression of dystrophin at the expected molecular weight in the AVI-4658-treated muscle by immunoblot.

INTERPRETATION

Intramuscular AVI-4658 was safe and induced the expression of dystrophin locally within treated muscles. This proof-of-concept study has led to an ongoing systemic clinical trial of AVI-4658 in patients with DMD.

FUNDING

UK Department of Health.

Clinical outcome measures in spinal muscular atrophy

Spinal muscular atrophy is one of the most devastating neurological diseases of childhood. Affected infants and children suffer from often severe muscle weakness caused by degeneration of lower motor neurons in the spinal cord and brainstem. Identification of the causative genetic mutation in most cases has resulted in development of potential treatment strategies. To test these new drugs, clinically feasible outcomes are needed. Several different assessments, validated in spinal muscular atrophy or similar disorders, are being used by national and international research groups; however, their sensitivity to detect change is unknown. Acceptance of a few standardized, easily administered, and functionally meaningful outcomes, applicable to the phenotypic spectrum of spinal muscular atrophy, is needed. Consensus is imperative to facilitate collaboration and explore the ability of these measures to identify the therapeutic effect of disease-modifying agents. Following is an evidence-based review of available clinical outcome measures in spinal muscular atrophy.

Pattern of skeletal muscle involvement in primary dysferlinopathies: a whole-body 3.0-T magnetic resonance imaging study

OBJECTIVES AND METHODS

Mutations in the gene encoding dysferlin cause limb girdle muscular dystrophy type 2B (LGMD2B), distal Miyoshi myopathy (MM), and a rare form of distal anterior compartment myopathy. To study the correlations between clinical manifestations and muscle imaging changes we conducted a 3.0-T magnetic resonance imaging (MRI) study in six German patients with primary dysferlinopathies defined by absence of dysferlin expression in muscle (MM, n = 3; LGMD2B, n = 2; hyperCKemia without clinical symptoms, n = 1).

RESULTS

Patients with manifest myopathy had widespread muscular pathology. In analogy to previous imaging studies, we confirmed an involvement of the anterior and posterior thigh compartments and a predominant involvement of posterior lower legs. However, our whole-body MRI study further provided evidence of signal alterations in the glutei, erector spinae and shoulder girdle muscles. Correlation of clinical findings with imaging demonstrated the potential of MRI to detect subclinical muscle pathology.

CONCLUSIONS

Whole-body 3.0-T MRI is a non-invasive method to demonstrate various degrees of skeletal muscle alterations and disease progression in muscular dystrophies. Furthermore, whole-body high-field MRI may serve as a helpful diagnostic tool in differentiating primary dysferlinopathies from other forms of LGMD and distal myopathies.

Muscle MRI in FHL1-linked reducing body myopathy

Reducing body myopathy is a rare progressive myopathy identified by characteristic pathological findings and secondary to dominantly acting mutations in the X-linked FHL1 gene. We report muscle MRI findings in two patients affected by reducing body myopathy and in their carrier mothers. All four showed a distinctive pattern of muscle alteration, with a predominant involvement of postero-medial muscle at thigh level and of soleus at calf level, with a striking sparing of glutei muscles that also appeared to be hypertrophic. These findings may help in the differential diagnosis of these disorders.

Lower limb radiology of distal myopathy due to the S60F myotilin mutation

Distal myopathies are a clinically and genetically heterogenous group of disorders in which the distal limb musculature is selectively or disproportionately affected. Precisely defining specific categories is a challenge because of overlapping clinical phenotypes, making it difficult to decide which of the many known causative genes to screen in individual cases. In this study we define the distinguishing magnetic resonance imaging findings in myotilin myopathy by studying 8 genealogically unrelated cases due to the same point mutation in TTID. Proximally, the vastii, biceps femoris and semimembranosus were involved with sparing of gracilis and sartorius. Distally, soleus, gastrocnemius, tibialis anterior, extensor hallicus and extensor digitorum were involved. This pattern contrasts with other distal myopathies and provides further support for the role of imaging in the clinical investigation of muscle disease.

Quantitative MR imaging of individual muscle involvement in facioscapulohumeral muscular dystrophy

The purpose of this study was to implement a quantitative MR imaging method for the determination of muscular and fat content in individual skeletal muscles of patients with facioscapulohumeral muscular dystrophy (FSHD). Turbo Inversion Recovery Magnitude (TIRM) and multiecho MR images were acquired from seven FSHD patients and healthy volunteers. Signal decay in the multiecho MR images was fitted to a biexponential function with fixed relaxation rates for muscle and fat tissue and used to calculate the degree of fatty infiltration in eight muscles in the lower leg. Considerable differences in fatty infiltration between different muscles were observed in FSHD patients, suggesting that this could be used as a biomarker for disease progression. TIRM imaging indicated an inflammatory component of the disease previously only observed in muscle biopsies. Typically, muscle involvement was non-uniform even within one muscle, indicating that MRI can be used as a valuable tool to study pathophysiology and therapy evaluation in FSHD.

