Magnetic resonance imaging of muscle and brain in myotonic dystrophy

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.

Functional Ambulation Profile (FAP) Score as a Potential Marker of Gait Analysis in Myotonic Dystrophy Type 1

Recent studies on Myotonic dystrophy type 1 (DM1) have shown profound impairments in gait, leading to falls. We analyzed functional ambulation profile (FAP) score that reflects the temporal and spatial gait characteristics and investigated correlations with the lower limb muscle magnetic resonance imaging (MRI) and 6 min walk test (6MWT). Twenty patients with DM1 and 20 controls participated in this study. The 6MWT and gait analysis including FAP scores via GAITRite were performed in all patients and controls. DM1 patients displayed slower gait, shorter stride length, shorter stance length, and lower FAP score. Among lower extremity muscles, the gastrocnemius, soleus and tibialis anterior showed the most severe fat infiltration and these crural muscles significantly correlated with FAP and 6MWT. Among crural muscles, tibialis anterior was the most important muscle affecting gait speed, whereas the gastrocnemius contributed substantially to gait instability. FAP score correlated with the muscle imaging and 6MWT in DM1. Therefore, FAP score maybe used as an non-invasive marker that reflects deterioration of gait and a possible surrogate biomarker in DM1.

Lower extremity muscle pathology in myotonic dystrophy type 1 assessed by quantitative MRI

Objective

To determine the value of quantitative MRI in providing imaging biomarkers for disease in 20 different upper and lower leg muscles of patients with myotonic dystrophy type 1 (DM1).

Methods

We acquired images covering these muscles in 33 genetically and clinically well-characterized patients with DM1 and 10 unaffected controls. MRIs were recorded with a Dixon method to determine muscle fat fraction, muscle volume, and contractile muscle volume, and a multi-echo spin-echo sequence was used to determine T2 water relaxation time (T2_water), reflecting putative edema.

Results

Muscles in patients with DM1 had higher fat fractions than muscles of controls (15.6 ± 11.1% vs 3.7 ± 1.5%). In addition, patients had smaller muscle volumes (902 ± 232 vs 1,097 ± 251 cm³), smaller contractile muscle volumes (779 ± 247 vs 1,054 ± 246 cm³), and increased T2_water (33.4 ± 1.0 vs 31.9 ± 0.6 milliseconds), indicating atrophy and edema, respectively. Lower leg muscles were affected most frequently, especially the gastrocnemius medialis and soleus. Distribution of fat content per muscle indicated gradual fat infiltration in DM1. Between-patient variation in fat fraction was explained by age (≈45%), and another ≈14% was explained by estimated progenitor CTG repeat length (r² = 0.485) and somatic instability (r² = 0.590). Fat fraction correlated with the 6-minute walk test (r = −0.553) and muscular impairment rating scale (r = 0.537) and revealed subclinical muscle involvement.

Conclusion

This cross-sectional quantitative MRI study of 20 different lower extremity muscles in patients with DM1 revealed abnormal values for muscle fat fraction, volume, and T2_water, which therefore may serve as objective biomarkers to assess disease state of skeletal muscles in these patients.

ClinicalTrials.gov identifier

NCT02118779.

Current Progress in CNS Imaging of Myotonic Dystrophy

Neuroimaging in myotonic dystrophies provided a major contribution to the insight into brain involvement which is highly prevalent in these multisystemic disorders. Particular in Myotonic Dystrophy Type 1, conventional MRI first revealed hyperintense white matter lesions, predominantly localized in the anterior temporal lobe. Brain atrophy and ventricle enlargement were additional early findings already described almost 30 years ago. Since then, more advanced and sophisticated imaging methods have been applied in Myotonic Dystrophy Types 1 and 2. Involvement of actually normal appearing white matter and widespread cortical affection in PET studies were key results toward the recognition of diffuse and not only focally localized brain pathology in vivo. Later, structural abnormalities of both, gray and white matter, have been found in both forms of the disorder, albeit more prominent in myotonic dystrophy type 1. In Type 1, a consistent widespread cortical and subcortical involvement of gray and white matter affecting all lobes, brainstem and cerebellum was observed. Spectroscopy studies gave additional evidence of neuronal and glial damage in both types. Central questions regarding the origin and spatiotemporal evolution of the CNS involvement and its relevance for clinical symptoms had already been raised 30 years ago, however are still not answered. Results of correlation analyses between neuroimaging and clinical parameters are diverse and with few exceptions not well reproducible across studies. It may be related to the fact that most of the reported studies included only small numbers of subjects, sometimes even not separating Myotonic Dystrophy Type 1 from Type 2. But this heterogeneity may also support the current point of view that the clinical impairments are not simply linked to specific and regionally circumscribed structural or functional brain alterations. It seems more convincing that disturbed networks build the functional and structural substrate of clinical symptoms in these disorders as it is proposed in other neuropsychiatric diseases. Consecutively, structural and functional network analyses may provide additional information regarding the link between brain pathology and clinical symptoms. Up to now, only cross-sectional neuroimaging studies have been published. To analyze the temporal evolution of brain affection, longitudinal studies are urgently needed, and systematic natural history data would be useful to identify potential biomarkers for therapeutic studies.

