Diagnostic value of electromyography and muscle biopsy in arthrogryposis multiplex congenita

Neuromuscular problems of the critically Ill neonate and child

Acute neuromuscular disorders occasionally occur in the Pediatric Neurologic Intensive Care Unit. Many of these are primary disorders of the motor unit that may present acutely or exacerbate during an intercurrent illness. Additionally, acute neuromuscular disorders may develop during an acute systemic illness requiring intensive care management that predispose the child to another set of acute motor unit disorders. This chapter discusses acute neuromuscular crises in the infant, toddler, and adolescent, as well as neuromuscular disorders resulting from critical illness.

Pathophysiology of Dyt1-Tor1a dystonia in mice is mediated by spinal neural circuit dysfunction

Dystonia, a neurological disorder defined by abnormal postures and disorganized movements, is considered to be a neural circuit disorder with dysfunction arising within and between multiple brain regions. Given that spinal neural circuits constitute the final pathway for motor control, we sought to determine their contribution to this movement disorder. Focusing on the most common inherited form of dystonia in humans, DYT1-TOR1A, we generated a conditional knockout of the torsin family 1 member A (Tor1a) gene in the mouse spinal cord and dorsal root ganglia (DRG). We found that these mice recapitulated the phenotype of the human condition, developing early-onset generalized torsional dystonia. Motor signs emerged early in the mouse hindlimbs before spreading caudo-rostrally to affect the pelvis, trunk, and forelimbs throughout postnatal maturation. Physiologically, these mice bore the hallmark features of dystonia, including spontaneous contractions at rest and excessive and disorganized contractions, including cocontractions of antagonist muscle groups, during voluntary movements. Spontaneous activity, disorganized motor output, and impaired monosynaptic reflexes, all signs of human dystonia, were recorded from isolated mouse spinal cords from these conditional knockout mice. All components of the monosynaptic reflex arc were affected, including motor neurons. Given that confining the Tor1a conditional knockout to DRG did not lead to early-onset dystonia, we conclude that the pathophysiological substrate of this mouse model of dystonia lies in spinal neural circuits. Together, these data provide new insights into our current understanding of dystonia pathophysiology.

Diagnostic workup in children with arthrogryposis: description of practices from a single reference centre, comparison with literature and suggestion of recommendations

INTRODUCTION

Arthrogryposis multiplex congenita (AMC) refers to a clinical presentation of congenital contractures involving two or more body areas. More than 400 distinct conditions may lead to AMC, making the aetiological diagnosis challenging. The objective of this work was to set up evidence-based recommendations for the diagnosis of AMC by taking advantage of both data from our nation-wide cohort of children with AMC and from the literature.

MATERIAL AND METHODS

We conducted a retrospective single-centre observational study. Patients had been evaluated at least once at a paediatric age in the AMC clinic of Grenoble University Hospital between 2007 and 2019. After gathering data about their diagnostic procedure, a literature review was performed for each paraclinical investigation to discuss their relevance.

RESULTS

One hundred and twenty-five patients were included, 43% had Amyoplasia, 27% had distal arthrogryposis and 30% had other forms. A definitive aetiological diagnosis was available for 66% of cases. We recommend a two-time diagnostic process: first, non-invasive investigations that aim at classifying patients into one of the three groups, and second, selected investigations targeting a subset of patients.

CONCLUSION

The aetiological management for patients with AMC remains arduous. This process will be facilitated by the increasing use of next-generation sequencing combined with detailed phenotyping. Invasive investigations should be avoided because of their limited yield.

Schwann cell functions in peripheral nerve development and repair

The glial cell of the peripheral nervous system (PNS), the Schwann cell (SC), counts among the most multifaceted cells of the body. During development, SCs secure neuronal survival and participate in axonal path finding. Simultaneously, they orchestrate the architectural set up of the developing nerves, including the blood vessels and the endo-, peri- and epineurial layers. Perinatally, in rodents, SCs radially sort and subsequently myelinate individual axons larger than 1 μm in diameter, while small calibre axons become organised in non-myelinating Remak bundles. SCs have a vital role in maintaining axonal health throughout life and several specialized SC types perform essential functions at specific locations, such as terminal SC at the neuromuscular junction (NMJ) or SC within cutaneous sensory end organs. In addition, neural crest derived satellite glia maintain a tight communication with the soma of sensory, sympathetic, and parasympathetic neurons and neural crest derivatives are furthermore an indispensable part of the enteric nervous system. The remarkable plasticity of SCs becomes evident in the context of a nerve injury, where SC transdifferentiate into intriguing repair cells, which orchestrate a regenerative response that promotes nerve repair. Indeed, the multiple adaptations of SCs are captivating, but remain often ill-resolved on the molecular level. Here, we summarize and discuss the knowns and unknowns of the vast array of functions that this single cell type can cover in peripheral nervous system development, maintenance, and repair.