Congenital muscular dystrophy. Part I: a review of phenotypical and diagnostic aspects

The congenital muscular dystrophies (CMDs) are a group of genetically and clinically heterogeneous hereditary myopathies with preferentially autosomal recessive inheritance, that are characterized by congenital hypotonia, delayed motor development and early onset of progressive muscle weakness associated with dystrophic pattern on muscle biopsy. The clinical course is broadly variable and can comprise the involvement of the brain and eyes. From 1994, a great development in the knowledge of the molecular basis has occurred and the classification of CMDs has to be continuously up dated. We initially present the main clinical and diagnostic data concerning the CMDs related to changes in the complex dystrophin-associated glycoproteins-extracellular matrix: CMD with merosin deficiency (CMD1A), collagen VI related CMDs (Ullrich CMD and Bethlem myopathy), CMDs with abnormal glycosylation of alpha-dystroglycan (Fukuyama CMD, Muscle-eye-brain disease, Walker-Warburg syndrome, CMD1C, CMD1D), and the much rarer CMD with integrin deficiency. Finally, we present other forms of CMDs not related with the dystrophin/glycoproteins/extracellular matrix complex (rigid spine syndrome, CMD1B, CMD with lamin A/C deficiency), and some apparently specific clinical forms not yet associated with a known molecular mechanism. The second part of this review concerning the pathogenesis and therapeutic perspectives of the different subtypes of CMD will be described in a next number.

"Necklace" fibers, a new histological marker of late-onset MTM1-related centronuclear myopathy

Mutations in the gene encoding the phosphoinositide phosphatase myotubularin 1 protein (MTM1) are usually associated with severe neonatal X-linked myotubular myopathy (XLMTM). However, mutations in MTM1 have also been recognized as the underlying cause of "atypical" forms of XLMTM in newborn boys, female infants, female manifesting carriers and adult men. We reviewed systematically the biopsies of a cohort of patients with an unclassified form of centronuclear myopathy (CNM) and identified four patients presenting a peculiar histological alteration in some muscle fibers that resembled a necklace ("necklace fibers"). We analyzed further the clinical and morphological features and performed a screening of the genes involved in CNM. Muscle biopsies in all four patients demonstrated 4-20% of fibers with internalized nuclei aligned in a basophilic ring (necklace) at 3 microm beneath the sarcolemma. Ultrastructurally, such necklaces consisted of myofibrils of smaller diameter, in oblique orientation, surrounded by mitochondria, sarcoplasmic reticulum and glycogen granules. In the four patients (three women and one man), myopathy developed in early childhood but was slowly progressive. All had mutations in the MTM1 gene. Two mutations have previously been reported (p.E404K and p.R241Q), while two are novel; a c.205_206delinsAACT frameshift change in exon 4 and a c.1234A>G mutation in exon 11 leading to an abnormal splicing and the deletion of nine amino acids in the catalytic domain of MTM1. Necklace fibers were seen neither in DNM2- or BIN1-related CNM nor in males with classical XLMTM. The presence of necklace fibers is useful as a marker to direct genetic analysis to MTM1 in CNM.

Pathological defects in congenital myopathies

Congenital myopathies are a molecularly, pathologically and clinically heterogenous group of disorders defined by hypotonia and muscle weakness, that usually present at birth or early childhood, in association with a characteristic morphological defect. The most common morphological defects are nemaline rods, cores of varying size, central nuclei, and type I fibre hypotrophy, with or without an additional abnormality. The defective genes responsible for many of the congenital myopathies are known, but there is considerable clinico-pathological overlap. In particular, defects in more than one gene are associated with the presence of the same pathological feature, while defects in the same gene can result in more than one pathological feature. Understanding the complexities of these spectra is paramount to the elucidation of pathogenesis, and to the development of therapies.

Dysferlin-deficient muscular dystrophy: gadofluorine M suitability at MR imaging in a mouse model

PURPOSE

To compare the usefulness of gadofluorine M with that of Gadomer in assessment of dysferlin-deficient muscular dystrophy at 7.0-T magnetic resonance (MR) imaging.

MATERIALS AND METHODS

All experiments were approved by local review boards. SJL/J mice (n = 24) with dysferlin-deficient muscular dystrophy and C57BL/6 control mice (n = 24) were imaged at 12-15 weeks (young) or older than 30 weeks (old) by using dynamic contrast material-enhanced imaging with inversion-prepared steady-state free-precession sequence before, during, and after administration of gadofluorine M at 2 micromol or Gadomer at 4 micromol intravenously. After imaging, regions of interest were determined from the upper extremity and left ventricular chamber; fractional extravascular extracellular volume, v(e), and permeability surface tissue density product, PS rho, were measured by using a two-compartment pharmacokinetic model. The natural history of muscular dystrophy was assessed histologically in 70 mice (seven five-mouse groups each of SJL/J mice and of control mice) at 4-week intervals from 8 to 32 weeks. In addition, three SJL/J mice and three control mice at age 33 weeks were sacrificed, and fluorescence microscopy was performed for visualization of intravenously administered carbocyanine-labeled gadofluorine M in muscle cells. Statistical analysis was performed by using the t test.

