Skeletal muscle disease: patterns of MRI appearances

A protocol for scoping reviews on the role of whole-body and dedicated body-part magnetic resonance imaging for assessment of adult and juvenile idiopathic inflammatory myopathies

Currently, standardized magnetic resonance imaging (MRI) scoring systems and protocols for assessment of idiopathic inflammatory myopathies (IIMs) in children and adults are lacking. Therefore, we will perform a scoping review of the literature to collate and evaluate the existing semi-quantitative and quantitative MRI scoring systems and protocols for the assessment and monitoring of skeletal muscle involvement in patients with IIMs. The aim is to compile evidence-based information that will facilitate the future development of a universal standardized MRI scoring system for both research and clinical applications in IIM. A systematic search of electronic databases (PubMed, EMBASE, and Cochrane) will be undertaken to identify relevant articles published between January 2000 and October 2023. Data will be synthesized narratively. This scoping review seeks to comprehensively summarize and evaluate the evidence on the scanning protocols and scoring systems used in the assessment of diagnosis, disease activity, and damage using skeletal muscle MRI in IIMs. The results will allow the development of consensus recommendations for clinical practice and enable the standardization of research methods for the MRI assessment of skeletal muscle changes in patients with IIMs.

Magnetic resonance imaging signal changes at the intramuscular injection site in dogs: Comparison of medetomidine and saline

Intramuscular administration is a commonly used method for delivering sedatives and anesthetics in veterinary medicine. Previous studies have reported inflammation at the intramuscular injection site in laboratory animals and observed signal changes on MRI following intramuscular injections in humans. We hypothesized that following intramuscular injection, the site would exhibit T2 hyperintensity and contrast enhancement on MRI. To investigate this, this prospective study evaluated the pattern of signal changes and grade of T2 signal intensity and contrast enhancement over time after the intramuscular injection of medetomidine at a premedication dosage, comparing it to saline. MRI scans were performed immediately postinjection into the biceps femoris and quadriceps femoris muscles, as well as at 2, 8, 24, and 72 h, and 7 days postinjection. A semiquantitative scale was utilized to grade signal intensity and contrast enhancement. Both medetomidine and saline injections showed T2 hyperintensity immediately after injection and contrast enhancement from 2 h postinjection, manifesting as flame-shaped. These signal changes decreased up to 24 h postinjection (p < .05). The signal changes induced by medetomidine showed higher T2 hyperintense change and stronger contrast enhancement compared with saline at most time points, with the signal changes persisting for a longer duration (p < .05). These findings suggest that intramuscular administration of medetomidine induces a more severe tissue reaction compared with saline, and the results are expected to aid in the differentiation of various muscle diseases that present with similar MRI findings.

Imaging spectrum of atraumatic muscle disorders: a radiologist's guide

Atraumatic muscle disorders comprise a very wide range of skeletal muscle diseases, including metabolic, inflammatory, autoimmune, infectious, ischemic, and neoplastic involvement of the muscles. Therefore, one must take clinical and laboratory data into consideration to elucidate the differential diagnoses, as well as the distribution of the muscle compromise along the body-whether isolated or distributed along the body in a symmetric or asymmetrical fashion. Assessment of muscular disorders often requires imaging investigation before image-guided biopsy or more invasive procedures; therefore, radiologists should understand the advantages and limitations of imaging methods for proper lesion evaluation and be aware of the imaging features of such disorders, thus contributing to proper decision-making and good patient outcomes. In this review, we propose a systematic approach for the assessment of muscle disorders based on their main imaging presentation, dividing them into patterns that can be easily recognized.

Muscle Healing in Sports Injuries: MRI Findings and Proposed Classification Based on a Single Institutional Experience and Clinical Observation

MRI plays a crucial role in assessment of patients with muscle injuries. The healing process of these injuries has been studied in depth from the pathophysiologic and histologic points of view and divided into destruction, repair, and remodeling phases, but the MRI findings of these phases have not been fully described, to our knowledge. On the basis of results from 310 MRI studies, including both basal and follow-up studies, in 128 athletes with muscle tears including their clinical evolution, the authors review MRI findings in muscle healing and propose a practical imaging classification based on morphology and signal intensity that correlates with histologic changes. The proposed phases, which can overlap, are destruction (phase 1), showing myoconnective tissue discontinuity and featherlike edema; repair (phase 2), showing filling in of the connective tissue gaps by a hypertrophic immature scar; and remodeling (phase 3), showing scar maturation and regression of the edema. A final healed stage can be identified with MRI, which is characterized by persistence of a slight fusiform thickening of the connective tissue. This information can be obtained from a truncated MRI protocol with three acquisitions, preferably performed with a 3-T magnet. During MRI follow-up of muscle injuries, other important features to be assessed are changes in muscle edema and specific warning signs, such as persistent intermuscular edema, new connective tear, and scar rupture. An understanding of the MRI appearance of normal and abnormal muscle healing and warning signs, along with cooperation with a multidisciplinary team, enable optimization of return to play for the injured athlete. ©RSNA, 2024 See the invited commentary by Flores in this issue.