Recognizable Pattern of Arthrogryposis and Congenital Myopathy Caused by the Recurrent TTN Metatranscript-only c.39974-11T > G Splice Variant

INTRODUCTION

Arthrogryposis is characterized by the presence of multiple contractures at birth and can be caused by pathogenic variants in TTN (Titin). Exons and variants that are not expressed in one of the three major isoforms of titin are referred to as "metatranscript-only" and have been considered to be only expressed during fetal development. Recently, the metatranscript-only variant (c.39974-11T > G) in TTN with a second truncating TTN variant has been linked to arthrogryposis multiplex congenita and myopathy.

METHODS

Via exome sequencing we identified the TTN c.39974-11T > G splice variant in trans with one of three truncating variants (p.Arg8922*, p.Lys32998Asnfs*63, p.Tyr10345*) in five individuals from three families. Clinical presentation and muscle ultrasound as well as MRI images were analyzed.

RESULTS

All five patients presented with generalized muscular hypotonia, reduced muscle bulk, and congenital contractures most prominently affecting the upper limbs and distal joints. Muscular hypotonia persisted and contractures improved over time. One individual, the recipient twin in the setting of twin-to-twin transfusion syndrome, died from severe cardiac hypertrophy 1 day after birth. Ultrasound and MRI imaging studies revealed a recognizable pattern of muscle involvement with striking fibrofatty involvement of the hamstrings and calves, and relative sparing of the femoral adductors and anterior segment of the thighs.

CONCLUSION

The recurrent TTN c.39974-11T > G variant consistently causes congenital arthrogryposis and persisting myopathy providing evidence that the metatranscript-only 213 to 217 exons impact muscle elasticity during early development and beyond. There is a recognizable pattern of muscle involvement, which is distinct from other myopathies and provides valuable clues for diagnostic work-up.

Postnatal Diagnostic Workup in Children With Arthrogryposis: A Series of 82 Patients

OBJECTIVE

To describe a postnatal series of patients with arthrogryposis multiplex congenita by the causal mechanisms involved.

METHODS

In this single-center study, the local data warehouse was used to identify patients with arthrogryposis multiplex congenita. Patients were classified into different etiologic groups.

RESULTS

Of 82 patients included, the most frequent cause of arthrogryposis multiplex congenita was a neuromuscular disorder (39%), including skeletal muscle (n = 19), neuromuscular junction (n = 3), and peripheral nerve (n = 11) involvement. In other subgroups, 19 patients (23%) were classified by disorders in the central nervous system, 5 (6%) in connective tissue, 7 (8.5%) had mixed mechanisms, and 18 (22%) could not be classified. Contractures topography was not associated with a causal mechanism. Cerebral magnetic resonance imaging (MRI), electroneuromyography, and muscle biopsy were the most conclusive investigations. Metabolic investigations were normal in all the patients tested. Targeted or whole exome sequencing diagnostic rates were 51% and 71%, respectively. Thirty-three percent of patients died (early death occurred in patients with polyhydramnios, prematurity, and ventilatory dependency).

DISCUSSION

The benefits of a precise diagnosis in the neonatal period include more tailored management of arthrogryposis multiplex congenita and better genetic information.

Electromyography in infants: experience from a pediatric neuromuscular center

Electromyography plays a pivotal role in diagnosing neuromuscular disorders. The purpose of this study was to investigate the role of electromyography in infants. We performed a retrospective study of the infants who underwent electromyography from 2003 to 2017 and recorded demographic profile, indication, electrodiagnostic findings, and final diagnosis from the follow-up data. 179 studies were completed; electromyography was abnormal in 109 (60.9%) patients. The most common referral indication was hypotonia followed by birth trauma related injuries and rule out neuromuscular disorders. The most common electrodiagnostic diagnosis was localized to muscles followed by plexus and motor neurons. Among the patients with normal electromyography, the most common diagnosis was due to myopathies. Electromyography plays an important role in the workup of neuromuscular disorders in infants though with increased utilization of genetic testing we observed a declining trend in the number of electromyography performed in the latter half the study.