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.

Brain imaging in myotonic dystrophy type 1: A systematic review

OBJECTIVE

To systematically review brain imaging studies in myotonic dystrophy type 1 (DM1).

METHODS

We searched Embase (index period 1974-2016) and MEDLINE (index period 1946-2016) for studies in patients with DM1 using MRI, magnetic resonance spectroscopy (MRS), functional MRI (fMRI), CT, ultrasound, PET, or SPECT. From 81 studies, we extracted clinical characteristics, primary outcomes, clinical-genetic correlations, and information on potential risk of bias. Results were summarized and pooled prevalence of imaging abnormalities was calculated, where possible.

RESULTS

In DM1, various imaging changes are widely dispersed throughout the brain, with apparently little anatomical specificity. We found general atrophy and widespread gray matter volume reductions in all 4 cortical lobes, the basal ganglia, and cerebellum. The pooled prevalence of white matter hyperintensities is 70% (95% CI 64-77), compared with 6% (95% CI 3-12) in unaffected controls. DTI shows increased mean diffusivity in all 4 lobes and reduced fractional anisotropy in virtually all major association, projection, and commissural white matter tracts. Functional studies demonstrate reduced glucose uptake and cerebral perfusion in frontal, parietal, and temporal lobes, and abnormal fMRI connectivity patterns that correlate with personality traits. There is significant between-study heterogeneity in terms of imaging methods, which together with the established clinical variability of DM1 may explain divergent results. Longitudinal studies are remarkably scarce.

CONCLUSIONS

DM1 brains show widespread white and gray matter involvement throughout the brain, which is supported by abnormal resting-state network, PET/SPECT, and MRS parameters. Longitudinal studies evaluating spatiotemporal imaging changes are essential.

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.

Magnetic resonance imaging patterns of muscle involvement in genetic muscle diseases: a systematic review

A growing body of the literature supports the use of magnetic resonance imaging as a potential biomarker for disease severity in the hereditary myopathies. We performed a systematic review of the medical literature to evaluate patterns of fat infiltration observed in magnetic resonance imaging studies of muscular dystrophy and congenital myopathy. Searches were performed using MEDLINE, EMBASE, and grey literature databases. Studies that described fat infiltration of muscles in patients with muscular dystrophy or congenital myopathy were selected for full-length review. Data on preferentially involved or spared muscles were extracted for analysis. A total of 2172 titles and abstracts were screened, and 70 publications met our criteria for inclusion in the systematic review. There were 23 distinct genetic disorders represented in this analysis. In most studies, preferential involvement and sparing of specific muscles were reported. We conclude that magnetic resonance imaging studies can be used to identify distinct patterns of muscle involvement in the hereditary myopathies. However, larger studies and standardized methods of reporting are needed to develop imaging as a diagnostic tool in these diseases.

MRI of tibialis anterior skeletal muscle in myotonic dystrophy type 1

OBJECTIVE

The aim of this study was to evaluate whether magnetic resonance imaging (MRI) can be used as a noninvasive approach to assessment of disease severity and muscle damage in Myotonic Dystrophy type 1 (DM1).