Studying Edema Formation After Release of the Infraspinatus Muscle as an Experimental Model of Rotator Cuff Lesions in Sheep: A Histological Analysis

BACKGROUND

Muscle edema formation and inflammatory processes are early manifestations of acute rotator cuff lesions in sheep. Histological analysis of affected muscles revealed edema formation, inflammatory changes, and muscle tissue disruption in MRs.

HYPOTHESIS

Edema contributes to inflammatory reactions and early muscle fiber degeneration before the onset of fatty infiltration.

STUDY DESIGN

Controlled laboratory study.

METHODS

Osteotomy of the greater tuberosity, including the insertion of the infraspinatus tendon, was performed on 14 sheep. These experimental animal models were divided into 2 groups: a nontrauma group with surgical muscle release alone (7 sheep) and a trauma group with standardized application of additional trauma to the musculotendinous unit (7 sheep). Excisional biopsy specimens of the infraspinatus muscle were taken at 0, 3, and 4 weeks.

RESULTS

Edema formation was histologically demonstrated in both groups and peaked at 3 weeks. At 3 weeks, signs of muscle fiber degeneration were observed. At 4 weeks, ingrowth of loose alveolar and fibrotic tissue between fibers was detected. Fatty tissue was absent. The diameter of muscle fibers increased in both groups, albeit to a lesser degree in the trauma group, and practically normalized at 4 weeks. Immunohistology revealed an increase in macrophage types 1 and 2, as well as inflammatory mediators such as prostaglandin E2 and nuclear factor kappa-light-chain-enhancer of activated B cells.

CONCLUSION

Early muscle edema and concomitant inflammation precede muscle fiber degeneration and fibrosis. Edema formation results from tendon release alone and is only slightly intensified by additional trauma.

CLINICAL RELEVANCE

This study illustrates that early edema formation and inflammation elicit muscle fiber degeneration that precedes fatty infiltration. Should this phenomenon be applicable to human traumatic rotator cuff tears, then surgery should be performed as soon as possible, ideally within the first 21 days after injury.

Magnetic resonance imaging shows spinal curvature in Chinook salmon (Oncorhynchus tshawytscha) is associated with chronic inflammation of peri-vertebral soft tissues

Chinook salmon (Oncorhynchus tshawytscha) farmed in New Zealand are known to develop abnormal spinal curvature late in seawater production. Its cause is presently unknown, but there is evidence to suggest a neuromuscular pathology. Using magnetic resonance imaging (MRI), we evaluated the relationship between soft tissue pathology and spinal curvature in farmed Chinook salmon. Regions of interest (ROIs) presenting as pathologic MRI signal hyper-intensity were identified from scans of 24 harvest-sized individuals: 13 with radiographically-detectable spinal curvature and 11 without. ROIs were excised from individuals using anatomical landmarks as reference points and histologically analysed. Pathologic MRI signal was observed more frequently in individuals with radiographic curvature (92%, n = 12) than those without (18%, n = 2), was localized to the peri-vertebral connective tissues and musculature, and presented as three forms: inflammation, fibrosis, or both. These pathologies are consistent with a chronic inflammatory process, such as that observed during recovery from a soft tissue injury, and suggest spinal curvature in farmed Chinook salmon may be associated with damage to and/or compromised integrity of the peri-vertebral soft tissues. Future research to ascertain the contributing factors is required.

Severity of muscle impairment and its progression assessed using musculoskeletal magnetic resonance imaging and diffusion tension imaging in 78 boys with Duchenne muscular dystrophy: a retrospective study

Purpose

Duchenne muscular dystrophy (DMD) is the most common and severe form of muscular dystrophy. Current diagnostic tests like genetic testing, needle electromyography, and muscle biopsy are either not easily available or invasive, and they are impractical for assessing disease progression and treatment outcomes. Therefore, there is a need for a non-invasive and accurate investigative modality for DMD. In recent years, musculoskeletal magnetic resonance imaging (MRI-MSK) along with fractional anisotropy (FA) and diffusion tensor imaging (DTI) have become major non-invasive tools.

Material and methods

T1-weighted MRI-MSK and FA measures of DTI of 78 DMD patients were retrospectively studied to identify the distinct pattern of muscle involvement and fatty infiltration as age and/or disease progresses. Correlation analysis was performed between MRI-MSK grade score vs. age, muscle strength, and Vignos scale. Spearman's rank correlation coefficient was used.

Results

As age increased, the MRI grade score and Vignos score increased. There was a statistically significant high positive correlation between MRI-MSK grade score and age, and low positive correlation with Vignos scores. With increasing age, the muscle strength on manual muscle testing (MMT) and FA value decreased. There was high negative correlation with muscle strength on MMT and low positive correlation between FA values and MMT score.

Conclusions

On T1-weighted MRI, a distinct pattern, extent, and distribution of lower limb muscle involvement can be seen. MRI-MSK grade score worsens with progressing age, reducing strength, and increasing functional impairment. FA alone may not be an accurate marker in assessing progression of DMD. MRI-MSK and other DTI measures should be further explored as diagnostic and prognostic tools for DMD.

Congenital tremor and myopathy secondary to novel MYBPC1 variant

Congenital myopathy with tremor (MYOTREM) is a recently described disorder characterized by mild myopathy and a postural and intention tremor present since early infancy. MYOTREM is associated with pathogenic variants in MYBPC1 which encodes slow myosin-binding protein C, a sarcomere protein with regulatory and structural roles. Here, we describe a family with three generations of variably affected members exhibiting a novel variant in MYBPC1 (c.656 T > C, p.Leu219Pro). Among the unique features of affected family members is the persistence of tremor in sleep. We also present the first muscle magnetic resonance images for this disorder, and report muscle atrophy and fatty infiltration.