Arthrogryposis Multiplex Congenita

Arthrogryposis multiplex congenita (AMC) is a complex, etiologically diverse, clinical descriptor identified in a variety of diagnoses characterized by multiple congenital joint contractures. The root cause of AMC is decreased fetal movement in-utero, whether resulting from maternal or pregnancy influences, nervous system pathology, or an underlying genetic abnormality. Prenatal diagnosis via ultrasonography can be challenging and may require additional imaging techniques or studies. After birth, these infants may require assistance breathing and feeding depending on the underlying diagnosis. Physical therapy and surgical intervention of the contractures are the mainstays of therapy, and outcomes can be good when intervention is provided in a timely manner. Those infants with syndromic causes of arthrogryposis are more likely to have poor outcomes; therefore, determining the underlying etiology for AMC is important as this can influence counseling regarding individual prognosis as well as future pregnancies. [Pediatr Ann. 2020;49(7):e299-e304.].

Emery-Dreifuss muscular dystrophy

Emery-Dreifuss muscular dystrophy (EDMD) is a rare muscular dystrophy, but is particularly important to diagnose due to frequent life-threatening cardiac complications. EDMD classically presents with muscle weakness, early contractures, cardiac conduction abnormalities and cardiomyopathy, although the presence and severity of these manifestations vary by subtype and individual. Associated genes include EMD, LMNA, SYNE1, SYNE2, FHL1, TMEM43, SUN1, SUN2, and TTN, encoding emerin, lamin A/C, nesprin-1, nesprin-2, FHL1, LUMA, SUN1, SUN2, and titin, respectively. The Online Mendelian Inheritance in Man database recognizes subtypes 1 through 7, which captures most but not all of the associated genes. Genetic diagnosis is essential whenever available, but traditional diagnostic tools can help steer the evaluation toward EDMD and assist with interpretation of equivocal genetic test results. Management is primarily supportive, but it is important to monitor patients closely, especially for potential cardiac complications. There is a high potential for progress in the treatment of EDMD in the coming years.

The diagnostic workup in a patient with AMC: Overview of the clinical evaluation and paraclinical analyses with review of the literature

Arthrogryposis multiplex congenita, or AMC, is a clinical sign defined as congenital contractures of at least two joint levels. These joint contractures are always secondary to diminished fetal movement which can have numerous causes that affect any part of the anatomical structures implicated in movement: the central nervous system, the anterior horn cell, the nerve, the neuromuscular junction, the muscle, or the joint itself. Make a precise diagnosis of the cause in a patient with multiple joint contractures is therefore challenging. The aim of this article is to summarize the use and diagnostic value of common examinations and analyses performed postnatally in patients affected by AMC from a literature review. We also compare this data with results from our clinical practice. Even though it is difficult to give precise guidelines today, it appears that genetic studies, such as whole exome or genome analysis in all patients and chromosomal microarray analysis in patients with intellectual disability and AMC should be preferred as first tier investigations over EMG and muscle biopsy.

Diagnostic yield of electromyography in children with myopathic disorders

BACKGROUND

Interpretation of pediatric electromyography interpretation in myopathic disorders is technically challenging. We assessed our electromyographic experience with respect to sensitivity and specificity in pediatric myopathy.

METHODS

We did a retrospective chart review of patients ≤18 years between 2009 and 2013. Two hundred twenty-four electromyographic studies were reviewed with the following referral diagnoses: myopathy, muscle weakness, neuromuscular disorders, myositis, myalgia, myoglobinuria, myasthenia, myotonia, cramps, periodic paralysis, hypotonia, and developmental delay. Only children who had an electromyography and muscle biopsy were included for analysis. Patients with neurogenic electromyography and neuromuscular junction disorders were excluded. Myopathic electromyography was defined as short duration, low amplitude, polyphasic motor unit potentials with rapid recruitment.

RESULTS

Seventy-two patients were included (age range, 6 months-18 years). The following observations were made: group A: myopathic electromyography or pathognomonic of muscle disease and biopsy or genetically confirmed myopathy (32 cases); group B: myopathic electromyography but biopsy normal or nondiagnostic (12 cases); group C: normal electromyography but biopsy or genetically confirmed myopathy (three cases, all with metabolic myopathy); and group D: electromyography normal and biopsy normal or nondiagnostic (25 cases). The most common diagnoses were congenital myopathy (seven cases), metabolic myopathy (six cases), muscular dystrophy (six cases), genetically confirmed myopathy (five cases), myopathy, undefined (five cases), and inflammatory myopathy (four cases).

CONCLUSIONS

Pediatric electromyography was 91% sensitive and 67% specific in myopathic disorders. The metabolic myopathies were commonly missed by electromyography.