RESULTS

Gadofluorine M enhancement was significantly greater in skeletal muscle of 30-week-old mice with dysferlin-deficient muscular dystrophy, compared with control mice. Gadofluorine M demonstrated both increased rate of enhancement (PS rho sec(-1) +/- standard error of the mean: 0.004 e(-)(4) +/- 3 vs 0.002 e(-)(4) +/- 3; P < .05) and increased level of enhancement (v(e) +/- standard error of the mean: 0.035 +/- 0.004 vs 0.019 +/- 0.004; P < .05). Gadomer showed no differential enhancement in the two mouse groups. Histologic examination confirmed the presence of labeled gadofluorine M in muscle cells.

CONCLUSION

Gadofluorine M-enhanced MR imaging may be of value in monitoring dysferlin-deficient muscular dystrophy disease progression in this animal model and could prove to be a useful tool in following the course of chronic muscle diseases in humans.

Congenital myopathies

PURPOSE OF REVIEW

The present review aims to discuss the pathological and clinical heterogeneity of congenital myopathies, and the overlap between the different variants highlighted by recent studies.

RECENT FINDINGS

The spectrum of pathological changes associated with known gene defects has widened, and new genes responsible for rare structural defects have been identified. The complexity of the classification of these conditions is highlighted by the realization that defects in the same gene can result in diverse phenotypes, including disorders traditionally classified as congenital myopathies with structural abnormalities, adult-onset disorders, conditions characterized by distal weakness and wasting, or distal arthrogryposis. There is a wider appreciation of the complexities of inheritance and of the value of noninvasive assessment, such as muscle MRI. New animal models provide a better understanding of pathogenesis and are highlighting therapeutic possibilities.

SUMMARY

The overlap of clinical and pathological features in the congenital myopathies has led to the recognition that diverse disorders are often associated with the same causative gene, and is challenging traditional classifications. Identification of further causative genes and development of new models will further the understanding of pathogenesis and development of therapies.

Limb-girdle muscular dystrophies

PURPOSE OF REVIEW

The aim of this review is to provide an up-to-date analysis of current knowledge about limb-girdle muscular dystrophies (LGMDs).

RECENT FINDINGS

Over the last few years, new and interesting studies have been published on LGMD. New LGMD genes have been discovered and the clinical and genetic heterogeneity in this group of muscular dystrophies has been further enlarged by the description of new forms of LGMD. Several studies have demonstrated involvement of genes causing posttranslational modifications of alpha-dystroglycan in the pathogenesis of autosomal recessive LGMD. This has highlighted an important overlap in pathogenesis between LGMD and congenital muscular dystrophies, prompting further research. Moreover, new pathogenic mechanisms and pathways are emerging for LGMD, in particular calpainopathies, dysferlinopathies and titinopathies. Such new findings may suggest novel therapeutic approaches and future clinical trials.

SUMMARY

The increased understanding of the genes and pathogenic mechanism of the LGMDs will improve diagnostic processes and prognostic accuracy, and promote therapeutic strategies. European and global LGMD patient registries will increase current knowledge on natural history and facilitate translational research.

MR imaging evaluation of disorders of the chest wall

Chest wall lesions constitute a diverse group of thoracic diseases, including those of soft tissue and osseous origin. MR imaging, with its superior tissue-resolving capability and multiplanar image acquisition, is an important tool for assessing chest wall lesions. In this article, the authors review common and uncommon diseases of the chest wall, with an emphasis on the MR imaging characteristics of these diseases. Among the diseases they discuss are diseases of the soft tissue including lipoma, hibernoma, liposarcoma, hemangioma, and lymphoma. They also examine diseases of the osseous thorax, including benign osseous tumors, fibrous dysplasia, and aneurysmal bone cyst. In addition, they discuss such malignant osseous tumors as osteosarcoma and Ewing's sarcoma.

Magnetic resonance imaging of skeletal muscle

PURPOSE OF REVIEW

Clinical investigations of neuromuscular diseases routinely involve genetic, neurophysiological, biochemical and histopathological methods. More recently, various magnetic resonance imaging techniques have become available and extended the differential diagnostic possibilities.

RECENT FINDINGS

Using magnetic resonance imaging it is now possible to quantify muscle volume in selected body regions and measure wasting and exercise-induced muscle hypertrophy. Evidence is forthcoming that many hereditary myopathies are characterized by distinct patterns of muscle degeneration and this helps in selecting other relevant genetic and biochemical investigations. With diffusion-weighted tensor imaging it is possible to identify the microstructure of normal and diseased muscles. Arterial spin labelling is an emerging non-invasive tool to assess blood-flow changes in individual muscles. Magnetic resonance spectroscopy now provides an exciting opportunity to visualize metabolic changes and the pathophysiologically relevant cellular perturbations in muscle channelopathies affecting the muscle-specific sodium-channel isoform Na(v)1.4.

SUMMARY

Magnetic resonance imaging supplements investigations for the differential diagnosis of neuromuscular diseases. An advantage over routine neurophysiological or histopathological methods is that they are operator-independent, non-invasive and painless. Magnetic resonance imaging also has the advantage of providing a lasting detailed topographical picture of regional variations and allows robust measurements of muscle volume and various functional parameters.