High-Resolution Imaging Insights into Shoulder Joint Pain: A Comprehensive Review of Ultrasound and Magnetic Resonance Imaging (MRI)

Shoulder joint pain is a complex and prevalent clinical concern affecting individuals across various ages and lifestyles. This review delves into the pivotal role of high-resolution imaging techniques, namely ultrasound and magnetic resonance imaging (MRI), in the comprehensive assessment and management of shoulder joint pain. We explore the anatomical foundations of the shoulder, common etiologies of pain, and the significance of precise diagnosis. High-resolution imaging facilitates the identification of various shoulder pathologies and is crucial in treatment planning, surgical interventions, and long-term prognosis assessment. We examine emerging technologies, discuss challenges and limitations, and chart potential future developments, emphasizing the ongoing evolution of imaging in this critical healthcare domain. In conclusion, high-resolution imaging is an indispensable tool, continually advancing to meet the diagnostic and therapeutic needs of individuals grappling with shoulder joint pain.

Homozygous splice variant (c.1741-6G>A) of the COL6A1 gene in three patients with Ullrich congenital muscular dystrophy

The three major collagen VI genes: COL6A1, COL6A2, and COL6A3 encode microfibrillar components of extracellular matrices in multiple tissues including muscles and tendons. Pathogenic variants in the collagen VI genes cause collagen VI-related dystrophies representing a continuum of conditions from Bethlem myopathy at the milder end to Ullrich congenital muscular dystrophy at the more severe end. Here we describe a pathogenic variant in the COL6A1 gene (NM_001848.3; c.1741-6G>A) found in homozygosity in three patients with Ullrich congenital muscular dystrophy. The patients suffered from severe muscle impairment characterised by proximal weakness, distal hyperlaxity, joint contractures, wheelchair-dependency, and use of nocturnal non-invasive ventilation. The pathogenicity was verified by RNA analyses showing that the variant induced aberrant splicing leading to a frameshift and loss of function. The analyses were in line with immunocytochemistry studies of patient-derived skin fibroblasts and muscle tissue demonstrating impaired secretion of collagen VI into the extracellular matrix. Thereby, we add the variant c.1741-6G>A to the list of pathogenic, recessive, splice variants in COL6A1 causing Ullrich congenital muscular dystrophy. The variant is listed in ClinVar as of "uncertain significance" and "likely benign" and may presumably have been overlooked in other patients.

Muscle MRI patterns for limb girdle muscle dystrophies: systematic review

Limb girdle muscle dystrophies (LGMDs) are a group of inherited neuromuscular disorders comprising more than 20 genes. There have been increasing efforts to characterize this group with Muscle MRI. However, due to the complexity and similarities, the interpretation of the MRI patterns is usually done by experts in the field. Here, we proposed a step-by-step image interpretation of Muscle MRI in LGDM by evaluating the variability of muscle pattern involvement reported in the literature. A systematic review with an open start date to November 2022 was conducted to describe all LGMDs' muscle MRI patterns. Eighty-eight studies were included in the final review. Data were found to describe muscle MRI patterns for 15 out of 17 LGMDs types. Although the diagnosis of LGMDs is challenging despite the advanced genetic testing and other diagnostic modalities, muscle MRI is shown to help in the diagnosis of LGMDs. To further increase the yield for muscle MRI in the neuromuscular field, larger cohorts of patients need to be conducted.

Early shoulder-girdle MRI findings in severe COVID-19-related intensive care unit-acquired weakness: a prospective cohort study

OBJECTIVE

To describe clinical and early shoulder-girdle MR imaging findings in severe COVID-19-related intensive care unit-acquired weakness (ICU-AW) after ICU discharge.

METHODS

A single-center prospective cohort study of all consecutive patients with COVID-19-related ICU-AW from November 2020 to June 2021. All patients underwent similar clinical evaluations and shoulder-girdle MRI within the first month and then 3 months (± 1 month) after ICU discharge.

RESULTS

We included 25 patients (14 males; mean [SD] age 62.4 [12.5]). Within the first month after ICU discharge, all patients showed severe proximal predominant bilateral muscular weakness (mean Medical Research Council total score = 46.5/60 [10.1]) associated with bilateral, peripheral muscular edema-like MRI signals of the shoulder girdle in 23/25 (92%) patients. At 3 months, 21/25 (84%) patients showed complete or quasi-complete resolution of proximal muscular weakness (mean Medical Research Council total score > 48/60) and 23/25 (92%) complete resolution of MRI signals of the shoulder girdle, but 12/20 (60%) patients experienced shoulder pain and/or shoulder dysfunction.

CONCLUSIONS

Early shoulder-girdle MRI findings in COVID-19-related ICU-AW included muscular edema-like peripheral signal intensities, without fatty muscle involution or muscle necrosis, with favorable evolution at 3 months. Precocious MRI can help clinicians distinguish critical illness myopathy from alternative, more severe diagnoses and can be useful in the care of patients discharged from intensive care with ICU-AW.