Arthrogryposis and fetal hypomobility syndrome

Arthrogryposis is a heterogeneous condition, evident from birth, which can be defined as multiple contractures of the joints. The etiology is multifold: genetic disorders of the central or peripheral nervous system, or of the connective tissue leading to decreased fetal movements, and vascular and environmental causes. The problem begins in utero. There may be overlapping conditions between sporadic, syndromic, neurogenic, myopathic and metabolic types. The workup should include a family tree. Systemic involvement, for example of the renal and pulmonary systems, may be encountered in associated syndromes. Motor neuron disorders leading to the condition are the most commonly seen type. Fetal or neonatal akinesia/hypokinesia is at the severe end of the spectrum, in which there is literally intrauterine limitation of movement. Children with amyplasia are born with little or diminished muscle bulk of the extremities. Distal arthrogryposis is almost always a dominantly inherited condition. A multidisciplinary care approach is required in order to provide optimum healthcare. The management team should include a nutritionist and a physiotherapist. Genetic counseling is possible in most instances. A truly genetic cause can be identified in more than 50% of cases. Survivors, though handicapped, can lead near normal lives.

Electrophysiologic evidence for anterior horn cell disease in amyoplasia

Amyoplasia is the most common subtype of arthrogryposis multiplex congenita. Children exhibit congenital muscle aplasia or hypoplasia, resulting in symmetric limb contractures that occur in a characteristic pattern. A high incidence of midforehead capillary hemangiomas, micrognathia, and minor genital anomalies also occurs with this disorder. The etiology and specific site of injury in amyoplasia remain unclear. Previous muscle biopsy and electrophysiologic studies could not differentiate between neurogenic or myogenic causes. We describe five children with amyoplasia. Four children demonstrated electrophysiologic features consistent with motor neuronopathy. A careful segmental needle electromyography study revealed variable involvement at different myotomes. We hypothesize that the anterior horn cell may represent the site of disease in a subset of children with amyoplasia.

Temporary diazepam responsive apneic attacks and congenital myasthenic syndrome

Congenital myasthenic syndromes are a genetically and phenotypically heterogeneous group of hereditary disorders affecting neuromuscular junction. Mutations in the gene encoding choline acetyltransferase cause presynaptic defects. The missense mutation I336T has been identified in Turkish population, and most of the cases carrying this mutation present with exercise-induced fatigability and ptosis. Although apneic attacks occur in these cases during febrile illness in childhood, the number of reported respiratory distress episodes during infancy is scarce. Another important feature of these cases is that response to esterase inhibitors is satisfactory. We present a case of congenital myasthenic syndrome with I336T choline acetyltransferase mutation who presented with numerous attacks of respiratory distress in the infancy period. Interestingly, the patient had myopathic findings on electromyography and diazepam decreased severity of apneic attacks. There was also no improvement with esterase inhibitors.

Diagnostic approach to neonatal hypotonia: retrospective study on 144 neonates

The objectives of our study were to determine the actual frequency of the different disorders causing neonatal hypotonia and to assess the reliability of the first physical examination as well as the contribution of the main standard diagnostic tests. One hundred and forty-four infants diagnosed with neonatal hypotonia between January 1st 1999 and June 30th 2005 in our tertiary care facility were retrospectively included in the study. Perinatal history, clinical type of hypotonia, results of standard diagnostic tests, final diagnosis and outcome were abstracted from the original charts. A final diagnosis was reached in 120 cases. Central (cerebral) causes represented 82% of the elucidated cases, mostly hypoxic and hemorrhagic lesions of the brain (34%), chromosomal aberrations and syndromic disorders (26%) and brain malformations (12%). Peripheral (neuromuscular) causes were mainly represented by spinal muscular atrophy (6%) and myotonic dystrophy (4%). Positive predictive value of the initial clinical examination was higher in central type hypotonia. Neuroimaging, karyotype analysis and DNA-based tests were the most helpful diagnostic tools. These recent clinical data can be used to improve our strategy in investigating neonatal hypotonia and a diagnostic algorithm is proposed based on our findings.