METHODS

The MRI findings in legs of 41 patients with DM1 were evaluated with respect to the tibialis anterior (TA) skeletal muscle impairment. Magnetic resonance imaging findings were compared with TA strength measurements obtained by quantitative manual testing, duration of the disease and with the length of the CTG repeats.

RESULTS

Muscle MRI abnormalities were observed in 80% of DM1 patients, ranging from edema-like abnormalities alone to severe atrophy/fatty replacement. Edema-like abnormalities seem to be an earlier MRI marker of the disease. Fatty infiltration/atrophy correlated with the TA muscle force (r = 0.95), the severity (P = 0.00001) of the disease but not with the duration of the disease (P = 0.3) or the length of the CTG repeats (P > 0.10), measured in peripheral leukocytes. Evaluation of other muscles of the legs revealed that the medial gastrocnemius and soleus muscles were the most frequently and severely affected muscles, while tibialis posterior muscles were relatively spared. Edema-like abnormalities are most frequently observed in the skeletal muscles of the anterior compartment.

CONCLUSION

Muscle MRI is helpful to depict muscle abnormalities but does not seem to be a reliable indicator of skeletal muscle involvement in DM1 since the decrease in TAmuscle force is not correlated with MRI abnormalities in some patients.

White matter abnormalities and neurocognitive correlates in children and adolescents with myotonic dystrophy type 1: a diffusion tensor imaging study

Diffusion tensor imaging was used to evaluate cerebral white matter in eight patients (ages 10-17), with myotonic dystrophy type 1 (3 congenital-onset, 5 juvenile-onset) compared to eight controls matched for age and sex. Four regions of interest were examined: inferior frontal, superior frontal, supracallosal, and occipital. The myotonic dystrophy group showed white matter abnormalities compared to controls in all regions. All indices of white matter integrity were abnormal: fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity. With no evidence of regional variation, correlations between whole cerebrum white matter fractional anisotropy and neurocognitive functioning were examined in the patients. Strong correlations were observed between whole cerebrum fractional anisotropy and full-scale intelligence and a measure of executive functioning. Results indicate that significant white matter abnormality is characteristic of young patients with myotonic dystrophy type 1 and that the white matter abnormality seen with neuroimaging has implications for cognitive functioning.

Morphologic imaging in muscular dystrophies and inflammatory myopathies

OBJECTIVE

To determine if magnetic resonance imaging (MR imaging) is useful in the diagnostic workup of muscular dystrophies and idiopathic inflammatory myopathies for describing the topography of muscle involvement.

MATERIALS AND METHODS

MR imaging was performed in 31 patients: 8 with dystrophic myotony types 1 (n = 4) or 2 (n = 4); 11 with limb-girdle muscular dystrophy, including dysferlinopathy, calpainopathy, sarcoglycanopathy, and dystrophy associated with fukutin-related protein mutation; 3 with Becker muscular dystrophy; and 9 with idiopathic inflammatory myopathies, including polymyositis, dermatomyositis, and sporadic inclusion body myositis.

RESULTS

Analysis of T1 images enabled us to describe the most affected muscles and the muscles usually spared for each muscular disease. In particular, examination of pelvis, thigh, and leg muscles demonstrated significant differences between the muscular diseases. On STIR images, hyperintensities were present in 62% of our patients with muscular dystrophies.

CONCLUSION

A specific pattern of muscular involvement was established for each muscular disease. Hyperintensities observed on STIR images precede fatty degeneration and are not specific for inflammatory myopathies.

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.

Ophthalmoplegia as the presenting muscle-related manifestation of myotonic dystrophy

INTRODUCTION

Myotonic dystrophy type 1 (DM1) is a genetic disorder caused by expanded CTG repeats within the 3' untranslated region of the dystrophia myotonia protein kinase (DMPK) gene on chromosome 19. Diplopia is rare in this disease and has only been reported in patients with diffuse neuromuscular disorders.

OBSERVATION

We report here on the case of a 58-year-old woman in whom ophthalmoplegia was the first neuromuscular manifestation of DM1 and led to the diagnosis. Among the multisystem abnormalities associated with DM1, muscle-related symptoms are prominent, and usually involve the facial and neck muscles early on in the disease. This case provides additional evidence of oculomotor muscle involvement in DM1.