KEY POINTS

• We describe the clinical and shoulder-girdle MRI findings of COVID-19-related severe intensive care unit-acquired weakness. • This information can be used by clinicians to achieve a nearly specific diagnosis, distinguish alternative diagnoses, assess functional prognosis, and select the more appropriate health care rehabilitation and shoulder impairment treatment.

[Rare diseases in the differential diagnosis of myalgia]

Myalgia describes pain in the skeletal muscles. According to the current German clinical guidelines from 2020 (AWMF register number: 030/051), the initial diagnostic assessment consists of the anamnesis, clinical examination, electrophysiological examination and standard laboratory tests. Additional special examinations, such as molecular genetic investigations, special laboratory tests, medical imaging and muscle biopsy are only needed in certain cases. This article focuses on rare neurological diseases that are classically associated with myalgia. In this context etiologically different diseases are considered, whereby some genetically linked diseases (fascioscapulohumeral dystrophy, FSHD, dystrophia myotonica, McArdle's disease, Pompe's disease, limb girdle muscular dystrophy) are contrasted with diseases with an (auto)immune-related pathogenesis (stiff-person syndrome, Isaacs syndrome). The aspects relevant for the diagnosis are particularly highlighted. The therapeutic aspects of the diseases are not part of this article.

A Bioelectrical Impedance Analysis for the Assessment of Muscle Atrophy in Patients with Chronic Inflammatory Demyelinating Polyneuropathy

Objective Muscle atrophy is observed in a subset of patients with chronic inflammatory demyelinating polyneuropathy (CIDP). Its manifestation is associated with a poor functional prognosis and poor response to immunomodulatory therapies. We evaluated muscle atrophy in patients with CIDP using a bioelectrical impedance analysis (BIA). Methods We enrolled 12 patients with CIDP for a BIA of muscle atrophy. Of these 12 patients, 10 were diagnosed with typical CIDP, 1 with multifocal acquired demyelinating sensory and motor neuropathy, and 1 with distal acquired demyelinating symmetric neuropathy. All 12 patients underwent a series of assessments and evaluations, including a BIA and computed tomography (CT). A correlation was found between the skeletal muscle mass determined by the BIA and that found using CT of the muscles. Results The BIA provided values for each patient's skeletal muscle mass index (SMI) ranging from 4.1 to 8.1 kg/m². Four of the patients with CIDP had SMI values below the threshold for sarcopenia. CT of the patients' muscles provided scores indicating grades of muscle atrophy in the upper and lower extremities. A comparison of the outcomes from these two measures showed a good correlation between their muscle atrophy ratings (p <0.05). Conclusions We found that a BIA and muscle CT provided muscle atrophy assessments of equivalent accuracy. Therefore, a BIA can be a simple alternative to muscle CT that is suitable for regular use in daily clinical practice as a reliable tool for assessing muscle atrophy in patients with CIDP.

Case Report: Unable to Jump Like a Kangaroo Due to Myositis Ossificans Circumscripta

A male 10-year-old captive red kangaroo (Macropus rufus) was presented with a chronic progressive pelvic limb lameness and reluctance to jump. The general examination revealed a palpable induration of the lumbar epaxial muscles. Magnetic resonance imaging performed under general anesthesia revealed bilateral almost symmetric, well-circumscribed mass lesions in superficial erector spinae muscles. The lesions had irregular to multilobulated appearance with hyper-, hypo-, and isointense areas in T2- and T1-weighted (w) sequences without contrast enhancement. On computed tomography, a peripheral rim of mineralization was apparent. Histopathological analysis of a muscle biopsy showed osseous trabeculae with rare clusters of chondrocytes indicating metaplasia of muscle tissue to bone. No indications of inflammation or malignancy were visible. The clinical, histopathological, and imaging workup of this case was consistent with myositis ossificans circumscripta. This disorder is particularly well-known among human professional athletes such as basketball players, where excessive, chronic-repetitive force or blunt trauma causes microtrauma to the musculature. Metaplasia of muscle tissue due to abnormal regeneration processes causes heterotopic ossification. The kangaroo's clinical signs improved with cyto-reductive surgery, cage rest, weight reduction, and meloxicam without further relapse.

[Rare diseases in the differential diagnosis of myalgia]

Myalgia describes pain in the skeletal muscles. According to the current German clinical guidelines from 2020 (AWMF register number: 030/051), the initial diagnostic assessment consists of the anamnesis, clinical examination, electrophysiological examination and standard laboratory tests. Additional special examinations, such as molecular genetic investigations, special laboratory tests, medical imaging and muscle biopsy are only needed in certain cases. This article focuses on rare neurological diseases that are classically associated with myalgia. In this context etiologically different diseases are considered, whereby some genetically linked diseases (fascioscapulohumeral dystrophy, FSHD, dystrophia myotonica, McArdle's disease, Pompe's disease, limb girdle muscular dystrophy) are contrasted with diseases with an (auto)immune-related pathogenesis (stiff-person syndrome, Isaacs syndrome). The aspects relevant for the diagnosis are particularly highlighted. The therapeutic aspects of the diseases are not part of this article.