Electromyography (EMG) accuracy compared to muscle biopsy in childhood

Reports show wide variability of electromyography (EMG) in detecting pediatric neuromuscular disorders. The study's aim was to determine EMG/nerve conduction study accuracy compared to muscle biopsy and final clinical diagnosis, and sensitivity for myopathic motor unit potential detection in childhood. Of 550 EMG/nerve conduction studies performed by the same examiner from a pediatric neuromuscular service, 27 children (ages 6 days to 16 years [10 boys; M:F, 1:1.7]) with muscle biopsies and final clinical diagnoses were compared retrospectively. Final clinical diagnoses were congenital myopathies (5 of 27,18%), nonspecific myopathies (biopsy myopathic, final diagnosis uncertain; 6 of 27, 22%), congenital myasthenic syndrome (3 of 27, 11%), juvenile myasthenia gravis (1 of 27, 4%), arthrogryposis multiplex congenita (2 of 27, 7%), hereditary motor and sensory neuropathy (1 of 27, 4%), bilateral peroneal neuropathies (1 of 27, 4%), and normal (8 of 27, 30%). There were no muscular dystrophy or spinal muscular atrophy patients. EMG/nerve conduction studies had a 74% agreement with final clinical diagnoses and 100% agreement in neurogenic, neuromuscular junction, and normal categories. Muscle biopsies concurred with final diagnoses in 87%, and 100% in myopathic and normal categories. In congenital myasthenic syndrome, muscle biopsies showed mild variation in fiber size in 2 of 3 children and were normal in 1 of 3. EMG sensitivity for detecting myopathic motor unit potentials in myopathies was 4 of 11 (36%), greater over 2 years of age (3 of 4, 75%), compared to infants less than 2 years (1 of 7, 14%), not statistically significant (P = .0879). EMGs false-negative for myopathy in infants < 2 years of age were frequently neurogenic (3 of 6, 50%). In congenital myopathies EMG detected myopathic motor unit potentials in 40%, with false-negative results neurogenic (20%) or normal (40%). Because our study has no additional tests for active myopathies, for example Duchenne muscular dystrophy genetic testing, our sensitivity for myopathies is lower than if we used a more global view. In conclusion, EMG detection rate of myopathic motor unit potentials at a young age was low, improving in children over 2 years of age. In neurogenic and neuromuscular junction disorders, the EMG has a very high detection rate. In children with mild to moderate neurogenic EMG findings and normal nerve conduction, a myopathy should always be considered.

Benign infantile neurogenic muscle atrophy predominantly involving the upper extremities

An eight year-old girl was first noted to be hypotonic at 4 months of age. She had a delay in achieving developmental milestones and showed apparent weakness predominantly affecting muscles of the upper extremities. In the left biceps brachii muscle biopsy at the age of 5 months, there were groups of atrophic fibers and marked fiber type grouping, but intramuscular nerves were well myelinated and there were few type 2C fibers. She improved with age and learned to walk at 1 year and 4 months and had minimal weakness of the forearm muscles and mild atrophy of the muscles of the right upper extremity. She recently developed a mild scoliosis. Since the EMG was not neurogenic and no mutations were found in the survival motor neuron (SMN) gene, we believe that she does not have a degenerative neurogenic disorder but rather has an abnormal innervation of the skeletal muscles due either to anterior horn cell dysgenesis or anomalous peripheral nerve branching.

Arthrogryposis Multiplex Congenita

Arthrogryposis multiplex congenita (AMC) is a disorder that encompasses a range of severity of congenital joint contractures from mild to severe. The etiologies of this condition are numerous but can generally be classified into endogenous and exogenous factors. Endogenous factors are related to those conditions that originate within the fetus and can further be classified into central nervous system disorders, musculoskeletal abnormalities, and abnormalities of the joints and connective tissues. The sonographic presentation of AMC includes decreased or absent fetal movement with contractures of multiple extremities. Treatment and medical management of AMC depends on the severity of the contractures and the absence or presence of associated syndromes. Accurate diagnosis of AMC allows for accurate prenatal counseling regarding future morbidity and mortality of the fetus and includes options regarding treatment, medical management, and pregnancy termination depending on the severity of the condition.

Brown-Vialetto-Van Laere syndrome; variability in age at onset and disease progression highlighting the phenotypic overlap with Fazio-Londe disease

We report four siblings showing features of a pontobulbar palsy, a mixed spinal and upper motor neuropathy and variable deafness. The observation of affected males and females born to consanguineous first cousin parents suggests autosomal recessive inheritance. Two children presented in the first 16 months of life with stridor and died of respiratory failure by the age of 2 years. Hearing loss was not apparent in these infants. In contrast, 2 further siblings developed a bulbar palsy in their sixth year followed by the onset of deafness and features of an anterior horn neuropathy with corticospinal tract involvement. They exhibited a relatively slow but relentless decline over a period of several years. These cases highlight the phenotypic overlap of Brown-Vialetto-Van Laere syndrome with Fazio-Londe disease. Rather than representing two separate disorders, our findings suggest the possibility of a single disease entity which may usefully be considered a form of juvenile amyotrophic lateral sclerosis.