CONCLUSION

DM1 should, therefore, be considered during the diagnostic workup of any unexplained ophthalmoplegia of muscle origin, especially if there has been a previous history of cataract, even in the absence of typical muscle-related features.

Functional MRI changes in the central motor system in myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1) is a multisystemic disease involving multiple organ systems including central nervous system (CNS) and muscles. Few studies have focused on the central motor system in DM1, pointing to a subclinical abnormality in the CNS. The aim of our study was to investigate patterns of cerebral activation in DM1 during a motor task using functional MRI (fMRI). Fifteen DM1 patients, aged 20 to 59 years, and 15 controls of comparable age were scanned during a self-paced sequential finger-to-thumb opposition task of their dominant right hand. Functional MRI images were analyzed using SPM99. Patients underwent clinical and genetic assessment; all subjects underwent a conventional MR study. Myotonic dystrophy type 1 patients showed greater activation than controls in bilateral sensorimotor areas and inferior parietal lobules, basal ganglia and thalami, in the ipsilateral premotor area, insula and supplementary motor area (corrected P<.05). Analysis of the interaction between disease and age showed that correlation with age was significantly greater in patients than in controls in bilateral sensorimotor areas and in contralateral parietal areas. Other clinical and MR characteristics did not correlate with fMRI. Functional changes in DM1 may represent compensatory mechanisms such as reorganization and redistribution of functional networks to compensate for ultrastructural and neurochemical changes occurring as part of the accelerated aging process.

Myotonic dystrophy 1 in the nervous system: from the clinic to molecular mechanisms

Myotonic dystrophy type 1 (DM1) is a dominant neuromuscular disorder caused by the expansion of trinucleotide CTG repeats in the 3'-untranslated region (3'-UTR) of the DMPK gene. Prominent features of classical DM1 are muscle wasting and myotonia, whereas mental retardation is distinctive for congenital DM1. The main nervous system symptoms of DM1 are cognitive impairment, neuroendocrine dysfunction, and personality and behavior abnormalities. It is thought that expansion of CTG repeats causes DM1 pathology through different molecular mechanisms; however, a growing body of evidence indicates that an RNA gain-of-function mechanism plays a major role in the disease development. At the skeletal muscle level, three main molecular events can be distinguished in this model: 1) formation of nuclear foci that are composed at least of mutant DMPK mRNA and recruited RNA-binding proteins, such as splicing regulators and transcription factors; 2) disturbance of alternative splicing of specific genes; and 3) impairment of cell differentiation. Contrasting with the substantial advances in understanding DM1 muscle pathology, the molecular basis of DM1 in the nervous system has just started to be revealed. This review focuses in the DM1 nervous system pathology and provides an overview of the genetic and molecular studies analyzing the effects of the DMPK gene CUG expanded repeats on cell function in neuronal systems. A comparison between the molecular mechanisms of DM1 in the skeletal muscle and those identified in DM1 nervous system models is provided. Finally, future directions in the study of DM1 in the nervous system are discussed.

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.

Brain magnetic resonance image changes in a family with congenital and classic myotonic dystrophy

We present the clinical manifestations, brain magnetic resonance images (MRI), and genetic analysis of a family with 2 siblings with congenital myotonic dystrophy type 1 (DM1) and 4 patients with classic DM1. These 2 patients with congenital DM1 had severe mental retardation and a characteristic feature of hyperintensity of white matter at the posterior-superior trigone (HWMPST), in addition to ventricular dilatation in T2-weighted images (T2WI) of brain MRI. In 2 of the 4 classic DM1 patients, brain T2WI MRI showed hyperintensity lesions in the bilateral frontal and/or temporal regions, which were absent in congenital DM1. In conclusion, we suggest that the HWMPST in brain MRI is a characteristic finding in congenital DM1, and that the severe cognitive impairments are not only attributable to the subcortical white matter lesions. In congenital DM1, the cognitive function is a diffuse impairment, which is different from that in classic DM1.

Diffusion tensor imaging of cerebral white matter in patients with myotonic dystrophy

PURPOSE

To determine whether myotonic dystrophy (MyD) patients have diffusion tensor abnormalities suggestive of microstructural changes in normal-appearing white matter (NAWM).