Screening Power of Short Tau Inversion Recovery Muscle Magnetic Resonance Imaging in Critical Illness Myo-neuropathy and Guillain–Barre Syndrome in the Intensive Care Unit

Introduction

Critical illness myoneuropathy (CIMN) or intensive care unit (ICU)-acquired weakness (AW) is a common cause of weakness in ICU patients. Guillain–Barre syndrome (GBS) is also a common cause of acute neurological weakness in the ICU. It is diagnosed by clinical features, nerve conduction studies (NCS), and muscle/nerve biopsies.

Methods

The short tau inversion recovery (STIR) muscle magnetic resonance (MR) images of seven patients with suspected CIMN and seven GBS patients over a 5-year period from February 2015 till May 2020 were analyzed.

Results

All seven patients with CIMN showed diffuse muscle edema, predominating in the lower limbs. Only one patient with GBS showed abnormal magnetic resonance imaging (MRI) changes (14%) and MRI was normal in 86%. The sensitivity of MRI to detect CIMN was 100%, whereas the specificity was 85.7%. Thus, the positive predictive value (PPV) of MRI in this situation was 87.5% and the negative predictive value (NPV) was 100%.

Conclusion

Muscle STIR imaging may help to differentiate between CIMN and GBS.

How to cite this article

Maramattom BV. Screening Power of Short Tau Inversion Recovery Muscle Magnetic Resonance Imaging in Critical Illness Myoneuropathy and Guillain–Barre Syndrome in the Intensive Care Unit. Indian J Crit Care Med 2022;26(2):204–209.

A Muscle Biosignature Differentiating Between Limb-Girdle Muscular Dystrophy and Idiopathic Inflammatory Myopathy on Magnetic Resonance Imaging

Background: The overlapping clinical presentations of limb-girdle muscular dystrophy (LGMD) and idiopathic inflammatory myopathy (IIM) make clinical diagnosis challenging. This study provides a comprehensive evaluation of the distributions and characteristics of muscle fat substitution and edema and aims to differentiate those two diseases.

Methods: This retrospective study reviewed magnetic resonance imaging (MRI) of seventeen patients with pathologically proved diagnosis, comprising 11 with LGMD and 6 with IIM. The fat-only and water-only images from a Dixon sequence were used to evaluate muscle fat substitution and edema, respectively. The degrees of muscle fat substitution and edema were graded and compared using the appropriate statistical methods.

Results: In LGMD, more than 50% of patients had high-grade fat substitution in the majority of muscle groups in the thigh and calf. However, <50% of IIM patients had high-grade fat substitution in all muscle groups. Moreover, LGMD patients had significantly higher grade fat substitution than IIM patients in all large muscle groups (p < 0.05). However, there was no significant difference in edema in the majority of muscle groups, except the adductor magnus (p = 0.012) and soleus (p = 0.009) with higher grade edema in IIM. Additionally, all the adductor magnus muscles in LGMD (100%) showed high-grade fat substitution, but none of them showed high-grade edema.

Conclusions: MRI could be a valuable tool to differentiate LGMD from IIM based on the discrepancy in muscle fat substitution, and the adductor magnus muscle could provide a biosignature to categorizing LGMD.

Clinical features and diagnostic tools in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIMs) are rare autoimmune disorders affecting primarily muscles, but other organs can be involved. This review describes the clinical features, diagnosis and treatment for IIMs, namely polymyositis (PM), dermatomyositis (DM), sporadic inclusion body myositis (sIBM), immune-mediated necrotizing myopathy (IMNM), and myositis associated with antisynthetase syndrome (ASS). The diagnostic approach has been updated recently based on the discovery of circulating autoantibodies, which has enhanced the management of patients. Currently, validated classification criteria for IIMs allow clinical studies with well-defined sets of patients but diagnostic criteria to guide the care of individual patients in routine clinical practice are still missing. This review analyzes the clinical manifestations and laboratory findings of IIMs, discusses the efficiency of modern and standard methods employed in their workup, and delineates optimal practice for clinical care. Α multidisciplinary diagnostic approach that combines clinical, neurologic and rheumatologic examination, evaluation of electrophysiologic and morphologic muscle characteristics, and assessment of autoantibody immunoassays has been determined to be the preferred approach for effective management of patients with suspected IIMs.

Impaired aerobic capacity and premature fatigue preceding muscle weakness in the skeletal muscle Tfam-knockout mouse model

Mitochondrial diseases are genetic disorders that lead to impaired mitochondrial function, resulting in exercise intolerance and muscle weakness. In patients, muscle fatigue due to defects in mitochondrial oxidative capacities commonly precedes muscle weakness. In mice, deletion of the fast-twitch skeletal muscle-specific Tfam gene (Tfam KO) leads to a deficit in respiratory chain activity, severe muscle weakness and early death. Here, we performed a time-course study of mitochondrial and muscular dysfunctions in 11- and 14-week-old Tfam KO mice, i.e. before and when mice are about to enter the terminal stage, respectively. Although force in the unfatigued state was reduced in Tfam KO mice compared to control littermates (wild type) only at 14 weeks, during repeated submaximal contractions fatigue was faster at both ages. During fatiguing stimulation, total phosphocreatine breakdown was larger in Tfam KO muscle than in wild-type muscle at both ages, whereas phosphocreatine consumption was faster only at 14 weeks. In conclusion, the Tfam KO mouse model represents a reliable model of lethal mitochondrial myopathy in which impaired mitochondrial energy production and premature fatigue occur before muscle weakness and early death.

Summary: A time-course study of mitochondrial and muscular dysfunctions in a mouse model of mitochondrial myopathy reveals that decreased resistance to fatigue together with decreased oxidative capacities arise ahead of muscle weakness.

Whole-body muscle MRI in McArdle disease

This study describes muscle involvement on whole-body MRI (WB-MRI) scans at different stages of McArdle disease. WB-MRI was performed on fifteen genetically confirmed McArdle disease patients between ages 25 to 80. The degree of fatty substitution was scored for 60 muscles using Mercuri's classification. All patients reported an intolerance to exercise and episodes of rhabdomyolysis. A mild fixed muscle weakness was observed in 13/15 patients with neck flexor weakness in 7/15 cases, and proximal muscle weakness in 6/15 cases. A moderate scapular winging was observed in five patients. A careful review of the MRI scans, as well as hierarchical clustering of patients by Mercuri scores, pointed out recurrent muscle changes particularly in the subscapularis, anterior serratus, erector spinae and quadratus femoris muscles. WB-MRI imaging provides clinically relevant information and is a useful tool to orient toward the diagnosis of McArdle disease.

Early predominant inflammatory myopathy in anti-glycyl-tRNA synthetase (EJ) antibody positive antisynthetase syndrome

It is important to consider antisynthetase syndrome in the differential diagnosis of patients presenting with weakness, respiratory distress, and a constellation of complaints spanning multiple organ systems, as this will change clinical management.

Muscle Imaging

Evaluation and characterization of skeletal muscle pathology is a frequently encountered indication for musculoskeletal imaging. Causes of muscle pathology are diverse and include traumatic, autoimmune, infectious, inflammatory, neurologic, and neoplastic. Each etiology while dramatically different in the pathophysiology may present with similar imaging features. An understanding of the subtle differences in imaging features between the pathologic conditions may serve to guide diagnosis and treatment in these often complex cases. In this section, we will discuss the various skeletal muscle pathologies and the imaging features associated with each.

Sports-related lower limb muscle injuries: pattern recognition approach and MRI review

Muscle injuries of the lower limbs are currently the most common sport-related injuries, the impact of which is particularly significant in elite athletes. MRI is the imaging modality of choice in assessing acute muscle injuries and radiologists play a key role in the current scenario of multidisciplinary health care teams involved in the care of elite athletes with muscle injuries. Despite the frequency and clinical relevance of muscle injuries, there is still a lack of uniformity in the description, diagnosis, and classification of lesions. The characteristics of the connective tissues (distribution and thickness) differ among muscles, being of high variability in the lower limb. This variability is of great clinical importance in determining the prognosis of muscle injuries. Recently, three classification systems, the Munich consensus statement, the British Athletics Muscle Injury classification, and the FC Barcelona-Aspetar-Duke classification, have been proposed to assess the severity of muscle injuries. A protocolized approach to the evaluation of MRI findings is essential to accurately assess the severity of acute lesions and to evaluate the progression of reparative changes. Certain MRI findings which are seen during recovery may suggest muscle overload or adaptative changes and appear to be clinically useful for sport physicians and physiotherapists.

Quantitative MRI in myositis patients: comparison with healthy volunteers and radiological visual assessment

AIM

To assess whether magnetic resonance imaging (MRI)-based measurements of T2, fat fraction, diffusion tensor imaging, and muscle volume can detect differences between the muscles of myositis patients and healthy controls, and to identify how they compare with semi-quantitative MRI diagnosis.

MATERIALS AND METHODS

Sixteen myositis patients and 16 age- and gender-matched healthy controls underwent MRI of their thigh. Quantitative MRI measurements and radiologists' semi-quantitative scores were assessed. Strength was assessed using an isokinetic dynamometer.

RESULTS

Fat fraction and T2 values were higher in myositis patients whereas muscle volume was lower compared to healthy controls. There was no difference in diffusion. Muscle strength was lower in myositis patients compared to healthy controls. In a subgroup of eight patients, scored as unaffected by radiologists, T2 values were still significantly higher in myositis patients.

CONCLUSIONS

Quantitative MRI measurements can detect differences between myositis patients and healthy controls. Changes in the muscles of myositis patients, undetected by visual, semi-quantitative scoring, can be detected using quantitative T2 measurements. This suggests that MRI T2 values may be useful for the management of myositis patients.

Differentiation of Myositis-Induced Models of Bacterial Infection and Inflammation with T2-Weighted, CEST, and DCE-MRI