MATERIAL AND METHODS

Conventional and diffusion tensor magnetic resonance images of the brain were obtained in 19 MyD patients and 19 age-matched normal control subjects. Fractional anisotropy (FA) and mean diffusivity (MD) values were calculated in white matter lesions (WMLs) and NAWM in MyD patients and in the white matter of normal control subjects. Differences between WML and NAWM values and between MyD patient and control subject values were analyzed statistically.

RESULTS

Significantly lower FA and higher MD values were found in all regions of interest in the NAWM of MyD patients than in the white matter of control subjects (P<0.01), as well as significantly lower FA and higher MD values in WMLs than in NAWM of MyD patients (P < 0.05). There was no significant correlation of mean FA or MD values in NAWM with patient age, age at onset, or duration of illness (P>0.1).

CONCLUSION

Diffusion tensor imaging analysis suggests the presence of diffuse microstructural changes in NAWM of MyD patients that may play an important role in the development of disability.

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.

Magnetization transfer measurements of cerebral white matter in patients with myotonic dystrophy

To determine whether patients with myotonic dystrophy (MyD) have structural changes in the cerebral white matter, we performed magnetization transfer (MT) imaging of the cerebral white matter in 14 MyD patients and 11 age-matched normal controls. We calculated MT ratios in both the white matter lesions (WMLs) and the normal-appearing white matter (NAWM) of MyD patients using region of interest (ROI) analysis. MT ratios in WMLs were markedly decreased, and all ROIs in NAWM also showed significantly lower MT ratios in MyD patients than in normal controls. The average MT ratio of all ROIs in WMLs and NAWM in each patient showed a significant negative correlation with duration of illness, but not with the patient's age or age at onset. The results of the present study indicate not only the presence of pathological changes in WMLs but also the widespread involvement of NAWM in MyD patients. The results also suggest that structural changes in the white matter may be progressive during the clinical course of MyD.

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.

Patterns of muscle involvement in inclusion body myositis: clinical and magnetic resonance imaging study

The differential patterns of muscle involvement in the upper and lower limbs in sporadic inclusion body myositis (sIBM) were examined in 18 patients using both quantitative and manual muscle testing as well as magnetic resonance imaging (MRI) in 9 patients. Weakness of the quadriceps femoris and the forearm flexors was present in most patients, but there was considerable variability in the patterns and severity of muscle involvement. MRI disclosed preferential patterns of muscle involvement within functional groups such as the quadriceps femoris, in which there was severe involvement of the vasti with relative sparing of the rectus femoris, and the triceps surae, in which selective involvement of the medial gastrocnemius was common. Involvement of flexor digitorum profundus on MRI was found in only one third of patients. The results emphasize the variability in the clinical phenotype and differential susceptibility of muscles to the disease process in sIBM.

Postpartum neuralgic amyotrophy

We report 11 women with at least one episode of neuralgic amyotrophy occurring postpartum. One woman had three episodes-two postpartum and a third occurring after minor foot surgery. Two others had a second episode, one following a first trimester spontaneous abortion and one after a viral syndrome. Pain followed delivery from as little as 1 to 2 hours to up to 2 weeks and usually lasted from a few weeks to several months. Weakness, if delayed, followed onset of pain by 2 or 3 days up to 5 weeks. Four of the episodes were bilateral. Clinical weakness and electrodiagnostic findings varied widely, from involvement of a single peripheral nerve (e.g., long thoracic, anterior interosseous) to multiple bilateral proximal and distal nerves. Functional recovery was excellent (90 to 100%) in 8 of the 10 with adequate follow-up, requiring as little as 2 weeks or up to 3 years. Two women have moderate persisting weakness (both bilateral) at 3 years and 2 years. Five patients went on to subsequent deliveries without recurrence of neuralgic amyotrophy. Only one of the 11 women had a history suggesting familial neuralgic amyotrophy, a disorder generally thought to be associated particularly with postpartum episodes. Although the etiology of postpartum neuralgic amyotrophy remains unknown, an immunologic mechanism is suspected. Focal demyelination may play a role in some, but clearly axonal degeneration is predominant in the majority.