We used T₂ relaxation, chemical exchange saturation transfer (CEST), and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) to assess whether bacterial infection can be differentiated from inflammation in a myositis-induced mouse model. We measured the T₂ relaxation time constants, %CEST at 5 saturation frequencies, and area under the curve (AUC) from DCE-MRI after maltose injection from infected, inflamed, and normal muscle tissue models. We applied principal component analysis (PCA) to reduce dimensionality of entire CEST spectra and DCE signal evolutions, which were analyzed using standard classification methods. We extracted features from dimensional reduction as predictors for machine learning classifier algorithms. Normal, inflamed, and infected tissues were evaluated with H&E and gram-staining histological studies, and bacterial-burden studies. The T₂ relaxation time constants and AUC of DCE-MRI after injection of maltose differentiated infected, inflamed, and normal tissues. %CEST amplitudes at −1.6 and −3.5 ppm differentiated infected tissues from other tissues, but these did not differentiate inflamed tissue from normal tissue. %CEST amplitudes at 3.5, 3.0, and 2.5 ppm, AUC of DCE-MRI for shorter time periods, and relative K^trans and k_ep values from DCE-MRI could not differentiate tissues. PCA and machine learning of CEST-MRI and DCE-MRI did not improve tissue classifications relative to traditional analysis methods. Similarly, PCA and machine learning did not further improve tissue classifications relative to T₂ MRI. Therefore, future MRI studies of infection models should focus on T₂-weighted MRI and analysis of T₂ relaxation times.

Sonographic and 3T-MRI-based evaluation of the tongue in ALS

A few systematic imaging studies employing ultrasound (HRUS) and magnetic resonance imaging (MRI) have suggested tongue measures to aid in diagnosis of amyotrophic lateral sclerosis (ALS). The relationship between structural tongue alterations and the ALS patients' bulbar and overall motor function has not yet been elucidated. We here thus aimed to understand how in-vivo tongue alterations relate to motor function and motor function evolution over time in ALS. Our study included 206 ALS patients and 104 age- and sex-matched controls that underwent HRUS and 3T MRI of the tongue at baseline. Sonographic measures comprised coronal tongue echointensity, area, height, width and height/width ratio, while MRI measures comprised sagittal T1 intensity, tongue area, position and shape. Imaging-derived markers were related to baseline and longitudinal bulbar and overall motor function. Baseline T1 intensity was lower in ALS patients with more severe bulbar involvement at baseline. Smaller baseline coronal (HRUS) and sagittal (MRI) tongue area, smaller coronal height (HRUS) and width (HRUS) as well as more rounded sagittal tongue shape predicated more rapid functional impairment - not only of bulbar, but also of overall motor function - in ALS. Our results suggest that in-vivo sonography und MRI tongue measures could aid as biomarkers to reflect bulbar and motor function impairment.

Glossary of terms for musculoskeletal radiology

Members of the International Skeletal Society compiled a glossary of terms for musculoskeletal radiology. The authors also represent national radiology or pathology societies in Asia, Australia, Europe, and the USA. We provide brief descriptions of musculoskeletal structures, disease processes, and syndromes and address their imaging features. Given the abundance of musculoskeletal disorders and derangements, we chose to omit most terms relating to neoplasm, spine, intervention, and pediatrics. Consensus agreement was obtained from 19 musculoskeletal radiology societies worldwide.

Muscle Toxicity of Drugs: When Drugs Turn Physiology into Pathophysiology

Drugs are prescribed to manage or prevent symptoms and diseases, but may sometimes cause unexpected toxicity to muscles. The symptomatology and clinical manifestations of the myotoxic reaction can vary significantly between drugs and between patients on the same drug. This poses a challenge on how to recognize and prevent the occurrence of drug-induced muscle toxicity. The key to appropriate management of myotoxicity is prompt recognition that symptoms of patients may be drug related and to be aware that inter-individual differences in susceptibility to drug-induced toxicity exist. The most prevalent and well-documented drug class with unintended myotoxicity are the statins, but even today new classes of drugs with unintended myotoxicity are being discovered. This review will start off by explaining the principles of drug-induced myotoxicity and the different terminologies used to distinguish between grades of toxicity. The main part of the review will focus on the most important pathogenic mechanisms by which drugs can cause muscle toxicity, which will be exemplified by drugs with high risk of muscle toxicity. This will be done by providing information on key clinical and laboratory aspects, muscle electromyography patterns and biopsy results, and pathological mechanism and management for a specific drug from each pathogenic classification. In addition, rather new classes of drugs with unintended myotoxicity will be highlighted. Furthermore, we will explain why it is so difficult to diagnose drug-induced myotoxicity, and which tests can be used as a diagnostic aid. Lastly, a brief description will be given of how to manage and treat drug-induced myotoxicity.

Mitochondrial dysfunction is the cause of one of the earliest changes seen on magnetic resonance imaging in Charcot neuroarthopathy - Oedema of the small muscles in the foot

The hypothesis laid out in this thesis states that the early changes seen on an MR imaging in those with early Charcot neuroarthopathy may be due to mitochondrial dysfunction. In a Charcot foot, there is movement between bones. In an attempt to prevent this movement, the small muscles of the foot contract continuously when the foot is weight bearing. This contraction takes energy in the form of ATP. However, the reduction of glucose transport into the muscle cells due to insulin resistance / insufficiency, leads to reduction in the ATP producing capacity of the mitochondria. The ATP depletion affects the cell membrane gradient leading to mitochondrial and cellular swelling. These early cellular changes could then be picked up with MR imaging as muscle oedema.

Localization of Muscle Edema and Changes on Muscle Contractility After Dry Needling of Latent Trigger Points in the Gastrocnemius Muscle

In this article, we aimed to describe what happens in skeletal muscle after dry needling intervention using magnetic resonance imaging (to show if there is edema) and tensiomyography (to measure contractile properties). At the same time, we describe the relationship between pain, edema, and contractility. Our results suggest that in asymptomatic patients, the application of dry needling over latent trigger points produce intra-muscular edema, an increase in muscle stiffness and an improved muscle contraction time.

A case report of an atypical presentation of pyogenic iliopsoas abscess

Background

Iliopsoas abscess is a collection of pus in the iliopsoas muscle compartment. It can be primary or secondary in origin. Primary iliopsoas abscess occurs as a result of hematogenous or lymphatic seeding from a distant site. This is commonly associated with a chronic immunocompromised state and tends to occur in children and young adults. Secondary iliopsoas abscess occurs as a result of the direct spread of infection to the psoas muscle from an adjacent structure, and this may be associated with trauma and instrumentation in the inguinal region, lumbar spine, or hip region. The incidence of iliopsoas abscess is rare and often the diagnosis is delayed because of non-specific presenting symptoms.

Case presentation

We describe a patient with iliopsoas abscess who presented to the Emergency Department at X Hospital on three separate occasions with non-specific symptoms of thigh pain and fever before finally being admitted for treatment. This case illustrates how the diagnosis can be delayed due to its atypical presentation. Hence, highlighting the need for clinicians to have a high index of clinical suspicion for iliopsoas abscess in patients presenting with thigh pain and fever.

Conclusion

The classic triad of fever, flank pain, and hip movement limitation is presented in only 30% of patients with iliopsoas abscess. Clinicians should consider iliopsoas abscess as a differential diagnosis in patients presenting with fever and thigh pain. The rare condition with the varied clinical presentation means that cross-sectional imaging should be considered early to reduce the risk of fulminant sepsis.

Detecting Toxic Myopathies as Medication Side Effect

The goal of this article is to provide physiatrists, neurologists, and neuromuscular medicine physicians a framework that can be easily used in the process of evaluating, identifying, and treating patients with toxic myopathies. This review attempts to classify these rare but potentially deadly conditions in clinical patterns and distinguishes the cellular mechanisms in which the offending agents tend to impact the structure and function of myocytes.

Adult thigh muscle injuries-from diagnosis to treatment: what the radiologist should know

Muscle injuries are one of the major problems facing elite athletes, representing a significant source of time lost from competition, with substantial consequences for teams and athletes. There are considerable pressures for a rapid return, but players who return to competition too soon have an increased risk of recurrent muscle injuries, which are associated with longer lay-offs. Imaging plays a key role in achieving the correct diagnosis, and magnetic resonance imaging (MRI) has emerged as the method of choice for skeletal muscle imaging. Several authors have reported prognostic MRI features, but it is difficult to predict the exact length of time to return to full training afterwards due to considerable discrepancy and overlap between different injuries. Therefore, development of a universally applicable classification and grading system is challenging. This paper aims to: (a) review the contemporary role of imaging in the setting of muscle injuries, with special focus on thigh muscles; (b) list the most accepted terminology used to describe muscle injuries;

Clinics in diagnostic imaging (179). Severe rhabdomyolysis complicated by myonecrosis

A 32-year-old man presented to the emergency department with severe right lower limb pain and swelling of three days' duration. He had multiple prior admissions for recurrent seizures and suicide attempts. Markedly elevated serum creatine kinase levels and urine myoglobinuria were consistent with a diagnosis of rhabdomyolysis. Initial magnetic resonance imaging of the right lower limb revealed diffuse muscle oedema and features of myositis in the gluteal muscles and the adductor, anterior and posterior compartments of the thigh. Follow-up magnetic resonance imaging performed 11 days later showed interval development of areas of myonecrosis and haemorrhage. The causes, clinical presentation and imaging features of rhabdomyolysis are discussed.

MR Imaging of Atraumatic Muscle Disorders

Atraumatic disorders of skeletal muscles include congenital variants; inherited myopathies; acquired inflammatory, infectious, or ischemic disorders; neoplastic diseases; and conditions leading to muscle atrophy. These have overlapping appearances at magnetic resonance (MR) imaging and are challenging for the radiologist to differentiate. The authors organize muscle disorders into four MR imaging patterns: (a) abnormal anatomy with normal signal intensity, (b) edema/inflammation, (c) mass, and (d) atrophy, highlighting each of their key clinical and imaging findings. Anatomic muscle variants, while common, do not produce signal intensity alterations and therefore are easily overlooked. Muscle edema is the most common pattern but is nonspecific, with a broad differential diagnosis. Autoimmune, paraneoplastic, and drug-induced myositis tend to be symmetric, whereas infection, radiation-induced injury, and myonecrosis are focal asymmetric processes. Architectural distortion in the setting of muscle edema suggests one of these latter processes. Intramuscular masses include primary neoplasms, metastases, and several benign masslike lesions that simulate malignancy. Some lesions, such as lipomas, low-flow vascular malformations, fibromatoses, and subacute hematomas, are distinctive, but many intramuscular masses ultimately require a biopsy for definitive diagnosis. Atrophy is the irreversible end result of any muscle disease of sufficient severity and is the dominant finding in disorders such as the muscular dystrophies, denervation myopathy, and sarcopenia. This imaging-based classification, in correlation with clinical and laboratory data, will aid the radiologist in interpreting MR imaging findings in patients with atraumatic muscle disorders. ^©RSNA, 2018.