A family with an unusual myotonic and myopathic phenotype and no CTG expansion (proximal myotonic myopathy syndrome): a challenge for future molecular studies

Myotonic dystrophy (DM) is a well-defined autosomal dominant disorder characterized by myotonia, muscle weakness, cardiac conduction defects, cataracts, and endocrine abnormalities. Recently a newly recognized disorder, similar to but distinct from DM, has been observed with multisystem findings including intermittent myotonia, proximal myopathy, and occasional cardiac conduction disturbances. This disorder has been called proximal myotonic myopathy (PROMM). No history of anticipation is present and there is no linkage to the gene locus for DM or to the loci for the muscle sodium or chloride channels. This report describes a family with a normal size of the CTG trinucleotide repeat expansion of the DM gene in which affected individuals have myotonia (intermittent, exacerbated by cold), bilateral cataracts, mild hypogonadism and mild temporal atrophy. Affected individuals also have proximal muscle weakness, facial involvement, nonspecific abnormalities on muscle biopsy, normal cardiac conduction, and no glucose intolerance. The absence of trinucleotide repeat expansion in the DM gene is consistent with this family being affected by a disorder distinct from DM, possibly a form of PROMM.

Histopathologic and MRI findings in hypokalemic myopathy induced by glycyrrhizin

Histopathologic studies and magnetic resonance images of the leg muscles were conducted in two patients with glycyrrhizin-induced hypokalemic myopathy (GHM). Muscle biopsy showed myopathic changes and vacuolated fibers with light microscopy, and dilatation of the sarcoplasmic reticulum, various types of vacuoles and myofibrillar degeneration with electron microscopy. High signal intensities in T2-weighted images obtained during severe muscle weakness were widely distributed in the leg muscles, especially the pretibial and soleus muscles. These high signal intensities disappeared after full recovery of muscle weakness. We suggest that high signal intensity in T2-weighted images can be seen and correspond to histopathologic changes in the muscles of GHM patients.

CT muscle imaging and the clinical assessment of neuromuscular disease

Twenty patients with neurogenic disorders, polymyositis, or muscular dystrophies were assessed clinically and by CT imaging of limb, limb girdle, and trunk muscles, using a standard protocol. On each side of these patients 26 movements were graded by the MRC scale, and 20 muscles were assessed by CT imaging. The clinical and CT findings could be compared, in a blind evaluation, in 10 muscles on each side. A quantitative assessment of the CT muscle images were also made. The CT images showed striking abnormalities, even in many muscles of normal strength by clinical testing. Asymmetrical involvement of muscles was found in all the disorders studied, even when not suspected on clinical examination. Muscles in patients with muscular dystrophy were more abnormal than those in patients with neurogenic disorders. In polymyositis the attenuation values were intermediate to the other two groups. A "washed-out" appearance with very low attenuation values was very suggestive of muscular dystrophy. Involvement of paraspinal and rectus abdominis muscles was uncommon in neurogenic disorders. The gracilis muscle was relatively resistant to degeneration. CT imaging can enhance the clinical assessment of patients with neuromuscular disease, often revealing unexpected abnormalities.

White matter lesions and cognitive deficits: relevance of lesion pattern?

Magnetic resonance imaging (MRI) permits efficient visualization of white matter lesions (WML). A growing body of literature deals with the correlation of WML and cognitive dysfunction with conflicting results. We studied the influence of lesion pattern as well as size by analyzing MRI and psychometric test performance in 2 patient collectives with different WML patterns. 22 patients with myotonic dystrophy (MD) and mainly subcortical WML were compared with 39 patients with multiple sclerosis (MS) and mainly periventricular lesions. 73% of MD patients had WML, the extent of which correlated with cognitive deficits. Severely impaired patients had psychometric findings compatible with "subcortical" dementia. In MS the extent of WML alone did not correlate significantly with cognitive deficits. Significant cognitive dysfunction was observed with extension of WML to areas of white matter immediately underlying cortex, but not with exclusively periventricular lesions. Cerebral atrophy had less impact. Comparison of MD and MS indicates that WML immediately subjacent to cortex are likely to cause significant cognitive deficits, whereas extensive periventricular demyelination may cause no major dysfunction. This may relate to early disturbance of associative fibers by subcortical lesions. Our results emphasize the significance of pattern as well as total extent of WML. Myotonic dystrophy is a useful model to study the effect of subcortical lesions, due to a typical lesion pattern unusual in other conditions.